2. TCP/IP Protocol Suite2
Assume Maria and Ann are neighbors with a lot of common
ideas. However, Maria speaks only Spanish, and Ann speaks
only English. Since both have learned the sign language in their
childhood, they enjoy meeting in a cafe a couple of days per
week and exchange their ideas using signs. Occasionally, they
also use a bilingual dictionary. Communication is face to face
and Happens in one layer as shown in Figure .
Example
3. TCP/IP Protocol Suite3
Now assume that Ann has to move to another town because of her job.
Before she moves, the two meet for the last time in the same cafe. Although
both are sad, Maria surprises Ann when she opens a packet that contains
two small machines. The first machine can scan and transform a letter in
English to a secret code or vice versa. The other machine can scan and
translate a letter in Spanish to the same secret code or vice versa. Ann takes
the first machine; Maria keeps the second one. The two friends can still
communicate using the secret code.
Example
4. Layer Architecture
Layer architecture simplifies the network design.
It is easy to debug network applications in a layered
architecture network.
The network management is easier due to the layered
architecture.
Network layers follow a set of rules, called protocol.
The protocol defines the format of the data being
exchanged, and the control and timing for the handshake
between layers.
OSI Model
5. Open Systems Interconnection (OSI) Model
International standard organization (ISO) established a
committee in 1977 to develop an architecture for computer
communication.
Open Systems Interconnection (OSI) reference model is the
result of this effort.
In 1984, the Open Systems Interconnection (OSI) reference
model was approved as an international standard for
communications architecture.
Term “open” denotes the ability to connect any two
systems which conform to the reference model and
associated standards.
OSI Model
6. OSI Reference Model
The OSI model describes how information or data makes its
way from application programmes (such as spreadsheets)
through a network medium (such as wire) to another
application programme located on another network.
The OSI reference model divides the problem of moving
information between computers over a network medium
into SEVEN smaller and more manageable problems .
This separation into smaller more manageable functions is
known as layering.
OSI Model
8. OSI: A Layered Network Model
The process of breaking up the functions or tasks of networking
into layers reduces complexity.
Each layer provides a service to the layer above it in the protocol
specification.
Each layer communicates with the same layer’s software or
hardware on other computers.
The lower 3 layers (network, data link and physical —Layers 3, 2,
and 1) are concerned with the flow of data from end to end
through the network.
The upper four layers of the OSI model (application, presentation
and session—Layers 7, 6 and 5) are orientated more toward
services to the applications.
Data is Encapsulated with the necessary protocol information as it
moves down the layers before network transit.
OSI Model
11. The TCP/IP protocol
suite was developed
prior to the OSI
model.
Therefore, the layers
in the TCP/IP
protocol suite do not
match exactly with
those in the OSI
model.
• Troubleshooting, file
sharing, internet
Application
• Flow control, error
control
Transport
• IP addressing and
routing of network
traffic
Internet
• Interface with the
physical network
Network
Access
11TCP/IP Protocol Suite
TCP/IP Model
12. Comparison between OSI and TCP/IP
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Transport
Internet
Network
Access
OSI Model TCP/IP Model
14. TCP/IP Protocol Suite14
Figure 2.10 Communication at the physical layer
A
Physical
layer
Physical
layer
R1 R3 R4 B
Source DestinationLegend
011 ... 101
011...101
011 ... 101 011 ... 101
Link 3 Link 5 Link 6Link 1
15. Physical Layer
Provides physical interface for transmission of information.
Defines rules by which bits are passed from one system to
another on a physical communication medium.
Covers all - mechanical, electrical, functional and procedural
- aspects for physical communication.
Such characteristics as voltage levels, timing of voltage
changes, physical data rates, maximum transmission
distances, physical connectors, and other similar attributes
are defined by physical layer specifications.
OSI Model
17. TCP/IP Protocol Suite17
Figure 2.11 Communication at the data link layer
A
Physical Physical
Data linkData link
R1 R3 R4 B
Source Destination DataD HeaderHLegend
Link 1 Link 3 Link 5 Link 6
Frame
D2 H2
FrameD2
H2
Frame
D2 H2
Frame
D2 H2
18. TCP/IP Protocol Suite18
A node with physical address 10 sends a frame to a node with
physical address 87.
