5.4 VPI/VCI Detect
ADSL data travels by way of Asynchronous Transfer Mode (ATM) Cells across Permanent Virtual
Circuits (PVCs). Each PVC consists of one Virtual Channel across one Virtual Path as identified by a
Virtual Channel Identifier (VCI) and Virtual Path Identifier (VPI). The AAM8000 supports one PVC per
port.
z
VPI (Virtual Path Identifier): an 8-bit field in ATM cell headers that routes the cell
over the correct Virtual Path (VP)
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VCI (Virtual Channel Identifier): a 16-bit field in ATM cell headers identifying the
Virtual Channel (VC), within the VP, over which a stream of cells will travel.
5.4.1 ON (Default)
When the VPI/VCI Detect function is set to ON, a port will automatically "snoop" the line to
determine the VPI and VCI settings of the remote ADSL modem to which its connected and
then set itself accordingly. If, however, no ATM cells are detected (at any VPI/VCI setting), the
port will default to VPI 0 and VCI 35 until such time as it does detect ATM cells from the remote
ADSL modem. The port will then automatically reconfigure the VPI and VCI with the same
settings at which the ATM cells were detected.
5.4.2 OFF
When the VPI/VCI Detect function is set to OFF, the VPI and VCI values for that port default to 0
and 35 (respectively) UNLESS the port was previously set at VPI/VCI Detect ON and had
already detected the VPI and VCI settings of the remote ADSL modem. In this case, turning the
VPI/VCI Detect function OFF will essentially lock in those previously detected settings until
such time as the VPI and VCI values are altered manually.
5.5 Frame Type
Frame type is the ADSL data encapsulation method for carrying traffic over an ATM network as
defined by the Internet Engineering Task Force (IETF) Request for Comment (RFC) 1483:
G.lite ADSL Distance Capabilities
UPSTREAM
kbps
512
416
288
192
128
DOWNSTREAM
1,536
1,536
1,056
768
448
DISTANCE
feet
15,000 16,000 17,000 18,000 19,000
meters 4,572
4,877
5,182
5,486
5,791
N
OTE
If you wish to set VPI and VCI values manually, the VPI/VCI Detect function should be set to OFF
before
the VPI and VCI values are entered. When manually configuring VPI and VCI, each port must be
assigned the same VPI and VCI values as the remote ADSL modem to which it's connected or the units
will not be able to communicate.
210-0000039 rev 07
