McDATA StorageWorks 2/140 - Director Switch Planning Manual page 165

Implementing SAN Internetworking Solutions
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From the standpoint of fabric build events, the only difference
between a local and stretched E_Port connection is the latency
introduced by the TCP/IP link and associated WDM or FCIP
hardware.
A disruptive build fabric event at one local site propagates to the
connected site. Likewise, a disruption in the TCP/IP link may cause
the extended SAN to segment into separate SAN islands. For
mission-critical storage over distance (such as disaster recovery
applications) an extended SAN may inadvertently create instabilities
that defeat the intent of highly-reliable data access.
iFCP operates at a higher level and addresses problems that direct
connectivity and FCIP do not. iFCP is similar to FCP but uses IP for
OSI Layer 3 (network layer) and TCP for OSI Layer 4 (transport
layer). In contrast, mFCP uses IP for OSI Layer 3 and UDP for OSI
Layer 4. Connectivity is provided through an iSNS database with a
WWN-to-IP address look-up table in each fabric.
When a Fibre Channel frame is transmitted to a device in a different
fabric, the frame is encapsulated and sent over the TCP/IP link to the
destination fabric. The encapsulating wrapper is stripped off by iFCP
and the Fibre Channel frame delivered to the destination device. iFCP
can accommodate up to 64 TCP sessions per port. A TCP session
opens for each pair of port WWNs that initiate a process login.
SAN routers have both FCP and IP interfaces. The Eclipse 1620 SAN
router has two ports that provide IP network connectivity at up to
full-duplex 100 Base-T Fast Ethernet (100 Mbps) transmission speed.
The Eclipse 2640 SAN router has four ports that provide IP network
connectivity at up to full-duplex GbE (1,000 Mbps) transmission
speed. Figure 4-6 shows the physical connectivity of two mSANs
(to form an iSAN) through Eclipse 2640 SAN Routers and an IP wide
area network (WAN).
Implementing SAN Internetworking Solutions
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