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Fibre Channel long distance FLOGI BBC Information automatic modification Disclosure Number: IPCOM000126508D
Original Publication Date: 2005-Jul-22
Included in the Prior Art Database: 2005-Jul-22
Document File: 2 page(s) / 16K

Publishing Venue



Disclosed is a system that enables SAN distance extension is provided by FC switch or end storage device to ensures the source storage device never reaches its maximum allowed BBC count, and so enables it to maintain full throughput even at very long distances. Fibre Channel devices employ a credit-based flow control mechanism to guarantee delivery between storage devices in the network and to ensure that the rate at which the data is sent by the source does not exceed that at which it can be received at the destination. To establish a link by link flow control, ports of the two connected storage devices first exchange and agree on the number of frames each can receive. This is called the Buffer-to-Buffer Credit (BBC). Whenever the source device sends out a frame, it increments the credit counter (or BBC counter) by 1. The receiving device will send back an acknowledgement message, called R_RDY,upon receipt of each transmitted frame. Once the source device receives the R_RDY, it lowers the BBC counter by 1. If the BBC counter reaches the previously agreed credit threshold, the source device simply stops sending frames until the BBC counter is lowered below its threshold by receiving another R_RDY from the destination.

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Fibre Channel long distance FLOGI BBC Information automatic modification


FC switch or end storage device can increase additional buffer credit memory. it is costly.

FC switch or end storage device additional buffer credit memory is fixed and it is difficult to change depend on the SAN distance.

As the source storage device sends a Fibre Channel frame more than  receiving storage device exceed that at which can received at the destination until certain number,  all transmitted Fibre Channel frames are buffered in the  long distance WAN connection and receiving storage device. The certain number is related the delay of WAN connection. If certain  number is fare enough, it is no need to use storage device additional  buffer credit. 

2. Operation
2.1 Manual operation Following are done by human provisioning

Calculate the delay of value using SAN distance between FC switches or end storage devices.

Calculate the BBC credit equivalent value using the delay.

Calculate the fake BBC value. The fake BBC value = Real BBC buffer + The BBC value equivalent the delay
Use the fake BBC value as BBC credits of ELP or PLOGI/FLOGI frame .

2.2 Automatical operation Following are done by automatic provisioning using Test explore frame.

Send the Test frame to calculate the delay of value using SAN distance...