© McLean HIGHER COMPUTER NETWORKING Lesson 1 – Protocols and OSI What is a network protocol Description of the OSI model

© McLean HIGHER COMPUTER NETWORKING Introduction Protocols Are sets of rules that govern how two devices communicate and exchange data when connected over a network. Examples are TCP/IP, HTTP, FTP, SMTP etc.

© McLean HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model The OSI is a theoretical model that standardises network architecture and protocols within a seven layer hierarchy. PhysicalData Link (MAC)NetworkTransportSessionPresentationApplication Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 “Application layers” “Transport layers”

© McLean HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model Top level layer where users actually interact with applications that create the data that will be sent over the network. e.g. when using a web browser the browser requests a web page from a server Examples of application-layer programs include web browsers, ftp programs, telnet, , and so forth. The user interacts with these directly. 7 Application layer

© McLean HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model This layer is concerned with the actual format that the data is presented in. It is home to a number of data presentation standards including JPG, GIF, and MPEG. This layer is also usually responsible for data encryption and compression. 6 Presentation layer

© McLean HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model The responsibility of this layer is to create, manage, and terminate communication sessions between systems. Think of the session layer as a coordinator of communication between systems A variety of protocols exist at the session layer, including Remote Procedure Calls (RPCs), the Network File System (NFS), SQL, and the AppleTalk Zone Information Protocol (ZIP). 5 Session layer

© McLean HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model Its responsibilities include : segmenting data that comes from the upper layers establishing a connection between end-to-end systems that defines the parameters of the connection and ensuring that data actually gets to its destination in the correct order and error free Examples of protocols found at this layer include TCP and UDP. 4 Transport layer

© McLean HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model This layer is responsible for two main functions – network addressing and routing. It identifies systems uniquely on an internetwork, and also handles how to get from one part of the network to another. Most of the network configuration takes place, since protocols such as IP, IPX, and equipment such as routers work here Its concerned with ‘where am I going (the address), and how do I get there (the routing). 3 Network layer

© McLean HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model is concerned with how upper level data is formatted for transmission over a given network technology. For example, if your network is running Ethernet, this layer will format data packets accordingly, and follow the rules of Ethernet transmission on the network. Examples of Data Link protocols include Ethernet, Token Ring and FDDI At this layer, systems are generally identified by what is referred to as their hardware or MAC address. 2 Data Link (MAC) layer

© McLean HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model it defines the actual media and characteristics used to send the 1’s and 0’s over the network. This includes the actual wiring itself, the connectors used, voltage levels, maximum media distances and so forth. For example, a packet might start on twisted-pair wiring, move onto a wireless network, and then ultimately end up on fibre – each of which using different media and methods during the transfer process. In this case, copper wiring, then air, and then fibre optic cable. 1 Physical layer

© McLean HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model So, in summary… PhysicalData Link (MAC)NetworkTransportSessionPresentationApplication Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Type of communications e.g. , ftp Encryption, data conversion Starts, stops session Ensures delivery of entire file or message Routes data over LANs or WANs via IP address Transmits packets via MAC address Electrical signals and cabling