CPEG514 Advanced Computer Networks Week 6 Multiplexing Atef Abu Salim University of Nizwa Spring 2013/2014 CPEG512 Advanced Computer Networks 2
Multiplexing Categories CPEG512 Advanced Computer Networks
Frequency Division Multiplexing Analog signaling is used to transmit the signals. Broadcast radio and television, cable television, and the AMPS cellular phone systems use frequency division multiplexing. This technique is the oldest multiplexing technique. Since it involves analog signaling, it is more susceptible to noise. CPEG512 Advanced Computer Networks
Frequency Division Multiplexing Frequency Division Multiplexing (FDM) Primarily used for Analog data. Bandwidth of medium equals or exceeds the sum of all channel bandwidths Each signal is modulated to a different carrier frequency Carrier frequencies separated so signals do not overlap (guard bands) Can carry multiple telephone conversations over a single transmission channel. Frequencies in each call are changed so they can be placed side-by-side in a wide-band channel and be transmitted as a group. At the other end, the frequencies in each call are changed back to the original frequencies. CPEG512 Advanced Computer Networks
Frequency Division Multiplexing Frequency Division Multiplexing (FDM) More efficient in terms of bandwidth than digital systems. Downside is that noise is amplified along with the voice. Has been replaced with Time Division Multiplexing (TDM). e.g. broadcast radio Channel allocated even if no data CPEG512 Advanced Computer Networks
Frequency Division Multiplexing FDM is an analog multiplexing technique that combines signals. CPEG512 Advanced Computer Networks
Frequency Division Multiplexing Frequency Division Multiplexing (FDM) Assignment of non-overlapping frequency ranges to each “user” or signal on a medium. A multiplexor accepts multiple analog inputs and assigns frequencies to each device. Modulation is used to move input signals into the assigned frequency ranges. The multiplexor is attached to a high-speed communications line. A corresponding demultiplexor on the other end of the line separates the multiplexed signals. FDM is only used with analog signals. CPEG512 Advanced Computer Networks
FDM Process CPEG512 Advanced Computer Networks
FDM Demultiplexing Process CPEG512 Advanced Computer Networks
FDM Question #1 Question Solution Assume that a voice channel occupies a bandwidth of 4 KHz. We need to combine three voice channels into a link with a bandwidth of 12 KHz, from 20 to 32 KHz. Show the configuration using the frequency domain without the use of guard bands. Solution Shift (modulate) each of the three voice channels to a different bandwidth, as shown on the next slide. CPEG512 Advanced Computer Networks
Frequency Division Multiplexing of Three Voice Calls CPEG512 Advanced Computer Networks
Frequency Division Multiplexing CPEG512 Advanced Computer Networks
Frequency Division Multiplexing Why stop there? Group 12 Voice channels Frequency range: 60 – 108 kHz Super Group 5 Groups 60 Voice channels Frequency range: 312 – 552 kHz Master Group 10 Super Groups 600 Voice channels Frequency range: 564 – 3084 kHz CPEG512 Advanced Computer Networks
Frequency Division Multiplexing Why stop there? (cont.) Jumbo Group 6 Master Groups 3600 Voice channels Frequency range: 564 – 17,548 Jumbo Group Multiplex 3 Jumbo Groups 10,800 Voice channels Frequency range: 3124 – 60,556 kHz CPEG512 Advanced Computer Networks
Frequency Division Multiplexing CPEG512 Advanced Computer Networks
Frequency Division Multiplexing Using FDM for data transmissions CPEG512 Advanced Computer Networks
FDM Question #2 Question Solution Five channels, each with a 100-KHz bandwidth, are to be multiplexed together. What is the minimum bandwidth of the link if there is a need for a guard band of 10 KHz between the channels to prevent interference? Solution For five channels, we need at least four guard bands. This means that the required bandwidth is at least: (5 x 100) + (4 x 10) = 540 KHz CPEG512 Advanced Computer Networks
