What is a Network?

What is a Network?

Spider Net(work)

Introduction to Computer Networks

INTRODUCTION TO COMPUTER NETWORKS

Computer Networks

Computer network connects two or more autonomous computers.

The computers can be geographically located anywhere.

Introduction to Computer Networks

LAN, MAN & WAN

Introduction to Computer Networks

Network in small geographical Area (Room, Building or a Campus) is called LAN (Local Area Network)

Network in a City is call MAN (Metropolitan Area Network)

Network spread geographically (Country or across Globe) is called WAN (Wide Area Network)

Metropolitan Area Networks (MAN)

Covers a geographicarea such as a town,

city or suburb

Middle groundbetween LAN and

WAN

MAN

Supports both dataand voice Private or public

network

Circuit Switching• Uses a dedicated communications path Connected sequence of physical links between nodes• Logical channel dedicated on each link Rapid transmission •The most common example of circuit switching is the telephone network

Technologies used in WAN

Packet Switching• Data are sent out in a sequence of small chunks called packets.• Packets are passed from node to node along a path leading from source to destination• Packet-switching networks are commonly used for terminal-to-terminal computer and computer-to- computer communications

Applications of Networks

Introduction to Computer Networks

Resource SharingHardware (computing resources, disks, printers)Software (application software)

Information SharingEasy accessibility from anywhere (files, databases)Search Capability (WWW)

CommunicationEmailMessage broadcast

Remote computingDistributed processing (GRID Computing)

Network Topology

The network topology defines the way in which computers, printers, and other devices are connected. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions.

Introduction to Computer Networks

Bus Topology

Commonly referred to as a linear bus, all the devices on a bus topology are connected by one single cable.

Introduction to Computer Networks

Star & Tree Topology

Introduction to Computer Networks

The star topology is the most commonly used architecture in Ethernet LANs. When installed, the star topology resembles spokes in a bicycle wheel.Larger networks use the extended star topology also called tree topology. When used with network devices that filter frames or packets, like bridges, switches, and routers, this topology significantly reduces the traffic on the wires by sending packets only to the wires of the destination host.

Ring Topology

Introduction to Computer Networks

A frame travels around the ring, stopping at each node. If a node wants to transmit data, it adds the data as well as the destination address to the frame.

The frame then continues around the ring until it finds the destination node, which takes the data out of the frame.

Single ring – All the devices on the network share a single cable

Dual ring – The dual ring topology allows data to be sent in both directions.

Mesh Topology

The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance. It is used in WANs to interconnect LANs and for mission critical networks like those used by banks and financial institutions. Implementing the mesh topology is expensive and difficult.

Introduction to Computer Networks

Network Components

Introduction to Computer Networks

Physical MediaInterconnecting DevicesComputersNetworking SoftwareApplications

Networking Media

Networking media can be defined simply as the means by which signals (data) are sent from one computer to another (either by cable or wireless means).

Introduction to Computer Networks

Networking Devices

Introduction to Computer Networks

HUB, Switches, Routers, Wireless Access Points, Modems etc.

Computers: Clients and ServersIn a client/server network arrangement, network services are located in a dedicated computer whose only function is to respond to the requests of clients.

The server contains the file, print, application, security, and other services in a central computer that is continuously available to respond to client requests.

Introduction to Computer Networks

What is Internet Protocol?

human protocols:“what’s the time?”“I have a question” introductions… specific msgs sent… specific actions takenwhen msgs received, orother events

network protocols:machines rather than humans all communication

activity in Internet governed by protocolsprotocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

A human protocol and a computer network protocol:

Networking Protocol: TCP/IP

Introduction to Computer Networks

Applications

E-mailSearchable Data (Web Sites)E-CommerceNews GroupsInternet Telephony (VoIP)Video ConferencingChat GroupsInstant Messengers Internet Radio

Introduction to Computer Networks

OSI Model

OSI MODEL

Communication ArchitectureStrategy for connecting host computers and other communicating equipment.Defines necessary elements for data communication between devices.A communication architecture, therefore, defines a standard for the communicating hosts.A programmer formats data in a manner defined by the communication architecture and passes it on to the communication software.Separating communication functions adds flexibility, for example, we do not need to modify the entire host software to include more communication devices.

OSI Model

Layer ArchitectureLayer architecture simplifies the network design.It is easy to debug network applications in a layered architecture network.The network management is easier due to the layered architecture.Network layers follow a set of rules, called protocol.The protocol defines the format of the data being exchanged, and the control and timing for the handshake between layers.

OSI Model

Open Systems Interconnection (OSI) Model

International standard organization (ISO) established a committee in 1977 to develop an architecture for computer communication.Open Systems Interconnection (OSI) reference model is the result of this effort.In 1984, the Open Systems Interconnection (OSI) reference model was approved as an international standard for communications architecture.Term “open” denotes the ability to connect any two systems which conform to the reference model and associated standards.

