TOPOLOGY
“The Topology is the geometric representation of the relationship of the links and the linking devices (Nodes) in a Network”Or
“Topology defines the physical or the Logical Agreement of Links in a Network”
Topology of a Network is suggestive of how a network is laid out. It refers to the specific configuration and structure of the connections between the Links and the Nodes. Two or more devices connect to a Link and two or more Links form a Topology
Categories of TOPOLOGY
- Question: What to consider when choosing a Topology????????
- Answer: Relative status of the devices to be linked.
- PEER-TO-PEER: Devices share the link equally
- PRIMARY-SECONDARY: One device controls traffic and the others must transmit through it
MESH TOPOLOGY
- Every device has dedicated a 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
- Each device must have I/O Ports
Example Mesh Topology
In figure above, we have 5 Nodes, therefore:- No. of Links= 5(5-1)/2 = 10
- No. of I/O Ports= 5-1 = 4
- e.g. for 6 nodes = 15 Links
- 7 Nodes=21 Links
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
Star Topology
- Each device has a dedicated point-to-point link to a central controller ( Hub)
- Devices are not directly connected to each other
- Controller (Hub) acts as an exchange
- 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
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
Tree Topology
- A variation of Star Topology
- Nodes in a Tree are linked to a central hub that controls the traffic to and from network
- Difference b/w star and tree is not all the devices plug directly into the central HUB
- Majority connects to secondary hub that is connected to central hub
CENTRAL HUB in Tree Topology
- Central Hub in a Tree is an ACTIVE HUB
- ACTIVE HUB contains a repeater
- Repeater is a hardware device that regenerates the received bit pattern before sending them out.
- Repeater strengthens TX. And increases the distance a signal can travel
Secondary HUB in Tree Topology
- Secondary Hub in a Tree may be Active or Passive HUB
- Passive Hub simply provides physical connection between attached devices
Advantages of Tree Topology
- Because of Secondary Hub, More devices can be attached to a Central Hub and therefore increase the distance a signal can travel
- Enables Differentiated Services: Allows to prioritize communication, e.g. computers attached to one secondary hub can be given priority over others
- Therefore, TIME SENSITIVE data will not have to wait for access to the network
- Rest of the advantages are almost the same as STAR
CABLE TV
- Main cable from main office is divided into many branches and each branch is divided into smaller branches and so on
- Hubs are used when cable is divided
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 or
Punctures the sheathing of a cable to create connection with the metallic core
- Tap is a connector that;
- Signal degrades as it travels, therefore there is a limit on:
- The number of Taps a Bus can support and
- The distance between those Taps
Advantages of BUS TOPOLOGY
- Easy to install
- Backbone can be laid on the most efficient path and then rest of the nodes can be connected using Drop Lines
- Less cabling than Mesh , Star or Tree
- Difference b/w Star Cabling and Bus Cabling
Disadvantages of BUS Topology
- Difficult Reconfiguration
- Difficult to add new devices
- adding new devices may require modification of backbone
- No Fault Isolation
- A fault or break in backbone can disable communication even on the same side of the problem
- Damaged area reflects signals back in the direction of origin creating Noise in both directions
Summary
- Topology
- Categories of Topologies
Reading Sections
- Section 2.2 “Data Communications and Networking” 4th Edition by Behrouz A. Forouzan