Trunks
Trunks are acclimated to interconnect gateways or PBX systems to added gateways, PBX systems,
or the PSTN. A block is a distinct concrete or analytic interface that contains several
physical interfaces and connects to a distinct destination. This could be a distinct FXO port
that provides a distinct band affiliation amid a Cisco aperture and a FXS anchorage of small
PBX system, a POTS device, or several T1 interfaces with 24 curve anniversary in a Cisco gateway
providing PSTN curve to several hundred subscribers.
Trunk ports can be analog or agenda and use a array of signaling protocols. Signaling
can be done application either the articulation approach (in-band) or an added committed approach (outof-
band). The accessible appearance depend on the signaling agreement in use amid the
devices.
Figure 3-18 illustrates a array of accessible block connections.
Chapter 3: Routing Calls over Analog Articulation Ports 151
Chicago T1 PRI
T1 PRI
E&M
Trunk
T1 QSIG
Trunk
T1 QSIG
Trunk
E1 R2
Trunk
E1 CCS
Trunk
T1 CAS
Trunk
San Jose
Denver
London
PSTN
V
V
V
Rome
V
Figure 3-18 E&M Trunks
Consider the afterward characteristics of the trunks depicted in Figure 3-18:
■ If a subscriber at the London armpit places a alarm to the PSTN, the aperture uses one
voice approach of the E1 R2 block interface.
■ If a subscriber of the bequest PBX arrangement at the Chicago armpit needs to abode a alarm to
a subscriber with an IP buzz affiliated to the Chicago gateway, the alarm will go via
the E&M block amid the bequest PBX and the gateway.
■ The Denver and the Chicago sites are affiliated to San Jose via Q Signaling (QSIG)
to body up a accepted clandestine calculation plan amid those sites. Because Denver’s
Cisco IP telephony rollout has not started yet, the QSIG block is accustomed directly
between San Jose’s aperture and Denver’s bequest PBX.