Information Technology Reference
In-Depth Information
For example, if 300 c alls occ urred during the busy hour, w ith an average duration of 150
seconds, the BHT is calculated as follows:
BHT = (150 seconds * 300 calls per hour) / (3600 seconds per hour)
BHT = 12.5 Erlangs
Blocking Probability
In voice environments, it is nearly impossible or at least cost-ineffective to provision ca-
pacity so that no calls are ever blocked. Therefore, planning for a target GoS is an impor-
tant aspect in voice networks. The term
blocking
refers to those calls that cannot be
completed due to capacity constraints, usually during peak periods or call spikes.
The blocking probability is the probability that a call will be blocked. Blocking probability
is described as a percentage of calls. For example, a blocking probability of 0.02 means
that 2 percent of the calls will be blocked, or 20 per every 1000 calls.
Call Detail Records
Call detail records include statistical and other information related to all calls placed. In-
for mat ion included in CDRs include s c all t ime, c all durat ion, s ource phone number, dialed
(destination) phone number, and the amount billed. For VoIP networks, the CDR may also
include source and destination IP addresses.
The introduction of packetized voice technology allows the convergence of data and voice
networks. This lets companies save toll charges on voice telephone calls. It also reduces
companies' total cost of ownership by not having to build and operate separate networks
for voice, v ideo, and data . Fig ure 14 -6 shows an example of a Cisco Unified Communica-
tions network. The network provides a resilient and redundant foundation with QoS en-
abled to support the voice and video streams and Unified Communication applications.
Call admission control is a QoS mechanism for identifying capacity issues as part of the
call routing process.
Call processing
is the term used to define the logical operations of a
phone system.
The dial plan is used to define call routing (the physical/network paths that voice calls can
take to connect two endpoints). It is responsible for defining what gateways, phone cir-
cuits, PSTN providers, or network paths should be taken to connect a call end to end
based on goals such as cost, reliability, utilization, and redundancy.
Packetized voice systems allow for applications and services including voice mail and email
combinations (unified messaging), multiparty calls (conferencing), integration of a user's
availability status (presence), mobility, call centers, and collaboration applications such as
integrated instant messaging, web meetings, and other rich communication applications.
