Riverstone Networks WICT1-12 - Manual (Page 137)

Riverstone Networks RS Switch Router User Guide Release 8.0 8-3
ATM Configuration Guide Configuring ATM Ports
8.1.2 Setting Parameters for the Multi-Rate Line Card
On the multi-rate line card you can do the following:
• Enable cell scrambling for the PDH (plesiochronous digital hierarchy) physical (PHY) interfaces
available on the ATM line card, such as the T3 and E3 PHYs.
• Select the format for mapping ATM cells into PDH (plesiochronous digital hierarchy) T3 and E3
frames.
• Change the default number of bits allocated for the Virtual Path Identifier (VPI).
Cell Scrambling
Cell scrambling is useful for optimizing the transmission density of the data stream. Since all transmissions use the
same source clock for timing, scrambling the cell using a random number generator converts the data stream to a more
random sequence. This ensures optimal transmission density of the data stream.
Note Refer to the SONET Chapter in the Riverstone RS Switch Router Command Line
Interface Reference Manual for information about cell scrambling on SONET
PHY interfaces.
In the following example, cell scrambling is enabled on port at.5.1:
Cell Mapping
The ATM cells are mapped into a PDH (E3, T3) frame using two different mapping formats. The default mapping
format for the ATM multi-rate line card is direct ATM cell mapping (default). For compatibility purposes, you can
change the mapping format to physical layer convergence protocol (PLCP) as shown in the following example:
VPI Bit Allocation
The VPI defines a virtual path. A virtual path is a bundling of virtual channels transversing across the same physical
connection. The actual number of virtual paths and virtual channels available on an ATM port depends upon how many
bits are allocated for the VPI and VCI, respectively.
The number of bits allocated define the number of VPI and VCI values available for that port. The following equations
define the number of virtual paths and virtual channels:
# of virtual paths = 2
n
; where n is the number of bits allocated for VPI
# of virtual channels = 2
(12-n)
; where (12-n) is the number of bits allocated for VCI, and n is the number of
bits allocated for VPI
rs(config)# atm set port at.5.1 pdh-cell-scramble on
rs(config)# atm set port at.5.1 cell-mapping plcp