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ADVANCED COMPUTER INVESTIGATION TOPIC


(CEOO298-M)

SUBMITTED BY : GOGUMALLA PRASHANTH MOHAN

REGISTRATION NO : GV006352

AWARD : M.SC COMPUTER SCIENCE

SUBMITTED TO : STELLA MILLS

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S.NO INDEX PG NO

1. ABSTRACT...........................................................................................................3

2. INTRODUCTION TO INTERNET.......................................................................3

2.1.WHO RUNS INTERNET....................................................................................4

2.2.HOW TO ACCESS INTERNET.........................................................................5

3. INTRODUCTION TO COMPUTER NETWORKS .............................................7

4. TYPES OF INTERNET CONNECTIONS.............................................................84.1.CLIENT-SERVER MODEL.................................................................................8

4.2.TYPES OF SERVER PROCESSES......................................................................9

4.3.BENEFITS.............................................................................................................9

4.4.PITFALLS..............................................................................................................9

5. CONNECTION-ORIENTED, CONNECTION-LESS MODE PROTOCOLS.......9

5.1.CONNECTION-ORIENTED OPERATIONS.......................................................10

5.2.CONNECTION-LESS OPERATIONS..................................................................10

6. TYPES OF PROTOCOLS........................................................................................11

7. OSI-REFERENCE MODEL....................................................................................12

7.1.ADVANTAGES.....................................................................................................13

7.2.DISADVANTAGES...............................................................................................13

7.3.COMPARISON OF OSI AND TCP/IP MODELS.................................................13

8. TCP/IP MODEL.........................................................................................................13

8.1.TRANSMISSION CONTROL PROTOCOL(TCP)................................................14

8.2.MAJO CHARACTERISTICS OF TCP...................................................................15

9. INTERNET PROTOCOL(IP)....................................................................................16

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9.1.LAYERING IN THE INTERNET PROTOCOL SUITE........................................18

10. USER DATAGRAM PROTOCOL(UDP)...........................................................18

10.1. 4-LAYER MODEL SHOWING UDP, TCP & IP...............................................1910.2. FORMAT OF UDP DATAGRAM20

11. TRANSMISSION CONTROL PROTOCOL AND USER DATAGRAM PROTOCOL

11.1. RELATIONSHIP OF TRANSPORT LAYER TO OTHER LAYERS....................23

11.2. COMPARISON OF PROTOCOL FEATURES FOR UDP AND TCP....................23

12.USING MULTIPLEXING TO SUPPORT SOCKETS2412.1. PASSIVE AND ACTIVE

OPEN..24

12.2. SEGMENTS25

12.3. TCP SEGMENT (PDU).25

13. CONCLUSION.......................................................................................................25

14. REFERENCE LIST.27

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A BRIEF INSIGHT OF INTERNET, CRITIQUE

ON NETWORKING MODELS & PROTOCOLS

1. ABSTRACT:

This paper gives a comprehensive review and evaluates the quality of services required for

networking. This paper briefly explains the growth and need of INTERNET and

NETWORKING. Research is mainly done on the working concepts, design structures,

architectures, data communication of both the networking models i.e. OSI model and TCP/IP

model. It brings out the pros and cons of both connection-oriented services and connection-less

services. Finally, this paper shows the deployment and working procedure of the protocols in

data transfer for a network.

2. INTRODUCTION TO INTERNET:

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The internet is a vast international network of networks that allows different computers

to communicate and share information, services mutually as if they belong to one global

computing system. The Internet is also known as the NET, largest computer network: The global

communication system that connects millions of computers through the TCP/IP protocol. The

Internet could represent the interconnectivity of hundreds of thousands of computers around the

world.

The seed of internet emerged out in 1957 from the U.S defense department as the fault

tolerant wide area computer networking paradigm, one that would survive a nuclear the most

potent and definitely the most uncontrollable force in the world (Comer, 2006).

Four American universities joined together to form the first distributed packing-

switching network by December 1969.during 1970s and the early years of 1980s, the Internet

Protocol (IP), a procedure that determines the packets address and appropriate rooting of data

over the network. ARPANET continued to grow and, By August 1983 there were 562

networking host computers. Other independent networks were also being created at the sametime. USENET (UNIX Users Group Network) started in 1979, and CSNET (Computer and

Science Network) and BITNET (Because Its Time) in 1981. Networks also began to spring up in

Europe, Including EARN (European Academic research network) and JANET (Joint Academic

Network).

