Spanning Tree Instances; Cbr Application - 3Com 3C63100-AC-C - PathBuilder S600 Bridge/router Reference Manual

88 C 4: P B
HAPTER ATH UILDER

CBR Application

S600 M A
ODULE AND PPLICATION
The management card STAP module examines the packet, reads the MAC
n
address of the sender, and analyzes the costs reported by the sender.
When state of a port changes, the STAP module notifies the port card of the
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change.
When a port card receives change information for a port, it updates the
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operational state of the port so as to change the bridging operation on the
port. For instance, if a port in a forwarding state (normal operation mode of
receiving and forwarding packets) is discovered to be forming a loop, it can be
put in a blocking state. Once the port goes in the blocking state, the port card
will stop receiving frames on the port.

Spanning Tree Instances

The Spanning Tree logic supports a maximum of 255 physical and virtual ports,
thereby allowing a maximum of 254 ATM VCs. (One Ethernet port is required be
set aside for other purposes.)
For the purpose of Spanning Tree operation, each set of one Ethernet port and its
associated ATM VCs is treated as one bridge entity. The STAP module runs a
separate instance for each bridge entity. Since the PathBuilder S600 shelf can be
filled with a maximum of three Ethernet cards, each with two Ethernet ports, a
maximum of six instances of STAP can be running on the management card.
Each STAP instance runs independently of the other STAP instances and processes
configuration packets as if they came from a different physical bridge device. This
approach helps segregate Ethernet ports completely for the purposes of bridging
and Spanning Tree and enables the PathBuilder S600 to operate as six separate
bridges.
VC-VC Bridging operation The Ethernet module supports full-mesh bridging
between its Ethernet port and all of its associated VCs. This bridging must be
bidirectional and should be conditional upon the operational status of the
Spanning Tree. If Spanning Tree operation is disabled, VC-VC bridging is not
necessary since the PathBuilder S600 is not expected to forward traffic coming
from the ATM network.
For instructions on enabling and disabling the Spanning Tree, see "Enabling and
Disabling the Spanning Tree" in Chapter 5.
The CBR module consists of 8 DSX T1 interfaces capable of accepting superframe
or extended superframe DS1 inputs. The DS1 signal is then mapped over a
Constant Bit Rate (CBR) virtual channel. Encapsulation of the T1 within the ATM
service is based on the ATM Forum (AF-SAA-0032.000) Circuit Emulation Service
Interoperability specification. The ATM Forum specification designates two modes
of operation:
Structured —Modeled after fractional T1. Only the timeslots which will be used
are sent.
Unstructured —Merely encapsulates the entire DS1 onto an ATM path. It allows
timing and FDL to pass through.
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VERVIEW