Specifications

25-9
Cisco BPX 8600 Series Installation and Configuration
Release 9.3.0, Part Number 78-10674-01 Rev. D0, July 2001
Chapter 25 Configuring BXM Virtual Trunks
Connection Management
Because the BNI cards use a Strata-UNI format across a virtual trunk, BNI virtual trunks are not
compatible with BXM/UXM virtual trunks which use either the standard UNI or NNI cell header
formats. Therefore, BXM to BXM, UXM to UXM, and BXM to UXM virtual trunks are supported,
while BNI to BXM or BNI to UXM virtual trunks are not supported.
Figure 25-5 ATM Virtual Trunk Header Types
Bit Shifting for Virtual Trunks
The ATM-STI header uses four of the VPI bit spaces for additional control information. When the cell
is to be transferred across a public network, a shift of these bit spaces is performed to restore them to
their normal location so they can be used across a network expecting a standard header.
This bit shifting is shown in Table 25-2. A BNI in the Cisco subnetwork can interface to a BXM (port
configured for port mode) in the cloud. The BXM in the cloud is configured for no shift in this case.
A BXM in the Cisco subnetwork can interface to a BXM UNI port or other UNI port in the cloud. The
BXM in the cloud is configured for bit shifting as shown in Table 25-2.
Virtual Trunk Bandwidth
The total bandwidth of all the virtual trunks in one port cannot exceed the maximum bandwidth of the
port. The trunk loading (load units) is maintained per virtual trunk, but the cumulative loading of all
virtual trunks on a port is restricted by the transmit and receive rates for the port.
Virtual Trunk Connection Channels
The total number of connection channels of all the virtual trunks in one port cannot exceed the
maximum number of connection channels of the card. The number of channels available is maintained
per virtual trunk
HCF 00 PID
CID
PYLD
PID
CID
PTIFST
HEC
ATM-STI
VCIVPI
PTIVCI
HEC
ATM-UNI
VPI
VCIVPI
PTIFS (unused)
HEC
Strata-UNI through cloud
VPIGFCI GFCI
VCI VCI
25067
Table 25-2 Bit Shifting for Virtual Trunking
Subnetwork FW Rev Shift Cloud FW Rev Shift
BXM -- > BXM (port mode) Yes**
BNI -- > BXM (port mode) No