Lecture 8 - LANs

Why a LAN?

Purpose of a Local Area Network: to share things within a fairly small area, perhaps 100 - 500 meters. You might set up a LAN in order to share hardware, software, or information:

Hardware

(Laser printer, hard disk, plotter, modem, fax, etc.)

Hardware sharing might extend to creation of a SAN (Storage Area Network).

Software

First, application software might be stored on the server and downloaded to workstations as needed.

"Groupware" is another type of software that can facilitate group work

Advantages of LAN

Cheaper than mainframes. More efficient than mainframes

Administrative Advantages Easier to update software that is used by

staff at their workstations Encourages use of common application

software Saves disk space: one copy of application

on LAN server vs. scores on each PC Control issues improved Security is easier to maintain

Administrative Advantages Backups can be made on the server Intranets Cheap, tough, ready-made system for

distribution of internal information Not platform specific Might have access To (but not BY)

outsiders, ie, the internet

Type of Networks

Server based: this is the model that most often comes to mind

Peer to peer: You may not need a server, especially for smaller LANs. Peer to peer is simpler, cheaper, and easier to maintain. Go with peer to peer if you can.

Peer to peer has no server, although all PC can act as a server. Can share hard drive, CD ROM drive, printer, modem, etc

Disadvantages Can be troublesome to install and maintain Components/aspects of system may conflict with

other components/aspects; it can be hard to pin down cause of problems

Complex systems may suffer from Murphy's Law Managers don't always recognize the problems

that come with this complexity: they expect LANs to run themselves or for some suffering staff to administer the LAN in their "spare time."

Possible Components

In order to set up a LAN you might need: workstations/nodes, a server, peripherals (see Hardware above), networking facilities like a Network Interface Card

(NIC). You will also need Network Operating System

(NOS). These might include Unix/Linux, Windows NT (and its

progeny XP etc.) and Novell Netware. It is increasingly unlikely but you might also see Lantastic and Banyon Vines in older, smaller library LANs.

LAN hardware protocols Hardware protocols are blueprints or

standards that define how the nodes recognize each other, how messages are sent so they don't collide, and such.

They are not software or hardware or even wires: they are the blueprint for defining elements of the LAN.

There are a number of hardware protocols but you are most likely to see ethernet and possibly token ring.

Ethernet Standard.

Fast, cheap, rigorous, and everywhere. Original ethernet was 10 million bps, but most

today operate at 100 Mbps. Newer ethernet tech extends up to a gig bps, and

there's more coming. Ten gigabit ethernet is on the way and then, after that,

yet another jump in speed is being drafted. Ethernet avoids conflicts by sending node

broadcasting over network, and other nodes listen for messages intended for them.

IBM Token Ring

Slower. Losing market share

Uses virtual token to avoid conflicts. Speed 4+ Mbps.

Connecting one LAN to other LANs:

Bridges. connect networks with the same OS

Gateways. connect networks with different OSs, and/or mainframes

Routers. Like a smart Bridge/Gateway. Knows the exact address of messages and thus can choose the best route. Can serve as a firewall.

Cabling

Most expensive component of a LAN Can run to 50 or even 75 percent of the LAN cost.

Most LANs consist of a combination of wire types: Twisted pair - Copper telephone wiring, cheaper and

slower. Unshielded is around 16 cents a foot in bulk Shielded TP is around 20 cents per foot 10baseT runs 100 meters without a repeater using 4 pairs Deciphering 10baseT: 10 means a signaling rate of 10 Mbps,

base means baseband,

Cabling

Coaxial cable -Seldom seen today except in old LANs.

Fiber optics -Fast but expensive, can be tricky to install. No electrical interference, can transmit long distances, does not corrode or spark. Difficult to tap. Often used between buildings or even between floors with copper wire used within a building or floor.

Alternatives to Cabling:

Because pulling cable is expensive, libraries and other organizations sometimes look for ways to set up LANs without physically installing wires. These alternatives include:

Installed phone wires, Home PNA, Tut Homerun for example

Building's electrical grid, the electrical wires in the building.

Wireless: Hot Technology Based on IEEE 802.11 standard. May also be called Wi-

Fi (Wireless Fidelity). There are currently 3 standards: 802.11b offers up to 11Mbps on a 2.4GHz frequency.

A disadvantage with the 2.4GHz band is interference from cordless phones and microwaves.

The next protocol is standard 802.11a. Rarely used and not compatible with other protocols as it operates on a 5 GHz frequency. 802.11a is capable of speeds up to 54Mbps, yet the distance is short: approximately 100 feet as against 300 feet for 802.11b.

The 3rd standard is 802.11g. It can also run at a speed of 54Mbps, but also can maintain a range of 100-150 feet and is compatible with standard 802.11b. Since it runs on 2.4GHz, interference with household appliances remains a problem.

Wireless: Hot Technology

High-tech companies led by Intel joined in an international effort to support wireless technology and applications for governments and communities. T

The Digital Communities initiative supports 13 communities that are designing, developing, and deploying Wi-Fi, mesh, or other wireless networks and applications.

In the United States, Portland, Oregon; Corpus Christi, Texas; Philadelphia, and Cleveland are participants. Applications include support for municipal inspections and repair, law enforcement, and emergency response. Taipei, Taiwan, and Jerusalem, Israel, will also test Wi-Max.

Wireless: Hot Technology

Topologies:

Bus: Rarely installed today. Tough to troubleshoot

Ring and token ring Star: Most common topology today.

Easy to troubleshoot. Can piggyback on existing phone wiring system

Combinations/hybrids

Staffing!

Perhaps the most important, but most overlooked component of a LAN.

Some authorities recommend one LAN administrator for every 50 Workstations installed.