HP StorageWorks 2/24 FW 07.00.00/HAFM SW 08.06.00 McDATA Products in a SAN Env - Page 210

Physical Planning Considerations 5 Data Transmission Distance Consider the following when determining the number and type of transceivers to use: • Distance between a director or fabric switch and the attached Fibre Channel device or between fabric elements communicating through an ISL. • Cost effectiveness. • Device restrictions or requirements with respect to existing fiber-optic (multimode or singlemode) or copper cable. Data transmission distance is a factor governing the choice of transceiver type, fiber-optic cable type, and transmission rate. When using multimode cable, if the core diameter or data transmission rate increases, the data transmission distance decreases. Link budget is another governing factor. A link budget is the attenuation (in dB) a connection between devices can sustain before significant link errors or loss of signal occur. When using multimode cable, if the core diameter or data transmission rate increases, the link budget decreases. Cable-conversion, repeater, patch-panel, or other connections within a link also decrease the link budget. Each connection introduces a nominal signal loss of at least one dB through the link. Patch panel connections (with one connection at each side of the panel) typically introduce a two dB signal loss through a link. Other variables such as the grade of fiber-optic cable, device restrictions, application restrictions, buffer-to-buffer credit limits, and performance requirements can also affect data transmission distance and link budget. Table 5-1 lists unrepeated data transmission distance and link budget as a function of fiber-optic cable type and data transmission rate. When using multimode cable, note the decrease in performance as the cable core diameter or data transmission rate increases. When using singlemode cable, performance is a function of transceiver type. Data transmission distance and link budget are not affected by data transmission rate. 5-4 McDATA Products in a SAN Environment - Planning Manual