Buffer Sizing for 802.11 Based Networks

[ashish0505gt]

Buffer Sizing for 802.11 Based Networks
[attachment=53]
Abstract:-
We consider the sizing of network buffers in 802.11 based networks. Wireless networks face a number of fundamental issues that do not arise in wired networks. We demonstrate that the use of fixed size buffers in 802.11 networks inevitably leads to either undesirable channel under-utilization or unnecessary high delays. We present two novel dynamic buffer sizing algorithms that achieve high throughput while maintaining low delay across a wide range of network conditions. Experimental measurements demonstrate the utility of the proposed algorithms in a production WLAN and a lab test bed.
Architecture:-
Algorithm Details:-
eBDP algorithm
Dynamic buffer sizing algorithm,
Adaptive Limit Tuning (ALT) Feedback Algorithm
Explanation:-
The algorithms in this paper perform similarly when the DCF is used and when TCP ACKs are prioritized using the EDCA as in. Per flow behavior does, of course, differ due to the inherent unfairness in the DCF and we therefore mainly present results using the EDCA to avoid flow-level unfairness
Abbreviation
DCF-Distributed Coordinated Function (DCF)
EDCA -Enhanced distributed channel access (EDCA)
Existing System:-
The distribution of packet service times is also strongly dependent on the WLAN offered load. This directly affects the burstiness of transmissions and so buffering requirements.
IEE 802.11b support up to 11 MBps, sometimes this is not enough far lower than 100 Mbps fast Ethernet
In co-existing environment, the probability of frequency collision for one 802.11 frame vary from 48% 62%
Disadvantages
Unaware of interference from/to other networks
Weak security policy
Poor performance (coverage, throughput, capacity, security)
Unstable service
Customer dissatisfaction
Proposed System:-
In this paper we demonstrate the major performance costs associated with the use of fixed buffer sizes in 802.11WLANs and present two novel dynamic buffer sizing algorithms that achieve significant performance gains. The stability of the feedback loop induced by the adaptation is analyzed, including when cascaded with the feedback loop created by TCP congestion control action. using the A* algorithm proposed in this paper, the RTTs observed when repeating the same experiment fall to only 90-130 ms. This reduction in delay does not come at the cost of reduced throughput, i.e., the measured throughput with the A* algorithm and the default buffers is similar
in this paper is on TCP traffic since this continues to constitute the bulk of traffic in modern networks (80 90% of current Internet traffic and also of WLAN traffic ), although we extend consideration to UDP traffic at various points during the discussion and also during our experimental tests.
Advantages
The reduction in network delay not only benefits UDP traffic, but also short-lived TCP connections
Comes from easy maintenance, cabling cost, working efficiency and accuracy
Network can be established in a new location just by moving the PCs!
Main Modules:-
1. Buffer Sizing
Buffers play a key role in 802.11/802.11e wireless networks. To illustrate this, we present measurements from the production WLAN of the Hamilton Institute, which show that the current state of the art which makes use of fixed size buffers, can easily lead to poor performance. . We recorded RTTs before and after one wireless station started to download a 37MByte file from a web-site. Before starting the download, we pinged the access point (AP) from a laptop 5 times, each time sending 100 ping packets. The RTTs reported by the ping program was between 2.6-3.2 ms. However, after starting This work is supported by Irish Research Council for Science, Engineering and Technology and Science Foundation Ireland Grant 07/IN.1/I901. the download and allowing it to continue for a while (to let the congestion control algorithm of TCP probe for the available bandwidth), the RTTs to the AP hugely increased to 2900-3400 ms. During the test, normal services such as web browsing experienced obvious pauses/lags on wireless stations using the network. Closer inspection revealed that the buffer occupancy at the AP exceeded 200 packets most of the time and reached 250 packets from time to time during the test. Note that the increase in measured RTT could be almost entirely attributed to the resulting queuing delay at the AP, and indicates that a more sophisticated approach to buffer sizing is required.