Computer Network

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COMPUTER NETWORK

Shabir Ali, Assistant Professor, GLNA Institute of technology.

Data Communication
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The Exchange of information or data between two devices via some form of transmission medium such as wire cable.

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Component
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Message Sender Receiver Transmission Medium Protocol

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Data Representation
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Text Number Images Audio Video

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Data Flow
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Simplex--- One-Way for ex. Monitor, printer etc. Half Duplex² one can send at a time for ex. Walkie-Takie Full Duplex² both can receive and send data simultaneously. For Ex. Telephone.
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Physical Structure
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Type of Connection
† Point


to Point

The entire capacity of entire channel is reserved The capacity of channel shared.

† Multipoint


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Physical Topology
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Mesh Topology

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Physical Topology
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Star Topology

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Physical Topology
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Bus Topology

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Physical Topology
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Ring Topology

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Physical Topology
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Hybrid Topology

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Catagories of network
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LAN (Local Area Network)
† With

in building, office or campus. † LAN size is limited to few kilometers † Early LAN had 4-16 Mbps range † Today 100-1000 Mbps.

MAN(Metropolitan) WAN (Wide Area network)

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MAN
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Town or cities, Regional offices

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WAN(Wide Area Network)
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LAN
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A local area network is a communication network that interconnects a variety of data communicating devices within a small geographic area and broadcasts data at high data transfer rates with very low error rates Since the local area network first appeared in the 1970s, its use has become widespread in commercial and academic environments

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Primary Function of Local Area Networks (continued)
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Connecting Devices

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Hubs/ layer 1 switch
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Hub interconnects two or more workstations into a local area network When a workstation transmits to a hub, hub immediately resends the data frame out to all connecting links Layer 1 switch

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Hubs (continued.. )
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Hubs are classified as Layer 1 (physical layer) devices in the OSI model. At the physical layer, hubs support little in the way of sophisticated networking. Hubs do not read any of the data passing through them and are not aware of their source or destination. A hub simply receives incoming Ethernet frames, regenerates the electrical signal, and broadcasts these packets out to all other devices on the network.
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Hubs (continued.. )
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HUB(continued..)
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A network hub, or repeater, is a fairly unsophisticated network device. Hubs do not manage any of the traffic that comes through them. Any packet entering a port is broadcast out or "repeated" on every other port, except for the port of entry. Since every packet is repeated on every other port, packetcollisions result, which slows down the network.

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Bridges/ Layer 2 switch
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A bridge (or bridge-like device) can be used to connect two similar LANs, such as two CSMA/CD LANs Can also be used to connect two closely similar LANs, such as a CSMA/CD LAN and a token ring LAN. Examines destination address in a frame and either forwards this frame onto next LAN or does not

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Bridges (continued)
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Examines source address in a frame and places this address in a routing table, to be used for future routing decisions A network bridge, operating at the Media Access Control (MAC) sublayer of the data link layer, may interconnect a small number of devices in a home or the office. This is a trivial case of bridging, in which the bridge learns the MAC address of each connected device.
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Bridges (continued)
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Transparent Bridge
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A bridge observes each frame that arrives at a port, extracts the source address from the frame, and places that address in the port·s routing table A transparent bridge is found with CSMA/CD LANs

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Transparent Bridge (continued)
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Transparent Bridge (continued)
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Switches (Layer 2)
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A combination of hub and bridge Can interconnect two or more workstations, but like a bridge, it observes traffic flow and learns When a frame arrives at a switch, switch examines destination address and forwards frame out the one necessary connection Workstations that connect to a hub are on a shared segment Workstations that connect to a switch are on a switched segment
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Switches (continued)
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Switches (continued)
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Router / layer 3 switch
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Routers forward data packets across computer networks. If the router finds a match in its address tables, it routes it to that destination address.

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Router (continued)
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Router table
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Source Address

Destination Address

Network id

Network Mask

Source Physical Address

Destin. Physical Address

Port or Interface

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Network
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Virtual LANs
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Virtual LAN (VLAN) ² logical subgroup within a LAN that is created via switches and software rather than by manually moving wiring from one network device to another Even though employees and their actual computer workstations may be scattered throughout the building, LAN switches and VLAN software can be used to create a ´network within a networkµ

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Wired Ethernet
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Most common form of LAN today Star-wired bus is most common topology but bus topology still not totally dead yet Comes in many forms depending upon medium used and transmission speed and technology

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Wired Ethernet (continued)
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Originally, CSMA/CD was 10 Mbps Then 100 Mbps was introduced
† Most

NICs sold today are 10/100 Mbps

Then 1000 Mbps (1 Gbps) was introduced 10 Gbps is now being installed in high-end applications

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Wired Ethernet (continued)
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1000 Mbps introduces a few interesting wrinkles:
† Transmission

is full-duplex (separate transmit and receive), thus no collisions † Prioritization is possible using 802.1p protocol


Topology can be star or mesh (for trunks)

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Wired Ethernet (continued)
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OSI Model

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Open Systems Interconnection (OSI) is a set of internationally recognized, non-proprietary standards for networking and for operating system involved in networking functions.

