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Unformatted text preview: CS 168 Computer Networks Jannotti Homework 2 Due: 13 March 2010, 4pm Problem 1 Sec. 4, prob. 22 The minimum Ethernet frame is 64 bytes, including both addresses in the Ethernet frame header, the type/length field, and the checksum. Since the header fields occupy 18 bytes and the packet is 60 bytes, the total frame size is 78 bytes, which exceeds the 64-byte minimum. Therefore, no padding is used. Sec. 4, prob. 26 The smallest Ethernet frame is 512 bits, so at 1 Gbps we get 1,953,125 or almost 2 million frames/sec. However, this only works when frame bursting is operating. Without frame bursting, short frames are padded to 4096 bits, in which case the maximum number is 244,140. For the largest frame (12,144 bits), there can be as many as 82,345 frames/sec. Sec. 4, prob. 32 One reason is the need for real-time quality of service. If an error is dis- covered, there is no time to get a retransmission. The show must go on. Forward error correction can be used here. Another reason is that on very low quality lines (e.g., wireless channels), the error rate can be so high that practically all frames would have to be retransmitted, and the retransmission would probably damaged as well. To avoid this, forward error correction is used to increase the fraction of frames that arrive correctly. Even another scenario in which error correction can be preferred over error detection is a multicast/broadcast scenario. Consider a server serving a large number of clients through multicast. Instead of having the server handle retransmis- sions on a client-by-client basis, error correction at the client side may help reduce server overhead. CS 168...
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This note was uploaded on 12/03/2010 for the course CS 168 taught by Professor Jj during the Spring '10 term at Brown.
- Spring '10
- Computer Networks