EIE325: Telecommunication TechnologiesM aciej J. Ogorzałek, PolyU, EIE Telecommunication Technologies Week 10 Interfacing

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Interfacing

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Characteristics of Interface  Mechanical Connection plugs  Electrical Voltage, timing, encoding  Functional Data, control, timing, grounding  Procedural Sequence of events

Mechanical Specification

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Electrical Specification 0 1 ?????? +3V -3V

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Functional Specification  Various functional tasks of interchange circuits data (4) control (16) transmission (13) loopback testing (3) timing (3) ground

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Loopback testing  Provide testing of DCE  Fault isolation  Common on modern modems  Output connected to input – isolated from the transmission line  Remote or Local loopback

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Local and Remote Loopback

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies The interchange circuits

Transmission on primary channel Transmission on secondary channel Loopback

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies The interchange circuits

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Procedural Specification  Defines the sequence of operation, correct request/response sequences and requirements to send and receive data

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies A Modem  Asynchronous private line modem Connecting two DTE over a short distance  Only six circuits required AB: Ground (102) BA: Transmit (103) BB: Receive (104) CA: Request to Send (105) CB: Clear to Send (106) CC: DCE ready (107) CF: Received line signal detector (109)

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies A Modem  When turned on and ready, modem (DCE) asserts DCE ready (CC)  When DTE ready to send data, it asserts Request to Send (CA) Also inhibits receive mode in half duplex  Modem responds when ready by asserting Clear to send (CB)  DTE sends data (BA)  When data arrives (BB), local modem asserts Receive Line Signal Detector (CF) and delivers data

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Public line modem  Previous example is insufficient for modem operating on public network  Also need CD: DTE ready (108.2) CE: Ring Indicator (125)

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Dial Up Operation

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Dial Up Operation

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Dial Up Operation

HDLC example

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies

Null Modem  For direct communicati on between peer DTE (no DCE!)

EIE325: Telecommunication TechnologiesM aciej J. Ogorzałek, PolyU, EIE Telecommunication Technologies Week 10 Multiplexing

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Multiplexing

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Multiplexing  Frequency Division Multiplexing Wavelength Division Multiplexing  Time Division Multiplexing Synchronous TDM Statistical TDM  Code Division Multiplexing

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Frequency Division Multiplexing

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies 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)  NB: Channel allocated even if no data  e.g. broadcast radio

FDM of Three Voiceband Signals

FDM System: Transmitter

FDM System: Transmission

FDM System: Receiver

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Example: Analog Carrier Systems  AT&T (USA)  Hierarchy of FDM schemes  Group 12 voice channels (4kHz each) = 48kHz Range 60kHz to 108kHz  Supergroup 60 channel FDM of 5 group signals on carriers between 420kHz and 612 kHz  Mastergroup 10 supergroups

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies 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

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies ADSL Design  Asymmetric Greater capacity downstream than upstream  Frequency division multiplexing Lowest 25kHz for voice Plain old telephone service (POTS) Use echo cancellation or FDM to give two bands Use FDM within bands  Range 5.5km

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies ADSL Channel Configuration

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies xDSL  High data rate DSL (HDSL) 2Mbps over two twisted pair lines BW of less than 200kHz  Single line DSL (SDSL) Single twisted pair Echo cancellation  Very high data rate DSL (VDSL) New: increase data rate at the expense of distance

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Time Division Multiplexing

TDM System

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies TDM: Transmitter

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies TDM: Transmission

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies TDM: Receiver

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Synchronous Time Division Multiplexing  Data rate of medium exceeds data rate of digital signal to be transmitted  Multiple digital signals interleaved in time  May be at bit level of blocks  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

Synchronous TDM

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Statistical TDM  In Synchronous TDM many slots are wasted  Statistical TDM allocates time slots dynamically based on demand  Multiplexer scans input lines and collects data until frame full  Data rate on line lower than aggregate rates of input lines

