Network and Protocol Mechanisms: How well do they collaborate? Ageliki Tsioliaridou

What we investigate Transport Protocols come at various versions - some aggressive some conservative Network mechanisms differ in sophistication regarding the scheduling, forwarding and dropping policy

We claim that Evaluation of a new mechanism cannot be investigated alone; that is, one has to study its impact on the different mechanisms. A protocol may lack the sophistication needed to exploit the potential of a new network mechanism, and vice versa the chicken or the egg

More specifically We select two widely used network mechanisms (DT and RED); we also introduce a new mechanism, namely Fr-RED; and we discuss the potential of another mechanism which we will develop soon We monitor the interaction of these mechanisms with the congestion control mechanisms of Tahoe, Reno, NewReno and Vegas

1 st scenario Many flows compete for low bandwidth. The contention level is high. Congestion event is persistent 2 nd scenario A small number of flows occupy the transmission channel. The contention level is low. Congestion event is transient 3 rd scenario Some flows co-exist in the communication channel and suddenly some other flows enter the link 4 th scenario Some flows co-exist in the communication channel and suddenly some of them finish their task and leave the channel

Experiments Topology: dumbbell

1 st scenario Topology:dumbbell bw_1=0.1Mbps, bw_2=1Mbps, bw_3=0.1Mbps Remarks that have to be highlighted: 1.If the protocol is Vegas or Tahoe, the combination with drop give us better results in throughput 2.If the protocol is Reno or Newreno, the combination with red give us better results not only in goodput but also in throughput 3.When the router’s algorithm is drop, the performance of Vegas in goodput is higher than the other three

TCP Tahoe goodput throughput

TCP Vegas goodput throughput

TCP Reno goodput throughput

TCP NewReno goodput throughput

DropTail

2 nd scenario Topology:dumbbell bw_1=1Mbps, bw_2=50Mbps, bw_3=10Mbps Remarks that have to be highlighted: 1.If the protocol is Tahoe the combination with drop give us better results 2.If the transport protocol is Vegas the value of goodput doesn’t get influence from the router’s algorithm, and it is higher than the value of other three protocols.

TCP Tahoe goodput throughput

TCP Vegas goodput throughput

RED

3 nd scenario Topology:dumbbell bw_1=1Mbps, bw_2=50Mbps, bw_3=10Mbps Remarks that have to be highlighted: The combination of Vegas and Drop Tail algorithm gives us the worst value in fairness When of the transport protocol is Tahoe, the Drop Tail algorithm performs better in goodput If the transport protocol is Vegas it gives the best value in goodput

Fairness

TCP Tahoe goodput

goodput throughput TCP Vegas

4 th scenario Topology:dumbbell bw_1=1Mbps, bw_2=50Mbps, bw_3=10Mbps Remarks that have to be highlighted: When the transport protocol is Reno, the Drop algorithm results better in fairness When of the transport protocol is Tahoe, the drop algorithm perfumes better in goodput If the transport protocol is Vegas the value of goodput is higher than the value of other three protocols.

TCP Reno fairness

TCP Tahoe goodput

goodput throughput

Random Early Drop (RED) A router that implements RED uses two threshold values to mark positions in the queue: T min and T max AvgLen T min T max 2* T max

A drop event is characterize either as FORCED drop nor as UNFORCED drop DROP LOGIC 1.If avg > 2* maxthresh, this is a FORCED drop 2.If T min < avg < 2*maxthresh, this may be an UNFORCED drop. The drop probability changes from 0 to max_p as the avg varies from T min to T max and from max_p to 1 as the avg varies from T max to twice T max (max_p=1/linterm) 3.If (q+1) > hard q limit, this is a FORCED drop

RED drop principle: FORCED drop The victim is either the arriving packet (default) or the front packet of the queue or any packet of packet (random) UNFORCED drop The victim is the arriving packet fr-RED drop principle : FORCED drop The victim is the arriving packet UNFORCED drop The victim is the front packet of the queue

Our goal is: To indicate senders faster that the congestion is going to happen The TCP congestion mechanism of senders will be triggered faster

Experiments Topology: dumbbell scenario bw_1=bw_2=bw_3=1Mbps

TCP Tahoe Buffer_size (bs):100 Link_delay:7ms Tmax:3*bs/4=75 Tmin:Tmax/3=25

TCP Tahoe Buffer_size (bs):100 Buffer_size (bs):200

The concept of a new network mechanism: When congestion is going to happen rearrange the order of the packets at the queue The concept of a new congestion control mechanism: The sender should adjust its rate, depending on the reordering of the incoming packets at the receiver.

Future work Evaluation of fr-red at high-speed networks Implementation of the new concept of congestion avoidance mechanism