The Internet is a three level hierarchy composed of backbone networks (For example

APRANET, NSANET, MILNET), mid level networks and sub networks. The sub net includes

among others, commercial (.COM, or .CO) university (.AC or .EDU), research networks

(.ORG, .NET) and military networks (.MIL).

2.1.WHO RUNS INTERNET:

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No one runs it or owns it. Internet can be imagined as working like mail. Internet works

by many entities such as universities, government agencies, Business and individuals, each

maintaining their own computer networks. These separate entities have agreements that allow

each other to send and receive information over each other networks to make this all work under

a body, called the internet society that sets international standards for the internet. However, a

voluntary members organization called Internet Society (ISOC) is then set up by vendors, users

and network provides to promote global information exchanging through Intranet technology. It

invites volunteers to the Internet Architecture Board, or the IAB to take up the technical

management and setting direction of the Internet (American University, 2002).

2.2.HOW TO ACCESS THE INTERNET:

To access the Internet, one needs a computer, a modem, an Internet Service Provider

(ISP) and communication software. Having a high powered computer is not necessary. However

some of the newest software may have certain minimum requirements. A modem of at least

14,000 bits per second (14.4) is best for accessing the Internet, and it is a minimum requirementfor accessing the web. This is because the web is a graphical environment. To view, graphics

requires more data to be transferred over ones modem, making the speed of the modem a crucial

element.

3. INTRODUCTION TO COMPUTER NETWORKS:

Growth in the field of science and technology led to a high level change in the 21 st

century with the need of information rising beyond expectations. Communication plays a vital

role and is increasing in importance with a steady pace with the human needs. Data collection,

data retrieval and data storing is very important. Computers a revolutionary device is mainly

used in this context. Communication between the computers is mainly done in three ways such

as

LAN- Local Area Network

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WAN- Wide Area Network

MAN- Metropolitan Area Network

In our day to day life, computer networking has pervaded from electronic mail services,

to automated teller machines, to e-reservation, to e-business, to e-commerce and have

revolutionised the use of computers. Major factors for the drastic growth in the field of computer

networking are:

Demand for networks has been fuelled by the proliferation of workstations and

computers during the early 80s.

Computer networks used to be expensive and were restricted to large

universities, government research sites and large co-operations. Establishing

computer network have been reduced vastly in terms of cost due to technology

and are mostly found in organisations of different magnitude.

Many computer manufacturers now package networking software as part of the basic operating

system (Tanenbaum, 2002).

These days networking software is packaged along with the basic operatingsystems by all the computer manufacturers.

In the era of information, computer networks are becoming an entire part in the

broadcasting and communication.

Earlier computer systems were separate entities with the required hardware peripheralsand software for doing a task. If a task is to be carried out such as line printing, a line printer is

required to connect the computer. This brought a change in the realisation that systems and its

users need information and resource sharing. This is achieved using electronic mail, file transfer

etc. exchanging magnetic tapes, decks of punched cards, and line printer listings were used in file

and information sharing. Today computer systems can be linked using various electronic

techniques called networks. A network is a simple connection between personal computers

connected together using a 1200 baud modem, or as complex as the TCP/IP Internet. Some of the

network applications are

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Exchange files between systems. For many applications it is just as to distribute

the application electronically, instead of mailing diskettes or magnetic tapes. File

transfer across the network also provides faster delivery.

Share peripheral devices. Example, range from the sharing of line printers to

the sharing of magnetic tape drives. A large push towards the sharing of peripheral

devices has come from the personal computer and workstation marker, since often the

cost of a peripheral can exceed the cost of the computer. In an organisation with many

personal computers or workstations, sharing peripherals makes sense.

Execute a program on another computer. These are cases where some other

computer is better suited to run a particular program. For example, time-sharing or aworkstation with good program development tools might be the best system on which

to edit and debug a program. Another system, however, might be better equipped to

run the program. This is often with programs that require special features, such as

parallel processing or vast amounts of storage.

