LAN / WAN / Extranet and Network Topology

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Motivation

 Local Area Networks (LAN) were motivated by: – Decreasing computer size – Decreasing computer cost – Realizing computers could help with many tasks 2

Interchangeable Media

  The first data transfers: – Used: • Magnetic tapes • Disks Data transferred between computers in a method similar to using floppy disks.

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LAN Generations

   First – CSMA/CD and token ring – Terminal to host and client server – Moderate data rates Second – FDDI – Backbone – High performance workstations Third – ATM – Aggregate throughput and real time support for multimedia applications 4

Third Generation LANs

   Support for multiple guaranteed classes of service – Live video may need 2Mbps – File transfer can use background class Scalable throughput – Both aggregate and per host Facilitate LAN/WAN internetworking 5

LAN technologies

   MAC protocols used in LANs, to control access to the channel Token Rings: IEEE 802.5 (IBM token ring), for computer room, or Department connectivity, up to 16Mbps; FDDI (Fiber Distributed Data Interface), for Campus and Metro connectivity, up to 200 stations, at 100Mbps.

Ethernets: employ the CSMA/CD protocol; 10Mbps (IEEE 802.3), Fast E-net (100Mbps), Giga E-net (1,000 Mbps); by far the most popular LAN technology 6

A Computer Consists Of Circuit Boards

 Inside a computer are electronic components on circuit boards.

– Containing electronic components – Containing wires  Computers having different circuit boards for external devices.

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Circuit Boards Plug Into A Computer

 Computers are built so it contains a set of sockets.

– Using wires to connect sockets together – Using wires to carry power and data – Plugging circuit boards into sockets to control external devices 8

Illustrations of the components visible in a computer when the cover has been removed. A circuit board can plug into each socket; wires connect the sockets to other components.

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Connecting Computers In Early Systems

 Transferring data between two computers consisted of two circuit boards connected by a cable.

Figure 7.2 Illustration of an early computer communication system formed using two circuit boards plugged into sockets in two computers.

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Early Systems

 The computers use cables to transfer data electronically.

– Operating like an I/O device – Writing data to circuit board Figure 7.3 Two pairs of interface boards connecting three computers. Each new computer added to the set requires a new pair of interface boards and an additional cable.

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Early Systems

 Advantage of early LANs were speed.

 Disadvantages of early LANs were inconvenience and cost. Requiring effort to: – Add a new computer – Connect incompatible hardware 12

Connecting A Computer to A LAN

 A computer needs additional hardware to connect it to a LAN.

 The speed of the LAN does not depend on the speed of the computer attached to it.

– Communication by heterogeneous computers 13

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In many LAN systems, a cable connects each computer to a hub.

Computers connected to a LAN. Each computer attaches to the hub with a cable; the computers can then communicate directly.

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  NIC A computer needs network interface hardware and a cable that connects to the LAN.

A computer uses the network interface to send and receive data.

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The Importance Of LAN Technology

 LANs changed the way people used computer networks.

– Sharing resources – Connecting machines within a building 16

Relationship To The Internet

 Xerox gave universities a prototype of a new LAN technology.

– Beginning of Ethernet – Developing the idea of inexpensive and widely available LANs 17

Many Independent Networks

 By late 1970s, many organizations began installing Local Area Networks because they: – Were inexpensive.

– Were easy to install – Could operate them independently of a central administration.

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The Proliferation of LANs

 Advantages  Disadvantages – An organization can: – Independent groups can: • budget funds • decide who has access • devise policies for use • Encourage proliferation of different LAN technologies 19

Facts About LANs

 Engineers have devised many LAN technologies  LAN performance determines cost.

 LAN technology may only work with specific computers.

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LANs Are Incompatible

 Various LAN technologies are completely incompatible.

– Connecting multiple LANs is not possible • Engineered to operate over limited distance • May be electrically incompatible • Encoding information may not make sense to another LAN 21

IEEE802.3 Medium Access Control

 Random Access – Stations access medium randomly  Contention – Stations content for time on medium 22

IEEE 802.3 Frame Format

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10Mbps Specification (Ethernet)

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10Base5 10Base2 10Base-T

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Medium

Coaxial Coaxial Signaling Baseband Baseband Manchester Manchester Topology Bus

Nodes

100 Bus 30 UTP Baseband Manchester Star -

10Base-FP

850nm fiber Manchester On/Off Star 33 24

100Mbps (Fast Ethernet)

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100Base-TX 100Base-FX 100Base-T4

  2 pair, STP 2 pair, Cat 5UTP

MLT-3

MLT-3 2 optical fiber 4B5B,NRZI 4 pair, cat 3,4,5 8B6T,NRZ 25

Gigabit Ethernet Configuration

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Gigabit Ethernet - Differences

 Carrier extension  At least 4096 bit-times long (512 for 10/100)  Frame bursting 27

Gigabit Ethernet - Physical

    1000Base-SX – Short wavelength, multimode fiber 1000Base-LX – Long wavelength, Multi or single mode fiber 1000Base-CX – Copper jumpers <25m, shielded twisted pair 1000Base-T – 4 pairs, cat 5 UTP  Signaling - 8B/10B 28

Wide Area Technologies Exist

 WAN technology includes an additional special-purpose computer at each site that: – Connects to the transmission lines – Keeps communication independent of the computer 29

Few WANs, Many WANs

 WANs cost much more than LANs.

