Chapter 5: Multiplexing: Sharing a Medium Data Communications and Computer Networks: A Business User’s Approach Third Edition Chapter 5: Multiplexing: Sharing a Medium

After reading this chapter, you should be able to: Objectives After reading this chapter, you should be able to: Describe frequency division multiplexing and list its applications, advantages, and disadvantages Describe synchronous time division multiplexing and list its applications, advantages, and disadvantages Outline the basic multiplexing characteristics of both T-1 and ISDN telephone systems Data Communications & Computer Networks: A Business User's Approach, Third Edition

Objectives (continued) Describe statistical time division multiplexing and list its applications, advantages, and disadvantages Cite the main characteristics of wavelength division multiplexing and its advantages and disadvantages Describe the basic characteristics of discrete multitone Cite the main characteristics of code division multiplexing and its advantages and disadvantages Apply a multiplexing technique to a typical business situation Data Communications & Computer Networks: A Business User's Approach, Third Edition

Introduction Under the simplest conditions, a medium can carry only one signal at any moment in time For multiple signals to share one medium, the medium must somehow be divided, giving each signal a portion of the total bandwidth The current techniques that can accomplish this include frequency division multiplexing, time division multiplexing, and wavelength division multiplexing Data Communications & Computer Networks: A Business User's Approach, Third Edition

Frequency Division Multiplexing Assignment of non-overlapping frequency ranges to each “user” or signal on a medium Thus, all signals are transmitted at the same time, each using different frequencies A multiplexor Accepts inputs and assigns frequencies to each device Is attached to a high-speed communications line Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Frequency Division Multiplexing Corresponding multiplexor, or demultiplexor Is on the end of the high-speed line Separates the multiplexed signals Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Frequency Division Multiplexing Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Frequency Division Multiplexing Analog signaling is used to transmit signals Broadcast radio and television, cable television, and AMPS cellular phone systems use frequency division multiplexing Oldest multiplexing technique Involves analog signaling  more susceptible to noise Data Communications & Computer Networks: A Business User's Approach, Third Edition

Time Division Multiplexing Sharing signal is accomplished by dividing available transmission time on a medium among users Digital signaling is used exclusively Time division multiplexing comes in two basic forms: Synchronous time division multiplexing Statistical, or asynchronous time division multiplexing Data Communications & Computer Networks: A Business User's Approach, Third Edition

Synchronous Time Division Multiplexing The original time division multiplexing Multiplexor Accepts input from attached devices in a round-robin fashion Transmits data in a never ending pattern T-1 and ISDN telephone lines are common examples of synchronous time division multiplexing Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Synchronous Time Division Multiplexing Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Synchronous Time Division Multiplexing If one device generates data at a faster rate than other devices, then the multiplexor must either Sample incoming data stream from that device more often than it samples other devices OR Buffer faster incoming stream If a device has nothing to transmit, Multiplexor must still insert a piece of data from that device into the multiplexed stream Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Synchronous Time Division Multiplexing Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Synchronous Time Division Multiplexing Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Synchronous Time Division Multiplexing So that the receiver may stay synchronized with the incoming data stream, the transmitting multiplexor can insert alternating 1s and 0s into the data stream Data Communications & Computer Networks: A Business User's Approach, Third Edition

T-1 multiplexor stream is a continuous series of frames T-1 Multiplexing T-1 multiplexor stream is a continuous series of frames Data Communications & Computer Networks: A Business User's Approach, Third Edition

ISDN multiplexor stream is also a continuous stream of frames ISDN Multiplexing ISDN multiplexor stream is also a continuous stream of frames Each frame contains various control and sync info Data Communications & Computer Networks: A Business User's Approach, Third Edition

SONET/SDH Multiplexing Data Communications & Computer Networks: A Business User's Approach, Third Edition

Statistical Time Division Multiplexing Statistical multiplexor - transmits only the data from active workstations If a workstation is not active, no space is wasted on the multiplexed stream A statistical multiplexor Accepts incoming data streams Creates a frame containing only the data to be transmitted Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Statistical Time Division Multiplexing Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Statistical Time Division Multiplexing To identify each piece of data, an address is included Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Statistical Time Division Multiplexing If data is of variable size, length is also included Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Statistical Time Division Multiplexing More precisely, the transmitted frame contains a collection of data groups Data Communications & Computer Networks: A Business User's Approach, Third Edition

