TCP/IP PROTOCOL SUITE

TCP/IP PROTOCOL

SUITE

Networks Lecter 3-part 2

Edited by

Dr Athraa Juhi

TCP/IP PROTOCOL SUITE

The first layered protocol model for

internetwork communications was created in

the early 1970s

This model is referred to as the Internet model

It defines four categories of functions that

must occur for communications to be

successful.

TCP/IP protocol suite follows the structure of

this model.

TCP/IP PROTOCOL SUITE

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.

TCP/IP PROTOCOL SUITE

The TCP/IP Model was created in the 1970s

by DARPA, an agency of the United States

Department of Defense (DOD).

The original TCP/IP protocol suite was

defined as four software layers built upon

the hardware.

TCP/IP PROTOCOL SUITE

Today, TCP/IP is thought of as a five-layer model

with the layers named similarly to the ones in the

OSI model.

TCP/IP PROTOCOL SUITE

Comparison between OSI and TCP/IP

Protocol Suite

In TCP/IP two layers, session and

presentation, are missing from the TCP/IP

protocol suite.

 These two layers were not added to the

TCP/IP protocol suite after the publication

of the OSI model.

Comparison between OSI and TCP/IP

Protocol Suite

The application layer in the suite is usually

considered to be the combination of three

layers in the OSI model.

TC/IP becomes a standard, a standard for

software, and a standard for hardware

Comparison between OSI and TCP/IP Protocol

Suite

Comparison between OSI and TCP/IP Protocol

Suite

OSI Overview

Data Encapsulation

a) Each protocol on the

diff. layer has its own

format.

b) Headers are added

while a packet is going

down the stack at each

layer.

c) Trailers are usually

added on the second

layer.

Two reasons were mentioned for this

decision.

First, TCP/IP has more than one transport-

layer protocol.

Some of the functionalities of the session

layer are available in some of the transport

layer protocols.

Comparison between OSI and TCP/IP

Protocol Suite

Two reasons were mentioned for this decision.

Second, the application layer is not only one piece

of software.

 Many applications can be developed at

this layer.

 If some of the functionalities

mentioned in the session and

presentation are needed for a particular

application, it can be included in the

development of that piece of software.

Comparison between OSI and TCP/IP

Protocol Suite

Layers in the TCP/IP Protocol Suite

 When we study the purpose of each layer, it is easier to

think of a private internet, instead of the global

Internet.

 Such an internet is made up of several small networks

called links.

 A link is a network that allows a set of computers to

communicate with each other.

 A link can be a LAN or WAN.

 Our imaginary internet that is used to show the purpose of

each layer.

Layers in the TCP/IP Protocol Suite

Physical Layer TCP/IP

TCP/IP does not define any specific protocol

for the physical layer. It supports all of the

standard protocols.

At this level, the communication is between

two hops or nodes, either a computer or router.

Physical Layer TCP/IP

The unit of communication is a single bit.

When the connection is established between

the two nodes, a stream of bits is flowing

between them.

The physical layer, however, treats each bit

individually.

Physical Layer TCP/IP

We are assuming that at this moment the two computers have

discovered that the most efficient way to communicate with

each other is via routers R1, R3, and R4.

Physical

layer

Physical

layer

R1 R3 R4

Source Destination

Legend

Link 3

Link 5

Link 6

Link 1

Physical Layer TCP/IP

From the figure in the previous slide:

 Computer A sends each bit to router R1 in the format of

the protocol used by link 1.

 Router 1 sends each bit to router R3 in the format

dictated by the protocol used by link 3. And so on.

 Note that if a node is connected to n links, it needs n

physical-layer protocols, one for each link.

Physical Layer TCP/IP

The physical layer coordinates the functions

required to carry a bit stream over a physical

medium.

It deals with the mechanical and electrical

specifications of the interface and transmission

media.

Physical Layer TCP/IP

It also defines the procedures and functions

that physical devices and interfaces have to

perform for transmission to occur.

The unit of communication at the

physical layer is a bit.

General responsibilities of Physical layer

 Physical characteristics of interfaces and

media.

 The physical layer defines the characteristics of

the interface between the devices and the

transmission media.

 It also defines the type of transmission media.

General responsibilities of Physical layer

Representation of bits.

 To be transmitted, bits must be

encoded into signals : electrical or

optical.

 The physical layer defines the type

of encoding (how 0s and 1s are

changed to signals).

General responsibilities of Physical layer

Data rate.

The transmission rate-the number of bits sent

each second.

Synchronization of bits.

 the sender and the receiver clocks must be

synchronized.

General responsibilities of Physical layer

Line configuration (point-to-point, multipoint).

 Physical topology (mesh, bus, star, ring)

Transmission mode (simplex mode, half-duplex,

full-duplex)

 TCP/IP does not define any specific protocol for the

data link layer either.