– Require more planning – Require more hardware  Only a few companies build their own WAN.

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WANs And LANs Are Incompatible

 Many Wide Area Networks and Local Area Networks exist.

– Cannot connect a WAN to a LAN – Cannot interconnect the wires from two different networks 31

WANs for Voice

 Requires very small and nonvariable delays for natural conversation--difficult to provide this with packet-switching  As a result, the preferred method for voice transmission is circuit-switching  Most businesses use public telephone networks, but a few organizations have implemented private voice networks 32

WANs for Data

 Public packet-switched networks (X.25)  Private packet-switched networks  Leased lines between sites (non-switched)  Public circuit-switched networks  Private circuit-switched networks (interconnected digital PBXs)  ISDN (integrated X.25 and traditional circuit switching) 33

WAN Considerations

 Nature of traffic – stream generally works best with dedicated circuits – bursty better suited to packet-switching  Strategic and growth control--limited with public networks  Reliability--greater with packet-switching  Security--greater with private networks 34

Wireless LANs

   IEEE 802.11

Basic service set (cell) – Set of stations using same MAC protocol – Competing to access shared medium – May be isolated – May connect to backbone via access point (bridge) Extended service set – Two or more BSS connected by distributed system – Appears as single logic LAN to LLC level 35

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Wireless LAN

—links clients within the vicinity of each other. A network adapter card that is connected to a transmitter, called an access point, via a cable.

The transmitter located on a wall gives the signal an uninterrupted path to a wall-mounted receiver on the far side of the room.

Data packets are transmitted over the airwaves to the receiver, which is also connected to network clients by a cable.

    

Wireless Extended LAN

—connections to clients a couple of miles away.

Similar connectivity is an Extended LAN.

Transmitter and receiver are typically located outside the buildings.

Forms an electronic data communication bridge called a wireless bridge.

Data packets up to 25 miles away from the transmitter use spread spectrum radio technology.

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Wireless LAN - Physical

    Infrared – 1Mbps and 2Mbps – Wavelength 850-950nm Direct sequence spread spectrum – 2.4GHz ISM band – Up to 7 channels – Each 1Mbps or 2Mbps Frequency hopping spread spectrum – 2.4GHz ISM band – 1Mbps or 2Mbps Others under development 37

Wireless LANs

     Mobility Flexibility Hard to wire areas Reduced cost of wireless systems Improved performance of wireless systems 38

LAN Extension

    Buildings with large open areas – Manufacturing plants – Warehouses Historical buildings Small offices May be mixed with fixed wiring system 39

Single Cell Wireless LAN

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Multi Cell Wireless LAN

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Client/Server Architecture

 Combines advantages of distributed and centralized computing  Cost-effective, achieves economies of scale  Flexible, scalable approach 42

Intranets

 Uses Internet-based standards & TCP/IP  Content is accessible only to internal users  A specialized form of client/server architecture 43

Extranets

 Similar to intranet, but provides access to controlled number of outside users – Vendors/suppliers – Customers 44

Every computer network has the same basic components: • Cables or wireless connection • Network adapter cards that transmit and receive information • Client software that makes all these components work together

Topology: The way in which components are assembled.

There are six topologies used in the design of a computer network: • Bus • Star • Ring • Token Passing • Hubs • Hybrid 45

Topologies

    Tree Bus – Special case of tree • One trunk, no branches Ring Star 46

LAN Topologies

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A bus topology requires:

• Clients are connected to the same cable known as a trunk, segment, or backbone. • All data packets are received by every client regardless of whether the data packet is addressed. • Data packets not addressed to the client are ignored.

• Data packets addressed to the client are accepted and processed by the client.

• Data packets travel the complete length of the cable, then bounce back.

• This is called signal bounce and continues until the signal loses energy and dissipates. • The network operating system has the responsibility to keep the transmission moving along the cable. • A client can malfunction and the network continues to operate, which is called a passive topology. • A passive topology is easy to construct, highly reliable, and susceptible to slow performance during heavy network traffic. • A break in the cable is commonly caused by an improper network connection.

• Breaks are hard to track down because every client and device on the network could be suspect. • A network outage does not shut down a client's operation. Clients work as a stand-alone.

