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11 Data Link Protocol

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treat each character in a bit stream independently ... WACK. DLE and 0. DLE and 1. DLE. ENQ. EOT. ETB. ETX. US. NAK. NULL. DLE and SOH. STX. SYN. STX and ENQ ... – PowerPoint PPT presentation

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Title: 11 Data Link Protocol


1
11? Data Link Protocol
  • 11.1 Asynchronous protocol
  • 11.2 Synchronous protocol
  • 11.3 Character-Oriented protocol
  • 11.4 Bit-Oriented protocol
  • 11.5 ??

2
  • Data Link Protocol
  • is a set of specifications used to
    implementation the data link layer

3
  • Data Link Protocol
  • Asynchronous protocol
  • treat each character in a bit stream
    independently
  • Synchronous protocol
  • take the whole bit stream and chop it into
    characters of equal size

4
11.1 Asynchronous protocol
  • used primarily in modems, feature start and
    stop bits and variable length gabs between
    characters

5
Asynchronous protocol(contd)
  • Xmodem
  • Ward christiansen designed a file transfer
    protocol for telephone-line communication between
    PCs(1979)
  • half-duplex stop-and-wait ARQ protocol

6
Asynchronous protocol(contd)
  • XMODEM frame

7
Asynchronous protocol(contd)
  • XMODEM frame
  • SOH(start of Header) 1 byte
  • Header 2 byte(Sequence number, check the
    validity of sequence number)
  • Data(Binary, ASCII, Boolean, Text, etc.) 128
    byte
  • CRC check for error in the data field

8
Asynchronous protocol(contd)
  • YMODEM
  • is a protocol similar to XMODEM
  • data unit is 1024 bytes
  • Two CANs are sent to abort a transmission
  • ITU-T CRC-16 is used for error checking
  • Multiple files can be sent simultaneously

9
Asynchronous protocol(contd)
  • ZMODEM
  • is a newer protocol combining features of both
    XMODEM and YMODEM
  • BLAST(Blocked Asynchronous Transmission)
  • is full-duplex with sliding window flow control
  • Kermit
  • designed at Columbia University
  • is the most widely used asynchronous protocol

10
11.2 Synchronous protocol
  • for LAN, MAN, WAN

11
Synchronous protocol(contd)
  • character-oriented protocol
  • frame or packet is interpreted as a series of
    characters
  • bit-oriented protocol
  • frame of packet is interpreted as a series of
    bits

12
11.3 Character-Oriented protocol
  • are not as efficient as bit-oriented protocols
    and therefore one now seldom used
  • popular protocol BSC(Binary synchronous
    communication)

13
Character-Oriented protocol(contd)
  • BSC(Binary Synchronous Communication)
  • developed by ZBM in 1964
  • usable in both point-to-point and multipoint
    configuration
  • support half-duplex transmission using
    stop-and-wait ARQ flow control and error
    correction
  • do not support full-duplex transmission or
    sliding window protocol

14
Character-Oriented protocol(contd)
  • Control character for BSC

Character
ASCII Code
Function
ACK 0 ACK 1 DLE ENQ EOT ETB ETX ITB NAK NUL RVI SO
H STX SYN TTD WACK
DLE and 0 DLE and 1 DLE ENQ EOT ETB ETX US NAK NUL
L DLE and lt SOH STX SYN STX and ENQ DLE and
Good even frame received or ready to receive Good
odd frame received Data transparency
maker Request for a response Sender
terminating End of transmission block ACK
required End of text in a message End of
intermediate block in a multiblock
transmission Bad frame received nothing to
send Filler character Urgent message from
receiver Header information beings Text
beings Alerts receiver to incoming frame Sender
is pausing but not relinquishing the line Good
frame received but not ready to receive more
15
Character-Oriented protocol(contd)
  • ASCII code
  • whatever the system, not all control
    characters can be represented by a single
    character. Often they must be represented by two
    or three characters(table 11.1)

