User's Manual

• At the IPE backplane interface – when all 32 speech channels to the DS30X interface on
the a DMC8 are occupied, calls to and from handsets that have that specific DMC8 as
their home DMC8 are rejected.
• At the Network interface – usually the IPE shelf connectivity is a blocking configuration,
where the number of network timeslots provided for a shelf is less than the actual number
of terminals configured on that shelf.
Traffic definitions
Busy hour traf
fic – Busy hour traffic is the hour of the day during which a telephone system
carries the most calls, voice or data. The unit for busy hour traffic is the Erlang or Centi Call
Second (CCS).
Erlang – One Erlang is equal to the continuous use of a circuit for one hour.
CCS – One hundred Call Seconds (CCS) or 100 seconds of continuous use of a circuit.
Normally referred to as CCS per hour. For example, a call on a circuit for one hour is equal to
36 CCS. (60 minutes x 60 seconds = 3600/100 = 36 CCS)
Blocking – A condition when a telephone call does not complete, and the calling party normally
hears a busy signal.
Grade of Service – Grade of Service, given as a decimal fraction, indicates the probability of
call blocking. For most applications, acceptable figures for blocking are between 0.01 and
0.03.
Traffic assumptions used for table calculations
The following are traf
fic assumptions used for table calculations:
• A handset that always has good radio contact with a basestation assumes that the radio
deployment is acceptable.
• The Grade of Service used in all calculations is 1%.
• There is little or no overlap between basestations. (In practice, there is overlap, but to
apply standard traffic calculations, it is necessary to simplify the calculation). For example,
two 6-channel basestations in the same cell deliver a higher traffic flow.
• Ignore radio channels for handover. The traffic calculations allocate a slightly higher traffic
capability to a basestation than it can have in practice.
• Blocking occurs at three main areas: the basestations, the backplane, and the network
loops. The traffic calculations only use the Erlang values where blocking occurs. For
example, if there are three areas each delivering 10 Erlangs, traffic calculations take the
total traffic capability as 10 Erlangs, not as 30 Erlangs. Real traffic capacity in this example
is possibly more than 10 Erlangs.
Engineering guidelines
38 DMC DECT Fundamentals August 2012
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