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U. Glaeser

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node, to which the user is connected to, will establish a connection if a connection-oriented service has<br />

been opted. Otherwise, the information will be transmitted in a connectionless environment. In either<br />

case, switching nodes play a key role in determining path of the information flow according to some<br />

well-established routing criteria. The criteria include performance (delay and throughput) objectives<br />

among other factors based on user needs. For keeping the network traffic within a reasonable range,<br />

some traffic flow control mechanisms are necessary. In late 1960s and early 1970s, when data rates of<br />

transmission media used in computer networks were low (a few thousands of bits per second), these<br />

mechanisms were fairly simple. A common method used for controlling traffic over a transmission link<br />

or a path was an understanding that sender will continue sending information until the receiver sends<br />

a request to stop. The information flow will resume as soon as the receiver sends another request to<br />

resume transmission. Basically the receiver side had the final say in controlling the flow of information<br />

over a link or a path. As the data rates of transmission media started increasing, this method was not<br />

deemed efficient. To control the flow of information in relatively faster transmission media, a sliding<br />

window scheme was used. According to this scheme, sender will continuously send information packet<br />

but no more than a certain limit. Once the limit has reached, the sender will stop sending the information<br />

packets and will wait for the acknowledgement of the packets that have been transmitted. As soon as an<br />

acknowledgement is received, the sender may send another packet. This method ensures that there are no<br />

more than a certain specific number of packets in transit from sender to receiver at any given time. Again<br />

the receiver has the control over the amount of information that sender can transmit. These techniques<br />

for controlling the information traffic are referred to as reactive or feedback based techniques because<br />

the decision to transmit or not to transmit is based on the current traffic conditions.<br />

The reactive techniques are acceptable in low to moderate data rates of transmission media. As the<br />

data rates increase from kilobits per second to megabits and gigabits per second, the situation changes.<br />

Over the past several years, the data rates have increased manifold. Optical fibers provide enormously<br />

high data rates. Size of the computer networks has also experienced tremendous increase. The amount<br />

of traffic flowing through these networks has been increasing exponentially. Given that, the traffic control<br />

techniques used in earlier networks are not quite effective anymore [11,12,22]. One more factor that has<br />

added to the complexity of the situation is that users are now exchanging different types of information<br />

through the same network. Consider the example of Internet. The geographical scope of Internet is<br />

essentially global. Extensive use of optical fiber as transmission media provides very high data rates for<br />

exchanging information. In addition, users are using Internet for exchanging any type of information<br />

that they come across, including voice, video, data, etc. All these factors have essentially necessitated use<br />

of modified approach for traffic management in computer networks. The main factor leading to this<br />

change is that the information packets are moving so fast through the computer networks that any<br />

feedback-based (or reactive) control will be too slow to be of any use. Therefore, some preventive mechanisms<br />

have been developed to maintain the information traffic inside a computer network to a comfortable<br />

level. Such techniques are implemented at the sender side by ensuring that only as much<br />

information traffic is allowed to enter the network as can be comfortably handled by the networks<br />

[1,20,22]. Based on the users’ needs and state of the technology, providing faster communications for<br />

different types of services (voice, video, data, and others) in the same computer network in an integrated<br />

and unified manner, has become a necessity. These computer networks are referred to as broadband<br />

integrated services digital networks (BISDNs). Broadband ISDNs provide end-to-end digital connectivity<br />

and users can access any type of communication service from a single point of access. Asynchronous<br />

transfer mode (ATM) is expected to be used as a transfer mechanism in broadband ISDNs. ATM is<br />

essentially a fast packet switching technique where information is transmitted in the form of small fixedsize<br />

packets called cells. Each cell is 53 bytes long and includes a header of 5 bytes. The information is<br />

primarily transported using connection-oriented (virtual circuit) environment [3,4,8,12,17].<br />

Another aspect of wide area networks is the processing speed of switching nodes. As the data rates of<br />

transmission media increases, it is essential to have faster processing capability at the switching nodes.<br />

Otherwise, switching nodes become bottlenecks and faster transmission media cannot be fully utilized.<br />

When transmission media consists of optical fibers, the incoming information at a switching node is<br />

© 2002 by CRC Press LLC

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