LGW2ECh5solutions

LGW2ECh5solutions - Communication Networks (2 nd Edition)...

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Unformatted text preview: Communication Networks (2 nd Edition) Chapter 5 Solutions Solutions to Chapter 5 Version 1.01 (list of changes on last page) 1. Explain the difference between connectionless unacknowledged service and connectionless acknowledged service. How do the protocols that provide these services differ? Solution: In an acknowledged connectionless service, reliable delivery can be achieved through the use of ACK and NAK control messages. Such protocols are suited for communication over networks in which higher layers are sensitive to loss and the underlying network is inherently unreliable with a significant probability of loss or error. For example, HDLC provides for unnumbered acknowledgment service for connection setup and release. Unacknowledged networks provide simpler and faster communication for networks that are inherently reliable or provide service to higher layers that can tolerate information loss or have built-in error recovery mechanisms. 2. Explain the difference between connection-oriented acknowledged service and connectionless acknowledged service. How do the protocols that provide these services differ? Solution: The use of acknowledgments can provide reliable transfer over links or networks that are prone to error, loss, and or resequencing. In a connection-oriented service, a setup phase between the sending user and receiving user establishes a context for the transfer of information. In a connection- oriented acknowledged service acknowledgments are provided to the sending user for all SDUs. In a connectionless service, there is no prior context provided for the transfer of information between the sending user and the receiving user. The sender passes its SDU to the underlying layer without prior notice. In an acknowledged connectionless service, the sending user requires an acknowledgment of delivery of its SDU. The protocols that provide these services are very different. Connection-oriented acknowledged service requires the use of stateful protocols that keep track of sequence numbers, acknowledgments, and timers. Connectionless services use much simpler protocols that are stateless in nature. Connectionless acknowledged service does require that the transmitting protocol track the acknowledgment of a PDU. In the simplest instance, the receiver would be required to send an ACK for correctly received PDU and the transmitter would keep a timer. If an ACK was not received in time, the transmitter would inform the user of a failure to deliver. 3. Suppose that the two end systems and in Figure 5.6 communicate over a connection-oriented packet network. Suppose that station sends a 10-kilobyte message to station and that all packets are restricted to be 1000 bytes (neglect headers); assume that each packet can be accommodated in a data link frame. For each of the links, let p be the probability that a frame incurs errors during transmission....
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LGW2ECh5solutions - Communication Networks (2 nd Edition)...

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