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Chapter 11 Data Link Control

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Chapter 11 Data Link Control Framing Flow and Error Control Protocols Noiseless Channels Noisy Channels HDLC Point-to-Point Protocol – PowerPoint PPT presentation

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Date added: 18 July 2019
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Title: Chapter 11 Data Link Control


1
Chapter 11 Data Link Control
  1. Framing
  2. Flow and Error Control
  3. Protocols
  4. Noiseless Channels
  5. Noisy Channels
  6. HDLC
  7. Point-to-Point Protocol

2
Framing
  • Data link layer needs to pack bits into frames,
    so that each frame is distinguishable from
    another
  • Separate a message from one source to a
    destination, or from other messages to other
    destinations, by adding a sender address and a
    destination address
  • Fixed-size framing ATM (Chapter 18)
  • Variable-size framing
  • Need a way to define the end of the frame and the
    beginning of the next
  • Character-oriented approach and bit-oriented
    approach

3
Character-Oriented Protocols
  • Frame structure
  • Byte stuffing process of adding 1 extra byte
    whenever there is a flag or escape character in
    the text

4
Bit-Oriented Protocols
  • Frame structure
  • Bit stuffing process of adding one extra 0
    whenever five consecutive 1s follow a 0 in the
    data

5
Flow and Error Control
  • Data link control flow control error control
  • Flow control refers to a set of procedures used
    to restrict the amount of data that the sender
    can send before waiting for acknowledgement
  • Error control in the data link layer is based on
    automatic repeat request (ARQ), which is the
    retransmission of data
  • ACK, NAK(Negative ACK), Piggybacking (ACKs and
    NAKs in data frames)

6
Noiseless Channels Simplest Protocol
  • Simplest protocol with no flow or error control

7
Simplest Protocol
  • Sender-site algorithm
  • Receiver-site algorithm

8
Stop-and-Wait Protocol
  • Simple tokens of ACK and flow control added

9
Stop-and-Wait Protocol
  • Sender-site algorithm
  • Receiver-site algorithm

10
Stop-and-Wait Protocol Example
11
Noisy Channels Stop-and-Wait ARQ
  • Stop-and-wait Automatic Repeat Request (ARQ)
  • Error correction in Stop-and-Wait ARQ is done by
    keeping a copy of the sent frame and
    retransmitting of the frame when the timer
    expires
  • In Stop-and-Wait ARQ, we use sequence numbers to
    number the frames. The sequence numbers are based
    on modulo-2 arithmetic
  • Acknowledgment number always announces in
    modulo-2 arithmetic the sequence number of the
    next frame expected.

12
Stop-and-Wait ARQ
13
Stop-and-Wait ARQ
  • Sender-site algorithm

14
Stop-and-Wait ARQ
  • Receiver-site algorithm

15
Stop-and-Wait ARQ Example
16
Go-Back-N ARQ
  • Pipelining improves the efficiency of the
    transmission
  • In the Go-Back-N Protocol, the sequence numbers
    are modulo 2m, where m is the size of the
    sequence number field in bits
  • The send window is an abstract concept defining
    an imaginary box of size 2m - 1 with three
    variables Sf, Sn, and Ssize
  • The send window can slide one or more slots when
    a valid acknowledgment arrives.

17
Go-Back-N ARQ
  • Receive window for Go-Back-N ARQ
  • The receive window is an abstract concept
    defining an imaginary box of size 1 with one
    single variable Rn. The window slides when a
    correct frame has arrived sliding occurs one
    slot at a time.

