Module 1 - ISO OSI Model-TCP IP Model (1).ppt

2.1
Lecture 4 – ISO OSI Model
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2.2
2-1 LAYERED TASKS
2-1 LAYERED TASKS
We use the concept of
We use the concept of layers
layers in our daily life. As an
in our daily life. As an
example, let us consider two friends who communicate
example, let us consider two friends who communicate
through postal mail. The process of sending a letter to a
through postal mail. The process of sending a letter to a
friend would be complex if there were no services
friend would be complex if there were no services
available from the post office.
available from the post office.
Sender, Receiver, and Carrier
Hierarchy
Topics discussed in this section:

2.3
Figure 2.1 Tasks involved in sending a letter

 Each layer at the sending site uses the
services of the layer immediately below it.
 The sender at the higher layer uses the
services of the middle layer.
 The middle layer uses the services of the
lower layer.
 The lower layer uses the services of the
carrier.
2.4

2.5
2-2 THE OSI MODEL
2-2 THE OSI MODEL
Established in 1947, the International Standards
Established in 1947, the International Standards
Organization (
Organization (ISO
ISO) is a multinational body dedicated to
) is a multinational body dedicated to
worldwide agreement on international standards. An ISO
worldwide agreement on international standards. An ISO
standard that covers all aspects of network
standard that covers all aspects of network
communications is the Open Systems Interconnection
communications is the Open Systems Interconnection
(
(OSI
OSI) model. It was first introduced in the late 1970s.
) model. It was first introduced in the late 1970s.
Layered Architecture
Peer-to-Peer Processes
Encapsulation

2.6
ISO is the organization.
OSI is the model.
Note

 An open system is a set of protocols
 allows any two different systems to communicate
regardless of their underlying architecture.
 How to facilitate communication between different
systems without requiring changes to the logic of the
underlying hardware and software?
 Flexible, robust, and interoperable model.
 Layered framework for the design of network systems that
allows communication between all types of computer
systems.
2.7
2-2 THE OSI MODEL
2-2 THE OSI MODEL

2.8
Figure 2.2 Seven layers of the OSI model

OSI Layered Architecture
 Each layer - family of functions distinct from those of the other
layers.
 Comprehensive and flexible Architecture.
 Allows complete interoperability between incompatible systems.
 Within a single machine, each layer calls upon the services of the
layer just below it.
 Peer-to-peer processes
 Each interface defines the information and services a layer must
provide for the layer above it.
 Well-defined interfaces and layer functions

provide modularity to a network.
 Specific implementation of its functions can be modified or replaced

without requiring changes to the surrounding layers.
2.9

2.10
Figure 2.3 The interaction between layers in the OSI model

2.12
Figure 2.4 An exchange using the OSI model (ENCAPSULATION)
User Support Layers
Network Support
Layers

2.13
2-3 LAYERS IN THE OSI MODEL
2-3 LAYERS IN THE OSI MODEL
In this section we briefly describe the functions of each
In this section we briefly describe the functions of each
layer in the OSI model.
layer in the OSI model.
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer

2.14
The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
Note

2.15
Figure 2.5 Physical layer

Physical Layer

Physical characteristics of interfaces and transmission medium.
 Representation of bits
 To be transmitted, bits must be encoded into signals- electrical or
optical.
 Data rate
 The transmission rate-the number of bits sent each second
 Synchronization of bits

sender and receiver (same bit rate) - clocks
 Line configuration

Connection of devices to the media (Point to Point, Multipoint)
 Physical topology

How devices are connected to make a network
 Transmission mode

Direction of transmission between two devices (Simplex, Half/Full
Duplex)
2.16
Coordinates the functions required to
carry a bit stream over a physical medium

2.17
The data link layer is responsible for moving
frames from one hop (node) to the next.
Note

2.18
Figure 2.6 Data link layer
Hop to Hop (Node to Node) delivery

Data-Link Layer
 Makes physical layer appear error-free to the upper layer

Reliable Link
 Framing
 divides the stream of bits received from the network layer into manageable data units
 Physical addressing
 adds a header to the frame to define the sender and/or receiver of the frame
 Flow control

Flow of data must not be allowed to overwhelm receiver ; rate of absorption by RX
less than rate at which data produced by TX
 Error control

adds reliability to the physical layer by adding mechanisms to detect and retransmit
damaged or lost frames

Trailer added to the end of the frame
 Access control
 Two or more devices are connected to the same link ?
2.19

2.20
Figure 2.7 Hop-to-hop delivery

2.21
Figure 2.8 Network layer
End-to-end delivery

2.22
The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
Note

Network Layer
 Source-to-destination delivery of a packet across
multiple networks (links).
 Logical addressing
 Routing
2.23

2.24
Figure 2.9 Source-to-destination delivery

2.25
The transport layer is responsible for the delivery
of a message from one process to another.
Note

Transport Layer
 Process-to-process delivery of the entire message
 Segmentation and Reassembly
 Gets the entire message to the correct process on that computer
 Ensures whole message arrives intact and in order
 Service-point Addressing (or Port address)
 Relationship between packets
 Error control and Flow control at the source-to-
destination level
 Entire message arrives at the receiving transport layer without
error (damage, loss, or duplication).

