Category Archives: RFCs & Standards

Basic CAMEL Charging Flow

GSM, Mobile Networks, Notes, RFCs & Standards, , , , , ,

CAMEL handles charging in 2G and 3G networks, much like Diameter handles charging in LTE.

CAMEL runs on top of SS7, specifically it sits on top of TCAP, which sits on top of SCCP, which can ride on M3UA or MTP3 (so it sits at the same layer as MAP).

CAMEL is primarily focused on charging for Voice & SMS services, as data generally uses Diameter, so it’s voice and SMS we’ll focus on.

CAMEL is spoken between the MSC (gsmSSF) and the OCS (gsmSCF).

Basic Call State Model

CAMEL is closely related to the Intelligent Network stuff on the 1980s, and steals a lot of it’s ideas from there, unfortunately if you’re to read the CAMEL standard it also implies you were involved in IN stuff and had been born at that point, alas I was neither.

So the key to understanding CAMEL is the Basic Call State Model (BCSM) which is a model of all the different states a call can be in, such as ringing, answered, abandoned, call failed, etc, etc.

Over CAMEL, our OCS can be told by the MSC when a certain event happens; the MSC can tell the OCS, that the call has changed state. For example a BCSM event might indicate the call has hung up, is ringing, cancelled, etc.

Below is the list of all the valid BCSM states:

List of BCSM states for events

Basic MO Call with CAMEL

Our subscriber makes an outbound call.

Based on the data the MSC has in it from the HLR, it knows that we should use CAMEL for this call, and it has the SCCP Address of the OCS (gsmSCF) it needs to send the CAMEL messages to.

So the MSC sends an InitialDP message to the OCS (via it’s Global Title Address) to Authorize the call that the user is trying to make.

This is like any other Authorization step for an OCS, which allows the OCS to authorize the call by checking the subscriber is valid, check if they’re allowed to call that destination and they’ve got the balance to do so, etc.

initialDP message from an MSC to an OCS

The initialDP (Initial Detection Point) is telling our OCS all about the call event that’s being requested, who’s calling, what number they’ve dialed, where they are in the network (of note especially if they’re roaming), etc, etc.

The OCS runs through it’s own checks to see if it wants to allow the call to proceed by checking if the subscriber has got enough balance, unit reservation, etc, etc, and if it does, the OCS sends back a Continue message to the MSC to allow the call to continue.

Generally the OCS also uses this message as a chance to subscribe to BCSM Events using RequestReportBCSMEventArg so the OCS will get notified by the MSC when the state of the call changes. This means the MSC will tell us when the state of the call changes; events like the call getting answered, disconnected, etc. This is critical so we know when the call gets answered and hung-up, so we can charge correctly.

In the below example, as well as sending the Continue and RequestReportBCSMEventArg the OCS is also setting the ChargingArgs for this call, so the MSC knows who to charge (the caller) set via sendingSide and that the MSC must send an Apply Charging Report (ACR) messages every 300 units (1 unit = 100 ms, so a value of 300 = 300 x 100 milliseconds = 30 seconds) so the OCS keeps track of what’s going on.

continue sent by the OCS to the MSC, also including reportBCSMEvent and applyCharging messages

At this point the call can start to proceed – In ISUP terms the InitialDP is triggered between the Initial Address Message and the Address Complete message is sent after the continue is sent back.

Or in a slightly less appropriate analogy but easier to understand for SIP folks, the InitialDP is sent for INVITE and the 180 RINGING is sent once the continue message is received.

Call is Answered

So at this stage our call can start to ring.

As we’ve subscribed to BCSM events in our last message, the MSC is going to tell us when the call gets answered or the call times out, is abandoned or the sun burns out.

The MSC provides this info a eventReportBCSM, which is very simple and just tells us the event that’s been triggered, in the example below, the call was answered.

eventReportBCSM from MSC to OCS

These eventReportBCSM are informational from the MSC to the OCS, so the OCS doesn’t need to send anything back, but the OCS does need to mark the call as answered so it can start timing the call.

At this stage, the call is connected and our two parties are talking, but our MSC has been told it needs to send us applyChargingReports every 30 seconds (due to the value of 300 in maxCallPeriodDuration) after the call was connected, so the MSC sends the OCS it’s first applyChargingReport 30 seconds after the call was answered:

applyChargingReport sent by the MSC to the OCS every reporting period

We can calculate the duration of the call so far based on the time of the eventReportBCSM, then the OCS must make a decision of if it should allow the call to continue or not.

For simplicity’s sake, let’s imagine we’re still got a balance in the OCS and the OCS wants the call to continue, the OCS send back an applyCharging message to the MSC in response, and includes the current allowed maxCallPeriodDuration, keeping in mind the value is x100 and in nanoseconds (so this is 30 seconds).

applyCharging from the OCS back to the MSC

Perfect, our call is good to go for another 30 more seconds, son in 30 seconds we’ll get another ACR messages from MSC to the OCS to keep it abreast of what’s going on.

Now one of two things is going to happen, either subscriber is going to burn through all of their minutes, and get their call cutoff, or the call will end while they’ve still got balance, let’s look at both scenarios.

Normal Hangup Scenario

When the call ends, we get an applyChargingReport from the MSC to the OCS.

As we’ve subscribed to reportBCSMEvent we get both the applyChargingReport with legActive: False` so we know the call has hungup, and we’ve got an event report to tell us more about the event, in this case a hangup from the Originating Side.

reportBCSMEvent and applyChargingReport Sent by the MSC to the OCS to indicate the call has ended, note the legActive flag is now false

Lastly the OCS confirms by sending a releaseCall to the MSC, to indicate all legs should now terminate.

releaseCall Sent by OCS to MSC at the very end

So that’s it!

Obviously there are other flows, such as running out of balance mid-call, rejecting a call, SMS and PBX / VPN services that rely on CAMEL, but hopefully you now understand the basics of how CAMEL based charging looks and works.

If you’re looking for a CAMEL capable OCS or a CAMEL to Diameter or API gateway, get in touch!

GTPv2 Source Ports

EPC, LTE, Mobile Networks, Notes, RFCs & Standards, ,

Ask anyone in the industry and they’ll tell you that GTPv2-C (aka GTP-C) uses port 2123, and they’re right, kinda.

Per TS 129.274 the Create Session Request should be sent to port 2123, but the source port can be any port:

The UDP Source Port for a GTPv2 Initial message is a locally allocated port number at the sending GTP entity.

So this means that while the Destination Port is 2123, the source port is not always 2123.

So what about a response to this? Our Create Session Response must go where?

Create Session request coming from 166.x.y.z from a random port 36225
Going to the PGW on 172.x.y.z port 2123

The response goes to the same port the request came on, so for the example above, as the source port was 36225, the Create Session Response must be sent to port 36225.

Because:

The UDP Destination Port value of a GTPv2 Triggered message and for a Triggered Reply message shall be the value of the UDP Source Port of the corresponding message to which this GTPv2 entity is replying, except in the case of the SGSN pool scenario.

But that’s where the association ends.

So if our PGW wants to send a Create Bearer Request to the SGW, that’s an initial message, so must go to port 2123, even if the Create Session Request came from a random different port.

A tale of two CPRIs

5G SA, EUTRAN, GSM, History, LTE, Mobile Networks, RFCs & Standards, , , ,

It was the best of times, it was the worst of times. It was the age of wisdom, it was the age of foolishness. It was the epoch of belief, it was the epoch of incredulity. It was the season of Light, it was the season of Darkness. It was the spring of hope, it was the winter of despair.

A tale of two Cities

When Dickens wrote of Doctor Manette in the 1859, I doubt his intention was to write about the repeating history of RAN fronthaul standards – but I can’t really say for sure.

Setting the Scene

Our story starts with introducing CPRI (Common Public Radio Interface) interface, having been imprisoned in the Bastille of vendor lock in for the better part of twenty years.

Think of CPRI is less of a hard interoperable standard and more like how the Italian and French languages are both derived from Latin; it doesn’t mean that the two languages are the same, but they’ve got the same root and may share some common words and structures.

In practice this means that taking an Ericsson Radio and plugging it into a Huawei Baseband simply won’t work – With CPRI you must use the same vendor for the Baseband and the Radios.

Huawei BBU 3900 Architecture
Image from my post on setting up Huawei Base stations, showing the Huawei Baseband (BBU) connecting to the Huawei Radios (RRUs) via CPRI (in Yellow)

The Unexpected Plot Twist

“Nuts to this” the industry said after being stuck locked between the same radios and baseband for years; we should create a standard so we can mix and match between radio vendors, and even standardize some other stuff that’s been bothering us, so we’ll have a happy world of interoperability.

A world with interoperable fronthaul

With kit created that followed this standard, we’d be able to take components from vendor A, B & C, and fit them together like Lego, saving you some money along the way and giving you’ve got a working solution made of “best of breed” components, where everything is interoperable.

Omnitouch Lego base stations, which also fit together like Lego – Part of the Omnitouch Network Services “swag” from 2024

So the industry created a group to chart a path for a better tomorrow by standardizing these interfaces.

The group had many industry heavyweights like Nokia, NEC, LG, ZTE and Samsung joining.

The key benefits espoused on their website:

An open market will substantially reduce the development effort and costs that have been traditionally associated with creating new base station product ranges. The availability of off-the-shelf base station modules will enable manufacturers to focus their development efforts on creating further added value within the base station, encouraging greater innovation and more cost-effective products. Furthermore, as product development cycles will be reduced, new base station functions will become available on the market more quickly.

Mission statement of the group

In addition to being able to mix and match radios and basebands from different vendors, the group defined standards for centralized baseband, and interoperable standards, to allow a multi-vendor ecosystem to flourish.

And here’s the plot twist – The text above, was not written about OpenRAN, and it was not written about the benefits of eCPRI.

It was written about Open Base Station Architecture Initiative (OBSAI) and it was written 22 years ago.

*record screech sound*

This image was called "Confused Ernie" but it's clearly Bert...

