Chapter 2
Basic Concepts
Line Configuration
Topology
Transmission Mode
Categories of Networks
Internetworks
Line Configuration
defines the attachment of communication devices to a link

a link is a physical communication pathway that transfers data
from one device to another
Line Configuration
Point-to-point

A dedicated link between two devices, i.e. the entire capacity of
the channel is reserved for transmission

e.g. wire
Line Configuration
Point-to-point

A dedicated link between two devices, i.e. the entire capacity of
the channel is reserved for transmission

e.g. wire
Line Configuration
Point-to-point

A dedicated link between two devices, i.e. the entire capacity of
the channel is reserved for transmission

e.g. microwave and satellite links, etc.
Line Configuration
Multipoint

more than two devices share a single link


spatially shared– several devices can share the link simultaneously
time-shared – devices take turn to use the link
Topology
defines the physical or logical arrangement of links in a
network

geometric representation of the relationship of all links and nodes
Topology - Mesh
each node has a dedicated point-to-point link to every
other node
Topology – Mesh
Advantages




each connection can carry its own data load – eliminating traffic
problems
if one link becomes unusable, it does not incapacitate the entire
system – robust
a dedicated line guarantees security
easy fault identification and fault isolation - reroutable
Disadvantages


the amount of cabling and number of i/o ports required
expensive
Topology – Star
Each device has a dedicated point-to-point link only to a
central controller (or hub).
Topology – Star
Advantages




only one link and one I/O port required per device
less expensive than mesh topology
if one link fails, only that link is affected – robust
easy fault identification and fault isolation (as long as the hub is working)
Disadvantages


if the hub fails, the network is down
requires more cabling than tree, ring and bus topologies
Topology – Tree
A variation of a star – majority of devices are connected to
secondary hubs (active/passive) than a central hub (active).
Topology – Tree
Advantages



generally similar to star
secondary hubs allow more devices to be connected – increase
the distance
allows the network to isolate and prioritize communications from
different computers
Disadvantages

generally similar to star
Topology – Bus
One long cable (the backbone) link all the devices in the
network – multipoint
Topology – Bus
Advantages


easy installation
use less cabling than mesh, star or tree
Disadvantages


difficult reconfiguration and fault isolation
a fault or break in the bus cable stops all transmission
Topology – Ring
Each device is linked only to its immediate neighbors
Topology – Ring
Advantages


each device incorporates a repeater
easy to install and reconfigure
Disadvantages

in unidirectional traffic, a break in the ring can disable the entire
network (some implementations use a dual ring or a switch)
Topology – Hybrid
combination of several topologies as subnetworks linked
together in a larger topology.
Transmission Modes
the direction of signal flow between two linked
devices.
Transmission Mode
simplex – the communication is unidirectional – only of the two
devices on a link can transmit, the other receive
Transmission Mode
half-duplex – each device can both transmit and receive, but not
at the same time.
Transmission Mode
full-duplex (or duplex) – both devices can transmit and
receive simultaneously
Categories of Networks
Determined by its size, ownership, distance covered and
physical architecture
Local Area Network (LAN)
Usually privately owned and links the devices in a single
office,
building or
campus
Local Area Network (LAN)
Size limited to a few
kilometers
Common topologies
are bus, ring and
star
High data rate –
4/10/16 Mbps to
100 Mbps or
gigabits
Metropolitan Area
Network (MAN)
Extend over entire city, may be wholly owned by a private
company, popular service SMDS
Wide Area Network (WAN)
long-distance transmission over large geographical areas
(continent/world)
utilize public,
leased or private
communication in
combinations
An enterprise
network is a WAN
owned by one
company
Internetworks
internet – network of networks