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Transcript
HIGHER COMPUTER NETWORKING Lesson 1 – Protocols and OSI What is a network protocol Description of the OSI model © McLean 2006 1 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 2006 2 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. Layer 7 Application Layer 6 Presentation Layer 5 Session Layer 4 Transport Layer 3 Network Layer 2 Data Link (MAC) Layer 1 Physical © McLean 2006 “Application layers” “Transport layers” 3 HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model 7 Application layer • 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, email, and so forth. • The user interacts with these directly. © McLean 2006 4 HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model 6 Presentation layer • 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. © McLean 2006 5 HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model 5 Session layer • 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). © McLean 2006 6 HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model 4 Transport layer 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. © McLean 2006 7 HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model 3 Network layer • 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). © McLean 2006 8 HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model 2 Data Link (MAC) layer • 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. © McLean 2006 9 HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model 1 Physical layer • 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. © McLean 2006 10 HIGHER COMPUTER NETWORKING The Open Systems Connection (OSI) model So, in summary… Type of communications Layer 7 Application Layer 6 Presentation Layer 5 Session Starts, stops session Layer 4 Transport Ensures delivery of entire file or message Layer 3 Network Layer 2 Data Link (MAC) Transmits packets via MAC address Layer 1 Physical Electrical signals and cabling © McLean 2006 e.g. email, ftp Encryption, data conversion Routes data over LANs or WANs via IP address 11