Standards War you’ve never heard of: OBSAI vs CPRI

When OBSAI was defined it was not without competition; there was another competing fronthaul standard; that’s right, the mustache twirling lowlife from earlier in the story – CPRI.

Supported by Huawei, Nortel, NEC & Ericsson (among others), CPRI took a “gentle parenting” approach to the standards world, in contrast to OBSAI.
Instead of telling all the vendors to agree on an interoperable front haul standard, CPRI just encouraged everyone to implement what their heart told them and what felt right to them.

As it happened, the industry favored the CPRI approach.

If a vendor wanted to add a new “word” in their CPRI “language” to add a new feature, they just went ahead and added it – It didn’t require anyone else to agree with them or changes to a common standard used by the industry, vendors could talk to the kit they made how they wanted.

CPRI has been the defacto non-standard used by all the big kit vendors for the past ~10 years.

The Death of OBSAI & the Birth of OpenRAN’s eCPRI

Why haven’t you heard of OBSAI? Why didn’t the OBSAI standard just serve as the basis for eCPRI – After all the last OBSAI release was less than 5 years before TIP started working on eCPRI publicly.

Is no more. It has ceased to be.

Did a schism over “uplink performance improvement” options lead to “irreconcilable differences” between parties leading to the breakup of the OBSAI group?

Nope.

Customers (MNOs) didn’t buy OBSAI based equipment in measurably larger quantities than CPRI kit. That’s it.

This meant the vendors invested less in paying teams to further develop the standards, the OBSAI group met less frequently, and in the end, member vendors didn’t bother adding support for OBSAI to new equipment and just used the easier and more flexible CPRI option instead.

At some point someone just stopped paying for the domain renewal and that was it, OBSAI was no more.

This is how the standards body ends, not with a bang, but with a whimper.

T.S. Elliot’s writings on the death of obsai

Those who do not learn from history…

The goals of the OBSAI Group and OpenRAN working groups are almost identical, so what lessons did Marconi, Motorola and Alcatel learn as members of OBSAI that other vendors could learn about OpenRAN strategy?

There are no mentions of OBSAI in any of the information published by OpenRAN advocates, and I’m wondering if folks aren’t aware that history tends to repeat and are ignorant to what came before it, or they’re just not learning lessons from the past?

So what can the OpenRAN industry learn from OBSAI?

Being a nerd, I started detailing the technical challenges, but that’s all window dressing; The biggest hurdle facing CPRI vs eCPRI are the same challenges OBSAI vs CPRI faced a decade prior:

To be relevant, OpenRAN kit has to be demonstrably better than what we have today AND provide a tangible cost saving.

OBSAI failed at achieving this, and so failed to meet it’s other more noble goals.

[At the time of writing this at least] I’d contend that neither of those two criteria have been met by OpenRAN.

What does the future hold for OpenRAN?

Looking into the crystal ball, will OpenRAN and eCPRI go the way of OBSAI, or will someone keep the OpenRAN dream alive?

Today, we’re still seeing the MNOs continue to provide tokenistic investment in OpenRAN. But being a cynic, I’d say the MNOs are feigning interest in OpenRAN products because it’s advantageous for them to do so.

The threat of OpenRAN has proven to be a great stick to beat the traditional vendors with to force them to lower their prices.

Think about the $14 billion USD Ericsson deal with AT&T, if chucking a few million at OpenRAN pilots / trials lead to AT&T getting even a 0.1% reduction in what they’re paying Ericsson, then the numbers would have worked out well in AT&Ts favor.

From the MNOs perspective, the cost to throw the odd pilot or trial to a hungry OpenRAN vendor to keep them on the hook is negligible, but the threat of OpenRAN provides leverage and bargaining power every time it’s contract renewal time with the big RAN vendors.

Already we’ve seen all the traditional RAN vendors move to neutralize this threat by introducing “OpenRAN compatible” equipment and talking up their commitment to openness.

This move by the RAN vendors takes this sting out of the OpenRAN threat, and means MNOs won’t have much reason to continue supporting OpenRAN.

This leaves the remaining OpenRAN vendors like Miss Havisham, forever waiting in their proverbial wedding dresses, having being left at the altar.

Okay, I’m mixing my Dickens’ references here, but it was too good not to.

Appendix

I’ve been enjoying writing more analysis than just technical content, let me know if this is something you’re interested in seeing more of.

I’ve been involved in two big OpenRAN integration projects, both of which went poorly and probably tainted my perspective. Enough time has passed to probably write up how it all went with the vendor names removed, but that’s a post for another time!

If you wanted to learn more about OBSAI Archive.org has their old website available for reading.

TFTs & Create Bearer Requests

5G SA, EPC, IMS / VoLTE, LTE, Mobile Networks, Notes, RFCs & Standards, , , , ,

What is included in the Charging Rule on Gx ultimately turns into a Create Bearer Request on GTPv2-C.

But the mapping it’s always obvious, today I got stuck on the difference between a Single remote port type, and a single local port type, thinking that the Packet Filter Direction in the TFT controlled this – It doesn’t – It’s controlled by the order of your Traffic Flow Template rule.

Input TFT:

"permit out 17 from any 50000 to any"

Leads to Packet filter component type identifier: Single remote port type

Whereas a TFT of:

permit out 17 from any to any 50000

Leads to Packet filter component type identifier: Single local port type (64)

Flash SMS Messages

IMS / VoLTE, Mobile Networks, Notes, RFCs & Standards, , , , ,

Stumbled across these the other day, while messing around with some values on our SMSc.

Setting the Data Coding Scheme to 16 with GSM7 encoding flags the SMS as “Flash message”, which means it pops up on the screen of the phone on top of whatever the user is doing.

While reading a quality telecom blog bam! There’s the flash SMS popping over whatever I was reading.

Oddly while there’s plenty of info online about Flash SMS, it does not appear in the 3GPP specifications for SMS.

Turns out they still work, move over RCS and A2P, it’s all about Flash messages!

There’s no real secret to this other than to set the Data Coding Scheme to 16, which is GSM7 with Flash class set. That’s it.

If you’re interested in the internal machinations of how SMS works, I’ve got a few posts on the topic – You can find a list of them here.

Obviously to take advantage of this you’d need to be a network operator, or have access to the network you wish to deliver to. Recently more A2P providers are filtering non vanilla SMS traffic to filter out stuff like SMS OTA message or SIM specific messages, so there’s a good chance this may not work through A2P providers.

Background to the “VoLTE Mess”

5G SA, IMS / VoLTE, LTE, Mobile Networks, RFCs & Standards, VoIP, , , ,

I’ve been writing a fair bit recently about the “VoLTE Mess” – It’s something that’s been around for a long time, mostly impacting greenfield players rolling out LTE only, but now the big carriers are starting to feel it as they shut off their 2G and 3G networks, so I figured a brief history was in order to understand how we got here.

Note: I use the terms 4G or LTE interchangeably

The Introduction of LTE

LTE (4G) is more “spectrally efficient” than the technologies that came before it. In simple terms, 1 “chunk” of spectrum will get you more speed (capacity) on LTE than the same size chunk of spectrum would on 2G or 3G.

From my post on 5G being a bit overhyped

So imagine it’s 2008 and you’re the CTO of a mobile network operator.
Your network is congested thanks to carrying more data traffic than it was ever designed for (the first iPhone had launched the year before) and the network is struggling under the weight of all this new data traffic.
You have two options here, to build more cell sites for more density (very expensive) or buy more spectrum (extremely expensive) – Both options see you going cap in hand to the finance team and asking for eye-wateringly large amounts of capital for either option.

But then the answer to your prayers arrives in the form of 3GPP’s Release 8 specification with the introduction of LTE. Now by taking some 2G or 3G spectrum, and by using it on 4G, you can get ~5x more capacity from the same spectrum. So just by changing spectrum you own from 2G or 3G to 4G, you’ve got 5x more capacity. Hallelujah!

So you go to Nortel and buy a packet core, and Alcatel and Siemens provide 4G RAN (eNodeBs) which you selectively deploy on the cell sites that are the most congested.
The finance team and the board are happy and your marketing team runs amok with claims of 4G data speeds.
You’ve dodged the crisis, phew.

This is the path that all established mobile operators took; throw LTE at the congested cell sites, to cheaply and easily free up capacity, and as the natural hardware replacement cycle kicked in, or cell sites reached capacity, swap out the hardware to kit that supports LTE in addition to the 2G and 3G tech.

Circuit Switched Fallback

But it’s hard to talk about the machinations of late 2000s telecom executives, without at least mentioning Hitler.

This video below from 15 years ago is pretty obscure and fairly technical, but the crux of it it is that Hitler is livid because LTE does not have a “CS Domain” aka circuit switched voice (the way 2G and 3G had handled voice calls).

It was optional to include support for voice calls in the LTE network (Voice over LTE) when you launched LTE services. So if you already had a 2G or 3G network (CS Network) you could just keep using 2G and 3G for your voice calls, while getting that sweet capacity relief.

So our hypothetical CTO, strapped for cash and data capacity, just didn’t bother to support VoLTE when they launched LTE – Doing so would have taken more time to launch, during which time the capacity problem would become worse, so “don’t worry about VoLTE for now” was the mantra.

All the operators who still had 2G and 3G networks, opted to just “Fallback” to using the 2G / 3G network for calling. This is called “Circuit Switched Fallback” aka CSFB.

Operators loved this as they got the capacity relief provided by shifting to 4G/LTE (more capacity in the network is always good) and could all rant about how their network was the fastest and had 4G first, this however was what could be described as a “Foot gun” – Something you can shoot yourself in the foot with in the future.

Operators eventually introduce VoLTE

Time ticked on an operators built out their 4G networks, and many in the past 10 years or so have launched VoLTE in their own networks.

For phones that support it, in areas with blanket 4G coverage, they can use VoLTE for all their calls.

But that’s the sticking point right there – If the phones support it.

