Virtual Leased Line Services
7750 SR OS Services Guide Page 237
PWE3 N-to-1 Cell Mode
The endpoints of an N-to-1 mode VLL can be:
• ATM VCs — VPI/VCI translation is supported (i.e., the VPI/VCI at each endpoint does
not need to be the same).
• ATM VPs — VPI translation is supported (i.e., the VPI at each endpoint need not be the
same, but the original VCI will be maintained).
• ATM VTs (a VP range) — No VPI translation is supported (i.e., the VPI/VCI of each cell
is maintained across the network).
• ATM ports — No translation is supported (i.e., the VPI/VCI of each cell is maintained
across the network).
For N-to-1 mode VLLs, cell concatenation is supported. Cells will be packed on ingress to the
VLL and unpacked on egress. As cells are being packed, the concatenation process may be
terminated by:
• Reaching a maximum number of cells per packet.
• Expiry of a timer.
• (Optionally) change of the CLP bit.
• (Optionally) change of the PTI bits indicating end of AAL5 packet.
In N-to-1 mode, OAM cells are transported through the VLL as any other cell. The PTI and CLP
bits are untouched, even if VPI/VCI translation is carried out.
PWE3 AAL5 SDU Mode
The endpoints of an AAL5 SDU mode VLL must be ATM VCs specified by port/vpi/vci. VPI/
VCI translation is supported. The endpoint can also be a FR VC, specified by port/dlci. In this case
FRF.5 FR-ATM network interworking is performed between the ATM VC SAP or the SDP and the
FR VC SAP.
In SDU mode, the mandatory PWE3 control word is supported. This allows the ATM VLL to
transport OAM cells along with SDU frames, using the “T” bit to distinguish between them, to
recover the original SDU length, and to carry CLP, EFCI and UU information.
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