In the local area network technology, the two words collision domain and broadcast domain have a great impact on network performance. Let's take a look at how these two words affect network performance.
1. Conflict domain of LAN technology
Suppose you want to drive your car off the highway, but every time you try, there is a car blocking your way. If it is forced out, a collision will occur, which is very similar to the situation that occurs on the Ethernet using the Carrier Sense Multiple Access (CSMA/CD) protocol with collision detection. The Institute of Electrical and Electronics Engineers (IEEE) defines CSMA/CD Ethernet as the 802.3 standard. Today, this standard is used throughout the entire network community. The medium access control (MAC) sublayer of the second layer of the Open System Interconnection Model (OSI) uses the CSMA/CD protocol to access the physical medium.
All nodes in the network can send data at any time, but the CSMA/CD network strives to ensure that only one node sends data at any time. However, two nodes may send data at the same time, such as node 1 and node 4 in Figure 1-1. When this happens, it will cause a collision. This is the same as driving the car out of the highway we just talked about, because no other car was seen blocking the way. Just as you were driving out, another car hit you at a speed of 100 miles per hour.
However, one thing is different from a crash on a highway, it is difficult to recover after a collision, but the network node can continue to listen to the line. If a device detects a collision, it stops sending and notifies other nodes of the collision. All other sending nodes will stop sending after being notified. The collision only occurs in Ethernet. The only thing we care about is how often the collision frequency will affect the network performance. I wonder if this analogy makes you understand what a conflict domain is?
The concept of conflict domain can also be explained by the following figure. The LED indicator on the front panel of the Ethernet hub can help users detect when the conflict on the network segment is saturated. Even though there are several tools that can detect network slowdowns and bottlenecks, I still find it fast and convenient to use the LED lights on the hub. There is a network segment, and the LED lights on the hub that indicate the collision are always on, but what is surprising is that I have never heard any user complaints on this network segment. I know this may be unbelievable, but it is indeed true!
2. The broadcast domain of LAN technology
Before discussing the broadcast domain, you must first understand what broadcast is. Broadcasting is to send data to all nodes on the network segment, rather than a single node or a group of nodes. The node to be broadcast sends the data to the MAC address 0xFFFFFFFFFFFF to achieve the above purpose. Therefore, the broadcast domain is composed of a group of nodes that can receive broadcast messages from all other nodes in the same group. Normally, all nodes connected to a port of the router through a hub, etc.
For the above-mentioned network, all 16 nodes constitute this broadcast domain. Node 2 on H u b 3 not only broadcasts to the host on h u b 3, but also broadcasts to all hosts on h u b 1, h u b 2, and h u b 4. The hosts on h u b 1, h u b 2 and h u b 4 also broadcast to all other nodes.
The number of encounters of broadcast messages in the broadcast domain also increases with the expansion of the network scale. All these broadcast messages will indeed affect the performance of the network. If not managed properly, it may even lead to the collapse of the entire network.
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