chapter 1.ppt

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Chapter 1

Introducing Computer Network

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What is a Network?

A network is a connection between terminals, computers, servers,

and components which allows for the easy flow of data and use of

resources between one another.

Different networks that we come across in our day to day life are

telephone network, cable T.V network, transport network of a city

etc.

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Introducing Computer Networking

Stand-alone environment Elementary Form of Computer Networking

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Introducing Computer Networking

The sneaker net

A simple computer network

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What is a Computer Network?

Computer networking means sharing of data and resources

between two or more computers with a communication between

them through a medium. The communication medium can be

through radio waves, wires (Ethernet cable), leased lines, router,

infrared, optical fibers etc.

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Networking Application Areas

Sharing information (or data).

Sharing resources (hardware and software).

Centralizing administration and support

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Sharing Information

The ability to share information quickly and inexpensively has proven

to be one of the most popular uses of networking technology.

The computer can help you centralize the information and maintain

control over it

By making information available for sharing, networks can reduce the

need for paper communication, increase efficiency, and make nearly

any type of data available simultaneously to every user who needs it.

Managers can use these utilities to communicate quickly and

effectively with large numbers of people and to organize and

schedule meetings with people drawn from an entire company or

business enterprise far more easily than was previously possible.

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Sharing Hardware Resources

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Sharing Software Resources

Networks can be used to share and standardize applications, such

as word processors, spreadsheets, inventory databases, and so on,

to ensure that everyone on the network is using the same

applications and the same versions of those applications. This

allows documents to be shared easily and creates training

efficiencies: it is easier for people to master one word processing

application thoroughly than to try to learn four or five different word

processing applications.

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Centralizing Administration and Support

Electronic-mail (e-mail): Preserving Information Protecting Information A network provides a more Administrator can centrally install and configure

the software and also restrict access to the software. It is easier than doing it on every one of the computers in an organization.

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Understanding Networking Architecture

Explaining Client, Server and Peers

Explaining Server (domain) / Client Networks

Explaining Peer Networks

Explaining Hybrid Networks

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Identifying Components of Network

Client computers

Server computers:

Network interface cards (NICs):

Cable:

Switches:

Wireless networks:

Network software:

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Identifying Types of Network

LAN (Local area network)

PAN (Personal area network)

MAN (Metropolitan area network)

WAN (Wide area network)

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What is a Topology?

In Computer Networking “topology” refers to the layout or design of

the connected devices. Network Topologies can be physical or

logical.

Physical Topology means the physical design of a network

including the devices, location and cable installation.

Logical Topology refers to the fact that how data actually transfers

in a network as opposed to its design.

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Identifying Main Types of Physical Topologies

Bus

Ring

Star

Mesh

Hybrids

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Explaining Bus Topology

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Explaining Bus Topology continue

All workstations connect to the same cable segment

Commonly used for implementing Ethernet at 10mbps

The cable is terminated at each end

Wiring is normally done point to point

A faulty cable or workstation will take the entire LAN down

Two wire, generally implemented using coaxial cable during the

1980's

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There are THREE common wiring implementations for bus networks

10Base2 (thin-net, Cheaper Net) 50-ohm cable using BNC T connectors, cards provide transceiver

10Base5 (Thick Net) 50-ohm cable using 15-pin AUI D-type connectors and external transceivers

10BaseT (UTP) UTP cable using RJ45 connectors and a wiring centre

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Computers can connect to coaxial cables on a bus by tapping directly through the core of the cable. The vampire taps pierce the thick net cable but not the BNC.

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BNC-style T-connectors make attaching computers to a bus a

simpler operation. This is shown in the following figure.

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Ethernet 802.3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

Multiple access refers to the fact that in bus systems, each station has access to the common cable.

Carrier sense refers to the fact that each station listens to see if no other station is transmitting before sending data.

Collision detection refers to the principle of listening to see if other stations are transmitting whilst we are transmitting.