OSI Model

OSI Reference ModelThe OSI model is now considered the primary Architectural model for inter-computer communications.

The OSI model describes how information or data makes its way from application programmes (such as spreadsheets) through a network medium (such as wire) to another application programme located on another network.

The OSI reference model divides the problem of moving information between computers over a network medium into SEVEN smaller and more manageable problems .

This separation into smaller more manageable functions is known as layering.

OSI Model

OSI Reference Model: 7 Layers

OSI Model

OSI: A Layered Network ModelThe process of breaking up the functions or tasks of networking into layers reduces complexity.Each layer provides a service to the layer above it in the protocol specification. Each layer communicates with the same layer’s software or hardware on other computers. The lower 4 layers (transport, network, data link and physical —Layers 4, 3, 2, and 1) are concerned with the flow of data from end to end through the network. The upper four layers of the OSI model (application, presentation and session—Layers 7, 6 and 5) are orientated more toward services to the applications. Data is Encapsulated with the necessary protocol information as it moves down the layers before network transit.

OSI Model

Physical LayerProvides physical interface for transmission of information.

Defines rules by which bits are passed from one system to another on a physical communication medium.Covers all - mechanical, electrical, functional and procedural - aspects for physical communication.Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications.

OSI Model

Data Link LayerData link layer attempts to provide reliable communication over the physical layer interface.

Breaks the outgoing data into frames and reassemble the received frames.Create and detect frame boundaries.Handle errors by implementing an acknowledgement and retransmission scheme.Implement flow control.Supports points-to-point as well as broadcast communication.Supports simplex, half-duplex or full-duplex communication.

OSI Model

Network LayerImplements routing of frames (packets) through the network.

Defines the most optimum path the packet should take from the source to the destinationDefines logical addressing so that any endpoint can be identified. Handles congestion in the network.Facilitates interconnection between heterogeneous networks (Internetworking).The network layer also defines how to fragment a packet into smaller packets to accommodate different media.

OSI Model

Transport LayerPurpose of this layer is to provide a reliable mechanism for the exchange of data between two processes in different computers.

Ensures that the data units are delivered error free.Ensures that data units are delivered in sequence.Ensures that there is no loss or duplication of data units.Provides connectionless or connection oriented service.Provides for the connection management.Multiplex multiple connection over a single channel.

OSI Model

Session LayerSession layer provides mechanism for controlling the dialogue between the two end systems. It defines how to start, control and end conversations (called sessions) between applications.

This layer requests for a logical connection to be established on an end-user’s request.Any necessary log-on or password validation is also handled by this layer.Session layer is also responsible for terminating the connection.This layer provides services like dialogue discipline which can be full duplex or half duplex.Session layer can also provide check-pointing mechanism such that if a failure of some sort occurs between checkpoints, all data can be retransmitted from the last checkpoint.

OSI Model

Presentation LayerPresentation layer defines the format in which the data is to be exchanged between the two communicating entities. Also handles data compression and data encryption (cryptography).

OSI Model

Application LayerApplication layer interacts with application programs and is the highest level of OSI model.Application layer contains management functions to support distributed applications.Examples of application layer are applications such as file transfer, electronic mail, remote login etc.

OSI Model

OSI in ActionA message begins at the top application layer and moves down the OSI layers to the bottom physical layer. As the message descends, each successive OSI model layer adds a header to it. A header is layer-specific information that basically explains what functions the layer carried out. Conversely, at the receiving end, headers are striped from the message as it travels up the corresponding layers.

OSI Model

TCP/IP Model

TCP/IP MODEL

OSI & TCP/IP Models

TCP/IP Model

TCP/IP Model

TCP/IP Model

Application LayerApplication programs using the network

Transport Layer (TCP/UDP)Management of end-to-end message transmission,

error detection and error correction

Network Layer (IP)Handling of datagrams : routing and congestion

Data Link LayerManagement of cost effective and reliable data delivery,

access to physical networks

Physical LayerPhysical Media

Physical Media

PHYSICAL MEDIA

Physical Media

Physical Media

Physical MediaCopper

Coaxial Cable - Thick or ThinUnshielded Twisted Pair - CAT 3,4,5,5e&6

Optical FiberMultimodeSinglemode

WirelessShort RangeMedium Range (Line of Sight)Satellite

Physical Media

Copper Media: Coaxial CableCoaxial cable is a copper-cored cable surrounded by a heavy shielding and is used to connect computers in a network.

Outer conductor shields the inner conductor from picking up stray signal from the air.

High bandwidth but lossy channel.

Repeater is used to regenerate the weakened signals.

Physical Media

Category Impedance Use

RG-59 75 W Cable TV

RG-58 50 W Thin Ethernet

RG-11 50 W Thick Ethernet

Copper Media: Twisted PairTwisted-pair is a type of cabling that is used for telephone communications and most modern Ethernet networks.

