The War Between Mice and Elephants By Liang Guo & Ibrahim Matta In Proceedings of ICNP'2001: The 9th IEEE International Conference on Network Protocols, Riverside, CA, November Presented By Eswin Anzueto

Outline Introduction Introduction Analyzing Short TCP Flow Performance Analyzing Short TCP Flow Performance Architecture and Mechanism –RIO-PS Architecture and Mechanism –RIO-PS Simulations Simulations Discussions Discussions Conclusions and Future work Conclusions and Future work

Introduction Internet traffic: Most (80%) of the traffic is actually carried by only small number of connection (elephants), while the remaining large amount of connections are very small in size or lifetime (mice) Internet traffic: Most (80%) of the traffic is actually carried by only small number of connection (elephants), while the remaining large amount of connections are very small in size or lifetime (mice) In a fair network environment, short connections expect relatively fast service that long connection. However, some times we can not observe such a nice property in the current internet. In a fair network environment, short connections expect relatively fast service that long connection. However, some times we can not observe such a nice property in the current internet.

Introduction (cont) Factors effecting the performance of mice Factors effecting the performance of mice  TCP tries to conservatively ramp up its transmission rate to the maximum available bandwidth. Therefore the sending window is initiated at the minimum possible value regardless of what is available in the network.

Introduction (cont)  For short connections, since most of the time the congestion window is very small, packet loss always requires timeout to detect. (not enough packets to activate the duplicate ACK mech.)  ITO (initial timeout) is very conservative. (no sampling data is available), Short Connection performance is degraded due to large timeout period.

Introduction (cont) In this paper, we propose to give preferential treatment to short flows with help from an Active Queue Management policy inside the network. We also rely on the proposed Diffserv-like architecture to classify flows into short and long at the edge of the network. We also rely on the proposed Diffserv-like architecture to classify flows into short and long at the edge of the network.

Related work Crovella et al 2001 [16] and Bansal et al 2001 [17] comment that size aware job scheduling helps enhance the response time of short jobs without hurting the performance of long jobs. Crovella et al 2001 [16] and Bansal et al 2001 [17] comment that size aware job scheduling helps enhance the response time of short jobs without hurting the performance of long jobs. Seddigh et al [2] shows the negative impact of the initial timeout value on the short TCP flow latency and propose to reduce the default recommended value Seddigh et al [2] shows the negative impact of the initial timeout value on the short TCP flow latency and propose to reduce the default recommended value

Outline Introduction Introduction Analyzing Short TCP Flow Performance Analyzing Short TCP Flow Performance Architecture and Mechanism –RIO-PS Architecture and Mechanism –RIO-PS Simulations Simulations Discussions Discussions Conclusions and Future work Conclusions and Future work

Sensitivity Analysis for Short and Long TCP Flows Transmission time of short TCP flows is not very sensitive to loss rate when the loss rate is relatively small, but it increases drastically as loss rate becomes larger.

Sensitivity Analysis of Transmission Time For small-size TCP flows, increasing the loss probability can lead to increased variability, while for long TCP flows, large rate reduces the variability of transmission times

Factors Effecting Variability When Loss rate high TCP Congestion control is more likely to enter exponential back off phase, which can cause significantly high variability in transmission time of each individual packet of a flow. When Loss rate high TCP Congestion control is more likely to enter exponential back off phase, which can cause significantly high variability in transmission time of each individual packet of a flow. When loss rate low, TCP either in slow start or congestion avoidance phase. This dimension of variability is more pronounced for long flows. When loss rate low, TCP either in slow start or congestion avoidance phase. This dimension of variability is more pronounced for long flows. Since the first source of variability is on individual packets of a flow, the law of large numbers indicates that its impact is more significant on short flows Since the first source of variability is on individual packets of a flow, the law of large numbers indicates that its impact is more significant on short flows

Sensitivity Analysis of Transmission Time We thus conclude that reducing the loss probability is more critical to help short TCP flows experience less variations in transmission (response) time. We thus conclude that reducing the loss probability is more critical to help short TCP flows experience less variations in transmission (response) time. Observe that the C.O.V. of transmission times is closely related to the fairness of the system— smaller values imply higher fairness. Observe that the C.O.V. of transmission times is closely related to the fairness of the system— smaller values imply higher fairness. Such interesting behavior motivates us to give preferential treatment to short TCP flows. Such interesting behavior motivates us to give preferential treatment to short TCP flows.

