SolutionsChap4_09

SolutionsChap4_09 - Chapter 4 Review Questions 1 A...

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Chapter 4 Review Questions 1. A network- layer packet is a datagram. A router forwards a packet based on the packet’s IP (layer 3) address. A link- layer switch forwards a packet based on the packet’s MAC (layer 2) address. 2. Datagram-based network layer: forwarding; routing. Additional function of VC-based network layer: call setup. 3. Forwarding is about moving a packet from a router’s input link to the appropriate output link. Routing is about determining the end-to-routes between sources and destinations. 4. Yes, both use forwarding tables. For descriptions of the tables, see Section 4.2. 5. Single packet: guaranteed delivery; guaranteed delivery with guaranteed maximum delay. Flow of packets: in-order packet delivery; guaranteed minimal bandwidth; guaranteed max imum jitter. None of these services is provided by the Internet’s network layer. ATM’s CBR service provides both guaranteed delivery and timing. ABR does not provide any of these services. 6. Interactive live multimedia applications, such as IP telephony and video conference, could benefit from ATM CBR’s service, which maintains timing. 7. With the shadow copy, the forwarding decision is made locally, at each input port, without invoking the centralized routing processor. Such decentralized forwarding avoids creating a forwarding processing bottleneck at a single point within the router. 8. Switching via memory; switching via a bus; switching via an interconnection network 9. Packet loss occurs if queue size at the input port grows large because of slow switching fa bric speed and thus exhausting router’s buffer space. It can be eliminated if the switching fabric speed is at least n times as fast as the input line speed, where n is the number of input ports. 10. Packet loss can occur if the queue size at the output port grows large because of slow outgoing line-speed. 11. HOL blocking a queued packet in an input queue must wait for transfer through the fabric because it is blocked by another packet at the head of the line. It occurs at the input port. 12. Yes. They have one address for each interface. 13. 11011111 00000001 00000011 00011100 14. Students will get different correct answers for this question.
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15. 8 interfaces; 3 forwarding tables 16. 50% overhead 17. The 8-bit protocol field in the IP datagram contains information about which transport layer protocol the destination host should pass the segment to.
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