Question:
I am looking for performance information regarding TCP/IP. I have 13 devices connected to a host. Assuming a constant packet rate and frame size, how will the addition of new devices affect the performance of my system?
Answer:
This is a classic scenario that faces many network engineers and administrators.
Let us assume 10 Mbps Ethernet as an example. This means that the data rate at any given instant cannot exceed 10 million bits per second on the network segment.
Let us make some key observations concerning Ethernet now. Ethernet network transport technology is based on the CSMA/CD principle (this stands for Carrier Sense Multiple Access/Collision Detection). When simplified, this means that at any given instant any node may place traffic on the segment. If the segment is busy, the node will stop its transmission, back off for a random period of time and then try again; otherwise the transmission of packets to the intended destination(s) proceeds.
In the above example, we have 13 devices on the network. The addition of new devices increases the possibility of a node discovering that the segment is being used for the transmission of packets when it tries to place traffic on the network. Therefore, the addition of new nodes into an existing network will decrease the performance of the network, assuming that the new nodes do indeed contribute to the traffic.
Note that other factors such as the type of applications being used, the average length of the files, the number of broadcast frames, the number of host devices, etc. will also contribute significantly to the performance of the network segment. The critical concept is the fact that 10 Mbps Ethernet has a bandwidth of 10 million bits of information that can occupy the medium at any given instant.
Observation of real life network environments has revealed that when the bandwidth utilization exceeds 30 percent for extended periods of time, network performance will begin to decay, exhibiting such signs as file retransmissions, timeouts, excessive collisions between frames, etc.
Switched Ethernet, on the other hand, provides 10 Mbps on each of the switched segments. The rules of Ethernet apply to each segment; therefore, if nodes are grouped into workgroups on each switched segment, performance gains can be realized.
If many switched ports are available, consider dedicating a port in its entirety to the server, ensuring a dedicated 10 Mbps pipe to the serving device on your network.
One important fact to note is that if all the workstations on your network access one server, moving the server to its own switched port will move the traffic bottleneck to that port. However, if you have multiple workgroups with their own servers, a switching environment can provide significant gains in performance.
