IEEE 802.11無線網路之TCP傳輸效能評估
Performance Evaluation of TCP over IEEE 802.11 Networks
Date Issued
2006
Date
2006
Author(s)
Chu, Hsia-Chun
DOI
zh-TW
Abstract
In this paper we are inspired from two important downstream TCP behaviors in infrastructure WLAN：(1) constant channel pps(packets per second) throughput (2) average active wireless station(WS) number always <=2 (active WS are those who have TCP_ACKs in MAC transmission queue and tend to actively contend for channel access to reply TCP_ACK to AP), and conclude that the channel utilization is low. Therefore, we investigated causes and effects that limit TCP throughput, and propose enhancement mechanisms which adopt the concept of 802.11e TXOP(transmission opportunity) to improve TCP throughput.
We propose four measures：(1)TXOP (AP-k, WS-1), (2)TXOP (AP-k, WS-k), (3)TXOP (AP-k, WS-∞), and(4)TXOP (AP-k, WS-∞)+ACK prioritization and at most one transmission. The first method employs TXOP at AP to increase the number of active WS, and indeed improve TCP throughput in infrastructure WLAN. The reason is that the transmission efficiency of downstream and upstream is both increased. Downstream rate rises due to multiple packets transmitted by AP per channel access. Upstream rate increases because the number of active WS gets larger and the probability for WS to grab channel to reply ACK has grown. However, when TXOP value get larger, the common problem of asymmetry TCP has shown：the reverse path throughput cannot catch up with the forward path throughput. Therefore, we propose the second, third, and fourth method to improve TCP throughput by speeding up the reverse path rate.
We also propose an analytic model to characterize TCP throughput in infrastructure WLAN when the number of TCP connections equals one. Validated by simulation, we show that our model can precisely evaluate TCP throughput. In addition, we also characterize TCP throughput of the first method by modifying the model of Conti[11]. We closely evaluate the number active station and based on the estimation we can characterize the TCP throughput.
Subjects
傳輸控制協定
802.11
802.11e
中控式無線網路
正確認信號
傳輸效能
主動競爭無線站台
TCP
infrastructure WLAN
ACK
throughput
active WS
Type
other
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