Network protocols


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Network protocols

  1. 1. Network Protocols Govern the Communications between Computers on a NetworkA protocol is a set of rules that governs the communications betweencomputers on a network. These rules include guidelines that regulate thefollowing characteristics of a network: access method, allowed physicaltopologies, types of cabling, and speed of data transfer.Types of Network ProtocolsThe most common network protocols are: Ethernet Local Talk Token Ring FDDI ATMThe follow is some common-used network symbols to draw differentkinds of network protocols.
  2. 2. EthernetThe Ethernet protocol is by far the most widely used. Ethernet uses anaccess method called CSMA/CD (Carrier Sense Multiple Access/CollisionDetection). This is a system where each computer listens to the cablebefore sending anything through the network. If the network is clear, thecomputer will transmit. If some other node is already transmitting on thecable, 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 andwaits a random amount of time before attempting to retransmit. Withthis access method, it is normal to have collisions. However, the delaycaused by collisions and retransmitting is very small and does notnormally affect the speed of transmission on the network.
  3. 3. The Ethernet protocol allows for linear bus, star, or tree topologies. Datacan be transmitted over wireless access points, twisted pair, coaxial, orfiber optic cable at a speed of 10 Mbps up to 1000 Mbps.Fast EthernetTo allow for an increased speed of transmission, the Ethernet protocolhas developed a new standard that supports 100 Mbps. This iscommonly called Fast Ethernet. Fast Ethernet requires the use ofdifferent, more expensive network concentrators/hubs and networkinterface cards. In addition, category 5 twisted pair or fiber optic cable isnecessary. Fast Ethernet is becoming common in schools that have beenrecently wired.Local TalkLocal Talk is a network protocol that was developed by Apple Computer,Inc. for Macintosh computers. The method used by Local Talk is calledCSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). It issimilar to CSMA/CD except that a computer signals its intent to transmitbefore it actually does so. Local Talk adapters and special twisted paircable can be used to connect a series of computers through the serialport. The Macintosh operating system allows the establishment of a
  4. 4. peer-to-peer network without the need for additional software. With theaddition of the server version of AppleShare software, a client/servernetwork can be established.The Local Talk protocol allows for linear bus, star, or tree topologies usingtwisted pair cable. A primary disadvantage of Local Talk is speed. Itsspeed of transmission is only 230 Kbps.Token RingThe Token Ring protocol was developed by IBM in the mid-1980s. Theaccess method used involves token-passing. In Token Ring, thecomputers are connected so that the signal travels around the networkfrom one computer to another in a logical ring. A single electronic tokenmoves around the ring from one computer to the next. If a computerdoes not have information to transmit, it simply passes the token on tothe next workstation. If a computer wishes to transmit and receives anempty token, it attaches data to the token. The token then proceedsaround the ring until it comes to the computer for which the data ismeant. At this point, the data is captured by the receiving computer. TheToken Ring protocol requires a star-wired ring using twisted pair or fiberoptic 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
  5. 5. school environments has decreased.FDDIFiber Distributed Data Interface (FDDI) is a network protocol that is usedprimarily to interconnect two or more local area networks, often overlarge distances. The access method used by FDDI involves token-passing.FDDI uses a dual ring physical topology. Transmission normally occurs onone of the rings; however, if a break occurs, the system keepsinformation moving by automatically using portions of the second ring tocreate a new complete ring. A major advantage of FDDI is speed. Itoperates over fiber optic cable at 100 Mbps.ATMAsynchronous Transfer Mode (ATM) is a network protocol that transmitsdata at a speed of 155 Mbps and higher. ATM works by transmitting alldata in small packets of a fixed size; whereas, other protocols transfervariable length packets. ATM supports a variety of media such as video,CD-quality audio, and imaging. ATM employs a star topology, which canwork with fiber 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 utilize
  6. 6. high-speed access to the Internet for their clients. As ATM technologybecomes more cost-effective, it will provide another solution forconstructing faster local area networks.Gigabit EthernetThe most recent development in the Ethernet standard is a protocol thathas a transmission speed of 1 Gbps. Gigabit Ethernet is primarily used forbackbones on a network at this time. In the future, it will probably beused for workstation and server connections also. It can be used withboth fiber optic cabling and copper. The 1000BaseTX, the copper cableused for Gigabit Ethernet, is expected to become the formal standard in1999.Compare the Network ProtocolsProtocol Cable Speed Topology Twisted Pair, Coaxial, Linear Bus, Star,Ethernet 10 Mbps Fiber TreeFast Twisted Pair, Fiber 100 Mbps StarEthernetLocal Talk Twisted Pair .23 Mbps Linear Bus or StarToken Ring Twisted Pair 4 Mbps - 16 Star-Wired Ring
