Manual

Layer 2 Tunnel Protocol Version 3
Information About Layer 2 Tunnel Protocol Version 3
23
Cisco IOS Releases 12.0(29)S and 12.2(25)S
ATM VP Mode Single Cell Relay over L2TPv3
The ATM VP Mode Single Cell Relay over L2TPv3 feature allows cells coming into a predefined PVP
on the ATM interface to be transported over an L2TPv3 pseudowire to a predefined PVP on the egress
ATM interface. A single ATM cell is encapsulated into each L2TPv3 data packet.
ATM Single Cell Relay VC Mode over L2TPv3
The ATM Single Cell Relay VC mode over L2TPv3 feature maps one VC to a single L2TPv3 session.
All ATM cells arriving at an ATM interface with the specified VPI and VCI are encapsulated into a single
L2TP packet. Each ATM cell will have a 4-byte ATM cell header without Header Error Control
Checksum (HEC) and a 48-byte ATM cell payload.
The ATM Single Cell Relay VC mode feature can be used to carry any type of AAL traffic over the
pseudowire. It will not distinguish OAM cells from User data cells. In this mode, Performance and
Security OAM cells are also transported over the pseudowire.
ATM Port Mode Cell Relay over L2TPv3
The ATM Port Mode Cell Relay over L2TPv3 feature packs ATM cells arriving at an ingress ATM
interface into L2TPv3 data packets and transports them to the egress ATM interface. A single ATM cell
is encapsulated into each L2TPv3 data packet.
ATM Cell Packing over L2TPv3
The ATM Cell Packing over L2TPv3 feature enhances throughput and uses bandwidth more efficiently
than the ATM cell relay features. Instead of a single ATM cell being packed into each L2TPv3 data
packet, multiple ATM cells can be packed into a single L2TPv3 data packet. ATM cell packing is
supported for Port mode, VP mode, and VC mode. Cell packing must be configured on the PE devices.
No configuration is required on the CE devices.
ATM AAL5 over L2TPv3
The ATM AAL5 over L2TPv3 feature maps the AAL5 payload of an AAL5 PVC to a single L2TPv3
session. This service will transport OAM and RM cells, but does not attempt to maintain the relative
order of these cells with respect to the cells that comprise the AAL5 common part convergence sublayer
protocol data unit (CPCS-PDU). OAM cells that arrive during the reassembly of a single AAL5
CPCS-PDU are sent immediately over the pseudowire, followed by the AAL5 payload without the AAL5
pad and trailer bytes.
OAM Transparent Mode
In OAM transparent mode, the PEs will pass the following OAM cells transparently across the
pseudowire:
• F5 segment and end-to-end Fault Management (FM) OAM cells
• RM OAM cells, except Performance Management (PM) and Security OAM cells
Note The Cisco 7200 and the Cisco 7500 ATM driver cannot forward RM cells over the PSN for ABR ToS.
The RM cells will be locally terminated.