Error correction - retransmission
2.26

2.27
Figure 2.10 Transport layer

2.28
Figure 2.11 Reliable process-to-process delivery of a message

Session Layer
 Establishes, maintains, and synchronizes the
interaction among communicating systems.
 Dialog control
 Allows two systems (processes) to enter into a dialog.
 Allows communication – Half or Full-Duplex
 Synchronization
 Allows a process to add checkpoints or synchronization
points to data stream
 Acknowledge – retransmission – insert checkpoints
2.29

2.30
Figure 2.12 Session layer

2.31
The session layer is responsible for dialog
control and synchronization.
Note

Presentation Layer
 Syntax and Semantics of the information exchanged between
two systems.
 Translation
 Interoperability between these different encoding methods
 Sender-dependent format –> common format

Common format -> receiver-dependent format
 Encryption

Ensure privacy

Encrypt data for security purposes. For ex, password encryption.

Decryption – reverse process
 Compression
 Reduces the number of bits contained in the information

Transmission of multimedia such as text, audio, and video
2.32

2.33
Figure 2.13 Presentation layer

2.34
The presentation layer is responsible for translation,
compression, and encryption.
Note

Applications –
The Interface Between Human and Data Networks
 Explain that applications provide the means for generating
and receiving data that can be transported on the network

Applications –
 Explain the role of applications, services and protocols in
converting communication to data that can be transferred
across the data network

2.37
The application layer is responsible for
providing services to the user.
Note

Application Layer
 Enables the user, whether human or software, to
access the network.
 Provides user interfaces and support for services
 Electronic mail,
 Remote file access and transfer,
 Shared database management,
 Network virtual terminal
 Allows a user to log on to a remote host.
 Application creates a software emulation of a terminal
 File transfer, access, and management.
 Mail & Directory services
2.38

2.39
Figure 2.15 Summary of layers

Layers with TCP/IP and OSI Model

2.41
2-4 TCP/IP PROTOCOL SUITE
2-4 TCP/IP PROTOCOL SUITE
The layers in the
The layers in the TCP/IP protocol suite
TCP/IP protocol suite do not exactly
do not exactly
match those in the OSI model. The original TCP/IP
match those in the OSI model. The original TCP/IP
protocol suite was defined as having four layers:
protocol suite was defined as having four layers: host-to-
host-to-
network
network,
, internet
internet,
, transport
transport, and
, and application
application. However,
. However,
when TCP/IP is compared to OSI, we can say that the
when TCP/IP is compared to OSI, we can say that the
TCP/IP protocol suite is made of five layers:
TCP/IP protocol suite is made of five layers: physical
physical,
,
data link
data link,
, network
network,
, transport
transport, and
, and application
application.
.
Physical and Data Link Layers
Network Layer
Transport Layer
Application Layer

2.42
Figure 2.16 TCP/IP and OSI model

Applications –
 Define the separate roles applications, services and protocols
play in transporting data through networks

Applications –
 Describe the role protocols play in networking and be able to
identify several message properties that can be defined by a
protocol

The Role of Protocols in Supporting Communication
 Describe the roles of client and server processes in data
networks

 List common Application Layers services and protocols

 Compare and contrast client server networking with peer-to-
peer networking and peer-to-peer applications

Features, Operation, and Use of Application Layer
Services
 Describe the features of the DNS protocol and how this
protocol supports DNS services

Services
 Describe the features of the HTTP protocol and how this
protocol supports the delivery of web pages to the client

Services
 Describe the features of the Telnet protocol and identify
several of its uses in examining and managing networks

Internetworking Protocol (IP)
 Unreliable and connectionless protocol.
 Best Effort Delivery Service
 Transports data in packets – Datagrams
 No Reordering
 No Error Checking
 No tracking of routes
2.51

Internet Control Message Protocol
(ICMP)
 Network protocol useful in IP network management and
administration
 Control protocol
 Errors in the underlying communications of network applications
 Availability of Remote hosts, Network congestion
 Overall round-trip time of the probe messages (PING)
 Facilitate simultaneous transmission of a message to a group of
recipients.
2.52
Internet Group Message Protocol
(IGMP)

