Expen­sive RF analy­sis tools are avail­able to mea­sure a vari­ety of para­me­ters that only an RF engi­neer has a clue what they mean and the impli­ca­tions of their val­ues. But when it comes to net­works — wired or wire­less — ulti­mately, what one should be most inter­ested in is through­put per­for­mance. 802.11 (i.e. Wi-​​Fi) is a robust stan­dard that includes a vari­ety of pro­to­cols that help it com­mu­ni­cate wire­lessly with other devices. Unless one has inti­mate knowl­edge of the 802.11 stan­dard and its inner work­ings, then it is not pos­si­ble to pre­dict how an 802.11 net­work will behave when you are armed solely with RF mea­sure­ments. This is why it is impor­tant to focus on per­for­mance met­rics — since these more accu­rately pre­dict how a wire­less net­work will actu­ally behave in a real-​​world environment.

What fol­lows is a brief intro­duc­tion to 4 trou­bleshoot­ing tech­niques (net­work dis­cov­ery, RF spec­trum analy­sis, WiFi chan­nel analy­sis, and WiFi con­nec­tion analy­sis). We begin with a sum­mary of the pros and cons of the dif­fer­ent trou­bleshoot­ing tech­niques, which should give you a high-​​level view of the direc­tion in which the field of WiFi diag­nos­tics is cur­rently headed:

Sum­mary:

1. Net­work Dis­cov­ery:
Advan­tages: Inex­pen­sive
Dis­ad­van­tages: Of lim­ited use since it only detects bea­con pack­ets trans­mit­ted by 802.11 access points. It does not “see” or mea­sure RF energy trans­mit­ted by non-802.11 devices (which dom­i­nate the RF envi­ron­ment) or, even, actively trans­mit­ting 802.11 stations.

2. RF Spec­trum Analy­sis:
Advan­tages: Detects all RF trans­mis­sions within a fre­quency band. Based on the trans­mis­sion pat­tern you might be able to iden­tify the source of the inter­fer­ence.
Dis­ad­van­tages: Expen­sive — since it requires pro­pri­etary hard­ware. When it detects RF inter­fer­ence in the 2.4x or 5.x GHz ISM bands, it can not pre­dict how this will affect 802.11 devices or WiFi net­work per­for­mance — since it knows noth­ing about the 802.11 stan­dard nor how its under­ly­ing pro­to­cols work to mit­i­gate poten­tial sources of interference.

3. WiFi Chan­nel Analy­sis:
Advan­tages: Inex­pen­sive — uses off-​​the-​​shelf 802.11 devices. Mea­sures RF inter­fer­ence through the eyes of an 802.11 device — hence, can bet­ter pre­dict how an 802.11 Wi-​​Fi net­work will actu­ally per­form in the cur­rent envi­ron­ment. Can quan­tify the expected per­for­mance for each Wi-​​Fi chan­nel, thereby allow­ing you to choose the opti­mal chan­nel.
Dis­ad­van­tages: Of lim­ited use when attempt­ing to iden­tify the source of interference.

4. Con­nec­tion Analy­sis:
Advan­tages: Inex­pen­sive — uses off-​​the-​​shelf 802.11 devices or your built-​​in 802.11 adapters. Mea­sures through­put per­for­mance of your 802.11 devices when con­nected to a Wi-​​Fi net­work — which is the ulti­mate met­ric when it comes to trou­bleshoot­ing a net­work.
Dis­ad­van­tages: Of lim­ited use when attempt­ing to iden­tify the source of interference.

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Descrip­tions:

1. Net­work Dis­cov­ery An 802.11 net­work dis­cov­ery tool will report the Ser­vice Set Iden­ti­fier (SSID) for each access point (AP) it detects, along with the chan­nel used by the AP. Approx­i­mately every 100 mSec an AP trans­mits a small bea­con packet and a dis­cov­ery tool (run­ning on your lap­top and using its 802.11 wire­less adapter) detects the bea­con and adds the packet infor­ma­tion (includ­ing the AP’s SSID) to its list of known access points. In addi­tion, the dis­cov­ery util­ity may report sig­nal strength (in dBm units) of the bea­con as detected by the client adapter. The beacon’s sig­nal strength is a reflec­tion of how close the AP is to your cur­rent loca­tion. Though this is use­ful infor­ma­tion, it does not tell you any­thing about non-802.11 devices or even how busy the access points are. That is, your lap­top could be sit­ting next to a microwave oven and the dis­cov­ery tool would be clue­less as to its exis­tence. The dis­cov­ery tool only knows about bea­con pack­ets trans­mit­ted by 802.11 devices and can not see non-802.11 trans­mis­sions.
Net­work dis­cov­ery tools use the 802.11 adapter built into your lap­top or an exter­nal USB 802.11 adapter. Since they do not require addi­tional pro­pri­etary hard­ware, then they are rel­a­tively inex­pen­sive (even free).