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Physical Bus Cable Limits

10Base2 Thin Ethernet Network Layout Limitations Maximum number of trunk segments = 5 Maximum trunk segment length = 607 feet (185 meters) Maximum network trunk cable = 3035 feet (925 meters) Maximum number of stations on a trunk segment = 30 Minimum distance between t connectors = 1.5 feet (0.5 meters) Rules Each end of the trunk segment is terminated in 50-ohms One of the terminators is grounded Connector splices are kept to a minimum Cabling BNC-T type connectors RG58-AU 50-ohm cable, 0.2"

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Physical Bus Cable Limits continue

A 10Base2 Thin Ethernet Network Layout

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10Base5 Thick Ethernet Network Layout

Limitations Maximum number of trunk segments = 5 Maximum trunk segment length = 1640 feet (500 meters) Maximum network trunk cable = 8200 feet (2500 meters) Maximum number of stations on a trunk segment = 100 Minimum distance between transceivers = 8 feet (2.5 meters) Maximum transceiver cable length = 165 feet (50 meters) Rules Each end of the trunk segment is terminated in 50-ohm One of the terminators is grounded Connector splices are kept to a minimum Cabling Transceivers 802.3 50-ohm cable RG-11 Male DIX connector

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10Base5 Thick Ethernet Network Layout

A 10Base5 Thick Ethernet Network Layout

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10BaseT UTP Network Layout

Limitations Maximum segment length of 100 Meters Hub to Hub or repeater to repeater links limited to 100 Meters Rules Star topology 4 repeater/5 segment rule of 10base5 is retained Only two nodes per segment are allowed Cabling RJ-45 Connectors Category 3 UTP minimum, preferably Category 5

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10BaseT UTP Network Layout

A 10Base5 Thick Ethernet Network Layout

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Bus Network Topology Summary

Advantages Disadvantages

Easy to implementLimits on cable length and Workstation numbers

Low Cost

Difficult to isolate network faultsA cable fault affects all workstationsAs the number of workstations increase, the speed of the network slows down

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Explaining Ring Topology

The main features are: Workstations connect to the ring Faulty workstations can be bypassed More cabling required than bus The connectors used tend to cause a lot of problems Commonly used to implement token ring at 4 and 16 Mbps Four wire, generally STP or UTP

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Explaining Ring Topology continue

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Physical Implementation of a Ring Network

Each workstation is connected back to a Multiple Access Unit (MAU), which supports up to eight workstations. Additional MAU are cascaded to provide greater workstation numbers.

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IEEE 802.5 Token Ring

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Either

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Or

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Physical Ring Cable Limits: TOKEN RING NETWORK LAYOUT

Limitations Maximum number of workstations = 96 Maximum number of 8228 MAU's = 12 Maximum patch cable distance between an 8228 MAU and a station (not including 8'

adapter cable) = 150 feet (45 meters) Maximum patch cable distance between two 8228's = 150 feet (45 meters) Maximum patch cable connecting all 8228's = 400 feet (120 meters) Rules Stations are connected into the jacks of the 8228 units Patch cables interconnect RO to RI for 8228 units. The last RO is connected to the first RI to form a ring. Cable Patch cables generally type 6 (26 awg) or 1 (22 awg) Type 1 for lengths > 66 feet (20 meters) IBM 8310574 MIC connectors Alternatively, UTP with RJ45 connectors

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Ring Topology: Summary


Cable failures affect limited users Costly Wiring

Equal access for all users Difficult Connections

Each workstation has full access speed to the ring

Expensive Adaptor Cards

As workstation numbers increaseperformance diminishes slightly

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Explaining Star Topology

The main features are: All wiring is done from a central point (the server or hub) Each node (file server, workstations, and peripherals) connected

directly to a central network hub or concentrator Data on a star network passes through the hub or concentrator

before continuing to its destination The hub or concentrator manages and controls all functions of the

network. It also acts as a repeater for the data flow Has the greatest cable lengths of any topology (and thus uses the

most amount of cable) This configuration is common with twisted pair cable; however, it

can also be used with coaxial cable or fiber optic cable Generally STP or UTP, four wire

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Star Topology

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Star-Wired Ring

A star-wired ring topology may appear (externally) to be the same

as a star topology. Internally, the MAU (multistation access unit) of a

star-wired ring contains wiring that allows information to pass from

one device to another in a circle or ring. The Token Ring protocol

uses a star-wired ring topology

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Star Topology: Summary


Easy to add new workstations

Hub failure cripples all workstationsconnected to that hub

Centralized controlHubs are slightly more expensive than thin-Ethernet

Centralized network/hub monitoring

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Explaining FDDI Topology

The main features are: Has a speed of 100 Mbps Normally implemented over fiber optic (fast-Ethernet, UTP) Dual redundancy built in by use of primary and secondary

ring Automatic bypassing and isolation of faulty nodes

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Explaining FDDI Topology

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Fiber Distributed Data Interface

FDDI is based on two counter rotating 100-Mbit/sec token-passing

rings. The rings consist of point to point wiring between nodes which

repeat the data as it is received.

