In this section:



The supports up to six media streams per session. Additional streams received are rejected.

  • One media stream is typically reserved for audio. The can establish SIP calls without the Audio m line on the condition that any other supported streams such as video, application or msrp are present.
  • The streams are shared between video, BFCP-UDP, BFCP-TCP (RFC 4583), and Far End Camera Control (RFC 4753).

The supports the following media functionality:

  • Establishing SIP calls when the incoming offer has two or more m lines (maximum of six) with an audio m line with RTP port 0.
  • Establishing calls when the incoming Offer has single audio m line with port # of 0. The Offer sent by the will have a single m line with a port number of "0".
  • Accepting call modification requests with a single audio m line with port # of 0. The Modify Offer sent by the includes a single m line with port number of "0".
  • Audio-only calls when the peer answers by disabling the audio m line in the answer by setting the port to 0. The Answer sent by the to the opposite peer in this case will have port # of 0.
  • Removal of audio/image stream from a call that has already been set up with audio and at least one additional stream. The removal can be achieved by:
    • A Modify Offer with the port for the audio/image line set to "0".
    • A Modify Offer with the audio/image media line completely removed.
  • Adding audio streams for calls setup without audio via modify offers.
  • Setting ingress and egress bearer type in callMediaStatus to “multimedia” if the call contains multiple streams or no audio.
  • SIP REFER and/or REPLACES for calls without Audio.
  • Direct Media for calls without Audio.


H.323 Audio Calls

The  supports ITU H.323 audio calls, including protocol and codec inter-working with SIP and GW calls. The following H.323 call types are supported:

  • H323 fast-start
  • H323 with tunneled H245
  • H323 with separate H245

The call rate and call capacity for H.323 depends on the specific type of H.323 calls, and is listed on the SBC Product Specifications page.

The  also supports H.323 video calls. See Video Support page for details.

SIP Audio Calls

The  SIP call handling functionality is described on this page.

Call rates are defined as maximum sustained call rates while meeting design criteria. Peak rates are understandably higher, but network planning should use sustained rates since they apply across a wider range of network conditions:

  • Uses only ~60% CPU for basic call; leaves ample headroom for anomalous event handling
  • 99.999% call completion rate
  • 99.9% call setup within 50 ms
  • Usable matching between call rates and other common background loads
  • High-availability recovery within acceptable thresholds

The maximum call rate applies across many variants of SIP calls:

  • SIP 7-message flow (INVITE, 100 INVITE, 18x INVITE, 200 INVITE, ACK, BYE, 200 BYE)
  • SIP 9-message flow (INVITE, 100 INVITE, 18x INVITE, PRACK, 200 PRACK, 200 INVITE, ACK, BYE, 200 BYE)
  • SIP over UDP
  • SIP over TCP
  • SIP-GW

The maximum call rate is unaffected by many useful functions. There is no de-rating for:

  • Transcoding between any combination of supported codecs
  • SMM of typical use cases (<4 criteria, <4 actions)
  • Rx interface (on 1 leg)
  • sRTP/sRTCP

Different types of call (policy) routing are possible. Maximum call rates still apply unless otherwise stated:

  • Routing via internal ERE policy engine
  • Routing via an external PSX
  • Routing via co-located EPX. If there are no services, full call rating applies. If services are enabled, call de-rating depends on the specific services used.

The maximum call rate is unaffected by the number of active calls. This rating applies whether there are few calls in box as well as when the number of active calls is near the full capacity.

Call capacity is limited only by the box-wide limit (150,000 calls), the maximum number of DSPs (depends on the codec combinations), or the physical limits of the network interfaces. Call capacity is not limited by:

  • Call rate
  • Security protocols in use
  • Lawful intercept or other tapping applications in use (though those sessions have their own limits)
  • Type of call routing used

 SIP call rates and capacities are listed on the SBC Product Specifications page.