The two nodes are connected by a link (a LAN).
At the data link layer, this frame contains physical (link) addresses
in the header. These are the only addresses needed. The rest of
the header contains other information needed at this level.
The data link layer at the sender receives data from an upper
layer.
It encapsulates the data in a frame.
The frame is propagated through the LAN.
Each station with a physical address other than 87 drops the frame
because the destination address in the frame does not match its
own physical address.
The intended destination computer, however, finds a match
between the destination address in the frame and its own physical
address.
20. Data Link Layer
Data link layer attempts to provide reliable communication
over the physical layer interface.
Breaks the outgoing data into frames and reassemble the
received frames.
Handle errors by implementing an acknowledgement and
retransmission scheme.
Implement flow control.
Supports points-to-point as well as broadcast
communication
OSI Model
22. TCP/IP Protocol Suite22
Figure 2.12 Communication at the network layer
A
Physical Physical
Data linkData link
R1 R3 R4 B
NetworkNetwork
Source Destination DataD HeaderHLegend
Datagram
D3 H3
Datagram
D3 H3
23. TCP/IP Protocol Suite23
Figure 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. So each router has three pairs of addresses, one for each
connection.
The computer with logical address A and physical address 10 needs
to send a packet to the computer with logical address P and physical
address 95.
Example
25. TCP/IP Protocol Suite25
The physical addresses will change from
hop to hop, but the logical addresses
remain the same.
26. Network Layer
Implements routing of packets through the network.
Defines the most optimum path the packet should take from
the source to the destination
Defines logical addressing so that any endpoint can be
identified.
Handles congestion in the network.
Facilitates interconnection between heterogeneous networks
(Internetworking).
The network layer also defines how to fragment a packet
into smaller packets to accommodate different media.
OSI Model
28. TCP/IP Protocol Suite28
Figure 2.13 Communication at transport layer
A
Physical Physical
Data linkData link
R1 R3 R4
B
NetworkNetwork
Transport Transport
Source Destination DataD HeaderHLegend
Segment
D4 H4
Segment
D4 H4
29. TCP/IP Protocol Suite29
Figure 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 both
computers are using the same application, FTP, for example,
the port addresses are different because one is a client program
and the other is a server program.
Example
30. TCP/IP Protocol Suite30
A Sender Receiver P
Internet
Figure 2.18 Example 2.6: port numbers
a DatajA PH2
a DatajA P
a Dataj
Data
a DatajA PH2
a DatajA P
a Dataj
Data
31. Transport Layer
Purpose of this layer is to provide a reliable mechanism for
the exchange of data between two processes in different
computers
Ensures that the data units are delivered error free.
Ensures that data units are delivered in sequence.
Ensures that there is no loss or duplication of data units.
Provides connectionless or connection oriented service.
Provides for the connection management.
Multiplex multiple connection over a single channel.
OSI Model
32. Session Layer
Session layer provides mechanism for controlling the dialogue
between the two end systems. It defines how to start, control and
end conversations (called sessions) between applications.
This layer requests for a logical connection to be established on
an end-user’s request.
Any necessary log-on or password validation is also handled by
this layer.
Session layer is also responsible for terminating the connection.
Session layer can also provide check-pointing mechanism such
that if a failure of some sort occurs between checkpoints, all data
can be retransmitted from the last checkpoint.
OSI Model
33. Presentation Layer
Presentation layer defines the format in which the data is to
be exchanged between the two communicating entities.
Also handles data compression and data encryption
(cryptography).
OSI Model
34. TCP/IP Protocol Suite34
Figure Communication at application layer
A
Physical Physical
Data linkData link
R1 R3 R4
B
NetworkNetwork
Transport Transport
ApplicationApplication Source Destination DataD HeaderHLegend
Message
D5 D5
D5 D5
Message
35. Application Layer
Application layer interacts with application programs and is
the highest level of OSI model.
Application layer contains management functions to
support distributed applications.
Examples of application layer are applications such as file
transfer, electronic mail, remote login etc.
OSI Model