A pair of wires forms a circuit that can transmit data. The pairs are twisted to provide protection against crosstalk, the noise generated by adjacent pairs.

There are two basic types, shielded twisted-pair (STP) and unshielded twisted-pair (UTP).

Physical Media

Shielded Twisted Pair (STP)

Physical Media

Unshielded Twisted Pair (UTP)

Physical Media

Unshielded Twisted Pair (UTP)Consists of 4 pairs (8 wires) of insulated copper wires typically about 1 mm thick.The wires are twisted together in a helical form. Twisting reduces the interference between pairs of wires.High bandwidth and High attenuation channel.Flexible and cheap cable.Category rating based on number of twists per inch and the material usedCAT 3, CAT 4, CAT 5, Enhanced CAT 5 and now CAT 6.

Physical Media

Categories of UTPUTP comes in several categories that are based on the number of twists in the wires, the diameter of the wires and the material used in the wires. Category 3 is the wiring used primarily for telephone connections.Category 5e and Category 6 are currently the most common Ethernet cables used.

Physical Media

Categories of UTP: CAT 3

Bandwidth 16 Mhz11.5 dB Attenuation100 ohms ImpedanceUsed in voice applications and 10baseT (10Mbps) Ethernet

Physical Media

Categories of UTP: CAT 4

20 MHz Bandwidth7.5 dB Attenuation100 ohms ImpedanceUsed in 10baseT (10Mbps) Ethernet

Physical Media

Categories of UTP: CAT 5

100 MHz Bandwidth24.0 dB Attenuation100 ohms ImpedanceUsed for high-speed data transmissionUsed in 10BaseT (10 Mbps) Ethernet & Fast Ethernet (100 Mbps)

Physical Media

Categories of UTP: CAT 5e

150 MHz Bandwidth24.0 dB Attenuation100 ohms ImpedanceTransmits high-speed dataUsed in Fast Ethernet (100 Mbps), Gigabit Ethernet (1000 Mbps) & 155 Mbps ATM

Physical Media

Categories of UTP: CAT 6

250 MHz Bandwidth19.8 dB Attenuation100 ohms ImpedanceTransmits high-speed dataUsed in Gigabit Ethernet (1000 Mbps) & 10 Gig Ethernet (10000 Mbps)

Physical Media

Fiber Media

Optical fibers use light to send information through the optical medium.It uses the principal of total internal reflection.Modulated light transmissions are used to transmit the signal.

Physical Media

Total Internal Reflection

Physical Media

Fiber MediaLight travels through the optical media by the way of total internal reflection. Modulation scheme used is intensity modulation.Two types of Fiber media :

MultimodeSinglemode

Multimode Fiber can support less bandwidth than Singlemode Fiber.Singlemode Fiber has a very small core and carry only one beam of light. It can support Gbps data rates over > 100 Km without using repeaters.

Physical Media

Single and Multimode FiberSingle-mode fiber

Carries light pulses along single pathUses Laser Light Source

Multimode fiberMany pulses of light generated by LED travel at different angles

Physical Media

Fiber MediaThe bandwidth of the fiber is limited due to the dispersion effect.Distance Bandwidth product of a fiber is almost a constant.Fiber optic cables consist of multiple fibers packed inside protective covering.62.5/125 µm (850/1310 nm) multimode fiber 50/125 µm (850/1310 nm) multimode fiber 10 µm (1310 nm) single-mode fiber

Physical Media

Fiber-Optic CableContains one or several glass fibers at its coreSurrounding the fibers is a layer called cladding

Physical Media

Fiber Optic CableFO Cable may have 1 to over 1000 fibers

Physical Media

Wireless MediaVery useful in difficult terrain where cable laying is not possible.Provides mobility to communication nodes.Right of way and cable laying costs can be reduced.Susceptible to rain, atmospheric variations and Objects in transmission path.

Physical Media

Wireless MediaIndoor : 10 – 50m : BlueTooth, WLAN

Short range Outdoor : 50 – 200m: WLAN

Mid Range Outdoor : 200m – 5 Km : GSM, CDMA, WLAN Point-to-Point, Wi-Max

Long Range Outdoor : 5 Km – 100 Km : Microwave Point-to-Point

Long Distance Communication : Across Continents : Satellite Communication

Physical Media

Frequency Bands

Physical Media

Band RangePropagatio

n Application

VLF 3–30 KHz Ground Long-range radio navigation

LF 30–300 KHz GroundRadio beacons and

navigational locators

MF 300 KHz–3 MHz Sky AM radio

HF 3–30 MHz SkyCitizens band (CB),

ship/aircraft communication

VHF 30–300 MHzSky and

line-of-sightVHF TV, FM radio

UHF 300 MHz–3 GHzLine-of-

sightUHF TV, cellular phones,

paging, satellite

SHF 3–30 GHzLine-of-

sight Satellite communication

EHF 30–300 GHzLine-of-

sight Long-range radio navigation

Wireless LAN

Physical Media

Internet Router Switch

Access Point

Access Point

PC

PC

Terrestrial MicrowaveMicrowaves do not follow the curvature of earthLine-of-Sight transmissionHeight allows the signal to travel fartherTwo frequencies for two way communicationRepeater is used to increase the distance Hop-by-Hop

