E-6 Cisco BPX 8600 Series Reference
control port
An RS-232 port on the face plate of a back card for a controller card (BCC, NPC, NPM.) that
may used for connecting a control terminal. This port is bi-directional.
COS (Class of Service)
The priority assigned each user connection. Defines which circuits get rerouted first during a
network failure.
courtesy downing
A software feature that is used to conserve network bandwidth by automatically “downing” a
voice connection when the signalling status indicates an inactive (on-hook) circuit. The circuit is
automatically “upped” when the circuit becomes active.
CRC (Cyclical Redundancy Check)
A method of error checking that detects errors in a block of data. Unlike parity checks, the CRC
can detect multiple data errors within the block and thus equipment using a CRC error check can
derive a error rate.
crosspoint switch
A two-dimensional data switch type that is arranged in a matrix of all input connections along
one axis and all output connections along the other axis. Each input and output line has a switch
point where the two axis intersect that can be enabled (switch closed) or disabled (switch open).
The central matrix switch providing the switching matrix for traffic routing by the BPX switch.
CSU (Channel Service Unit)
A network protection unit that terminates any T1 span line connected to the carrier's central
office, providing receive direction regeneration and maintenance loopback for the 1.544 Mbps
signal.
D
D4-format
A digital signal format with 24 eight-bit channels plus one synchronizing bit per T1 line.
Channels are assigned in a straight, numeric sequence.
DACS (Digital Access and Control System)
Equipment, usually found in the telephone company central office, that is used to groom and
retime the 24 channels in a DS1 signal. Individual DS0 channels can be cross-connected from
one DS1 source and inserted in another DS1 source either with the same or with a different
channel number.
DAS Server Shelf
The adjunct processor used in INS Dial-Up Frame Relay applications to provide frame relay
dial-up and dial-backup circuits. The DAS Server Shelf is co-located with and connected to an
IPX or IGX switch.
DCE (Data Communications Equipment)
As defined by the RS-232 standard, any device that transmits or receives information. Usually
used with data terminal equipment (DTE, like a computer or network node).
D channel
A message-oriented ISDN signalling channel, typically carried in DS24 of a PRI on T1 facilities
or TS16 of a PRI on E1 facilities. Compare to B channel.
