MGCP Alarm Flows
Figure 5-19 illustrates a chat amid a alarm abettor and two gateways.
Chapter 5: Examining VoIP Gateways and Aperture Control Protocols 283
Gateway A Aperture B
Off Hook and
Dialed
5551234
On Hook
Ringing
Then Answer
Call
GWA Abettor GWA
RQNT
RQNT Response
NTFY
MDCX (Encapsulated
RQNT, SDP)
CRCX Response (SDP)
CRCX
MDCX Response
NTFY
DLCX Response
DLCX
CRCX
(SDP, Encapsulated
RQNT)
RQNT Response
RQNT
CRCX
Response (SDP)
DLCX Response
DLCX
RTP Stream
RTP Stream
RTCP Stream
Figure 5-19 Alarm Flows
Although the gateways in this archetype are both residential gateways, the attempt of
operation listed actuality are the aforementioned for added aperture types:
1. The alarm abettor sends a RQNT to anniversary gateway. Because they are residential gateways,
the appeal instructs the gateways to delay for an off-hook alteration (event). When
the off-hook alteration accident occurs, the alarm abettor instructs the gateways to supply
dial accent (signal). The alarm abettor asks the aperture to adviser for added contest as well.
By accouterment a chiffre map in the request, the alarm abettor can accept the aperture collect
digits afore it notifies the alarm agent.
2. The gateways acknowledge to the request. At this point, the gateways and the alarm agent
wait for a triggering event.
3. A user on Aperture A goes off-hook. As instructed by the alarm abettor in its earlier
request, the aperture provides a punch tone. Because the aperture is provided with a
digit map, it begins to aggregate digits (as they are dialed) until either a bout is made
or no bout is possible. For the butt of this example, accept that the digits
match a chiffre map entry.
4. Aperture A sends a NTFY to the alarm abettor to admonish the alarm abettor that a requested
event was observed. The NTFY identifies the endpoint, the event, and in this case
the dialed digits.
5. After acknowledging that a alarm is accessible based on the dialed digits, the alarm agent
instructs Aperture A to CRCX with its endpoint.
6. The aperture responds with a affair description if it is able to board the
connection. The affair description identifies at atomic the IP abode and UDP port
for use in a consecutive RTP session. The aperture does not accept a affair description
for the alien ancillary of the call, and the affiliation enters a delay state.
7. The alarm abettor prepares and sends a affiliation appeal to Aperture B. In the request,
the alarm abettor provides the affair description acquired from Aperture A. The connection
request is targeted to a distinct endpoint, if alone one endpoint is able of
handling the call, or to any one of a set of endpoints. The alarm abettor additionally embeds a
notification appeal that instructs the aperture about the signals and contest it should
now accede relevant. In this example, in which the aperture is residential, the signal
requests campanology and the accident is an off-hook transition.
284 Authorized Self-Study Guide: Cisco Voice over IP (CVOICE)
Note The alternation amid Aperture B and its absorbed user has been simplified.
8. Aperture B responds to the appeal with its affair description. Notice that Gateway
B has both affair descriptions and recognizes how to authorize its RTP sessions.
9. The alarm abettor relays the affair description to Aperture A in an MDCX. This
request ability accommodate an encapsulated NTFY appeal that describes the accordant signals
and contest at this date of the alarm setup. Now Aperture A and Aperture B have
the appropriate affair descriptions to authorize the RTP sessions over which the audio
travels.
10. At the cessation of the call, one of the endpoints recognizes an on-hook transition.
In the example, the user on Aperture A hangs up. Because the alarm abettor requested
the gateways to acquaint in such an event, Aperture A notifies the alarm agent.
11. The alarm abettor sends a DLCX appeal to anniversary gateway.
12. The gateways annul the access and respond.