6-6
Cisco ONS 15454 Reference Manual, R7.0
78-17191-01
Chapter 6 Storage Access Networking Cards
6.2 6.2.3 Link Integrity
• Negotiation mechanism to identify whether a far-end FC-over-SONET card supports the Cisco
proprietary B2B mechanism
• Auto detection of FC switch B2B credits from FC-SW standards-based exchange link parameters
(ELP) frames
• Support for manual provisioning of credits based on FC switch credits
• Automatic GFP buffers adjustment based on roundtrip latency between two SL ports
• Automatic credits recovery during SONET switchovers/failures
• Insulation for FC switches from any SONET switchovers; no FC fabric reconvergences for SONET
failures of less than or equal to 60 ms

6.2.2.4 Differential Delay Features

The combination of VCAT, SW-LCAS, and GFP specifies how to process information for data and
storage clients. The resulting operations introduce delays. Their impact depends on the type of service
being delivered. For example, storage requirements call for very low latency, as opposed to traffic such
as e-mail where latency variations are not critical.
With VCAT, SONET paths are grouped to aggregate bandwidth to form VCGs. Because each VCG
member can follow a unique physical route through a network, there are differences in propagation
delay, and possibly processing delays between members. The overall VCG propagation delay
corresponds to that of the slowest member. The VCAT differential delay is the relative arrival time
measurement between members of a VCG. The FC_MR-4 card is able to handle VCAT differential delay
and provides these associated features:
• Supports a maximum of 122 ms of delay difference between the shortest and longest paths.
• Supports diverse fiber routing for VCAT circuit.
• All protection schemes are supported (path protection, automatic protection switching [APS],
2-fiber BLSR, 4-fiber BLSR).
• Supports routing of VCAT group members through different nodes in the SONET network.
• Differential delay compensation is automatically enabled on VCAT circuits that are diverse (split
fiber) routed, and disabled on VCAT circuits that are common fiber routed.
Note Differential delay support for VCAT circuits is supported by means of a TL1 provisioning parameter
(EXTBUFFERS) in the ENT-VCG command.

6.2.2.5 Interoperability Features

The interoperability features are as follows:
• Maximum frame size setting to prevent accumulation of oversized performance monitoring
parameters for virtual SAN (VSAN) frames
• Ingress filtering disable for attachment to third-party GFP-over-SONET/SDH equipment
6.2.3 Link Integrity
The link integrity features are as follows:
• Data port disabled if upstream data port is not able to send over SONET/SDH transport