Bandwidth management

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In computer networking, bandwidth management is the process of measuring and controlling the communications (traffic, packets) on a network link, to avoid filling the link to capacity or overfilling the link, which would result in network congestion and poor performance.

1 Overview
2 Finding the culprit
3 Fixing the problem
4 Tools and techniques
5 References
6 See also
7 External links

[edit] Overview

Almost everyone who has an Internet connection has at some time downloaded a large file, or run a peer-to-peer file sharing program, and noticed that Web pages start to load very slowly, or fail to load.

The reason is, of course, that the capacity (or bandwidth) of their Internet connection is limited, like the size of a highway, and when one tries to send too much information down it, more than its capacity, a virtual traffic jam results. This is also known as network congestion.

This analogy is important to understand the terms used: bandwidth is the width of the road, and traffic is the amount of data trying to use it. Controlling or managing traffic reduces bandwidth use, and is often described as bandwidth management, also known as bandwidth control, traffic control, congestion control, traffic shaping or traffic management.

[edit] Finding the culprit

The user of the only computer on a connection will probably know what application caused the problem or (barring spyware that hides itself deep within a system) figure it out pretty quickly. However, this task is much harder for network administrator, who does not necessarily know what applications other people are running on their computers, or how they use the network.

Conversely, this task is much more important for network administrators. A user downloading large files can happily go and do something else while they wait for the download to finish. But on a network, if one user does this, the others will start complaining that they can't access web pages, or their access is slow, and demand that the administrator fix it.

[edit] Fixing the problem

To keep your Internet connection working fast and smoothly, you must control your use of bandwidth, to stay below the maximum capacity of the network link. To control something, you must be able to measure it.

These tasks are usually viewed separately: much software exists for network traffic measurement and network traffic control, but these are normally not integrated. And indeed it may not be necessary to integrate them. Once the cause of the heavy traffic is identified, it is usually simpler, and may be more effective, and to shut it down or reschedule it than to try to manage its bandwidth use.

Many aspects of the Internet protocol suite prevent communications links from reaching their maximum capacity in practice. Therefore, it is necessary to keep the link utilisation below the maximum theoretical capacity of the link, in order to ensure fast responsiveness and eliminate bottleneck queues at the link endpoints, which increase latency. This is called congestion avoidance.

Some issues which limit the performance of a given link are:

TCP determines the capacity of a connection by flooding it until packets start being dropped (Slow-start)
Queueing in routers results in higher latency and jitter as the network approaches (and occasionally exceeds) capacity
TCP global synchronisation when the network reaches capacity results in waste of bandwidth
Burstiness of web traffic requires spare bandwidth to rapidly accommodate the bursty traffic
Lack of widespread support for explicit congestion notification and Quality of Service management on the Internet
Internet Service Providers typically retain control over queue management and quality of service at their end of the link

[edit] Tools and techniques

Software for measuring network traffic can be divided into two broad classes: packet sniffers, which look at individual packets, and management applications which give a broader overview of network traffic.

Packet sniffers are very useful for network experts tracking down tricky problems. But the volume of information they generate is enormous. A fast broadband connection can transmit thousands or millions of packets per second, and inspecting each one in detail is unlikely to help you make your network faster. In addition, understanding the output of these analysers requires a detailed understanding of network protocols such as TCP/IP and HTTP. For most network administrators, the broad overview is likely to be more useful, at least as a starting point for tracking down rogue users of their networks.

Many companies sell expensive solutions to help manage a network, which may or may not include managing the bandwidth of an upstream connection. There are also a few lower cost options. Some are researched and described on the network traffic measurement page.

[edit]

References

"Deploying IP and MPLS QoS for Multiservice Networks: Theory and Practice" by John Evans, Clarence Filsfils (Morgan Kaufmann, 2007, ISBN 0-123-70549-5)

[edit] See also

INASP runs bandwidth management training workshops and produces reports
The Authorization part of the AAA protocol makes reference to traffic management and bandwidth control
Bandwidth management using NetFlow and IPFIX data
Network congestion avoidance lists some techniques for prevention and management of congestion on routers
Traffic shaping and Rate limiting are bandwidth management (traffic control) techniques
Bandwidth management is a subset of Network management and Performance management
Network traffic measurement is a subset of Network monitoring