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7 Layers
7. Application Layer
6. 5. 4. 3. 2. 1.
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Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer
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Tasks involved in sending letter
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LAYER 7 ± The APPLICATION Layer
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The top layer of the OSI model Provides a set of interfaces for sending and receiving applications to gain access to and use network services, such as: networked file transfer, message handling and database query processing.

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Application Layer
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Network virtual terminal File transfer, access and management Mail services Directory services

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

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LAYER 6 ± The PRESENTATION Layer
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Manages data-format information for networked communications (the network¶s translator) For outgoing messages, it converts data into a generic format for network transmission; for incoming messages, it converts data from the generic network format to a format that the receiving application can understand This layer is also responsible for certain protocol conversions, data encryption/decryption, or data compression/decompression A special software facility called a ³redirector´ operates at this layer to determine if a request is network related on not and forward network-related requests to an appropriate network resource

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Presentation layer
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Translation Encryption Compression

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

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LAYER 5 ± The SESSION Layer
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Enables two networked resources to hold ongoing communications (called a session) across a network Applications on either end of the session are able to exchange data for the duration of the session This layer is: Responsible for initiating, maintaining and terminating sessions Responsible for security and access control to session information (via session participant identification) Responsible for synchronization services, and for checkpoint services
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Dialog Control Synchronization Check point

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The session layer is responsible for dialog control and synchronization.

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LAYER 4 ± The TRANSPORT Layer
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Manages the transmission of data across a network Manages the flow of data between parties by segmenting long data streams into smaller data chunks (based on allowed ³packet´ size for a given transmission medium) Reassembles chunks into their original sequence at the receiving end Provides acknowledgements of successful transmissions and requests resends for packets which arrive with errors
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The transport layer is responsible for the delivery of a message from one process to another.

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LAYER 3 ± The NETWORK Layer
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Handles addressing messages for delivery, as well as translating logical network addresses and names into their physical counterparts Responsible for deciding transmissions between computers how to route

This layer also handles the decisions needed to get data from one point to the next point along a network path This layer also handles packet switching and network congestion control
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The network layer is responsible for the delivery of individual packets from the source host to the destination host.

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LAYER 2 ± The DATA LINK Layer
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Handles special data frames (packets) between the Network layer and the Physical layer At the receiving end, this layer packages raw data from the physical layer into data frames for delivery to the Network layer At the sending end this layer handles conversion of data into raw formats that can be handled by the Physical Layer
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The data link layer is responsible for moving frames from one hop (node) to the next.

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LAYER 1 ± The PHYSICAL Layer
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Converts bits into electronic signals for outgoing messages Converts electronic signals into bits for incoming messages This layer manages the interface between the the computer and the network medium (coax, twisted pair, etc.) This layer tells the driver software for the MAU (media attachment unit, ex. network interface cards (NICs, modems, etc.)) what needs to be sent across the medium The bottom layer of the OSI model
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The physical layer is responsible for movements of individual bits from one hop (node) to the next.

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Remember
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A convenient aid for remembering the OSI layer names is to use the first letter of each word in the phrase: All People Seem To Need Data Processing

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TCP/IP Model

TCP/IP MODEL

TCP/IP Model

OSI & TCP/IP Models

OSI: Open Systems Interconnect

OSI and Protocol Stack
66 OSI Model 7th Application Layer 6th Presentation Layer 5th Session Layer 4th Transport Layer 3rd Network Layer 2nd Link Layer Link Layer 1st Physical Layer Transport Layer Network Layer Application Layer TCP/IP Hierarchy Protocols

Link Layer : includes device driver and network interface card Network Layer : handles the movement of packets, i.e. Routing Transport Layer : provides a reliable flow of data between two hosts Application Layer : handles the details of the particular application

Adressing
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Class A 1byte net id and 3 byte for host id. Class B 2 for net id and 2 for host id Class C for 3 for net id and 1 for host id Class D for multicast. Class E reserved for future use.

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