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Module 2.2: ADSL, ISDN, SONET

Module 2.2: ADSL, ISDN, SONET. WDM FDM TDM T-1 ADSL ISDN SONET. Wavelength Division Multiplexing. Used for fiber optics Multiplexing and demultiplexing involve light signals Combining and splitting of light sources are done by prisms. Frequency Division Multiplexing. FDM

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Module 2.2: ADSL, ISDN, SONET

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  1. Module 2.2: ADSL, ISDN, SONET • WDM • FDM • TDM • T-1 • ADSL • ISDN • SONET K. Salah

  2. Wavelength Division Multiplexing • Used for fiber optics • Multiplexing and demultiplexing involve light signals • Combining and splitting of light sources are done by prisms. K. Salah

  3. Frequency Division Multiplexing • FDM • Useful bandwidth of medium exceeds required bandwidth of channel • Each signal is modulated to a different carrier frequency • Carrier frequencies separated so signals do not overlap (guard bands) • e.g. broadcast radio • Channel allocated even if no data K. Salah

  4. FDM System K. Salah

  5. FDM Example • Touch Tone Dialing • When dialing 8, two bursts of analog signal with frequencies 852 and 1336 Hz are sent to the Central Office K. Salah

  6. TDM System K. Salah

  7. T-1 Frame K. Salah

  8. DS Hierarchy K. Salah

  9. Digital Carrier Systems • Hierarchy of TDM • US/Canada/Japan use one system, Europe uses different. • US system is based on DS-1 format. • For voice each channel contains one word of digitized data (PCM, 8000 samples per sec) • Data rate 8000x193 = 1.544Mbps • Signaling bits form stream for each channel containing control and routing info • Data: 56,000 bps per channel at 24 channels = 1,344,000 bps • Control: 8000 bps per channel at 24 channels = 192,000 bps • Framing: 8000 bps for frame synchronization = 8000 bps • For digital data • Same format is used • The effective data rate in general is 56k x 24 = 1.344 Mbps K. Salah

  10. Leased T1 • A typical configuration scheme of a leased T1 WAN connection between two sites involves a V.35 link between a router’s V.35 port and a CSU/DSU. • The CSU/DSU provides the interface to the T1 circuit. This circuit terminates at the telco’s CO either directly or via a POP located near the customer’s premises. The CO then provides connectivity to the network. K. Salah

  11. Asynchronous TDM • Called also statistical time-division multiplexing • Synchronous TDM doesn’t guarantee high link utilization because timeslots are pre-assigned and fixed. If a device is not transmitting, the corresponding timeslot is empty. • Suppose you have multiplexed the output of 20 computers to a single line. • In synchronous TDM, the speed of the line must be at least 20 times the speed of each input line. • Half of this capacity is wasted if we have 10 computers only in use at a time. • Asynchronous TDM is designed to avoid this type of waste by filling up all timeslots. Timeslot is not fixed per device. Multiple devices could share the same timeslot. • Statistical TDM allocates time slots dynamically based on demand • Multiplexer scans input lines and collects data until frame full • In asynchronous TDM, the total speed of the input lines can be greater than the capacity of the path. • In synchronous TDM, if we have n input lines, the frame contains at least n timeslots • In asynchronous TDM, if we have n input lines, the frame contains m slots, with m less than n. K. Salah

  12. Synchronous vs. Asynchronous TDM K. Salah

  13. ISDN User Network Interface • ISDN allows multiplexing of devices over single ISDN line • Two interfaces • Basic ISDN Interface • Primary ISDN Interface K. Salah

  14. 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% • 2B1Q or AMI digital baseband line encoding • Data rate 192kbps • Basic access is two 64kbps B channels and one 16kbps D channel (2B+D) • This gives 144kbps multiplexed over 192kbps • Remaining capacity used for framing and sync • B channel is basic isdn channel • Data • PCM voice • Separate logical 64kbps connections to different destinations • D channel used for control or data: LAPD frames • Each frame 48 bits long • One frame every 250s K. Salah

  15. Primary ISDN • Point to point • Typically supporting PBX • 1.544Mbps • Based on US DS-1 • Used on T1 services • 23 B plus one D channel • 2.048Mbps • Based on European standards • 30 B plus one D channel • Line coding is AMI using HDB3 K. Salah

  16. Asymmetrical Digital Subscriber Line • ADSL uses Analog signaling (DMT or Discrete Multitone) • Link between subscriber and network • Local loop • Uses currently installed twisted pair cable • Can carry broader spectrum • 1 MHz or more • Asymmetric • Greater capacity downstream than upstream • Frequency division multiplexing • Lowest 25kHz for voice • Plain old telephone service (POTS) • Use FDM to give two bands • Use FDM within bands • Range 5.5km K. Salah

  17. DMT Transmitter • ADSL uses Discrete Multitone (DMT) • Upstream and downstream bands are divided into 4 khz channel, each capable of transfering 60 kbps. • With 256 downstream subchannels, we can transmit up to 15.36 Mbps, but transmission impairments prevent this. • Current rates go from 1.5 to 9 Mbps. • HDSL and SDSL use digital signaling, AMI and 2B1Q line coding. • ADSL and VDSL use analog signaling, DMT modulation. K. Salah

  18. ADSL Terminology • ATU-C: ADSL Transmission Unit, Central • The ADSL point of termination in the central office • An ADSL modem • ATU-R: ADSL Transmission Unit, Remote • The remote user’s ADSL modem • The CPE • DSLAM: DSL Access Multiplexer • Central office device that concentrates many ADSL connections into one • DSLAM contains ATU-Cs K. Salah

  19. End-to-End ADSL Architecture PSTN DSLAM IP ATU-R IP ISP ATM/Frame Relay Network ISP L2/L3 Services Aggregator Corporate UCP ATU-R Content Providers Local Loop Central Office Broadband Network K. Salah

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