SBC makes audio port 0 when number of m lines do not match (Doc ID 2699728.1)

Last updated on AUGUST 15, 2023

Applies to:

Symptoms

SBC makes audio port to 0 when number of m lines do not match in offer and response.

Initial Invite from A-party had only one m line and 200 OK from B-party also had a single m line.

B-party initiates a re-invite with multiple m-lines but now A-party responds with a 200 OK having single m line.

200 Ok from A-party as below.

Session Initiation Protocol (200)
Status-Line: SIP/2.0 200 OK
Message Header
Message Body
Session Description Protocol
Session Description Protocol Version (v): 0
Owner/Creator, Session Id (o): - 59593 59593 IN IP4 10.x.x.x
Session Name (s): -
Connection Information (c): IN IP4 10.x.x.x
Time Description, active time (t): 0 0
Media Description, name and address (m): audio 50148 RTP/AVP 8
Media Attribute (a): rtpmap:8 PCMA/8000
Media Attribute (a): ptime:20

Now SBC forwards the 200 Ok to B-party by setting the audio port to 0 as below.

Status-Line: SIP/2.0 200 OK
Message Header
Message Body
Session Description Protocol
Session Description Protocol Version (v): 0
Owner/Creator, Session Id (o): - 59593 59593 IN IP4 10.x.x.x
Session Name (s): -
Connection Information (c): IN IP4 10.x.x.x
Time Description, active time (t): 0 0
Media Description, name and address (m): audio 0 RTP/AVP 8 <======
Media Attribute (a): rtpmap:8 PCMA/8000
Media Attribute (a): ptime:20

Cause

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