From ee37483661e1792ec0d2cee2a85f69ff7a1d136a Mon Sep 17 00:00:00 2001 From: Harald Welte Date: Thu, 28 Jan 2021 23:36:45 +0100 Subject: [PATCH] cs7-config: Describe special meaning of M3UA routing context '0' Osmocom has a special interpretation of the routing-context '0'. Let's document that. Change-Id: Iac0bc1e754d04b2e798263bfa029d26376e4e92f --- common/chapters/cs7-config.adoc | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/common/chapters/cs7-config.adoc b/common/chapters/cs7-config.adoc index a0957fd..62e85bb 100644 --- a/common/chapters/cs7-config.adoc +++ b/common/chapters/cs7-config.adoc @@ -307,3 +307,29 @@ routing-key RCONTEXT DPC si (aal2|bicc|b-isup|h248|isup|sat-isup|sccp|tup) routing-key RCONTEXT DPC ssn SSN routing-key RCONTEXT DPC si (aal2|bicc|b-isup|h248|isup|sat-isup|sccp|tup) ssn SSN ---- + +==== M3UA without Routing Context IE / Routing Context '0' + +As per the M3UA specification, the use of the routing context IE is +optional as long as there is only one AS within an ASP. As soon as +there are multiple different AS within one ASP, the routing context IE +is mandatory, as it is the only clue to differentiate which of the ASs a +given message belongs to. + +In the Osmocom M3UA implementation, it is generally assumed that a +routing context IE is always used, for the sake of clarity. + +However, the routing context ID of '0' has the special meaning of _do +not encode a routing context IE on transmit_. + +So if you configure an application like OsmoBSC to use routing context +0, then no routing context IE will be included in outbound M3UA +messages. + +This special interpretation of '0' within the Osmocom M3UA +implementation however means that we can not represent M3UA with a +routing context IE that actually contains '0' as a numeric identifier. + +So you only have the following options: +* Using M3UA with routing context (1..N) +* Using M3UA without routing context (0)