For Outgoing Flows

This section describes the way all three settings behavior for outgoing flows.

  • rtp—If the outgoing media security policy associated with a realm has rtp set as its mode, then the E-SBC converts any RTP/SAVP media lines from incoming offer SDP to RTP/AVP for the offer SDP it sends out.

    Incoming offer SDP might look like this: 

    v=0
o=MxSIP 0 1480968866 IN IP4 192.168.22.180
s=SIP Call
c=IN IP4 192.168.22.180
t=0 0
m=audio 5010 RTP/SAVP 0 8 18 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=silenceSupp:off - - - -
a=fmtp:18 annexb=no
a=fmtp:101 0-15
a=crypto:0 AES_CM_128_HMAC_SHA1_80 inline:f0oLKTuMYwXqrKa7Ch+MOBvLe8YnXnD6Kmnj4LQ2

    The E-SBC will take that and convert it to the following for outgoing traffic. 

    v=0
o=MxSIP 0 1480968866 IN IP4 172.16.22.180
s=SIP Call
c=IN IP4 172.16.22.180
t=0 0
m=audio 6000 RTP/AVP 0 8 18 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=silenceSupp:off - - - -
a=fmtp:18 annexb=no
a=fmtp:101 0-1

    This conversion can result in multiple media lines with RTP/AVP for the same media profile and an RTP/SAVP media line for the same media profile. To prevent duplicate lines in the SDP the E-SBC sends, the E-SBC inspects incoming SDP to determine is RTP/AVP and RTP/SAVP media lines exist for the same media profile. If it finds such a media profile, the E-SBC disables the RTP/AVP (by setting the port to 0 in the outgoing offer SDP) corresponding to the RTP/AVP media line for that media profile. Doing so forces the UA answering the SDP offer to choose the media lines corresponding to the RTP/SAVP media lines in the incoming offer SDP. An SRTP-RTP session results.

    The incoming offer SDP might look like this: 

    v=0
o=MxSIP 0 1480968866 IN IP4 192.168.22.180
s=SIP Call
c=IN IP4 192.168.22.180
t=0 0
m=audio 5012 RTP/AVP 0 8 18 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=silenceSupp:off - - - -
a=fmtp:18 annexb=no
a=fmtp:101 0-15
m=audio 5010 RTP/SAVP 0 8 18 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=silenceSupp:off - - - -
a=fmtp:18 annexb=no
a=fmtp:101 0-15
a=crypto:0 AES_CM_128_HMAC_SHA1_80 inline:f0oLKTuMYwXqrKa7Ch+MOBvLe8YnXnD6Kmnj4LQ2

    And the outgoing offer SDP will look like this: 

    v=0
o=MxSIP 0 1480968866 IN IP4 172.16.22.180
s=SIP Call
c=IN IP4 172.16.22.180
t=0 0
m=audio 0 RTP/AVP 0 8 18 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=silenceSupp:off - - - -
a=fmtp:18 annexb=no
a=fmtp:101 0-15
m=audio 6002 RTP/AVP 0 8 18 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=silenceSupp:off - - - -
a=fmtp:18 annexb=no
a=fmtp:101 0-15
  • srtp—If the outgoing media security policy associated with a realm has srtp set as its mode, the E-SBC converts any RTP/AVP media lines from an incoming offer SDP to RTP/SAVP for the offer SDP the E-SBC sends.

    The incoming offer SDP might look like this: 

    v=0
o=MxSIP 0 1480968866 IN IP4 192.168.22.180
s=SIP Call
c=IN IP4 192.168.22.180
t=0 0
m=audio 5012 RTP/AVP 0 8 18 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=silenceSupp:off - - - -
a=fmtp:18 annexb=no
a=fmtp:101 0-15

    And the outgoing offer SDP will look like this: 

    v=0
o=MxSIP 0 1480968866 IN IP4 172.16.22.180
s=SIP Call
c=IN IP4 172.16.22.180
t=0 0
m=audio 6000 RTP/SAVP 0 8 18 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=silenceSupp:off - - - -
a=fmtp:18 annexb=no
a=fmtp:101 0-1
a=crypto:0 AES_CM_128_HMAC_SHA1_80 inline:f0oLKTuMYwXqrKa7Ch+MOBvLe8YnXnD6Kmnj4LQ2

    This conversion might result in multiple media lines with RTP/SAVP for the same media profile if the incoming offer SDP has an RTP/AVP media line and an RTP/SAVP media for the same media profile. To prevent multiple identical media lines in the SDP it sends, the E-SBC inspects the incoming SDP to determine whether both RTP/AVP and RTP/SAVP media lines exist for the same media profile. If it finds such a media profile, the E-SBC disables the RTP/SAVP (by setting the port to 0 in the outgoing offer SDP) corresponding to the RTP/AVP media line for that media profile. Doing so forces the UA answering the SDP offer to choose the media lines corresponding to the RTP/SAVP media lines in the incoming offer SDP. An SRTP-SRTP session results.

    The incoming offer SDP might look like this: 

    v=0
o=MxSIP 0 1480968866 IN IP4 192.168.22.180
s=SIP Call
c=IN IP4 192.168.22.180
t=0 0
m=audio 5012 RTP/AVP 0 8 18 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=silenceSupp:off - - - -
a=fmtp:18 annexb=no
a=fmtp:101 0-15
m=audio 5010 RTP/SAVP 0 8 18 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=silenceSupp:off - - - -
a=fmtp:18 annexb=no
a=fmtp:101 0-15
a=crypto:0 AES_CM_128_HMAC_SHA1_80 inline:f0oLKTuMYwXqrKa7Ch+MOBvLe8YnXnD6Kmnj4LQ2

    And the outgoing offer SDP will look like this: 

    v=0
o=MxSIP 0 1480968866 IN IP4 172.16.22.180
s=SIP Call
c=IN IP4 172.16.22.180
t=0 0
m=audio 0 RTP/SAVP 0 8 18 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=silenceSupp:off - - - -
a=fmtp:18 annexb=no
a=fmtp:101 0-15
m=audio 6002 RTP/SAVP 0 8 18 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=silenceSupp:off - - - -
a=fmtp:18 annexb=no
a=fmtp:101 0-1
a=crypto:0 AES_CM_128_HMAC_SHA1_80 inline:f0oLKTuMYwXqrKa7Ch+MOBvLe8YnXnD6Kmnj4LQ2
  • any—If the outgoing media security policy associated with a realm has any set as its mode, the E-SBC creates offer SDP based on the value configured in the egress-offer-format, which is set either in the sdes-profile configuration.
    • If the value is same-as-ingress, the E-SBC leaves the profile of the media lines unchanged.
    • If the value is simultaneous-best-effort, the E-SBC inspects the incoming offer SDP and:
      • Adds an RTP/SAVP media line for any media profile that has only the RTP/AVP media profile
      • Adds an RTP/AVP media line for any media profile that has only the RTP/SAVP media profile

      Should the media profile in the incoming offer SDP already have two media lines (one fore RTP/AVP and on for RTP/SAVP), the E-SBC does not have to make these additions. It will map the media lines in the answer it receives with the media lines from the incoming offer SDP. It will also ensure that media lines in the answer SDP it sends match the media lines from the incoming offer SDP.

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