ZyXEL Communications MSC1000G Series, Руководство пользователя

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Chapter 9 Subscriber Port Setup Screens
Management Switch Card User’s Guide
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9.11 Permanent Virtual Circuits
A Permanent Virtual Circuit (PVC) is a logical point-to-point circuit between sites. PVCs are low-
delay circuits because routing decisions do not need to be made along the way. Permanent means
that the circuit is pre-programmed by the carrier as a path through the network. It does not need
to be set up or torn down for each session. PVCs are also called virtual channels.
The system can handle multiple IEEE 802.1p priority queues on a single PVC. You can also define up
to eight PVCs on a DSL port and use them for different services or levels of service. You set the
PVID that is assigned to untagged frames received on each channel. You also set an IEEE 802.1p
priority for each of the PVIDs. In this way you can assign different priorities to different channels
(and consequently the services that get carried on them or the subscribers that use them).
For example, you want to give high priority to voice service on one of the ADSL ports. First
configure a static VLAN on the system for voice on the port. Then do the following:
• Configure a channel on the port for voice service.
• Set the channel to use the PVID of the static VLAN you configured.
• Assign the channel a high priority.
9.11.1 LLC
LLC is a type of encapsulation where one VC (Virtual Circuit) carries multiple protocols with each
packet header containing protocol identifying information. Despite the extra bandwidth and
processing overhead, this method may be advantageous if it is not practical to have a separate VC
for each carried protocol, for example, if charging heavily depends on the number of simultaneous
VCs.
9.11.2 VC Mux
VC Mux is a type of encapsulation where, by prior mutual agreement, each protocol is assigned to a
specific virtual circuit, for example, VC1 carries IP, VC2 carries IPX, and so on. VC-based
multiplexing may be dominant in environments where dynamic creation of large numbers of ATM
VCs is fast and economical.
The Negotiated
Noise Margin
Mode Specify how the target noise margin value is acquired.
Select normal to have each end of the connection determine the target noise margin to
be used by the other end.
Select forced to set the upstream and downstream parameters according to the target
noise margin value set in the SHDSL profile.
Apply Click Apply to save the changes in this screen to the system’s volatile memory. The
system loses these changes if it is turned off or loses power, so use the Config Save link
on the navigation panel and then the Save button to save your changes to the non-
volatile memory when you are done configuring.
Cancel Click Cancel to begin configuring the fields again.
Table 113
SHDSL Port Setup: Advanced Features (continued)
LABEL DESCRIPTION