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3-3
PacketStar
®
PSAX 4500 Multiservice Media Gateway User Guide
, Issue 2
Release 8.0.0
Chapter 3 System Features
Connections Support
•
Physical media access—The physical media access layer handles functions
specific to each physical interface, connecting each user port to other users
or network elements.
•
Service protocol translation—The service protocol translation process per-
forms segmentation and reassembly (SAR) to adapt non-native ATM ser-
vices to ATM-based services and back again. It ensures that the data stream
is mapped to standard ATM Adaptation Layer (AAL) protocols.
•
ATM addressing—ATM addressing provides user-specified virtual path
identifier/virtual channel identifier (VPI/VCI) coding, bandwidth alloca-
tion, and quality of service (QoS) information.
•
Queuing—Queuing provides a means through which ATM cells are placed
in input and output queues based on their QoS parameters. Employing the
AQueMan
adaptive
queue management algorithm, the PSAX 4500 Multi-
service Media Gateway transports these cells from the ATM switching fab-
ric to the I/O port.
Connections Support
The Multiservice Media Gateway system software uses permanent virtual cir-
cuits (PVCs) and switched virtual circuits (SVCs) to provide end-to-end con-
nectivity for transmission over a network. Because virtual connections are
logical and not physical, multiple connections can be defined simultaneously
across a single network facility, with each connection having flexible band-
width.
Because PVCs establish end-to-end connections, a PVC eliminates the need
to establish a new route (call setup) each time a transmission is sent to a
remote location. When establishing a connection with a PVC, the user only
needs to select a class of service for each connection.
Soft Permanent Virtual Circuit (SPVC) Connections
The SPVC feature is a semipermanent virtual circuit enabled by management
action. It is a PVC circuit in which SVCs are used for call setup and (auto-
matic) rerouting. Once either a PVC or a permanent VPC has been config-
ured, an SPVC can be established between the two network interfaces serv-
ing the PVC by using signaling procedures. Consequently, this type of
connection has attributes of both an SVC and a PVC.
Specifically, an SPVC is established and released between the two network
interfaces serving the PVC. The user assigns unique ATM addresses, including
the SEL octet in the case of a private ATM address (see Section 3.1 of the UNI
4.0 signaling specification), to the corresponding NIs, thus identifying the
starting point and ending point of the SPVC.
This feature supports ATM-to-ATM VPC at both ends of a network interface.
It uses ATM UNI 4.0 or ATM PNNI 1.0 protocol to set up the SVC connection
depending on the egress route/protocol selected and based on the called
party number and TNS given by the NMS on initiation.
