Question

The router uses a fair queueing scheduling discipline.

1. If we have two streams, one is a small packet and the other is a large packet. Depending on the arrival time, FQ may unfairly prefer large packets. How to use segmentation to improve the fairness of the FQ scheme?

2. Why is this method of segmentation impractical?

Answer 1

1. Fair queuing(FQ) is an algorithm for scheduling, used for network schedulers.
The aim of the algorithm is to attain the fairness within a limited resource is shared and it consists a bit-by-bit round-robin (BR) strategy.

The fair queuing scheduling algorithm manages various quantities at same time:
1. Bandwidth
2. Amount of data each flow is allowed to transport
3. Buffer space for each flow
4. Timing of individual flows are transmitted

Example: If we prevent the flows within large packets or processes that generate small jobs from consuming large output or CPU time greater than other processes.Fair queuing is used routers and network switches.

An effective segmentation should include six characteristics mainly:
1.Substantial
2.Stable
3.Actionable
4.Accessible
5.Identifiable
6.Differentiable
By using the segmentation to improve the fairness of the FQ scheme.

Step 1: Understanding the client (user) expectations thoroughly.
Step 2: Collecting the necessary data.
Step 3: Performing the segmentation procedures and develop multiple models.
Step 4: Interaction with the client

2. This method of segmentation impractical because data center networks in multi-rooted tree topologies can lead to severe unfairness, which we called TCP Outcast problem, under many traffic patterns.

In TCP outcast problem many flows and a few flows from two ports of a switch destined to one common output port, the small set of flows lose out on their productivity share significantly .The Outcast problem occurs in taildrop queues by which that commodity switches use.

Two conditions are met:
1. The network comprises of commodity switches that employ the simple taildrop queuing discipline.
In this situation is easily met as data center networks typically use low- to mid-end commodity switches and taildrop queues at lower levels of the network hierarchy.The network consist of COTS switches that use the taildrop queue management
2. A large set of flows and a small set of flows arriving at two different input ports compete for a bottleneck output port at a switch.
  
Throughput unfairness results by which one flow from each sender is initiated to the destination, and show that it results in the TCP Outcast problem.
Therefore the segmentation is impractical.