The primary ring is used for data transmission; the secondary is

used for data transmission or to back up the primary ring in the

event of a link or station failure. FDDI supports a sustained transfer

rate of about 80Mbps, a maximum of 1000 connections (500 nodes)

and a total distance of 200 kilometers end to end. There is a

maximum distance of 2 kilometers between active nodes.

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FDDI Station Types

There are two main types of stations, class A which attach directly

to dual rings; or class B which attach to a station acting as a

concentrator.

A concentrator is a specialized workstation that attaches to the ring

and has multiple ports that allow attachment of other devices in a

physical star configuration. These may be cascaded.

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Explaining Mesh Topology

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Understanding Hybrid Networks

Hybrid networks are the complex networks, which can be built of

two or more above mentioned topologies .

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Tree Network

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Hierarchical Star Network

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Star-Wireless Network

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Considerations When Choosing a Topology

Money. A linear bus network may be the least expensive way to

install a network; you do not have to purchase concentrators.

Length of cable needed. The linear bus network uses shorter

lengths of cable.

Future growth. With a star topology, expanding a network is easily

done by adding another concentrator.

Cable type. The most common cable in schools is unshielded

twisted pair, which is most often used with star topologies.

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Understanding Wi-Fi Connectivity

What Is Wi-Fi? The very short version is that Wi-Fi is a way for

wireless devices to communicate. Wi-Fi, short for wireless fidelity, is the Wi-Fi Alliance's name for a wireless standard, or protocol, used for wireless communication, Known collectively as IEEE 802.11.

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The 802.11 Standard and Its Variations

Generally, the core 802.11 standard is intended to specify a way for

computers to network using the 2.4GHz and 5GHz free spectrums.

(When computers network, it is said that they are forming a local

area network, or LAN. When computers network wirelessly, it is

called a Wireless LAN, or WLAN.)

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The 802.11b Standard

The key things to know about 802.11b: The 802.11b standard uses the 2.4GHz spectrum. The 802.11b standard uses a technology called Direct

Sequence Spread Spectrum (DSSS) to minimize interference with other devices transmitting on the 2.4GHz spectrum.

The 802.11b standard has a theoretical throughput speed of 11 megabytes per second (Mbps).

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The 802.11a and 802.11g Standards

The 802.11a standard uses the 5GHz band for transmission, which minimizes the possibility of interference with the plethora of 2.4GHz devices out there (think microwaves, garage door openers, and so on) and promises a theoretic throughput of 24Mbps.

Still newer than 802.11a, 802.11g operates on the 2.4GHz spectrum and boasts throughput as fast as 54Mbps.

In other words, both 802.11a and 802.11g show the promise of being considerably faster than 802.11b.

The chief advantage of 802.11a is that it will run into less interruption from other devices because it does not use the crowded 2.4 GHz band.

Moving to 802.11a has some pluses and minuses, but moving to 802.11g is a no-brainer—because 802.11g systems are backward-compatible with 802.11b, and faster. This backward compatibility of 802.11g devices is a requirement for Wi-Fi certification.

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The 802.11i Standard

The IEEE is in the process of developing a new security standard

for 802.11 that is named 802.11i. The Wi-Fi Alliance has released a

subset of the 802.11i standard that the Alliance has developed

called "Wi-Fi Protected Access."

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Understanding Half- and Full-Duplex Modes

Half-duplexCollision detection is turned on The device can only

send or receive at any given time Devices connected to a hub must

use half-duplex communication Up to the rated bandwidth (10 Mbps

for 10BaseT, 100 Mbps for 100BaseT, etc.)

Full-duplexCollision detection is turned off The device can send and

receive at the same time Requires full-duplex capable NICs

Requires switches with dedicated switch ports (a single device per

port) Double the rated bandwidth (20 Mbps for 10BaseT, 200 Mbps

for 100BaseT, etc.)

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