Glossary P
Centillion 1200N ATM Switch User Manual B-59
NTP 297-8103-903
PNNI Routing Hierarchy
The hierarchy of peer groups used for PNNI routing.
PNNI Topology State Packet
A type of PNNI Routing packet that is used for flooding PTSEs among logical
nodes within a peer group.
POH
Path Overhead: A maintenance channel transmitted in the SONET overhead
following the path from the beginning multiplexer to the ending demultiplexer.
This is not implemented in SONET Lite.
Point-to-Multipoint Connection
A Point-to-Multipoint Connection is a collectio n of associated ATM VC or VP
links, with associated endpoint nodes, with the following properties:
• One A TM link, called the Root Link, serv es as the root in a simple tree to pology.
When the Root Node sends information, all of the remaining nodes on the
connection, called Leaf Nodes, receive copies of the information.
• Each of the Leaf Nodes on the connection can send information directly to the
Root Node. The Root Node cannot distinguish which Leaf is sending
information without additional (higher layer) information. (See note belo w for
User Network Interface (UNI) 4.0 support)
• The Leaf Nodes cannot communicate directly to each other with this connect ion
type.
Note: UNI 4.0 does not support traffic sent from a Leaf to the Root.
Point-to-Point Connection
A connection with only two endpoints.
Port Identifier
The identifier assigned by a logical node to represent the point of attachment of a
link to that node.
Partial Packet Discard (PPD)
Partial Packet Discard (PPD) is a congestion control technique that drops all of the
ATM cells in a Classical IP over ATM packet. When congestion occurs and any
one cell of a particular frame is dropped, PPD discards the rest of the cells (since
the frame is errored and will need to be sent again anyway).