Physical Media

Satellite Communication

Physical Media

Cabling

UTP AND FIBER CABLING

Structured Cabling InfrastructureMounted and permanentAllows patchingComfort that infrastructure is OKComponents:

Information Outlet with Face PlatePatch PanelUTP CablePatch Cord

Cabling

I/O & FaceplatesFaceplate mounts on or in wall or in racewaySingle or Dual Information Outlet (I/O)Provide network connectivity to the Hosts through a Patch Cord

Cabling

Patch PanelTermination punchdown in backPatch cord plugin in front

Cabling

Patch Cord & UTP Connectors

Cabling

Color CodesData Tx: 1 & 2 Data Rx: 3 & 6Crossover

1 32 6

PoE +VDC: 4 & 5 PoE -VDC: 7 & 8

Cabling

Cutting, Striping & Crimping ToolsMake your own patch cordsCuts and strips pairsRJ45 end crimped onto ends of wire

Cabling

Punching ToolTerminates wires to back of patch panels and in Information Outlets

Cabling

Making Cables

Cabling

Wire Testing EquipmentTest wire for correct termination of 8 wiresTest for speed capabilities

Cabling

Cabling RulesTry to avoid running cables parallel to power cables.Do not bend cables to less than four times the diameter of the cable.If you bundle a group of cables together with cable ties (zip ties), do not over-cinch them. You should be able to turn the tie with fingers.Keep cables away from devices which can introduce noise into them. Here's a short list: copy machines, electric heaters, speakers, printers, TV sets, fluorescent lights, copiers, welding machines, microwave ovens, telephones, fans, elevators, motors, electric ovens, dryers, washing machines, and shop equipment.Avoid stretching UTP cables (tension when pulling cables should not exceed 25 LBS).Do not run UTP cable outside of a building. It presents a very dangerous lightning hazard!Do not use a stapler to secure UTP cables. Use telephone wire/RJ6 coaxial wire hangers which are available at most hardware stores.

Cabling

Fiber Optic Cabling Infrastructure

Components:Fiber Cable Fiber PigtailFiber ConnectorsLIUCouplerFiber Patch Cord

Cabling

Fiber Optic ConnectorsTerminates the fibersConnects to other fibers or transmission equipment

Cabling

Fiber Patch Cords & PigtailsEnds are typically either SC or STPigtails have connectors on only one side and Patch Cords have it on both sides.Pigtails are spliced to the fiber to terminate the fiberPatch Cord connects switches to the Fiber cable

Cabling

LIU & Couplers

Cabling

Fiber Optic Installation – Outside Plant

Cabling

Fiber Optic Installation – Outside Plant

Fiber is blown in HDPE Pipes, 1 m deep. The HDPE pipes is covered with sand and brick liningFiber Roles are typically 2 Km. Fiber cables are spliced using JointersFaults like fiber cut are located using OTDR (Optical Time Domain Reflectometer)

Cabling

LAN Technologies

LAN TECHNOLOGIES

Technology OptionsEthernetFast EthernetGigabit Ethernet10 Gig Ethernet

WLAN

LAN Technologies

Media AccessEthernet and Wi-Fi are both “multi-access” technologies

Broadcast medium, shared by many hostsSimultaneous transmissions will result in collisions

Media Access Control (MAC) protocol requiredRules on how to share medium

The Data Link Layer is divided into two Part MAC Media Access Control) Sublayer and LLC (Logic Link Control) Sublayer

LAN Technologies

802.3 EthernetCarrier-sense multiple access with collision detection (CSMA/CD).

CS = carrier sense MA = multiple accessCD = collision detection

Base Ethernet standard is 10 Mbps.100Mbps, 1Gbps, 10Gbps standards came later

LAN Technologies

Ethernet CSMA/CDCSMA/CD (carrier sense multiple access with collision detection) media access protocol is used.

Data is transmitted in the form of packets. Sense channel prior to actual packet transmission.Transmit packet only if channel is sensed idle; else, defer the transmission until channel becomes idle.After packet transmission is started, the node monitors its own transmission to see if the packet has experienced a collision.If the packet is observed to be undergoing a collision, the transmission is aborted and the packet is retransmitted after a random interval of time using Binary Exponential Backoff algorithm.

LAN Technologies

Ethernet AddressEnd nodes are identified by their Ethernet Addresses (MAC Address or Hardware Address) which is a unique 6 Byte address.

