CBCN4103CBCN4103

Open Systems Interconnection (OSI) is a t d d d i ti " f d l" fstandard description or "reference model" for

how messages should be transmitted between any two points in a y ptelecommunication network. Its purpose is to guide product implementers so that their products will consistently work with otherproducts will consistently work with other products.OSI is an ISO Standard: OSI was officially adopted as an international standard by the International Organisation of Standards (ISO).

Main Idea in OSI: the process of i ti b t t d i t icommunication between two end points in a

telecommunication network can be divided into layers, with each layer adding its own set y , y gof special, related functions.OSI is the most widely used method for talking about network communicationstalking about network communications. However, remember that it is only a theoretical model that defines standards for programmers and network administrators, not a model of actual physical layers.

7. Application Layer All7. Application Layer

6. Presentation LayerAll People

5. Session Layer

4. Transport Layer

Seem To p y

3. Network Layer Need Data

2. Data Link Layer1. Physical Layer

Data Processing

Layer x on one machine communicates with layer x on another machine is called Peer-to-yPeer Processes.Interfaces between Layers◦ Each interface defines what information and

services a layer must provide for the layer above it.◦ Well defined interfaces and layer functions provide e de ed te aces a d aye u ct o s p o de

modularity to a networkOrganizations of the layersN t k t l L 1 2 3◦ Network support layers : Layers 1, 2, 3

◦ User support layer : Layer 5, 6, 7It allows interoperability among unrelated software systems

◦ Transport layer (Layer 4) : links the two subgroups◦ Transport layer (Layer 4) : links the two subgroups

The data portion of a packet at level N-1 carries the whole packet from level N. The concept is called encapsulationconcept is called encapsulation.

Physical layer coordinates the functions required to transmit a bit stream over a physical medium.

The physical layer is responsible for movements p y y pof individual bits from one hop (node) to the next.

Physical layer is concerned with the following:(deal with the mechanical and electrical specification of the primary connections: cable, connector)◦ Physical characteristics of interfaces and medium◦ Representation of bitsep ese tat o o b ts◦ Data rate : transmission rate◦ Synchronization of bits◦ Line configurationLine configuration◦ Physical topology◦ Transmission mode

The data link layer is responsible for moving frames from one hop (node) to the next.

Major duties◦ Framing

Physical addressing◦ Physical addressing◦ Flow control◦ Error control◦ Access control

Hop-to-hop (node-to-node) delivery

The network layer is responsible for the delivery of individual packets from the source h h d i i hhost to the destination host.

Logical addressing (e.g. IP Address)Routing

The transport layer is responsible for the delivery of a message from one process to y g panother.

Service port addressingSegmentation and reassemblyConnection controlFlow controlError control

The session layer is responsible for dialog control and synchronization.

The session layer allows users on different machines to establish sessions between them.This layer maintains a groundwork or connection between the nodes on the network so that when two applications neednetwork so that when two applications need to communicate or share data over the network, the Session layer establishes anetwork, the Session layer establishes a communication session between them.A session might be used to log into a remote g gtime-sharing system or to transfer a file between two machines.

The presentation layer is responsible for translation, compression, and encryption

The application layer is responsible for providing services to the user.

The major duties of the application◦ Network virtual terminal◦ File transfer access and managementFile transfer, access, and management◦ Mail services◦ Directory services

Provides a common language or reference point between network professionalsbetween network professionals Divides networking tasks into logical layers for easier comprehension Allows specialization of features at different levels Aids in troubleshootingAids in troubleshooting Promotes standards interoperability between networks and devices P id d l i i ki fProvides modularity in networking features (developers can change features without changing the entire approach)

OSI layers are theoretical and do not actually perform real functions. Industry implementations rarely have a layer-to layer correspondence with the OSI layersto-layer correspondence with the OSI layers. Different protocols within the stack perform different functions that help send or receivedifferent functions that help send or receive the overall message. A particular protocol implementation may not p p p yrepresent every OSI layer (or may spread across multiple layers).

TCP/IP stands for Transmission Control Protocol/Internet Protocol (TCP/IP)IP roughly corresponds to the Network layer (Layer 3) in the OSI model,Wh TCP d t th T tWhereas TCP corresponds to the Transport layer (layer 4) in OSI model.The U S Department of Defense (DoD)The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any t a ted a et o t at cou d su e a yconditions.

