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Xdsl dsl for digital subscriber line adsl a for

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Unformatted text preview: Digital Subscriber Line, ADSL, A for “Asymmetrical”. Downstream data rate depends on local loop quality. Maximum of 8 megabits/second is allowed for. Trunks and Multiplexing - sharing a common cable, wire or optical fiber. Categories of multiplexing 1. Time division multiplexing (TDM), Synchronous or Statistical. 2. Frequency division multiplexing (FDM). 3. Combined TDM and FDM. 4. Wavelength division multiplexing in optical fiber. Frequency multiplexing with carriers. T elephone network digital voice. Used by telephone network after A/D conversion of voice signals - 8000 samples/second. 1/8000 = 125 microsec. frames time multiplex 24 channels. Raw bit rate is (24 x 8 + 1) x 8000 = 1.544 Megabits/second. Called a T1 carrier The channel data rate is 7 x 8000 = 56 kb/s. Hierarchies of successively higher rates AT&T had T2 = 4 T1 Streams; T3 = 7 T2 streams; T4 = 6 T3 streams. On voice A/D conversion - redundancy allows data compression. Can be as low as 8 kb/s, even 4 kb/s, with some quality sacrifice. The Mobile Telephone System First generation: Analog voice AMPS (Advanced Mobile Phone System) Second Generation Mobile Phones: Digital Voice 1. D- AMPS (Digital Advanced Mobile Phone Service) 3 users can share a 30 khz channel, using time multiplexing. (or six with 4 kb/s coding). 2. GSM (Global System for Mobile Communications) Frequency channels are 200 khz instead of 30 khz. Time Division Multiplex 8 users instead of 3 users - more data rate per user (200/8 > 30/3). 3. CDMA (Code Division Multiple Access) The Data Link Layer Grouping bits into frames, handling errors, regulating flow, proper sequencing of frames. Link layer takes into its payload field whatever higher layers give it. Framing - breaking a bit stream into frames. first task -define the start and end of a frame. Asynchronous case - determine the bit sampling time and start of packet. Physical...
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