Twisted Pair Cables PDF

Twisted Pair Cables Dr. Atef Abdrabou 6 Shannon Channel Capacity (Section 3.5.2) C = Bc log2 (1 + SNR) bps ⚫ ⚫ ⚫ ⚫ ⚫ If the channel bandwidth is Bc , the maximum data transmission rate over the channel is C given certain signal-to-noise ratio (SNR) at the receiver Reliable communications is pos...

Twisted Pair Cables Dr. Atef Abdrabou 6 Shannon Channel Capacity (Section 3.5.2) C = Bc log2 (1 + SNR) bps ⚫ ⚫ ⚫ ⚫ ⚫ If the channel bandwidth is Bc , the maximum data transmission rate over the channel is C given certain signal-to-noise ratio (SNR) at the receiver Reliable communications is possible if the transmission rate R < C If R > C, then reliable communications is not possible. C can be used as a measure of how close a system design is to the best achievable performance. Bandwidth Bc & SNR determine C Dr. Atef Abdrabou 20 Multiplexing (Section 6.1) ⚫ Multiplexing involves using a transmission link (resource) by several connections or data flows ⚫ ⚫ Significant savings can be achieved by combining many signals into one ⚫ ⚫ One Link = 1 cable, 1 optical fiber, or 1 frequency band Fewer wires; fiber replaces thousands of cables Information is needed to demultiplex the data flows. (a) One Link , 3 channels (b) A A A B B B C C C Dr. Atef Abdrabou A MUX MUX B C 50 Frequency-Division Multiplexing (Section 6.1.1) ⚫ Channel divided into frequency slots A 0 (a) Individual signals occupy Wu Hz f Wu ⚫ B 0 f Wu ⚫ C 0 (b) Combined signal fits into channel bandwidth f Wu ⚫ ⚫ A 0 B C Dr. Atef Abdrabou W f Guard bands required AM or FM radio stations TV stations in air or cable Analog telephone systems 51 Time-Division Multiplexing ⚫ (Section 6.1.3) High-speed digital channel divided into time slots A1 0T … A2 t 6T 3T ⚫ (a) Each signal transmits 1 unit every 3T seconds B1 0T 0T 1T 2T C1 A2 3T 4T ⚫ … C2 t 6T 3T A1 B1 t 6T 3T 0T C1 (b) Combined signal transmits 1 unit every T seconds … B2 B2 C2 … t ⚫ Framing required Telephone digital transmission Digital transmission in backbone network 5T 6T Dr. Atef Abdrabou 52 T-Carrier System ⚫ Digital telephone system uses TDM PCM voice channel is basic unit for TDM ⚫ ⚫ 1 channel = 8 bits/sample x 8000 samples/sec. = 64 kbps T-1 carrier carries Digital Signal 1 (DS-1) that combines 24 voice channels into a digital stream: 1... 2 24 1 MUX MUX 22 23 24 b 1 2... 24 b Frame 2... ⚫ 24 Framing bit Bit Rate = 8000 frames/sec. x (1 + 8 x 24) bits/frame Dr. Atef Abdrabou = 1.544 Mbps 53 Telephone Networks (Section 14.1) Hierarchical Network Structure Toll CO = central office Tandem Tandem CO CO CO CO CO Telephone subscribers connected to local CO (central office) 54 Tandem & Toll switches connect CO’s Dr. Atef Abdrabou Circuit Switching Network Example Telephone Network Architecture ⚫ Digital transmission & multiplexing ⚫ ⚫ Circuit switching ⚫ ⚫ ⚫ ⚫ ⚫ User signals for call setup and tear-down Route selected during connection setup End-to-end connection across network Signaling coordinates connection setup Hierarchical Network ⚫ ⚫ ⚫ Digital voice; Time Division Multiplexing Decimal numbering system Hierarchical structure; simplified routing; scalability Signaling Network ⚫ Intelligence inside the network Dr. Atef Abdrabou 55 Delay in Circuit Switched Networks ⚫ Example ⚫ Total Delay = Connection Establishment time + Data Transfer time + Connection Tear Down time Connection Est. Time = 2τ + 2 Tsg ⚫ τ is the propagation time = (Distance between A & B) / (speed of light) ⚫ Tsg is the request or response signal transmission time Data Transfer Time = Transmission Time = Data Size / Data Rate Connection Tear Down Time = τ + Tsg ⚫ ⚫ ⚫ Dr. Atef Abdrabou 56