Computer Physical Data Link Network Transportation Session Presentation Application Layer Protocol

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 Chapter 2: Protocol

•  Introduction

• Ethernet (Physical/Data Link Layers)

• IP/IPX (Network Layer)

• TCP/SPX (Transportation Layer) 

• HTTP/FTP/Telnet/SMTP/DNS (Session/Presentation/Application Layers)

• Introduction

PROTOCOLS :- An agreement that governs the procedures 

used to exchange information between entities in a 

computer network is called as Protocol.

 Protocols are the actual hardware and software 

components that carry out the OSI model guidelines for 

transferring information on a network. A network often uses 

multiple protocols that work together to carry out a task.

A protocol is a set of rules that governs the communications 

between computers on a network. In order for two 

computers to talk to each other, they must be speaking the 

same language.   

PROTOCOLS STACKS:-    A protocol stack, also called a 

suite, is composed of several protocols that are used to 

send information between computers. Common protocol 

stacks are IPX/SPX and TCP/IP. In the TCP/IP stack, the 

TCP protocol is used to exchange information between two 

devices, while the IP protocol is responsible for addressing 

information and directing information to its proper 

destination. 

LAYERS :- A layer, section of a protocol stack is 

responsible for performing one particular aspect of 

information transfer.

The OSI model determines which protocols should be uesd 

at each layer. Since some protocols are capable of 

performing more than one function, one layer in a protocol 

stack may not be necessary correspond to one layer in the 

OSI model.

COMPATIBILITY :- Computers and network devices must employ the same protocols to transfer information. 

For example, a computer and a network printer must use the same protocol before the computer can successfully send print jobs to the printer.

A layer in a protocol stack on one computer must be able to communicate with the same layer in the protocol stack on an another computer or device. 

STANDARDS :-  When a networking device is designed to exchange information using an accepted protocol, the device can exchange information with any other device that uses the same protocol. The OSI model and protocol standards make sure that networking devices will be able to work together on a network.

OSI MODEL :-  The OSI (Open Systems Interconnection) 

Reference Model defines seven layers of networking 

protocols that describes the tasks that must be carried out to communicate on a network.

When data is being sent over a network, it must pass through each layer of the OSI model. As the data passes through each layer,information is added to the data. When the data reaches the destination, the data must again pass through the layers of the OSI model. The additional information is removed at each layer.

The OSI MODEL showing the seven layers of computer network protocol.

7. Application Layer 

The Application Layer is responsible for transferring information between the programs running on a computer and the services running on a network, such as database or print services. 

6. Presentation Layer 

The  Presentation Layer  converts information from one format to another.

5. Session Layer

The Session Layer determines how two computer devices communicate. This layer establishes and monitors connections between computers.

4. Transport Layer

The Transport Layer checks for errors in transmission and make sure that information is delivered reliably.

3.Network Layer

The Network Layer identifies computers on a network and determines how to direct information transferring over a network.

2. Data Link Layer

The  Data Link Layer groups data into sets to prepare the data for transferring over a network.

1. Physical Layer

The Physical Layer determines how a transmission medium, such as a cable, connects to a computer. This layer also specifies how electrical  information transfers on the transmission medium.

• Ethernet (Physical/Data Link Layers)           

The physical layer of the network focuses on hardware 

issues, such as cables, repeaters, and network interface 

cards. 

The most common protocol used at the physical layer is 

Ethernet.

 For example, an Ethernet network (such as 10BaseT or 

100BaseTX) specifies the type of cables that can be used; 

the optimal topology (star vs. bus, etc.), the maximum length 

of cables, etc. 

The data link layer of the computer network addresses the 

way the data packets are sent from one node to another. 

Ethernet uses an access method called CSMA/CD (Carrier 

Sense Multiple Access/Collision Detection). 

This is a system where each computer listens to the cable 

before sending anything through the network. 

If the network is clear, the computer will transmit. 

If some other node is already transmitting on the cable, the 

computer will wait and try again when the line is clear. 

Sometimes, two computers attempt to transmit at the same 

instant,when this happens a collision occurs. 

Each computer then backs off and waits a random amount 

of time before attempting to re transmit with this access 

method, it is normal to have collisions. The delay caused by 

collisions and re transmitting is very small and does not 

normally effect the speed of transmission on the network.


                    Ethernet Protocol Summary

Protocol	Cable	Speed
Ethernet	Twisted Pair, Coaxial, Fiber	10 Mbps
Fast Ethernet	Twisted Pair, Fiber	100 Mbps
Gigabit Ethernet	Twisted Pair, Fiber	1000 Mbps

Ethernet

The original Ethernet was developed in 1983 and 

had a maximum speed of 10 Mbps. The Ethernet protocol 

allows for bus, star, or tree topologies, depending on the 

type of cables used and other factors .

The current standard at the 10 Mbps level is 10BaseT, where 

•  "10" stands for the speed of transmission (10 megabits per second).

