Transmission of digital data
A network is defined as an interconnected collection of computers. Two computers are said to be interconnected, if they are capable of exchanging information. The term topology, in context of a communication network, refers to the way in which the end systems or stations are interconnected. Topology has been used in past to categories the local area networks because it determined the way in which the network operated. But today, we find same topology can be operated in many ways.
LOCAL AREA NETWORK (LAN)
A networked of interconnected computers, which exists within a limited geographical area, such as a room, a building or a campus, is termed as a Local Area Network. Few characteristics of LAN are as below:
• Speed 4, 10, 16 up to 100MBPS
• Distance Few KMs (Typically 1.5KMs)
Common LAN topologies are Bus, Ring and Star, Network requirements of these topologies are:
• Flexible to accommodate
- Changes in physical location of the stations
- Increase in number of stations. (MP GK)
In bus topology, a single transmission medium interconnects all the stations. All stations share this medium for transmission to any other station. Every stations listens to all the transmissions on the bus. Every transmission has source and destination address so that stations can pick the messages meant for them and identify their senders.
Advantages of bus topology:
- Stations are connected to the bus using a passive tap.
- Least amount of media is used.
- Coverage can be increased by extending the bus using repeaters.
- New stations are easily added by tapping working bus.
Disadvantages of bus topology :
- Fault diagnostics is difficult
- Fault isolation is difficult
- Nodes must be intelligent
A ring network (CET) consists of a number of transmission links joined together in form of a ring through repeaters called Ring interface Units (RIU). The transmission is usually unidirectional on the ring Thus each repeater receives the signals at its input and after regeneration, sends it to the repeater of the next station. If the frame belongs to the station, a copy of the incoming frame is retained. Each frame contains source and destination addresses.
Advantages of Ring topology:
• Short cable length
• Suitable for optical fiber
Disadvantages of Ring:
• Node failure cause network failure
• Difficult to diagnose fault
• Network reconfiguration is difficult
A star network consists of dedicated links from the stations to the central controller. Each interconnection supports two-way communication. The central controller acts as a switch to route the frames from source to the destination unlike ring or bus topologies where communication is in broadcast mode.
Advantages of star topology:
• Control/fault diagnostics is centralized.
• Simple access protocols are employed.
• Ease of service
• One device per connection