Basic Concepts

Basic Concepts

Five general concepts provide the basis for the

relationship between the communicating devices.

Line configuration

Topology

Transmission mode

Categories of Networks

Internetworks

(Line configuration)

~ refers to the way two or more communication devices attach to a link

~ defines the attachment of communication devices to a link

Line configurationLine configuration

MultipiontMultipiontPoint-to-pointPoint-to-point

Line configuration (cont’d) (Point-to-point)

~ provides a dedicated link between two devices.

(Multipoint) : multidrop

~ is configuration in which more than two specific devices share

a single link

Line configuration (cont’d)

Link

Line configuration (cont’d)

Link

Line configuration (cont’d)

Line configuration (cont’d)

Link

(Topology)

~ refers to the way a network is laid out, either physically or logically

~ defines the physical or logical arrangement of link in a network

A consideration when choosing a topology is the relative status of the devices to be linked.

peer-to-peer : the devices share the link equally (ring, mesh)

primary-secondary : one device controls traffic and the others

must transmit through it (star, tree)

(Categories of topology)

TopologyTopology

MeshMesh StarStar TreeTree BusBus RingRing

(Mesh) Every device has a dedicated point-to-point link to every

other device.

A fully connected mesh network therefore has n(n-1)/2 physical channels to link n devices.

Mesh (cont’d) Mesh topology

Mesh (cont’d)

Advantages

The use of dedicated links guarantees that each

connection can carry its data load.

Mesh topology is robust.

Privacy and security.

Point-to-point links make fault identification and fault

isolation easy.

Mesh (cont’d) Disadvantages

~ are related to the amount of cabling and the number of I/O ports

because every device must be connected to every other device, installation and reconfiguration are difficult

More wiring space requirement

the hardware required to connect each link (I/O port and cable) can be prohibitively expensive

(Star )

Each device has a dedicated point-to-point link only to a

central controller, usually called a hub

Star (cont’d) Star topology

Star (cont’d)

Advantage

Each device needs only one link and one I/O port to

connect it to any number of others (easy to install and

reconfigure)

Robustness

if one link fails, only that link is affected Disadvantage

failure of the central hub leads to the failure of the entire network.

(Tree)

is a variation of a star

active hub(central hub)

~ contains a repeater, which is a hardware device that

generates the received bit patterns before sending

them out

passive hub

~ provides a simple physical connection between the

attached devices

Tree (cont’d) Tree topology

Hub Hub

Hub

Tree (cont’d) Advantage & Disadvantage

are generally the same as those of a star

(Bus) is multipoint. One long cable acts as a backbone to link all

the devices in the network

Nodes are connected to the bus cable by drop lines and taps

drop line

~ is a connection running between the device and the main cable

tap

~ is a connector either splices into the main cable or punctures the

sheathing of a cable to create a contact with the metallic core

Bus (cont’d) Bus topology

Bus (cont’d) AdvantagesAdvantages

– ease of installation

– best suited for small networks.

DisadvantagesDisadvantages

– cable length is limited. This limits the number of stations that can be connected

– difficult reconfiguration and fault isolation

Twenty network devices on a segment, and the segment cannot exceed 185 meters in total length

By using repeater we can have up to five segments on a network.

However, only three of these segments can have devices attached to them.

The other two segments are used to link the three populated segments, giving you a maximum number of sixty devices with a total network length of 925 meters.

(Ring) Each device has a dedicated point-to-point line configuration only with the two

devices on either side of it

AdvantageAdvantage

– Relatively easy to install and reconfigure

– Fault isolation is simplified

– Central node is not required

DisadvantageDisadvantage

unidirectional traffic

break in the ring (due to failure of a node or a link) can disable the entire network

needs dual ring

Ring (cont’d) Ring topology

(Hybrid topology)

2.3 (Transmission mode)

~ is used to define the direction of signal flow between

two link devices

(Simplex)

is unidirectional, as on a one-way street (keyboard, monitor)

(Half-Duplex)

each station can both transmit and receive, but not at the same

time

(Full-Duplex)

both stations can transmit and receive simultaneously

Transmission Mode (cont’d)

Transmission modesTransmission modes

Half-duplexHalf-duplexSimplexSimplex Full-duplexFull-duplex

Transmission Mode (cont’d) 단방향 (Simplex)

MainframeMonitor

Direction of data

Transmission Mode (cont’d) 반이중 (Half-Duplex)

Workstation Workstation

Direction of data at time 1

Direction of data at time 2

Transmission Mode (cont’d) 전이중 (Full-Duplex)

Workstation Workstation

Direction of data at all the time

2.4 (Categories of Networks) three primary categories

(LAN)

(MAN)

(WAN)

size, ownership, distance it cover, physical architecture

Categories of Networks (cont’d)

Metropolitan area network(MAN)

Metropolitan area network(MAN)

Local area networks(LAN)

Local area networks(LAN)

Wide area network(WAN)

Wide area network(WAN)

NetworkNetwork

Categories of Networks (cont’d) LAN(Local Area Networks)

~ is usually privately owned and links the devices in a single office, building or campus

Categories of Networks (cont’d) Single building LAN

Categories of Networks (cont’d) Multiple building LAN

Backbone

Categories of Networks (cont’d) MAN(Metropolitan Area Networks)

~ is designed to extend over an entire city

Categories of Networks (cont’d) MAN

Public city network

Categories of Networks (cont’d) WAN(Wide Area networks)

~ provides long-distance transmission of data, voice, image, and video information over large geographical areas that may comprise a country, a continent, or even the whole world

Categories of Networks (cont’d) WAN

2.5 (Internetworks)

~ is an interconnection of networks by the use of internetworking device (router and gateway)

internet: an interconnection of networks

Internet: a specific worldwide network

Internet is a global system of interconnected computer networks that use the standard Internet protocol suite (TCP/IP) to serve billions of users worldwide.

Internetworks (cont’d)

Internetwork (internet)