Return-path: Received: from nz-out-0506.google.com ([64.233.162.232]:31012 "EHLO nz-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752829AbXCZPlk (ORCPT ); Mon, 26 Mar 2007 11:41:40 -0400 Received: by nz-out-0506.google.com with SMTP id s1so2066616nze for ; Mon, 26 Mar 2007 08:41:39 -0700 (PDT) Message-ID: <43e72e890703260841v56047559y90b7c25c9c458564@mail.gmail.com> Date: Mon, 26 Mar 2007 11:41:38 -0400 From: "Luis R. Rodriguez" To: "David Young" Subject: Re: RFC: radiotap discrepancy in Linux vs OpenBSD Cc: "Pavel Roskin" , linux-wireless@vger.kernel.org, "Scott Raynel" , radiotap@mail.ojctech.com In-Reply-To: <20070326033839.GA24097@che.ojctech.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed References: <20070325232416.64xwkc0kw04oosg0@webmail.spamcop.net> <20070326033839.GA24097@che.ojctech.com> Sender: linux-wireless-owner@vger.kernel.org List-ID: CC'ing radiotap list, this time with your comments inline. On 3/25/07, David Young wrote: > On Sun, Mar 25, 2007 at 11:24:16PM -0400, Pavel Roskin wrote: > > Hello! > > (Oops, this time cc'd radiotap.) > > The place to discuss this is the mailing list > radiotap@ojctech.com, which I have cc'd. Subscribe at > . Please feel free > to circulate the URL. > > > I have noticed two different incompatible changes to enum > > ieee80211_radiotap_type in ieee80211_radiotap.h. > > > > One is found in the current wireless-2.6.git: > > > > IEEE80211_RADIOTAP_RX_FLAGS = 14, > > IEEE80211_RADIOTAP_TX_FLAGS = 15, > > IEEE80211_RADIOTAP_RTS_RETRIES = 16, > > IEEE80211_RADIOTAP_DATA_RETRIES = 17, > > These fields are slated to become part of the standard, I just haven't got > around to updating the manual page, yet. I have time to do that tonight. > > > It was added together with Marvell Libertas USB driver. > > > Another set of the flags can be found in CVS OpenBSD: > > > > IEEE80211_RADIOTAP_FCS = 14, > > IEEE80211_RADIOTAP_HWQUEUE = 15, > > IEEE80211_RADIOTAP_RSSI = 16, > > These fields are not part of the standard, and they will not become part > of the standard with these numbers. This is the first time I have ever > heard of HWQUEUE and RSSI, actually. What are they for? RSSI is Received Signal Strength Indication. Its a measurement of the received radio signal strength. Unfortunately though RSSI units used are arbitrary and the maximum value differs amongst chipsets. From wikipedia: -- RSSI measurements will vary from 0 to 255 depending on the vendor. It consists of a one byte integer value. A value of 1 will indicate the minimum signal strength detectable by the wireless card, while 0 indicates no signal. The value has a maximum of RSSI_Max. For example, Cisco Systems cards will return a RSSI of 0 to 100. In this case, the RSSI_Max is 100. The Cisco card can report 101 distinct power levels. Another popular Wi-Fi chipset is made by Atheros. An Atheros based card will return a RSSI value of 0 to 60. -- As Samuel Barber had recommended before, we should probably instead adopt RCPI. Quoting from his e-mail: --- Here is the full text of the definition from 802.11k draft 5.0: received channel power indicator (RCPI): An indication of the total channel power (signal, noise, and interference) of a received IEEE 802.11 frame measured on a single channel and at the antenna connector used to receive the frame. The RCPI indicator is a measure of the received RF power in the selected channel for a received frame. This parameter shall be a measure by the PHY sublayer of the received RF power in the channel measured over the entire received frame or by other equivalent means which meet the specified accuracy. RCPI shall be a monotonically increasing, logarithmic function of the received power level defined in dBm. The allowed values for the Received Channel Power Indicator (RCPI) parameter shall be an 8 bit value in the range from 0 through 220, with indicated values rounded to the nearest 0.5 dB as follows: 0: Power < -110 dBm 1: Power = -109.5 dBm 2: Power = -109.0 dBm and so on where RCPI = int{(Power in dBm +110)*2} for 0dbm > Power > -110dBm 220: Power > -0 dBm 221-254: reserved 255: Measurement not available RCPI shall equal the received RF power within an accuracy of +/-5 dB (95% confidence interval) within the specified dynamic range of the receiver. The received RF power shall be determined assuming a receiver noise equivalent bandwidth equal to the channel bandwidth multiplied by 1.1. --