6.2 Bandwidth Management Options

This topic describes bandwidth management options in a Cisco Unified Communications Manager deployment.

Bandwidth in the IP WAN can be conserved by using these options:

  • Techniques that reduce required bandwidth of RTP streams:
    1. RTP header compression (as part of QoS link efficiency mechanisms)
    2. Low-bandwidth codecs
  • Techniques that influence the flow of RTP streams:
    1. Local media resources such as conference bridges
  • Other solutions:
    1. Transcoders
    2. Multicast MOH from branch router flash

You can use various techniques to conserve valuable IP WAN bandwidth. One technique is to reduce the required bandwidth of RTP streams by using RTP header compression is a QoS link efficiency mechanism. Another technique is to use low-bandwidth codecs. You can also use a combination of these two solutions.

Other options for managing IP WAN bandwidth are techniques that influence where RTP streams are sent. If three phones, all located at a remote site, establish an ad hoc conference, there is a great difference in bandwidth usage that is based on the location of the conference bridge. If the conference bridge is located at the remote site, the bridge is local to the phones that are members of the conference. If the conference is located at the main site, the bridge must be accessed over the IP WAN. In the latter case, all three phones are sending their RTP stream to the conference bridge over the IP WAN. The conference bridge mixes the received media and then streams the media back to all conference members (in three separate streams). Although the call appears to be local to the remote site, because all conference members are located at that site, the IP WAN is occupied by three calls because of the remotely located conference bridge.

Other bandwidth management solutions include the use of transcoders or the implementation of special features such as multicast MOH from branch router flash. Transcoders are devices that can transcode audio or video streams. For example, an audio transcoder changes the way that the audio payload is encoded (such as when a G.711 audio stream is changed to a G.729 audio stream). Transcoders allow the use of low-bandwidth codecs over the IP WAN even if one of the endpoints is limited to a high-bandwidth codec such as G.711. Multicast MOH from branch router flash allows a multicast MOH stream to be generated by a Cisco IOS router that is located at the remote site, instead of being sent over the IP WAN from a centralized MOH server.