Sorry,buddy. I dont really know much about PABXs.

its OK bud's...

Extensions are the lines connecting the PABX to the telephones. Usually there is one extension per telephone. Trunks are the lines connecting the PABX to the outside world. The number of trunks needed depends on how many phones you have, and how much talking is going on. You might start with one trunk for 10 phones, and then add trunks as needed.

SSCpal.. tanx.. how about if we have 210 telephone connected to the PABX.. it means we need also 21 trunks and 210 extensions? is it the trunk refer to the number of incoming call you can accomodate in thesame time from outside world?

That's right. Each trunk carries one call. In your example 21 calls to the outside can be going on simultaneously.

"Extension" refers to a phone number, which could be different from the actual count of telephones. For example, several numbers could be directed to a single telephone. Or you could have one number that would ring at several telephones. It can get complicated. Where are you located?

ah.. ic, tanx so much.. now its clear to me... actually im an electrical engr, filipino, but working here in riyadh, ksa.. here in riyadh they dont knw the communication engr.. all low current system are responsible also by electrical engr which not included in our corriculum during school days.. thats y im starting to study about telephone system, cctv, fire alarm and public address even in BMS and access control.. huhuhuhu.. tanx again to your help.. it helps me a lot..

Hi,

I was going to inquire about your technical background before going into details but you have availed me the answer.

Already you have an answer to the question you asked, but being able to choose the exact number of Trunks and extensions and knowing their functions is just the beginning.

In addition to the advice from post No.7, you need some level of training on generic PBX and probably some equipment specifics too.

To start with, you will appreciate the hows and whys of selecting trunks and extensions by googling ERLANG, the single most important quantity in traffic engineering. Also, check out entries on PBX or PABX to appreciate the system itself.

See also http://www.erlang.com/whatis.html , http://www.infortel-systems.com/Downloads/TrafEngwhitepaper.pdf and http://en.wikipedia.org/wiki/Private_branch_exchange

I have referenced all these sites for your quick access and not as last resort. There are a number of good books on Telecommunication fundamentals to aid your understing the subject.

Meanwhile, what is the make and model of the PABX you have?

Cheers,

ethobil

Greetings.

Have a meeting with all of the department heads in your company and determine what the usage is going to be for your PABX. You want as many involved so ALL of you help make the decisions.

1. Determine how many people are making mostly outgoing calls, taking incoming calls and whether the calls are local, 800 numbers, or outgoing watts. This helps figure how many local trunks, how many 800 incoming, how many outgoing only trunks, how many incoming only trucks, etc that you will need.

2. Determine if you have a department that has mostly incoming calls and if you will be having a queue to hold the calls until answered this ties up a trunk.

3. Determine how many fax machines are going to be used and how often during the day for that will tie up a trunk for some time.

4. Determine how many will be using a dial up modem to access a particular computer not accessible through the internet or in case of internet failure.

Now that you all together have some kind of basic information call a number of PABX vendors and have them come out and give you an assessment of your needs. Get it in the form of a proposal with the trunking, cost of extentions, telephone sets, etc. Check all of the options sometimes it doesn't cost a lot more for for some really neat features like voice mail, that can be a real asset to your company.

Now go back to the same people that you had the first meeting with. Then you ALL together try to come up with the best solution for your business.

Some things to remember besides cost is the support and maintenance of your system and if you are remote to their technicians how many spare circuit cards will you need in case of a trouble. You don't want the system to go down and no body can use it. If the system is down how will you get in contact with their troubleshooting service and does that service work 24 hours a day 7 days a week. A uninterruptible power supply (UPS) with battery backup is essential as is power conditioning. Sometimes when you buy a whole system you can get some of the options free or at a reduced price. Some systems come with all the options included. Take your time for ALL of you to read each proposal and then decide.

My advice is don't try to configure your system by yourself without input from your company and input from the vendors. I have seen to many inexperienced people try decide on a system and its makeup and spend a lot of unnecessary money and create a big awkward mess that leads to their dismisal or demotion in my 43 years of telecommunication experience. Remember its a team effort.