IA-TCP A Rate Based Incast- Avoidance Algorithm for TCP in Data Center Networks Communications (ICC), 2012 IEEE International Conference on 曾奕勳

Introduction Many online service providers have vastly invested in building data centers. The data center applications generally shows the Partition/Aggregate communication pattern. Incast communication pattern may cause network congestion.

Introduction TCP does not work well –The Top of Rack (ToR) switches typically use small buffer memories to reduce cost. –A few packet losses may result in TCP timeouts. Incast-Avoidance TCP –a rate-based congestion control algorithm –designed to operate only at the aggregator side

Related Work Reducing the duplicate ACK threshold and disabling the slow-start Reducing the RTOmin from a millisecond to a microsecond granularity. –effective for cluster-based storage systems –not adequate for soft real-time applications A delay based congestion avoidance algorithm

Data packet rate control The incast congestion is avoided when the total number of outstanding packets does not exceed the network pipe size. For examplein –a network path has 1Gbps of link capacity and 100μs of delay, –the BDP is 12.5kB or 8.3MSS(1MSS=1.5KB)

Data packet rate control The data packet rate of the workers to be less than or equal to the link capacity. The aggregator first controls the window size of the workers and then adds Δ(s) to the RTTmin for fine-grained rate control.

Data packet rate control Control the window sizes of all connections to be equal to W. We now set the advertisement window as

Data packet rate control The aggregator adds the delay Δ for each ACK packet when advertise size equal 1. If Δ is negative, the ACK is sent immediately without any delay. Set the delay of the first ACK in each connection, as a random value from [0,(RTTmin + Δ)].

simulation ToS buffer size is 56 packets (assuming 4MB of shared memory / 52 ports / 1.5kB of MSS). Link capacity is set to 1Gbps the round trip propagation delay between workers and aggregator is set to 100μs. the aggregator sends 10B of request query to workers. worker replies a specific size of data to the aggregator. The packet size is fixed at 1500 bytes RTOmin is set to 200ms

Ratio of TCP timeout

Query Completion time

Conclusion A rate-based congestion control algorithm, to effectively avoid the incas congestion. IA-TCP is implemented only at the aggregator node. IA-TCP is scalable in goodput and query completion time.