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Transcript
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.
1
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 .
2
4.1 Communication Protocols
The rules of a protocol
 Size of information
 How to represent information
 Error detection
 Receipt or non-receipt of information .
3
4.1 Communication Protocols
Common network protocols
 TCP/IP:Internet
 IPX/SPX:Novell Netware
 NetBEUI:for small LAN
 NWlink: Microsoft version of
IPX/SPX.
4
Chapter 4
Standards Organization and OSI Model
4.2 Open System
Interconnection Model
5
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.
6
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.
7
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).
8
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).
9
Data Link Layer
Protocols for Data Link layer
 SDLC (SNA)
 HDLC (OSI)
 LAPB (ITU).
10
11
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) .
12
Network Layer
Routing
13
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.
14
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 .
15
4.2 Open System Interconnection Model
Session Layer
 Establish a logical connection between
the applications of two computers.
16
4.2 Open System Interconnection Model
Presentation Layer
 Receive information then convert it to
ASCII or Unicode, encrypt or decrypt
data, compress data.
17
4.2 Open System Interconnection Model
Application Layer
 Performs information processing such
as file transfer, e-mail, and Telnet.
18
Chapter 4
Standards Organization and OSI Model 19
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.
20
21
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
22
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
Chapter 4
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.
24
Stop-and-Wait ARQ
25
If No Error
Destination: ACK
Source: transmit next frame
If Error
Destination: NACK
Source: retransmit the frame
Stop-and-Wait ARQ
26
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.
27
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
28
Continuous ARQ
Go-Back-N ARQ
The source should hold a copy of those
frames not receiving ACK
29
Continuous ARQ
Go-Back-N ARQ
When the source receives ACK for a
frame, it can remove the frame from the
buffer
30
Continuous ARQ
Selective Reject ARQ
Source will retransmit only those
frames for which the destination has
sent a NACK
31
Continuous ARQ
Selective Reject ARQ
The destination should have the
capability to recoder frames which are
out of order
32
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.
33
Sliding Window Method
A source with a window of four frames
means the source will stop transmitting
after four unacknowledged frames .
34
Sliding Window Method
35
When the source receives acknowledgment
for a frame, it removes the frame from its
buffer and transmits the next frame.
Chapter 4
Standards Organization and OSI Model 36
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.
37
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.
38
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.
39
Chapter 4
Standards Organization and OSI Model 40
Short answer questions
 4 and explain their function
 39