
Glossary
Glossary-25
NT1
Network termination 1 device. The device that provides an interface between the ISDN 
Basic Rate Interface (BRI) line used by the telephone company and a customer’s terminal 
equipment. The NT1 also provides power for the terminal equipme nt, if necessary. In 
North America, where ISDN BRI is a U loop, the  customer must supply the NT1 device; in 
Japan and the European countries where BRI is an S/T bus, the telephone company 
supplies the NT1. The PortMaster integrates the NT1 device into its  ISDN BRI ports that 
are U interfaces.
NVRAM
Nonvolatile random access memory. Nonvolatile storage that can be erased and 
reprogrammed electronically, allowing software images to be stored, booted, and 
rewritten as necessary.
OODI
Open Datalink Interface. A Novell specification that isolates the protocol stack from the 
network adapter drivers to provide hardware independence for network connectivity.
Open Datalink Interface
See ODI.
open message
A message sent between BGP peers to establish communication. See also keepalive 
message; notification message; update message.
Open Shortest Path First 
See OSPF.
OSPF
Open Shortest Path First. A link-state interior gateway routing protocol designed fo r a 
hierarchical routing structure. OSPF chooses routes on a be st-path, least-cost basis and 
supports variable-length subnet masks (VLSMs)  for “classless” networking, allows up to 
255 hops between routers, and provides packet authentication. See also RI P.