Remove login. If two systems are connected using a network, the users should

be able to login from one another. It is usually easier to connect computers using a

network, and provides a remote login application, than to connect every terminal in an

organisation to every computer.

Electronic-commerce. The new developments in the field of computer

networks enable us to perform commercial transactions (like bank transactions)

electronically.

Multimedia and networking have made home-shopping possible. An

atmosphere similar to the one in the mall is simulated, a connection to the mall is

established and the customer can shop as though he/she is in the mall even though at

home (Tanenbaum, 2002).

4. TYPES OF INTERNET CONNECTIONS:

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Depending on how to link to the Internet, there are a number of choices for the

physical connection to the Internet. These physical connections vary in capacity from the low

28.8 KBPS modem to the 45 MBPS T3 line. To run a web site on your computer you need,

bandwidths between 56 KBPS and 1.544 MBPS (T1 LINE).

Listed here are some physical connection options:

Dial-up modem

ISDN

B-ISDN

DSL

Cable internet connections

Wireless internet connections

T-1 lines

T-3 lines

Satellite (Webopedia.com, 2009).

5. CLIENT-SERVER MODEL:

Client-server model is a basic and standard model used for network applications. A

client is a process that requests information and the server is a process waiting to get connected

and communicate with it. The client server scenario is as follows,

A host system initiates the server process that initiates itself, waits for a request

from the client process and goes to sleep until pinged.

The client process is user initiated on a different host system by a command to

the time-sharing system with a network connection between them. A server provides

various kinds of services to the client such as

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11 Returning the time and day

11 File printing on the printer

11 File read/write on the servers system

11Login access to the servers system

11 Execute a command for the client on the servers system.

The server system immediately goes to sleep, waits for a request from a client

after providing the desired service to the client system.

5.1. TYPES OF SERVER PROCESSES:

Iterative servers- servers that handle a clients request itself when the request

can be handled in a short period of time.

Concurrent servers- servers that typically handle the clients request in a

concurrent approach when the time to service entirely depends on the request itself. Aconcurrent server appeals and allows other processes to handle the clients request in

order to get back to sleep, waiting for the next request. Client requests that deal mostly

with file information such as printing, read/write are concurrently handled by the server

because the amount of the time taken to service is proportionate to the file size and

type.

5.2. BENEFITS OF CLIENT/SERVER:

In a client-server model, it is an added advantage if the client and server run on different

computers. It is always preferred to use computers with high performance processors, highmemory and disk space to run the server. This helps the server to store huge amounts of data and

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handle different client requests simultaneously. In contrary, it is always preferred to use a

computer with low processor speed, a graphic card, minimal memory and disk space for running

the client application.

The client-server model adapts and reacts aptly for all changes in the hardware and software.

Such as, if a computer delivering high performance and service at almost half the price then the

system disconnects the old server and automatically connects with the new server.

Every functional component in the system is specialized to carry out a specific task in different

style.

5.3. PITFALLS OF CLIENT/SERVER:

Reliability of a client/server system, management of hardware and software components

is comparatively low than compared with a centrally managed homogeneous system. Cost savingrely on choosing the appropriate application for running the model.

11 CONNECTION-ORIENTED AND CONNECTIONLESS-MODE PROTOCOLS:

Internet uses two types of communication protocols namely connection-oriented

operations and connection-less operations. Their key characteristics and features are as follows

6.1. CONNECTION-ORIENTED OPERATIONS:

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In creating an end-to-end connection, devices perform handshaking process. It does not

work in uni-directional environment and works only in bi-directional environments. This process

can be as easy as synchronization in TCP or can be as intricate as communicating parameters

with a modem. Both devices must be able to convey a connection. This operates mainly in three

phases i.e. connection setup, data transfer and connection release. While the first phase deals

with establishing a connection and conveys the parameters defining the connection. In the second

phase, messages exchanges under advocacy of the connection. In the last phase, it terminates the

connection as it is no longer needed.

6.2. CONNECTIONLESS-MODE OPERATIONS:

In creating an end-to-end data transmission between the host and the network, logical

connection is not established. This type of operations user uses PDUs for transmitting data as

separate entities. There is no association between consecutive data transfers, and some records

are stored on the progress of user-to-user connections process over the network. In the operation

of data transfer, options are not negotiated and the created tables are managed. The QOS features

must be predetermined, and the interacted entities should have a brief agreement before. For each

PDU transmitted QOS is provided, and every single PDU comprises of fields that recognize

types and levels of service.