MAC Address is represented in Hexa Decimal format e.g 00:05:5D:FE:10:0A

The first 3 bytes identify a vendor (also called prefix) and the last 3 bytes are unique for every host or device

LAN Technologies

Ethernet Frame StructurePreamble:

7 bytes with pattern 10101010 followed by one byte with pattern 10101011Used to synchronize receiver, sender clock rates

Addresses: 6 bytes, frame is received by all adapters on a LAN and dropped if address does not matchLength: 2 bytes, length of Data fieldCRC: 4 bytes generated using CR-32, checked at receiver, if error is detected, the frame is simply droppedData Payload: Maximum 1500 bytes, minimum 46 bytes

If data is less than 46 bytes, pad with zeros to 46 bytes

LAN Technologies

Length

Ethernet10 Base 5 (Thicknet) (Bus Topology)10 Base 2 (Thinnet) (Bus Topology)10 Base T (UTP) (Star/Tree Topology)10 Base FL (Fiber) (Star/Tree Topology)

LAN Technologies

Ethernet BUS Topology

LAN Technologies

Repeater

Ethernet STAR Topology

LAN Technologies

Hub

EthernetPhysical Media :-

10 Base5 - Thick Co-axial Cable with Bus Topology 10 Base2 - Thin Co-axial Cable with Bus Topology 10 BaseT - UTP Cat 3/5 with Tree Topology 10 BaseFL - Multimode/Singlemode Fiber with Tree

Topology

Maximum Segment Length 10 Base5 - 500 m with at most 4 repeaters (Use Bridge to extend the network) 10 Base2 - 185 m with at most 4 repeaters (Use Bridge to extend the network) 10 BaseT - 100 m with at most 4 hubs (Use Switch to extend the network)

LAN Technologies

Fast Ethernet100 Mbps bandwidthUses same CSMA/CD media access protocol and packet format as in Ethernet.100BaseTX (UTP) and 100BaseFX (Fiber) standards Physical media :-

100 BaseTX - UTP Cat 5e100 BaseFX - Multimode / Singlemode Fiber

Full Duplex/Half Duplex operations.

LAN Technologies

Fast EthernetProvision for Auto-Negotiation of media speed: 10 Mbps or 100Mbps (popularly available for copper media only).

Maximum Segment Length100 Base TX - 100 m100 Base FX - 2 Km (Multimode Fiber)100 Base FX - 20 km (Singlemode Fiber)

LAN Technologies

Gigabit Ethernet1 Gbps bandwidth.Uses same CSMA/CD media access protocol as in Ethernet and is backward compatible (10/100/100 modules are available).1000BaseT (UTP), 1000BaseSX (Multimode Fiber) and 1000BaseLX (Multimode/Singlemode Fiber) standards.Maximum Segment Length

1000 Base T - 100m (Cat 5e/6)1000 Base SX - 275 m (Multimode Fiber)1000 Base LX - 512 m (Multimode Fiber) 1000 Base LX - 20 Km (Singlemode Fiber)1000 Base LH - 80 Km (Singlemode Fiber)

LAN Technologies

10 Gig Ethernet10 Gbps bandwidth.

Uses same CSMA/CD media access protocol as in Ethernet.

Propositioned for Metro-Ethernet

Maximum Segment Length1000 Base-T - Not available10GBase-LR - 10 Km (Singlemode Fiber)10GBase-ER - 40 Km (Singlemode Fiber)

LAN Technologies

802.11 Wireless LAN

Provides network connectivity over wireless media

An Access Point (AP) is installed to act as Bridge between Wireless and Wired Network

The AP is connected to wired network and is equipped with antennae to provide wireless connectivity

LAN Technologies

Network connectivity

to the legacy

wired LAN

Desktop with PCI 802.11 LAN card

Laptop with PCMCIA 802.11 LAN card

Access Point

802.11 Wireless LANRange ( Distance between Access Point and WLAN client) depends on structural hindrances and RF gain of the antenna at the Access Point

To service larger areas, multiple APs may be installed with a 20-30% overlap

A client is always associated with one AP and when the client moves closer to another AP, it associates with the new AP (Hand-Off)

Three flavors:802.11b802.11a802.11g

LAN Technologies

Multiple Access with Collision Avoidance (MACA)

Before every data transmission Sender sends a Request to Send (RTS) frame containing the length of the transmissionReceiver respond with a Clear to Send (CTS) frameSender sends dataReceiver sends an ACK; now another sender can send data

When sender doesn’t get a CTS back, it assumes collision

LAN Technologies

sender receiverother node in sender’s range

RTSCTS

ACK

data

other node in receiver’s range

WLAN : 802.11bThe most popular 802.11 standard currently in deployment.Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4 GHz ISM (Industrial-Scientific-Medical) band

LAN Technologies

WLAN : 802.11aOperates in the 5 GHz UNII (Unlicensed National Information Infrastructure) band Incompatible with devices operating in 2.4GHzSupports Data rates up to 54 Mbps.

