Prestige 645M-A1 ADSL Bridge
3-4
Internet Access
3.6 VPI
&
VCI
Be sure to use the correct Virtual Path Identifier (VPI) and Virtual Channel Identifier (VCI) numbers supplied
by your telephone company. The valid range for the VPI is 1 to 255 and for the VCI is 32 to 65535 (1 to 32 is
reserved for local management of ATM traffic). Please see the appendix on VPI and VCI for more information.
3.7 Multiplexing
There are two conventions to identify what protocols the virtual circuit (VC) is carrying. Be sure to use the
multiplexing method required by your ISP.
3.7.1 VC-based multiplexing
In this case, by prior mutual agreement, each protocol is assigned to a specific virtual circuit, e.g., VC1 carries
IP, VC2 carries IPX, etc. VC-based multiplexing may be dominant in environments where dynamic creation of
large numbers of ATM VCs is fast and economical.
3.7.2 LLC-based multiplexing
In this case one VC carries multiple protocols with protocol identifying information being contained in each
packet header. 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, e.g., if charging heavily depends on the number
of simultaneous VCs.
3.8 Encapsulation
Be sure to use the encapsulation method required by your ISP. The Prestige supports the following methods.
3.8.1 PPPoA
Please refer to RFC 2364 for more information on PPP over ATM Adaptation Layer 5 (AAL5). Refer to RFC
1661 for more information on PPP.
3.8.2 RFC 1483
RFC 1483 describes two methods for Multiprotocol Encapsulation over ATM Adaptation Layer 5 (AAL5).
The first method allows multiplexing of multiple protocols over a single ATM virtual circuit (LLC-based
multiplexing) and the second method assumes that each protocol is carried over a separate ATM virtual circuit
(VC-based multiplexing). Please refer to the RFC for more detailed information.