Preferential Treatment to Short TCP flows Assumption Assumption Giving preferential treatment to short TCP flows can significantly enhance their transmission time, without degrading long flow performance. Simulation using NS simulator Simulation using NS simulator  10 long(10000-packet) TCP-NewReno flows and 10 short(100-packet) TCP-Newreno flows over 1.25Mbps link.  Queue Management Policy – Drop Tail, RED,RIO with preference to short flows.

Link Utilization under Drop Tail, RED and RIO-PS

Network Goodput Under Different Schemes

Preferential Treatment to Short TCP flows (cont) In fact, this preferential treatment might even enhance the transmission of long flows since they operate in a more stable network environment (less disturbed by short flows) for longer periods. In fact, this preferential treatment might even enhance the transmission of long flows since they operate in a more stable network environment (less disturbed by short flows) for longer periods. In a congested network, reducing the packet drops experienced by short flows can significantly enhance their response time and fairness among them. In a congested network, reducing the packet drops experienced by short flows can significantly enhance their response time and fairness among them.

Outline Introduction Introduction Analyzing Short TCP Flow Performance Analyzing Short TCP Flow Performance Architecture and Mechanism –RIO-PS Architecture and Mechanism –RIO-PS Simulations Simulations Discussions Discussions Conclusions and Future work Conclusions and Future work

Proposed Architecture Proposed Architecture

Edge Router Determines packet coming from long or short flow. Determines packet coming from long or short flow. Accurate flow characterization can be very complicated, instead we simply maintain a counter (L t) that tracks how many packets have been observed so far for a flow. Once L t exceeds a certain threshold we consider the flow to be long. Per flow state information are softly maintained to detect the termination of flow. The flow hash table is updated periodically every T u time units. Per flow state information are softly maintained to detect the termination of flow. The flow hash table is updated periodically every T u time units. It is configured with SLR (Short to Long ratio). It then periodically (every T c time units) performs AIAD control over the threshold to achieve the target SLR It is configured with SLR (Short to Long ratio). It then periodically (every T c time units) performs AIAD control over the threshold to achieve the target SLR

Core Router Gives preferential treatment to short packets. Gives preferential treatment to short packets. RIO (Red In and Out) queuing policy is used because its conformity to the Diff-serv specification. RIO (Red In and Out) queuing policy is used because its conformity to the Diff-serv specification. The probability of dropping short packets depends on the average backlog of short packets queue. On the contrary, for long packets the total average queue size is used to detect incipient congestion and those flows have to give up some resources. The probability of dropping short packets depends on the average backlog of short packets queue. On the contrary, for long packets the total average queue size is used to detect incipient congestion and those flows have to give up some resources. No packet reordering will happen in the FIFO queue with RIO No packet reordering will happen in the FIFO queue with RIO RIO inherits all features of RED RIO inherits all features of RED

RIO Queue with preferential treatment to short flows

Outline Introduction Introduction Analyzing Short TCP Flow Performance Analyzing Short TCP Flow Performance Architecture and Mechanism –RIO-PS Architecture and Mechanism –RIO-PS Simulations Simulations Discussions Discussions Conclusions and Future work Conclusions and Future work

Simulation Edge router Core router

Simulation (cont)

4000 secs simulation time,2000 secs warm up time secs simulation time,2000 secs warm up time. Average response time relative to RED Average response time relative to RED

Simulation (cont)

