Data Comm. & Networks

Data Comm. & Networks

Instructor: Ibrahim Tariq

Lecture 3


2.
2

Figure 2.2
Seven layers of the OSI model

3

Physical layer

Transporting bits from one end node to the next

-

type of the transmission media
(twisted
-
pair, coax, optical fiber, air)

-

bit representation
(voltage levels of logical values)

-

data rate
(speed)

-

synchronization of bits
(time synchronization)

physical

connection

4

The physical layer is responsible for movements of

individual bits from one hop (node) to the next.

Note

5

Data Link layer

Transporting frames from one end node to the next one

logical

connection


-

framing
-

physical addressing


-

flow control
-

error control

-

access control

6

Data Link layer

-

hop
-
to
-
hop delivery
-

7

The data link layer is responsible for moving

frames from one hop (node) to the next.

Note

8

Network layer


End
-
to
-
End
packet
delivery


From the original source to a destination


Needed when 2 devices are attached to
different networks


What is the network definition here?


Main duties:

1.
Logical addressing

2.
Routing

3.
Congestion control and QoS

Not a message

2.
9

Figure 2.8
Network layer

10

Source to destination delivery

Data Link

Network layer

11

Network layer

-

example
-

Network layer addresses

Data Link layer addresses

12

The network layer is responsible for the

delivery of individual packets from

the source host to the destination host.

Note

13

Transport layer

•
Process
-
to
-
Process

delivery of the entire
message

–
From the original source to a destination


•
Needed when several processes (running programs)
active at the same time


•
Main tasks:

–
Port addressing

–
Segmentation and reassembly

–
Congestion control

–
Flow control

–
Error control


2.
14

Figure 2.10
Transport layer

2.
15

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

16

The transport layer is responsible for the delivery

of a message from one process to another.

Note

2.
17

Figure 2.12
Session layer

18

The session layer is responsible for dialog

control and synchronization.

Note

2.
19

Figure 2.13
Presentation layer

20

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

Note

2.
21

Figure 2.14
Application layer

22

Application layer

•
Enables user to access the network

•
Provides services to a user

–
E
-
mail

–
Remote file access and transfer (Telnet, FTP)

–
Access to WWW (HTTP)


23

The application layer is responsible for

providing services to the user.

Note

24

OSI Reference Model

•
A convenient aid for remembering the OSI
layer names is to use the first letter of each
word in the phrase:

•
A
ll
P
eople
S
eem
T
o
N
eed
D
ata
P
rocessing

2.
25

Figure 2.15
Summary of layers