But if the phones don’t support it, they’re roaming or making emergency calls, there is always been the safety blanket of 2G or 3G and Circuit Switched fallback to well, fall back to.

There’s no driver for operators who plan to (or are required to) operate a 2G or 3G network for the foreseeable future, to ensure a high level of VoLTE support in their devices.

For an operator today with 2G or 3G, Voice over LTE is still optional.
Many operators still rely exclusively on Circuit Switched Fallback, and there are only a handful of countries that have turned off 2G and 3G and rely solely on VoLTE.

VoLTE Handset Support

For the past 16 years phone manufacturers have been making LTE capable phones.

But that does not mean they’ve been making phones that support Voice over LTE.

But it’s never been an issue up until this point, as there’s always been a circuit switched (2G/3G) network to fall back to, so the fact that these chips may not support VoLTE was not a big problem.

Many of the cheaper chipsets that power phones simply don’t support VoLTE – These chips do support LTE for data connections but rely on Circuit Switched Fallback for voice calls. This is in part due to the increased complexity, but also because some of the technologies for VoLTE (like AMR) required intellectual property deals to licence to use, so would add to the component cost to manufacture, and in the chips game, keeping down component cost is critical.

Even for chips that do support Voice over LTE, it’s “special”. Unlike calling in 2G or 3G that worked the same for every operator, phone manufacturers require a “Carrier Bundle” for each operator, containing that specific operators’ special flavor of VoLTE, that operator uses in their network.

This is because while VoLTE is standardized (Despite some claims to the contrary) a lot of “optional” bits have existed, and different operators built networks with subtle differences in the “flavor” of their Voice over LTE (IMS) stack they used. The OEMs (Phone / Chip manufacturers) had to handle these changes in the devices they made, for in order to sell their phones through that operator.

This means I can have a phone from vendor X that works with VoLTE on Network Y, but does not support VoLTE on Network Z.

Worse still, knowing which phones are supported is a bit of a guessing game.

Most operators sell phones directly to their customer base, so buying an Network Y branded phone from Vendor X, you know it’s going to support Network Y’s VoLTE settings, but if you change carriers, who knows if it’ll still support it?

When you’ve still got a Circuit Switched network it’s not the end of the world, you’ll just use CSFB and probably not realize it, until operators go to shut down 2G / 3G networks…

IMS Profile selection on an engineering mode MTK based Android handset

Navigating the Maze of VoLTE Compatibility

Here are some simple checklist you can ask your elderly family members if they ask if their phone is VoLTE compatible:

  • Does the underlying chipset the phone is based on support VoLTE? (you can find this out by disassembling the phone and checking the datasheets for the components from the OEMs after signing NDAs for each)
  • Does the underlying chipset require a “carrier bundle” of settings to have been loaded for this operator in order to support VoLTE (See Qualcomm MBM as an example)?
  • What version of this list am I currently on (generally set in the factory) and does it support this operator? (You can check by decapping the ICs and dumping their NVRAM and then running it through a decompiler)
  • Does my phones OS (Android / iOS) require a “carrier bundle” of it’s own to enable VoLTE? Is my operator in the version of the database on the phone? (See Android’s Carrier Database for example) (You can find the answer by rooting the phone and running some privileged commands to poke around the internal file system)
  • Does my operator / MNO support VoLTE – Does my plan / package support VoLTE? (You can easily find the answer by visiting the store and asking questions that don’t appear on the script)

If you managed to answer yes to all of the above, congratulations! You have conditional VoLTE support on your phone, although you probably don’t have a working phone anymore.

Wait, conditional VoLTE support?

That’s right folks, VoLTE will work in some scenarios with your operator!

If you plan on traveling, well your phone may support VoLTE at home, but does the phone have VoLTE roaming enabled?
Many phones support VoLTE in the home network, but resort to CSFB when roaming.

If it does support VoLTE roaming, does the network you’re visiting support VoLTE roaming? Has the roaming agreement (IRA) between the operator you’re using while traveling and your home operator been updated to include VoLTE Roaming? These IRAs (AA.12 / AA.13 docs) also indicate if the network must turn off IPsec encryption for the VoLTE traffic when roaming, which is controlled by the phone anyway.

Phew, all this talk of VoLTE roaming while traveling scares me, I think I’ll stay home in the safety of the Australian bush with all these great friendly animals around a phone that supports VoLTE on my home network.

Ah – After spending some time in the Australian bush one of our many deadly animals bit me. Time to call for help! Wait, what about emergency calls over VoLTE? Again, many phones support VoLTE for normal calls, fall back to 2G or 3G for the emergency call, so if you have one of those phones (You’ll only find out if you try to make an emergency call and it fails) and try to make an emergency call in a country without 2G or 3G, you’d better find a payphone.

There’s many real world examples of this, our friends at OptimERA have been lobbying the FCC since 2019 on this.

Sarcasm aside, there’s no dataset or compatibility matrix here – No simple way to see if your phone will work for VoLTE on a given operator, even if the underlying chip does support VoLTE.

Operators in Australia which recently shut down their 3G network, were mandated to block devices that didn’t support VoLTE for emergency calling. They did this using an Equipment Identity Register, and blocking devices based on the Type Allocation Code, but this scattergun approach just blocked non-carrier issued devices, regardless of it they supported VoLTE or VoLTE emergency calling.

Blame Game

So who’s to blame here?

There’s no one group to blame here, the industry has created a shitty cycle here:

  • Standards orgs for having too many “flavors” available
  • Operators deploying their own “Flavors” of VoLTE then mandating OEMs / Chip manufacturers comply with their “flavor”.
  • OEMs / Chip manufactures respond by adding “Carrier Bundles” to account for this per-operator customization

I’ve got some ideas on a way to unscramble this egg, and it’s going to take a push from the industry.

If you’re in the industry and keen to push for a fix, get in touch!

It’s time to get a long term solution to this problem, and we as an industry need to lead the change.

Tales from the Trenches – IMS TCP Socket Handling

IMS / VoLTE, Mobile Networks, RFCs & Standards, VoIP, , , ,

Oh boy this has been a pain in the backside with IMS / VoLTE devices using TCP and how they handle the underlying TCP sockets.

A mobile phone from manufacturer A, wants every SIP dialog to be in it’s own TCP session, while a phone from manufacturer B wants a unique TCP session per transaction, while manufacturer C thinks that every SIP message should reuse the same transaction.

So an MT call to manufacturer A, who wants every SIP dialog in it’s own transaction would look something like this:

PCSCF:44738 -> UE:5060; TCP SYN
UE:5060 -> PCSCF:44738; TCP SYN/ACK
PCSCF:44738 -> UE:5060; TCP ACK
--- TCP connection is now open to UE from P-CSCF---
--- Start of new SIP Transaction 1 & Dialog ---
PCSCF:44738 -> UE:5060; TCP PSH - SIP INVITE....
UE:5060 -> PCSCF:44738; TCP ACK


UE:5060 -> PCSCF:44738; TCP PSH - SIP 200....
PCSCF:44738 -> UE:5060; TCP ACK, PSH - SIP ACK....
UE:5060 -> PCSCF:44738; TCP ACK
--- End of SIP Transaction 1 ---

--- Start of SIP Transaction 2 ---
PCSCF:44738 -> UE:5060; TCP PSH - SIP BYE....
UE:5060 -> PCSCF:44738; TCP ACK, PSH - SIP 200....
--- End of SIP Transaction 2 & SIP Dialog ---
PCSCF:44738 -> UE:5060; TCP FIN
UE:5060 -> PCSCF:44738; TCP ACK
--- End of TCP Connection ---

Where UE:5060 – is the IP & port of the UE, as advertised in the Contact: header, while PCSCF:44738 is the PCSCF IP and a random TCP port used for this connection.

But for manufacturer B, who wants a unique TCP session per transaction, they want it to look like this:

PCSCF:44738 -> UE:5060; TCP SYN
UE:5060 -> PCSCF:44738; TCP SYN/ACK
PCSCF:44738 -> UE:5060; TCP ACK
--- TCP connection is now open to UE from P-CSCF---
--- Start of new SIP Transaction 1 & Dialog ---
PCSCF:44738 -> UE:5060; TCP PSH - SIP INVITE....
UE:5060 -> PCSCF:44738; TCP ACK


UE:5060 -> PCSCF:44738; TCP PSH - SIP 200....
PCSCF:44738 -> UE:5060; TCP ACK, PSH - SIP ACK....
UE:5060 -> PCSCF:44738; TCP ACK
PCSCF:44738 -> UE:5060; TCP FIN
UE:5060 -> PCSCF:44738; TCP ACK
--- End of SIP Transaction 1 & TCP Session 1 ---

--- Start of TCP Session 2 ----
PCSCF:32627 -> UE:5060; TCP SYN
UE:5060 -> PCSCF:32627; TCP SYN/ACK
PCSCF:32627 -> UE:5060; TCP ACK
--- Start of SIP Transaction 2 ---
PCSCF:32627 -> UE:5060; TCP PSH - SIP BYE....
UE:5060 -> PCSCF:32627; TCP ACK, PSH - SIP 200....
--- End of SIP Transaction 2 & SIP Dialog ---
PCSCF:32627 -> UE:5060; TCP FIN
UE:5060 -> PCSCF:32627; TCP ACK
--- End of TCP Connection 2 ---

And then manufacturer C wants just the one TCP session to be used for everything, so they open the TCP connection when they register, and that’s all we use for everything.

Is there any logic to this? Nope, seems to be tied to the underlying chipset (Qualcomm vs Mediatek vs Unisoc) and the SIP stack used (Qualcomm, MTK, Unisoc, Samsung, Apple).

We’ve profiled devices into one of 3 behaviors, and then we tag them based on user agent as to what “persona” they demand from the network.

I can’t believe I’m still talking about VoLTE / IMS handset support and it’s almost 2025…. For context IMS was “standardized” 17 years ago.

All about Global Title Translation & SCCP Routing

GSM, History, Mobile Networks, RFCs & Standards, , ,

This is the next post in my series on SS7, and today we’re taking a look at SCCP the Signalling Connection Control Part (SCCP).

