WAN

• Wide geographic area, national or international

• Low to High speed links

• Remote links: operational LANs or groups of workstations

• Trad. Definition: LAN becomes WAN when your network goes beyond premises and you lease lines from public carrier

Apart from geographic spread, benefits/features are the same

Resource sharing (low cost, higher user productivity)

Common apps. (network aware, easy user transition, lower cost of network licensing)

File sharing (e.g. Databases. Higher user productivity)

Data security (centralised storage, easier backups)

Fault tolerance (UPS, RAID, etc.)

Centralised security (can meet organisational needs)

Communications (messaging, email)

Peer-to-Peer

• Often called 'workgroup solution'

• Each system acts a bit like a server, managing it's own security and resources

• E.g. OS: Win for Workgroups, Win 95/98/NTws, Mac OS 8.x

Hardware

• Servers

  • e.g. Multiple CPUs, heavy-duty cooling, higher RAM and storage, redundant PSUs,

  • Maybe RISC-based, minicomputers or mainframes

  • Shared peripherals (e.g. Modems, printers, CD-ROM)

• NIC

  • Each server/workstation will have at least one

  • Goes to cable plant

• Cable plant

  • The communications path between server(s) and client(s)

  • May contain e.g. bridges, routers and gateways

Pressures to link LANs:

• Physical limitation

• Common user needs in different locations

• Resource management and troubleshooting improvement

Decision criteria when linking networks:

• Organisation structure

• Network management style

• Flexibility/Scalability requirements

• Consistent interface

Even though a LAN may be defined as 'a network within a building', this may require more than one LAN connected via a vertical backbone

MAN (Metropolitan Area Network)

• Networks that are non-contiguous but in same calling area (i.e. Local Access Transport Areas (LATAs) )

• Local phone Co. or Alternate Service Providers (ASPs) supply the comms to link them.

WAN (Wide Area Network)

• links networks that are in different LATAs .

• Uses public carriers (dial-up lines, dedicated lines, packet switching)

Major difference between LAN/CAN and MAN/WAN:

• COST!

  • LAN/CAN

    • One time cable installation, low cost of maintenance

  • MAN/WAN

    • Low cost installation, but costly monthly usage fees

• SPEED!

  • LAN/CAN – 10/16/100 Mbps

  • MAN/WAN – e.g. T1 (1.544 Mbps)

  • LAN/WAN bottleneck (10 lanes of traffic into 1!)

Broadband

• Different frequencies are used to separate concurrent signals

• Each freq. can only be used for one-way communication

• cf. Cable TV

• Dramatically increased speed, but equipment costs more

Full-duplex

• Can transmit and receive at the same time

• cf. Traditional phone conversation

• Benefit: increased speed

• Drawback: increased cost of equipment

Traditionally LANs have been half-duplex

Recently some are going full-duplex, especially for servers

Commonly used for telephone and LAN comms

Classifications

• 'Levels' from Underwriters Laboratories (UL)

• 'Categories' from Electrical Industries Association (EIA)

  • Category 3 UTP (#24 AWG)

    • 10 to 100 Mbps, depending on installation

    • EMI and imperfections can problems

  • Category 5 UTP (#24 AWG)

    • More twists per foot and better insulation than Cat3

    • More reliable up to 100 Mbps

Basic facts:

• Low Cost

• Easy to install (Crimpers and punch-down tool)

• Capacity (1 to 100 Mbps, 10 Mbps the most common)

• Rapid Attenuation (limited to 100s of metres)

• Very susceptible to EMI

Basic Facts:

• Moderate Cost

• Not as easy to install as UTP (shielding must be grounded, special connectors/techniques)

• Capacity (up to 500 Mbps, some 155 Mbps exist, though usually implemented as 16 Mbps)

• Attenuation similar to UTP (100m for 500 Mbps, longer for lower speeds)

• Lower EMI than UTP because of shield, though some exists

Star topology

No. of stations set by concentrator (hub) ports, hubs can be linked together

Up to 1024 stations per network

#24 AWG unshielded dual twisted pair

One network device per cable

Distance to concentrator: <100m (328ft), >0.6m (2ft)

