Computer Network : What is Computer Network Protocols

A computer Network protocol means a set of rules, governing the Format and meaning of the packets, or message that are exchanged by the peer entities within a layer. Entities used protocols to implement their service definition. Protocols exist at the several levels of the OSI (open system inter-connectivity) layers model. 

Computer Network Protocols:

The word protocol is derived from the Greek word “protocollon” which means a leaf of paper glued to manuscript volume. On the internet, there is a suite of the protocols known as TCP/IP protocols that are consisting of transmission control protocol, internet protocol, file transfer protocol, dynamic host configuration protocol, Border gateway protocol and a number of other protocols.


What is Computer Network Protocols:

A protocol is a set of rules that governs the communications between computers on a network. These rules include guidelines that regulate the following characteristics of a network: access method, allowed physical topologies, types of cabling, and speed of data transfer. 

In computer networks, communication occurs between entities in different systems. An entity is anything capable of sending or receiving information. Examples include application programs, file transfer packages, browsers, database management systems, and electronic mail software. A system is a physical object that contains one or more entities, Examples include computers and terminals. But two entities cannot just send bit streams to each other and expect to be understood. For communication to occur, the entities must agree on a protocol. A protocol is a set of rules that govern data communication. A protocol defines what is communicated, how it is communicated, and when it is communicated. The key elements of a protocol are syntax, semantics, and timing.

Syntax: Syntax refers to the structure or format of the data, meaning the order in which they are presented. For example, a simple protocol might expect the first eight bits of data to be the address of the sender, the second eight bits to be the address of the receiver, and the rest of the stream to be the message itself.

Semantics: Semantics refers to the meaning of each section of bits. How are a particular pattern to be interpreted, and what action is to be taken based on that interpretation? For example, does an address identify the route to be taken or the final destination of the message?
Timing: Timing refers to two characteristics: when data should be sent and how fast they can be sent. For example, if a sender produces data at 100 Mbps but the receiver can process data at only 1 Mbps, the transmission will overload the receiver and data will be largely lost. In data communication, a protocol is a set of rules that govern all aspects of information communication.
Type Of Network Protocols:
There are many standard protocols to choose from, standard protocols have their own advantage and disadvantage i.e., some are simpler than the others, some are more reliable, and some are faster. From a user’s point of view, the only interesting aspect about protocols is that our computer or device must support the right ones if we want to communicate with other computers. The protocols can be implemented either in hardware or in software. Some of the popular protocols are:
NetBIOS: Network basic input/output system is an application programming interface (API). Applications located on different computers; use NetBIOS to communicate each other over a local area network (LAN). NetBIOS is widely used in Ethernet, token ring, and Windows NT networks. NetBIOS provides services at the transport and session layer of the OSI model. NetBIOS supports three services i.e. Name service for name registration and resolution, Session service for connection-oriented communication, Datagram services for connection less communication.
TCP/IP: TCP (Transmission Control Protocol) and IP (Internet Protocol) are two different procedures that are often linked together. The linking of several protocols is common since the functions of different protocols can be complementary so that together they carry out some complete task. The combination of several protocols to carry out a particular task is often called a “stack” because it has layers of operations. In fact, the term “TCP/IP” is normally used to refer to a whole suite of protocols, each with different functions. This suite of protocols is what carries out the basic operations of the Web. TCP/IP is also used on many local area networks. When information is sent over the Internet, it is generally broken up into smaller pieces or “packets”. The use of packets facilitates speedy transmission since different parts of a message can be sent by different routes and then reassembled at the destination. It is also a safety measure to minimise the chances of losing information in the transmission process. TCP is the means for creating the packets, putting them back together in the correct order at the end, and checking to make sure that no packets got lost in transmission. If necessary, TCP will request that a packet be resent.
Internet Protocol (IP) is the method used to route information to the proper address. Every computer on the Internet has to have its own unique address known as the IP address. Every packet sent will contain an IP address showing where it is supposed to go. A packet may go through a number of computer routers before arriving at its final destination and IP controls the process of getting everything to the designated computer. Note that IP does not make physical connections between computers but relies on TCP for this function. IP is also used in conjunction with other protocols that create connections.
Address Resolution Protocol (ARP): The data packets travel through various physical networks to reach the destination. At the physical layer, routers and hosts are recognised by their physical address, which is a local address. It is usually implemented in hardware. To communicate within the same network, the physical address can solve the purpose. However, to communicate between different networks, both the physical (MAC) and logical (IP) address are required. The user should be able to map a logical address to its corresponding physical address and vice versa. There are two protocols used for this purpose. The ARP maps the logical address to a physical address and the RARP maps the physical address to a logical address. Address resolution protocol associates an IP address with its physical address whenever a host or router want to determine the physical address of other host or router on the network it broadcast ARP query packet containing the physical and IP address of the receiver over the network. Every device and router on the network receives the packet checks for the IP address and processes it. The interred recipient identifies its IP address and responds with an ARP reply packet, which contains its IP and physical address. Now the sender can send all the packet intended for this receiver.
Reverse Address Resolution Protocol (RARP): In a network, each device and router is assigned a unique logical address, which is required while creating the IP datagram. This address is normally saved in a configuration file, which is stored on the hard disk. However, when a diskless machine is booted from ROM, it can’t discover its IP address. Reverse address resolution protocol (RARP) is used to determine the logical address when the physical address is known. A device booted for the first time gets it a physical address from the NIC card. The device creates an RARP request packet and broadcasts it over the network. Another device on the network working as the server and having all the IP address responds with an RARP reply packet. This packet includes the IP address of the sender.
Internet Control Message Protocol (ICMP): Internet control message protocol message (ICMP) is an extension to internet protocol, which supports packets containing error, control and information messages. It provides a method for communicating error messages and other transmission information. Two types of ICMP messages are an error-reporting message and query messages.
Error Reporting Message: Error messages report any problem that a router or host may come across while processing the IP datagram. The messages are:-

