Datasheet

6-5
Cisco ONS 15454 SDH Reference Manual, R7.0
October 2008
Chapter 6 Storage Access Networking Cards
6.2.2 Enhanced Card Mode
• VCG is flexible when SW-LCAS is enabled. (VCG can run traffic as soon as the first cross-connect
is provisioned on both sides of the transport.)
6.2.2.3 Distance Extension
This following list describes FC_MR-4 card distance extension capabilities:
• Enabling of a storage access networking (SAN) extension over long distances through B2B credit
spoofing:
– 2300 km for 1G ports (longer distances supported with lesser throughput)
– 1150 km for 2G ports (longer distances supported with lesser throughput)
• Negotiation mechanism to identify if far-end FC-over-SONET card supports Cisco proprietary B2B
mechanism.
• Autodetection of FC switch B2B credits from FC-SW standards-based ELP frames
• Support for manual provisioning of credits based on FC switch credits
• Automatic GFP buffer adjustment based on round trip latency between two SL ports
• Automatic credit 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, SDH 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 (SNCP [CCAT circuits only], MS-SPRing, protection channel
access [PCA]).
• Supports routing of VCAT group members through different nodes in the SDH cloud.
• Differential delay compensation is automatically enabled on VCAT circuits that are diversely
(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
(BUFFERS) in the ENT-VCG command.