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Dated: Jul. 04, 2012

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Overview of Data Transfer Domains

In computer networks, scope (area) up to where data that is transferred over the cables or the wireless media with certain conditions is categorized in two domain main types. They are:

Collision Domain: Collision domain is the scope (area) in which collisions may occur between the data packets while they get transferred over guided (wired) or unguided (wireless) media. An example can be of Bus Topology where data packets are likely to collide if two computers initiate the transfer process simultaneously.

Broadcast Domain: Broadcast domain is the scope (area) up to where a data packet may reach if it is initiated to be broadcasted. For example if two network segments namely A and B are connected via a Router and if a data packet from segment A is initiated to be broadcasted, the packet would not cross the Router and would never reach segment B. Therefore broadcast domain for a broadcasted data packet of segment A would be all the computers that reside in segment A only.

Collision/Broadcast Domains and Complex Networked Environments

Collision and Broadcast DomainsIn complex network setups, because multiple segments are connected to each other via different types of central devices, it becomes important for the administrators to separate broadcast domains and reduce the numbers of collision domains. A central device in which collisions may occur is Hub because of it logical Bus Topology. In such environments, multiple Hubs are connected to a single switch which isolates the collision domains. In this way even if multiple PCs connected to a Hub initiate the transfer simultaneously, the collision remains limited to that very Hub only. Whereas when a data packet is broadcasted from any computer, it is transferred to every Hub via LAN Switch.

In medium or large network setups, if a Router is connected to multiple LAN Switches and each LAN Switch is further connected to multiple Hubs, the packet that is broadcasted from a PC of one segment remains limited to that segment (broadcast domain) only.

Best Practices While Implementing Medium or Large Network Setups

Because network Hubs are no longer available in the markets and neither are they used any more, the chances of collisions are 0%. Since LAN Switches work on virtual circuits that are temporarily created when the data packets are transferred and are automatically discarded when the transmission process completes, every single PC connected to LAN Switch port has its own collision domain (no collision domain as collisions can never occur in a single PC). Therefore, in today’s era collision domains no longer exist.

In order to reduce network congestions administrators should create multiple broadcast domains by dividing a large network into multiple small segments and connecting them via Routers. Since Routers never transfer broadcast packets from one segment to another, network congestion on one LAN segment remains limited to that segment only, hence leaving other segments of the network untouched and unaffected.


To summarize, broadcast domains are created by the administrators to reduce network congestions and are considered positive aspects. On the other hand, collisions occur due to the characteristics of Hubs and collision domains help administrators isolate network congestions in their respective collision domains only where multiple collision domains may belong to a single broadcast domain.

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sanjay bari's Comment
this is the very best side for networking education .
18 Sat Aug 2012
Admin's Reply:

You know Sanjay, I totally agree 100% :)

Samir Palit's Comment
This is very nice side for all of the real education
16 Mon Jul 2012
Admin's Reply:

Thanks Samir.