Understanding Alarm Legs
Call legs are analytic access amid any two telephony devices, such as gateways,
routers, Cisco Unified Communication Managers, or telephony endpoint devices.
Additionally, alarm legs are router-centric. Back an entering alarm arrives, it is processed
separately until the destination is determined. Then a additional outbound alarm leg is established,
and the entering alarm leg is switched to the outbound articulation port. The topology
shown in Figure 3-23 illustrates the four alarm legs complex in an end-to-end alarm between
two voice-enabled routers.
164 Authorized Self-Study Guide: Cisco Articulation over IP (CVOICE)
Packet
Network
Source Destination
Call Leg 1
(POTS Punch Peer)
Call Leg 2
(VoIP Punch Peer)
Call Leg 3
(VoIP Punch Peer)
Call Leg 4
(POTS Punch Peer)
V V
Figure 3-23 Punch Aeon and Alarm Legs
An end-to-end alarm consists of four alarm legs: two from the antecedent router’s angle and
two from the destination router’s perspective. To complete an end-to-end alarm from either
side and accelerate articulation packets aback and forth, you charge configure all four punch peers. Dial
peers are acclimated alone to set up calls. After the alarm is established, punch aeon are no longer
employed.
An entering alarm leg occurs back an admission alarm comes into the router or gateway. An
outbound alarm leg occurs back a alarm is placed from the router or gateway, as depicted in
Figure 3-24.
Figure 3-24 End-to-End Calls
A alarm is anecdotal into alarm legs, and a punch associate is associated with anniversary alarm leg. The
process for alarm setup, as diagrammed in Figure 3-24, is the following:
■ The POTS alarm arrives at R1, and an entering POTS punch associate is matched.
■ After advertence the admission alarm to an entering POTS punch peer, R1 creates an
inbound POTS alarm leg and assigns it a alarm ID (call leg 1).
■ R1 uses the dialed cord to bout an outbound VoIP punch peer.
■ After advertence the dialed cord to an outbound articulation arrangement punch peer, R1 creates
an outbound articulation arrangement alarm leg and assigns it a alarm ID (call leg 2).
■ The articulation arrangement alarm appeal arrives at R2, and an entering VoIP punch associate is
matched.
■ After R2 assembly the admission alarm to an entering VoIP punch peer, R2 creates the
inbound articulation arrangement alarm leg and assigns it a alarm ID (call leg 3). At this point, both
R1 and R2 accommodate articulation arrangement capabilities and applications, if required. The
originating router or aperture ability appeal nondefault capabilities or applications.
When this is the case, the absolute router or aperture charge bout an inbound
VoIP punch associate that is configured for such capabilities or applications.
■ R2 uses the dialed cord to bout an outbound POTS punch peer.
■ After advertence the admission alarm bureaucracy with an outbound POTS punch peer, R2
creates an outbound POTS alarm leg, assigns it a alarm ID, and completes the alarm (call
leg 4).
Source
R1 R2
Originating
Gateway
Terminating
Gateway
Destination
POTS POTS
Call Leg 1
(POTS Punch Peer)
Call Leg 2
(Voice Network
Dial Peer)
Call Leg 3
(Voice Network
Dial Peer)
Call Leg 4
(POTS Punch Peer)
R1 Entering R1 Outbound R2 Entering R2 Outbound