Control Word Support
Martini draft encapsulation includes a control word with the following fields:
•
T bit for transport type
•
E bit for explicit forward congestion indication (EFCI)
•
C bit for cell loss priority (CLP)=1 indication
•
U bit for command/response indication based on AAL5 common part convergence
sublayer user-to-user indication (CPCS-UU)
•
Optional sequence number
The current JunosE implementation supports the T bit and optional sequence number
fields.
VCC Cell Relay Encapsulation
E Series routers support virtual channel connection (VCC) cell relay encapsulation for
ATM layer 2 services over MPLS. VCC cell relay encapsulation enables a router to emulate
ATM switch behavior by forwarding individual ATM cells over an MPLS pseudowire (also
referred to as an MPLS tunnel) created between two ATM VCCs, or as part of a local
ATM cross connect between two ATM 1483 subinterfaces on the same router. The JunosE
implementation conforms to the required N-to-1 cell mode encapsulation method
described in the Martini draft, with the provision that only a single ATM virtual circuit (VC)
can be mapped to an MPLS pseudowire.
VCC cell relay encapsulation is useful for voice-over-ATM applications that use ATM
Adaptation Layer 2 (AAL2)–encapsulated voice transmission.
AAL0 Raw Cell Mode
VCC cell relay encapsulation supports ATM Adaptation Layer 0 (AAL0) encapsulation,
also referred to as raw cell mode or null encapsulation. AAL0 is often used to carry
signaling ATM cells, which the router treats as raw cells.
When you create an ATM PVC as part of a VCC cell relay configuration, you must use the
aal0 encapsulation.
Cell Concatenation Parameters
VCC cell relay encapsulation supports the concatenation (aggregation) of multiple ATM
cells in a single encapsulated packet that is transmitted on the MPLS pseudowire.
You can use the atm cell-packing and atm mcpt-timers commands to configure the
following parameters that control how the router performs cell concatenation:
•
Maximum number of ATM cells that the router can concatenate in a single packet.
•
Values (in microseconds) for each of the three ATM Martini cell packing timers
maintained on the router. These timers define the time threshold that the router uses
to concatenate ATM cells and transmit the cells in an MPLS packet on the pseudowire.
•
Numeric identifier (1, 2, or 3) that indicates which of the three ATM Martini cell packing
timers you want to use to detect timeout of the cell collection threshold.
Copyright © 2010, Juniper Networks, Inc.518
JunosE 11.2.x BGP and MPLS Configuration Guide
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