Bandwidth Management Introduction

Standard Accleration

Bandwidth management, in general, is a simple concept. The idea is to be able to differentiate orclassify user traffic according to a wide array of criteria and then assign various priorities to eachclassified packet or session. For example, bandwidth management allows an administrator togive HTTP traffic a higher priority over SMTP traffic, which in turn may have higher priority overFTP traffic. A bandwidth management solution can also track the bandwidthused by each application and set limits as to how much each classified traffic pattern can utilize. There are a variety of methods used to enforce the bandwidth management policies configured by an administrator. The simplest method would be to discard packets when certain thresholds are reached or when certain pre-allocated session buffers are overflowing. More complex mechanisms include TCP rate shaping and priority based queuing.

TCP rate shaping uses the inherent flow control mechanisms of the TCP protocol. By adjusting parameters in the packets’ TCP headers, a bandwidth management solution can signal the end nodes to throttle the rate at which to transmit packets. Needless to say, the mechanism only works with TCP sessions. TCP rate shaping also has some uncertainties associated with it, as the amount of bandwidth associated with sessions can rarely be exactly enforced. Rate shaping also does not work well with protocols that use short lived sessions (such as HTTP), since such sessions usually end before the bandwidth manager has decided how to shape the rate of the session.

Priority based queuing is a means by which all classified packets are placed in packet queues,each with its own preset priority. A number of queues are available and when it comes to traffic forwarding, packets are forwarded from the higher priority queues first. This is an oversimplified version of what really happens, but it presents the general concept. Various algorithms and safety measures should be deployed to ensure methodical packet forwarding and protection against “starvation”, where lower priority packets wait in queues for intolerably long amounts of time. Radware’s bandwidth management solution uses priority queues as the fundamental framework behind its operation.