LAN Technologies

WLAN : 802.11gSupports data rates as high as 54 Mbps on the 2.4 GHz bandProvides backward compatibility with 802.11b equipment

LAN Technologies

Repeater, HUB, Bridge & Switch

REPEATER, HUB, BRIDGE AND SWITCH

RepeaterA repeater receives a signal, regenerates it, and passes it on. It can regenerate and retime network signals at the bit level to allow them to travel a longer distance on the media.It operates at Physical Layer of OSIThe Four Repeater Rule for 10-Mbps Ethernet should be used as a standard when extending LAN segments. This rule states that no more than four repeaters can be used between hosts on a LAN. This rule is used to limit latency added to frame travel by each repeater.

Repeater, Hub, Bridge & Switch

HubHubs are used to connect multiple nodes to a single physical device, which connects to the network. Hubs are actually multiport repeaters.

Using a hub changes the network topology from a linear bus, to a star.

With hubs, data arriving over the cables to a hub port is electrically repeated on all the other ports connected to the same network segment, except for the port on which the data was sent.

Repeater, Hub, Bridge & Switch

BridgeBridges are used to logically separate network segments within the same network. They operate at the OSI data link layer (Layer 2) and are independent of higher-layer protocols. The function of the bridge is to make intelligent decisions about whether or not to pass signals on to the next segment of a network.

When a bridge receives a frame on the network, the destination MAC address is looked up in the bridge table to determine whether to filter, flood, or copy the frame onto another segment

Broadcast Packets are forwarded

Repeater, Hub, Bridge & Switch

SwitchSwitches are Multiport Bridges. Switches provide a unique network segment on each port, thereby separating collision domains. Today, network designers are replacing hubs in their wiring closets with switches to increase their network performance and bandwidth while protecting their existing wiring investments.

Like bridges, switches learn certain information about the data packets that are received from various computers on the network. Switches use this information to build forwarding tables to determine the destination of data being sent by one computer to another computer on the network.

Repeater, Hub, Bridge & Switch

Switches: Dedicated AccessHosts have direct connection to switchFull Duplex: No collisionsSwitching: A-to-A’ and B-to-B’ simultaneously, no collisionsSwitches can be cascaded to expand the network

Repeater, Hub, Bridge & Switch

switch

A

A’

B

B’

C

C’

WAN Technologies

WAN TECHNOLOGIES

Technology OptionsDial-upLeased LineISDNX.25Frame RelayATMDSLCable ModemMicrowave Point-to-Point LinkVSAT

WAN Technologies

Dial-upUses POTS (Plain Old Telephone System)

Provides a low cost need based access.

Bandwidth 33.6 /56 Kbps.

On the Customer End: Modem is connected to a Telephone Line

On the Service Provider End: Remote Access Server (RAS) is connected to Telephone Lines (33.6 Kbps connectivity) or E1/R2 Line (56 Kbps connectivity)

RAS provide dialin connectivity, authentication and metering.

Achievable bandwidth depends on the line quality.

WAN Technologies

Dial-up

WAN Technologies

Dial-up

WAN Technologies

RAS

Dial-up

WAN Technologies

33.6 Kbps

Modem

Telephone switch

Telephone switch

Telephone switch ?

Access server

Modem

Modem

E1

Analog line

56 Kbps

Leased LineUsed to provide point-to-point dedicated network connectivity.Analog leased line can provide maximum bandwidth of 9.6 Kbps.Digital leased lines can provide bandwidths : 64 Kbps, 2 Mbps (E1), 8 Mbps (E2), 34 Mbps (E3) ...

WAN Technologies

Leased Line Internet Connectivity

WAN Technologies

ISP Broadba

nd Internet Connecti

vity

ISPRouter

Interface Converter

LL ModemG.703

LLModem

V.35Router

ISP PREMISES CUSTOMER PREMISES

PSTN

ISDNAnother alternative to using analog telephones lines to establish a connection is ISDN.

Speed is one advantage ISDN has over telephone line connections.

ISDN network is a switched digital network consisting of ISDN Switches.

Each node in the network is identified by hierarchical ISDN address which is of 15 digits.

ISDN user accesses network through a set of standard interfaces provided by ISDN User Interfaces.

WAN Technologies

ISDN

WAN Technologies

Two types of user access are defined Basic Access - Consists of two 64Kbps user channels (B channel) and one 16Kbps signally channel (D channel) providing service at 144 Kbps.

Primary access - Consists of thirty 64Kbps user channels (B channels) and a 64 Kbps signally channel (D channel) providing service at 2.048Mbps (One 64 Kbps channel is used for Framing and Synchronization).

BasicB

BD

Information 128 Kbps(Voice & Data)

Signaling 16Kbps

Primary

B

B

D

Information 1920 KbpsVoice & Data

Signaling 64 Kbps

ISDN

WAN Technologies

TE1

TE2 TA

NT12W4W

ISDN devices

S/T interface U interface

DevicesNT1 - Interface ConverterTE1 - ISDN devicesTE2 – Non ISDN Devices (need TA)TA - Terminal Adapter (ISDN Modem)

X.25Packet switched Network consisting of X.25 switches.X.25 is a connection oriented protocol (Virtual Circuits).End nodes are identified by an X .25 address.Typical bandwidth offered is 2.4/9.6 kbps. IP networks interface with X .25 through IP- X.25 routers.