16
Character-Oriented protocol(contd)
  • BSC frame

17
Character-Oriented protocol(contd)
  • Data frame

18
Character-Oriented protocol(contd)
  • Header field

One or more bytes defining address and/or other
information(nonstandardized)
19
Character-Oriented protocol(contd)
  • Multiblock Frame
  • text in a message is often divide between several
    blocks

20
Character-Oriented protocol(contd)
  • Multiframe Transmission

21
Character-Oriented protocol(contd)
  • Control Frame
  • is used by one device to send commands to, or
    solicit information from, another device

One or more characters
22
Character-Oriented protocol(contd)
  • Control Frame
  • serve three purpose
  • establishing connections
  • maintaining flow and error control during data
    transmission
  • terminating connection

23
Character-Oriented protocol(contd)
  • Control Frame(1)

24
Character-Oriented protocol(contd)
  • Control Frame(2)

25
Character-Oriented protocol(contd)
  • Control Frame(3)

26
Character-Oriented protocol(contd)
  • Data Transparency
  • means we should be able to send any
    combination of bits as data(bit stuffing)

27
11.4 Bit-Oriented protocol
  • can pack more information into shorter frames
    and avoid the transparency problem of
    character-oriented protocol

28
Bit-Oriented protocol(contd)
  • SDLC(Synchronous Data Link Control)
  • developed by ZBM in 1975
  • HDLC(High-Level Data Link Control)
  • developed by ISO in 1979
  • LAPs(LAPS, LAPD, LAPM, LAPX, etc)
  • developed by ITU-T since 1981
  • PPP, frame relay
  • developed by ITU-T and ANSI

29
Bit-Oriented protocol(contd)
  • HDLC
  • All bit-oriented protocols are related to
    high-level data link control(HDLC), which
    published by ISO.
  • HDLC support both half-duplex and full-duplex
    modes in point-to-point and multipoint
    configurations
  • HDLC can be characterized by their station types,
    their their configurations, and their response
    modes

30
Bit-Oriented protocol(contd)
  • Station Types
  • primary send commands
  • secondary send response
  • combined send command and response

31
Bit-Oriented protocol(contd)
  • Configuration
  • refers to the relationship of hardware devices
    on a link

32
Bit-Oriented protocol(contd)
33
Bit-Oriented protocol(contd)
34
Bit-Oriented protocol(contd)
  • Mode of communication
  • describes who controls the link
  • NRM(Normal Response Mode)
  • ARM(Asynchronous Response Mode)
  • ABM(Asynchronous Balanced Mode)

35
Bit-Oriented protocol(contd)
  • NRM(Normal Response Mode)
  • refers to the standard primary-secondary
    relationship
  • secondary device must have permission from the
    primary device before transmitting

36
Bit-Oriented protocol(contd)
  • ARM(Asynchronous Response Mode)
  • secondary may initiate a transmission without
    permission from the primary whenever the channel
    is idle
  • do not alter the primary-secondary relationship
    in any other way

37
Bit-Oriented protocol(contd)
  • ABM(Asynchronous Balanced Mode)
  • all stations are equal and therefore only
    combined stations connected in point-to-point are
    used
  • Either combined station many initiate
    transmission with the other combined station
    without permission

38
Bit-Oriented protocol(contd)
  • HDLC modes

39
Bit-Oriented protocol(contd)
  • Frame
  • I( Information ) Frame
  • used to transport user data and control
    information relating to user data
  • S( Supervisory ) Frame
  • used to only to transport control information,
    primarily data link layer flow and error
    controls
  • U( Unnumbered) Frame
  • are reserved for system management

40
Bit-Oriented protocol(contd)
  • HDLC Frame types

41
Bit-Oriented protocol(contd)
  • Frame
  • many contain up to six field
  • beginning flag
  • address
  • control
  • information
  • FCS(Frame Check Sequence)

