Medianet Reference Guide - Cisco

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Solution Chapter 1 Medianet Architecture Overview To summarize: the targets for media-ready campus and data center networks in terms of packet loss is 0.05% with a network convergence target of 200 ms; on WAN and branch networks, loss should still be targeted to 0.05%, but convergence targets will be higher depending on topologies, service providers, and other constraints. Finally, it should be noted that by designing the underlying network architecture for high availability, all applications on the converged network benefit. Bandwidth and Burst There is no way around the fact that media applications require significant network bandwidth. An important step to implement a medianet is to assess current and future bandwidth requirements across the network. Consider current bandwidth utilization and add forecasts for media applications, especially for video-oriented media applications. Because video is in a relatively early stage of adoption, use aggressive estimates of possible bandwidth consumption. Consider bandwidth of different entry and transit points in the network. What bandwidth is needed at network access ports both in the campus as well as branch offices? What are the likely media streams needing transport across the WAN? It is important to consider all types of media applications. For example, how many streaming video connections will be utilized for training and communications? These typically flow from a central point, such as the data center, outward to employees in campus and branch offices. As another example, how many IP video surveillance cameras will exist on the network? These traffic flows are typically from many sources at the edges of the network inward toward central monitoring and storage locations. Map out the media applications that will be used, considering both managed and un-managed applications. Understand the bandwidth required by each stream and endpoint, as well as the direction(s) in which the streams will flow. Mapping those onto the network can lead to key bandwidth upgrade decisions at critical places in the network architecture, including campus switching as well as the WAN. Another critical bandwidth-related concern is burst. So far, we have discussed bandwidth in terms of bits per second (i.e., how much traffic is sent over a one second interval); however, when provisioning bandwidth, burst must also be taken into account. Burst is defined as the amount of traffic (generally measured in Bytes) transmitted per millisecond which exceeds the per-second average. For example, a Cisco TelePresence 3000 system may average 15 Megabits per second, which equates to an average per millisecond rate of 1,875 Bytes (15 Mbps ÷ 1,000 milliseconds ÷ 8 bits per Byte). Cisco TelePresence operates at 30 frames per second, which means that every 33 ms a video frame is transmitted. Each frame consists of several thousand Bytes of video payload, and therefore each frame interval consists of several dozen packets, with an average packet size of 1,100 bytes per packet. However, because video is variable in size (due to the variability of motion in the encoded video), the packets transmitted by the codec are not spaced evenly over each 33 ms frame interval, but rather are transmitted in bursts measured in shorter intervals. Therefore, while the overall bandwidth (maximum) averages out to 15 Mbps over one second, when measured on a per millisecond basis, the packet transmission rate is highly variable, and the number of Bytes transmitted per millisecond for a 15 Mbps stream can burst well above the 1,875 Bytes per millisecond average. Therefore, adequate burst tolerance must be accommodated by all switch and router interfaces in the path. Given these considerations, it can be noted that converging voice onto a common IP-based network is a significantly simpler exercise than converging video onto the same network. The principle reason is that VoIP is a very well-behaved application, from a networking perspective. For instance, each VoIP packet size is known and constant (for example, G.711 codecs generate packets that are always 160 Bytes [+ Layer 2 overhead]); similarly, VoIP packetization rates are known and constant (the default packetization rate for VoIP is 50 packet-per-second, which produces a packet every 20 ms). Furthermore, VoIP has very light bandwidth requirements (as compared to video and data) and these requirements can be very cleanly calculated by various capacity planning formulas (such as Erlang and Endset formulas). 1-14 Medianet Reference Guide OL-22201-01
Chapter 1 Medianet Architecture Overview Solution In contrast, video is a completely different type of application in almost every way. Video packet sizes vary significantly and video packetization rates also vary significantly (both in proportion to the amount of motion in the video frames being encoded and transmitted); furthermore, video applications are generally quite bursty—especially during sub-second intervals—and can wreak havoc on underprovisioned network infrastructures. Additionally, there are no clean formulas for provisioning video, as there are with VoIP. This contrast—from a networking perspective—between voice and video traffic is illustrated in Figure 1-6 Figure 1-6 Sub-Second Bandwidth Analysis—Voice versus Video 1400 Voice Packets 1400 Video Frame Video Packets Video Frame Video Frame 1000 1000 Bytes 600 Audio Samples 600 200 200 20 msec Time 33 msec 224376 Summing up, converging media applications-especially video-based media applications-onto the IP network is considerably more complex than converging voice and data, due to the radically different bandwidth and burst requirements of video compared to voice. While deployment scenarios will vary, in most cases, capacity planning exercises will indicate that Campus and Data Center medianets will require GigabitEthernet (GE) connections at the edge and 10 GigabitEthernet (10GE) connections-or multiples thereof-in the core; additionally, medianets will likely have a minimum bandwidth requirement of 45 Mbps/DS3 circuits. Furthermore, network administrators not only have to consider the bandwidth requirements of applications as a function of bits-per-second, but also they must consider the burst requirements of media, such as video, as a function of Bytes-per-millisecond, and ensure that the routers and switches have adequate buffering capacity to handle bursts. Latency and Jitter Media applications, particularly interactive media applications, have strict requirements for network latency. Network latency can be broken down further into fixed and variable components: • Serialization (fixed) OL-22201-01 Medianet Reference Guide 1-15
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Page 3: About the Authors Solution Authors
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Page 8 and 9: Contents The Globalization of the W
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An Introduction to Securing a Media
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Medianet Reference Guide - Cisco

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