Saturday, March 14, 2009

A practicle analysis of Airtel fair use policy

From the moment Airtel introduced the speed cap, I was thinking of doing a analysis of download loss due to Fair Usage policy. Finally the time has come.. :)

Here is my practicle analysis of Airtel fair use policy.

In this article, I have done some assumptions for ease of calculations, They are
  1. Broadband usage is assumed to be download only. ie; you use internet only for downloading purposes. (If you torrents then this assumption no longer holds good, as torrents generally upload huge amount of data)
  2. All calculations are based on theoretical download speed. The actual download speed which you get may vary depending upon several factors.
So, here I begin..

Let me first start with 256 kbps unlimited plan,

Theoretical Maximum download speed: 256 kbps

256 kbps mean 256 kilo bits per second, Not 256 kilo bytes per second as people think. Also, here kilo is 1000, not 1024.

so, 256 kilo bits per second means = 1000 * 256 bits per second = 256000 bits per second.

8 bit = 1 byte, so in bytes this becomes

256000 / 8 = 32000 bytes

Now 1024 bytes = 1 KB

32000/1024 = 31.25 KB or kilo bytes per second

per minute download = 31.25 * 60 = 1875 kilo bytes = 1.8310 MB (1 MB = 1024 KB)

Download per 1 Hr = 1.8310 * 60 = 109.8633 MB

So, you keep downloading something whole day, you can download 109.8633 * 24 = 2636.71875 MB or 2.5749 GB per day

so, per month (thinking a month has 30 days) theoretical max download possible is 77.2476 GB.

Now you may be wondering what happened to upload?

In ADSL, upload is a separate stream. which is separate from the download bandwidth.

So, unless you do a lot of uploads (which will happen if you use torrents), most of your bandwidth will be download only. (say 95% to 98%)

P.S.: All calculations done based on theoritical speed. Remember that speed cap limit includes download + upload usage!

Thinking that your usage is download only, with 256 kbps plan, you can download 77.25 GB of data per month. (When there are no speed restrictions)

Similarly with 384 kbps unlimited plan,

speed = 384 kbps
384 kbps = 384 * 1000 kilo bit = 384000 bits = 48000 bytes = 46.875 KB
per minute = 46.875 * 60 = 2812.5 KB = 2.7466 MB
per Hr 2.7466 * 60 = 164.7949 MB
per day = 164.7949 * 24 = 3955.0781 MB = 3.8624 GB
per month (30 days) = 3.8624 * 30 = 115.8714 GB

and with 512 kbps,

speed = 512 kbps
512 kbps = 512 * 1000 bits = 512000 bits = 64000 bytes = 62.5 KB
per minute 62.5 * 60 = 3750 KB = 3.6621 MB
per Hr 3.6621 * 60 = 219.7266 MB
per day = 219.7266 * 24 = 5273.4375 MB = 5.1498 GB
per month (30 days) 5.1498 * 30 = 154.4952 GB

Now the cost analysis,


Broadband plan
Speed Cap (download+upload)
Normal Speed (Before crossing Speed cap)
Reduced Speed (After crossing Speed cap)
256 kbps Unlimited
50GB
256 kbps
128 kbps
384 kbps Unlimited
75GB
384 kbps
256 kbps
512 kbps Unlimited
100GB
512 kbps
256 kbps

Now the analysis, with old broadband rate plans,

Broadband plan
Monthly rental
Theoretical max download
Cost per GB
Max download with Speed Cap (normal speed + reduced speed)
Cost per GBTotal download loss (GB)
256 kbps unlimited
Rs. 799
77.25 GB
Rs. 10.343063.625 GB
Rs. 12.557913.625 GB
384 kbps unlimited
Rs. 999
115.87 GB
Rs. 8.62173102.2467 GB
Rs. 9.7705
13.6233 GB
512 kbps unlimited
Rs. 1499
154.4952 GB
Rs. 9.70257127.2476 GB
Rs. 11.780227.2476 GB

If you are wondering about how I got "Max download with Speed Cap" field, here is how,

for 256 kbps plan, Only for first 50 GB you will get 256 kbps download speed later the speed is reduced to half.

So, total downlaod possible with speed cap = 50 GB + (Max download possible - 50 GB) / 2

= 50 GB + (77.25 - 50) /2 = 50 GB + 13.625 GB = 63.625 GB. Here 13.625 GB is your loss in GB.

For 384 kbps, Once you cross your speed cap, The speed is not reduced to half. instead it is reduced to 256 kbps.

So, total download possible with speed cap = 75 GB + (Max download possible - 75 GB) * 256/384

= 75 GB + (115.87 -75) * 256/384 = 75 GB + 40.87 * 256/384 = 75 GB + 27.2467 GB = 102.2467 GB

and same calculations with the new rate plans,

Broadband plan
Monthly rental
Theoretical max download
Cost per GB
Max download with Speed Cap (normal speed + reduced speed)
Cost per GBTotal download loss (GB)
256 kbps unlimited
Rs. 899
77.25 GB
Rs. 11.637563.625 GB
Rs. 14.129713.625 GB
384 kbps unlimited
Rs. 1199
115.87 GB
Rs. 10.3478102.2467 GBRs. 11.7265
13.6233 GB
512 kbps unlimited
Rs. 1499
154.4952 GB
Rs. 9.70257127.2476 GB
Rs. 11.780227.2476 GB

As usual, 384 kbps is the best plan to go for. It has the best "cost per GB" when you do lot of downloads. Also, once you cross your speed cap, virtually there is no difference between 512 kbps and 384 kbps unlimited plans. (Both gives you 256 kbps download speed)

Conclusion: So, what is the final conclusion ?
Nothing! These are just numbers, and they them self have no meaning! Speed cap still sucks!  />:-]

However, when compared to previous speed cap limits, current speed cap limits are not that bad. (Check my previous article for more info.)

Note: If you do lot of uploads, above calculations are no longer significant for you.

Please comment..



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