Statistical TDM

An international brokerage firm has its head office in Hong Kong, and a smaller branch office in Singapore. The firm's interests lie in trading on the futures markets of Hong Kong, London, and New York; and data related to these trades should be communicated over a private leased line between Hong Kong and Singapore. The company finds that a single leased line between Hong Kong and Singapore is insufficient for its needs. Instead, the Hong Kong, London and New York trading arms each maintain a separate link and these three lines are multiplexed together for transmission between Hong Kong and Singapore. Each of these three lines is utilised 24 hours per day, but varies according to the following table: Compute the capacity required on the multiplexed line using: (i)synchronous time division multiplexing. (ii)statistical time division multiplexing if 5% of capacity is required for framing overhead. Expected Link Usage (kbps)9am – 5pm5pm – 1am1am – 9am HK trading line1213 London trading line5193 New York trading line1421

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Synchronous vs. Statistical TDM

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies TDM Link Control  No headers and tails  Data link control protocols not needed  Flow control Data rate of multiplexed line is fixed If one channel receiver cannot receive data, the others must carry on The corresponding source must be quenched This leaves empty slots  Error control Errors are detected and handled by individual channel systems

Data Link Control on TDM Inputs: Transmission:

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Framing  No flag or SYNC characters bracketing TDM frames  Must provide synchronising mechanism  Added digit framing One control bit added to each TDM frame Looks like another channel - “control channel” Identifiable bit pattern used on control channel e.g. alternating …unlikely on a data channel Can compare incoming bit patterns on each channel with sync pattern

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Pulse Stuffing  Problem - Synchronising data sources  Clocks in different sources drifting  Data rates from different sources not related by simple rational number  Solution - Pulse Stuffing Outgoing data rate (excluding framing bits) higher than sum of incoming rates Stuff extra dummy bits or pulses into each incoming signal until it matches local clock Stuffed pulses inserted at fixed locations in frame and removed at demultiplexer

TDM of Analog and Digital Sources

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Examples: Digital Carrier Systems  Hierarchy of TDM  USA/Canada/Japan use one system  ITU-T use a similar (but different) system  US system based on DS-1 format  Multiplexes 24 channels  Each frame has 8 bits per channel plus one framing bit  193 bits per frame

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Digital Carrier Systems  For voice each channel contains one word of digitised data (PCM, 8000 samples per sec) Data rate 8000x193 = 1.544Mbps Five out of six frames have 8 bit PCM samples Sixth frame is 7 bit PCM word plus signaling bit Signalling bits form stream for each channel containing control and routing info  Same format for digital data 23 channels of data 7 bits per frame plus indicator bit for data or systems control 24th channel is sync

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Mixed Data  DS-1 can carry mixed voice and data signals  24 channels used  No sync byte  Can also interleave DS-1 channels DS-2 is four DS-1 giving 6.312Mbps

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies ISDN (Integrated Services Digital Network) User Network Interface (digital telephony+data transport services = voice,data, text, graphics,music, video and other sources over telephone wires)  ISDN allows multiplexing of devices over single ISDN line  Two interfaces Basic ISDN Interface Primary ISDN Interface

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies 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

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Basic ISDN Interface  B channel is basic user channel  Data  PCM voice  Separate logical 64kbps connections for different destinations  D channel used for control or data LAPD frames  Each frame 48 bits long  One frame every 250  s

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies 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

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Sonet/SDH  Synchronous Optical Network (ANSI)  Synchronous Digital Hierarchy (ITU-T)  Compatible  Signal Hierarchy Synchronous Transport Signal level 1 (STS-1) or Optical Carrier level 1 (OC-1) 51.84Mbps Carry DS-3 or group of lower rate signals (DS1 DS1C DS2) plus ITU-T rates (e.g Mbps) Multiple STS-1 combined into STS-N signal ITU-T lowest rate is Mbps (STM-1)

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies SONET Frame Format

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Code Division Multiplexing  CDMA: Code division Multiple Access  TDM and FDM work in either time or frequency space… CDMA is a combination of both  Each user is given a unique sequence (code) and transmits messages using that sequence orthogonal pseudo-random

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies FDM, TDM and CDMA Time Frequency CDMA FDM Time Frequency TDM Time Frequency Time Frequency Time Frequency

M aciej J. Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies How?  Each bit is represented by a “chip” of G bits  The chips are combined and transmitted  At the other end they may be recovered  Either mutually orthogonal mutually “random”