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Frame Transmission - Bus LAN

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Bus and Tree

Multipoint medium Transmission propagates throughout medium Heard by all stations – Need to identify target station • Each station has unique address Full duplex connection between station and tap – Allows for transmission and reception Need to regulate transmission – To avoid collisions – To avoid hogging • Data in small blocks - frames Terminator absorbs frames at end of medium 50

• Clients connect to a central device called a concentrator or hub.

• Clients transmit and receive data packets to and from the concentrator.

• It is the job of the concentrator to redirect data packets to the appropriate client.

• Clients only receive data packets addressed to them. • Star topology reduces the network traffic clients must handle.

• The concentrator detects if a client is not connected to the network and returns data packets to the sender. • Failure of one client does not disable the entire network.

• Network services become unavailable if the concentrator malfunctions. • Clients use 10BaseT network adapter cards that automatically detect trouble with the concentrator. • The client then stops any transmission of data packets and operates as a stand-alone computer until the concentrator becomes operational.

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Ring Topology

   Repeaters joined by point to point links in closed loop – Receive data on one link and retransmit on another – Links unidirectional – Stations attach to repeaters Data in frames – Circulate past all stations – Destination recognizes address and copies frame – Frame circulates back to source where it is removed Media access control determines when station can insert frame 52

Frame Transmission Ring LAN

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• Each client is connected consecutively to the single cable. • There are no ends to the ring network that must be sealed with a terminator.

• Data packets pass clockwise from one client to the next. • If the data packet isn't addressed to the client, the client resends the data packet to the next client. • The client strengthens the signal, allowing the data packet to travel a further distance.

• Clients connect to a hub. Within the hub is the ring. • If one client is not working properly, there is a good chance the entire network will fail. • This depends on the network operating system. • IBM token ring automatically ignores inactive clients. 54

• A token ring is a ring-like topology. • Clients are connected together to form a ring.

• Each data packet is transmitted to each client on the network. • A special packet, called a token, is used to control transmissions on the network.

• The token packet is delivered to a client clockwise along the network. • The client can accept the token and transmit a data packet. • Addresses, data, and other necessary information are added to the token packet. • The modified token packet becomes the new data packet and is sent to the hub for delivery to the destination.

• The destination client acknowledges the data packet.

• The client that sent the data packet creates a new token packet and passes it to the next client.

• The client can ignore the token packet, which is then passed along to the next client on the ring. • This is called token passing. • Token packets can travel more than 10,000 times around the network per second.

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Star Topology

   Each station connected directly to central node – Usually via two point to point links Central node can broadcast – Physical star, logical bus – Only one station can transmit at a time Central node can act as frame switch 56

Hubs

• A hub is a central processing device on a network.

• A hub is used with the star and ring topologies as a concentrator for network traffic. • Hub topology is used to divide large network requirements into smaller, serviceable LANs called segments. • A hub enables a network administrator to monitor and manage network traffic.

• A hub is used to link segments together; cabling used by various clients can be mixed and matched.

Types of Hubs

• Networks use one of two kinds of hubs: • Passive hubs • Active hubs

Passive Hubs

• A passive hub acts as a connector box known as a wiring panel. • A passive hub connects cables from all clients. • A passive hub only provides connectivity among network clients. It does not interrupt transmissions on the network.

Active Hubs

• An active hub ID known as a multi-port repeater.

• An active hub joins together clients. • An active hub boosts the signal along the network like a repeater.

• An active hub can, in some cases, redirect data packets to the appropriate client.

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Hybrid Topology

• The disadvantage of each topology is reduced by combining topologies.

• The combined topology is called a hybrid network. • There are two common hybrid networks: star bus and star ring topology.

Star Bus Topology

• The star bus topology combines the star topology and the bus topology. • Clients of the smaller networks use the star topology to connect to its network concentrator. • Network concentrators are linked together in a bus topology.

• The star bus topology controls traffic flow on the network.

• Traffic between concentrators is less demanding than traffic among clients. • The bus topology is a more direct and efficient design for connecting concentrators.

• The star topology avoids transmission conflicts among clients.

• The star bus topology enables network expansion. • If network response time is slow because of an increase in traffic, clients can be transferred to a different segment with its own concentrator.

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• The star ring topology combines the best of the star and ring topologies. • The star ring topology is referred to as the star wired ring topology. • The star ring topology divides the network into smaller networks each having a concentrator or hub used to connect clients. • Concentrators are joined together using a master concentrator (sometimes called the main hub) in the form of a ring. • The advantage is that network traffic is handled by a topology that best suits the volume of traffic. • The network is scalable.

• A hybrid network reduces the chance that a complete network failure will occur. • Only clients directly linked to a concentrator will lose access to network services if the concentrator malfunctions.

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Question ???

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