Address Resolution Protocol (ARP)
 Associate Logical address with Physical address
 To find the physical address of the node when its Internet
address is known
 Allows host to discover its Internet address when
physical address is only known.
 Used when computer is connected to network for first
time.
2.53
Reverse Address Resolution Protocol
(RARP)

Transport Layer
 User Datagram Protocol (UDP) vs Transmission Control
Protocol (TCP)
 Process-to-process protocol
 TCP
 Reliable stream transport protocol (connection-oriented)
 UDP
 Connection less protocol
 Packet delay is more serious than packet loss.
 Stream Control Transmission Protocol (SCTP)
 Voice over the Internet
 Combines the best features of UDP and TCP
2.54

2.55
2-5 ADDRESSING
2-5 ADDRESSING
Four levels of addresses are used in an internet employing
Four levels of addresses are used in an internet employing
the TCP/IP protocols:
the TCP/IP protocols: physical
physical,
, logical
logical,
, port
port, and
, and specific
specific.
.
Physical Addresses
Logical Addresses
Port Addresses
Specific Addresses

2.56
Figure 2.17 Addresses in TCP/IP

2.57
Figure 2.18 Relationship of layers and addresses in TCP/IP

2.58
In Figure 2.19 a node with physical address 10 sends a
frame to a node with physical address 87. The two nodes
are connected by a link (bus topology LAN). As the
figure shows, the computer with physical address 10 is
the sender, and the computer with physical address 87 is
the receiver.
Example 2.1

2.59
Figure 2.19 Physical addresses

2.60
As we will see in Chapter 13, most local-area networks
use a 48-bit (6-byte) physical address written as 12
hexadecimal digits; every byte (2 hexadecimal digits) is
separated by a colon, as shown below:
Example 2.2
07:01:02:01:2C:4B
A 6-byte (12 hexadecimal digits) physical address.

2.61
Figure 2.8: Encapsulation / Decapsulation

2.62
Figure 2.20 shows a part of an internet with two routers
connecting three LANs. Each device (computer or
router) has a pair of addresses (logical and physical) for
each connection. In this case, each computer is
connected to only one link and therefore has only one
pair of addresses. Each router, however, is connected to
three networks (only two are shown in the figure). So
each router has three pairs of addresses, one for each
connection.
Example 2.3

2.64
Figure 2.21 shows two computers communicating via the
Internet. The sending computer is running three
processes at this time with port addresses a, b, and c. The
receiving computer is running two processes at this time
with port addresses j and k. Process a in the sending
computer needs to communicate with process j in the
receiving computer. Note that although physical
addresses change from hop to hop, logical and port
addresses remain the same from the source to
destination.
Example 2.4

2.65
Figure 2.21 Port addresses

2.66
The physical addresses will change from hop to hop,
but the logical addresses usually remain the same.
Note

2.67
A port address is a 16-bit address represented by one
decimal number as shown.
753
A 16-bit port address represented
as one single number.

2.68
The physical addresses change from hop to hop,
but the logical and port addresses usually remain the same.
Note

2.69
Port
Number
Description
1
TCP Port Service Multiplexer
(TCPMUX)
5 Remote Job Entry (RJE)
7 ECHO
18 Message Send Protocol (MSP)
20 FTP -- Data
21 FTP -- Control
22 SSH Remote Login Protocol
23 Telnet
25
Simple Mail Transfer Protocol
(SMTP)
29 MSG ICP
37 Time
42 Host Name Server (Nameserv)
43 WhoIs
49 Login Host Protocol (Login)
53 Domain Name System (DNS)
69 Trivial File Transfer Protocol (TFTP)
70 Gopher Services
79 Finger
80 HTTP
103 X.400 Standard
108 SNA Gateway Access Server
109 POP2
110 POP3
115 Simple File Transfer Protocol (SFTP)
118 SQL Services
119 Newsgroup (NNTP)
137 NetBIOS Name Service
139 NetBIOS Datagram Service
143 Interim Mail Access Protocol (IMAP)
150 NetBIOS Session Service
156 SQL Server
161 SNMP
179 Border Gateway Protocol (BGP)
190 Gateway Access Control Protocol (GACP)
194 Internet Relay Chat (IRC)
197 Directory Location Service (DLS)
389
Lightweight Directory Access
Protocol (LDAP)
396 Novell Netware over IP
443 HTTPS
444 Simple Network Paging Protocol (SNPP)
445 Microsoft-DS
458 Apple QuickTime
546 DHCP Client
547 DHCP Server
563 SNEWS
569 MSN
1080 Sock

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