Wavelength Division Multiplexing Wavelength division multiplexing multiplexes multiple data streams onto a single fiber optic line Different wavelength lasers (called lambdas) transmit the multiple signals Each signal carried on the fiber can be transmitted at a different rate from the other signals Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Wavelength Division Multiplexing Dense wavelength division multiplexing combines many (30, 40, 50, 60, more?) onto one fiber Coarse wavelength division multiplexing combines only a few lambdas Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Wavelength Division Multiplexing Data Communications & Computer Networks: A Business User's Approach, Third Edition

Discrete Multitone (DMT) A multiplexing technique commonly found in digital subscriber line (DSL) systems DMT combines hundreds of different signals, or subchannels, into one stream Each subchannel is quadrature amplitude modulated recall - eight phase angles, four with double amplitudes Theoretically, 256 subchannels, each transmitting 60 kbps, yields 15.36 Mbps Unfortunately, there is noise Data Communications & Computer Networks: A Business User's Approach, Third Edition

Code Division Multiplexing Also known as code division multiple access Advanced technique that allows multiple devices to transmit on the same frequencies at the same time Each mobile device is assigned unique 64-bit code Chip spreading code To send a binary 1, mobile device transmits the unique code To send a binary 0, mobile device transmits the inverse of code Data Communications & Computer Networks: A Business User's Approach, Third Edition

Code Division Multiplexing (continued) Receiver Gets summed signal Multiplies it by receiver code Adds up resulting values Interprets as a binary 1 if sum is near +64 Interprets as a binary 0 if sum is near –64 Data Communications & Computer Networks: A Business User's Approach, Third Edition

Code Division Multiplexing Example For simplicity, assume 8-chip spreading codes 3 different mobiles use the following codes: Mobile A: 10111001 Mobile B: 01101110 Mobile C: 11001101 Assume Mobile A sends a 1, B sends a 0, and C sends a 1 Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Code Division Multiplexing Example Signal code: 1-chip = +N volt; 0-chip = -N volt Three signals transmitted: Mobile A sends a 1, or 10111001, or +-+++--+ Mobile B sends a 0, or 10010001, or +--+---+ Mobile C sends a 1, or 11001101, or ++--++-+ Summed signal received by base station: +3, -1, -1, +1, +1, -1, -3, +3 Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Code Division Multiplexing Example Base station decode for Mobile A: Signal received: +3, -1, -1, +1, +1, -1, -3, +3 Mobile A’s code: +1, -1, +1, +1, +1, -1, -1, +1 Product result: +3, +1, -1, +1, +1, +1, +3, +3 Sum of Product results: +12 Decode rule: For result near +8, data is binary 1 Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Code Division Multiplexing Example Base station decode for Mobile B: Signal received: +3, -1, -1, +1, +1, -1, -3, +3 Mobile B’s code: -1, +1, +1, -1, +1, +1, +1, -1 Product result: -3, -1, -1, -1, +1, -1, -3, -3 Sum of Product results: -12 Decode rule: For result near -8, data is binary 0 Data Communications & Computer Networks: A Business User's Approach, Third Edition

Comparison of Multiplexing Techniques Data Communications & Computer Networks: A Business User's Approach, Third Edition

Business Multiplexing in Action XYZ Corporation has two buildings separated by a distance of 300 meters A 3-inch diameter tunnel extends underground between the two buildings Building A has a mainframe computer and Building B has 66 terminals List some efficient techniques to link the two buildings Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Business Multiplexing in Action Data Communications & Computer Networks: A Business User's Approach, Third Edition

(continued) Business Multiplexing in Action Possible Solutions: Connect each terminal to mainframe computer using separate point-to-point lines Connect all terminals to mainframe computer using one multipoint line Connect all terminal outputs and use microwave transmissions to send data to the mainframe Collect all terminal outputs using multiplexing and send data to mainframe computer using conducted line Data Communications & Computer Networks: A Business User's Approach, Third Edition

Frequency division multiplexing Synchronous time division multiplexing Summary Frequency division multiplexing Synchronous time division multiplexing Basic multiplexing characteristics of T-1 and ISDN telephone systems Statistical time division multiplexing Wavelength division multiplexing Discrete multitone Data Communications & Computer Networks: A Business User's Approach, Third Edition

Code division multiplexing Summary (continued) Code division multiplexing Applying multiplexing techniques to typical business situations Data Communications & Computer Networks: A Business User's Approach, Third Edition