Auxiliary Unit Interface (AUI) can attach workstations to TP cable via RJ-45

Pentium-grade PCs with PCI keep up, though older ISA may improve it will not be as fast

100BaseT4

• Uses Cat 3, 4 or 5 UTP (all eight wires) - Cat 5 most reliable

• Needs 100BaseT4 hubs and NICs

• Limitations compared to older 10 Mbps:

  • 5m connections between backbone hubs

  • 100m connections between workstation and hub

100BaseTX

• Requires Cat 5 UTP

• More reliable and will perform better under heavy load

• More devices manufactured, so competitive pricing

• Distance limitations identical to 100BaseT4

100BaseFX

• Fiber Optic – see later

Originally used STP and IBM hermaphroditic connectors

Adopted to use UTP and RJ-45

Will run at either 4 Mbps or 16 Mbps (cannot be mixed)

IBM Token Ring Wiring Specification:

Requires 100VG-AnyLAN NICs, repeaters, hubs, etc.

Will integrate with existing LAN technologies

Uses a frame format at the Data Link Layer that supports MAC and LLC sublayer, so will integrate with existing NOS and apps using appropriate NICs and drivers

Physical star topology

Uses Demand Priority channel access method

• Type of packet determines priority – normal or high

• High...

  • destined for high priority repeater port

  • time-sensitive (audio, video, other critical data, etc.)

  • Normal traffic that has been waiting over 200ms

Repeaters don't allow promiscuous mode – good security!

Offers many benefits, but take-up has been slow

RJ-45 Pin out (used):

Always check what's being transmitted on the wire!

Special apps may damage hardware

Modular Cable Termination Process (Crimping)

Must be terminated at both ends

• Connect inner to outer conductor with specified resistor

• Creates circuit allowing data transmission

• Many terminators have grounding wire (e.g. To water pipe)

Outer conductor must be grounded at ONE end

For networking, primarily used for Ethernet

May be baseband (for Ethernet) or broadband (for TV)

Basic Facts:

• Moderate Cost

• Clumsy to install for workstations, good for hub-to-hub / building-to-building

• Capacity (1 to 100 Mbps, 10 Mbps the most common)

• Moderate to low attenuation (with repeaters, 1000s of metres)

• Some EMI sensitivity

• Some coaxial cable types:

10Base2 requires BNC and RG58 cable

Pin out:

Linear bus topology

Often called “Cheapernet” or “Thinnet”

5-4-3 rule:

• 5 cable segments, 4 repeaters, 3 populated segments

Inter-repeater links: unpopulated segments

Transceivers attaches nodes to cable

Cables are only grounded on one end

Most of cost goes into the interfaces (data-to-light and vice versa)

Ideal for hazardous, high-voltage or secure environments

Classified based on diameter of core

• Most LAN <span>fiber</span> networks use 62.5 micron cable

Fiber is Type 5 in the IBM cabling system

Basic Facts:

• Moderate to expensive cost

• Tedious and expensive to install

• Capacity (up to 4 Gbps)

• Extremely low attenuation (up to 2km)

• Immune to EMI (very secure)

ST

• most common

• keyed BNC-style

SC

• international standard push-pull connector

• advantage: both TX and RX fibers in a single duplexed clip

SMA

• obsolete threaded connector

• (dis)connecting tended to scratch the end of the fiber strand

Installation

• cutting and polishing the end of the glass strand then mounting to the connector

• Used to be very skilled, but new tools help a lot

Eliminates EMI (interference) and EMR (radiation)

Very costly to implement

Direct

• must have line of sight between devices

• this is a limitation, but hard to intercept so more secure.

• Mostly used to link devices in same room

Indirect

• signal bounces off walls, ceilings, objects, etc.

• not confined to pathway so insecure

Can work at 100 Mbps and probably higher

Can span distances of up to 1,000 m. (c.f. Multi-mode fibre)

Can permeate walls so useful, but easy to intercept

Subject to EMI and interference from other RF sources

Frequency and location must be licensed from FCC

Two common technologies

• Narrowband

  • high energy at a single frequency

  • easy to intercept

• Spread spectrum

  • lower-level signal over several frequencies simultaneously

  • quite secure

Moderate throughput, can be as high as 10 Mbps