  • Destination unreachable: If a router is unable to deliver a datagram to the destination, it sends a ‘destination unreachable’ message back to the source that transmitted the datagram.
  • Source Quench: This message is used for flow control at the network layer. The router sends a ‘source quench’ message to the sender to slow down the transmission rate as congestion has occurred in the network.
  • Time exceeded: When the TTL value zero, the router discards the datagram and sends a ‘time exceeded’ message back to the sender.
  • Parameter Problem: If there is an ambiguity in the header of the datagram, then the ‘parameter problem’ message is sent back to the sender by the host or router.
  • Redirection: If the host forwards a datagram to a wrong router the router will forward it to the correct router and send a ‘redirection message’ to the host to update its routeing table.

Query Message: ICMP query messages are used to identify network problems. The messages are:-
Echo request and reply: A device can also check whether another device is reachable or unreachable. One device sends an ‘echo-request’ message to another device, which replies with an ‘echo-reply’ message.
Timestamp Request and Reply: This message is used to determine the round-trip time requested for a datagram to travel between two machines.
Address mark Request and Reply: A host may have its full IP address but may not know the corresponding mask. To know its mask, a host sends the address mask request message to a router, which replies with the address mask reply message. This message contains the required mask for the host.
Router solicitation and advertisement: This message is used to determine whether the routers in a network are working properly. All the routers that receive router solicitation message from a host broadcast their routeing information through the ‘router advertisement message’.
Internet Group Message Protocol (IGMP): Internet group message protocol (IGMP) allows hosts to participate in multicasting. A message can be forwarded to a large number of recipients simultaneously using multicasting. Multicast routers are used for forwarding the multicast packets to hosts or other routers.
There are three types of IGMP messages. These are the query, the membership report and the leave report.

  1. The Query: Query messages are used to determine multicast groups of hosts or devices. They are of two types.
  2. Membership Report: When a host joins a multicast group, it sends a multicast report. Some time the IGMP router can function as queries, which can send a query message to the host. In such a condition, the host replies with a membership report message.
  3. Leave Report: When a host leaves a multicast group, it sends this message to all the members.

User Datagram Protocol (UDP): User datagram protocol (UDP) is a transport layer connection less protocol that uses port numbers to provide process-to-process communication. The protocol accepts smaller data units from the processes and delivers them to the receiver. If the UDP detects any kind of error in the data unit, it drops that unit. UDP sends each datagram independently. The individual datagram is not related to each other even if they come from the same source application and reach same destination application program. There are three stages; encapsulation, encapsulation, and queuing. In UDP, data is passed in the form of packets are called as user datagram’s. User datagram’s consists of 8-bytes header and data.
Data Link Control (DLC): Data link control (DLC) protocols are setup transmission protocols used at the data link layer. DLC protocols are two types i.e. Asynchronous and synchronous. Asynchronous protocols have no synchronisation between the sender and receiver during data transfer.

