Page 732

690

Glossary

control direct VCC

One of three control connections defined by Phase I

LAN emulation; a bidirectional virtual control connection (VCC) estab-
lished in ATM by an LEC to an LES. See also: control distribute VCC.

control distribute VCC

One of three control connections defined by

Phase 1 LAN emulation; a unidirectional virtual control connection (VCC)
set up in ATM from an LES to an LEC. Usually, the VCC is a point-to-
multipoint connection. See also: control direct VCC.

convergence

The process required for all routers in an internetwork to

update their routing tables and create a consistent view of the network, using
the best possible paths. No user data is passed during a convergence time.

core layer

Top layer in the Cisco three-layer hierarchical model, which

helps you design, build, and maintain Cisco hierarchical networks. The core
layer passes packets quickly to distribution-layer devices only. No packet
filtering should take place at this layer.

cost

Also known as path cost, an arbitrary value, based on hop count,

bandwidth, or other calculation, that is typically assigned by a network
administrator and used by the routing protocol to compare different routes
through an internetwork. Routing protocols use cost values to select the best
path to a certain destination: the lowest cost identifies the best path. Also
known as "path cost." See also: routing metric.

count to infinity

A problem occurring in routing algorithms that are slow

to converge where routers keep increasing the hop count to particular net-
works. To avoid this problem, various solutions have been implemented into
each of the different routing protocols. Some of those solutions include
defining a maximum hop count (defining infinity), route poising, poison
reverse, and split horizon.

CPCS

Common Part Convergence Sublayer: One of two AAL sublayers

that is service-dependent, it is further segmented into the CS and SAR sub-
layers. The CPCS prepares data for transmission across the ATM network;
it creates the 48-byte payload cells that are sent to the ATM layer. See also:
AAL and ATM layer.

CPE

customer premises equipment: Items such as telephones, modems, and

terminals installed at customer locations and connected to the telephone
company network.

www.sybex.com