Hello Patrick, With all due respect I don't think anyone here doubts the Alvarion VL is not simply a plain vanilla CSMA product. However, unfortunately the end result is the same when deployed in a RF hostile environment.
All the items you list below while impressive are of little use in RF hostile environments. Believe me I wish this wasn't the case as I'd love to make use of some of the many nifty VL features. Unfortunately until VL makes the turn and offers the tools required in today's unlicensed fixed wireless world it is best suited for bursty, best effort applications. The VL can scream in the right environment, but unfortunately the days of friendly RF and clean unlicensed airways are long gone in many markets and disappearing quickly in the rural markets as well. As unlicensed users we require greater flexibility out of the products we purchase not less flexibility. Best, Brad -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Patrick Leary Sent: Tuesday, December 26, 2006 12:21 PM To: WISPA General List Subject: [WISPA] once again, several of the key... ...features that make VL NOT a basic CSMA/CA product. - Configurable Minimum and Maximum Contention Windows: The BreezeACCESS VL system uses a special mechanism based on detecting the presence of a carrier signal and analyzing the information contained in the transmissions of the AU to estimate the activity of other SUs served by the AU.) The available values are 0, 7, 15, 31, 63, 127, 255, 511 and 1023. A value of 0 means that the contention window algorithm is not used and that the unit will attempt to access the medium immediately after a time equal to DIFS. The default min. value is 15. The default maximum is 1023. - Cell Distance Mode feature: The higher the distance of an SU from the AU that is serving it, the higher the time it takes for messages sent by one of them to reach the other. To ensure appropriate services to all SUs regardless of their distance from the AU while maintaining a high overall performance level, two parameters should be adapted to the distances of SUs from the serving AU: The time that a unit waits for a response message before retransmission (ACK timeout) should take into account the round trip propagation delay between the AU and the SU (The one-way propagation delay at 5 GHz is 3.3 microseconds per km/5 microseconds per mile.). The higher the distance from the AU of the SU served by it, the higher the ACK timeout should be. The ACK timeout in microseconds is: 20+Distance (km)*2*3.3 or 20+Distance (miles)*2*5. To ensure fairness in the contention back-off algorithm between SUs located at different distances from the AU, the size of the time slot should also take into account the one-way propagation delay. The size of the time slot of all units in the cell should be proportional to the distance from the AU of the farthest SU served by it. The Cell Distance Mode parameter in the AU defines the method of computing distances. When set to Manual, the Maximum Cell Distance parameter should be configured with the estimated distance of the farthest SU served by the AU. When set to Automatic, the AU uses a special algorithm to estimate its distance from each of the SUs it serves, determine which SU is located the farthest and use the estimated distance of the farthest SU as the maximum cell distance. The value of the maximum cell distance parameter (either computed or configured manually) is transmitted in the beacon messages to all SUs served by the AU, and is used by all units to calculate the size of the time slot, that must be the same for all units in the same sector. When the Per SU Distance Learning option is enabled, the AU uses the re-association message to send to each SU its estimated distance from the AU. The per-SU distance is used to calculate the ACK timeout to be used by the SU. When the Per SU Distance Learning option is disabled (or if it cannot be used because the SU uses a previous SW version that does not support this feature), the SU will use the maximum cell distance to calculate the ACK timeout. The AU always uses the maximum cell distance to calculate the ACK timeout. It should be noted that if the size of the time slot used by all units is adapted to the distance of the farthest unit, then no unit will have an advantage when competing for services. However, this reduces the overall achievable throughput of the cell. In certain situations, the operator may decide to improve the overall throughput by reducing the slot size below the value required for full fairness. This means that when there is competition for bandwidth, the back-off algorithm will give an advantage to SUs that are located closer to the AU. The Cell Distance Parameters menu includes the following parameters: fairness factor, per SU distance learning, show cell distance parameters. - Low Priority Traffic Minimum Percent feature ensures a selectable certain amount of the traffic is reserved to low priority packets to prevent starvation of low priority traffic when there is a high demand for high priority traffic. - Layer-2 traffic prioritization based on IEEE 802.1p and layer-3 traffic prioritization based on either IP ToS Precedence (RFC791) or DSCP (RFC2474). It also supports traffic prioritization based on UDP and/or TCP port ranges. In addition, it may use the optional Wireless Link Prioritization (WLP) feature to fully support delay sensitive applications, enabling Multimedia Application Prioritization (MAP) for high performance voice and video. (MAP can increase VoIP capacity by as much as 500%) - Auto or configurable maximum cell distance - Automatic distance learning: Per SU Distance Learning mechanism controlled by the AU enables each SU to adapt its Acknowledge timeout to its actual distance from the AU, minimizing delays in the wireless link. - Configurable threshold for lost beacon watchdog - Intelligent ATPC (The algorithm is controlled by the AU that calculates for each received frame the average SNR at which it receives transmissions from the specific SU. The average calculation takes into account the previous calculated average, thus reducing the effect of short temporary changes in link conditions. The weight of history (the previous value) in the formula used for calculating the average SNR is determined Menus and Parameters Operation and Administration by a configurable parameter. In addition, the higher the time that has passed since the last calculation, the lower the impact of history on the calculated average. If the average SNR is not in the configured target range, the AU transmits to the SU a power-up or a power-down message. The target is that each SU will be received at an optimal level, or as high (or low) as possible if the optimal range cannot be reached because of specific link conditions. Each time that the SU tries to associate with the AU (following either a reset or loss of synchronization), it will initiate transmissions using its Transmit Power parameters. If after a certain time the SU does not succeed to synchronize with the AU, it will start increasing the transmit power level. In an AU the maximum supported transmit power is typically used to provide maximum coverage. However, there may be a need to decrease the transmitted power level in order to support relatively small cells and to minimize the interference with the operation of neighboring cells, or for compliance with local regulatory requirements. In some cases the maximum transmit power of the SU should be limited to ensure compliance with applicable regulations or for other reasons. - And ATPC is highly configurable (only highly advanced operators should do so), with parameters like: ATPC min. SNR level, ATPC Delta from min. SNR level, Min. interval between ATPC messages, ATPC power level change step (1-20dB with default of 5dB) Patrick Leary AVP WISP Markets Alvarion, Inc. o: 650.314.2628 c: 760.580.0080 Vonage: 650.641.1243 [EMAIL PROTECTED] **************************************************************************** ******** This footnote confirms that this email message has been scanned by PineApp Mail-SeCure for the presence of malicious code, vandals & computer viruses. **************************************************************************** ******** -- WISPA Wireless List: email@example.com Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ -- WISPA Wireless List: firstname.lastname@example.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/