HP StorageWorks 2/24 FW 07.00.00/HAFM SW 08.06.00 McDATA Products in a SAN Env - Page 186
Distance Extension Through, BB_Credit, SONET and SDH
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Implementing SAN Internetworking Solutions 4 SONET and SDH • Requires sufficient BB_Credits assigned to the link (such as credits available through the Intrepid 10000 Director buffer pool). Because WDM is a method to transmit multiple signals over the same fiber-optic cable, there is no BB_Credit limitation difference between WDM and dark fiber. Refer to Distance Extension Through BB_Credit for information about requirements. • Creates one logical Fibre Channel fabric through a stretched E_Port connection. The connection is vulnerable to disruptions caused by events at each site or to disruptions caused by problems with the extended-distance WDM link. Several network service providers provide metropolitan and longdistance (intercity) WDM transport services. WDM service can be purchased on a monthly basis in accordance with a negotiated service level agreement (SLA). A typical SLA specifies the availability, minimum dedicated bandwidth (usually scalable), latency, security level, monitoring level, packet loss, and mean time to repair (MTTR). Like dark fiber, WDM is not practical for long-distance ADR applications. In addition, WDM technology is still evolving and equipment is relatively expensive. The telecommunications industry developed SONET and SDH standards for transport of time division multiplexed (TDM) data over fiber-optic cable. SONET is used in North America (United States and Canada) and Japan. SDH is used elsewhere, primarily in Europe. SONET and SDH are closely related standards that specify interface parameters, rates, framing formats, multiplexing methods, and management for synchronous TDM data transport. The physical-layer protocol multiplexes n incoming bit streams, optically modulates the result, and transmits the signal at a rate equal to the incoming bit rate times n. As an example, four data streams arriving at a SONET multiplexer at 2.5 Gbps are transmitted as one stream at 10 Gbps (four times 2.5 Gbps). Low bit-rate streams of information are multiplexed into higher bit-rate streams and transmitted at the rate of the SONET or SDH network. TDM ensures a constant stream of data through a network and takes advantage of the available bandwidth. 4-42 McDATA Products in a SAN Environment - Planning Manual