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You can also specify concatenation of multiple ATM cells to be sent in a single
MPLS-labeled packet for efficient usage of the backbone bandwidth. If you do not
specify cell concatenation, each individual ATM cell is MPLS-labeled and transmitted
on the pseudowire. You can use the
mpls-relay atm cell-packing mcpt-timers
command 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.
Based on this configuration, the router attempts to concatenate the specified
maximum number of ATM cells into an MPLS packet within the time interval allowed
by the ATM Martini cell packing timer you selected. When the router detects that the
allotted time interval has expired, the router forwards the MPLS packet even if it
contains fewer than the specified maximum number of aggregated cells per packet.
The cell concatenation functionality is controlled by the timer values and the
maximum number of cells to be concatenated. The LDP signaling protocol option to
negotiate cell concatenation (maximum number of concatenated ATM cells) is not
used.
For more information on the guidelines to be followed when you configure cell
concatenation and cell packing timer identifiers for transporation of ATM VCs on a
single pseudowire, see “Guidelines for Configuring Cell Concatenation and Cell Packing
Timer for an ATM Port” on page 522.
When you add the MPLS Martini circuit configuration on an ATM port, you cannot
add the interface label space RSVP configuration on the same ATM port. Therefore,
you can configure an ATM port with either the interface label space RSVP configuration
or the MPLS Martini circuit at the same time. You cannot configure both the interface
label space RSVP configuration or the MPLS Martini circuit on the same ATM port at
the same time.
The ATMx port is not changed to the Loss of Signal (LOS) state, which denotes the
number of times for which the incoming optical signal is all zeros for at least 100
microseconds, when a failure is detected on the pseudowire. Possible causes might
include a cable disconnection, excessive attenuation of the signal, or faulty equipment.
The changeover to the LOS state for the ATM port is not performed because only a
subset of the ATM virtual circuits are configured to be transported on the pseudowire.
The ATM virtual circuits on the same ATM port that are not associated with the single
pseudowire and are not present in the specified subset continue to function in the
desired manner, without being affected by the failure detected on the pseudowire.
If the ATM port was moved to an LOS state, all ATM virtual circuits on the same port
that are configured for functionality other than the multiple VCs over single
pseudowire functionality are also disrupted.
The F5 Operations Administration and Maintenance (OAM) cells and Integrated Local
Management Interface (ILMI) cells are carried on the pseudowire because F5 OAM
cells arrive with the same VPI/VCI values as the data cells. In such cases, you can
configure the ILMI VPI/VCI as part of the range to enable the ILMI cells be carried on
the pseudowire. However, F4 OAM cells are not carried over the pseudowire because
520 ■
Multiple ATM Virtual Circuits over a Single Pseudowire Overview
JUNOSe 11.0.x BGP and MPLS Configuration Guide