Reduced TCP Window Size for Legacy LAN QoS II Niko Färber Sept. 20, 2000

Outline Summary of previous work Basic idea: Reduce TCP window size for LAN traffic! NS simulation results 10-BASE-T measurements NS simulation for extended LAN topology Worst case scenario Is communication between T2s necessary? NS simulation for simple traffic model Average case scenario Bi-directional traffic Future work

Scenario: Single Switch LAN Voice is received from WAN File is loaded from file server Both have to go through buffer at output port T2 10/100 Legacy Switch Router File Server bottle neck A E D C B QoS provided WAN

Basics Idea Reduce TCP window size for intra-LAN traffic No loss in throughput when: NxW = BxD Set TCP window size according to delay constraint D MAX, e.g., D MAX = 10 ms B = 10 Mbps 1480 Byte packets N=2 connection Advertised window in ACK can be modified in T2 without knowledge of sender/receiver W = 4 packets

NS Simulation Results voice delay [ms] data throughput [Mbps] time [s] 64 KB 3 KB ftp start TCP window size

10-BASE-T Measurements voice delay [ms] data throughput [Mbps] time [s] 16 KB 4 KB ftp start TCP window size

Scenario: 2 Switch LAN Voice is received from WAN Files are loaded from B i to A i Appropriate W depends on N! How bad is mismatch? Is communication between T2s needed? T2 S1S1 R A1A1 ANAN A2A2 QoS provided WAN … B1B1 B2B2 BNBN … S2S2

Variation of N, W N={1,2,4,8,16,32} x W={1,2,4,8,16,32,64} N=1 N=2 W=124 8 data throughput [Mbps] voice delay [ms]

Variation of N, W - stretched Similar performance for WxN = const. For W=4 reasonable performance for N<16 WxN=32 N= data throughput [Mbps] voice delay [ms] W=4

Scenario: N to N Communication Voice received from WAN Each terminal sends/receives data to/from every other terminal Balanced N to N communication N=8, W={4, 64} T2 S R A1A1 ANAN A2A2 QoS provided WAN …

Traffic Model and Measurement Random file size B i distributed uniformly within packets (1 packet = 1480 Byte) Waiting time in between file transfers: W i = BiBi N-1 R0R0 R 0 = 10 Mbps  = load in [0,1] time B1B1 B2B2 B3B3 W1W1 W2W2 T1T1 T2T2 request serve R =  B i  T i

Voice Delay N=8, =0.3 time [s] D MAX = 57 ms D MAX = 12 ms voice delay [ms] R = 4.9 Mbps R = 5.3 Mbps W = 64 W = 4

time [s] voice delay [ms] W = 64 W = 4 Voice Delay - Detail Strong correlation: nice for adaptive play-out control!

Future Work Refine traffic model and LAN simulation Implement NS module that acts like T2 Integrate Networking and Signal Processing parts Use trace files from NS simulations for adaptive play-out time control Conjecture: Fixed TCP window is ok, since remaining delay jitter can be controled by adaptive play-out