Exceeding Erlang capacity in GSM systems

[Aasem_sadek]

Hello,
can the served traffic by GSM system exceeds the value of erlangs in the table? i saw a report were the capacity were 21 erlangs & the served traffic for busy hour was 26 erlangs!!! can anyone tell me how this can happen? the only explanation i got is cuz (queuing) was on,..if so how queuing can increase traffic above the capacity?

Best Regards
Assem Sadek

 

[nadermokari]

erlang per subscriber

please discribe concept of erlang?

 

[vanjula]

erlang gsm explanation

Erlang is a standard unit to represent the traffic in a system. It can be explained as below :

One erlang of traffic means that a switch is occupied for a given period of observation.

Consider the observation period for occupancy of a switch is 60 sec ( which is standard ).

Then , the offered load to the system can be calculated in terms of erlangs as :

A= Q * T / 60

where Q = call arrival rate ( calls/min)
T = call holding time (minutes per call)

So, if say for an example .... in a system maximum calls per hour is 3000 (i.e. the total call attempts made by the subscriber)
and the average calling time is1.76 min (i.e. each subscriber has occupied the switch for 1.76 mins on an average)

then load on system in terms of erlangs is calculated as :

A = 3000*1.76/60

= 88 erlangs...


thus an erlang is just an unit to measure the capacity of a system in terms of offered load....


I HOPE U HAVE NOW UNDERSTOOD WHAT DOES AN ERLANG MEAN ....

 

[Prince Maini]

erlang subscriber value

the concept given above completely describes the concept of erlang ... for further help refer book - telecommunication network by THIAGARAJAN VISHWANATHAN

 

[desperado1]

mean holding time per subscriber

Erlang is a standard unit to represent the traffic in a system. It can be explained as below :

One erlang of traffic means that a switch is occupied for a given period of observation.

Consider the observation period for occupancy of a switch is 60 sec ( which is standard ).

Then , the offered load to the system can be calculated in terms of erlangs as :

A= Q * T / 60

where Q = call arrival rate ( calls/min)
T = call holding time (minutes per call)

So, if say for an example .... in a system maximum calls per hour is 3000 (i.e. the total call attempts made by the subscriber)
and the average calling time is1.76 min (i.e. each subscriber has occupied the switch for 1.76 mins on an average)

then load on system in terms of erlangs is calculated as :

A = 3000*1.76/60

= 88 erlangs...


thus an erlang is just an unit to measure the capacity of a system in terms of offered load....


I HOPE U HAVE NOW UNDERSTOOD WHAT DOES AN ERLANG MEAN ....

I have a couple of questions regarding your answer. In the problem you have solved you've mentioned 3000 calls per hour but from in the formula you've placed 3000 cals per min....

Also if the traffic in erlangs is 1 if a call is occupied for 1 hour then what is the traffic in erlangs if it is occupied for half an hour ?

thanks in advance....

 

[free_lo]

erlang as traffic capacity

Hello,
can the served traffic by GSM system exceeds the value of erlangs in the table? i saw a report were the capacity were 21 erlangs & the served traffic for busy hour was 26 erlangs!!! can anyone tell me how this can happen? the only explanation i got is cuz (queuing) was on,..if so how queuing can increase traffic above the capacity?

Best Regards
Assem Sadek

There was congestion, this is the explanation.

 

[leekk8]

what is standard of erlang per hour?

As you mentioned, One erlang of traffic means that a switch is occupied for a given period of observation.

What I understand is, one erlang of traffic is the switch is fully utilized over a period. So, how can the erlang can be more than 1? You mean the switch can operate at more than 100% utilization rate?

 

[free_lo]

capacity of 1 erlang

The capacity of the lines is calculated using Erlang B formula (see wikipedia for more) and will show the capacity offered and the capacity requested. The formula works on call attempts registered and mean holding time (average call time).

For an hour the node will count the nr of call attempts, mean holding time and based on other factors (explained in wikipedia) will give the Erlang capacity.

The switch can not operate at more than 100% utilization rate, there will be congestion. None of the call attempts after 100% will be successful and depending on the measuring tool for Erlang you may see the "Lost calls" value or something like that.

 

[asfandyar]

Erlang capacity

hey guys can any body help me. i want to calculate probability that call gets placed in queue if call center include a simple queue capable of holding 150 calls. also how many jobs would be held and how long, on average, would a caller be held in queue