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EIE325: Telecommunication TechnologiesMaciej Ogorza ł ek, PolyU, EIE Telecommunication Technologies Week 9 HDLC (ISO 33009, ISO 4335)

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Presentation on theme: "EIE325: Telecommunication TechnologiesMaciej Ogorza ł ek, PolyU, EIE Telecommunication Technologies Week 9 HDLC (ISO 33009, ISO 4335)"— Presentation transcript:

1 EIE325: Telecommunication TechnologiesMaciej Ogorza ł ek, PolyU, EIE Telecommunication Technologies Week 9 HDLC (ISO 33009, ISO 4335)

2 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies

3 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies

4 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies HDLC Syntax  HDLC (High level Data Link Control)  ISO 33009, ISO 4335  Stations: Primary, Secondary, Combined  Link Balance or Unbalanced  Transfer Modes NRM, ABM, ARM  Frames I-frames, S-frames, U- frames

5 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies HDLC Station Types  Primary station Controls operation of link Frames issued are called commands Maintains separate logical link to each secondary station  Secondary station Under control of primary station Frames issued called responses  Combined station May issue commands and responses

6 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies HDLC Link Configurations  Unbalanced One primary and one or more secondary stations Supports full duplex and half duplex  Balanced Two combined stations Supports full duplex and half duplex

7 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies HDLC Transfer Modes  Normal Response Mode (NRM) Unbalanced configuration Primary initiates transfer to secondary Secondary may only transmit data in response to command from primary Used on multi-drop lines Host computer as primary Terminals as secondary

8 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies HDLC Transfer Modes  Asynchronous Balanced Mode (ABM) Balanced configuration Either station may initiate transmission without receiving permission Most widely used No polling overhead

9 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies HDLC Transfer Modes  Asynchronous Response Mode (ARM) Unbalanced configuration Secondary may initiate transmission without permission form primary Primary responsible for line Rarely used

10 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies HDLC Frame Types  Three types of frames I-frames : Information (data) S-frames : Supervisory (ARQ) U-frames : Unnumbered (other)  Frame structure the same in each case

11 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Frame Structure  Synchronous transmission  All transmissions in frames  Single frame format for all data and control exchanges

12 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Frame Structure Diagram

13 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Flag Fields  Delimit frame at both ends  01111110  May close one frame and open another  Receiver hunts for flag sequence to synchronise  Bit stuffing used to avoid confusion with data containing 01111110 0 inserted after every sequence of five 1s If receiver detects five 1s it checks next bit If 0, it is deleted If 1 and seventh bit is 0, accept as flag If sixth and seventh bits 1, sender is indicating abort

14 Bit Stuffing  Example with possible errors

15 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Address Field  Identifies secondary station that sent or will receive frame  Usually 8 bits long  May be extended to multiples of 7 bits LSB of each octet indicates that it is the last octet (1) or not (0)  All ones (11111111) is broadcast

16 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Control Field  Different for different frame type Information - data to be transmitted to user (next layer up) Flow and error control piggybacked on information frames Supervisory - ARQ when piggyback not used Unnumbered - supplementary link control  First one or two bits of control field identify frame type

17 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Control Field Diagram

18 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Poll/Final Bit  Use depends on context  Command frame P bit 1 to solicit (poll) response from peer  Response frame F bit 1 indicates response to soliciting command

19 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Information Field  Only in information and some unnumbered frames  Must contain integral number of octets  Variable length

20 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Frame Check Sequence Field  FCS  Error detection  16 bit CRC  Optional 32 bit CRC

21 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies HDLC Operation  Exchange of information, supervisory and unnumbered frames  Three phases Initialisation Data transfer Disconnect

22 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies

23 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies HDLC commands

24

25 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies E.g.: Setup and disconnect  SABME: Set ABM, 7- bit sequence numbers  UA: Unnumbered ACK  DISC: Disconnect

26 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies E.g.: Exchange  I,n,m: Information  n & m are sender and receiver sequence numbers  RR: Receive ready

27 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies E.g.: Busy  RNR: Receive not ready

28 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies E.g.: Reject recovery  REJ: Reject

29 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies E.g.: Timeout recovery

30 EIE325: Telecommunication TechnologiesMaciej Ogorza ł ek, PolyU, EIE Telecommunication Technologies Week 9 Synchronisation

31 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Asynchronous and Synchronous Transmission  Timing problems require a mechanism to synchronise the transmitter and receiver data rate bit duration inter-frame spacing  Two solutions Asynchronous (data not contiguous) Synchronous (data blocks contiguous)

32 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Presumptions  Serial, not Parallel Transmission  One bit per signal element  Sender and receiver’s clocks are different  Errors in timing (sampling) as well as amplitude (quantisation)

33 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Asynchronous  Data transmitted one character (5-8 bits) at a time  Timing only needs maintaining within each character  Resynchronise for each character  Idle (binary 1) between characters  Start bit is a binary 0

34 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Asynchronous (diagram)

35 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Asynchronous Timing Error  10kbps transmission … bit duration of 0.1ms.  Over 8 bits a 5% timing error is acceptable  A 6% timing error is not.

36 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Asynchronous - Behavior  In a steady stream, interval between characters is uniform (length of stop element)  In idle state, receiver looks for transition 1 to 0  Then samples next seven intervals (char length)  Then looks for next 1 to 0 for next char  Simple  Cheap  Overhead of 2 or 3 bits per char (~20%)  Good for data with large gaps (keyboard/terminal)

37 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Asynchronous Errors  Timing errors extreme discrepancy between sender and receiver’s clocks.  Framing errors Erroneous start bits

38 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Synchronous - Bit Level  Block of data transmitted without start or stop bits  Clocks must be synchronised  Can use separate clock line Good over short distances Subject to impairments  Embed clock signal in data Manchester encoding Carrier frequency (analog)

39 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Synchronous - Block Level  Need to indicate start and end of block  Use preamble and “postamble” e.g. series of SYN (hex 16) characters e.g. block of 11111111 patterns ending in 11111110  More efficient (lower overhead) than asynchronous  E.g. HDLC

40 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Synchronous e.g. HDLC

41 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Echo Cancellation  Transceiver: Transmitter/Receiver  Two parties transmit on the same data path simultaneously  Each is aware of their own transmission and can subtract that from the resultant to receive the other!

42 EIE325: Telecommunication TechnologiesMaciej Ogorza ł ek, PolyU, EIE Telecommunication Technologies Week 9 Interfacing

43 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Interfacing  Data processing devices (or data terminal equipment, DTE) do not (usually) include data transmission facilities  Need an interface called data circuit terminating equipment (DCE) e.g. modem, NIC  DCE transmits bits on medium  DCE communicates data and control info with DTE Done over interchange circuits Clear interface standards required

44 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Interfacing

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

46 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Two examples  Modem  ISDN

47 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies E.g.: V.24/EIA-232-F  ITU-T V.24 specifies functional and procedural  EIA-232-F (USA) (originally RS-232): Mechanical ISO 2110 Electrical V.28 Functional V.24 Procedural V.24

48 Mechanical Specification

49 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Data Pins

50 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Control Pins

51 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Timing Pins

52 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Electrical Specification  Signaling specification  Values interpreted as data or control, depending on circuit  More than -3v is binary 1, more than +3v is binary 0 (NRZ-L)  Signal rate < 20kbps  Distance <15m  For control, more than-3v is off, +3v is on

53 Maciej Ogorzałek, PolyU, EIEEIE325: Telecommunication Technologies Electrical Specification 0 1 ?????? +3V -3V


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