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PPP packets arriving via a PPTP tunnel and PPP packets encapsulated on ATM
connections differ in format. The PPP format on AAL5 is shown in figure 43.
P_ID
Figure 43. PPP ATM Format
The PPP format within a tunnel is shown in figure 44. This format has two
additional bytes (FF and 03) in front of the packet, inherited from another
encapsulation method (PPP in HDLC-like framing).
Address
Control
FF
Figure 44. PPP/PPTP Tunnel Format
The ADSL modem adapts to the different formats based on the connection type. If
problems with operation occur, the modem can be configured to handle the
differing formats as follows:
When you set this field to never, the modem ensures that FF-03 is never
placed in front of a PPP packet encapsulated on an AAL5/ATM connection.
This is the default setting.
When you set this field to always, the modem ensures that FF-03 is always in
front of a PPP packet encapsulated on an AAL5/ATM connection. Although not
standard, some equipment may rely on this format.
When you set this field to keep, the modem does not alter the PPP packet
arriving via a tunnel; it keeps the two bytes in front of the PPP packet when it
performs the encapsulation.
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This page provides an instant overview of all ADSL channels on the ADSL modem.
It is a summary of the information provided on the Bridge page and the PPP/PPTP
page.
Information
Padding
P_ID
Information
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