Intranet Design Magazine-Infomration Mangement - Is Your E-business Strategy Ready for Wireless?

World graphic Feature
Network Traffic Management II
Quality of Service standards are the key to prioritizing
messages on an intranet or extrane

By Wick Keating

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RSVP is an IP-based protocol that allows a sender of information to temporarily reserve bandwidth at routers along the way to one or more designated receivers. The sender initiates the reservation by requesting bandwidth at each router along the path to the receiver. When the receiver replies along the same path, the temporary reservation is changed into a permanent one that lasts until the session is completed.

RSVP was originally intended to allow delay sensitive applications, such as voice and video, to reserve the bandwidth needed to avoid intolerable delays. RSVP does not address TCP, HTTP or FTP and there is no mechanism for central control or policy enforcement. It also works on a "first-come, first-served" basis, which means mission-critical applications can still be compromised by low-priority traffic if the lower priority traffic reserved bandwidth first. Additionally, although RSVP works to minimize network delay by reserving bandwidth, if bandwidth is unavailable, it resorts to the best-effort principle.

IP Precedence, another QoS approach, avoids many of RSVP's inherent problems. With IP precedence, each packet traveling across a network is assigned a priority. Network devices, such as routers, simply ship high-priority packets ahead of lower-priority ones. Network managers can define several classes of service and define network policies for congestion handling and bandwidth allocation for each class. For example, traffic from customers or business partners could be assigned the highest priority while other types of traffic receive lower priority. IP Precedence allows for considerable flexibility in precedence assignment.

Once either RSVP or IP Precedence has been employed to "set the ground rules" for traffic flow, either rate control or queuing mechanisms enforce them.

Rate control mechanisms essentially regulate the TCP/IP communication flow between the sender and the receiver of information according to those ground rules. In normal TCP/IP communication, the receiver submits acknowledgment packets to the sender, which tell the sender how many packets to send next (known as the TCP window size). Rate control mechanisms intercept acknowledgment packets from the receiver as they travel to the sender, and then modify the TCP window size in order to control the rate at which the sender receives the acknowledgments. Thus, high priority traffic will have its rate increased while low priority traffic will have its rate lowered.

Rate control mechanisms limit congestion and offer a significant side benefit by smoothing-out the typically "bursty" nature of TCP traffic. An example of a product which can be used to implement rate control on an intranet or extranet is PacketShaper from Packeteer, Inc.

Queuing mechanisms traditionally come into play in routers and queuing-based QoS is supported by all major router vendors. Using one of a variety of queuing algorithms based on IP Precedence, RSVP reservations or some other identifier, these mechanisms assign different priority traffic to different queues. The router allocates separate buffers for each queue, and sends high-priority traffic ahead of low-priority traffic. Additional features ensure that packets are not lost due to full queues, lower priority traffic is not kept waiting indefinitely as higher priority traffic is routed and unused bandwidth is reallocated to different queues to maximize traffic flow.

Summary

Intranets and extranets are rapidly becoming essential components of business success, with businesses constantly finding innovative uses for their network infrastructures. These new network uses are generating huge increases in network traffic. Network capacity is a limited resource, which in some cases is already being stretched to its limits.

Evolving business needs require that we start managing network traffic according to business priorities. Technologies already exist and others are emerging to make TCP/IP traffic management a reality. By taking these solutions into account while growing its network, an organization can cope with limited bandwidth while expanding the business uses of its data.

Wick Keating is a vice president and director of Distributed Computing in the AMS Center for Advanced Technologies. With over twenty years of experience in all aspects of information systems, Mr. Keating is responsible for the Center’s research and project support activities in distributed computing, object technology, Web technology, performance analysis, and testing.

He has an M.B.A. in Management Science from the University of Pennsylvania Wharton School of Finance and Commerce and has spoken at many conferences on the business applications of advanced information technology.