Visualizza wikitesto di TCP over Umts ← TCP over Umts

=TCP congestion control over a live UMTS network [http://c3lab.poliba.it/images/2/21/Umts_tcp_stacks_170407.pdf]=
We have performed an extensive campaign of measurements that involved around '''3000 flows and more than 40 hours of measurements''' using three different TCP stacks: 
* [http://www.ietf.org/rfc/rfc2582.txt TCP NewReno]: the congestion control algorithm standardized by IETF
* [http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/ TCP BIC]: the default congestion control algorithm adopted by the Linux o.s. 
* [[Westwood | TCP Westwood+]]: available in the Linux kernel (both 2.4 and 2.6 kernels).
The experimental evaluation has been carried out by accessing the public Internet using an UMTS card (see figure below).

[[Immagine:UmtsTestbed.png]]

The following instantaneous variable measurements have been collected by using the [[Libnetmeas | libnetmeas library]]:
* Goodput
* Round Trip Time
* packet loss ratios
* number of timeouts
We show cumulative distribution function plots to illustrate the main results of our investigation.

==Goodput==
[[Immagine:goodput_1_flow_downlink.png|350px|]][[Immagine:goodput_2_flows_downlink.png|350px]]
[[Immagine:goodput_4_flows_downlink.png|350px]][[Immagine:channel_utilization_downlink.png|350px]]

The channel utilization provided in the case of single flow accessing the downlink is '''less than 40%''' mainly due to the high number of timeouts (see below).