• the "Base" stands for "baseband" meaning it has full control of the wire on a single frequency.

• the "T" stands for "twisted pair" cable.                                                  

Older standards, such as 10Base2 and 10Base5, were used  

as coaxial cable, but these standards are seldom used in 

new installations. Fiber cable can also be used at this level 

in 10BaseFL.

Fast Ethernet

The Fast Ethernet protocol supports transmission up to 100 

Mbps. Fast Ethernet requires the use of different, more 

expensive network connectors/hubs and network 

interface cards. 

Fast Ethernet standards include:

•100BaseT - 100 Mbps over 2-pair category 5 or better UTP cable.

•100BaseFX - 100 Mbps over fiber cable.

•100BaseSX -100 Mbps over multi mode fiber cable.

•100BaseBX - 100 Mbps over single mode fiber cable.

Gigabit Ethernet

Gigabit Ethernet standard is a protocol that has a 

transmission speed of 1 Gbps (1000 Mbps). 

It can be used with both fiber optic cabling and copper. 

The 1000BaseT, the copper cable used for Gigabit Ethernet.

•1000BaseT - 1000 Mbps over 2-pair category 5 or better 

  UTP cable.

•1000BaseTX - 1000 Mbps over 2-pair category 6 or better 

   UTP cable.

•1000BaseFX - 1000 Mbps over fiber cable.

•1000BaseSX -1000 Mbps over multimode fiber cable.

•1000BaseBX - 1000 Mbps over single mode fiber cable.

          The Ethernet standards continue to evolve with 10 

Gigabit Ethernet (10,000 Mbps) and 100 Gigabit Ethernet 

(100,000 Mbps).

• IP/IPX (Network Layers)    

The network layer is in charge of routing network 

messages (data) from one computer to another. 

The common protocols at this layer are IP (which is paired 

with TCP at the transport layer for Internet network) and 

IPX (which is paired with SPX at the transport layer for 

some older Macintosh, Linus, UNIX,Novell and Windows 

networks). 

Every network device (such as network interface cards and 

printers) have a physical address called a MAC (Media 

Access Control) address.  

Networks using the IP (Internet Protocol) and IPX 

protocols assign logical addresses to the devices on the 

network.

         An Internet Protocol is responsible for addressing 

information and directing information to its proper destination

 on a TCP/IP network.

         An IPX (Internetwork Packet Exchange Protocol) is 

derived from a protocol developed by Xerox Corporation 

called Xerox Network System (XNS). 

The IPX is mostly used to exchange information between 

devices located on Netware networks. The IPX protocol 

uses addresses to keep track of devices located on different 

networks.

When the IPX protocol transfers data from one device to 

another, the protocol does not establish a connection 

between the two devices. The protocol also does not 

monitor the transmission or check the reliability of the data.

• TCP/SPX (Transportation Layers)  

The transport layer is concerned with efficient and reliable 
transportation of the data packets from one network to 
another. 
In most of the cases, a document or an e-mail message or other piece of information is not sent as one unit, instead it is broken into small data packets, each with header information that identifies its correct sequence and document.
         When the data packets are sent over a network, they may or may not take the same route. At the receiving end, the data packets are re-assembled into the proper order and after all packets are received, a message goes back to the originating network. If a packet does not arrive, a message to "re-send" is also sent back to the network.

TCP (Transmission Control Protocol) is a communication protocol developed under contract form of the U.S. Department of inter-network similar systems.

TCP is used to transfer information between two computers on a TCP/IP network. TCP uses virtual ports to make connections between computers  and also monitors the transmission of information.

SPX (Sequenced Packet Exchange) protocol is an extension of the IPX protocol. Unlike the IPX protocol, the SPX protocol establishes a connection between the two network computers  that want to exchange data and monitors the transmission. The SPX protocol also makes sure that the data exchanged has no errors.

• HTTP/FTP/Telnet/SMTP/DNS (Session/Presentation/Application Layers)    

Several protocols overlap the session layer, presentation layer, and application layer of networks. There protocols listed below are a few of the more well-known:

*FTP (File Transfer Protocol) is one of the most widely recognized and used TCP/IP protocols. FTP is used to transfer documents between different types of computers on a TCP/IP network.

*HTTP(HyperText Transfer Protocol) - An Internet-based protocol for sending and receiving webpages. This protocol is one of the most widely used protocols for exchanging information on the Internet. This protocol is used to send information from web servers to web browsers.

*Telnet-Telnet is a network protocol used on the Internet or local area networks to provide a interactive communication facility using a virtual connection. 
Telnet is a client-server protocol, based on a reliable connection-oriented transport. 

*SMTP (Simple Mail Transfer Protocol) - A protocol for      e-mail messages on the Internet. This protocol is an Internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks. 

*DNS (Domain Name System) - translates network address (such as IP addresses) into terms that is understood by humans (such as URLs). It is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network.


click here more some figures related to computer protocol:

NETWORKING