Mitel MiVOICE BUSINESS, Инструкция по инженерии

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Engineering Guidelines
58
PROVISIONING FOR TRAFFIC
All 3300 ICP controllers contain an internal TDM switching fabric. Calls between TDM sets, or
from TDM sets to trunks, will stay within this TDM switch. Calls between IP phones stream their
voice packets directly over the data network without going into the TDM domain in the 3300
ICP controller, but calls between IP sets and TDM devices (including both lines and trunks)
must go from the IP domain to the TDM switch fabric through the TDM gateway (E2T processor).
All of these calls require bandwidth or channels within the various domains and may require
specific resources (DSP tone generators and detectors, echo cancellation, etc.) within the
controller. The provisioning of these resources is done using the standard type of traffic analysis.
The TDM switching fabric in all of the 3300 ICP controllers is non-blocking, but the limitations
in the number of channels available in the number of channels available in the TDM gateway,
the fiber interfaces, and other resources mean that the system itself is not.
Under most ordinary conditions, the “rules of thumb” provisioning suggested in previous
sections gives a good estimate of the resources required for the number of lines (users) and
trunks in a system. For systems that are approaching the limits of the system, more detailed
calculations may be required through Customer Engineering Services.
Traffic analysis considerations:
• 36 CCS = 1 erlang (1 e) = 3600 call seconds during the busy hour.
• Call rates (CPH) and duration may vary from business to business. It may be necessary to
monitor a business to get more accurate values.
• Typical phone calls are 100 seconds in duration.
• Typically, a normal office phone is busy 16% of the time, or 0.16 e, or 6 CCS (this is 6 CPH
@ 100 seconds, i.e. 600 call seconds or 6 centum call seconds or 10 minutes).
• Typically, a hotel phone is busy 6% of the time, or 0.06 e, or 2 CCS.
• Typically, a busy office phone, such as one handling dispatch orders, can be busy 33% of
the time, or 0.33 e, or 12 CCS.
• Call volume is typically split in thirds, with 33% incoming from trunks, 33% outgoing to
trunks, and 33% handling internal calls (50% is making calls and 50% receiving calls).
• For normal users, typically one voice mail session is needed for 20 users. Modify this number
accordingly if you expect heavier or lighter voice mail traffic per user.
• Typically, ACD workers are busy 75% to 100% of the time. One ACD agent normally requires
one resource, such as one 1 E2T channel, one echo channel, one DSP channel (compres-
sion), and one trunk. ACD traffic ranges from 27 to 36 CCS (27 to 36 calls per hour).
• Typically, in a given ACD group, all calls are either incoming or outgoing trunks, rarely mixed.
• Traffic blocking is calculated using the ErlangB formula. Erlang adds a statistical blocking
factor and is always higher than the straight calculation. Add a further 10% to 20% to PI
estimates as a rough estimate, and round up.
• Operators or attendants can typically handle up to 100 calls per hour (as long as transfer
is handled quickly and number lookup is sufficiently quick). Most incoming trunk calls arrive
at the operator station.
• Traffic blocking probability for internal/intercom traffic is P.001 (1 in 1000 calls blocked).
• Traffic blocking probability for trunk traffic is P.01 (1 in 100 calls blocked).