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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   May close one frame and open another  Receiver hunts for flag sequence to synchronise  Bit stuffing used to avoid confusion with data containing 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 ( ) 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 patterns ending in  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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