Each PDU is handled as a different entity, so a connectionless network is more strong than

connection-oriented. To avoid congestion at a point in the network, data units follow different

circuitous path.

11 TYPES OF PROTOCOLS:

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Listed below are some of the protocols used in networking and in the OSI as well as the TCP/IP

models. They are,

HTTP- Hyper Text Transfer Protocol

POP3- Post Office Protocol

SMTP- Simple Mail Transfer Protocol

FTP- File Transfer protocol

IP- Internet Protocol

DHCP- Dynamic Host Configuration Protocol

IMAP- Internet Message Access Protocol

ARCNET

TELNET

FDDI

UDP

X.25

TFTP

SNMP

PPTP and so on (Networktutorials.info, 2007).

11 OSI-REFERENCE MODEL:

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Fig: architecture of OSI model

http://www.doc.ic.ac.uk/~nd/surprise_97/journal/vol4/mhl/archi.html

The OSI reference model is the basic conceptual model used for stacking the protocols

(networking). It is termed as open system interconnection model also reffered as 7-layer OSI

model. This model provides a level of abstraction. It is a seven layered model with different

protocols stacked in each layer. The above figure shows the layering of protocols and its

working. The specifications of each layer is discussed below,

Application layer: it is the top most layer of the model that defines the applications

procedure of interaction with the network, electronic mail, database and terminal

emulation program. A set of interfaces are provided for application to gain access to all

networks available. Ex: HTTP- Hyper Text Transfer Protocol.

Presentation layer: this layer is used only for transmission, data manipulation, data

encapsulation, data encryption. The data formation, presentation, encoding is defined by

this layer.

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Session layer: this layer is used for creating a session, data transmission and later ends

the session when the work is finished. As long the data is to be passed from presentation

layer, it will be active, communicating with the upper layer and performs a steady

session.

Transport layer: this layer defines the protocols for building messages and checking the

transmission validity with the help of checksums. It helps the data stream to resize itself

in order to pass through the packet.

Network layer: this layer defines the protocols for data routing and to check whether the

data has arrived at the desired destination or not.

Data link layer: this layer is used for synchronizing and controlling the data flow. Data

is packaged into special streams from bits to cells with special variations on checksums.

Physical layer: this layer is used to communicate the transmission medium and hardware

interface (Sheppard, 2005).

8.1. ADVANTAGES:

It is a model legally recognized and standardized by the ISO. It works both in connectionless and

connection-oriented services. All the protocols are well safe and are hidden and is flexible to

change when the technology changes.

8.2. DISADVANTAGES:

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More complex and is high in cost.

Not widely used for networking like that of TCP/IP model.

Basing on all the factors, a new model for networking is developed that overcomes all the

drawbacks of the OSI model with more effectiveness, robust, better performance and low in cost.

This model is termed as TCP/IP model.

8.3. COMPARISON OF OSI MODEL AND TCP/IP MODEL:

11 TCP/IP MODEL:

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Transmission Control Protocol/Internet Protocol is a standard network communication protocol

used to connect computer systems across the Internet. This model is an enhanced version with

almost all the features and working principles of the OSI model. Only difference is that TCP/IP

has only 4 layers (Comer, 2006).

9.1. TRANSMISSION CONTROL PROTOCOL (TCP):

TCP is a connection-oriented transport layer protocol that offers a full-duplex, reliable,data service. It is often called as TCP/IP protocol as it uses internet protocol.

OOSI OSI OSI LAYERS

LAYE 5-7

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USERPROCE

USERPROCE

Application

(HTTP, ftp, telnet,.)

Transport

(TCP/IP, UDP)

Network

(IP)

Link

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OSI LAYER

4

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TCP TCP

ICMP IP ARP RARP

Hardware

Interface

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9.2. MAJOR CHARACTERISTICS OF TCP:

The following services are provided by TCP to the upper layers.

