San Extension Transport Technologies - McDATA StorageWorks 2/140 - Director Switch Planning Manual

SAN Extension
Transport
Technologies
Dark Fiber
There are several extension transport technologies available to
connect geographically-dispersed SAN islands, all of which differ in
performance, latency, and implementation cost. The primary
technologies include:
• Dark fiber (repeated or unrepeated).
• Wavelength division multiplexing (WDM).
• Synchronous optical network (SONET) and synchronous digital
hierarchy (SDH).
• Internet protocol (IP).
Dark fiber refers to an installed fiber-optic infrastructure (including
cabling and possibly including repeaters) that is not in use. Dark fiber
strands (usually deployed in transmit and receive pairs) provide
point-to-point, unprotected connectivity between two locations.
Many corporations install excess fiber-optic cabling with the
expectation of leasing the infrastructure at a future date. When a
telecommunication company installs cable, they often lay additional
(unused) cables to avoid retrenching costs. Utility companies often
install unused cables coincident with pipelines or electrical power
lines. The dark fiber is then leased to companies (dark fiber service)
that require dedicated optical connectivity between separate
locations. Cable operation and connectivity are not controlled by the
service provider. The service lessee is responsible for laser
transceivers and other equipment that make the cabling functional.
Figure 4-8 illustrates extended-distance connectivity through a dark
fiber (dedicated FCP or FICON) interface. The technology:
• Is well suited as an extension technology for RDR/S applications
over metropolitan distances up to 22 miles (35 km) without
repeaters and up to 75 miles (120 km) with repeaters. The
supported bandwidth is dependent on fiber-optic quality and the
choice of multiplexing scheme.
• Requires sufficient buffer-to-buffer credits (BB_Credits) assigned
to the link (such as credits available through the Intrepid 10000
Director buffer pool). Refer to
BB_Credit for information about requirements.
Implementing SAN Internetworking Solutions
Distance Extension Through
Implementing SAN Internetworking Solutions
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