Sol20 - CHAPTER 20 Network Layer: Internet Protocol...

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1 CHAPTER 20 Network Layer: Internet Protocol Solutions to Review Questions and Exercises Review Questions 1. The delivery of a frame in the data link layer is node-to-node. The delivery of a packet at the network layer is host-to-host . 2. In a connectionless service , there is no setup and teardown phases. Each packet is independent from every other packet. Communication has only one phase: data transfer. In connection-oriented service, a virtual connection is established between the sender and the receiver before transferring data. Communication has three phases: setup, data transfer, and teardown. IPv4 provides a connectionless service; IPv6 normally provides a connectionless service, but it can provide a con- nection-oriented service if flow label field is used. 3. Each data link layer protocol has a limit on the size of the packet it can carry. When a datagram is encapsulated in a frame, the total size of the datagram must be less than this limit. Otherwise, the datagram must be fragmented . IPv4 allows fragmentation at the host and any router; IPv6 allows fragmentation only at the host. 4. First, the value of the checksum field is set to 0. Then the entire header is divided into16-bit sections and added together. The result (sum) is complemented and inserted into the checksum field. The checksum in the IPv4 packet covers only the header, not the data . There are two good reasons for this. First, all higher-level protocols that encapsulate data in the IPv4 datagram have a checksum field that covers the whole packet. Second, the header of the IPv4 packet changes with each visited router, but the data do not. The options, if present, are included in the checksum field. 5. Options can be used for network testing and debugging. We mentioned six options: no-operation, end-of-option, record-route, strict-source-route, loose- source-route, and timestamp. A no-operation option is a 1-byte option used as a filler between options. An end-of-option option is a 1-byte option used for padding at the end of the option field. A record-route option is used to record the Internet routers that handle the datagram. A strict-source-route option is used by the source to predetermine a route for the datagram. A loose-source-route option is
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2 similar to the strict source route, but it is less rigid. Each router in the list must be
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Sol20 - CHAPTER 20 Network Layer: Internet Protocol...

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