In synchronous transmission, the data packet contains the control information for synchronization. Two synchronous protocol used ate high-level data link control (HDLC) protocol and synchronous data link control (SDLC) protocol. These are bit-oriented protocol in which data frame are interpreted as series of bits. HDLC provides a data transmission mechanism at the data link layer. Data is encapsulated into the lower layers. HDLC has used both half-duplex and full-duplex communication. It ensures that the data is received error free without loss and in the correct order. SDLC protocol is a bit-oriented protocol invented by IBM and similar to HDLC. SDLC frame format is exactly same as that of HDLC. Earlier this protocol was used to link PCs to mainframe computers. Later on, Hewlett Packard (HP) adopted the DLC protocol for use by network printers.

HTTP (Hyper Text Transfer Protocol): Hypertext transfer protocol is a method of transmitting the information on the web. HTTP basically publishes and retrieves the HTTP pages on the World Wide Web. HTTP is a language that is used to communicate between the browser and web server. The information that is transferred using HTTP can be plain text, audio, video, images, and hypertext. HTTP “11qssis a request/response protocol between the client and server. Many proxies, tunnels, and gateways can be existing between the web browser (client) and server (web server). An HTTP client initializes a request by establishing a TCP connection to a particular port on the remote host (typically 80 or 8080). An HTTP server listens on that port and receives a request message from the client. Upon receiving the request, the server sends back 200 OK messages, its own message, an error message or other messages.
POP3 (Post Office Protocol): In computing, e-mail clients such as (MS outlook, outlook express and thunderbird) use Post office Protocol to retrieve emails from the remote server over the TCP/IP connection. Nearly all the users of the Internet service providers use POP 3 in the email clients to retrieve the emails from the email servers. Most email applications use POP protocol.
SMTP (Simple Mail Transfer Protocol): SMTP stands for simple mail transfer protocols, it is a TCP/IP protocols that specify how computers exchange electronic mail (EMAIL).Most email systems and email clients use the SMTP protocol to send messages to one server to another. In configuring an email application, we need to configure POP, SMTP and IMAP protocols in our email software. SMTP is a simple, text based protocol and one or more recipient of the message is specified and then the message is transferred. SMTP connection is easily tested by the Telnet utility. Windows 2000 includes an SMTP mail client.SMTP is a simple ASCII protocol.
FTP (File Transfer Protocol): FTP or file transfer protocol is an internet service that enables an internet user to move a file from one computer to another computer situated anywhere in the world by using the internet. IN another word, FTP used to transfer (upload/download) data from one computer to another over the internet or through or computer network. FTP is a most common communication protocol for transferring the files over the internet. Typically, there are two computers are involved in the transferring the files a server and a client. After successfully connected with the server, the client computer can perform a number of the operations like downloading the files, uploading, renaming and deleting the files, creating the new folders etc. Virtually operating system supports FTP protocols.
IP (Internet Protocol): An Internet protocol (IP) is a unique address or identifier of each computer or communication devices on the network and internet. Any participating computer networking device such as routers, computers, printers, internet fax machines and switches may have their own unique IP address. Personal information about someone can be found by the IP address. Every domain on the internet must have a unique or shared IP address. IP is responsible for the addressing and sending of data from one computer to another.
DHCP (Dynamic Host Configuration Protocol): The DHCP or Dynamic Host Configuration Protocol is a set of rules used by a communication device such as a router, computer or network adapter to allow the device to request and obtain an IP address from a server which has a list of the larger number of addresses. DHCP is a protocol that is used by the network computers to obtain the IP addresses and other settings such as a gateway, DNS, subnet mask from the DHCP server. DHCP (Dynamic Host Configuration protocols ensures that all the IP addresses are unique and the IP address management is done by the server and not by the human. The assignment of the IP addresses is expired after the predetermined period of time.
IMAP (Internet Message Access Protocol): The Internet Message Access Protocol known as IMAP is an application layer protocol that is used to access to access the emails on the remote servers. POP3 and IMAP are the two most commonly used email retrieval protocols. Most of the email clients such as outlook express, thunderbird and MS outlooks support POP3 and IMAP. The email messages are generally stored on the email server and the users generally retrieve these messages whether by the web browser or email clients. IMAP is generally used in the large networks. IMAP allows users to access their messages instantly on their systems.
