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Note: Broadcast Manager and Source Route Management are unavailable and
cannot be enabled if bus-mode is set to
adapter
.
LAN Emulation Reliability
A perceived lack of robustness has been one of the most widely proclaimed
criticisms of LAN emulation. While the ATM Forum is addressing this issue with
specifications for distributing the LE service, the router offers an answer in the
interim. Figure 17 provides a framework for describing the MSS redundancy
solution.
Each LES/BUS may be independently configured for redundancy (the default is no
redundancy). If redundancy is enabled, the LES/BUS is configured to assume the
role of a primary or a backup LES/BUS. Unless it has been configured as a
redundant LES/BUS, the LES/BUS is primary. The primary LES/BUS is typically the
only LES/BUS visible to the LE clients. It is responsible for setting up and
maintaining a Redundancy VCC to the backup LES. The presence of this VCC
indicates that the primary LES/BUS is operational. The backup LES will not accept
Control Direct VCC calls while the Redundancy VCC is established. However, if the
Redundancy VCC is
not
present, the backup LES/BUS services ELAN requests in
the usual manner.
For the redundancy protocol to be effective, LE clients must detect the failure of the
primary LES/BUS and connect to the backup. LE clients detect server failures by
means of released VCCs. Connection to the backup LES/BUS is accomplished
through the LECS.
Upon receiving an LE_CONFIGURE_REQUEST, the LECS assigns the LE client to
the appropriate LES and ELAN. If this LES has no configured backup, then the
LECS returns the ATM address of the LES. If the LES is configured with a backup
LES, then the LECS returns either the primary or backup LES address.
The LECS returns the backup LES address if the backup LES exists on the same
MSS Server as the LECS and is currently serving the ELAN, if the primary LES
exists on the same MSS Server as the LECS and it is not currently serving the
ELAN, or if neither LES exists on the same MSS Server as the LECS and the client
was last assigned to the primary LES (within the past 5 minutes). Otherwise, it
returns the primary LES address to the LE client.
Figure 17. LAN Emulation Redundancy
Overview of LAN Emulation
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MRS V3.2 Software User’s Guide