WAN Technologies

X.25 and Virtual Circuits

WAN Technologies

Frame RelayDesigned to be more efficient than X.25Developed before ATMCall control carried in separate logical connectionNo hop by hop error or flow controlEnd to end flow and error control (if used) are done by higher layerSingle user data frame sent from source to destination and ACK (from higher layer) sent backTwo type of Virtual Circuits defined

Permanent virtual circuits (PVCs) Switched virtual circuits (SVCs)

WAN Technologies

ATMSmall fixed size packets of 53 bytes, called cells, are used for transferring information.Each cell has 5 bytes of header and 48 bytes of payload for user information.Connection oriented protocol. A virtual Circuit is established between the communicating nodes before data transfer takes place.Can be seamlessly used in LANs and WANs.Almost unlimited scalability.Provides quality of service guaranties.

WAN Technologies

Digital Subscriber Line (DSL)Digital Subscriber Line (DSL) uses the Ordinary Telephone line and is an always-on technology. This means there is no need to dial up each time to connect to the Internet.Because DSL is highly dependent upon noise levels, a subscriber cannot be any more than 5.5 kilometers (2-3 miles) from the DSL ExchangeService can be symmetric, in which downstream and upstream speeds are identical, or asymmetric in which downstream speed is faster than upstream speed.DSL comes in several varieties:

Asymmetric DSL (ADSL)High Data Rate DSL (HDSL) Symmetric DSL (SDSL) Very High Data Rate DSL (VDSL)

WAN Technologies

ADSL

WAN Technologies

Cable ModemsThe cable modem connects a computer to the cable company network through the same coaxial cabling that feeds cable TV (CATV) signals to a television set.Uses Cable Modem at Home End and CMTS (Cable Modem Termination System) at Head End.Characteristics:

Shared bandwidth technology 10 Mbps to 30 Mbps downstream 128Kbps-3 Mbps upstream Maximum Distance from provider to customer site: 30 miles

WAN Technologies

Cable Modems

WAN Technologies

Point-to-Point Microwave Link

WAN Technologies

ISP Network

NetworkRFModem

RouterRF

ModemRouter

MICROWAVE LINK

ISP PREMISES

CUSTOMER PREMISES

Point-to-Point Microwave LinkTypically 80-100 MHz Band or 5 GHz Radio Link band2.4 GHz WiFi links are becoming popularRequires Line of Sight

WAN Technologies

VSATVery Small Aperture Terminal (VSAT) provide communication between two nodes through a powerful Earth station called a Hub.If two terminals want to communicate, they send their messages to the satellite, which sends it to the Hub and the Hub then broadcasts the message through the satellite.Typical Bandwidth offered is 9.6/19.2/32/64/128/256/512 Kbps.Operating modes are TDM/TDMA, SCPC PAMA & DAMA

WAN Technologies

VSATEach satellite sends and receives over two bands

Uplink: From the earth to the satelliteDownlink: From the satellite to the earth

Satellite frequency bandsBand Downlink UplinkC 3.7-4.2 GHz 5.925-6.425

GHzKu 11.7-12.2 GHz 14-14.5 GHz

Ku-band based networks, are used primarily in Europe and North America and utilize the smaller sizes of VSAT antennas.C-band, used extensively in Asia, Africa and Latin America, require larger antenna.

WAN Technologies

Internet Protocol

INTERNET PROTOCOL

IP as a Routed ProtocolIP is a connectionless, unreliable, best-effort delivery protocol. IP accepts whatever data is passed down to it from the upper layers and forwards the data in the form of IP Packets.All the nodes are identified using an IP address. Packets are delivered from the source to the destination using IP address

Internet Protocol

Packet Propagation

Internet Protocol

IP AddressIP address is for the INTERFACE of a host. Multiple interfaces mean multiple IP addresses, i.e., routers.

32 bit IP address in dotted-decimal notation for ease of reading, i.e., 193.140.195.66

Address 0.0.0.0, 127.0.0.1 and 255.255.255.255 carries special meaning.

IP address is divided into a network number and a host number.

Also bits in Network or Host Address cannot be all 0 or 1.

Internet Protocol

IP Address

Internet Protocol

IP Address

Internet Protocol

IP AddressClass A : Address begins with bit 0. It has 8 bit network number (range 0.0.0.0-to-127.255.255.255), 24 bit host number.Class B : Address begins with bits 10. It has 16 bit network number (range 128.0.0.0-to-191.255.255.255), 16 bit host number.Class C : Address begins with bits 110. It has 24 bit network number (range 192.0.0.0-to-223.255.255.255), 8 bit host number.Class D : Begins with 1110, multicast addresses (224.0.0.0-to-239.255.255.255)Class E : Begins with 11110, unused

Internet Protocol

Subnet Mask

Internet Protocol

Consider IP address = 192.168.2.25First few bits (left to right) identify network/subnet Remaining bits identify host/interface

Number of subnet bits is called subnet mask, e.g.