42
Bit-Oriented protocol(contd)
  • Flag Field
  • serve as a synchronization pattern for the
    receiver

43
Bit-Oriented protocol(contd)
  • Bit stuffing
  • is the process of adding one extra 0 whenever
    there are five consecutive 1s in the data so that
    the receiver does not mistake the data for flag

44
Bit-Oriented protocol(contd)
  • Bit Stuffing in HDLC

45
Bit-Oriented protocol(contd)
  • Address Field
  • contain the address of the secondary station
    that is either the originator or destination of
    the frame

46
Bit-Oriented protocol(contd)
  • Control field

47
Bit-Oriented protocol(contd)
  • Poll/Final field in HDLC

48
Bit-Oriented protocol(contd)
  • Information field

49
Bit-Oriented protocol(contd)
  • Pissybacking
  • means combining data to be sent and
    acknowledgment of the frame received in one
    single frame

50
Bit-Oriented protocol(contd)
  • FCS field

51
Bit-Oriented protocol(contd)
  • More about Frames
  • s-frame
  • are used for acknowledgment, flow control, and
    error control

52
Bit-Oriented protocol(contd)
  • RR(Receive Ready)
  • ACK
  • Poll
  • Negative response to poll
  • Positive response to select

53
Bit-Oriented protocol(contd)
  • RNR(Receive Net Ready)
  • ACK
  • Select
  • Negative response to select
  • REJ(Reject)
  • SREJ(Selective-reject)

54
Bit-Oriented protocol(contd)
  • Use of P/F bit in polling and selection

55
Bit-Oriented protocol(contd)
  • U-Frame
  • are used to exchange session management and
    control information between connected devices

56
Bit-Oriented protocol(contd)
57
Bit-Oriented protocol(contd)
  • U-Frame control command and response

Command/ response
Meaning
SNRM SNRME SARM SARME SABM SABME UP UI UA RD DISC
DM RIM SIM RSET XID FRMR
Set normal response mode Set normal response
mode(extended) Set asynchronous response mode Set
asynchronous response mode(extended) Set
asynchronous balanced mode Set asynchronous
balanced mode(extended) Unnumbered
poll Unnumbered information Unnumbered
acknowledgement Request disconnect Disconnect Disc
onnect mode Request information mode Set
initialization mode Reset Exchange ID Frame reject
58
Bit-Oriented protocol(contd)
  • U-Frame
  • can be divided into five basic functional
    category
  • Mode setting
  • Unnumbered-Exchange
  • Disconnection
  • Initialization Mode
  • Miscellaneous

59
Bit-Oriented protocol(contd)
  • Mode Setting Command
  • are sent by the primary station, or by a
    combined station wishing to control an exchange,
    to establish the mode of the session(table 11.2)
  • Unumbered-Exchange
  • are used to send or solicit specific pieces of
    data link information between device(table 11.2)
  • Disconnection
  • Initialization Mode
  • Miscellaneous

60
Bit-Oriented protocol(contd)
  • Example 1 Poll/Response

61
Bit-Oriented protocol(contd)
  • Example 2 Select/Response

62
Bit-Oriented protocol(contd)
  • Example 3 Peer Devices(1)

63
Bit-Oriented protocol(contd)
  • Example 3 Peer Devices(2)

64
Bit-Oriented protocol(contd)
  • LAP(Link Access Procedure)
  • LAPB(Link Access Procedure Balanced)
  • provide those basic control function required
    for communication between a DTE and a DLE
  • used only in balanced configuration of two
    device
  • is used in ISDN on B channel
  • LAPD(Link Access Procedure for D channel)
  • used in ISDN
  • use ABM(Asynchronous Balanced Mode)
  • LAPM(Link Access Procedure for Modem)
  • is designed to do asynchronous-synchronous
    conversation, error detection, and retransmission
  • has become developed to apply HDLC feature to
    modems

65
11.5 ??
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