William Stallings Data and Computer Communications Chapter 2 Protocols and Architecture

OSI - The Model zA layer model zEach layer performs a subset of the required communication functions zEach layer relies on the next lower layer to perform more primitive functions zEach layer provides services to the next higher layer zChanges in one layer should not require changes in other layers

The OSI Environment

OSI Layers (1) zPhysical yPhysical interface between devices xMechanical xElectrical xFunctional xProcedural zData Link yMeans of activating, maintaining and deactivating a reliable link yError detection and control yHigher layers may assume error free transmission

OSI Layers (2) zNetwork yTransport of information yHigher layers do not need to know about underlying technology yNot needed on direct links zTransport yExchange of data between end systems yError free yIn sequence yNo losses yNo duplicates yQuality of service

OSI Layers (3) zSession yControl of dialogues between applications yDialogue discipline yGrouping yRecovery zPresentation yData formats and coding yData compression yEncryption zApplication yMeans for applications to access OSI environment

How TCP/IP Works University of Brighton, Faculty of Information Technology, 8/24/2004

TCP/IP Model Layer 5 – Application zGives an application access to the communication environment. zExamples of protocols found at this layer: yTelnet, FTP (File Transfer Protocol), SNMP (Simple Network Management Protocol), HTTP (Hyper Text Transfer Protocol) and SMTP (Simple Mail Transfer Protocol).

TCP/IP Model Layer 4 - Transport zProvides an application layer delivery service. zThe two protocols found at the transport layer are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). zEither of these protocols are used by the application layer process, the choice depends on the application's transmission reliability requirements.

TCP/IP Model Layer 3 - Internet zResponsible for the routing and delivery of data across networks. zAllows communication across networks of the same and different types zCarries out translations to deal with dissimilar data addressing schemes. zIP (Internet Protocol) and ARP (Address Resolution Protocol) are both to be found at the Internet layer.

TCP/IP Model Layers 2 and 1 Network Access zThe combination of datalink and physical layers deals with pure hardware (wires, satellite links, network interface cards, etc.) and access methods such as CSMA/CD (carrier sensed multiple access with collision detection).

OSI Model