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
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