Network Dimensioning

To support the transport of video, IPTV distribution networks need to feature high bandwidth carrying capacities. The amount of bandwidth required to carryIPTV services is generally a multiple of the bandwidth required to support Voice over IP(VoIP) and Internet access services. The total bandwidth required to implement

IPTV services depends on a couple of factors:
The number of IPTV multicast channels on offer As noted a single copy of each channel is sent from the IPTV data center on to the distribution network. Once the channel is streamed onto the networking infrastructure the multicast process handles the copying of channels and routing to individual IPTV subscribers. Consider an example of a service provider who is offering its 10,000 subscribers a package of 100 standard definition (SD) IP broad cast TVchannels. If we assume that the provider is using H.264 to compress thechannels, this generally translates to a bandwidth requirement of at least 2 Mbps for each broadcast channel. In the scenario where at least one subscriber is accessing each channel at a particular instance in time then the Next Generation Network (NGN) core distribution network will require200 Mbps of bandwidth capacity. This is the bandwidth requirement from the IPTV data center to each of the regional offices. At these offices techniques such as IGMP snooping can be used to reduce the bandwidth required over the local access section of the network. Note that H.264 and 1GMP will be described in greater detail later in the book.

Inclusion of IP-VoD services The dimensioning of the network is further complicated by the addition of IP-VoD applications. These types of applications use the unicast transport mechanism to provide communications between the IPTV consumer devices and the on-demand video server. This mode of operation consumes a large amount of bandwidth and the network needs to accommodate this level of network traffic. Consider the same network of 10,000 end users and assume that at a particular instance in time there is 5% of the subscriber base accessing IP-VoD titles. By assuming again that the H.264 compression standard is used, this translates to a peak usage on the network of 1 Gbps (10,000 5% 2 Mbps). This is a significant
requirement for the core network.

Reliability
The IP networking infrastructure needs to be reliable in the event of device failures. There should be no single point of failure that could interrupt the delivery of IPTV services, both multicast or unicast applications. Redundant links should be used wherever possible.

Fast Responsiveness
The network needs to support minimum response times associated with channel zapping (refers to changing from one channel to another during a TV viewing experience).

Predictable Performance
The nature of video bit rate streams is variable due to the differing scene complexities, which are delivered to an IPTV access device on a frame-by-frame basis. Therefore, it is difficult to predict the exact requirements of a video transmission until the service is operating in real-time. IPTV operators have to bearthis in mind and assign appropriate network resources to cope with variable bit ratestreams.

5 Level of QoS
Owing to the fact that most IPTV services operate over a private IP broadband network, it is advisable to implement a QoS policy when delivering video contentto paying subscribers. A QoS system preserves a video signal and lessens theprobability of impairments as it gets transmitted over long distances. It allowsoperators to provide services that require strict performance guarantees such as IP-VoD and IP Multicast. It comprises of a number of network techniques and supporting protocols that guarantee IPTV subscribers a specific level of viewing quality. The subject of IPTV QoS is covered in greater detail later in the book.