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9
Cisco MDS 9000 Family Port Analyzer Adapter Installation and Configuration Note
OL-9077-01
Selecting Truncate Mode
The truncate modes can be hot switched (no power off is necessary). However, if you configure a new
speed setting (for example, changing the Fibre Channel port speed from 2 Gbps to 1 Gbps), the adapter
must be power cycled for the new setting to take effect. Power cycling consists of unplugging the adapter
wall plug, waiting for four seconds or more, and then plugging it back in and powering on.
No Truncate Mode (NTM) for Ethernet Encapsulation
In NTM, Fibre Channel frames are encapsulated into Ethernet frames without any modification to the
payload (the full 2164 bytes are transmitted). Ethernet devices must support jumbo frames for this mode
to work; otherwise, the Ethernet MAC may not work properly for the frames larger than the maximum
Ethernet size. Jumbo frames are Ethernet frames greater than 1520 bytes. (See Figure 4.)
Ethernet Truncate Mode (ETM) for Maximum Payload
This mode is appropriate when jumbo frames are not supported by the Ethernet devices. In that case, this
mode provides the maximum amount of Fibre Channel payload within a single Ethernet frame.
512 bytes NTM, ETM,
STM, or DTM
Frames may
be dropped.
DTM or STM Frames may be
dropped.
256 bytes (worst case to obtain
maximum data)
NTM, ETM,
STM, or DTM
Frames may
be dropped.
DTM Frames may be
dropped.
Table 3 Selecting the Truncate Mode to Achieve No Dropped Frames (continued)
Average Size of the FC Frame Fibre Channel to Ethernet Speed
1 Gbps to
1 Gbps
1 Gbps to
100 Mbps
2 Gbps to
1 Gbps
2 Gbps to
100 Mbps