CTC Union FRM220-NMC, User Manual, Page: 38 / 182

Appendix A
36
Operation Modes
The default operational mode for the FRM220-10/100i is 'switch mode' .
When the MC works in 'switch mode' mode, it does not begin to forward a packet to a destination port until
after the entire packet is received. The latency therefore depends on the packet length. The maximum packet
length supported is up to 2046 bytes in this mode. Different from a normal switch chip, the MC's chip supports
forwarding IEEE802.3x pause frame or 'flow control'. In
'switch mode' the MC operates with a 'store & forward'
method that supports a 1K MAC address table. The UTP side may be 10 or 100 speed and in full or half duplex,
while the fiber side always runs in 100Base, full duplex.
In 'converter mode' , the MC operates with low latency. The transmission does not wait until the entire frame is
received, but instead it forwards the received data immediately. Both transceivers (UTP and Fiber) in the MC are
interconnected via the OAM (Operation, Administration and Maintenance) engine while the internal switch engine
and data buffer are not used. The MC filters OAM frames and supports 9KB jumbo packet in this mode. Again, the
switch engine is disabled in this mode and the UTP must be 100Base, Full Duplex to match the fiber's 100Base-
Full Duplex.
Link Fault Pass Through (AKA LFP)
This media converter incorporates a Link Fault Forwarding feature based on standard IEEE802.3u which
allows indirect sensing of a Fiber or UTP Link Loss via both the 100 Base-TX UTP and 100Base-FX connections.
When this feature is enabled and the media converter detects a Link Loss condition on the Receive fiber (Fiber
LNK down), immediately sends a standard IEEE802.3u Far End Fault code by Transmit fiber to the remote
converter and it disables its UTP transmitter so that a Link Loss condition will be sensed on the receive UTP port.
(See the following figure) The link loss can then be sensed and reported by a Network Management agent at the
host equipment of local and remote UTP port and at the local fiber port. This feature is disabled by default.
Broken Fiber, remote receive
Remote UTP disconnected
Far End Fault (FEF)
The Far End Fault or FEF feature is a built-in part of the OAM. Besides alerting the local MC of a remote fiber
receive transmission break, the FEF is also used in reporting remote power failure or dying gasp.
Remote Rx fiber
Broken
fiber
remote local
2. UTP link
condition forwarded by FEF
3. Link fault
sensed locally
1. UTP
broken
MC
MC
fiber
remote local
3. Fault condition sent
via OAM to far end
4. FEF Led lit
1. fiber
broken
MC
MC
2. FX Link Down
fiber
remote local
2. UTP disabled
condition forwarded
4. Link fault
sensed locally
1. fiber
broken
MC
MC
3. Fiber link
condition forwarded by FEF