The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host to network internethaving four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that / p , ythe TCP/IP protocol suite is made of five layers: physical, data link, network, transport,

d li tiand application.

Handles high-level protocols, issues of representation encoding and dialog controlrepresentation, encoding, and dialog control.

The TCP/IP protocol suite combines all / papplication related issues into one layer and ensures this data is properly packaged before passing it on to the next layerpassing it on to the next layer.

Five basic services:S i l li i dSegmenting upper-layer application dataEstablishing end-to-end operationsSending segments from one end host toSending segments from one end host to another end hostEnsuring data reliabilityProviding flow control

The purpose of the Internet layer is to send packets from a network node and havepackets from a network node and have them arrive at the destination node independent of the path taken.

The network access layer is concerned withThe network access layer is concerned with all of the issues that an IP packet requires to actually make a physical link to the y p ynetwork media.It includes the LAN and WAN technology details and all the details contained in thedetails, and all the details contained in the OSI physical and data link layers.

Both have layers.yBoth have application layers, though they include very different services.Both have comparable transport and networkBoth have comparable transport and network layers.Packet-switched, not circuit-switched, technology is assumed.Networking professionals need to know both modelsmodels.

TCP/IP combines the presentation andTCP/IP combines the presentation and session layer into its application layer.TCP/IP combines the OSI data link and physical layers into one layerphysical layers into one layer.TCP/IP appears simpler because it has fewer layers.yTCP/IP transport layer using UDP does not always guarantee reliable delivery of packets as the transport layer in the OSI model doesas the transport layer in the OSI model does.

A protocol developed by Netscape. It is a whole new layer of protocol which operates above the Internet TCP protocol and below high level application protocolsbelow high-level application protocols

SSL uses TCP/IP on behalf of the higher-level protocols.Allows an SSL-enabled server to authenticate itself to an SSL enabled client;itself to an SSL-enabled client;Allows the client to authenticate itself to the server;server;Allows both machines to establish an encrypted connection.yp

SSL server authentication.SSL client authentication. (optional)An encrypted SSL connection or C fid i li Thi iConfidentiality. This protects against electronic eavesdropper.Integrity This protects against hackersIntegrity. This protects against hackers.

There exists a wide variety of software and hardware products that help network system administrators manage a network. Network management covers a wide area including:management covers a wide area, including:◦ Security: Ensuring that the network is protected

from unauthorised users.◦ Performance: Eliminating bottlenecks in the

network.◦ Reliability: Making sure the network is available toReliability: Making sure the network is available to

users and responding to hardware and software malfunctions.

Loss of connectivity (Link, Node, Interface)Duplicate IP address (Procedural)Intermittent (occurring at irregular intervals)

blproblemsNetwork configuration issuesPerformance problemsPerformance problems

Goal◦ To ensure that network users receive IT services with the

quality of service (QoS) that they expect

A Protocol that Facilitates the exchange of management information between network devices. To control and monitor status of networkTo control and monitor status of network devicesEnables network administrators to:Enables network administrators to:◦ Manage network performance◦ Find and solve network problems◦ Plan for network growth

SNMP works by sending messages, called protocol data units (PDUs) to different parts of aprotocol data units (PDUs), to different parts of a network.SNMP-compliant devices, called agents, store data about themselves in Management Information Bases (MIBs) a database of objects that can be monitored by a network management y gsystem.Both SNMP and RMON use standardised MIB formats that allows any SNMP and RMON tools toformats that allows any SNMP and RMON tools to monitor any device defined by a MIB and return this data to the SNMP requesters.

Extends the SNMP functionality without h i th t lchanging the protocol

Allows the monitoring of remote networks (internetwork management)(internetwork management)MAC-layer (layer 2 in OSI) monitoringWhereas SNMP gathers network data from a single type of Management Information Base (MIB), RMON defines nine additional MIBs that provide a much richer set of data aboutprovide a much richer set of data about network usage.

The fundamental function of the common M t I f ti S i El tManagement Information Service Element (CMISE) is the exchange of management information between two manager & agent g gentitiesCMISE is specified in two parts:

The common management information service◦ The common management information service (CMIS) which is a user interface specifying the services providedThe common management information protocol◦ The common management information protocol (CMIP) which specifies the protocol data unit (PDU) format and associated procedures