Connection-oriented data management

Reliable data transfer

Stream-oriented data transfer

Push functions

Re-Sequencing

Flow control(sliding window)

Multiplexing

Full-duplex transmission

Precedence and Security

Graceful close

TCP is a connection-oriented protocol. TCP maintains status and state information about each

user data stream flowing into and out of the TCP module. It is also responsible for end-to-end

transfer of data across one network or multiple networks to a receiving user application. TCP

ensures that data are transmitted and received between the two hosts by using the sequence

numbers and positive acknowledgments. A sequence number is assigned to each byte

transmitted. The receiving TCP module uses a checksum routine to check the data for damage

that might have occurred during transmission. If the data are acceptable, TCP returns a positive

acknowledgement (ACK) to the sending TCP module. If the data are damaged the receiving

TCP discards the data and uses a sequence number to inform the sending TCP about the problem.

TCP timers ensure that the lapse of time is not excessive before remedial measures are taken.

The upper layer protocol transmits data to TCP in a stream oriented fashion i.e. It sends

individual characters, not blocks, frames, or datagrams. The bytes are sent from the ULP on a

stream basis, byte-by-byte. When they arrive at the TCP layer, the bytes are grouped into TCP

segments. TCP allows the use of variable length segments because of its stream-oriented nature.

To preserve fixed block nature, action must be taken at the applicant level to delineate the blocks

within the TCP streams.

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TCP also checks for the duplicate data. In addition to using the sequence numbers for

acknowledgement, TCP uses them to re-sequence the segments if they arrive at the final

destination out of order. TCP uses an inclusive acknowledgement scheme that acknowledges

all bytes up to and including acknowledgement number minus one. Flow control of senders

data is also possible which is useful in preventing buffer overrun and possible saturation of the

receiving machine. TCP also has a facility for multiplexing multiple user sessions with in a

single host computer on to the ULPs. This is accomplished using simple naming conventions for

ports and sockets in the TCP and IP modules. Full-duplex transmission between two TCP

entities is provided. TCP also provides the user with the capability to specify levels of safety and

priority level for the link. TCP also provides a graceful close to the connection between the two

users.

Upper-layer user of a TCP in a host machine is recognized with a port number that should be

unique throughout the internet. A socket is created by linking the port value with the IP address.

A pair of sockets uniquely identifies each end-point connection. Such as:

Sending socket = source IP address + source PORT number

Receiving socket = destination IP address + destination PORT number

111 INTERNET PROTOCOL (IP):

IP is an internetworking protocol developed by the department of defense. IP is a data oriented

connectionless service protocol that enables flow of traffic among two host systems. Because

the IP is connectionless, loss of datagrams is possible between the two end users systems.

Internet protocol router can enforce a maximum queue length size and the buffer

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overflows if the queue length is disturbed. The remaining datagrams are later removed from the

network. Thus the higher layer protocol is neccesary to recover these drawbacks.

The sub-network is hidden from the end-user thus allowing it to create a virtual network used for

connecting an IP gateway to different networks. Due to robust and connectionless service, it is

easy to install. Most of the drawbacks are dealt by TCP, the next higher layer.

Some of the drawbacks of IP are as follows

As IP is unreliable, it provides no flow-control and reliability mechanisms.

Datagrams are volatile and can be lost, duplicated and may get altered in their arrival.

IP supports fragmentation operations. The term fragmentation refers to an operation wherein a

PDU is divided or segmented into smaller units. This feature can be quite useful because all

networks do not use the same size PDU. Without use of gragmentation, a router would be tasked

with trying to resolve incompatible PDU sizes between networks. IP solves the problem by

establishing the rules for fragmentation at the router and reassembly at the receiving host.

HOST A HOST B

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UPPERLAYER

PROTOCOLS

(ULP)

!

!

IP OR CLNP

!

!

SNP-1

IP or CLP

SNP-1 SNP-2 SNP-n

UPPERLAYER

PROTOCOLS

(ULP)

!

!

IP OR CLNP

!

!

SNP-2

Network

1

Network

2

Network

3

ROUTING

TABLE

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IP/CLNP MODEL:

10.1. LAYERING IN THE INTERNET PROTOCOL SUITE:

A port number is assigned for TCP protocol to identify itself. It is used to

recognize which application process is yet to obtain the incoming traffic amid host computers.

