Tim's guide to understanding / deciphering the info provided by the tech mode screens

Cell ID

Cell ID is one of the most common bits of data that you can get from a tech mode. It is also one of the most complex and interesting piece of info. The word Cell ID is sometime confused as meaning Cell broadcast or CB (this will be explained latter).

What is a Cell ID?

A Cell ID is the unique number that enables the network to identify each cell/tower on its network. Each Cell ID is unique and is NEVER used more than once.

The Cell ID contains lots of info. The info in this guide will concentrate with vodafone AU, But the information / meaning of the numbers in the Cell ID is the same for most networks.

A Cell ID contains 5 numbers, They can be displayed in Hexadecimal or Decimal, I will use decimal, as its easy to read and most phones display the Cell ID in decimal.

A Cell ID looks like this:-

44011

So what does this number tell us?

For a start lets think of the number in this format. SYXXC.

The 1st digit, S, stands for what state the tower is in. These are all the first digit of the post codes in AU. 4 means QLD, 2 for NSW, 3 for VIC ect...

The 2nd digit,Y, Normally stands for the year it was built or planed to be built. EG our example is 9"4". Is it was a 0 then its 2000 ect..

The 3rd and 4th digit, XX, Shows the roll out of the towers and can also tell us what the site does.

Eg  A tower with a XX of 22 was built before a tower with a XX of 86.

Also is a tower has a XX of 00 it is 99% likely a MSC site, If its 01 its a BSC or a main hub site.

The last but not least 5th digit, C,   tells us what cell on the tower we are connected to and what type of cell / tower it is. It also tells use what GSM frequency we are talking on (GSM 900 or GSM 1800).

Here is a pic to help explain the info listed above. If you look at my tower pics contained on my page, That will also help :-)

The picture is looking at a tower from above (at the Head Frame), The Red boxes are the transmit and receive antennas for GSM 900, the Green boxes are the transmit and receive antennas for GSM 1800 and the black dot in the middle is the pole (not to scale).

With the cell numbers they always go in a Clockwise direction, Usually starting from the north. So if you know were any of the 3 (or 4) cells are you can work out were the rest are. This is quite handy when you are at a tower site and your trying to figure out what antennas belong to which cell.

Eg. our example tower cell number is 1, so therefore it is the first GSM 900 cell on tower number 4401. the tower is also located in QLD.

Exceptions to the rules!

Unfortunately there are some IDs that don't follow the rules.. this could be because VodaFone has number them wrong or because each area can have its own sub-numbering scheme.

GSM Channel (CH) numbers

GSM uses channel numbers to identify pairs of transmit and receive frequencies. These are used between the mobile phone (Mobile Station,MS) and the tower (Base Transceiver Station,BTS). For each flavour of GSM there is a different set of CHs.

0 - 124 for GSM 900

512 - 885 for GSM 1800

In Australia we only use GSM 900 and GSM 1800. VodaFones network is primarily GSM 900 and uses GSM 1800 as a secondary network to overlap there GSM 900 cells to provide extra capacity in busy areas. GSM 900/1800 coverage (also known as Dual Band) is only available in limited areas. Info on were it is available is on my page.

Because GSM 900 and GSM 1800 use different CH numbers, it is easy to know what band you are on just by looking at the CH number. If its between 0-124 its GSM 900, if its 512-885 then its GSM 1800.

Each cell uses 1 CH as its BCCH (Broadcast Command CH). Its like a beacon that is on all the time that allows the mobile phone to find and new cell or to change/find another cell on another tower. Each tower can have 3 (or 4) cells. Have a look at the Cell ID before reading on.

On a tower each cell has a unique CH number.

Have a look at the example below:- (yes this is a real tower)

Cell Boardcast         Cell ID  CH

Park Ridge                  40011    119
Munruben                    40012    121
Greenbank                   40013    123

Ok what does this info tell us? Well from the Cell ID we know this site is 3 celled, Its a new tower (4001 is actual the first of the 40XX towers), Its located in QLD (4XXX). Also here you can see that it is also uses directional ants on each cell. Also it must be around the Park Ridge, Munruben and Greenbank area. I have had pics of this tower on my site for ages. Here is a pic of it

http://www.mrvfone.com.au/vfone/towerpics/tanks.htm

Its the first tower on the page (South of Browns Plains).

So using all the info you have just read (and seen on the pic), You should be getting a bit of a understanding of how the network works (well between the towers and mobile phones anyway :-). Don't worry if it doesn't sink in all at once. I have been studying the network from scratch since 1994. It took me a while to figure everything out :-)

(c) Tim Merrell 1997-2005.     http://www.mrvfone.com.au

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