Categories
RFCs & Standards Voice over IP

SIP Extensions – 100rel SIP (RFC3262)

When a final response, like a 200 OK, or a 404, etc, is sent, the receiving party acknowledges that it received this with an ACK. By provisional responses, such as 180 RINGING, are not acknowledged, this means we have no way of knowing for sure if our UAC received the provisional response. The issues start […]

Categories
Kamailio RFCs & Standards Voice over IP

Kamailio Bytes – Dispatcher Module

Using the Dispatcher Module for load balancing functionality and intelligent dispatching of SIP messages.

Categories
Linux Python RFCs & Standards

ASN.1 Encoding in a Nutshell

Introduction to Encoding & Decoding data in ASN.1 (Using Python)

Categories
EPC LTE Mobile Networks Notes RFCs & Standards Security SIM Cards Software Voice over IP

All About IMS Authentication (AKAv1-MD5) in VoLTE Networks

How the AKAv1-MD5 algorith derives keys and how it’s used in IMS Networks

Categories
RFCs & Standards Voice over IP

RTP – More than you wanted to know

Workhorse of VoIP / VoLTE / SIP / H.323 / IMS, we take a deep dive into what every bit of RTP means. Pun very much intended.

Categories
RFCs & Standards Voice over IP

What is a SIP Registrar?

Explanation of what a SIP Registrar does, Contact header and Address on Record, and how it all fits together to route messages correctly.

Categories
RFCs & Standards Voice over IP

SIP REGISTER status & why it’s not what you think it is.

SIP Register status, expires and why it’s often misunderstood.

Categories
RFCs & Standards Voice over IP

SIP Concepts – Record Routing

Explanation of Record-Routing, why it exists and how it’s used.

Categories
RFCs & Standards Voice over IP

SDP – Session Description Protocol – Overview

Understanding the SDP protocol and how it’s used to negotiate and setup media sessions.

Categories
RFCs & Standards Voice over IP

Why z9hG4bK?

Why does every SIP branch start with z9hG4bK?

Categories
RFCs & Standards Voice over IP

SIP Via Header

What a Via header does, how to interpret it and how it’s used in SIP routing.

Categories
RFCs & Standards Voice over IP

DTMF over IP – SIP INFO, Inband & RTP Events

DTMF’s implementation in VoIP and the 3 types of DTMF encoding (Inband, RTP Event and SIP INFO)

Categories
RFCs & Standards Voice over IP

RFC2976 / RFC6086 – SIP INFO

SIP INFO was designed to carry session related information during a session. SIP was designed to setup and tear down sessions, with little thought given to what happens after the setup, but before the teardown. SIP INFO (RFC2976) was designed to fill this gap. (Obsoleted by RFC6086) It’s predominantly used now to carry DTMF info […]

Categories
RFCs & Standards Voice over IP

RFC2833 – RTP Events

RFC2833 was designed to carry DTMF signalling, other tone signals and telephony events in RTP packets. This was later superseded by RFC4733, but everyone still referrers to this protocol as RFC2833, so I will too. RFC2833 a special RTP payload designed to carry DTMF signalling information, so it operates on the same source / destination […]

Categories
Linux Python RFCs & Standards Voice over IP

Reverse MD5 on SIP Auth

How the SIP Authentication mechanism works, and how we can reverse it to check the password we’re expecting is the encrypted value we’re seeing in captures.