Each application layer provides a multiplexing capability by enabling multiple programs to

correspond with one application program concurrently.

The port numbers identify these application entities. The concept is related to OSI models service

access point (SAP). In addition to the use of ports, TCP/IP based protocols use an abstract

identifier called a socket. The socket was derived from the network input output operations of

the 4.3 BSD UNIX system. It is quite similar to UNIX file access procedures in that it identifies

an endpoint communication process.

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In the Internet,some port numbers are preassigned. These are called as well known ports that are

used to identify widely used applications called well-known services. The well-known port

numbers occupy values ranging from 0 to 255. Organisations should not use the numbers within

these ranges because they are reserved.

111 USER DATAGRAM PROTOCOL (UDP):

UDP is used as an easy application interface to the Internet Protocol. Due to no reliability,

flow-control or error-recovery measures, it serves mainly as a port multiplexer/demultiplexer for

receiving and sending of application traffic and IP.

The UDP is classified as a connectionless protocol, although the operating system must maintain

information about each active UDP socket. A better description of UDP is that it is connection-

oriented, but does not employ the extensive state management operations normally used in

connection-oriented protocols. It is sometimes used as an alternative to TCP when all the features

of TCP are not required. Some of them that use UDP are:

trivial file transfer protocol (TFTP)

simple network management protocol (SNMP)

Remote procedure calls (RPC).

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PROCESS

LAYER

TRANSPORT

LAYER

NETWORK LAYER

DATA-LINK LAYER

11.1. 4-LAYER MODEL SHOWING UDP, TCP & IP:

UDP serves as a simple application interface to the IP. The figure illustrates how UDP

accepts datagram from IP.

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User

Process

User

Process

TCP TCP

IP

Hardware

Interfac

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UDP LAYER

IP LAYER

FIG-UDP MULTIPLEXING

11.2. FORMAT OF UDP DATAGRAM:

32 BIT

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SOURCE PORT DESTINATION PORT

LENGTH CHECKSUM

DATA

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The figure illustrates the format containing the following fields:

1. Source Port: This value identifies the port of the sending application process. This fieldis optional, and, if not used, a value of 0 is inserted.

2.Destination Port: This value identifies the receiving process on the destination host

machine.

3.Length: This value indicates the length of the user datagram, including the header and

data. This value implies that the minimum length is 8 octets.

4.Checksum: This optional value is the 16-bit ones complement of the ones complement

sum of the pseudo-IP header, the UDP header, and the data. It also performs a

checksum on any padding (if the message needed to contain a multiple of two octets).

The pseudo-header (also used in TCP) ensures that the UDP data unit has arrived at the proper

destination address. Therefore, the pseudo header includes the IP address and is included as part

of the checksum calculation. The final destination performs a complementary checksum on the

pseudo-header (and, of course, the remainder of the UDP data unit) to verify that the traffic is not

altered and it reached the correct destination address. UDP is minimal level of service used in

many transaction-based application systems that is quite useful if the full services of TCP are not

needed.

TCP provides a simple set of services for the UDPs of an Internet. TCP has relatively few

features, but the features are designed to provide end-to-end reliability, graceful closes,

unambiguous connections, handshakes, and several quality-of-service operations, the Internet

transport layer also provides a connectionless operation called, the UDP. UDP is minimal level

of service, principally offering source and destination ports for multiplexing. With UDP, the user

application is typically tasked with performing some end-to-end reliability operations that would

normally be done by TCP.

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111 TRANSMISSION CONTROL PROTOCOL AND USER DATAGRAMPROTOCOL:

The IP is not designed to recover from certain problems, nor does it gaurantee

traffic delivery. IP discards datagrams that have exceeded the number of permissible transit

hops. Certain user applications reuire assurance that all datagrams have been delivered safely to

the destination. The transmitting user might need to know lthat the traffic has been delivered at

the receiving host. The mechanism to achieve these important services resides in TCP; UDP,

however, does not provide delivery assurance services (Stevens, 2002).

