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Figure 3
Depending on compression technology used, each channel coming from a video head end or distribution point needs as much as 3.8 Mbps of bandwidth. Broadcast video channels are multicast in nature. If handled properly by the network infrastructure (with IGMP multicast at the network RTs), the amount of total bandwidth that multicast video consumes between the head end and RT can be minimized. In addition, video services such as VoD are unicast in nature-requiring individual bandwidth streams from the head end to the subscriber.
Video network bandwidth-capacity requirements depend mostly on the number of subscribers, the number of broadcast channels offered, and the concurrent use rate for VoD programs. Figure 3 provides an example of the amount of bandwidth required in a distribution network to support viable video services.
As indicated in the example, delivering sufficient bandwidth in the access network is a stretch for synchronous optical network (SONET) in current networks, and the cost of upgrades to speeds beyond optical carrier (OC)-3 or the addition of coarse wavelength division multiplexing (CWDM) equipment is prohibitive. GigE and N x GigE are the solution.
In Figure 3, the use of IP and Ethernet in the access network ensures that bandwidth is used efficiently. Although Ethernet is available at very high speeds and a Gigabit Ethernet (GbE) port is a fraction of the cost of an OC-48 port, efficient use of bandwidth is still essential. IGMP multicast at the RTs creates that efficiency, and an IP/Ethernet infrastructure for all services allows for dynamic bandwidth use. That is, bandwidth is consumed only when customer traffic—be it a voice call, data interchange, or video stream—is flowing.
