Multiplex communications – Diagnostic testing – Of a switching system
Reexamination Certificate
2002-01-30
2003-12-16
Pham, Chi (Department: 2663)
Multiplex communications
Diagnostic testing
Of a switching system
Reexamination Certificate
active
06665269
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to computerized communication networks for permitting computers to communicate with each other in an organized manner, and more particularly to a network troubleshooting tool for detecting, and diagnosing network failures, and providing a general overview of active communications originating on each channel in the spectrum of allowed frequency channels of IEEE 802.11(b) wireless LAN (Local Area Network).
BACKGROUND OF INVENTION
Over recent years, the wireless communication field has enjoyed tremendous growth and popularity. Wireless technology now reaches or is capable of reaching nearly every place on the face of the earth. Millions of people exchange information every day using pagers, cellular telephones, and other wireless communication devices. With the success of wireless telephony and messaging services, wireless technology has also made significant inroads into the area of personal and business computing. Without the constraints imposed by wired networks, network users can move about almost everywhere without restriction and access a communication network from nearly any location, enabling wireless transmission of a variety of information types including data, video, voice and the like through the network.
Different radio technologies are used to transmit wireless information. Wireless local area networks are most often using methods described in the IEEE 802.11(b) specification. The goal is to make certain radio channels shareable for many users, but also not to cause problems by overlapping signals, which disturb other communications using other channels but the same modulation types. Presently, three technologies are most common. These are Frequency Hopping Spread Spectrum, Direct Sequence Spread Spectrum, and Orthogonal Frequency Division Multiplexing. IEEE 802.11(b) describes both technologies and their usage in Wireless LAN environments. Valid Channel Traffic Filter, as described herein, presently operates with Direct Sequence Spread Spectrum, but the general idea is adaptable to other technologies, which also use some type of channels, modulations or patterns to build several logical channels, which allow users to communicate wirelessly.
TABLE 1
DSSS Channels
Direct
Frequency
1
2.412
2
2.417
3
2.422
4
2.427
5
2.432
6
2.437
7
2.442
8
2.447
9
2.452
10
2.457
11
2.462
12
2.467
13
2.472
14
2.484
An IEEE 802.11(b) network can run in two difference modes. One is called “infrastructure mode”. This is the most important one. Access points act as bridge devices between a wired network and wireless stations. The other mode is called “ad-hoc mode” and is used for peer-to-peer networking between wireless stations without an access point.
The focus of the invention is set on the infrastructure mode, but the concept will work in general. When setting up a wireless LAN infrastructure, all areas need to be covered by access point radio frequency (RF) signals. Every channel, which offers a maximum speed of 11 Mbit/sec, can only handle a certain number of clients. Each access point interface operates on a single channel. The working distance between an access point and a wireless station is limited from about 30 to 300 feet, depending upon the local environment (e.g. walls and other RF absorbing materials). Many access points are needed to fully cover an area with wireless access. Access points, which use the same frequency channel, and are close together, share the same segment and bandwidth. Neighboring channels overlap and interfere with each other, causing signals originating on one to crosstalk onto the other. There are only three totally non-overlapping channels, specifically 1, 6, and 11. Other channels can be used, if there is enough dead space in the specific local environment.
SUMMARY OF THE INVENTION
When performing network analysis in a wireless network environment, it is important to separate good and bad traffic. What are the right criteria to separate these two traffic types? In the case of an IEEE 802.11(b) wireless network, the separation is made on the IEEE 802.11(b) protocol layer which is the Data Link Layer, or even on the physical layer. In this case corrupted packets usually identify bad traffic. An error is detected for corrupted packets as a result of performing a general CRC (cyclic redundancy code) check against the CRC checksum appended to the packet. However, such error detection does not provide efficient analysis and troubleshooting in IEEE 802.11(b) wireless networks. As previously mentioned, the physical signals are not perfect. Every packet, when transmitted on one channel, will typically appear on other neighboring and overlapping channels due to crosstalk. Only channels 1, 6 and 11 are non-overlapping, thereby avoiding crosstalk therebetween. This means that a minimum of four channels between two active channels are required to provide a buffer space to avoid any overlapping and resulting crosstalk problems.
The present invention for Valid Channel Traffic Filtering enables a user to separate all of the traffic, which either belongs to a channel from which a Sniffer® Wireless is capturing data packets or frames, or which was observed on one channel, but originated on some other channel. Note that Sniffer® Wireless relates to an analyzer or monitoring tool for analyzing traffic on an IEEE 802.11(b) Wireless LAN, that is manufactured by Network Associates, Inc., Santa Clara, Calif. The user can now focus more readily on traffic associated with the channel being analyzed. Packets from overlapping radio transmissions are filtered out. This is a very important feature in case of WEP (Wired Equivalent Privacy) encrypted packet transmission. These packets are encrypted after the IEEE 802.11(b) packet header. Any useful analysis is obtained only from the limited information in the IEEE 802.11(b) header. The greater the amount of useless information that is captured, the more difficult the analysis. In environments where several wireless channels are used and channel By overlapping causes crosstalk to occur, the Valid Channel Traffic Filter of the present invention separates good and bad traffic. Analysis becomes easier and more effective because a large portion of the useless traffic is filtered out, leaving only the traffic associated with the channel of interest to analyze.
In another embodiment of the invention, the present Valid Channel Traffic Filter program permits programming a Sniffer® Wireless to capture traffic from a channel of interest, and generate two new traces for display. One trace, or ‘good’ trace, contains all traffic generated only on the channel of interest. The other trace, a ‘bad’ trace, includes all frames or traffic captured but generated on channels other than the channel of interest. As a result, a user is provided the ability to identify valid and invalid traffic captured from a channel of interest.
The present process of Valid Channel traffic filtering consists of two separate tasks. The first task analyzes all traffic to identify the correct channel for every station sending Beacon frames or Probe Response frames. A table is built, which includes the MAC (Medium Access Control) address of the radio transmitter and the correct channel number for this specific address. It will also include information indicating whether the station is an access point ESS (Extended Service Set) set to YES. The last field per record keeps the frame number, which was used to create this entry. This is important when stations change the channel during the trace capture period. A user always needs to refer to the last current channel. Therefore, it is possible to repeat some MAC addresses several times in the table, but with different channel numbers and different frame numbers, when a new channel is detected. New records will only be added, if they have updated information. Old records will not be deleted because they were valid at some time. When the network runs in infrastructure mode every access point sends Beacon frames at some constant rate. In case of a peer-to-peer netwo
Ferris Derrick W
Hamaty Christopher J.
Networks Associates Technology Inc.
Pham Chi
Silicon Valley IP Group PC
LandOfFree
Method and apparatus for filtering network traffic based on... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for filtering network traffic based on..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for filtering network traffic based on... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3158461