High Level

Global Title uses the routing features from SCCP, which is another layer on top of MTP3.

SCCP allows us to route on more than just point code, instead we can route based on two new fields, Subsystem Number and Global Title.

Subsystem Number is the type of system we are looking to reach, ie an HLR, MSC, CAMEL Gateway, etc.

The Global Title generally looks like an E.164 formatted phone number, and often it is just that.

Somewhere along the chain (typically at the end of it) an STP somewhere needs to perform Global Title Translation to analyse the SCCP header (Subsystem Number, Point Code & Global Title) and finally turn that into a single point code to route the MTP3 message to.

The advantage of this is we are no longer just limited to routing messages based on Point Code.

This is how the international SS7 Network used for roaming is structured and addressed – All using Global Title rather than Point Codes.

The need for SCCP

For starters, after all this talk of MTP3 and Point Codes, why the need to add SCCP?

Let’s go back in time and look at the motivators…

1. Address space is finite

Point codes are great, and when we’ve spoken about them before, I’ve compared them to IPv4 address, but rather than ranging from 0.0.0.0 to 255.255.255.255 (32 bits on IPv4) international signaling point codes range from 0.0.0 to 7.255.7 (14 bits).

The problem with IPv4’s 32 bit addresses is they run out. The problem with the ITU International Signaling Point Codes is that they too, are a limited resource with only 16,383 possible ISPCs.

~700 operators worldwide each with ~100 network elements would be 70k point codes to address them all – That’s not going to fit into our 16k possible Point Codes.

Global Title fixes this, because we’re able to use E.164 phone number ranges (which are plentiful) for addressing, we’re still not at IPv6 levels of address space, but pretty hefty.

2. Service Discovery by Subsystem

Now imagine you’re a VLR looking to find an HLR. The VLR and the HLR are both connected to an STP, but how does the VLR know where to reach the HLR?

One option would be to statically set every route for the Point Code of every HLR into every possible VLR and visa-versa, but that gets messy fast.

What if the VLR could just send a request to the STP and indicate that the request needs to be routed to any HLR, and the STP takes care of finding a SS7 node capable of handling the request, much a Diameter Routing Agent routes based on Application ID.

SCCP’s “Subsystem Number” routing can handle this as we can route based on SSN.

3. Service Discovery by MSISDN

Having an SMS destined to a given MSISDN requires the SMSc to know where to route it.

Likewise an MSC wanting to call a given number.

There’s a lot of MSISDN ranges. Like a lot. Like every phone mobile number.

Having every a table on every SSP/SCP in the network know where every MSISDN range is in the world and what point code to go through to reach it is not practical.

Instead, being able to have the SCP/SSPs (like our MSC or SMSc) send all off-net traffic to an STP frees us the individual SCP/SSPs from this role; they just forward it to their connected STP.

Our STP can analyse the destination MSISDN and make these routing decisions for us, using Global Title Translation based on rules in the Global Title Table on the STP.

For example by adding each of the domestic / national MSISDN ranges/prefixes into the Global Title Table on the STP (along with the corresponding point code to route each one to), the STP can look at the destination MSISDN in the message and forward to the STP for the correct operator.

Likewise a route can match anything where the Global Title address is outside of the local country and send it to an international signaling provider.

Global title takes care of this as we can route based on a phone number.

4. Tokenistic Security

By “Hiding” network elements behind Global Titles, you don’t expose as much information about your internal network, and the only way people can “find” your network elements would be scanning through all the possible addresses in your (publicly advertised) Global Title range (wardialing is back baby!).

But the phrases “Security” and “SS7” don’t really belong together…

The SCCP Header

The SCCP header has a Called Party and a Calling Party, and this is where the magic happens.

These can be made up for any number of 3 parts:

  • Global Title Address
  • Subsystem Number
  • Point Code

We can route on any combination of these.

To indicate we’re using SCCP, we set the Signaling Indicator bit in the M3UA / MTP3 message to SCCP:

Great, now we can look at our SCCP header.

It looks like there’s a lot going on, but we can see the calling and called party (888888888 is called by 9999999999) with the Subsystem number set (888888888 is called for subsystem HLR, from 999999999 which is a VLR).

The closest TCP/IP analogy I can think of here is that of port numbers, there’s still an IP (Point code) but the port number allows us to specify multiple applications that run at a higher layer. This analogy falls down when we consider that the Point Code is generally set to that of your STP, not the final STP.

For this to work, we’ve got to have at least one Signaling Transfer Point in the flow, where we send the request to.

Somewhere (generally at the end of the chain of STPs), an STP is going to perform Global Title Translation.

What does this look like? Well let’s have a look at my GT table for the example above, in my lab network, I’ve got two nodes attached (via M3UA but could equally be on MTP3 links), my test MAP client where I’m originating this traffic, and an SMS Firewall, I can see they’re both up here:

Now knowing this I need to setup my SCCP routing for Global Title. In the screenshot above, the Called Party was 888888888 with Subsystem Number 7. Inside the SCCP request, there’s a few other fields, the Translation Type we have set to 0, Global Title Indicator is 4 (route on Global Title), while Numbering Plan Indicator is 1 (ISDN) and Nature of Address Indicator is 4 (International).

So on my Cisco ITP I define a GTT Selector to target traffic with these values, Translation Type is 0, Global Title Indicator is 4, Number Plan is 1 and the Nature of Address Indicator is 4.

So we’d define a Global Title Translation selector like the one below to match this traffic:

cs7 instance 0 gtt selector GLOBAL_tt0 tt 0 gti 4 np 1 nai 4

But that’s only matching the group of traffic, it’s not going to match based on the actual SCCP Called Party. So now I need to define a translation for each Global Title address (Called /Calling party) or prefix I want to route, I’ve setup anything starting with 888 to route to the `SMSFirewall` ASP endpoint.

cs7 instance 0 gtt selector GLOBAL_tt0 tt 0 gti 4 np 1 nai 4
     gta 888  asname SMSFirewall gt ssn 6

I could stop here and my request addressed to 888888888 would make it to the SMSFirewall ASP, but the response never would, like in all SS7 routing, we need to define the return route translation too, which is what I’ve done for 999999 to route to the TestClient.

Lastly I’ve added a wildcard route, this means if this STP doesn’t know how to resolve a GT address matching the rules in the top line, it’ll forward the request to the STP at point code 1.2.3 – This is how you’d do your connection to an IPX / Signaling exchange.

Debugging this can be a massive pain in the backside, but if you enable logging you can see when GT rules are not matched, like in the example below.

If your network is quiet enough, it’s sometimes easier to just make your rules based on what you observe failing to route.

So with those routes in place, when we send a request with the Global Title called party starting with 8888888 it’s routed to M3UA ASP SMSFirewall, which handles the request, and then sends the response back to the MAPClient M3UA ASP.

Tales from the Trenches – SMS Data Coding Scheme 0

IMS / VoLTE, Mobile Networks, Notes, RFCs & Standards, , , , ,

The Data Coding Scheme (DCS or TP-DCS) header in an SMS body indicates what encoding is used in that message.

It means if we’re using UCS-2 (UTF16) special characters like Emojis etc, in in our message, the phone knows to decode the data in the message body using UTF, because the Data Coding Scheme (DCS) header indicates the contents are encoded in UTF.

Likewise, if we’re not using any fancy characters in our message and the message is encoded as plain old GSM7, we set set the DCS to 0 to indicate this is using GSM7.

From my experience, I’d always assumed that DCS0 (Default) == GSM7, but today I learned, that’s not always the case. Some SMSc entities treat DCS0 as Latin.

Let me explain why this is stupid and why I wasted a lot of time on this.

We can indicate that a message is encoded as Latin by setting the DCS to 0x03:

We cannot indicate that the message is encoded as GSM7 through anything other than the default alphabet (DCS 0).

Latin has it’s own encoding flag, if I wanted the message treated as Latin, I’d indicate the message encoding is Latin in the DCS bit!

I spent a bunch of time trying to work out why a customer was having issues getting messages to subscribers on another operator, and it turned out the other operator treats messages we send to them on SMPP with DCS0 as Latin encoding, and then cracks the sads when trying to deliver it.

The above diff shows the message we send (Right), and the message they dry to deliver (left).

Well, lesson learned…

5G Core – The Service Based Architecture concept

5G SA, Mobile Networks, RFCs & Standards, , ,

One of the new features of 5GC is the introduction of Service Based Interfaces (SBI) which is part of 5GC’s Service Based Architecture (SBA).

Let’s start with the description from the specs:

3GPP TS 23.501 [3] defines the 5G System Architecture as a Service Based Architecture, i.e. a system architecture in which the system functionality is achieved by a set of NFs providing services to other authorized NFs to access their services.

3GPP TS 29.500 – 4.1 NF Services

For that we have two key concepts, service discovery, and service consumption

Services Consumer / Producers

That’s some nice words, but let’s break down what this actually means, for starters, let’s talk about services.

In previous generations of core network we had interfaces instead of services. Interfaces were the reference point between two network elements, describing how the two would talk. The interfaces were the protocols the two interfaces used to communicate.

For example, in EPC / LTE S6a is the interface between the MME and the HSS, S5 is the interface between the S-GW and P-GW. You could lookup the 3GPP spec for each interface to understand exactly how it works, or decode it in Wireshark to see it in action.

5GC moves from interfaces to services. Interfaces are strictly between two network elements, the S6a interface is only used between the MME and the HSS, while a service is designed to be reusable.

This means the Service Based Interface N5g-eir can be used by the AMF, but it could equally be used by anyone else who wants access to that information.

3GPP defines the service in the form of service producer (The EIR produces the N5g-eir service) and the service consumer (The client connecting to the N5g-eir service), but doens’t restrict which network elements can

This gets away from the soup of interfaces available, and instead just defines the services being offered, rather than locking the

“service consumers” (which can be thought of clients in a client/server model) can discover “service producers” (like servers in a client/server model).