END-END COMMUNICATIONS

HOST GATEWAY HOST GATEWAY

A B

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Upper

Layers

TCP

IP

Data Link

Physical

IP

Data Link

Physical

IP

Data Link

Physical

Upper

Layers

TCP

IP

Data Link

Physical

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12.1. RELATIONSHIP OF TRANSPORT LAYER TO OTHER LAYERS:

TCP must establish and manage sessions between its local lusers and these users

remote communicating partners. Thus TCP must constantly be aware of the users on-goingactivities to support the users data transfer through the Internet.

The transport layer of the conventional seven-layered model holds the TCP. It is located below

the upper layers and over the IP. It is not loaded into the router to support user data transfer. It

resides in the machine or host system with end-to-end user data transfer and supports other

protocols.

12.2. COMPARISON OF PROTOCOL FEATURES FOR UDP AND TCP:

IP UDP TCP

Connection-

Oriented NoNo

Yes

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Subnet

1

Subnet

2

Subnet

3

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Message

boundaries?

Yes

Yes

No

Data checksum?

No

Opt

Yes

Positive ack.

No

No

Yes

Timeout &

remit?

No

No

Yes

Duplicate

detection?

No

No

Yes

Sequencing?

No

No

Yes

Flow control?

No

No

No

111 USING MULTIPLEXING TO SUPPORT SOCKETS:

Because the port numbers can be used by more than one end-point connection, users

can simultaneously share a port resource.

13.1. PASSIVE AND ACTIVE OPEN:

The passive-open mode allows the ULP to tell the TCP and the host operating system

to wait for the arrival of connection request from the remote system rather than issue an active-

open. Upon receiving this request, the host operating system assigns an identifier to this end.

This feature could be used to accommodate communications from remote users without

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encountering the delay of active-open. The applications process requesting the passive-open can

accept a connection request from any user.

The second form of connection establishment, the active-open, is used when the ULP designates

a specific socket through which a connection is to be established. Typically, the active-open is

issued to a passive-open port to establish a connection. Two active-opens can be issued at the

same time. The applications can therefore issue an open at any time without concern that

another application has also issued an open.

Transmission control block (TCB) is used to store the information in TCP. The following are the

entries stored in TCB:

Local and remote socket numbers.

Pointers to the send and receive buffers.

Pointers to the retransmit queue.

Security and precedence values for the connection.

Current segment.

13.2. SEGMENTS:

The PDUs exchanged between two TCP modules are called segments. The segment

comprises of a header and the data. The first two fields hold the source port and the destination

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port numbers. The sequence number is used during connection management operations. The

acknowledgement number is set to a value that acknowledges earlier received data.

13.3. TCP Segment (PDU):

TCP stream data is acknowledged by the receiver on a byte basis, not on a PDU. The

acknowledgement number, returned by the receiver, refers to the highest byte received in the data

stream. The sending TCP software keeps a copy of data until it has been acknowledged. Once

acknowledged, it turns off a retransmission timer and deletes the segment copy from a

retransmission queue. If necessary, TCP retransmits lost of error data. This technique is called

inclusive acknowledgement. It works well on systems that deliver data in sequential order, but

the underlying IP might data out of order or discard data. In such an event, TCP has no way to

notify the sender that it has received certain segments of a transmission. It can only relay the

value of the contiguous, accumulated bytes. Consequently the sending TCP software can timeout

and re-send the data segments that have already been successfully received. Finally, TCP can

provide considerable information to the network manager (For example, if TCP is sendingexcessive retransmissions, it might provide a clue to problems in the network, such as dead

routers or timers that are not functioning properly). The positive acknowledgements also could

be used to determine how well the components in an Internet are functioning.

111 CONCLUSION:

Growth in the field of information and technology and globalisation of the world made the need

for networking and mobility of data communication which led to the development of protocols

and networking models. A brief critique is done on the models which are extensively used for

networking, have their own limitation. On an all this paper will fetch a lot for a learner and can

give a brief overview of the internet, networking models, protocols.

