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V
V Series Recommendations
The V
Series recommendations are the ITU-T standards for sending data over the
telephone network. An example of some of the V Series standards are listed
below:
- V.21 is the standard for 300 bps duplex
modem.
- V.23 is the standard for 600/1200 bps duplex
modem.
- V.25 bis is the call and answering command
set used with asynchronous, bisynchronous and HDLC devices.
- V.32 bis is the standard for full-duplex
dial-up capabilities at 4.8, 7.2, 9.6 and 12Kbps
VC
VC stands for
virtual circuit or virtual channel.
Vector-Distance Routing
This
algorithm, which sometimes suffers from being computationally intensive on
large networks, is really quite straightforward. It simply expresses the
route to a network as a distance measured in hops. The entity that is
hopped over is other networks that must be traversed on the way to the
target network. The hop count is actually counting gateways (routers) that
a datagram encounters on the way to its destination. The router can then
make a decision, based upon distance to the target, in forwarding the
packet along a selected route. Examples of vector-distance routing
protocols are RIP (Routing Information Protocol) supported by TCP/IP and
Novell, as well as the IDRP (Interdomain Routing Protocol) specified by the
ISO for use in the OSI networking model.
Virtual Channels
A
virtual channel (VC) is a communications circuit that transports ATM cells
between two or more endpoints. The endpoints of a VC may be a user-to-user
connection, a user-to-network connection, or a network-to-network
connection. The point at which an ATM cell is passed to or from a higher
layer is considered to be the endpoint of a VC.
Virtual Circuit
A
virtual circuit is a communications path that appears to be a single
circuit even though the data may take varying routes between the source and
destination nodes. This concept has its roots in X.25 packet-switching.
There are two types of virtual circuits: permanent virtual circuits (PVCs)
and switched virtual circuit (SVCs).
Virtual Terminal
As
networks developed, many different terminals were in use, so to avoid the
problem of incompatibilities; the concept of the virtual terminal was
developed. Virtual terminal protocols provide an abstract definition of a
terminal that is specific in terms of the control codes required to produce
a specific result but is also general in nature. The virtual terminal
definition combines all of the common features of most real terminals but
leaves out the "bells and whistles" that make terminals unique to
their vendor.
VRRP
(VRRP) specifies an election
protocol that dynamically assigns responsibility for a virtual router to
one of the VRRP routers on a LAN. The VRRP router controlling the IP
address(es) associated with a virtual router is called the Master, and forwards
packets sent to these IP addresses. The election process provides dynamic
fail over in the forwarding responsibility should the Master become
unavailable. This allows any of the virtual router IP addresses on the LAN
to be used as the default first hop router by end-hosts. The advantage
gained from using VRRP is a higher availability default path without
requiring configuration of dynamic routing or router discovery protocols on
every end-host. This protocol is intended for use with IPv4 routers only.
VRRP packets are sent encapsulated in IP packets.
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