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Chapter 4: Circuit-Switching Networks Chapter 4 Circuit-Switching Networks Multiplexing SONET Transport Networks Circuit Switches The Telephone Network Signaling Traffic and Overload Control in Telephone Networks Cellular Telephone Networks 1 Circuit Switching Networks z End-to-end dedicated circuits between clients z Client can be a person or equipment (router or switch) z Circuit can take different forms z Dedicated path for the transfer of electrical current z Dedicated time slots for transfer of voice samples z Dedicated frames for transfer of Nx51.84 Mbps signals z Dedicated wavelengths for transfer of optical signals z Circuit switching networks require: z Multiplexing & switching of circuits z Signaling & control for establishing circuits z These are the subjects covered in this chapter 2 How a network grows (a) A switch provides the network to a cluster of users, e.g. a telephone switch connects a local community Network Access network (b) A multiplexer connects two access networks, e.g. a high speed line connects two switches 3 A Network Keeps Growing 1* a b 2 a b 4 (a) Metropolitan network A 3 viewed as Network A of A A Access Subnetworks c d c d Network of Metropolitan (b) National network viewed Access as Network of Regional Subnetworks Subnetworks (including A) A zVery high- speed lines α Network of Regional National & 4 Subnetworks International Chapter 4 Circuit-Switching Networks Multiplexing 5 Multiplexing z Multiplexing involves the sharing of a transmission channel (resource) by several connections or information flows z Channel = 1 wire, 1 optical fiber, or 1 frequency band z Significant economies of scale can be achieved by combining many signals into one z Fewer wires/pole; fiber replaces thousands of cables z Implicit or explicit information is required to demultiplex the information flows. (a) (b) Shared A A A Channel A B B B MUX MUX B C C C C 6 Frequency-Division Multiplexing z Channel divided into frequency slots A f 0 Wu (a) Individual signals occupy B z Guard bands f required Wu Hz 0 Wu z AM or FM radio stations C f z TV stations in 0 W u air or cable (b) Combined z Analog signal fits into telephone channel A B C systems f 7 bandwidth 0 W Time-Division Multiplexing z High-speed digital channel divided into time slots … A1 A2 t 0T 3T 6T z Framing B … required (a) Each signal 1 B2 t transmits 1 unit 0T 3T 6T z Telephone every 3T digital seconds … transmission C1 C2 t z Digital 0T 3T 6T transmission in (b) Combined backbone signal transmits A A B C … network 1 B1 C1 2 2 2 t 1 unit every T 0T 1T 2T 3T 4T 5T 6T seconds 8 T-Carrier System z Digital telephone system uses TDM. z PCM voice channel is basic unit for TDM z 1 channel = 8 bits/sample x 8000 samples/sec. = 64 kbps z T-1 carrier carries Digital Signal 1 (DS-1) that combines 24 voice channels into a digital stream: 1 1 2 MUX MUX 2 22 23 24 24 b . b 1 2 . 24 Frame 24 Framing bit Bit Rate = 8000 frames/sec. x (1 + 8 x 24) bits/frame 9 = 1.544 Mbps North American Digital Multiplexing Hierarchy The image cannot be displayed. 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Your computer may not have enough memory to open the image, or the 24 DS0 i h b t d R t t t d th th fil i If th d till . The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, 4 DS1 . Mux d th th fil i If th d till h t d l t th i d th i t it i The image cannot be displayed. Your computer 4 may not hav e enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. The image cannot be displayed. Your computer may not have enough memory to open the image, or the i h b t d R t t t d th th fil i If th d till The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. 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Your computer 7 may not hav e enough memory to open the image, or the image may have been corrupted. Restart y our computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. The image cannot be displayed. Your computer may not have enough memory to open the image, or th i h b t d R t t t d th th fil i If th d The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still a… The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still htdltthi dthititi 1 The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. The image cannot be displayed. Your computer may not have enough memory to open the image, or the i h b t d R t t t d th th fil i If th d till The image cannot be displayed. Your computer may not hav e enough memory to open the . image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.
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