Dimensioning Trunk Size

BHT in average = 60 secs in short
BHT in average = 180 secs in long

Although is 100% available but normally the traffic is very low which compared with local telephone lines.

Therefore we need to dimension in different type of trunks:
1. DID line for hotel,
2. DOD line for extn., direct line.

Different GOS will be used to dimension these two trunk type.
1. for DID – 0.5% GOS
2. for DOD – can be divided into seperate trunk group with overflow facility to ensure no blocking. For initial trunk group – 30% overflow and 0.5% GOS for final route.

Nevertheless, it will depend on the equipment investment from the company.

The suggestions Alex provided you are sound much more like suggestions for sizing an enterprise environment rather than a hotel environment.

Although I dont claim to work in that industry, I believe the requirements are different.i.e.
Is the hotel targeted towards business customers or vacationers?

I guarantee that vacationers will use the phone a lot less than business folks so if you are working on a phone system for the “fun and sun” in Florida the type of traffic they will see will be different from the Hyatt downtown Chicago.

Also 99.99% availability has more to do with the system and not the trunks. That type of availability means the system should be down no longer than 53 minutes per year.

IME rules of thumb are quick and easy but its better to get the right information first and the customer will be happier in the long run. You will be able to back all your decisions with data.

Johnny,

Take an example for a hotel has 200 rooms, with 10 DID line and 30 DOD lines.

The originating traffic rate & the terminating traffic rate for a hotel is much difference from residential subscriber line.

For normal residential subscriber line, the originating traffic will be only 0.04 to 0.05 erlang. But for business line is quite different, it will be 0.06 to 0.16 and depend the type of business line you have.

You can divide the rooms into say 5 trunk groups, with room no. 1,6,11,16… to be TG 1; room no. 2,7,12,17…. to be TG 2, room no. 3, 8, 13, 18….to be TG 3 and so on….. Each TG will have 5 DODs, the other DOD lines will be used by office.

You also can plan the overflow routes between the TGs. Suppose TG1 overflow to TG3 and then overflow to TG5.

It is only a simple configuration for such small size phone lines.

Karen,

(The traffic rates of residential lines had been already mentioned above. You also need to know the day to busy hour ratio, there should be have two different busy hour for residential lines, and the day to busy hour ratio will be 10 to 12)

Alex

Chris,

If you have one fat pipe, how many trunks for this fat pipe?
But if use several thin pipes, it can save a lot of trunks.
On the other hand, you can use the overflow criteria to ensure the blocking to near zero.
For dimensioning purpose, if you use overflow condition, it is on the save side for GOS and the needs of trunks.

Alex

Supose you have 200 subs generating 200 call/hour and 10 min of holding time:
L=200 call_h/60 min = 3.33call/min
t= 10 min
A= 3.33*10 = 33E
1% blocking means 40 trunks is sufficiently to this exemple.