Grade of Service

1
Grade of Service

• Telecom Analysis
• Roosevelt University
• Dr. Roger G. Clery
• March 20005

2
Blocked Calls

• When the offered load, that is traffic that would
  go through a switch if none was blocked, is
  greater than the capacity of the switch then some
  calls get blocked.
• Most switches are designed so that some traffic
  gets blocked.

3
The Grade of Service

• The Grade of Service as measured by the
  probability of blockage
• Smaller is better
• Grade of service is always measured during the
  Busy Hour
• Grade of service is a percentage
• Grade of service is by definition blocked
  calls/offered load

4
So you need to know 2 factors

• The blocked calls
• The offered load

5
The offered load is the total of all traffic that
would have gone through the switch if there was
NO blockage

• But you dont know what this is!
• The switch only has data on carried load and out
  going blocked calls

6
The offered load is the total of all traffic that
would have gone through the switch if there was
NO blockage

• The carried load is found by counting the number
  of calls that went through the switch look at
  SMDR/CDR data
• Or OFFERED LOAD CARRED LOAD TOTAL BLOCKED
  CALLS (during the busy hour)

7
Blocked Calls

• Outgoing blocked calls can be directly counted by
  SMDR CDR
• Incoming blocked calls can be estimated using the
  ratio if incoming to outgoing calls

IN
OUT
8
Estimating Incoming blocked calls

• Determine the ratio of incoming to out going
  calls (could be number for the day or the number
  for an hour)
• For example 400 incoming and 500 outgoing calls
  for one day then the ratio is 400 / 500
• If 8 outgoing calls are are blocked during the
  busy hour then
• Setup equation 400/500 X/8
  500X3200
• X6.4 Estimated number of incoming blocked
  calls
• Total blocked calls 86.4 14.4

9
Offered Load

• Offered load carried load Blocked
• If 200 calls went through the switch then the
  offered load was 200 14.4 or 214.4

10
Grade of service is

• Blocked calls / offered load
• 14.4 / 214.4 .067 or 6.7

11
end

• That is not too hard to do