Diameter and SIP: Registration-Termination-Request / Answer

These posts focus on the use of Diameter and SIP in an IMS / VoLTE context, however these practices can be equally applied to other networks.

The Registration-Termination Request / Answer allow a Diameter Client (S-CSCF) to indicate to the HSS (Diameter Server) that it is no longer serving that user and the registration has been terminated.


The RFC’s definition is actually pretty succinct as to the function of the Server-Assignment Request/Answer:

The Registration-Termination-Request is sent by a Diameter Multimedia server to a Diameter Multimedia client in order to request the de-registration of a user.

Reference: TS 29.229

The Registration-Termination-Request commands are sent by a S-CSCF to indicate to the Diameter server that it is no longer serving a specific subscriber, and therefore this subscriber is now unregistered.

There are a variety of reasons for this, such as PERMANENT_TERMINATION, NEW_SIP_SERVER_ASSIGNED and SIP_SERVER_CHANGE.

The Diameter Server (HSS) will typically send the Diameter Client (S-CSCF) a Registration-Termination-Answer in response to indicate it has updated it’s internal database and will no longer consider the user to be registered at that S-CSCF.

Packet Capture

I’ve included a packet capture of these Diameter Commands from my lab network which you can find below.

Other Diameter Cx (IMS) Calls

User-Authorization-Request / User-Authorization-Answer
Server-Assignment-Request / Server-Assignment-Answer
Location-Info-Request / Location-Info-Answer
Multimedia-Auth-Request / Multimedia-Auth-Answer
Registration-Termination-Request / Registration-Termination-Answer
Push-Profile-Request / Push-Profile-Answer


3GPP Specification #: 29.229

RFC 4740 – Diameter Session Initiation Protocol (SIP) Application

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