18
Go-Back-N ARQ
  • Sliding windows, Timers, ACK, Resending a frame

19
Go-Back-N ARQ Send Window Size
  • In Go-Back-N ARQ, the size of the send window
    must be less than 2m the size of the receiver
    window is always 1
  • Stop-and-Wait ARQ is a special case of Go-Back-N
    ARQ in which the size of the send window is 1

20
Go-Back-N ARQ Sender Algorithm
21
Go-Back-N ARQ Receiver Algorithm
22
Go-Back-N ARQ Example 1
23
Go-Back-N ARQ Example 2
24
Selective Repeat ARQ
  • Sender window size
  • Receive window size

25
Selective Repeat ARQ
26
Selective Repeat ARQ Window Size
  • The size of the sender and receiver window must
    be at most one-half of 2m

27
Selective Repeat ARQ Sender-Site Algorithm
28
Selective Repeat ARQ Receiver-Site Algorithm
29
Selective Repeat ARQ Example
30
Piggybacking
  • To improve the efficiency of the bidirectional
    protocols
  • Piggybacking in Go-Back-N ARQ

31
HDLC
  • High-level Data Link Control
  • Two common transfer mode normal response mode
    (NRM) and asynchronous balanced mode (ABM)

32
HDLC Frames
  • I(information)-frames, S(supervisory)-frames,
    U(unnumbered frame)-frames
  • Flag field 01111110 to identify both the
    beginning and the end of a frame and serve as
    synchronization pattern for receiver
  • FCS field 2- or 4-byte ITU-T CRC for error
    detection

33
HDLC Frames
  • Control Field 1- or 2-byte segment of the frame
    used for flow and error control
  • Determine the type of frame and define its
    functionality
  • Control field for I-frame P/F (poll/final bit
    for primary/secondary)

34
HDLC Frames
  • Control field for S-frame
  • Receive ready (RR), Receive not ready (RNR),
    Reject (REJ) Selective reject (SREJ)

35
HDLC Frames
  • Control field for U-frame

36
HDLC Example 1
  • Connection and disconnection

37
HDLC Example 2
  • Piggybacking without error

38
HDLC Example 3
  • Piggybacking with error

39
HDLC Bit Stuffing and Unstuffing
40
Point-to-Point Protocol PPP
  • One of the most common protocols for
    point-to-point access
  • Many Internet users who need to connect their
    home computer to the server of an Internet
    service provider use PPP
  • A point-to-point link protocol is required to
    control and manage the transfer of data
  • PPP defines/provides
  • the format of the frame to be exchanged between
    devices
  • how two devices negotiate the establishment of
    the link and the exchange of data
  • how network layer data are encapsulated in the
    data link frame
  • how two devices can authenticate each other
  • multiple network layer services
  • connection over multiple links
  • Network address configuration
  • But, several services are missing for simplicity
  • no flow control, simple error control (detection
    and discard), no sophisticate addressing for
    multipoint configuration

41
PPP Frame
  • Flag 01111110 the same as HDLC, but it treated
    as a byte because of PPP is a byte-oriented
    protocol
  • Address 11111111 (broadcast address)
  • Control No need because PPP has no flow control
    and limited error control
  • PPP is a byte-oriented protocol using byte
    stuffing with the escape byte 01111101

42
PPP Transition States
43
PPP Multiplexing
  • PPP uses another set of other protocols to
    establish the link, authenticate the parties, and
    carry the network layer data
  • Three sets of protocols defined for powerful PPP
    LCP, two APs, several NCPs

44
LCP Encapsulated in a Frame
45
LCP Common Options
  • Options are inserted in the information field of
    the configuration packets

46
Authentication
  • Authentication means validating the identity of a
    user who needs to access
  • PPP is designed for use over dial-up links
  • ? User authentication is necessary
  • PPP has two protocols for authentication
  • Password Authentication Protocol (PAP)
  • Challenge Handshake Authentication Protocol (CHAP)

47
Password Authentication Protocol (PAP)
48
Challenge Handshake Authentication Protocol (CHAP)
  • Three-way hand-shaking authentication protocol
    with greater security than PAP

49
Network Control Protocol NCP
  • PPP is a multiple-network layer protocol.
  • It can carry a network data packet from protocols
    defined by the Internet, OSI, Xerox, DECnet,
    AppleTalk, Novel
  • IPCP (IP Control Protocol)
  • Configures the link used to carry IP packets in
    the Internet

50
IPCP Packet
IP Datagram in a PPP frame
51
Multiple PPP
52
Example (1)
53
Example (2)
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