My thoughts of certification in 2012

Last week, I was in San Antonio, TX, attending a 5-day course for implementing Cisco Wireless VoWLAN networks course, IUWVN of the CCNP Wireless track. I got the chance to learn how to implement Cisco VoWLAN, configure Cisco 2504 WLC’s, WCS and 7921 Wireless IP Phones for voice & video over WLAN, and a lot of the details in between. The week was great — weather was beautiful, our instructor was awesome with 20 years of RF experience from the US Marine Corps and I got to interact with a lot of other network pros. 🙂

For this blog post, I wanted to pose a question regarding certification in our industry…and specifically, how much certification is too much? When does it show technical proficiency, and when does it become a check box for Layer 8? Working for a Cisco Partner usually means that there are times that certifications are business requirements for maintaining Partner status and not necessarily technical requirements for designing, implementing and maintaining an enterprise network. What about the average network wizard?

With how much any modern business depends on the IT staff to keep the data flowing, certification can certainly be an annoyance or a chore. On any given exam, you may be asked any number of esoteric protocol details, or vendor-specific implementation and design guidelines (trust me when I say that Cisco is certainly not the only culprit) but usually you’re not tested on applying your real-world skills in the testing centers. In fact, sometimes the gear we work with everyday behaves in ways that flies in the face of the Cisco Manifesto (I’m looking at you, Catalyst 6500). I would imagine this to be the position of most of the networking gurus out there – we’re all busy enough maintaining our environments and keeping our users happy.

What does this mean for the network newbie such as myself? Certification will most definitely help getting the ever-crucial “foot in the door”. But while having “CCNA” on your resume or LinkedIn profile will help with recruiter keyword searching, it doesn’t just end there. You have to be able to prove to the IT Manager in the interview you can apply it to solve real-world problems or at least have the drive to soak up as much knowledge and experience to become a productive network admin.

Certification, for me, means that for this technology, I have a declaration that “I believe” in the Dogma of the Vendor. But its the time outside of exam cramming that is spent in lab and solving difficult problems that will actually prove that I can make it in this business.

CCO Gems: Cisco Aironet Antennas and Accessories Reference Guide

In an attempt to wrap my head around a lot of the Layer 1 details in the Wireless LAN world, I came across the following doc on Cisco’s website under their wireless antennas product info:

Cisco Aironet Antennas and Accessories Reference Guide

One of the most important units of measure to understand when working with RF is the decibel (dB). While this unit is used in many other fields such as sound and audio, this doc presents it in a clear and concise manner as it relates to WLAN’s:

The decibel (dB) scale is a logarithmic scale used to denote the ratio of one power value to another.
For example:
X1`dB = 10 log10 (Power A/Power B)
An increase of 3 dB indicates a doubling (2x) of power. An increase of 6 dB indicates a quadrupling (4x) of power. Conversely, a decrease of 3 dB reduces power by one half, and a decrease of 6 dB results in a one fourth of the power.





0 dB

1 x (same)

0 dB

1 x (same)

1 dB

1.25 x

-1 dB

0.8 x

3 dB

2 x

-3 dB

0.5 x

6 dB

4 x

-6 dB

0.25 x

10 dB

10 x

-10 dB

0.10 x

12 dB

16 x

-12 dB

0.06 x

20 dB

100 x

-20 dB

0.01 x

30 dB

1000 x

-30 dB

0.001 x

40 dB

10,000 x

-40 dB

0.0001 x

If you’re a newbie like me, this makes a lot more sense than some of the other documentation I’ve read on the subject, especially with the table above that clearly shows how dB increases logarithmically.

Now that we know a decibel is a relative value, we need to know what values are being measured and referenced. In the wireless world, those two values are Received Signal Strength Indicator or RSSI, and Signal-To-Noise ratio (SNR).

RSSI is a vendor-specific grading of received signal strength. Because it is vendor-specific and not a standard measure, these values cannot be used to compare between vendors. It is usually measured in decibel milliwatt (dBm), which is basically the ratio of power referenced to 1 milliwatt. For example, 3 dBm is 2mW of power. Again, the Cisco Aironet Antenna reference guide provides a good chart for common dBm values to give you an idea of how dBm scales in reference to wattage.

Table 2. Common mW Values to dBm Values





0 dBm

1 mW

0 dBm

1 mW

1 dBm

1.25 mW

-1 dBm

0.8 mW

3 dBm

2 mW

-3 dBm

0.5 mW

6 dBm

4 mW

-6 dBm

0.25 mW

7 dBm

5 mW

-7 dBm

0.20 mW

10 dBm

10 mW

-10 dBm

0.10 mW

12 dBm

16 mW

-12 dBm

0.06 mW

13 dBm

20 mW

-13 dBm

0.05 mW

15 dBm

32 mW

-15 dBm

0.03 mW

17 dBm

50 mW

-17 dBm

0.02 mw

20 dBm

100 mW

-20 dBm

0.01 mW

30 dBm

1000 mW (1 W)

-30 dBm

0.001 mW

40 dBm

10,000 mW (10 W)

-40 dBm

0.0001 mW

Signal-To-Noise ratio is defined as the power ratio between a signal, such as a WLAN waveform, and the background noise. Again, we’re measuring in decibels since it is the ratio of the RSSI and the surrounding garbage RF noise.

Since I’m coming from a wired world where everything is essentially plug-and-play, I’m working from the ground up at Layer 1 to hone my WLAN skills.
Anyways, the Cisco Aironet document here gives a very succinct overview of various L1 WLAN concepts such as 802.11 modulation techniques, antennas ratings and specs, understanding RF power levels, as well as a slew of other little details. The first 1/3 of the document gives a nice overview of these concepts, while the other 2/3’s list all of Cisco’s Aironet antenna products.

This is one of those gems on Cisco’s site that I’m surely packing the PDF away for future reference (especially for my Cisco wireless studies).