4 Communication Protocol

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A protocol is a set of rules and conventions.The sender and the receiver, the two key parties indata communication must agree on a common set of

rules protocol before they can communicate witheach other.

Two devices wishing to communicate witheach other cannot just begin data transmissionarbitrarily. That is, one device cannot simply startsending bit streams to the other. The two devicesmust agree on a set of rules before this transmissioncan begin.


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- Start and end link.

Link between two entity that want communicate only can be set up if from entities that tell entity that want contacted him will the meaning.

- Move the envoy pass

Protocol interpret synchronization rule so that each envoy thatdelivered by something entity will be accepted properly by entity.

- Control link.

Link must be controlled to ensure not arise deadlock.


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Layer of protocol:

Layer 7 (Application layer)

Layer 6 (Presentation layer)

Layer 5 (Session layer)

Layer 4 (Transport layer)

Layer 3 (Network layer)

Layer 2 (Data link layer)

Layer 1 (Physical layer)


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Physical layer.

The physical layer is concerned with sending raw bits betweenthe source and destination nodes, which in this case are adjacentnodes. To do this, the source and the destination nodes have toagree on a number of factors , such us, what voltage constitutes a bitvalue 0 , what voltage constitutes bit value 1.When thecommunication is in only one or both, or the direction simultaneously.

It also deals with the electrical and mechanical specification of thecable, connectors and interfaces such as RS232C and RS449.


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Data link layer.

The data link layer is transforms the physical layer,arrow transmission facility to a reliable link. It makes thephysical layer appear error free to the upper layer (network layer)


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Transport layer.

The transport layer is responsible for process to processdelivery of the entire message. The process is an applicationprogram running on a host. Whereas the network layer overseessource to destination delivery of individual packets, it does notrecognize any relationship between those packets. The transportlayer on the other hand ensures that we whole message arriversintact and in order, overseeing both error control and flow control atthe source to destination level.


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Session layer.

The session layer is the network dialog control. Theservice provided by the first three layers (physical, datalink, and network) are not sufficient for same process. Itsestablishes, maintains and synchronizes the interaction

among communicating system.


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Presentation layer

The presentation layer concerned with thesyntax and semantics of the informationexchanged between two systems.


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Application layer.

The application layer enable the user, whether human or software, to access the network. It providesuser interfaces and support for services such aselectronic mail, remote file excess and transfer, shareddata base management and other types distributedinformation services.


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The OSI model is structured on the seven layers.The usual manner in which these seven layers arerepresented is shown. Suppose host X wants to send amessage to another host Y. This message would travel viaa number of intermediate nodes. These intermediatenodes as well as X and Y are concerned with the threelowermost OSI layers, i.e. physical, data link and network.The other fours layers are used by the sender (X) and therecipient (Y) only. Therefore, they are called end-to-end

layers.


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Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer


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System Network Architecture ( SNA ) Concept

Systems Network Architecture (SNA) is IBM's proprietarynetworking architecture created in 1974. It is a complete protocolstack for interconnecting computers and their resources. SNAdescribes the protocol and is, in itself, not actually a program. The

implementation of SNA takes the form of various communicationspackages, most notably Virtual Telecommunications Access Method(VTAM) which is the mainframe package for SNA communications.SNA is still used extensively in banks and other financial transactionnetworks, as well as in many government.
http://en.wikipedia.org/wiki/IBMhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Protocol_stackhttp://en.wikipedia.org/wiki/Protocol_stackhttp://en.wikipedia.org/wiki/Computerhttp://en.wikipedia.org/wiki/VTAMhttp://en.wikipedia.org/wiki/VTAMhttp://en.wikipedia.org/wiki/Computerhttp://en.wikipedia.org/wiki/Protocol_stackhttp://en.wikipedia.org/wiki/Protocol_stackhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/IBM


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This expansion was deemed Advanced Peer-to-Peer Networking (APPN) and Advanced Program-to-ProgramCommunication (APPC). Advanced Peer-to-Peer Networking (APPN) represents IBM's second-generationSNA. In creating APPN, IBM moved SNA from ahierarchical, mainframe-centric environment to a peer-to-peer (P2P) networking environment. At the heart of

APPN is an IBM architecture that supports peer-based

communications, directory services, and routing betweentwo or more APPC systems that are not directly attached.
http://www.javvin.com/protocolAPPN.htmlhttp://www.javvin.com/protocolAPPN.htmlhttp://www.javvin.com/protocolAPPN.htmlhttp://www.javvin.com/protocolAPPN.htmlhttp://www.javvin.com/protocolAPPN.htmlhttp://www.javvin.com/protocolAPPN.htmlhttp://www.javvin.com/protocolAPPN.htmlhttp://www.javvin.com/protocolAPPN.html


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IBM SNA model has many similarities with the OSI 7layers model. However, SNA model has only 6 layers anddoes not define specific protocols for its physical controllayer. The physical control layer is assumed to beimplemented via other standards. The functions of eachSNA layer are described as follows:

Data link control (DLC) - Defines several protocols, including

the Synchronous Data Link Control (SDLC) protocol for hierarchical communication, and the Token Ring Networkcommunication protocol for LAN communication betweenpeers. SDLC provided a foundation for ISO HDSL and IEEE802.2.


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Path control - Performs many OSI network layer functions,including routing and datagram segmentation and reassembly(SAR)Transmission control - Provides a reliable end-to-endconnection service (similar to TCP), as well as encrypting and

decrypting servicesData flow control - Manages request and responseprocessing, determines whose turn it is to communicate,groups messages, and interrupts data flow on requestPresentation services - Specifies data-transformationalgorithms that translate data from one format to another,coordinate resource sharing, and synchronize transactionoperationsTransaction services - Provides application services in theform of programs that implement distributed processing or management services


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Physical control - Transmits bits over industry standardphysical/electrical circuits. SNA generally relies onindustry standard LAN and WAN specifications at thislayer, although specifications for channel attachmentsare unique to SNA.


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4 Communication Protocol