Fibre Channel - Computer Busses - page 211

Fibre channel architecture is based on channel/network integration with an active, intelli-
gent interconnection among devices. A port in Fibre channel simply has to manage a simple
point-to-point connection. The transmission is isolated from the control protocol, so point-to-
point links, arbitrated loops, and switched topologies are used to meet the specific needs of
an application. The fabric is self-managing. Nodes do not need station management, which
greatly simplifies implementation.
12.4 Cables, hubs, adapters and connectors
Fibre channel uses either fibre optic cables (either multimode or single mode) or four types
of copper cables. Normally the copper cables use twin axial with DB-9 or HSSD connectors.
Typically, low-cost copper cables are used for short and medium length runs, and fibre optic
cable is used for longer lengths. Thus, most hubs and adapters have a standard copper inter-
face. For fibre optic cable one of the following is used:
• Multimode cable . This type is used for short distances of up to 22 km. It has a 62.5 mm
or 50 mm inner core diameter and allows light to propagate in multiple modes. These
modes tend to disperse the signal and thus limits the distance of the cable. Typical band-
width ratings for 62.5 mm cable are 200 MHz/km, which gives a range of 200 m at
1 Gbps.
• Single mode cable . This type is used for long cable runs. Its only limitation is the
transmitter power and receiver sensitivity. The inner core is 7 mm or 9 mm, which only al-
lows a single ray of light to propagate along the cable. There will thus be no dispersion
of the signal.
The three main types of connectors used are:
• SC connector . The SC connector is the standard connector for most fibre optic cables
and is also used for Fibre Channel. It is basically a push-pull connector and is preferred
over the ST screw-on connector.
• Galaxy connector . This is a new type of connector and reduces the size of the connector
by 50%, allowing increased connector densities.
There are also various connector/adapter modules, these include:
• Gigabit interface converters (GBIC) . These convert a copper cable connector to an
optical interface. They use an HSSD connector for the copper interface and media inter-
face converters use the DB-9 copper interface.
• Gigabit link modules (GLM) . These are pluggable modules which provide either a
copper or fibre optic interface, and allow users to easily change the media interface from
copper to fibre optics. GLMs include a serialiser-deserialiser (SERDES) and have a me-
dia independent parallel interface to the host bus adapter.
• Extenders . These provide for extended cable runs. They typically use multimode cable,
and they convert the multimode interface to single-mode, as well as boosting the laser