Considerations for bandwidth

Plan for sustained streaming media bandwidth requirements

Bandwidth is a critical issue for streaming media because streaming media demands a consistent amount of bandwidth and can consume a great amount of bandwidth over time. All connections between the server and the streaming media cache remain open for the length of time that the server takes to deliver the stream to the cache, plus the length of time the cache takes to deliver the stream to the last client viewing the stream. Poor performance for other network traffic can result if you do not have sufficient bandwidth to accommodate both streaming media, with its long open connections, and other traffic.

In contrast, Web objects are bursty, typically consuming large amounts of bandwidth over a relatively brief period of time. The following table describes the basic differences between Web and streaming media delivery.

Web object delivery	Streaming object delivery
All data must be reliably transferred. Packet loss is not acceptable.	Some packet loss is acceptable. Some data loss is acceptable
Delivery is at network speed. No real-time requirement exists.	Delivery is paced and synchronized. Real-time constraints exist.
A single connection is opened per object.	Data and control connections are usually separate.
Small amounts of data.	Large amounts of data.
Sequential whole-file access.	Sometimes random and partial access.

Unlike Web objects, streaming media requires a minimum amount of sustained bandwidth. Streaming media packets must be received in a reasonable amount of time because audio and video must arrive on time and in sequence.

For example, if your streaming clients require 500 kbps of sustained bandwidth and network congestion reduces the bandwidth to 300 kbps, the audio and video will become choppy and will eventually fail. Conversely, Web objects will burst to the bandwidth that is currently available. A user might notice that a Web page is loading more slowly if the network becomes congested, but eventually the Web page will appear. Such latency might be acceptable to Web users, but it is not acceptable to streaming media users who anticipate seeing or hearing the next action in the same smooth and vivid way they have experienced with television or radio.

Note
When you estimate the amount of bandwidth you need, be sure to take into account the amount of bandwidth that is used on your network at peak times.

Bandwidth and the location of streaming media caches

When you deploy a streaming media cache, the bulk of your bandwidth savings results from eliminating the need for each client to individually fetch the stream from the streaming server. The closer you deploy a streaming media cache to your clients, the more bandwidth you will save. This savings might be enough to eliminate the need to purchase more bandwidth or to reduce the amount of bandwidth that must be purchased. When you plan your streaming media deployment, consider several possible locations for your streaming media caches and evaluate the amount of bandwidth you should save with a cache in each location.

You can save bandwidth by pushing content that you anticipate your users will request to one or more NetCache appliances that you select. See Prefilling streaming media caches and Appendix D, Considerations When Pushing Content, for more information.

Bandwidth and your requirements for stream quality

Bandwidth has a direct relationship to the quality of streaming media presentations that you can provide. While you are estimating your bandwidth needs, you must also take into account the quality of service that you want to provide. If you need to provide high-quality service, plan for enough bandwidth to ensure that your network does not become congested.

By pushing streaming media content to your streaming media caches, you can reduce the impact of network congestion on streaming media delivered to users. As the distance the streaming media data needs to travel lessens, the possibilities of network problems that would affect the streaming media quality are likely to be fewer. Additionally, you are copying streaming media files to the streaming media cache rather than caching a stream that could have been affected by network conditions (for example, a thinned stream). See Prefilling streaming media caches and Appendix D, Considerations When Pushing Content, for more information.

Note
Quality of service is a particular challenge for an ISP because many users continue to use modems with speeds of 28.8, 33.6, and 56 kbps. Modems of 28.8 kbps are too slow to allow large-screen, good-quality video.