CBCN4103
Open Systems Interconnection (OSI) is a standard d description or "reference model" for how messages should be transmitted between any two points in a telecommunication network. Its purpose is to guide product implementers so that their products 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 communication between two end points in a telecommunication network can be divided into layers, with each layer adding its own set of special, related functions. OSI is the most widely used method for talking 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 6. Presentation Layer 5. Session Layer 4. Transport Layer All People Seem To 3. Network Layer Need 2. Data Link Layer 1. Physical Layer Data Processing
Layer x on one machine communicates with layer x on another machine is called Peer-to- Peer Processes. Interfaces between Layers Each interface defines what information and services a layer must provide for the layer above it. Well defined edinterfaces acesand layer functions cto spo provide modularity to a network Organizations of the layers Network support layers : Layers 1, 2, 3 User support layer : Layer 5, 6, 7 It allows interoperability among unrelated software systems 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 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 p of 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 ese of bits Data rate : transmission rate Synchronization of bits Line 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 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 host to the destination i host.
Logical addressing (e.g. IP Address) Routing
The transport layer is responsible for the delivery of a message from one process to another.
Service port addressing Segmentation and reassembly Connection control Flow control Error 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 need to communicate or share data over the network, the Session layer establishes a communication session between them. A session might be used to log into a remote time-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 management Mail services Directory services
Provides a common language or reference point between network professionals Divides networking tasks into logical layers for easier comprehension Allows specialization of features at different levels Aids in troubleshooting Promotes standards interoperability between networks and devices Provides 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 layers. Different protocols within the stack perform different functions that help send or receive the overall message. A particular protocol implementation may not represent 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, Whereas TCP corresponds to the Transport layer (layer 4) in OSI model. The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any conditions.
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, to internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application.
Handles high-level protocols, issues of representation, encoding, and dialog control. The TCP/IP protocol suite combines all application related issues into one layer and ensures this data is properly packaged before passing it on to the next layer.
Five basic services: Segmenting upper-layer application i data Establishing end-to-end operations Sending segments from one end host to another end host Ensuring data reliability Providing flow control
The purpose of the Internet layer is to send packets from a network node and have them arrive at the destination node independent of the path taken.
The network access layer is concerned with all of the issues that an IP packet requires to actually make a physical link to the network media. It includes the LAN and WAN technology details, and all the details contained in the OSI physical and data link layers.
Both have layers. Both have application layers, though they include very different services. Both have comparable transport and network layers. Packet-switched, not circuit-switched, technology is assumed. Networking professionals need to know both models.
TCP/IP combines the presentation and session layer into its application layer. TCP/IP combines the OSI data link and physical layers into one layer. TCP/IP appears simpler because it has fewer layers. TCP/IP transport layer using UDP does not always guarantee reliable delivery of packets as 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 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; Allows the client to authenticate itself to the server; Allows both machines to establish an encrypted connection.
SSL server authentication. SSL client authentication. (optional) An encrypted SSL connection or Confidentiality. i This protects against electronic eavesdropper. Integrity. 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: Security: Ensuring that the network is protected from unauthorised users. Performance: Eliminating bottlenecks in the network. Reliability: 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) problems Network configuration issues Performance 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 network devices 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 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 system. Both SNMP and RMON use standardised MIB formats 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 changing the protocol Allows the monitoring of remote networks (internetwork management) MAC-layer (layer 2 in OSI) monitoring Whereas 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 about network usage.
The fundamental function of the common Management Information Service Element (CMISE) is the exchange of management information between two manager & agent entities CMISE is specified in two parts: The common management information service (CMIS) which is a user interface specifying the services provided The common management information protocol (CMIP) which specifies the protocol data unit (PDU) format and associated procedures