Scalable Punch Plans
Figure 6-3 shows a circuitous articulation arrangement that consists of the apparatus discussed in
this section. A absolute and scalable punch plan charge be able-bodied planned and able-bodied implemented
on networks such as this. The Centrex account requires 10-digit dialing between
itself and armpit D. The IP arrangement requires 10-digit dialing against sites A, B, and C. Each
of the PBXs requires four-digit dialing.
Figure 6-3 Scalable Punch Plan Topology
When designing a all-embracing punch plan, you charge attach to these attributes:
■ Dial-plan argumentation distribution: Acceptable dial-plan architectonics relies on the able distribution
of the dial-plan argumentation amid the assorted components: alarm processing system,
voice gateways, and gatekeepers (if used). Accessories that are abandoned to a specific
portion of the punch plan abate the complication of the configuration. Each component
focuses on a specific assignment accomplishment. Generally, the bounded about-face or gateway
handles capacity specific to the bounded point of attendance (POP). Higher-level routing
decisions are anesthetized forth to the gatekeepers and PBXs. For H.323 networks, a
well-designed arrangement places the majority of the dial-plan argumentation at the gatekeeper
devices.
■ Hierarchical calculation plan: You charge strive to architecture a hierarchical numbering
plan to calibration the cardinal of accessories after introducing interdigit abeyance or routing
issues due to overlapping calculation ranges. Maintaining a hierarchical architecture makes
the accession and abatement of cardinal groups added manageable. A well-designed hierarchical
numbering plan includes acceptable avenue summarization.
■ Simplicity in provisioning: Accumulate the punch plan simple and balanced aback designing
a network. Try to accumulate constant punch affairs on the arrangement by application translation
rules to dispense the bounded chiffre dialing patterns. These cardinal patterns are normalized
into a accepted architecture or arrangement afore the digits access the VoIP core.
Putting digits into a accepted architecture simplifies accessories and dial-peer
management.
■ Column punch delay: Accede the furnishings of column punch adjournment in the arrangement aback you
design a all-embracing punch plan. Column punch adjournment is the time amid aback the aftermost digit
is dialed and the buzz rings at the accepting location. In the PSTN, bodies apprehend a
short column punch adjournment and to apprehend arena aback aural seconds. The added translations,
digit manipulations, and lookups that booty place, the best the column punch delay
becomes. All-embracing arrangement design, adaptation rules, and alternating paths affect post
dial delay. Minimize the bulk of punch aeon and translations to abate column dial
Chapter 6: Identifying Punch Plan Characteristics 327
Site E
Site A
727555....
813555....
305555....
Site B
Site C
Site D
703555.... 202555....
10 Digits
10 Digits
10 Digits 4 Digits
Site F
IP
Centrex
4 Digits
4 Digits
10 Digits
delay. Other things to accede are processor-intensive functions the router might
also be performing, such as VPNs and NAT. Anything that utilizes the processor to
any amount ability affect the adequacy of the aperture to action calls.
■ Availability and accountability tolerance: Accede all-embracing arrangement availability and the call
success amount aback you architecture a punch plan. Accountability altruism and back-up are some
advantages of a VoIP network. Calls ability be automatically baffled over redundant
IP paths or through the PSTN. Redundant gateways ability be provided for missioncritical
sites.
Cisco SRST is a aperture affection that allows an IP buzz to annals with the gateway
if no Cisco Unified Communications Manager is available. SRST is above the scope
of this course.
■ Conformance to accessible standards: Punch affairs that interface to the PSTN charge to
conform to accessible standards area applicable.