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Chapter 2 Network Models
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
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22--1 LAYERED TASKS1 LAYERED TASKS
A network model is a layered architecture Task broken into subtasks
Implemented separately in layers in stack
Functions need in both systems
Peer layers communicate
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
Protoco : A set of rules that governs data communication
It represents an agreement between the communicatingdevices
Sender, Receiver, and Carrier
Hierarchy (services)
Topics discussed in this section:Topics discussed in this section:
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22--2 THE OSI MODEL2 THE OSI MODEL
Established Established inin 1947 1947, , the the International International StandardsStandards
OrganizationOrganization ( ( ISO ISO ) ) isis a a multinational multinational body body dedicated dedicated to to worldwideworldwide agreement agreement on on international international
standards standards. .
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
An An ISO ISO isis the the OpenOpen SystemsSystems Interconnection Interconnection ( ( OSI OSI ) )
model model isis the the standard standard that that covers covers all all aspects aspects of of
network network communications communications from from ISO ISO. . It It waswas first firstintroduced introduced inin the the latelate 19701970s s. .
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ISO is the organization.
OSI is the model.
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
Layered Architecture
Peer-to-Peer Processes
Encapsulation
op cs scusse n s sec on: op cs scusse n s sec on:
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Layered Architecture
Layers
Layer 7. Application
Layer 6. Presentation
Layer 5. Session
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
Layer 4. Transport
Layer 3. Network
Layer 2. Data Link
Layer 1. Physical
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Layered Architecture
A layered model
Each layer performs a subset of the required
communication functions Each layer relies on the next lower layer to perform
more primitive functions
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
Each layer provides services to the next higher layer Changes in one layer should not require changes in
other layers
The processes on each machine at a given layer are
called peer-to-peer process
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Communication must move downward through the layers on
the sending device, over the communication channel, and
upward to the receiving device Each layer in the sending device adds its own information to
the message it receives from the layer just above it and passes
PEER – TO – PEER PROCESS
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
e w o e pac age o e ayer us e ow At the receiving device, the message is unwrapped layer by
layer, with each process receiving and removing the data
meant for it
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PEER – TO – PEER PROCESS
The passing of the data and network information down through
the layers of the sending device and backup through the layers
of the receiving device is made possible by interface betweeneach pair of adjacent layers
Interface defines what information and services a layer must
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
prov e or e ayer a ove .
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22--3 LAYERS IN THE OSI MODEL3 LAYERS IN THE OSI MODEL
1. Physical Layer
2. Data Link Layer
3. Network Layer
Topics discussed in this section:Topics discussed in this section:
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
4. Transport Layer
5. Session Layer
6. Presentation Layer
7. Application Layer
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The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
Function
Physical characteristics of interfaces and media
1. Physical Layer
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
Representat on o ts Data rate
Synchronization of bits
Line configuration (point-to-point or multipoint) Physical topology (mesh, star, ring or bus)
Transmission mode ( simplex, half-duplex or duplex)
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The data link layer is responsible for moving
frames from one hop (node) to the next.
Function
Framing
2. Data Link Layer
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Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
Physical addressing Flow control
Error control
Access control
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Example 1 Example 1
In following figure a node with physical address 10 sends a frame to a node
with physical address 87. The two nodes are connected within the same
network. At the data link level this frame contains physical addresses in the
header. These are the only addresses needed. The rest of the header contains
other information needed at this level at the receiver side. The trailer usually
contains extra bits needed for error detection
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Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
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The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
Source-to-destination delivery
3. Network Layer
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Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
espons e rom e e very o pac e s rom e or g na
source to the final destination
Functions
Logical addressing
routing
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Example 2 Example 2
We want to send data from a node
with network address A and
physical address 10, located on
one LAN, to a node with a
network address P and physical
address 95, located on another
LAN. Because the two devices are
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
,
cannot use physical addressesonly; the physical addresses only
have local influence. What we
need here are universal addresses
that can pass through the LANboundaries. The network
addresses have this characteristic.
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The transport layer is responsible for the delivery
of a message from one process to another.
Process-to- process delivery
Functions
4. Transport Layer
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Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
Port addressing
Segmentation and reassembly
Connection control ( Connection-oriented or connection-less)
Flow control
Error control
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Example 3 Example 3
Following Figure shows an example of transport layer communication. Data coming
from the upper layers have port addresses j and k (j is the address of the sending
process, and k is the address of the receiving process). Since the data size is larger
than the network layer can handle, the data are split into two packets, each packet
retaining the port addresses (j and k). Then in the network layer, network addresses(A and P) are added to each packet.
Source A Destination P
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Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
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The session layer is responsible for dialogcontrol and synchronization.
5. Session Layer
It establishes, maintains and synchronize the
interaction between communicating system
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
unc on
Dialog control
Synchronization (checkpoints)
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The presentation layer is responsible for translation,
compression, and encryption.
6. Presentation Layer
Concerned with the syntax and semantics of the
information exchanged between two system
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
Functions
Translation ( EBCDIC-coded text fileASCII-coded file)
Encryption and Decryption
Compression
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The application layer is responsible for
providing services to the user.
Functions
Network virtual terminal (Remote log-in)
7. Application Layer
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
e rans er an access
Mail services
Directory services (Distributed Database)
Accessing the World Wide Web
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Figure 2.15 Summary of layers
OSI Model
Data unit Layer Function
User
support
layers
Data
7. Application Network process to application
6. Presentation Data representation and encryption
-
Based on
Data Communications and Networking, 4th Edition. by Behrouz A. Forouzan, McGraw-Hill Companies, Inc., 2007 Dr. Mznah Al-Rodhaan
.
UserNetwork
Segment 4. Transport End-to-end connections and reliability
Network
supportlayers
Packet 3. Network Path determination and logical
addressing
Frame 2. Data Link Physical addressing
Bit 1. Physical Media, signal and binary transmission
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