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What is collision domain and broadcast domain?
Collision domain, first what is a collision: Maybe the
question you have is, what is the difference between a layer 2 and layer 3
broadcast. Collisions are considered part o…f the physical layer in the ISO model. The physical layer is the
cables. An example would be copper, also referred to as transmission media or
medium. A collision occurs when two or more computers attempt to transmit data
at the same time onto the same media (cable). Ethernet uses a media access
method known as contention (meaning all network cards have equal access to the
media). The complete definition is CSMACD or CSMACA Carrier Sense Multiple
Access Collision Detection or Collision Avoidance When an Ethernet card
transmit data onto the media it follows these rules Listen = Carrier Sense, the
intention is that if the media is in use the Ethernet adapter will not
transmit. When two or more adapters transmit simultaneously the result is a
collision. When a collision occurs all of the data is corrupted and un-usable.
Transmit = Multiple Access Because any adapter can transmit at any time the
media is not busy it is probable that two or more adapters will transmit
simultaneously causing a data collision as discussed above. Collision = either
detected, or not detected In wired media such as copper UTP (unshielded twisted
pair),CAT5e for example, each adapter has the ability to detect the collision
due to an incorrect voltage level in the signal as a result of the collision.
At this point every adapter involved in the collision will start a random timer
(known as the back off timer). The random timer is supposed to keep the
collision from just happening again when the adapters re-transmit their data.
There are many ways to isolate collision domains. Primarily in switched
networks, every port on the switch is considered a separate collision domain.
Bridges and Routers are another method for isolating collision domains.
Collisions occur at the OSI (Open Systems Interconnect) layer 1 or physical
layer. Broadcast domains: This would be a little difficult to explain without
knowing your level of knowledge. I'll try to keep this fairly simple. Broadcast
domains are the logical separation between networks. Unlike collisions they
occur at the OSI layer 3 level. Networks are logically segmented into subnets
to isolate or consolidate traffic. If we consider a simple IPv4 example we
might have 2 networks like 192.168.1.0 / 255.255.255.0 and 192.168.2.0 /
255.255.255.0 These 2 networks are separated by a router. A layer 3 broadcast
from the first network to 192.168.1.255 would not be forwarded to the
192.168.2.0 network. Obviously these two networks can communicate with each
other though they are logically separate. Here is where it gets a little more
difficult. Without looking at the specific broadcast, let us just say that a
broadcast can be sent to all of the networks in the 192.168.X.X network asking
for a response. So this would include both networks above. Hope this is
helpful... Other subjects that would be helpful would be ARP (Address
Resolution Protocol) and VLAN (Virtual LAN)