CSE 123 Fall 2010 Homework 1 Due 10/7/2010 beginning of class. Exercise 1 “Dry loop DSL” is a DSL connection that does not include a POTS (plain old telephone service) connection - this frees up some “room” on the line for more bandwidth to your DSL modem, in some cases enough for an additional 256 kbit/s of capacity. Use Shannon’s theorem to show the necessary signal-to-noise ratio for 3,000 Hz of bandwidth that will provide (a) 256 kbps, and (b) 128 kbps. Exercise 2 Consider a variation of the 4B/5B NRZI encoding scheme which sends the ﬁrst 4 bits of the data unchanged, and sets the 5th bit to the value one no matter what. What design considerations/features of the 4B/5B encoding in the book does this scheme provide? Which does it not provide? Exercise 3 Your boss has tasked you with implementing an Intrusion Detection System at Layer 1, using nothing but an oscilloscope and a tap on the wire, held to-gether with duct tape. This widget reads every voltage change oﬀ of the wire
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Plain old telephone service, DSL, CRC value pairs, Dry loop DSL, NRZI encoding scheme, necessary signal-to-noise ratio