Call Flow - Cisco AS5350XM Configuration Manual

Configuring Voice over IP
Figure 5
Source
Legs connecting a local device (typically a phone, fax machine, or PBX) to a gateway are called POTS
(plain old telephone service) legs. Legs connecting a gateway to the IP network are called VoIP legs. A
POTS or VoIP leg is either inbound or outbound, from the perspective of the associated gateway.
Table 12
Table 12
Call Leg Source
Originating device
Originating gateway
IP network
Destination gateway
A gateway uses two call legs—an inbound POTS with an outbound VoIP or an inbound VoIP with an
outbound POTS—to create an end-to-end call through the gateway. A call that passes through both an
originating gateway and a destination gateway has four call legs.

Call Flow

Table 13
gateway respectively.
Table 13
Event
User sends dialed digits using public switched telephone network to gateway.
Gateway does the following:
•
•
•
•
Call Legs
V
Call leg 1
(POTS dial peer) (VoIP dial peer)
describes the different types of call legs.
Call Legs
and Table 14 detail the general call flow from the perspective of an originating and destination
VoIP Call Flow, Originating Gateway View
Processes information (maps dialed digits, according to information stored
in dial-peer configuration tables, either to an IP host that connects directly
to the destination gateway or to a PBX at the destination that can complete
the call).
Initiates H.323 session across network.
Processes voice signals and sends packets over network. As appropriate,
sends call-progress and other in-band signals.
Ends session.
Cisco AS5350XM and Cisco AS5400XM Universal Gateways Software Configuration Guide
IP network
Call leg 2 Call leg 3
(VoIP dial peer)
Call Leg Destination
Originating gateway
IP network
Destination gateway
Destination device
Destination
V
Call leg 4
(POTS dial peer)
Call Leg Type
Inbound POTS
Outbound VoIP
Inbound VoIP
Outbound POTS
Leg Type
Inbound POTS
Outbound VoIP
VoIP Basics
3