Our AMF, which acts as a “service consumer” consuming services from the UDM/UDR and SMF.

Service Discovery – Automated Discovery of NF Services

Service-Based Architecture enables 5G Core Network Function service discovery.

In simple terms, this means rather that your MME being told about your SGW, the nodes all talk to a “Network Repository Function” that returns a list of available nodes.

I’ve written a full blog post on the NRF that explains the concepts.

Tuning SCTP Init with Linux’s SCTP module

Python, RFCs & Standards, , ,

The other side of the SCTP connection didn’t like my SCTP parameters.

My SCTP INIT looked like this:

By default, Linux includes support for the ECN and Supported Address Types parameters in the SCTP INIT.

But the other side did not like this, it sent back an ERROR stating that:

Okay, apparently it doesn’t like the fact that we support Forward Transmission Sequence Numbers – So how to turn it off?

I’m using P1Sec’s PySCTP library to interact with the SCTP stack, and I couldn’t find any referneces to this in the code, but then I rememberd that PySCTP is just a wrapper for libsctp so I should be able to control it from there.

The Manual (of course) has the answers.

Inside `/proc/sys/net/sctp` we can see all the parameters we can control.

To disable the Forward TSN I need to disable the feature that controls it – Forward Transmission Sequence numbers are introduced in the Partial Reliability Extension (RFC 3758). So it was just a matter of disabling that with:

sysctl -w net.sctp.prsctp_enable=1

And lo, now my SCTP INITs are happy!

Transport Keys & A4 / K4 Keys in EPC & 5GC Networks

5G SA, EPC, LTE, Mobile Networks, RFCs & Standards, SDM, Security, , , , , ,

If you’re working with the larger SIM vendors, there’s a good chance they key material they send you won’t actually contain the raw Ki values for each card – If it fell into the wrong hands you’d be in big trouble.

Instead, what is more likely is that the SIM vendor shares the Ki generated when mixed with a transport key – So what you receive is not the plaintext version of the Ki data, but rather a ciphered version of it.

But as long as you and the SIM vendor have agreed on the ciphering to use, an the secret to protect it with beforehand, you can read the data as needed.

This is a tricky topic to broach, as transport key implementation, is not covered by the 3GPP, instead it’s a quasi-standard, that is commonly used by SIM vendors and HSS vendors alike – the A4 / K4 Transport Encryption Algorithm.

It’s made up of a few components:

  • K2 is our plaintext key data (Ki or OP)
  • K4 is the secret key used to cipher the Ki value.
  • K7 is the algorithm used (Usually AES128 or AES256).

I won’t explain too much about the crypto, but here’s an example from IoT Connectivity’s KiOpcGenerator tool:

def aes_128_cbc_encrypt(key, text):
    """
    implements aes 128b encryption with cbc.
    """
    keyb = binascii.unhexlify(key)
    textb = binascii.unhexlify(text)
    encryptor = AES.new(keyb, AES.MODE_CBC, IV=IV)
    ciphertext = encryptor.encrypt(textb)
    return ciphertext.hex().upper()

It’s important when defining your electrical profile and the reuqired parameters, to make sure the operator, HSS vendor and SIM vendor are all on the same page regarding if transport keys will be used, what the cipher used will be, and the keys for each batch of SIMs.

Here’s an example from a Huawei HSS with SIMs from G&D:

%%LST K4: HLRSN=1;%%
RETCODE = 0 SUCCESS0001:Operation is successful

        "K4SNO" "ALGTYPE"     "K7SNO" "KEYNAME"
        1       AES128        NONE    G+D

We’re using AES128, and any SIMs produced by G&D for this batch will use that transport key (transport key ID 1 in the HSS), so when adding new SIMs we’ll need to specify what transport key to use.

NB-IoT Flows for NIDD

EPC, EUTRAN, LTE, Mobile Networks, RFCs & Standards, SDM, , ,

In our last post we covered the basics of NB-IoT Non-IP Data Deliver (NIDD), and if that acronym soup wasn’t enough for you, we’re going to take a deep dive into the flows for attaching, sending, receiving and closing a NIDD session.

The attach for NIDD is very similar to the standard attach for wideband LTE, except the MME establishes a connection on the T6a Diameter interface toward the SCEF, to indicate the sub is online and available.

The NIDD Attach

The SCEF is now able to send/receive NIDD traffic from the subscriber on the T6a interface, but in reality developers don’t / won’t interact with Diameter, so the SCEF exposes the T8 API that developers can interact with to access an abstraction layer to interact with the SCEF, and then through onto the UE.

If you’re wondering what the status of Open Source SCEF implementations are, then you may have already guessed we’re working on one! PyHSS should have support for NB-IoT SCEF features in the future.

NB-IoT provides support for Non-IP Data Delivery (NIDD) over 3GPP Networks, but to handle this, some new network elements are introduced, in a home network scenario that’s the SCEF and the SCF/AS.

On the 3GPP side the SCEF it communicates to the MME via the T6a Interface, which is based upon Diameter.

On the side towards our IoT Service Consumers (in the standards referred to as “SCS/AS” or “Service Capabilities Server Application Servers” (catchy names as always), via the RESTful HTTP based T8 interface.

I’ve written about Non-IP Data support in 5G for transporting Ethernet, but there’s another non-IP use case in 3GPP networks – This time for NB-IoT services.

Procedures

S1 Attach

The start of the S1 Attach procedure is very similar to a regular S1 attach.

The initial S1 PDU Connectivity Request indicates in the ESM Message Container that the PDN Type is Non IP.

S1 PDU Connectivity Request from attach procedure

Other than that, the initial attach procedure looks very similar to the regular S1 attach procedure.

On the S6a interface the Update Location Request from the MME to the HSS indicates that this is an EUTRAN-NB-IoT Radio Access Type.

And the Update Location Answer APN Configuration contains some additional AVPs on the APN to indicate that the APN supports Non-IP-PDN-Type and that the SCEF is used for Data Delivery.

The SCEF-ID (Diameter Host) and SCEF-Realm (Diameter realm) to serve this user is also specified in the APN Configuration in the Update Location Answer.

This is how our MME determines where to send the T6a traffic.

With this, the MME sends a Connection Management Request (CMR) towards the SCEF specified in the SCEF-ID returned by the HSS.

The Connection Management Request / Response

The MME now sends a Diameter T6a Connection Management Request to the SCEF in the Update Location Answer,

In it we have a Session-Id, which continues for the life of our NIDD session, the service-selection which contains our APN (In our case “non-ip”) and the User-Identifier AVP which contains the MSISDN and/or IMSI of the subscriber.

To accept this, the SCEF sends back a Connection-Management-Answer to confirm we’re all good to go:

At this point our SCEF now knows about the subscriber who’s just attached to our network, and correlates it with the APN and the session-ID.

On the S1 side the connection is confirmed and we’re ready to roll.

Mobile Originated Data Request / Response

When the UE wants to send NIDD it’s carried in NAS messaging, so we see an Uplink NAS transport from the UE and inside the NAS payload itself is our HEX data.

Our MME grabs this out and sends it in the form of of a Mobile-Originated-Data-Request (MODR) to the SCEF, along with the same Session-ID that was setup earlier:

At this stage our Non-IP Data is exposed over the T8 RESTful API, which we won’t cover in this post.

Uncomfortable Questions to ask about 5G Standalone at MWC – Part 3 – We *have* to do 5GC.

5G SA, Mobile Networks, RFCs & Standards, ,

This post follows on from Part 1 and Part 2 of this 3 part series.

We are forced to move to 5G-SA

Claim: We must use 5G-SA with this spectrum (It’s a condition of the license)

I’ll concede that if it is a requirement for a license or funding, that 5G-SA be used, then that’s a pretty ironclad reason to introduce 5G-SA.

Claim: Users will Leave if you don’t have 5G-SA

We could argue the opposite effect will happen; Shifting to SA will reduce your user base.
Here’s why:

Users experiencing 5G-NSA (Non-Standalone) today, are already getting the speed boost from “5G”.

From a user perspective, while 5G-NSA support has been becoming common on mid-to-high priced handsets, handsets supporting 5G-SA are far less common.

Dish’ Project Genesis is one of the only examples of a 5G SA network deployed on a large scale. It launched with only a single supported phone (A Motorola branded handset) and today the supported phone list is very short, limited to expensive flagships. This lack of handset support means users must purchase a handset through Dish rather than being able to bring their own phones, as the only way that compatibility can be guaranteed is by controlling the whole ecosystem.

Unless you are in a highly developed market with 2G and 3G turned off, where the majority of your user base has recent generation flagship phones capable of supporting these features, you’re shrinking your addressable market with 5G-SA, rather than expanding it.

Conclusion – 5G-SA doesn’t stack up, what do I do?

SA doesn’t make sense for a lot of operators and markets – for now. I’m sure this post will look pretty dated in a few years time as many of these factors change and as operators sunset 2G and 3G networks.

I’m not advocating for 5G-SA never, I’m advocating not 5G-SA today.

There are simply better options out there for spending that operations budget to make network improvements.

Off the bat some ideas to expore:

  • Optimize your existing network.
  • Roll out NSA to an even larger area.
  • Shutdown 2G/3G layers.
  • Simplify your operations.
  • Cut down the number of vendors and moving parts.
  • Simplify again.
  • Automate.
  • Simplify more.

Doing this will mean you can enjoy cost savings from reduced headcount thanks to a simpler network.
Simpler networks have better up-time, thanks to operating a network that’s less frankensteiny – less cobbled together from disparate legacy parts.
You’ll also Enjoy reduced opex from all the systems you’ve shut down and cheaper roaming from all the bilaterals you moved to VoLTE.

All of these tasks will keep project teams busy for years and put the MNO in a stronger position moving forward, without getting distracted by slick marketing and shiny brochures.

OPc vs OP in SIM keys

5G SA, GSM, LTE, Mobile Networks, RFCs & Standards, SDM, Security, SIM Cards, , , , ,

Years ago I wrote an article looking at how Key generation works inside SIM cards for LTE & 5G-NR.

