Network Models
2.1 what is the Protocol?
• A protocol defines the rules that both the
sender and receiver and all intermediate
devices need to follow, to be able to
communicate effectively.
• In the network telecommunication, we need
to divide the communication task between
different layers, in which case we need a
protocol or more at each layer.
Figure 2.16 Layers and protocols in the reference protocol model
2.3
Communication through an internet
Communication through an internet ()
Data units of each layer
messages
Segments or datagrams
packets
frames
bits
Figure 2.5 Physical layer
The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
2.7
Figure 2.6 Data link layer
The data link layer is responsible for moving
frames from one hop (node) to the next.
2.8
Figure 2.7 Hop-to-hop delivery
2.9
Figure 2.8 Network layer
The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
2.10
Figure 2.9 Source-to-destination delivery
2.11
Figure 2.10 Transport layer
The transport layer is responsible for the delivery
of a message from one process to another.
2.12
Figure 2.11 Reliable process-to-process delivery of a message
2.13
Figure 2.14 Application layer
2.14
The application layer is responsible for
1- providing services to the user.
2- dialog control and synchronization.
3- translation, compression, and encryption.
2.15
Figure 2.17 Addresses in TCP/IP
2.16
Figure 2.18 Relationship of layers and addresses in TCP/IP
2.17
Figure 2.19 Physical addresses
2.18
Figure 2.20 IP addresses
2.19
Figure 2.21 Port addresses
2.20
THE DATA LINK LAYER
3.1 DATA LINK LAYER functions
1. Providing a well-defined service interface to
the network layer.
2. Error control
3. Flow control: Regulating the flow of data so
that slow receivers are not swamped by fast
senders.
4. Framing: breaking up the bit stream into
discrete frames
Packets and Frames
Relationship between packets and frames.
3.1.2 Framing
• A good design of framing must make it easy
for a receiver to find the start of new frames
while using little of the channel bandwidth.
We will look at three methods:
– 1. Byte count.
– 2. Flag bytes with byte stuffing.
– 3. Flag bytes with bit stuffing.
2. Flag bytes with byte stuffing.
3. Flag bytes with bit stuffing.