 It supports all of the standard protocols.

 At this level, the communication is also between two

hops or nodes.

Data Link Layer TCP/IP

 The unit of communication however, is a packet

called a frame.

 A frame is a packet that encapsulates the data

received from the network layer with an added

header and sometimes a trailer.

Data Link Layer TCP/IP

 The head includes the source and destination address.

 The destination address is needed to define the right

recipient of the frame.

 The source address is needed for possible response or

acknowledgment as may be required by some protocols.

Data Link Layer TCP/IP

Physical Physical

Data linkData link

R1 R3 R4

Source Destination

Data

D Header

Legend

Link 1

Link 3

Link 5

Link 6

Frame

From the figure in the previous slide:

 Note that the frame that is travelling between computer

A and router R1 may be different from the one

travelling between router R1 and R3.

 When the frame is received by router R1, this router

passes the frame to the data link layer protocol (left).

Data Link Layer TCP/IP

From the figure in the previous slide:

 Then, the frame is opened, the data are removed.

 The data are then passed to the data link layer protocol

(right) to create a new frame to be sent to the router

R3.

Data Link Layer TCP/IP

Network Layer TCP/IP

 At the network layer (it also known as internetwork layer),

TCP/IP model supports the Internet Protocol (IP) in this

layer.

 The Internet Protocol (IP) is the transmission mechanism

used by the TCP/IP model.

Network Layer TCP/IP

 At the network layer (it also known as internetwork layer),

TCP/IP model supports the Internet Protocol (IP) in this

layer.

 The Internet Protocol (IP) is the transmission mechanism

used by the TCP/IP model.

Network Layer TCP/IP

 IP transports data in packets called Datagrams, each of

which is transported separately.

 Datagrams can travel along different routes and can

arrive out of sequence or be duplicated.

 IP does not keep track of the routes and has no facility for

reordering datagrams once they arrive at their destination.

Physical Physical

Data linkData link

R3 R4

NetworkNetwork

Source Destination DataD HeaderH

Legend

Datagram

Network Layer TCP/IP

Note that there is a main difference between the

communication at the network layer and the

communication at data link or physical layers:

Network Layer TCP/IP

Communication at the network layer is end to

end while the communication at the other two

layers are node to node.

Network Layer TCP/IP

 Figure in the slide 38 shows that:

 The datagram started at computer A is the one that reaches

computer B.

 The network layers of the routers can inspect (check) the

source and destination of the packet for finding the best

route, but they are not allowed to change the contents of

the packet.

Transport Layer TCP/IP

There is a main difference between the transport layer and

the network layer.

Although all nodes in a network need to have the

network layer, only the two end computers need

to have the transport layer.

Transport Layer TCP/IP

 The network layer is responsible for sending individual

datagrams from computer A to computer B.

 The transport layer is responsible for delivering the

whole message, which is called a Segment, a user

datagram, or a packet, from A to B.

Transport Layer TCP/IP

 A segment may consist of a few or tens of

datagrams.

 The segments need to be broken into datagrams

 Each datagram has to be delivered to the network

layer for transmission.

Physical Physical

Data linkData link

R1 R3 R4

NetworkNetwork

Transport Transport

Source Destination DataD HeaderH

Legend

Segment

Transport Layer TCP/IP

Notes about the figure in the previous slide

 Since the Internet defines a different route for each

datagram,

 the datagrams may arrive out of order and may be lost

 The transport layer at computer B needs to wait until

all of these datagrams to arrive, assemble them

and make a segment out of them.

Transport Layer TCP/IP

 Traditionally, the transport layer was represented in the

TCP/IP suite by two protocols:

1. Transmission Control Protocol (TCP):

 is a reliable connection-oriented protocol

 TCP allows a byte stream originating on one machine to be

delivered without error on any other machine in the

internet.

 TCP also handles flow control to make sure a fast sender

cannot swamp a slow receiver with more messages than it

can handle.

Transport Layer TCP/IP

2. User Datagram Protocol (UDP):

 UDP is an unreliable, connectionless protocol for

applications that do not want TCP’s sequencing or flow

control and wish to provide their own.

 It is also widely used for one-shot, client-server-type

request-reply queries and applications in which prompt

delivery is more important than accurate delivery, such as

transmitting speech or video.

 Its advantage low overhead.

Transport Layer TCP/IP

3. A new protocol called Stream Control Transmission

Protocol (SCTP) has been introduced in the last few years.

 SCTP provides some of the features of both UDP

and TCP

 it is message-oriented like UDP

 ensures reliable, in-sequence transport of

messages with congestion control like TCP.

 It differs from those protocols by providing

redundant paths to increase resilience and

reliability.

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Application Layer TCP/IP

 The application layer in TCP/IP is equivalent to the

combined session, presentation, and application layers

in the OSI model.

