MAPPING SAN NETWORKING PROTOCOLS OVER SONET/SDH

In the information age where storefronts are on the Internet, the security and reliability of data is paramount. If anything happens to a system driving your web presence, there has to be instantaneous means to hot switch to another systesms that is mirroring the first. At the heart of these on-line enterprises is the network of storage—massive disk farms linked in a high-speed storage area network. All this data must be mirrored at location geographically remote so as not to be affected by localized events such as natural disasters or power outages.

The great problem has been creating cost-effective high-speed networks that allow these two or more geographical dispersed storage area networks to be synchronized in real time. The ubiquitous SONET (Synchronous Optical NETwork) or SDH (Synchronous Digital Hierarchy) in Europe is a set of standards for interfacing the optical networks of telephone companies. These were built for voice communications but have been increasing pressed into service carrying incompatible data network protocols: ESCON, Fiber Channel, Ethernet, etc. The solution to the problem for enterprises using optical fiber networks in their own private wide area network or a leased network from a common carrier are four emerging technologies.

The first is General Framing Protocol being endorsed by the ITU (International Telecommunications Union) and ANSI (American National Standards Institute). GFP as its commonly called comes in two flavors GFP-T for transparent and GFP-F for framed. GFP is a mapping procedure for carrying storage area network protocols over heterogeneous networks and through heterogeneous switching equipment. It’s great benefit is low overhead. In the terminology of the industry GFP enables a transparent SAN network over an end-to-end SONET/SDH network with full quality of service QOS.

GFP allows this transparent transfer but it comes at a cost: unused capacity. To achieve this transfer a 160 Mbits/s SAN packet has to be carried in a 622 Mbits/s SONET/SDH network container—imagine a boxcar used to haul only a single new car. To solve the problem there is virtual concatenation. With VA, the common carrier uses smaller increment 51 Mbits/s bandwidth containers. Now, the carrier can concatenate four containers to carry the 160 Mbits/s SAN packet.

VA lets the carrier provide container capacity that better suits the customer’s bandwidth requirements. However the customer is still buying fixed capacity whether he uses all of it or not. Thus, he has to purchase enough capacity to meet his highest bandwidth requirement. That’s what LCAS is intended to address. LCAS, for link capacity adjustment scheme, enables the carrier to adjust the bandwidth containers on the fly. Thus, when the customer can order capacity based on his workload and not have to purchase more than he needs to anticipate worse case demand. LCAS also enables the carrier to provide transparent networks for different customer protocols: fiber channel and Ethernet for example. In addition, each customer network can order on the fly varying amounts of bandwidth.

The final element will more efficiently map Fiber Channel traffic to SONET/SDH traffic using Generic Framing Procedure (GFP). The emerging spec is the work of a group that's part of the T11 committee of the InterNational Committee for Information Technology Standards (INCITS).The potential for FC-BB-03 is to allow service providers to not only dynamically allocate bandwidth to customers but to adjust the bandwidth to carry varying amounts of Fiber Channel, ESCON, Ethernet, etc. bandwidth. Work is also focused on providing point-to-multipoint links—backing up in two geographic locations simultaneously, instead of just the point-to-point connections possible now, and on providing carriers with an interface for management and configuration. Also Fiber Channel over SONET/SDH networks are limited to the Metro SONET/SDH. FC-BB-3 would extend this to allow Fiber Channel traffic over the Metro, Regional, National, and International SONET/SDH. Corporations concerned about data outage due to local disasters, earthquake, hurricane, etc. would be able to have their data backed up thousand of miles away.

The four emerging technologies based on telecommunications standards have the additional benefit of requiring no changes within the existing communications network infrastructure. The technologies are incorporated on customer equipment sending and receiving the SAN data. The great benefit to the common carriers is to reduce the cost of transporting SAN data over the ubiquitous SONET/SDH infrastructure.

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