Hi, If anyone want to pass CCIE WIRELESS LAB then lets discuss on rea l lab questions and work on it lets break the lab share the questions and solutions
Add me on skype id is (*quad.quad4*) Thanks On Thu, Sep 12, 2013 at 7:17 PM, Jeen Sern Chew <[email protected]> wrote: > Thanks Jason and Jeff, > > It is really confusing, especially with conflicting information out there, > like with the hysteresis of being 3 dBm both ways or 3 dBm one and 6dBm the > other. > > Also after calculating, how would you know to increase or decrease the > power? > > The following is how I understand it after some thinking. Some of the > figures are just base on real world experience. Say you do a voice survey > and place your APs to provide coverage of -67 dBm, 20% overlap and power > level of 6-25 mW. The following are the assumptions: > - Cisco formula as mentioned above is correct > - TPC only decreases power > - Hysteresis of 3 dBm > - There's another APs see each other rather than by transmitting neighbour > message at full power > > Starts off at level 1 / 100mW. I chose the 3rd highest RSSI to be -50 dBm > as that would happen in a voice/high density survey. > > 20 - (-67 - (-50)) = 20 - (-17) = 37 Hysteresis met, decrease > from level 1 / 20dB to level 2 / 17dB > 20 - (-67 - (-60)) = 20 - (-7) = 27 Hysteresis met, decrease > from level 2 / 17dB to level 3 / 14dB > 20 - (-67 - (-70)) = 20 - 3 = 17 Hysteresis met, decrease > from level 3 / 14dB to level 4 / 11dB > 20 - (-67 - (-80)) = 20 - 13 = 7 Hysteresis met, decrease > from level 4 / 11dB to level 5 / 9dB > 20 - (-67 - (-85)) = 20 - 18 = 2 Hysteresis not met. Stay > at level 5 / 9dB > > At level 5, it is close to the figures of some deployments out there. > > Does this calculation make sense? Did I miss anything? If it correct, > great! Just need to confirm the assumptions above then. > > Thanks > J Chew > > > On 12 September 2013 01:39, Jeff Rensink <[email protected]> wrote: > >> This is a frustrating topic indeed. >> >> TPC will do both power decreases and increases as the environment >> changes. But the formula that the document references has a flaw that I >> haven't totally reconciled. >> >> Tx_Max for given AP + (Tx power control thresh – RSSI of 3rd highest >> neighbor above the threshold) >> >> Tx_Max for a given AP should be a static value, correct? It's supposedly >> the max possible power that the radio can transmit at for its chosen >> channel. The Tx power control threshold is also a static value that is >> configurable. So the assumption is that the RSSI of the 3rd loudest >> neighbor changes along with the current AP power level. >> >> If I understand things correctly, the RSSI of the 3rd loudest neighbor is >> determined by AP neighbor messages. According to documentation (and I >> believe I've tested this myself), neighbor messages are always sent out at >> the highest power level and lowest data rate. If that is indeed true, then >> the RSSI of the third loudest neighbor is yet another static value >> (assuming the environment isn't changing). >> >> So if none of the variables in the equation are actually variable, the >> results of the equation are always the same. That would mean either the >> power level would always settle into the max power or the minimum power. >> That's not true, so something seems off in the equation or the description >> of the variables in the equation. >> >> My guess is the formula is closer to (Max_AP_Power - Current_AP_Power) - >> (3rd_loudest_neighbor - TPC_Threshold) >> >> A positive result would result in a power increase. A negative result >> would result in a power decrease based on the 3 dBm hysteresis. According >> to Jerome Henry, it's 3 dBm in both directions in the 7.0.116.0 code. This >> assumes that the 3rd loudest neighbor measurement is pretty much always the >> same since neighbor messages are always sent as max power. >> >> So let's say we start at full power on the 2.4 GHz band with a 3rd >> loudest neighbor of -60 and threshold of -67. >> >> (20-20)-(-60-(-67)) = 