AN 2036
2
Flexible insulation Stiff insulation
3. Will the extra length of the Finisar 1000BASE-T SFP cause mechanical
interference problems in my system?
While there is a chance of interference problems, the probability is small. If you
compare the length of a Finisar 1000BASE-T SFP to a fiber SFP, with their
respective cables inserted, there is little difference in length. This is due to the strain
relief features on LC connectors that protrude much farther than the insulation on a
Cat 5 cable. An optical and 1000BASE-T SFP with cables inserted is shown in
Picture 1 below.
Picture 1: 1000BASE-T and optical SFP transceivers with cables inserted.
4. What cable type is recommended for use with the Finisar 1000BASE-T SFP?
The Finisar 1000BASE-T SFP was designed to operate using standard Cat 5 cable
that has been configured per IEEE802.3:2005. You can safely use Cat 5e or Cat 6
cables, as these are improved versions of Cat 5. For short cable runs, with intricate
routing, stranded cable is recommended, as it is more flexible.
5. What is the PHY and how can it be accessed?
The Finisar 1000BASE-T SFP uses the Marvell 88E1111 Physical Layer IC (PHY) to
convert between the serial interface and 1000BASE-T interfaces. The first generation
designs use Rev. B0 of this PHY; the second generation uses Rev. B2. This chip has
a number of useful features available on internal registers that can be accessed via the
2-wire bi-directional serial interface at address 0xAC. The contents at each register
address are 2 bytes wide; details for accessing the register can be found at
http://www.marvell.com .
6. What is SGMII mode?
SGMII stands for “Serial Gigabit Media Independent Interface.” SGMII is a mode of
communication between the MAC and PHY to allow for 10/100/1000BASE-T
operation. In 100BASE-TX mode, the MAC still transmits to the PHY at 1.25 Gb/sec,
but each byte is repeated 10 times. The PHY then converts this repeated data to
100BASE-TX format. The process is the same in 10BASE-T mode but each byte is
repeated 100 times. SGMII is a Cisco Systems specification, document EN-46158,
and is available for download at no cost over the internet: ftp://ftp-
eng.cisco.com/smii/sgmii.pdf. At the time this FAQ was written, the latest SGMII
version is 1.8.