Transmission Time of foreground traffic

Network goodput

Outline Introduction Introduction Analyzing Short TCP Flow Performance Analyzing Short TCP Flow Performance Architecture and Mechanism –RIO-PS Architecture and Mechanism –RIO-PS Simulations Simulations Discussions Discussions Conclusions and Future work Conclusions and Future work

Discussion Comments on the Simulation Model Our simulation is one-way traffic model. Our simulation is one-way traffic model. All TCP connections have similar end to end propagation delays, this is not common topology seen by internet users All TCP connections have similar end to end propagation delays, this is not common topology seen by internet users When there is also reverse traffic present, out proposed scheme will even have a superior performance over the traditional policies. When there is also reverse traffic present, out proposed scheme will even have a superior performance over the traditional policies.

Discussion Queue Management Policy RIO neither provides absolute aggregate (class based) nor relative flow based guarantees. RIO neither provides absolute aggregate (class based) nor relative flow based guarantees. To attack these problems, one may resort to AQM policies like the PI controlled RED queue, or a service model like the Proportional Diffserv proposed in for better control over the classified traffic and more predictable service To attack these problems, one may resort to AQM policies like the PI controlled RED queue, or a service model like the Proportional Diffserv proposed in for better control over the classified traffic and more predictable service

Discussion Deployment Issues Our proposed scheme requires edge devices to be able to perform per-flow state maintenance and per-packet processing. Our proposed scheme requires edge devices to be able to perform per-flow state maintenance and per-packet processing. The scheme does not require the queue mechanisms to be implemented at each router. The scheme does not require the queue mechanisms to be implemented at each router.

Discussion Flow Classification We use a threshold based classification method. We use a threshold based classification method.  Such method thus mistakenly classifies the first few packets of a long flow as if they came from a short flow. However, such “mistake” may help to enhance performance and make the system more fair to all TCP connections  The first few packets of a long flow are more vulnerable to packet losses and deserve to be treated with high preference.

Discussions Controller Design Our preliminary results indicate that the performance is not very sensitive to the target load ratio of active short to active long flows (the value of SLR at the edge). Our preliminary results indicate that the performance is not very sensitive to the target load ratio of active short to active long flows (the value of SLR at the edge). The “actual” SLR depends on the values of T c and T u, which determine how often the classification threshold and active flow table are updated, respectively. The “actual” SLR depends on the values of T c and T u, which determine how often the classification threshold and active flow table are updated, respectively.

Discussion Malicious Users One concern regarding our proposed scheme may be that users are then encouraged to break long transmissions into small pieces so that they can enjoy faster services. However, we argue that such initiative may not be so attractive to users given the large overhead of fragmentation and reassembly. One concern regarding our proposed scheme may be that users are then encouraged to break long transmissions into small pieces so that they can enjoy faster services. However, we argue that such initiative may not be so attractive to users given the large overhead of fragmentation and reassembly.

Outline Introduction Introduction Analyzing Short TCP Flow Performance Analyzing Short TCP Flow Performance Architecture and Mechanism –RIO-PS Architecture and Mechanism –RIO-PS Simulations Simulations Discussions Discussions Conclusions Conclusions

Conclusions The Performance of the majority of TCP flows (the short transfers or mice) is improved in terms of response time and fairness The Performance of the majority of TCP flows (the short transfers or mice) is improved in terms of response time and fairness The Performance of few elephants is also improved The Performance of few elephants is also improved Overall goodput of the system is also improved or at least stays almost the same Overall goodput of the system is also improved or at least stays almost the same

Conclusion (cont) The proposed architecture is flexible in that the functionality that defines this scheme can be largely tuned at the edge routers The proposed architecture is flexible in that the functionality that defines this scheme can be largely tuned at the edge routers

Thank you! Thank you to the following persons for the pictures used for this presentation Matt Hartling & Sumit Kumbhar Iris Su Preeti Phadnis