the full-mesh scenario can be quite costly. One alternative is the use of tandem PBXs.
number and can connect other PBX stations to the public network for both incoming and
outcoming calls. A tandem switch connects one trunk to another. A tandem switch is an
intermediate switch or connection between an originating telephone call location and the final
destination of the class.
protocol for signaling, messaging, and interfacing VoIP and PBX traffic. SS7 uses out-of-band
signaling to establish the appropriate path for the call through the carrier network before
establishing the actual transmission path. Many modern PBXs directly support the SS7
signaling protocol. This allows each PBX to make and process requests from the telephone
company network.
the call. Networks with these inherent signaling characteristics are called connection-
oriented networks.
Voice addressing relies on a combination of international and national standards, local
telephone company practices, and internal customer-specific codes.
international numbering plan for ISDN. In addition, E.164 has the country codes used for
dialing internationally. The international telephone service-numbering plan is a subset of this
numbering plan. Each country's national numbering plan must conform to the E.164
recommendation and work in conjunction with the international numbering plan. Providers of
Public-Switched Telephone Networks (PSTNs) must ensure that their numbering plan aligns
with the E.164 recommendation and that each of their customers' networks conform.
recommendation include Carrier Identification Code (CIC), a prefix to select different long-
distance carriers; prefixes to select tielines, trunk groups, and WATS lines; and private number
plans, such as seven-digit dialing. When you integrate voice and data networks, you need to
consider each of these numbering plans. The ITU-T has provided the international public