Glossary
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TRIP
Token Ring Interface Processor: A high-speed interface processor
used on Cisco 7000 series routers. The TRIP provides two or four ports for
interconnection with IEEE 802.5 and IBM media with ports set to speeds of
either 4Mbps or 16Mbps set independently of each other.
trunk link
Link used between switches and from some servers to the
switches. Trunk links carry information about many VLANs. Access links
are used to connect host devices to a switch and carry only VLAN informa-
tion that the device is a member of.
TTL
Time To Live: A field in an IP header, indicating the length of time a
packet is valid.
TUD
Trunk Up-Down: A protocol used in ATM networks for the moni-
toring of trunks. Should a trunk miss a given number of test messages being
sent by ATM switches to ensure trunk line quality, TUD declares the trunk
down. When a trunk reverses direction and comes back up, TUD recognizes
that the trunk is up and returns the trunk to service.
tunneling
A method of avoiding protocol restrictions by wrapping
packets from one protocol in another protocol's packet and transmitting this
encapsulated packet over a network that supports the wrapper protocol. See
also: encapsulation.
20/80 rule
This rule means that 20 percent of what the user performs on
the network is local, whereas up to 80 percent crosses the network segmen-
tation points to get to network services.
UART
The Universal Asynchronous Receiver/Transmitter: A chip that
governs asynchronous communications. Its primary function is to buffer
incoming data, but it also buffers outbound bits.
U reference point
Reference point between a TE1 and an ISDN network.
The U reference point understands ISDN signaling techniques and uses a
2-wire connection.
UDP
User Datagram Protocol: A connectionless transport layer protocol in
the TCP/IP protocol stack that simply allows datagrams to be exchanged
without acknowledgements or delivery guarantees, requiring other proto-
cols to handle error processing and retransmission. UDP is defined in
RFC 768.
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