Chapter 3 System Features
PSAX System Software Features
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255-700-447
PacketStar
®
PSAX 2300 Multiservice Media Gateway User Guide
, Issue 1
Release 9.0.0
The DHPVC feature enables users to set up a primary and a standby connec-
tion using one interface on the PSAX system. In other words, users do not
need to configure a separate interface that functions solely for a standby con-
nection. Rather, ATM trunk interfaces can be used in a load-sharing design
with the connection admission control (CAC) constraints automatically con-
sidered when the primary and standby connections are configured. This tech-
nique allows particular links to be used as the primary link for certain
DHPVCs while they are used simultaneously as the standby for other
DHPVCs.
Operation
When the DHPVC connection configuration is set up, both the primary and
standby (backup) connections are provisioned from the originating endpoint
to the terminating endpoint, through the ATM network. When provisioning
the primary connection, the user enters the parameters that are appropriate
for the type of PVC connection being established (ingress slot, ingress port,
egress slot, egress port, QoS, AAL type, peak cell rate, VPI, VCI, and so on).
When provisioning the standby connection, the user is required to enter only
the network parameters that are associated with the standby connection
(egress slot, egress port, VPI, and VCI). The remaining parameters are gov-
erned by the primary connection. Because DHPVC connections make use of
PVCs within the network, interoperability issues do not exist with interven-
ing network devices. During normal operation, the primary connection car-
ries the traffic. While the primary connection is operational, traffic is not sent
over the standby connection.
The DHPVC implementation makes use of ATM Forum OAM F5 flows to
automatically initiate rerouting. If a link failure is detected on the primary
connection (on either the transmitting path or the receiving path), the asso-
ciated network element that detects the failure generates an OAM F5 alarm
indication signal (AIS) to the downstream node, which in turn sends the AIS
to the destination edge node. At that point, the edge node converts the AIS to
remote defect indication (RDI) messages, which are transmitted to the origi-
nating node.
Intermediary nodes relay the RDI messages upstream, ultimately to the origi-
nating or terminating nodes. Upon detecting an AIS/RDI alarm on a DHPVC-
configured PVC connection, the PSAX system automatically switches the
traffic on a primary connection to its standby (backup) connection. In the
Debouncing Period field on the Site-Specific Configuration window, the user
can select a value from the range 1 sec (1,000 msec) to 300 sec
(300,000 msec). The value the user sets in this field specifies the length of
time that must elapse since receiving any AIS/RDI alarm on a primary PVC
connection before the PSAX system automatically switches the traffic from
the standby (backup) connection back to the primary connection. Currently,
the user cannot choose to prevent the automatic switchback from the
standby connection to the primary connection.