I got this great question the other day:

Hello Nick, thank you for the article.
What is the use of the OPc key to be derived from OP key ?
Why can’t it just be a random key like Ki ?

It’s a super good question, and something I see a lot of operators get “wrong” from a security best practices perspective.

Refresher on OP vs OPc Keys

The “OP Key” is the “operator” key, and was (historically) common for an operator.

This meant all SIMs in the network had a common OP Key, and each SIM had a unique Ki/K key.

The SIM knew both, and the HSS only needed to know what the Ki was for the SIM, as they shared a common OP Key (Generally you associate an index which translates to the OP Key for that batch of SIMs but you get the idea).

But having common key material is probably not the best idea – I’m sure there was probably some reason why using a common key across all the SIMs seemed like a good option, and the K / Ki key has always been unique, so there was one unique key per SIM, but previously, OP was common.

Over time, the issues with this became clear, so the OPc key was introduced. OPc is derived from mushing the K & OP key together. This means we don’t need to expose / store the original OP key in the SIM or the HSS just the derived OPc key output.

This adds additional security, if the Ki for a SIM were to be exposed along with the OP for that operator, that’s half the entropy lost. Whereas by storing the Ki and OPc you limit the blast radius if say a single SIMs data was exposed, to only the data for that particular SIM.

This is how most operators achieve this today; there is still a common OP Key, locked away in a vault alongside the recipe for Coca-cola and the moon landing set.

But his OP Key is no longer written to the SIMs or stored in the HSS.

Instead, during the personalization process (The bit in manufacturing where SIMs get the unique data written to them (The IMSI & keys)) a derived OPc key is written to the card itself, and to the output files the operator then loads into their HSS/HLR/AuC.

This is not my preferred method for handling key material however, today we get our SIM manufacturers to randomize the OP key for every card and then derive an OPc from that.

This means we have two unique keys for each SIM, and even if the Ki and OP were to become exposed for a SIM, there is nothing common between that SIM, and the other SIMs in the network.

Values stores on the LTE / EUTRAN / EPC Home Subscriber Server (HSS) including K Key, OP / OPc key and SQN SequenceNUmber

Do we want our Ki to leak? No. Do we want an OP Key to leak? No. But if we’ve got unique keys for everything we minimize the blast radius if something were to happen – Just minimizes the risk.

DNS’ role in S8-Home Routing Roaming

EPC, IMS / VoLTE, LTE, Mobile Networks, Notes, RFCs & Standards, , , , ,

S8 Home Routing is a really simple concept, the traffic goes from the SGW in the visited PLMN to the PGW in the home PLMN, so the PCRF, OCS/OFCS, IMS, IP Addresses, etc, etc, are all in the home network, and this avoids huge amounts of complexity.

But in order for this to work, the visited network MME needs to find the PGW of the home network, and with over 700 roaming networks in commercial use, each one with potentially hundreds of unique APNs each routing to a different PGW, this is a tricky proposition.

If you’ve configured your PGW peers statically on your MME, that’s fine, but it doesn’t scale very well – And if you add an MVNO who wants their own PGW for serving their APN, well you’ll be adding some complexity there to, so what to do?

Well, the answer is DNS.

By taking the APN to be served, the home PLMN and the interface type desired, with some funky DNS queries, our MME can determine which PGW should be selected for a request.

Let’s take a look, for a UE from MNC XXX MCC YYY roaming into our network, trying to access the “IMS” APN.

Our MME knows the network code of the roaming subscriber from the IMSI is MNC XXX, MCC YYY, and that the UE is requesting the IMS APN.

So our MME crafts a DNS request for the NAPTR query for ims.apn.epc.mncXXX.mccYYY.3gppnetwork.org:

Because the domain is epc.mncXXX.mccYYY.3gppnetwork.org it’s routed to the authoritative DNS server in the home network, which sends back the response:

We’ve got a few peers to pick from, so we need to filter this list of Answers to only those that are relevant to us.

First we filter by the Service tag, whihc for each listed peer shows what services that peer supports.

But since we’re looking for S8, we need to find a peer who’s “Service” tag string contains:

x-3gpp-pgw:x-s8-gtp

We’re looking for two bits of info here, the presence of x-3gpp-pgw in the Service to indicate that this peer is a PGW and x-s8-gtp to indicate that this peer supports the S8 interface.

A service string like this:

x-3gpp-pgw:x-s5-gtp

Would be excluded as it only supports S5 not S8 (Even though they are largely the same interface, S8 is used in roaming).

It’s also not uncommon to see both services indicated as supported, in which case that peer could be selected too:

x-3gpp-pgw:x-s5-gtp:x-s8-gtp

(The answers in the screenshot include :x-gp which means the PGWs advertised are also co-located with a GGSN)

So with our answers whittled down to only those that meet our needs, we next use the Order and the Preference to pick our best candidate, this is the same as regular DNS selection logic.

From our candidate, we’ve also got the Regex Replacement, which allows our original DNS request to be re-written, which allows us to point at a single peer.

In our answer, we see the original request ims.apn.epc.mncXXX.mccYYY.3gppnetwork.org is to be re-written to topon.lb1.pgw01.epc.mncXXX.mccYYY.3gppnetwork.org.

This is the FQDN of the PGW we should use.

Now we know the FQND we should use, we just do an A-Record lookup (Or AAAA record lookup if it is IPv6) for that peer we are targeting, to turn that FQDN into an IP address we can use.

And then in comes the response:

So now our MME knows the IP of the PGW, it can craft a Create Session request where the F-TEID for the S8 interface has the PGW IP set on it that we selected.

For more info on this TS 129.303 (Domain Name System Procedures) is the definitive doc, but the GSMA’s IR.88 “LTE and EPC Roaming Guidelines” provides a handy reference.

SMS over Diameter for Roaming SMS

EPC, GSM, LTE, Mobile Networks, RFCs & Standards, , , ,

I know what you’re thinking, again with the SMS transport talk Nick? Ha! As if we’re done talking about SMS. Recently we did something kinda cool – The world’s first SMS sent over NB-IoT (Satellite).

But to do this, we weren’t using IMS, it’s too heavy (I’ve written about NB-IoT’s NIDD functions and the past).

SGs-AP which is used for CSFB & SMS doesn’t span network borders (you can’t roam with SGs-AP), and with SMSoIP out of the question, that gave us the option of MAP or Diameter, so we picked Diameter.

This introduces the S6c and SGd Diameter interfaces, in the diagrams below Orange is the Home Network (HPMN) and the Green is the Visited Network (VPMN).

The S6c interface is used between the SMSc and the HSS, in order to retrieve the routing information. This like the SRI-for-SM in MAP.

The SGd interface is used between the MME serving the UE and the SMSc, and is used for actual delivery of the MO/MT messages.

I haven’t shown the Diameter Routing Agents in these diagrams, but in reality there would be a DRA on the VPLMN and a DRA on the HPMN, and probably a DRA in the IPX between them too.

The Attach

The attach looks like a regular roaming attach, the MME in the Visited PMN sends an Update Location Request to the HSS, so the HSS knows the MME that is serving the subscriber.

S6a Update Location Request to indicate the MME serving the Subscriber

The Mobile Terminated SMS Flow

Now we introduce the S6c interface and the SGd interfaces.

When the Home SMSc has a message to send to the subscriber (Mobile Terminated SMS) it runs a the Send-Routing-Info-for-SM-Request (SRR) dialog to the HSS.

The Send-Routing-Info-for-SM-Answer (SRA) back from the HSS contains the info on the MME Diameter Host name and Diameter Realm serving the subscriber.

S6t – Send-Routing-Info-for-SM request to get the MME serving the subscriber

With this info, we can now craft a Diameter Request that will get sent to the MME serving the subscriber, containing the SMS PDU to send to the UE.

SGd MT-Forward-Short-Message to deliver Mobile Terminated SMS to the serving MME

We make sure it’s sent to the correct MME by setting the Destination-Host and Destination-Realm in the Diameter request.

Here’s how the request looks from the SMSc towards our DRA:

As you can see the Destination Realm and Destination-Host is set, as is the User-Name set to the IMSI of the UE we want to send the message to.

And down the bottom you can see the SMS-TPDU, the same as it’s been all the way back since GSM days.

The Mobile Originated SMS Flow

The Mobile Originated flow is even simpler, because we don’t need to look up where to route it to.

The MME receives the MO SMS from the UE, and shoves it into a Diameter message with Application ID set to SGd and Destination-Realm set to the HPMN Realm.

When the message reaches the DRA in the HPMN it forwards the request to an SMSc and then the Home SMSc has the message ready to roll.

So that’s it, pretty straightforward to set up!

Uncomfortable Questions to ask about 5G Standalone at MWC – Part 2 – Has this Cash cow got Milk?

5G SA, EPC, Mobile Networks, RFCs & Standards, Software, , , , ,

This is the second post of 3 presenting the argument against introducing 5G-SA.

There’s an old adage that businesses spend money for one of three reasons:

  • To Save Money (Which I covered yesterday)
  • To make more Money (This post, congratulations, you’re reading it!)
  • Because they have to (Regulatory compliance, insurance, taxes, etc) – That’s the next post

So let’s look at SA in this context.

5G-SA can drive new revenue streams

We (as an industry) suck at this.

Last year on the Telecoms.com podcast, Scott Bicheno made the point that if operators took all the money they’d gambled (and lost) on trying to play in the sports rights, involvement in media companies, building their own streaming apps, attempts at bundling other utilities, digital identity, etc, and just left the cash in the bank and just operated the network, they’d be better off.

Uber, Spotify, “OTTs”, etc, utilize MNOs to enable their services, but operators don’t see this extra revenue.
While some operators may talk of “fair share” the truth is, these companies add value to our product (connectivity) which as an industry, we’ve failed to add ourselves.