0-7 = -7 >> >> -7 is lower than -3, so we drop the power down a level >> >> (20-17)-(-60-(-67)) = 3 - 7 = -4 >> >> -4 is lower than -3, so we drop the power once more. >> >> (20-14)-(-60-(-67)) = 6 - 7 = -1 >> >> -1 is not lower than -3, so it doesn't change. >> >> This is a total guess, but it makes more sense to me than the formula in >> the documentation. But in the real world, the higher the TPC threshold, >> the higher the power levels will be. For instance, a threshold of -60 >> would result in higher power levels than a threshold of -70. So if you are >> seeing your APs in a particular location settle in at too high or too low >> of power levels on average, tweak the threshold as needed. Every increment >> of 3 should result in powers going up/down one level on average. >> >> Jeff Rensink - CCIE #24834 (Wireless, R&S) >> Senior Technical Instructor - IPexpert >> >> >> On Wed, Sep 11, 2013 at 9:14 AM, Jason Boyers <[email protected]> wrote: >> >>> This is a confusing algorithm. Basically, think of it this way: >>> >>> 1) Three neighbors (at least) hear an APs radio at or stronger than the >>> TPC Tx mac value configured under the WLC TPC settings for that PHY >>> (802.11a/n or 802.11/b/g/n) >>> 2) If #1 is true, then that formula provided is used. >>> - The "Tx_Max for given AP" is the maximum transmit power for that >>> channel on that particular radio. So, for a 2.4GHz radio, that would be >>> 100mW (20 dBm), since that is the maximum for 802.11b. 5GHz is more >>> confusing, as it various based on channel and model of AP. >>> - The "Tx power control thresh" is the value that is entered in the WLC >>> - Note that there is an "hysteresis" value of 3dB for decreasing and 6dB >>> (or it was at one point - someone correct me for the current values) for >>> increasing the power levels. In other words, the value that is given at >>> the end of the formula has to be at least that dB difference from the >>> current value in order for a change to occur. >>> 3) The AP's radio that is heard by the other three APs is the one that >>> is decreased (or it can be increased) if the hysteresis value is exceeded. >>> 4) When the formula is run again, it is presumed that the three >>> neighbors that are hearing the APs signal are hearing a weaker signal. >>> 5) Keep in mind that the algorithm is always from the perspective of an >>> AP being heard by 3 or more neighbors, not an AP hearing 3 or more >>> neighbors. >>> >>> Hope this helps. >>> >>> Jason Boyers, CCIE #26024 (Wireless) >>> Blog: netboyers.wordpress.com >>> >>> >>> On Wed, Sep 11, 2013 at 9:36 AM, Jeen Sern Chew <[email protected]>wrote: >>> >>>> Hey guys, >>>> >>>> I have a TPC question. >>>> >>>> There are many conflicting information from different Cisco docs. Some >>>> say TPC increase and decrease power, some say TPC only decreases power >>>> while CHD increases power. Does TPC do both or only increase? >>>> >>>> Also Cisco gives the TPC formula of: >>>> Tx_Max for given AP + (Tx power control thresh – RSSI of 3rd highest >>>> neighbor above the threshold). >>>> >>>> Is the Tx_Max is the Tx_Max of the specific AP? or Is it the Tx_Max >>>> configured on under TPC in WLC? >>>> >>>> Also, when the calculation is done, I am assuming the power >>>> increase/decrease occurs on the neighbour with the third highest RSSI? >>>> >>>> Thanks >>>> >>>> Regards, >>>> J Chew >>>> >>>> _______________________________________________ >>>> For more information regarding industry leading CCIE Lab training, >>>> please visit www.ipexpert.com >>>> >>>> Are you a CCNP or CCIE and looking for a job? Check out >>>> www.PlatinumPlacement.com >>>> >>>> >>> >>> _______________________________________________ >>> For more information regarding industry leading CCIE Lab training, >>> please visit www.ipexpert.com >>> >>> Are you a CCNP or CCIE and looking for a job? Check out >>> www.PlatinumPlacement.com >>> >>> >> > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > >
_______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com
