NETWORKING

LECTURE 1

Topologies

What is a network

A network can be considered as being made up of components (nodes), some of the nodes can store data. The nodes are connected by channels. The channels facilitate transmission of data between nodes using data communications technology.

The arrangement of connections yields a particular structure (topology).

Everyday Networking

In our everyday life, computer networks have an impact e.g.

Supermarket POS. tills are networked to the main server and update a central database

Bank ATM Machines are part of the huge (global) financial network

Argos tills allow a stock check to be performed at the POS

The Internet is the largest network and hosts services such as the World Wide Web

LOCAL AREA NETWORK (LAN) .

Is defined as a group of nodes (microcomputers or terminals) located in the same general area (building or campus) connected by a common cable (channel).

LAN’s tend to offer higher speeds of data transmission (bandwidth). Generally LAN’s do not use public ptt services, the cables / channels used are normally wholly contained on private land.

Other Network Types

Wide area networks (WAN’s) are used to connect LANS and normally utilise the PSDN.

Metropolitan area networks (MANS).Networks that span a geographical area which usually encompasses a city or county area, such as the m25.

Mans tend to be very high speed and use similar technology to LAN’s.

Other Network Types

Value Added Networks (VAN’s) (Public Data Networks)

These are networks which can span a large geographical area but include software which give specialised functions or services: tradernet, dow-jones news retrieval service. pss.

Ethernet Terms

10base2 10Mb/s up to 200Mtrs 10base5 10Mb/s up to 500 Mtrs 100baseT 100Mb/s (Fast Ethernet) 100BASE-TX: Two pairs of high-quality

twisted-pair wires

100BASE-T4: Four pairs of normal-quality twisted-pair wires

100BASE-FX: Fiber Optic cablesFDDI “Fibre distributed data interface” 100Mb/s up to 100Km!

Ethernet 802 standards

IEEE 802.1: Standards related to network management. IEEE 802.2: General standard for the data link layer in the

OSI Reference Model. The IEEE divides this layer into two sublayers -- the logical link control (LLC) layer and the Media Access Control (MAC) layer. The MAC layer varies for different network types and is defined by standards IEEE 802.3 through IEEE 802.5.

IEEE 802.3: Defines the MAC layer for bus networks that use CSMA/CD. This is the basis of the Ethernet standard.

IEEE 802.4: Defines the MAC layer for bus networks that use a token-passing mechanism (token bus networks).

IEEE 802.5: Defines the MAC layer for token-ring networks. IEEE 802.6: Standard for Metropolitan Area Networks

(MANs).

Common LAN Topologies

Bus

Star

Ring

BusTerminator

Terminator

Workstation

Workstation

Workstation

Server

Printer

Data flow

Advantages of Bus Topology

Simplicity of layout and ease of connectivity Cheap because there is much less cable to run Location of cable faults is relatively easy and this

ensures minimum network “down time” in the event of a fault

Ideal for one to many transactions because all connected devices hear the traffic on the cable. This is because the traffic flow is bi-directional

A workstation can be disconnected from the network without disruption to the others.

Disadvantages of Bus Topology

There is a security disadvantage since eavesdropping on other stations traffic is relatively easy

There is no automatic acknowledgement of receipt because the signals stop when they reach the terminator (end of the BUS) and do not, by default, return to the sender

If there is a cable breakdown then all workstations on that segment of the BUS will be DOWN (Unable to access the network)

Star

Workstation

Workstation

Workstation

Workstation

WorkstationWorkstation

Workstation Mainframe (Router)

Data flow

Advantages of Star Topology

Star topology gives the highest speed and security because each workstation is connected to the server by its own unique link therefore no workstation can interact with another without going via the central node.

Bandwidth is less of a problem because data for one machine only is being sent down each of the single lines.

Disadvantages of Star Topology

Each station has to be cabled back to the central hub, this would be an expensive option with many workstations

If a link becomes severed then the computer on that link would become disabled. With some other systems the data could have been re-routed for example by using a double loop on a ring network.

Ring (Token ring)

Workstation

Server

Workstation

Workstation

Workstation

Workstation

Data flow

Advantages of Ring Topology

There is an opportunity to see the packet generated therefore it would be easy to implement automatic acknowledgements.

The signal regeneration facility allows longer cable runs

Disadvantages of Ring Topology

Security like the BUS topology is a problem Due to the signal regeneration in each ring interface

there is a delay of at least 1 bit (usually 2 or 3) to allow the facility to work this can slow the system down. therefore it follows that the more active nodes on the ring the greater this delay can become.

There is a risk of someone else holding the token when you want to access. This can also introduce a short delay before access is granted.

The network is lost to all stations if a workstation is disconnected from the cable run due to the repeater.

Star – Bus Networks

Hub Hub

HubTerminal

Network Server

Terminal

Terminal

Terminal

Laser printer

Terminal

Dot-matrix printer

Mac SE/Classic

Mac Quadra

Terminal

Terminal

Bus wiring (Hub to Hub)

Bus wiring (H

ub to Hub)

Bus wiring (Hub to Hub) Star wiring (Server to Hub)

Router implementation

X.25 Cloud

Bus network Star network

Computer

Computer

Router Router

Mesh Topology (WAN)Destination

Originator ofmessage

Fully and Partially connected MESH Topology

Partially connected MESHFully connected MESH

Peer to Peer Networking

Peer to Peer networking refers to networking between workstations each with equal “status” on the network

Used for small businesses/home use Is relatively easy to set up Danger of data duplication Limited security on Win 95/98…

Windows 2000/XP is much improved

Client/Server Networking

Client Server networking refers to workstations (Clients) accessing a central point (Server)

Used in large businesses Less risk of data duplication with CENTRAL

data store (the server) Much improved and more flexible security

via the NOS (Novell/NT etc) Easier to administrate centrally

Cable Types

Bandwidth

Band 1 Send

Band 1 Receive

Band 2 Send

Band 2 Receive

Band 3 Send

Band 3 Receive

Band 4 Receive

Band 4 Send

The motorway analogy make it easier to understand, the more lanes (bandwidth) there are on a motorway the more traffic it can carry at any one time. Also the less congested the motorway is, the faster traffic can flow, up to the speed limit (e.g. 10Mb/s or 100Mb/s) therefore there are less traffic jams which is the same as a computer seeing the network as busy.

Bandwidth is a physical limitation of any communication system. The lower the bandwidth the cheaper it is to produce but the rate at which data can be transferred is lower.

Summary

We have talked about:- What is a network? Types of network LAN/WAN/MAN Bus/Star/Ring/Mesh Topologies Ethernet standards Cable types Bandwidth Introduced P2P & Client-Server

Tea break…!