Last year at MWC we saw vendors were still beating the drum about 5G being critical for the “Metaverse”, just weeks before Meta announced they were moving away from the Metaverse.

Today the only device getting any attention from consumers is Apple’s Vision Pro, a very pricey, currently niche offering, which has no SIM card or cellular connectivity.

If the Metaverse does turn out to be a cash cow, it is unlikely the telecommunications industry will be the ones milking it.

Claim: Customers are willing to pay more for 5G-SA

This myth seems to be fairly persistent, but with minimal data to support this claim.

While BSS vendors talk about “5G Monetization”, the truth is, people use their MNO to provide them connectivity. If the coverage is adequate, and the speed enough to do what they need to do, few would be willing to pay any additional cash each month to see higher numbers on a speedtest result (enabled by 5G-NSA) and even fewer would pay extra cash for, well, whatever those features only enabled by 5G-Standalone are?

With most consumers now also holding onto their mobile devices for longer periods of time, and with interest rates reining in consumer spending across the board, we are seeing the rise of a more cost conscious consumer than ever before. If we want to see higher ARPUs, we need to give the consumer a compelling reason to care and spend their cash, beyond a speed test result.

We talk a little about APIs lower down in the post.

Claim: Users want Ultra-Low Latency / High Reliability Comms that only 5G-SA delivers

Wanting to offer a product to the market, is not the same as the market wanting a product to consume.

Telecom operators want customers to want these services, but customer take up rates tell a different story. For a product like this to be viable, it must have a wide enough addressable market to justify the investment.

Reliability

The URLCC standards focus on preventing packet loss, but the world has moved on from needing zero packet loss.

The telecom industry has a habit of deciding what customers want without actually listening.
When a customer talks about wanting “reliable” comms, they aren’t saying they want zero packet loss, but rather fewer dropouts or service flaps.
For us to give the customer what they are actually asking for involves us expanding RAN footprint and adding transmission diversity, not 5G-SA.

The “protocols of the internet” (TCP/IP) have been around for more than 50 years now.

These protocols have always flowed over transport links with varied reliability and levels of packet loss.

Thanks to these error correction and retransmission techniques built into these protocols, a lost packet will not interrupt the stream. If your nuclear command and control network were carried over TCP/IP over the public internet (please don’t do this), a missing packet won’t lead to worldwide annihilation, but rather the sender will see the receiver never acknowledged the receipt of the packet at the other end, and resend it, end of.

If you walk into a hospital today, you’ll find patient monitoring devices, tracking the vital signs for patients and alerting hospital staff if a patient’s vital signs change. It is hard to think of more important services for reliability than this.

And yet they use WiFi, and have done for a long time, if a packet is lost on WiFi (as happens regularly) it’s just retransmitted and the end user never knows.

Autonomous cars are unlikely to ever rely on a 5G connection to operate, for the simple reason that coverage will never be 100%. If your car stops because you’re in a not-spot, you won’t be a happy customer. While plenty of cars have cellular modems in them, that are used to upload telemetry data back to the manufacturer, but not to drive the car.

One example of wireless controlled vehicles in the wild is autonomous haul trucks in mines. Historically, these have used WiFi for their comms. Mine sites are often a good fit for Private LTE, but there’s nothing inherent in the 5G Standalone standard that means it’s the only tool for the job here.

Slicing

Slicing is available in LTE (4G), with an architecture designed to allow access to others. It failed to gain traction, but is in networks today.

See: Pre-5G Network Slicing.

What is different this time?

Low Latency

The RAN a piece of the latency puzzle here, but it is just one piece of the puzzle.

If we look at the flow a packet takes from the user’s device to the server they want to talk to we’ve got:

  1. Time it takes the UE to craft the packet
  2. Time it takes for the packet to be transmitted over the air to the base station
  3. Time it takes for the packet to get through the RAN transmission network to the core
  4. Time it takes the packet to traverse the packet core
  5. Time it takes for the packet to get out to transit/peering
  6. Time it takes to get the packet from the edge of the operators network to the edge of the network hosting the server
  7. Time it takes the packet through the network the server is on
  8. Time it takes the server to process the request

The “low latency” bit of the 5G puzzle only involves the two elements in bold.

If you’ve got to get from point A to point B along a series of roads, and the speed limit on two of the roads you traverse (short sections already) is increased. The overall travel time is not drastically reduced.

I’m lucky, I have access to a well kitted out lab which allows me to put all of these latency figures to the test and provide side by side metrics. If this is of interest to anyone, let me know. Otherwise in the meantime you’ll just have to accept some conjecture and opinion.

You could rebut this talking about Edge Compute, and having the datacenter at the base of the tower, but for a number of fairly well documented reasons, I think this is unlikely to attract widespread deployment in established carrier networks, and Intel’s recent yearly earning specifically called this out.


Claim: Customers want APIs and these needs 5G SA

Companies like Twilio have made it easy to interact with the carrier network via their APIs, but yet again, it’s these companies producing the additional value on a service operated by the MNOs.

My coffee machine does not have an API, and I’m OK with this because I don’t have a want or need to interact with it programatically.

By far, the most common APIs used by businesses involving telco markets are APIs to enable sending an SMS to a user.

These have been around for a long time, and the A2P market is pretty well established, and the good news is, operators already get a chunk of this pie, by charging for the SMS.

Imagine a company that makes medical booking software. They’re a tech company, so they want their stack to work anywhere in the world, and they want to be able to send reminder SMS to end users.

They could get an account manager with each of the telcos in each of the markets they work in, onboard and integrate the arcane complexities of each operators wholesale SMS system, or they could use Twilio or a similar service, which gives them global reach.

Often the cost of services like Twilio are cheaper than working directly with the carriers in each market, and even if it is marginally more expensive, the cost savings by not having to deal with dozens of carriers or integrate into dozens of systems, far outweighs this.

GSMA’s OpenGateway Initiative has sought to rectify this, but it lacks support for the use case we just discussed.

While it’s a great idea, in the context of 5G Standalone and APIs, it’s worth noting that none of the use cases in OpenGateway require 5G Standalone (Except possibly Edge discovery, but it is debatable).

Even Slicing existed before in LTE.

Critically, from a developer experience perspective:

I can sign up to services like Twilio without a credit card, and start using the service right away, with examples in my programming language of choice, the developer user experience is fantastic.

Jump on the OpenGateway website today and see if you can even find a way to sign up to use the service?

Claim: Fixed Wireless works best with 5G-SA

Of all the touted use cases and applications for 5G, Fixed Wireless (FWA) has been the most successful.

The great thing about FWA on Cellular networks is you can use the same infrastructure you use for your mobile customers, and then sell excess capacity in the network to deliver Fixed Wireless Access services, better utilizing an asset (great!).

But again, this does not require Standalone 5G. If you deploy your FWA network using 5G SA, then you won’t be able to sweat that same asset for both mobile subscribers and FWA subscribers.

Today at least, very few handsets short of this generation of flagship phones, supports 5G SA. Even the phones sold as supporting 5G over the past few years, are almost all only supporting 5G-NSA, so if you rolled out your FWA network as Standalone, you can’t better utilize the asset by sharing with your existing LTE/5G-NSA customers.

Claim: The Killer App is coming for 5G and it needs 5G SA

This space is reserved for the killer app that requires 5G Standalone.

Whenever that comes?

Anyone?

I’m not paying to build a marina berth for my mega yacht, mostly because I don’t have one. Ditto this.

Could you explain to everyone on an investor call that you’re investing in something where the vessel of the payoff isn’t even known to exist? Telecom is “blue chip”, hardly speculative.

The Future for Revenue Growth?

Maybe there isn’t one.

I know it’s an unthinkable thought for a lot of operators, but let’s look at it rationally; in the developed world, everyone who wants a mobile service already has one.

This leaves operators with two options; gaining market share from their competitors and selling more/higher priced services to existing customers.

You don’t steal away customers from other operators by offering a higher priced product, and with reduced consumer spending people aren’t queuing up to spend more each month.

But there is a silver lining, if you can’t grow revenues, you can still shrink expenditure, which in the end still gets the same result at the end of the quarter – More cash.

Simplify your operations, focus on what you do really well (mobile services), the whole 80/20 rule, get better at self service, all that guff.

There’s no shortage of pain points for consumers telecom operators could address, to make the customer experience better, but few that include the word Slicing.

Uncomfortable Questions to ask about 5G Standalone at MWC – Part 1 – Does $tandalone save $$$?

5G SA, EPC, EUTRAN, Mobile Networks, RFCs & Standards, , , ,

No one spends marketing dollars talking about the problems with a tech and vendors aren’t out there promoting sweating existing assets. But understanding your options as an operator is more important now than ever before.

Sidebar; This post got really long, so I’m splitting it into 3…

We’re often asked to help define a a 5G strategy for operators; while every case is different, there’s a lot of vendors pushing MNOs to move towards 5G standalone or 5G-SA.

I’m always a fan of playing “devil’s advocate“, and with so many articles and press releases singing the praises of standalone 5G/5G-SA, so as a counter in this post, I’ll be making the case against the narratives presented to operators by vendors that the “right” way to do 5G is to introduce 5G Standalone, that they should all be “upgrading” to Standalone 5G.

With Mobile World Congress around the corner, now seems like a good time to put forward the argument against introducing 5G Standalone, rebutting some common claims about 5G Standalone operators will be told. We’ll counterpoint these arguments and I’ll put forward the case for not jumping onto the 5G-SA bandwagon – just yet.

On a personal note, I do like 5G SA, it has some real advantages and some cool features, which are well documented, including on this blog. I’m not looking to beat up on any vendors, marketing hype or events, but just to provide the “other side” of the equation that operators should consider when making decisions and may not be aware of otherwise. It’s also all opinion of course (cited where possible), but if you’re going to build your network based on a blog post (even one as good as this) you should probably reconsider your life choices.

Some Arcane Detail: 5G Non-Standalone (NSA) vs Standalone (SA)

5G NSA (Non Standalone) uses LTE (4G) with an additional layer “bolted on” that uses 5G on the radio interface to provide “5G” speeds to users, while reusing the existing LTE (Evolved Packet Core) core and VoLTE for voice / SMS.