Subnet IP Address range is 192.168.2.0 – 192.168.2.255 or Mask = 255.255.255.0

Subnet IP Address range is 192.168.2.0 – 192.168.2.15 or Mask = 255.255.255.240

IP Address, Subnet Mask and Gateway

IP Address and Subnet Mask define the SubnetFor Example IP address 172.31.1.0 and Subnet Mask of 255.255.240.0 means that the subnet address ranges from 172.31.0.0 to 172.31.15.255Another notation is 172.31.1.0/28The first Address is the Network Address and the last Address is the Broadcast Address. They are reserved and cannot be assigned to any node.The Gateway Address is the Address of the router where the packet should be sent in case the destination host does not belong to the same subnet

Internet Protocol

IP Configuration of an Interface

Internet Protocol

Static DHCP

ARPARP (Address Resolution Protocol) is used in Ethernet Networks to find the MAC address of a node given its IP address.

Source node (say 192.168.2.32) sends broadcast message (ARP Request) on its subnet asking ``Who is 192.168.2.33’’.

All computers on subnet receive this request

Destination responds (ARP Reply) since it has 192.168.2.33

Provides its MAC address in response

Internet Protocol

IPv6Internet Protocol Version 4 is the most popular protocol in use today, although there are some questions about its capability to serve the Internet community much longer. IPv4 was finished in the 1970s and has started to show its age. The main issue surrounding IPv4 is addressing—or, the lack of addressing—because many experts believe that we are nearly out of the four billion addresses available in IPv4. Although this seems like a very large number of addresses, multiple large blocks are given to government agencies and large organizations. IPv6 could be the solution to many problems posed by IPv4

Internet Protocol

IPv6IPv6 uses 128 bit address instead of 32 bit address.

The IPv6 addresses are being distributed and are supposed to be used based on geographical location.

Internet Protocol

Internet Applications

INTERNET APPLICATIONS

Internet Applications

Internet Applications

Domain Name Service

Proxy Service

Mail Service

Web Service

DNS

DNS

Internet Naming Hierarchy

DNS

The silent dot at theend of all addresses

.com .net .org .in

.tcd

www

.ac .co

.iitk

www

DNS OperationDNS Setup

A DNS server maintains the name to IP address mapping of the domain for which it is the name server.

The DNS server for a domain is registered with the domain registrar and the entry is maintained by the Internet Root-Servers (13) or Country Level Root-Servers.

Whenever a server is queried, if doesn’t have the answer, the root servers are contacted.

The root servers refer to the DNS server for that domain (in case the domain is a top level domain) or the Country Root Server (in case the domain is country level domain).

Proxy Server

PROXY SERVER

Internet Connections

Proxy Server

• Customers connect to an ISP

• ISPs connect to backbone

Backbonenetworks

ISP networ

k

ISP networ

k

ISPnetwork

Customer Networks

Bandwidth-limitedlinks

Internet Connections

Proxy Server

Cost of connections is based on bandwidth

Cost of connection is a major part of network cost

Organisations only obtain as much bandwidth as they can afford

What is a Web Proxy?

Proxy Server

A proxy is a host which relays web access requests from clients

Used when clients do not access the web directly

Used for security, logging, accounting and performance

browser proxy web

What is Web Caching?Storing copies of recently accessed web pages

Pages are delivered from the cache when requested again

Browser caches

Proxy caches

Proxy Server

Why Cache?Shorter response time

Reduced bandwidth requirement

Reduced load on servers

Access control and logging

Proxy Server

Popular Proxy CachesApache proxy

MS proxy server

WinProxy

Squid

Squid is popular because it is powerful, configurable and free

Many others

Proxy Server

Web Server

WEB SERVER

Web ServerHTTP (Hyper Text Transfer Protocol) is used to transfer web pages from a Web Server to Web Client (Browser)

Web Pages are arranged in a directory structure in the Web Server

HTTP supports CGI (Common Gateway interface)

HTTP supports Virtual Hosting (Hosting multiple sites on the same server)

Popular Web ServersApacheWindows IISIBM Websphere

Web Server

Email

EMAIL

Mail Architecture

Email

Internet

Mail Server

Mail Server

Mail ClientMail Client

Mail Architecture

Email

Mail Architecture

Email

Simple Mail Transfer Protocol (SMTP) is used to transfer mail between Mail Servers over Internet

Post Office Protocol (PoP) and Interactive Mail Access Protocol (IMAP) is used between Client and Mail Server to retrieve mails

The mail server of a domain is identified by the MX record of that domain

Popular Mail Servers Sendmail/Postfix Microsoft Exchange Server IBM Lotus