ZyXEL Communications VES-1000 Series, Руководство пользователя, Страница: 52 / 227

VES-1000 Series Ethernet Switch
6-2 Port Setup
6.4 Rate Adaption
You can configure the maximum rate of an individual VDSL port using the port setup SMT menus or web
configurator screens. However poor line quality (due to poor wiring, line noise, cross-talk or VDSL modem-to-
switch distance) may affect actual VDSL speeds attainable.
Rate adaptation is the ability of the device to adjust the configured transmission rate to the attainable transmission
rate automatically depending on your telephone line quality. The VDSL transmission rate then stays at the new rate
or adjusts if line quality improves or further deteriorates.
If rate adaption is disabled and attainable speeds cannot match configured speeds, then:
The VDSL link may go down or
Link communications may be sporadic due to line errors and consequent retransmissions
The VES determines line quality using the Signal-to-Noise Ratio (SNR). SNR is the ratio of the amplitude of the
actual signal to the amplitude of noise signals at a given point in time. A low SNR indicates poor line quality. When
the SNR (upstream or downstream) falls below a pre-determined threshold, the device then uses rate adaption.
Rate adaption applies to VDSL line connections only – not Ethernet connections.
6.5 VDSL Default Values
The default values for the following VDSL parameters are shown in the next table.
Table 6-2 VDSL Default Values
VDSL PARAMETER DEFAULT VALUE
VDSL Mode 10BaseS mode
VDSL Active Off
VDSL Upstream Rate 12.5 Mbps
VDSL Downstream Rate 12.5 Mbps
6.6 GVRP
GVRP (GARP VLAN Registration Protocol) is a registration protocol that defines a way for switches to register
necessary VLAN members on ports across the network. Enable this function to permit VLANs groups beyond the
local switch. Please refer to the following table for common GVRP terminology.