This document discusses different network topologies including mesh, star, bus, ring, and hybrid topologies. It describes the advantages and disadvantages of each topology. It also discusses categories of networks like local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs). Finally, it covers network protocols, standards, and standards organizations that govern data communication.

1. Lecture#02
Computer Communications
& Networks CS-576

2. Physical Topology
 Topology refers to the physical or logical arrangement of a
network.

3. Mesh Topology
 In a mesh topology, every device has a dedicated point to point link to
every other device.
• Dedicated: Means that the link carries traffic only between these two
devices
• Links to connect ‘n’ devices.
• n(n-1)/2
• Number of I/O Ports: n-1

4.  Example
In figure above, we have 5 Nodes, therefore:
No. of Links= 5(5-1)/2 = 10
No. of I/O Ports= 5-1 = 4

5.  Advantages of mesh topology
• Use of Dedicated links guarantees that each connection can carry its
own load. This eliminates Traffic Problems as in case of Shared Link
• Mesh Topology is robust. If one link fails, it does not effect other
links
• Security & Privacy due to dedicated links
• Point – to –Point links make Fault Identification easy
 Disadvantages of Mesh Topology
 Amount of Cabling
 Makes Installation & Reconfiguration difficult
 Sheer bulk of wiring can be greater than the available space
 Number of I/O Ports Required
 Hardware required to connect each link can be
prohibitively expensive
 Therefore, Mesh topology has limited use

6. Star topology
• Each device has a dedicated point-to-point link to a central controller (
Hub).
• Controller (Hub) acts as an exchange
• Devices are not directly connected to each other .
• If one device wants to send data to the other, it sends the data to the
controller , which then relays it to the other connected device

7.  Advantages of star topology
• Less Cabling
• Less Expensive than Mesh as each device need sonly one link
and one I./O Port
• Easy to Install and Reconfigure
• Robust, if a link fails , only that link fails
• Easy Fault Detection
 Disadvantages of star topology
 Although Cabling required is far less than Mesh Still each
node must be connected to a Hub , so Cabling is still much
more than some other Topologies.
 Failure of the central hub renders the network inoperable

8. Bus topology
 Drop Lines and Taps
 Drop Line is the connection between device and the main
cable (Backbone)
 Tap is a connector that Splices into the main cable

9. • Advantages of Bus Topology
 Easy to install
 Less cabling than Mesh , Star or Tree
 Disadvantages of Bus Topology
 Difficult Reconfiguration
 A fault or break in backbone can disable communication.

10. Ring Topology
 Each device has point-to-point dedicated link with only two
devices on either side.
 Each device receives from previous device and transmits it to the
next device.
 The message flows in one direction.

11.  Advantages of Ring Topology
 It less expensive than star and mesh.
 Every device has equal access to the network.
 Disadvantages of Ring Topology
 Failure of one device in the ring can affect the whole network.
 Adding or removing networks affect the whole network

12. Hybrid Topologies
 Several topologies combined in a larger topology
 Example: One department of a business may have decided
to use a Bus while other has a Ring
 The two can be connected via a Central Controller in Star
Topology

13. Categories of Networks

14. Local Area Networks
 A local area network is usually privately owned and links
the devices in a single office, building, or campus.
 Data rates much higher

15. Metropolitan Area Networks
 A MAN is a data communication system covering an area
the size of a town or city.
 Middle ground between LAN and WAN
 High speed

16. Wide Area Network
 A WAN is a data communication system spanning states,
countries, or the whole world.
 Typically , it consists of a large number of Switching Nodes
 Transmission from any one device is routed through these
internal node to the specified destination device

17. WAN Implementation
Traditionally, WANs have been implemented using one of
two technologies:
 Circuit Switching
 Packet Switching
 Circuit Switching
In a circuit switching network, a dedicated communication
path is established between two stations through the
nodes of the network. Telephone network is a example of
Circuit switching.

18.  Packet Switching
In packet Switching it is not necessary to dedicate
communication path between two stations. Data are sent
out in a sequence of small chunks, called packets.
 Frame Relay
Packet switching systems have large overheads to
compensate for errors .Modern systems are more reliable.
Errors can be caught in end system..Most overhead for
error control is stripped out.
 ATM(Asynchronous Transfer Mode)
Evolution of frame relay. Little overhead for error control.
Fixed packet (called cell) length. Anything from 10Mbps to
many Gbps

19. Protocols and Standards
 Protocol
A protocol is a set of rules that govern data communication
 Protocol defines:
What is Communicated?
How it is Communicated?
When it is Communicated?
 KEY elements of a PROTOCOL
 Syntax: Syntax refers to the structure or format of the data. For
example, a simple protocol might expect the first 8 bits of data to be
the address of the sender, the second 8 bits to be the address of the
receiver, and the rest of the stream to the message itself.

20.  Semantics: Semantics refers to the meaning of each section
of bits. For example, does an address identify the route to be
taken or the final destination of the message?
 Timings :
Refers to 2 characteristics:
 When data should be sent?
 How fast it should be sent?
 For Example
 If sender produces data at 100 Mbps
 But Receiver can only process data at 1 Mbps
 The TX. will overload receiver and data will be lost

21. Protocols and Standards
 Standards
Standards are necessary to ensure that products from different
manufactures can work together as expected.
Data communication Standards fall in to two categories: de facto and de
jure.
 De facto(By fact or by convention)
Meaning by fact, standards that have not been approved by an
organized body but have been adopted as standards through
widespread, Often established originally by manufactures that
seek to define the functionality of a new product or technology.
 De jure(By law or by regulation)
Those that have been legislated by an officially recognized
body.

22. Standards Organizations
 International Organization for Standardization (ISO)
 International Telecommunication Union-
Telecommunication Standards (ITU-T)
 American National Standards Institute (ANSI)
 Institute of Electrical and Electronics Engineers (IEEE)
 Electronic Industries Association (EIA)