Network Topologies (Tutorial-4)

Topology refers to the way in which the network of computers is connected. The choice of topology is dependent upon---

• Type and number of equipment being used 
• Planned applications and rate of data transfers 
• Required response times 
• Cost

Types of Network Topologies

• Physical Topology: Physical topology defines how devices are connected to the network through the actual cables that transmit data(physical structure of the network) 
• Logical Topology: Logical Topology (also referred to as Signal Topology) is a network computing term used to describe the arrangement of devices on a network and how they communicate with one another.

1. BUS Topology

Bus Topology

In a BUS topology:

• A single cable connects each workstation in a linear, daisy-chained fashion. 
• Signals are broadcasted to all stations, but stations only act on the frames addressed to them.
• Standard is IEEE 802.3 

• Thin Ethernet (10Base2) has a maximum segment length of 200m 

• Max no. of connections is 30 devices 
• Four repeaters may be used to a total cable length of 1000m 
• Max no. of nodes is 150

• Thick Ethernet (10Base5) used for backbones 

• Limited to 500m 
• Max of 100 nodes per segment 
• Total of four repeaters , 2500m

2. RING Topology

Ring Topology

In a RING topology: 

• Unidirectional links connect the transmit side of one device to the receive side of another device. 
• Devices transmit frames to the next device (downstream member) in the ring.
• Each device has to wait its turn to transmit 
• Most common type is Token Ring (IEEE 802.5) 
• A token contains the data, reaches the destination, data extracted, acknowledgement of receipt sent back to transmitting device, removed, empty token passed on for another device to use.

3. STAR Topology

Star Topology

In a star topology:

• Each station is connected to a central Hub or Switch (concentrator) that functions as a multi-port repeater. 
• The HUB broadcasts data all of the devices connected to it. 
• The Switch transmits the data to the dedicated device for which the data is meant for. 

4. Extended Star Topology

Extended Star Topology

A Star Network which has been expanded to include an additional hub or hubs.

5. Mesh Topology

• Not common on LANs 
• Most often used in WANs to interconnect LANS 
• Each node is connected to every other node 
• Allows communication to continue in the event of a break in any one connection 
• It is “Fault Tolerant”

Mesh Topology

6. Hybrid Topology

Hybrid Topology

• Old networks are updated and replaced, leaving older segments (legacy). 
• Hybrid Topology – combines two or more different physical topologies.
• Commonly Star-Bus or Star-Ring.
• Star-Ring uses a MAU (Multistation Access Unit).