User`s guide

D-22
Glossary
TTRT (target token rotation time)
A time defined for tokens to travel around an FDDI ring; used to
synchronize the clocking of traffic on the ring.
UDP (user datagram protocol)
A TCP/IP protocol for the connectionless transport layer.
upstream
Refers to the relative position of a station in a ring or network to
another station in the same ring or network. A station is upstream
from its neighbor if it receives the token or data before its neighbor
receives the token or data.
virtual LANs
This implementation is capable of creating virtual LANs, i.e.
logical AppleTalk subnets that span more than one port and, by
extension, more than one router. A virtual LAN has a single
network range and zone list. Traffic arriving on one physical
network and destined for a different physical network on the same
VLAN is bridged between ports. Traffic arriving on one VLAN and
destined to another is routed with the output port being
determined via AARP
The address acquisition process raises the complexity relative to
non-AppleTalk protocols due to the fact that acquisition must be
performed on all ports of the VLAN simultaneously. Internal to the
routing engine this is accomplished using a single circuit which is
mapped via a mask to physical ports. Externally, this means that
modifications to the parameters of one VLAN port are applied to
all ports in the VLAN.
A VLAN is defined by setting the network range of multiple ports
to the same value with the exception that ports configured with
range 0-0 are on different virtual segments. Virtual LAN port