ARCNET is a local area network technology that uses token bus scheme for managing line sharing among the workstations. When a device on a network wants to send a message, it inserts a token that is set to 1 and when a destination device reads the message it resets the token to 0 so that the frame can be used by another device.
Fibre distributed data interface (FDDI) provides a standard for data transmission in a local area network that can extend a range of 200 kilometres. The FDDI uses token ring protocol as its basis. FDDI local area network can support a large number of users and can cover a large geographical area. FDDI uses fibre optic as a standard communication medium. FDDI uses dually attached token ring topology. An FDDI network contains two token rings and the primary ring offers the capacity of 100 Mb/s. FDDI is an ANSI standard network and it can support 500 stations in 2 kilometres.
LocalTalk: LocalTalk is a network protocol that was developed by Apple Computer, Inc. for Macintosh computers. The method used by LocalTalk is called CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). It is similar to CSMA/CD except that a computer signals its intent to transmit before it actually does so. LocalTalk adapters and special twisted pair cable can be used to connect a series of computers through the serial port. The Macintosh operating system allows the establishment of a peer-to-peer network without the need for additional software. With the addition of the server version of the AppleShare software, a client/server network can be established. The LocalTalk protocol allows for a linear bus, star, or tree topologies using twisted pair cable. A primary disadvantage of LocalTalk is speed. Its speed of transmission is only 230 Kbps.
The Token Ring protocol was developed by IBM in the mid-1980s. The access method used involves token-passing. In Token Ring, the computers are connected so that the signal travels through the network from one computer to another in a logical ring. A single electronic token moves around the ring from one computer to the next. If a computer does not have information to transmit, it simply passes the token on to the next workstation. If a computer wishes to transmit and receives an empty token, it attaches data to the token. The token then proceeds around the ring until it comes to the computer for which the data is meant. At this point, the data is captured by the receiving computer. The Token Ring protocol requires a star-wired ring using twisted pair or fibre optic cable. It can operate at transmission speeds of 4 Mbps or 16 Mbps. Due to the increasing popularity of Ethernet, the use of Token Ring in school environments has decreased.
Asynchronous Transfer Mode (ATM) is a network protocol that transmits data at a speed of 155 Mbps and higher. ATM works by transmitting all data in small packets of a fixed size; whereas, other protocols transfer variable length packets. ATM supports a variety of media such as video, CD-quality audio, and imaging. ATM employs a star topology, which can work with fibre optic as well as twisted pair cable. ATM is most often used to interconnect two or more local area networks. It is also frequently used by Internet Service Providers to utilise high-speed access to the Internet for their clients. As ATM technology becomes more cost-effective, it will provide another solution for constructing faster local area networks.
ETHERNET: The original Ethernet standard was developed in 1983 and had a maximum speed of 10 Mbps (phenomenal at the time) over coaxial cable. The Ethernet protocol allows for bus, star, or tree topologies, depending on the type of cables used and other factors. This heavy coaxial cabling was expensive to purchase, install, and maintain, and very difficult to retrofit into existing facilities.
The current standards are now built around the use of twisted pair wire. Common twisted pair standards are 10BaseT, 100BaseT, and 1000BaseT. The number (10, 100, 1000) and for the speed of transmission (10/100/1000 megabits per second); the “Base” stands for “baseband” meaning it has full control of the wire on a single frequency, and the “T” stands for “twisted pair” cable. Fibre 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 concentrators/hubs and network interface cards. In addition, category 5 twisted pair or fibre optic cable is necessary. Fast Ethernet standards include:

  • 100BaseT – 100 Mbps over 2-pair category 5 or better UTP cable.
  • 100BaseFX – 100 Mbps over fibre cable.
  • 100BaseSX -100 Mbps over multimode fibre cable.
  • 100BaseBX – 100 Mbps over single mode fibre 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 fibre optic cabling and copper.

  • 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.
Ethernet Protocol Summary:
Twisted Pair, Coaxial, Fiber
10 Mbps
Fast Ethernet
Twisted Pair, Fiber
100 Mbps
Gigabit Ethernet
Twisted Pair, Fiber
1000 Mbps

The Ethernet standards continue to evolve. with 10 Gigabit Ethernet (10,000 Mbps) and 100 Gigabit Ethernet (100,000 Mbps).



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