FDM Question #2 CPEG512 Advanced Computer Networks
Time Division Multiplexing Digital Technology. Can carry multiple telephone conversations over a single transmission channel. Analog speech signals are sampled and converted to pulses. The samples are then coded by Pulse Code Modulation (PCM) All the samples are transmitted in series over the same channel, one at a time. At the other end, the signals are demodulated and each sample from each channel is routed to the proper channel. CPEG512 Advanced Computer Networks
Time Division Multiplexing Sharing of the 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, and Statistical, or asynchronous time division multiplexing. CPEG512 Advanced Computer Networks
Time Division Multiplexing CPEG512 Advanced Computer Networks
Time Division Multiplexing CPEG512 Advanced Computer Networks
TDM System Synchronous Time Division Multiplexing The original time division multiplexing. Assigns a static fixed bandwidth (in bps) to each input device. The multiplexor accepts input from attached devices in a round-robin fashion and transmits the data in a never ending pattern. T1 and ISDN telephone lines are common examples of synchronous time division multiplexing. CPEG512 Advanced Computer Networks
Synchronous Time Division Multiplexing Data rate of medium equals or exceeds the sum of all the data rates of all the channels Multiple digital signals interleaved in time May be at bit level or block level Time slots preassigned to sources and fixed Time slots allocated even if no data Time slots do not have to be evenly distributed amongst sources CPEG512 Advanced Computer Networks
Synchronous Time Division Multiplexing CPEG512 Advanced Computer Networks
Synchronous Time Division Multiplexing If a device has nothing to transmit, the multiplexor will still insert a piece of data (typically just 0 bits) from that device into the multiplexed stream as a placeholder. CPEG512 Advanced Computer Networks
Synchronous Time Division Multiplexing CPEG512 Advanced Computer Networks
Synchronous Time Division Multiplexing CPEG512 Advanced Computer Networks
Statistical Time Division Multiplexing Sometimes called Asynchronous TDM Transmits data only from active users Does not transmit empty time slots The multiplexor must create a more complex frame that contains data only from those input sources that have something to send. Upon those devices wishing to transmit again, the statistical multiplexor must create a new frame containing data from all currently transmitting stations CPEG512 Advanced Computer Networks
T-1 Multiplexor The T-1 multiplexor stream is a continuous series of frames. CPEG512 Advanced Computer Networks
Multiplexing: Sharing a Medium T1 Frame Format Each DS0 called a time slot 8000 frames/sec * 8 bits/slot = 64 Kbps 24 * 8 + 1 = 193 bits/frame 8000 frames/sec * 193 bits/frame = 1.544 Mbps 8000 Framing bits sent per second CPEG512 Advanced Computer Networks
Transmission Technology Framing Bits are used for: Allow receiver to find the start-of-frame (frame synchronization). Group sets of 12 frames into superframes. Indicate which frames contain signaling bits. Provide error checking (CRC). Provide Facilities Data Link channel to transmit network management messages. CPEG512 Advanced Computer Networks
Framing Bits CPEG512 Advanced Computer Networks
Multiplexing Voice Calls on a T1 CPEG512 Advanced Computer Networks
T1 Frame Structure CPEG512 Advanced Computer Networks
DS and T line rates Service Line Rate (Mbps) Voice Channels DS-1 T-1 1.544 24 DS-2 T-2 6.312 96 DS-3 T-3 44.736 672 DS-4 T-4 274.176 4032 CPEG512 Advanced Computer Networks
DS hierarchy CPEG512 Advanced Computer Networks
Transmission Technology D4 Framing – Superframe T-1 (1970) Framing pattern is a repeating 12-bit sequence. F-bit pattern: 1000 1101 1100 Odd frames: 101010 Even frames: 001110 One Signaling Bit is “robbed” in the 6th and 12th frames for each time slot. D4 Frame Format Frames 1-5, 7-11: Frames 6, 12: CPEG512 Advanced Computer Networks
