A collision domain refers to a network segment where packets sent from one device can collide with packets sent from another device. Collisions occur when two devices on the same network segment transmit packets simultaneously. This causes the signals to interfere with each other, corrupting the data. The corruption renders the frames unusable, requiring retransmission. Excess collisions degrade network efficiency.
To prevent excessive collisions from impacting performance, networks are divided into multiple smaller collision domains. This segmentation ensures that collisions remain isolated to individual segments rather than propagating across the entire network. Keeping collision domains small increases available bandwidth.
How Collision Domains Are Created?
Collision domains are created by intelligently using network devices like hubs, switches, and routers to segment traffic.
- Hubs place all connected devices within a single large collision domain. Any transmission from one port can collide with transmissions from other ports since the hub simply rebroadcasts all incoming packets out every port.
- Switches create separate, isolated collision domains for each port. By learning device MAC addresses, switches can selectively forward frames directly from the source port to the destination port. This prevents collisions between different ports’ traffic streams.
- Routers provide complete isolation between the collision domains on each interface by forwarding packets based on logical network addresses rather than MAC addresses. Router interfaces connect distinct physical networks.
Identifying Collision Domains
When examining a network topology diagram, you can identify distinct collision domains by finding network segments where transmitted signals could interfere.
Some indicators to recognize collision domains include:
- All devices connected to a hub reside in the same large collision domain. The single hub represents one far-reaching collision domain.
- Each port on a switch is a separate isolated collision domain. If a switch has 48 ports, it has 48 distinct collision domains confined to each port.
- Each physical interface on a router connects to a different physical network, creating a distinct collision domain per interface. A router with two Ethernet interfaces has two collision domains, one per interface.
Look Here: How do routers create a Broadcast Domain Boundary?
Analyzing Sample Topologies
Below are some examples analyzing collision domains on sample network topologies:
| Topology | Collision Domains |
|---|---|
| 1 Hub (8 ports) | 1 |
| 3 Hubs (8 ports each) | 1 |
| 2 Switches (8 ports) + 1 Hub (8 ports) | 18 |
| 4 Switches (8 ports each) | 32 |
| 2 Switches (16 ports each) + 1 Router (4 ports) + 3 Hubs (8 ports each) | 36 |
As shown in the table, you can easily analyze a topology diagram and systematically calculate the number of distinct collision domains by understanding what creates collision domains.
Proper network segmentation using devices like switches and routers ensures efficient performance by isolating collisions to small, confined network segments. This prevents collisions from degrading overall network throughput.