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111 REFERENCE LIST:

1. Andrew S. Tanenbaum, 2002. Computer Networks. Prentice Hall PTR.

http://books.google.co.uk/books?id=Pd-z64SJRBAC&printsec=frontcover#PPA44,M1

[Internet] [Accessed on May 5, 2009]

2. Douglas E.Comer, 2006. Internetworking with TCP/IP: Principles, protocols, and

architecture. Prentice Hall.

http://books.google.co.uk/books?

hl=en&lr=&id=jonyuTASbWAC&oi=fnd&pg=PR23&dq=major+problems+of+tcp/ip+&ots=i3

WfT6-R_o&sig=1RawYAVxx9tHObfOhB6QyZzVnuc#PPA6,M1


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http://books.google.co.uk/books?id=Pd-z64SJRBAC&printsec=frontcover#PPA44,M1http://books.google.co.uk/books?hl=en&lr=&id=jonyuTASbWAC&oi=fnd&pg=PR23&dq=major+problems+of+tcp/ip+&ots=i3WfT6-R_o&sig=1RawYAVxx9tHObfOhB6QyZzVnuc#PPA6,M1http://books.google.co.uk/books?hl=en&lr=&id=jonyuTASbWAC&oi=fnd&pg=PR23&dq=major+problems+of+tcp/ip+&ots=i3WfT6-R_o&sig=1RawYAVxx9tHObfOhB6QyZzVnuc#PPA6,M1http://books.google.co.uk/books?hl=en&lr=&id=jonyuTASbWAC&oi=fnd&pg=PR23&dq=major+problems+of+tcp/ip+&ots=i3WfT6-R_o&sig=1RawYAVxx9tHObfOhB6QyZzVnuc#PPA6,M1http://books.google.co.uk/books?id=Pd-z64SJRBAC&printsec=frontcover#PPA44,M1http://books.google.co.uk/books?hl=en&lr=&id=jonyuTASbWAC&oi=fnd&pg=PR23&dq=major+problems+of+tcp/ip+&ots=i3WfT6-R_o&sig=1RawYAVxx9tHObfOhB6QyZzVnuc#PPA6,M1http://books.google.co.uk/books?hl=en&lr=&id=jonyuTASbWAC&oi=fnd&pg=PR23&dq=major+problems+of+tcp/ip+&ots=i3WfT6-R_o&sig=1RawYAVxx9tHObfOhB6QyZzVnuc#PPA6,M1http://books.google.co.uk/books?hl=en&lr=&id=jonyuTASbWAC&oi=fnd&pg=PR23&dq=major+problems+of+tcp/ip+&ots=i3WfT6-R_o&sig=1RawYAVxx9tHObfOhB6QyZzVnuc#PPA6,M1

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3. Behrouz A. Ferouzan, Sophia Chung Fegan, 2002. TCP/IP protocol suite. McGraw-

Hill Professional.

http://books.google.co.uk/books?id=HsCjH_V04tUC


4. Daryl Sheppard, 2005. Troubleshooting complex network problems with the OSI model.

http://www.toastermechanic.com/NetTroubleShoot.pdf


5. Richard W. Stevens, 2002. TCP/IP illustrated, volume 1, the protocols.

http://www.inf.ufes.br/~zegonc/material/Arquitetura%20TCP-IP/tcpipStevens.pdf


6. Craig Partridge, Timothy J. Shepard, 1997. TCP/IP performance over satellite links.

BBN technologies.

http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=620521&isnumber=13498


34 | P a g e
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7. Antony Paga Gumi, 2007. OSI VS TCP.

http://kerjaannyagumi.blogspot.com/search?q=osi+vs+tcp


8. Webopedia, N.D.

http://www.webopedia.com/quick_ref/internet_connection_types.asp


9. Networktutorials.info, 2007. Introduction to computer network protocols.

http://www.networktutorials.info/protocols_stacks.html


10. American University in Cairo, 2002. University Networks Services, Internet

Introduction.

http://unsweb.aucegypt.edu/UNSWEB2/NetIntro.htm


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http://kerjaannyagumi.blogspot.com/search?q=osi+vs+tcphttp://www.webopedia.com/quick_ref/internet_connection_types.asphttp://www.networktutorials.info/protocols_stacks.htmlhttp://unsweb.aucegypt.edu/UNSWEB2/NetIntro.htmhttp://kerjaannyagumi.blogspot.com/search?q=osi+vs+tcphttp://www.webopedia.com/quick_ref/internet_connection_types.asphttp://www.networktutorials.info/protocols_stacks.htmlhttp://unsweb.aucegypt.edu/UNSWEB2/NetIntro.htm

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