Transmission Technology D5 Framing – Extended Superframe T1 (1983) F-bit pattern marks 24-frame extended superframes F-bit pattern: Odd frames: Facilities Data Link Even frames alternating: Every 4th frame: 001011 (Framing pattern) Every 4th frame: CRC for previous ESF ESF Frame Advantages Facilities Data Link Network diagnostics and management messages sent between carrier equipment. Cyclic Redundancy Check (CRC) Allows error detection on T1 lines. Carrier can offer Automatic Protection Switching service to customer (switches to another T1 line if errors are detected.) CPEG512 Advanced Computer Networks
ISDN User Network Interface ISDN allows multiplexing of devices over single ISDN line Two interfaces Basic ISDN Interface Primary ISDN Interface CPEG512 Advanced Computer Networks
Basic ISDN Interface Digital data exchanged between subscriber and NTE - Full Duplex Separate physical line for each direction Pseudoternary coding scheme 1=no voltage 0=positive or negative 750mV +/-10% Data rate 192kbps Basic access is two 64kbps B channels and one 16kbps D channel This gives 144kbps multiplexed over 192kbps Remaining capacity used for framing and sync CPEG512 Advanced Computer Networks
Basic ISDN Interface B channel is basic user channel Data PCM voice Separate logical 64kbps connections o different destinations D channel used for control or data LAPD frames Each frame 48 bits long One frame every 250s CPEG512 Advanced Computer Networks
Asymmetrical Digital Subscriber Line ADSL Link between subscriber and network Local loop Uses currently installed twisted pair cable Can carry broader spectrum 1 MHz or more CPEG512 Advanced Computer Networks
Digital Subscriber Line xDSL Architecture Central Office Architecture PSTN was originally designed to carry voice traffic in 4kHz channels. DSL service lines bypass the circuit-switching infrastructure of the PSTN and terminate at DSL Access Multiplexer’s, called DSLAM’s, at the CO. The DSLAM routes data to your Internet Service Provider (ISP). The DSLAM strips off voice traffic and routes it to the PSTN for normal processing. CPEG512 Advanced Computer Networks
Digital Subscriber Line xDSL Architecture (cont.) ISP DSLAM PSTN Switch Internet HUB DSL CPE Splitter CPEG512 Advanced Computer Networks
Digital Subscriber Line xDSL Coding Discreet Multi-tone Modulation (DMT) Transmits simultaneously in parallel on multiple narrowband carriers. Each channel is modulated independently of each other on a carrier frequency located in the center of the frequency band being used by that channel. The American National Standards Institute (ANSI) selected DMT with the use of 256 sub-carriers, each with a bandwidth of 4.3125 kHz. Each sub-carrier can be modulated with a maximum of 15 bits per hertz, totaling 60 kbps. DMT Frequency Spectrum 0 kHz – 4 kHz = Voice (0 – 20 kHz is available). 4 kHz – 20 kHz = Separation. 20 kHz – 130 kHz = Upstream channel. 130 kHz – 140 kHz = Separation. 140 kHz – 1MHz = Downstream channel. CPEG512 Advanced Computer Networks
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. Dense WDM – High number of lambdas (up to 80) Coarse WDM – A few lambdas (5-6) CPEG512 Advanced Computer Networks
Wavelength-Division Multiplexing MUX CPEG512 Advanced Computer Networks
WDM WDM is an analog multiplexing technique to combine optical signal. Very narrow bands of light from different source are combined to make a wider band of light. At the receiver, the signal are separated by the demultiplexer. Combine Multiple light source into one single light. CPEG512 Advanced Computer Networks
WDM cont. Application of WDM the SONET network. DWDM is a new method can multiplex a very large number of channels very close to one other. It achieves even greater efficiency. CPEG512 Advanced Computer Networks
WDM cont. CPEG512 Advanced Computer Networks
Code Division Multiple Access The full bandwidth, i.e. 125MHz is shared by all users. Each user has a unique code which he uses to decode his information bits. Allows for sharing of resources instead of dedication, better utilization. CPEG512 Advanced Computer Networks