Cisco BPX 8650, Installation And Configuration Manual

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24-8
Cisco BPX 8600 Series Installation and Configuration
Release 9.3.30, Part Number 78-12907-01 Rev. E0, May 2005
Chapter 24 Configuring BXM Virtual Trunks
Connection Management
Figure 24-5 shows three different cell header types: ATM-STI, ATM-UNI, and Strata-UNI through a
cloud. The ATM-NNI header which is not shown, differs in format from the ATM-UNI only in that there
is no Generic Flow Control Interface (GFCI) field and those four bits are added to the VPI bits to give a
12-bit VPI.
The ATM-STI header is used with BNI trunks between BPX nodes within a Cisco switch subnetwork.
The ATM-UNI is the standard ATM Forum UNI supported by the BXM card along with standard NNI.
Virtual trunks terminating on BXMs or UXMs use the standard ATM-UNI or ATM-NNI header as
specified by the cloud administrator, for example, a service provider. Virtual trunks terminating on BNIs
use the Strata-UNI header.
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;
however, BNI to BXM or BNI to UXM virtual trunks are not supported.
Figure 24-5 ATM Virtual Trunk Header Types
Bit Shifting for Virtual Trunks
The ATM-STI header uses four of the VCI 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 are used across a network expecting a standard header.
For detailed information on how to configure bit shifting, see the General Procedures to Set Up Virtual
Trunking section.
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
PTI FST
HEC
ATM-STI
VCI VPI
PTI VCI
HEC
ATM-UNI
VPI
VCI VPI
PTI FS (unused)
HEC
Strata-UNI through cloud
VPI GFCI GFCI
VCI VCI
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