  7. 7. MbpsFDDI Fiber 100 Mbps Dual ring Linear Bus, Star,ATM Twisted Pair, Fiber 155-2488 Mbps TreeNetwork Diagramming SoftwareEdraw Network Diagrammer is a new, rapid and powerful network designsoftware for network drawings with rich examples and templates. Easy todraw network topology, Cisco network design diagram, LAN/WANdiagram, network cabling diagrams, active directory, network planformand physical network diagram.Network Protocol OverviewThe OSI model, and any other network communication model, providesonly a conceptual framework for communication between computers,but the model itself does not provide specific methods ofcommunication. Actual communication is defined by variouscommunication protocols. In the context of data communication, aprotocol is a formal set of rules, conventions and data structure thatgoverns how computers and other network devices exchangeinformation over a network. In other words, a protocol is a standardprocedure and format that two data communication devices must
  8. 8. understand, accept and use to be able to talk to each other.In modern protocol design, protocols are "layered" according to the OSI7 layer model or a similar layered model. Layering is a design principlewhich divides the protocol design into a number of smaller parts, eachpart accomplishing a particular sub-task and interacting with the otherparts of the protocol only in a small number of well-defined ways.Layering allows the parts of a protocol to be designed and tested withouta combinatorial explosion of cases, keeping each design relatively simple.Layering also permits familiar protocols to be adapted to unusualcircumstances.The header and/or trailer at each layer reflect the structure of theprotocol. Detailed rules and procedures of a protocol or protocol groupare often defined by a lengthy document. For example, IETF uses RFCs(Request for Comments) to define protocols and updates to theprotocols.A wide variety of communication protocols exists. These protocols weredefined by many different standard organizations throughout the worldand by technology vendors over years of technology evolution anddevelopment. One of the most popular protocol suites is TCP/IP, which is
  9. 9. the heart of Internetworking communications. The IP, the InternetProtocol, is responsible for exchanging information between routers sothat the routers can select the proper path for network traffic, while TCPis responsible for ensuring the data packets are transmitted across thenetwork reliably and error free. LAN and WAN protocols are also criticalprotocols in network communications. The LAN protocols suite is for thephysical and data link layers of communications over various LAN mediasuch as Ethernet wires and wireless radio waves. The WAN protocol suiteis for the lowest three layers and defines communication over variouswide-area media, such as fiber optic and copper cables.Network communication has slowly evolved. Todays new technologiesare based on the accumulation over years of technologies, which may beeither still existing or obsolete. Because of this, the protocols whichdefine the network communication are highly inter-related. Manyprotocols rely on others for operation. For example, many routingprotocols use other network protocols to exchange information betweenrouters.In addition to standards for individual protocols in transmission, thereare now also interface standards for different layers to talk to the onesabove or below (usually operating system specific). For example:
  10. 10. Winsock and Berkeley sockets between layers 4 and 5; NDIS and ODIbetween layers 2 and 3.The protocols for data communication cover all areas as defined in theOSI model. However, the OSI model is only loosely defined. A protocolmay perform the functions of one or more of the OSI layers, whichintroduces complexity to understanding protocols relevant to the OSI 7layer model. In real-world protocols, there is some argument as to wherethe distinctions between layers are drawn; there is no one black andwhite answer.To develop a complete technology that is useful for the industry, veryoften a group of protocols is required in the same layer or across manydifferent layers. Different protocols often describe different aspects of asingle communication; taken together, these form a protocol suite. Forexample, Voice over IP (VOIP), a group of protocols developed by manyvendors and standard organizations, has many protocols across the 4 toplayers in the OSI model.Protocols can be implemented either in hardware or software or amixture of both. Typically, the lower layers are implemented in hardware,with the higher layers being implemented in software.
  11. 11. Protocols could be grouped into suites (or families, or stacks) by theirtechnical functions, or origin of the protocol introduction, or both. Aprotocol may belong to one or multiple protocol suites, depending onhow you categorize it. For example, the Gigabit Ethernet protocol IEEE802.3z is a LAN (Local Area Network) protocol and it can also be used inMAN (Metropolitan Area Network) communications.Most recent protocols are designed by the IETF for Internetworkingcommunications and by the IEEE for local area networking (LAN) andmetropolitan area networking (MAN). The ITU-T contributes mostly towide area networking (WAN) and telecommunications protocols. ISO hasits own suite of protocols for internetworking communications, which ismainly deployed in European countries.