Transcript Chapter 4 Standards Organization and OSI Model 7 Physical Layer

Chapter 4
Standards Organization and OSI Model
Introduction
 Some of the standards organization
which develop standards for networks
and data communication are: IEEE,
ITU, EIA, ANSI, ISO and IETF.
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Chapter 4
Standards Organization and OSI Model
4.1 Communication Protocols
 a set of rules used by two computers in
order to communication with each
other
 Computers must follow certain rules in
order to able to communication each
other .
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4.1 Communication Protocols
The rules of a protocol
 Size of information
 How to represent information
 Error detection
 Receipt or non-receipt of information .
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4.1 Communication Protocols
Common network protocols
 TCP/IP：Internet
 IPX/SPX：Novell Netware
 NetBEUI：for small LAN
 NWlink: Microsoft version of
IPX/SPX.
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Chapter 4
Standards Organization and OSI Model
4.2 Open System
Interconnection Model
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Chapter 4
Standards Organization and OSI Model
4.2 Open System
Interconnection Model
 Developed by ISO
 Divides network communication into
seven layers
 Any device which meets the OSI
standards can be easily connected to
any other device that adheres to the
OSI model.
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4.2 Open System Interconnection Model
Physical Layer
 Define type of electrical signal, type of
connectors, cable type
 Coverts electrical signals to bits and
vise versa
 Transmits and receives electrical
signals.
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4.2 Open System Interconnection Model
Data Link Layer
 Define the frame format, Manages
frame, error detection, retransmission
of message
 Define the type of transmission (4.3).
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Data Link Layer
Function of data link layer
 Accept information from the Network
layer and break it into frames
 Accept the bits from the Physical layer
and forms them into a frame
 error detection, error control, and flow
control (4.4).
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Data Link Layer
Protocols for Data Link layer
 SDLC (SNA)
 HDLC (OSI)
 LAPB (ITU).
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Data Link Layer
HDLC
HDLC Frame Format
Flag Address Control Information FCS
Flag
Address field：give the address of destination
Control field：determine the type of
information in the information field, such as
Information Frame, Supervisory Frame, and
Unnumbered Frame (Fig 4.4)
4.2 Open System Interconnection Model
Network Layer
 Setup up connection, disconnect
connection
 deliver information from source to the
destination and route the information
 translate each logical address to a
physical address (MAC address) .
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Network Layer
Routing
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Network Layer
Two types of services
 connection-oriented service: make a
connection between source and
destination, then transmission start
 TCP, TELNET, SMTP, FTP, HTTP
 connectionless service: the source
transmits information regardless of
whether the destination ready or not
 IP, UDP, E-mail.
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4.2 Open System Interconnection Model
Transport Layer
 Provide reliable transmission of data
 Manage error control and flow control
 Assure quality of service
 The most important layer .
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4.2 Open System Interconnection Model
Session Layer
 Establish a logical connection between
the applications of two computers.
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4.2 Open System Interconnection Model
Presentation Layer
 Receive information then convert it to
ASCII or Unicode, encrypt or decrypt
data, compress data.
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4.2 Open System Interconnection Model
Application Layer
 Performs information processing such
as file transfer, e-mail, and Telnet.
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4.3 Frame Transmission Methods
 The Data Link layer offers two types of
transmission:
 Asynchronous : Character-oriented
 Synchronous: Character-oriented and
Bit-oriented .
4.3 Frame Transmission Methods
Asynchronous
 Character oriented: each character is
transmitted separately, each character
has start, stop, and parity bits
 Inefficient for transferring a large
volume of information.
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4.3 Frame Transmission Methods
Character-oriented
Synchronization
 Frame format:
SYN
SYN
STX
Information
ETX
SYN
SYN
DLE STX
STX ETX
DLE ETX
SYN
SYN
DLE STX
DLE DLE
DLE ETX
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4.3 Frame Transmission Methods
Bit-oriented Synchronization
 More efficient
Start Flag
Information Field
End Flag
01111110
110011001010110
01111110
01111110
111101111110111
01111110
01111110
1111011111010111
01111110
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Standards Organization and OSI Model 23
4.4 Error and Flow Control
 During the transmission, the frame
may get corrupted or lost
 Data Link layer of the destination
check for error in the frame and
inform the source, then the source
retransmit the frame
 One of the methods used is ARQ (stopand-wait ARQ and continuous ARQ) .
4.4 Error and Flow Control
Stop-and-Wait ARQ
 The source transmits a frame and waits
for a specific time for ACK from the
destination
 If the source does not receive ACK
during this time, the source retransmits
the frame
 Used for a network with half-duplex
connection.
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Stop-and-Wait ARQ
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If No Error
Destination: ACK
Source: transmit next frame
If Error
Destination: NACK
Source: retransmit the frame
Stop-and-Wait ARQ
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Source: not receive any ACK during a
period of time, then retransmit the frame.
4.4 Error and Flow Control
Continuous ARQ
 Source continues to transmit frames,
and the destination sends ACK or
NACK on different channels
 Used in packet-switching network with
the full-duplex connection
 Go-Back-N ARQ and Selective Reject
ARQ.
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Continuous ARQ
Go-Back-N ARQ
The source transmitted frame I5 and
received NACK from I3, the source will
retransmit frames I3,I4,and I5
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Continuous ARQ
Go-Back-N ARQ
The source should hold a copy of those
frames not receiving ACK
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Continuous ARQ
Go-Back-N ARQ
When the source receives ACK for a
frame, it can remove the frame from the
buffer
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Continuous ARQ
Selective Reject ARQ
Source will retransmit only those
frames for which the destination has
sent a NACK
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Continuous ARQ
Selective Reject ARQ
The destination should have the
capability to recoder frames which are
out of order
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4.4 Error and Flow Control
Sliding Window Method
 Continuous ARQ: no enough memory,
transmit frames fast ...
 Solution：limit number of frames
 the simplest way is “stop - and - go”
 The Sliding Window Method limits the
number of frames waiting for ACK in
the source.
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Sliding Window Method
A source with a window of four frames
means the source will stop transmitting
after four unacknowledged frames .
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Sliding Window Method
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When the source receives acknowledgment
for a frame, it removes the frame from its
buffer and transmits the next frame.
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4.5 IEEE 802 Standard
 The standard for the Physical layer
and Data Link layer by IEEE
 IEEE 802 divides the Data Link layer
into two sublayers: LLC and MAC.
4.5 IEEE 802 Standard
Media Access Control
 Defines the method that stations use to
access the network, such as:
 CSMA/CD
 Control Token.
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4.5 IEEE 802 Standard
Logical Link Control
 Defines the format of the frame (Fig
4.17) : DSAP, SSAP, Control Field
 Independent of network topology,
transmission media, and media access
control.
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4.5 IEEE 802 Standard
 802.2 LLC
 802.3 Ethernet
 802.4 Token Bus
 802.5 Token Ring
 802.8 FDDI
 802.9 ISDN
 802.11 Wireless Networks
 802.12 100VG-AnyLAN
 802.14 Cable Modem.
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Standards Organization and OSI Model 40
Short answer questions
 4 and explain their function
 39