Information Technology Reference
In-Depth Information
When IGMP snooping is enabled on a switch, IGMP Membership query, Membership report, and Leave packets are intercepted by
the NMP or ASICs, and the switch then determines from those IGMP packets which ports it should send or stop sending what type (if
any) of multicast traffic. IGMP snooping can impose a high processing overhead on low-end switches, however.
CGMP is a Cisco proprietary alternative to IGMP snooping that operates between a router and a switch, and it ensures that multicast
traffic is optimally distributed on switch ports. It imposes a lower overhead on low-end switches than IGMP snooping.
Video
Cisco CUCM supports video calls between SCCP, H.323, and SIP endpoints.
CUCM can support point-to-point video calls between endpoints, and it supports video conference calls by taking advantage of Cisco
IP/VC 3500 multipoint control units (MCU) and Cisco IP/VC 3500 H.320 gateways. CUCM supports a variety of video endpoints
including Cisco 9971 IP phones, Cisco Unified Video Advantage endpoints, Cisco Unified Personal Communicator, Tandberg video
conferencing endpoints, H.323 enabled clients (Tandberg, Polycom, Sony, and so on), and certain SIP endpoints.
CUCM 7.x includes Intelligent Bridge Selection, which enables CUCM to select conferencing resources based on whether the
endpoints involved in the conference are video enabled. If two or more of the endpoints are video enabled, videoconferencing
resources are selected (assuming that they are available). If there are no video-enabled endpoints or videoconferencing resources are
not available, an audio conferencing resource is chosen.
Intelligent Bridge selection also allows secure conferencing bridges to be selected based on device capabilities.
Numerous codecs can be used with video calls and conferences in CUCM, including H.261, H.263(+), H.264, and Cisco proprietary
wideband. CUCM also support far-end camera control with H.224.
H.261 is an ITU standard designed to operate between 40 Kbps and 2 Mbps and supports Common Intermediate Format (CIF, a
resolution of 352 * 288) and Quarter CIF (QCIF, 176 * 144).
H.263 is a low-bit-rate codec based on H.261 and MPEG-1 and MPEG-2. It was originally developed for H.324 PSTN and circuit-
switched videoconferencing and telephony, but is now also used for H.323, H.320, RTSP, and SIP solutions.
 
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