Cisco Cisco IOS Software Release 12.0(17)S

SNMP—Simple Network Management Protocol. A network management protocol used almost 
exclusively in TCP/IP networks. SNMP provides a means to monitor and control network devices, 
manage configurations, collect statistics, monitor performance, and ensure network security.

tail-end—The downstream, receive end of a tunnel.

traffic engineering—The techniques and processes used to cause routed traffic to travel through the 
network on a path other than the one that would have been chosen if standard routing methods had been 
used. 

trap(see notification)—A message sent by an SNMP agent to a network management station, console, 
or terminal to indicate that a significant event within Cisco IOS has occurred. Traps (notifications) are 
less reliable than inform requests, because the receiver of the trap does not send an acknowledgment of 
receipt; furthermore, the sender of the trap cannot determine if the trap was received. 

VCI—Virtual channel identifier. A 16-bit field in the header of an ATM cell. The VCI, together with the 
VPI (see below), is used to identify the next network VCL (see below) as the cell passes through a series 
of ATM switches on its way to its final destination. 

VCC—Virtual channel connection. A VCC is a logical circuit consisting of VCLs (see below) that 
carries data between two end points in an ATM network. Sometimes called a virtual circuit connection.

VCL—Virtual channel link. A VCL is the logical connection that exists between two adjacent switches 
in an ATM network.

VPI—Virtual path identifier. An 8-bit field in the header of an ATM cell. The VPI, together with the VCI 
(see above), is used to identify the next network VCL (see above) as the cell passes through a series of 
ATM switches on its way to its final destination.