 The application layer allows a user to access the services

of our private internet or the global Internet.

 Many protocols are defined at this layer to provide

services such as electronic mail, file transfer, accessing

the World Wide Web, and so on.

Application Layer TCP/IP

 Note: that the communication at the application

layer, like the one at the transport layer, is end to

end.

 A message generated at computer A is sent to

computer B without being changed during the

transmission.

Application Layer TCP/IP

Physical Physical

Data linkData link

R1 R3 R4

NetworkNetwork

Transport Transport

Application

Source Destination DataD HeaderH

Legend

Message

Four levels of addresses are used in an internet

employing the TCP/IP protocols:

 physical address,

 logical address,

 port address,

 and application-specific address.

Each address is related to a one layer in the TCP/IP

architecture as the folowing:

Addressing

 The physical address, also known as the link address, is

the address of a node as defined by its LAN or WAN.

 It is included in the frame used by the data link layer. It is

the lowest-level address.

 The size and format of these addresses vary depending

on the network.

Physical Addresses

 For example, Ethernet uses a 6-byte (48-bit) physical

address that is imprinted on the network interface card

(NIC).

 LocalTalk (Apple), however, has a 1-byte dynamic address

that changes each time the station comes up.

Physical Addresses

07:01:02:01:2C:4B

A 6-byte (12 hexadecimal digits) physical address

Physical Addresses

Layer 2 addresses are only used to communicate between

devices on a single local network

Data87 10

packet

accepted

Data87 10

 Physical addresses can be either unicast (one single

recipient), multicast (a group of recipients), or broadcast

(to be received by all systems in the network).

 Some networks support all three addresses. Ethernet

supports the unicast physical addresses (6 bytes), the

multicast addresses, and the broadcast addresses.

 Some networks do not support the multicast or

broadcast physical addresses.

Unicast, Multicast, and Broadcast Physical Addresses

 Logical addresses are necessary for universal

communications that are independent of underlying

physical networks.

 Physical addresses are not adequate in an internetwork

environment where different networks can have different

address formats.

Logical Addresses

 A universal addressing system is needed in which each

host can be identified uniquely, regardless of the

underlying physical network.

 The logical addresses are designed for this purpose.

 A logical address in the Internet is currently a 32-bit

address that can uniquely define a host connected to the

Internet.

 No two publicly addressed and visible hosts on the

Internet can have the same IP address.

Logical Addresses

DataA P2010 DataA P20 10

Physical

addresses

changed

DataA P33 99

Physical

addresses

changed

DataA P9566

DataA P95 66

The physical addresses will change from hop to hop, but the

logical addresses remain the same.

The Figure in the previous slide shows that:

 The network layer, however, needs to find the physical

address of the next hop before the packet can be delivered.

 The network Layer consults its routing table and finds the

logical address of the next hop to be F.

 Another protocol, Address Resolution Protocol (ARP),

finds the physical address of router 1 that corresponds to

its logical address (20).

Logical Addresses

Unicast, Multicast, and Broadcast Addresses

 The logical addresses can be either unicast (one single

recipient), multicast (a group of recipients), or broadcast

(all systems in the network).

 There are limitations on broadcast addresses.

Logical Addresses

 Computers are devices that can run multiple processes at

the same time.

 The end objective of Internet communication is a process

communicating with another process.

 For example, computer A can communicate with

computer C by using TELNET.

At the same time, computer A communicates with

computer B by using the File Transfer Protocol (FTP).

Port Addresses

 For these processes to receive data simultaneously, we

need a method to label the different processes.

 In the TCP/IP architecture, the label assigned to a process

is called a port address. A port address in TCP/IP is 16

bits in length.

 Port address is a 16-bit address represented by one

decimal number as shown in next figure.

Port Addresses

Some of these Addresses are:

 Domain Name System (DNS) - TCP/UDP Port 53

 Hypertext Transfer Protocol (HTTP) - TCP Port 80

 Simple Mail Transfer Protocol (SMTP) - TCP Port 25

 Post Office Protocol (POP) - UDP Port 110 Telnet - TCP Port 23

 Dynamic Host Configuration Protocol - UDP Port 67

 File Transfer Protocol (FTP) - TCP Ports 20 and 21

For more:

CCNA Exploration 4.0 Network Fundamentals, Chapter Three Application Layer

functionality & Protocols (P. 24).

Port Addresses

 Some applications have user-friendly addresses that are

designed for that specific application.

 Examples include the e-mail address (for example,

[email protected]du) and the Universal Resource Locator

(URL) (for example, www.mhhe.com).

The first defines the recipient of an e-mail; the second is used to

find a document on the World Wide Web.

 These addresses, however, get changed to the corresponding

port and logical addresses by the sending computer.

Application-Specific Addresses