Image source: Samsung

From an operator perspective there is almost no change required in the network to support NSA 5G, other than in the RAN, and almost all the 5G networks in commercial use today use 5G NSA.

5G NSA is great, it gives the user 5G speeds for users with phones that support it, with no change to the rest of the network needed.

Standalone 5G on the other hand requires an a completely new core network with all the trimmings.

While it is possible to handover / interwork with LTE/4G (Inter-RAT Handovers), this is like 3G/4G interworking, where each has a different core network. Introducing 5G standalone touches every element of the network, you need new nodes supporting the new standards for charging, policy, user plane, IMS, etc.

Scope

There’s an old adage that businesses spend money for one of three reasons:

  • To Save Money (Which we’ll cover in this post)
  • To make more Money (Covered next – Will link when published)
  • Because they have to (Regulatory compliance, insurance, taxes, etc)

Let’s look at 5G Standalone in each of these contexts:

5G Cost Savings – Counterpoint: The cost-benefit doesn’t stack up

As an operator with an existing deployed 4G LTE network, deploying a new 5G standalone network will not save you money.

From an capital perspective this is pretty obvious, you’re going to need to invest in a new RAN and a new core to support this, but what about from an opex perspective?

Claim: 5G RAN is more efficient than 4G (LTE) RAN

Spectrum is both finite and expensive, so MNOs must find the most efficient way to use that spectrum, to squeeze the most possible value out of it.

Let’s look at some numbers:

Breakdown of theoretical maximum downlink speed for 5Mhz of spectrum used in GSM, UMTS, LTE or NR.

In the case of 3G vs 4G (LTE) there was a strong cost saving case to be made; a single 5Mhz UMTS (3G) cell could carry a total of 14Mbps, while if that same 5Mhz channel was refarmed / shifted to a 4×4 LTE (4G) carrier we hit 75Mbps of downlink data.

In rough numbers, we can say we get 5x the spectral efficiency by moving from 3G to 4G. This means we can carry 5.2x more with the same spectrum on 4G than we can on 3G – A very compelling reason to upgrade.

The like-for-like spectral efficiency of 5G is not significantly greater than that of LTE.

In numbers the same 5Mhz of spectrum we refarmed from UMTS (3G) to 4G (LTE) provided a 5x gain in efficiency to deliver 75Mbps on LTE. The same configuration refarmed to 5G-NR would provide 80Mbps.

Refarming spectrum from 4G (LTE) to 5G (NR) only provides a 6% increase in spectral efficiency.

While 6% is not nothing, if refarmed to a 5G standalone network, the spectrum can no longer be used by LTE only devices (Unless Dynamic Spectrum Sharing is used which in itself leads to efficiency losses), which in itself reduces the efficiency and would add additional load to other layers.

The crazy speeds demonstrated by 5G are not due to meaningful increases in efficiency, but rather the ability to use more spectrum, spectrum that operators need to purchase at auction, purchase equipment to utilize and pay to run.

Claim: 5G Standalone Core is Cheaper to operate as it is “Cloud Native”

It has been widely claimed that the shift for the 5G Core Architecture to being “Cloud Native” can provide cost savings.

Operators should regard this in a skeptical manner; after all, we’ve been here before.

Did moving from big-iron to VNFs provide the promised cost savings to operators?

For many operators the shift from hardware to software added additional complexity to the network and increased the headcount to support this.

What were once big-iron appliances dedicated to one job, that sat in the corner and chugged away, are now virtual machines (VNFs).
Many operators have naturally found themselves needing a larger team to manage the virtual environment, compared to the size of the team they needed to just to plug power and data into a big box in an exchange before everything was virtualized.

Introducing a “Cloud Native” Kubernetes layer on top of the VNF / virtualization layer, on top of the compute layer, leaves us with a whole lot of layers. All of which require resources to be maintain, troubleshoot and kept running; each layer having associated costs for staffing, licensing and support.

Many mid size enterprises rushed into “the cloud” for the promised cost savings only to sheepishly admit it cost more than the expected.

Almost none of the operators are talking about running these workloads in the public cloud, but rather “Private Clouds” built on-premises, using “Cloud Native” best practices.

One of the central arguments about cloud revolves around “elastic scaling” where the network can automatically scale to match demand; think extra instances spun up a times of peak demand and shut down when the demand drops.

I explain elastic scaling to clients as having to move people from one place to another. Most of the time, I’m just moving myself, a push bike is fine, or I’ve got a 4 seater car, but occasionally I’ll need to move 25 people and for that I’d need a bus.

If I provide the transportation myself, I need to own a bike, a car and a bus.

But if use the cloud I can start with the push bike, and as I need to move more people, the “cloud” will provide me the vehicle I need to move the people I need to move at that moment, and I’ll just pay for the time I need the bus, and when I’m done needing the bus, I drop back to the (cheaper) push bike when I’m not moving lots of people.

This is a really compelling argument, and telecom operators regularly announces partnerships with the hyperscalers, except they’re always for non-core-network workloads.

While telecom operators are going to provide the servers to run this in “On-prem-cloud”, they need to dimension for the maximum possible load. This means they need to own a bike/car/bus, even if they’re not using it most of the time, and there’s really no cost savings to having a bus but not using it when you’re not paying by the hour to hire it.

Infrastructure aside, introducing a Standalone 5G Core adds another core network to maintain. Alongside the Circuit Switched Core (MSC/GGSN/SGSN) serving 2G/3G subscribers, Evolved Packet Core serving 4G (LTE) and 5G-NSA subscribers, adding a 5G Standalone Core to for the 5G-SA subscribers served by the 5G SA cells, is going to be more work (and therefore cost).

While the majority of operators have yet to turn off their 2G/3G core networks, introducing another core network to run in parallel is unlikely to lead to any cost savings.

Claim: Upgrading now can save money in the Future / Future Proofing

Life cycles of telecommunications are two fold, one is the equipment/platform life cycle (like the RAN components or Core network software being used to deliver the service) the other is the technology life cycle (the generation of technology being used).

The technology lifecycles in telecommunications are vastly longer than that for regular tech.

GSM (2G) was introduced into the UK in 1991, and will be phased out starting in 2033, a 42 year long technology life cycle.

No vendor today could reasonably expect the 5G hardware you deploy in 2024 to still be in production in 2066 – The platform/equipment life cycle is a lot shorter than the technology life cycle.

Operators will to continue relying on LTE (4G) well into the late 2030s.

I’d wager that there is not a single piece of equipment in the Vodafone UK GSM network today, that was there in 1991.
I’d go even further to say that any piece of equipment in the network today, didn’t even replace the 1991 equipment, but was probably 3 or 4 generations removed from the network built in 1991.

For most operators, RAN replacements happen between 4 to 7 years, often with targeted augmentation / expansion as needed in the form of adding extra layers / sectors between these times.

The question operators should be asking is therefore not what will I need to get me through to 2066, but rather what will I need to get to 2030?

The majority of operators outside the US today still operate a 2G or 3G network, generally with minimal bandwidth to support legacy handsets and devices, while the 4G (LTE) network does most of the heavy lifting for carrying user traffic. This is often with the aid of an additional 5G-NSA (Non-Standalone) layer to provide additional capacity.

Is there a cost saving angle to adding support for 5G-Standalone in addition to 2G/3G/4G (LTE) and 5G (Non-Standalone) into your RAN?

A logical stance would be that removing layers / technologies (such as 2G/3G sunsetting) would lead to cost savings, and adding a 5G Standalone layer would increase cost.

All of the RAN solutions on the market today from the major vendors include support for both Standalone 5G and Non Standalone, but the feature licensing for a non-standalone 5G is generally cheaper than that for Standalone 5G.

The question operators should be asking is on what timescale do I need Standalone 5G?

If you’ve rolled out 5G-NSA today, then when are you looking to sunset your LTE network?
If the answer is “I hope to have long since retired by that time”, then you’ve just answered that question and you don’t need to licence / deploy 5G-SA in this hardware refresh cycle.

Other Cost Factors

Roaming: The majority of roaming traffic today relies on 2G/3G for voice. VoLTE roaming is (finally) starting to establish a foothold, but we are a long way from ubiquitous global roaming for LTE and VoLTE, and even further away for 5G-SA roaming. Focusing on 5G roaming will enable your network for roaming use by a miniscule number of operators, compared to LTE/VoLTE roaming which covers the majority of the operators in the developed world who can utilize your service.

I decided to split this into 3 posts, next I’ll post the “5G can make us more money” post and finally a “5G because we have to” post. I’ll post that on LinkedIn / Twitter / Mailing list, so stick around, and feel free to trash me in the comments.

Android and Emergency Calling

GSM, IMS / VoLTE, LTE, Mobile Networks, RFCs & Standards, SDM, SIM Cards, VoIP, , , , , , ,

In the last post we looked at emergency calling when roaming, and I mentioned that there are databases on the handsets for emergency numbers, to allow for example, calling 999 from a US phone, with a US SIM, roaming into the UK.

Android, being open source, allows us to see how this logic works, and it’s important for operators to understand this logic, as it’s what dictates the behavior in many scenarios.

It’s important to note that I’m not covering Apple here, this information is not publicly available to share for iOS devices, so I won’t be sharing anything on this – Apple has their own ecosystem to handle emergency calling, if you’re from an operator and reading this, I’d suggest getting in touch with your Apple account manager to discuss it, they’re always great to work with.

The Android Open Source Project has an “emergency number database”. This database has each of the emergency phone numbers and the corresponding service, for each country.

This file can be read at packages/services/Telephony/ecc/input/eccdata.txt on a phone with engineering mode.

Let’s take a look what’s in mainline Android for Australia:

You can check ECC for countries from the database on the AOSP repo.

This is one of the ways handsets know what codes represent emergency calling codes in different countries, alongside the values set in the SIM and provided by the visited network.