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Cisco Bug: CSCvu28170 - LGW /CUBE doesn't pass the "mode" parameter in outgoing INVITEs for ilbc codec (w codec transparent)

Last Modified

Sep 11, 2020

Products (68)

  • Cisco IOS
  • Cisco Catalyst 9300-48P-A Switch
  • Cisco Catalyst 9300-48UXM-A Switch
  • Cisco Catalyst 9300-48T-A Switch
  • Cisco 4221 Integrated Services Router
  • Cisco Catalyst 9300-48U-A Switch
  • Cisco Catalyst 9800-40 Wireless Controller
  • Cisco Catalyst C9500-16X-E Switch
  • Cisco Catalyst 9400 Supervisor Engine-1XL-Y
  • Cisco Catalyst 9300-48UN-A Switch
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Known Affected Releases


Description (partial)

In recently CUCM/LGW testing against WebexCalling, we have noticed that CUBE incorrectly drops the iLBC codec's attributes received from CUCM before sending the INVITE to WebexCalling.

CUCM Sends the INVITE with the following iLBC media attributes to CUBE
a=rtpmap:116 iLBC/8000
a=fmtp:116 mode=20

CUBE Passes the INVITE to Webex Calling with
a=rtpmap:116 iLBC/8000

The "a=maxptime:20" and "mode=20" are missing. I have to use the Audio-Attribute rule to modify and add back the "mode=20".  Tenant 250 is the one used in this test.

Test Setup:
CP-8865 <=> CUCM/CUBE <=>WebexCalling <=> CP-8865

"iLBC" codec can have the 20ms or 30ms frame size.  As per RFC3952, it is important to specify and agree on the frame size in Offer/Answer exchange.  Without mode=20 or mode=30 specified, BroadWorks media service won't parse the message and error the call as is the case.

I understand that LGW/CUBE might not support the iLBC codec, but it must not drop the mode= parameter while allowing the iLBC codec to pass through.   It is fine if LGW/CUBE drop or allow the iLBC codec in entirety, but not partially.

Ilbc codec in incoming SIP INVITE  with mode parameter and CUBE/LGW configured with codec transparent.
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