Chapter 3 System Features
Multiservice Media Gateway Software Features
3-44
255-700-239
PacketStar
®
PSAX 4500 Multiservice Media Gateway User Guide
, Issue 2
Release 8.0.0
•
Existence in the same physical route for fault correlation and performance
information
User cells at the F5 level carry VCI cells which are defined below:
(Payload Type Indicator) PTI=4 is a segment OAM F5 flow cell. This flow is
identified by its standardized PTI, and is used for end-to-end VCC operations
communication.
PTI=5 is an end-to-end OAM F5 flow cell. This flow is identified by its stan-
dardized PTI, and is used for communicating operational information within
the bounds of one VCC link that is a part of multiple inter-connected VCC
links (called VCC segments).
ATM Layer OAM
Functions
OAM functions performed at the ATM layer are:
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Fault Management
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Alarm Indication Signals (AIS) — A network element (NE) transmits an
AIS alarm downstream when it receives a major alarm condition such as
a loss of frame. This prevents the generation of unnecessary alarms, and
maintains communications.
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Remote Defect Indication (RDI) — RDI cells are generated and tranmit-
ted while the AIS state persists in order to indicate in the backward direc-
tion an interruption of the cell transfer capability in the forward direc-
tion.
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Continuity Check — This check is used within a network to provide the
continuous detection of ATM layer failures. End points, of either the full
connection, or a segment, use activation procedures to request continu-
ity checking with the opposite end point, at predetermined intervals. If
the sink point does not receive continuity cells as expected, AIS and RDI
alarms are transmitted.
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Loopback — Loopback checks isolate failed entities if defect information
is insufficient. A loopback check detects faults in the physical and ATM
layers, and detects defects and declarations of failure within the network
elements. It is also used for on-demand connectivity monitoring and pre-
service connectivity verification.
A loopback procedure can be initiated at any connecting, segment, or
end point by a Network Management System (NMS) that also receives
the report on loopback performance.
A loopback location identifier is assigned to each connecting point at the
operator’s option. This identifier identifies a unique connecting point
within a segment or within the entire path. Then, a VPC or VCC end or
connecting point sends a loopback cell to a destination end or connecting
point, while a segment loopback is looped back at the destination point.
If the source receives a looped cell back within five seconds, the loopback
is considered successful. If the source does not receive a successful loop-
back, it declares a time out. The following types of loopback are sup-
ported:
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End-to-end: Sends cells from one designated end-point to another.
