Chapter 2. Technical description 39
2.5 Protection schemes
IBM 2029 channels are configured on a per-channel basis, in either base mode or
high availability mode. Base channels are design to meet high reliability
requirements. They are typically used when multipath devices (for example,
ESCON control units) are implemented, and performance and through-put are not
the predominating requirement. However, redundancy for base channels can be
attained with the Dual Fiber Switch (DFS); these channels are called switched
base channels. Switched base channels are protected against a fiber trunk failure
and can only be implemented in a point-to-point configuration. Fiber switching
time is 100ms.
In high availability mode the OCM cards manage the path connections between
the OCI card and the corresponding two OCLD cards within the shelf. By
provisioning a channel in this mode, the configuration provides end-to-end signal
protection from one OCI card in a hub site shelf to the corresponding OCI card in
the remote site shelf. High availability channels are protected against an IBM
2029 shelf component failure and a fiber trunk failure. Path switching time is
50ms. These channels can be provisioned in a point-to-point configuration as well
as a hubbed-ring configuration.
Each shelf in the IBM 2029 frame can consist of one of the following
combinations:
• 8 base channels
• 8 switched base channels
• 4 high availability channels
• 6 base channels and 1high availability channel
• 4 base channels and 2 high availability channels
• 2 base channels and 3 high availability channels
Channels provisioned with the 4TDM OCI card can be multiplied by a factor of
four. For example, 8 base channels, each with a 4TDM OCI card, equates to 32
base channels. The IBM 2029 uses TDM within a channel for some low data rate
protocols, making more efficient use of the available bandwidth.
Switched base channels and high availability channels are mutually
exclusive.
Note
40 Fiber Saver (2029) Implementation Guide
Figure 31 depicts the three protection schemes available with the IBM 2029.
Figure 31. Logical channel connectivity
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Switched Base
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Standby
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OCMs
The IBM 2029 base and high availability channels correspond to
SONET-based industry standard 1+1 protection switching configurations, in
which the base channel is an unprotected SONET channel and the high
availability channel is a protected SONET channel.
The IBM 2029 also supports the Dual Fiber Switch (DFS) with base channels,
known as switched base channels. DFSs protect against a fiber trunk failure;
however, they do not protect against circuit card failures, hence a switched
base channel is an unprotected channel.
Throughout this section the terms unprotected channel and protected channel
are synonymous with the terms base channel and high availability channel,
respectively.
Terminology
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