AP Bea­con Strength Is Not A Mea­sure Of Per­for­mance

The sig­nal strength reported by a net­work dis­cov­ery tool is the sig­nal strength of a bea­con as mea­sured by the 802.11 wire­less adapter installed on your lap­top or desk­top machine. Each access point (AP) sends out a short pulse or bea­con of infor­ma­tion approx­i­mately every 100 mSec. It’s equiv­a­lent to an ‘I’m over here!’ shout. It does not expect a response from the 802.11 client adapters that may hear it — it’s just a one-​​way shout. The sig­nal strength that the net­work dis­cov­ery tool reports is the sig­nal strength of a bea­con, and the sig­nal strength of a bea­con is a reflec­tion of how close that AP is located to you. It is not a reflec­tion of the per­for­mance or through­put you can expect by asso­ci­at­ing with that AP — rather, it is an indi­ca­tion of the AP’s phys­i­cal loca­tion rel­a­tive to you. If the AP with the strongest bea­con has 24 client adapters asso­ci­ated with it that are actively trans­mit­ting and receiv­ing infor­ma­tion, and if you con­nect with that AP then you will be client num­ber 25 and your net­work con­nec­tion will seem slow. On the other hand, if you instead choose to asso­ciate with an AP whose bea­con strength is weaker but which is not asso­ci­ated with other client adapters, then you will likely expe­ri­ence bet­ter per­for­mance. Fur­ther­more, the AP with the strongest bea­con sig­nal may be using a chan­nel that is sub­ject to RF inter­fer­ence — again, degrad­ing its per­for­mance. When it comes to net­work­ing (both wired and wire­less) what we care most about is per­for­mance. And the key to per­for­mance is ‘through­put’ (i.e. bytes-​​per-​​second). Though a beacon’s sig­nal strength can affect it’s per­for­mance, what’s more impor­tant is the num­ber of client sta­tions that are com­pet­ing for the same AP and whether the chan­nel cur­rently used by the AP is sub­ject to RF inter­fer­ence from other wire­less devices in the vicinity.

2. RF Spec­trum Analy­sis An RF spec­trum ana­lyzer is the instru­ment of choice for detect­ing and iden­ti­fy­ing sources of RF inter­fer­ence. Spec­trum ana­lyz­ers are a basic tool used for observ­ing radio fre­quency (RF) sig­nals. Since they detect all RF trans­mis­sions (both 802.11 and non-802.11) then they pro­vide a much bet­ter pic­ture of the RF envi­ron­ment, which then helps you iden­tify and, per­haps, locate devices that could be inter­fer­ing with your Wi-​​Fi net­work. Typ­i­cally an RF spec­trum ana­lyzer will employ a 2-​​dimensional dis­play where the ver­ti­cal axis (Y-​​axis) rep­re­sents the strength of a sig­nal and the hor­i­zon­tal axis (X-​​axis) rep­re­sents the fre­quency of a sig­nal. If the spec­tral trace of the inter­fer­ing RF trans­mis­sions have pre­vi­ously been doc­u­mented, then it might be pos­si­ble to deter­mine which type of device is caus­ing the dis­tur­bance. As for tracking-​​down and attempt­ing to locate an inter­ferer, in prac­tice this is more dif­fi­cult than it might seem on the sur­face. Not only does it require the use of a direc­tional antenna, but in an indoor envi­ron­ment with waves bounc­ing all over the place (off of objects and walls) then how do you dis­cern from which direc­tion the wave orig­i­nated. In other words, when your direc­tional antenna mea­sures a sig­nal from a wave you don’t know whether that’s the orig­i­nal wave or the result of a wave that has bounced off of an object or wall in the room.

3. WiFi Chan­nel Analy­sis Today, one of the hottest top­ics dis­cussed by Wi-​​Fi infra­struc­ture man­u­fac­tur­ers is “using the infra­struc­ture to trou­bleshoot the infra­struc­ture”. That is — using 802.11 devices to trou­bleshoot an 802.11 net­work. Chan­nel analy­sis is a new tech­nique we have cham­pi­oned and pio­neered. This type of tool uses 802.11 hard­ware to per­form data acqui­si­tion — hence, the results truly reflect how RF inter­fer­ence in the local envi­ron­ment affects through­put per­for­mance of 802.11 chan­nels. This is not pos­si­ble using an RF spec­trum ana­lyzer. By virtue of the fact an 802.11 chan­nel ana­lyzer views the RF world through the eyes of an 802.11 device, then the diag­nos­tic infor­ma­tion it pro­vides more closely mir­rors the per­for­mance you can expect from your own 802.11 client adapters. This makes it eas­ier to trou­bleshoot and fix prob­lems and allows you to make better-​​informed deci­sions regard­ing how best to con­fig­ure your wire­less net­work for opti­mal through­put performance.

4. Con­nec­tion Analy­sis Ulti­mately, the bot­tom line for any net­work (wired or wire­less) comes down to through­put per­for­mance — that is, how many bytes-​​per-​​sec can be trans­ferred from one node on the net­work to another. The dBm and RSSI val­ues that are often referred to in the con­text of wire­less net­works don’t mean much if you can’t some­how relate them to a per­for­mance met­ric. Before we can really begin to trou­bleshoot a wire­less net­work we need a way to bench­mark its per­for­mance, so as mod­i­fi­ca­tions are made we can deter­mine whether or not they really make a dif­fer­ence in the network’s per­for­mance. A con­nec­tion analy­sis tool allows you to directly com­pare the per­for­mance and reli­a­bil­ity of dif­fer­ent com­bi­na­tions of 802.11 adapters and access points.

Related posts:

1. Trou­bleshoot­ing Net­work Problems
2. Will a USB Wi-​​​​fi device solve my wire­less net­work problem?
3. Trou­bleshoot­ing Inter­net /​​ Net­work Con­nec­tiv­ity Using the Osi Model
4. Dish Net­work Problems
5. Net­work Con­fig­u­ra­tion Prob­lem Involv­ing Router and Fire­wall IP Addresses?