1553 vs. Fibre Channel
Is 1553's 1 Mbs enough or do we need Fibre Channel's 133+ Mbs?
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Michael Eckley, Fibre Channel Team Member Interphase Corporation
Today, the venerable MIL-STD 1553 data bus is a de facto standard. It is
also a slow standard. Over the last 20 years, the 1553 data bus has been
implemented extensively in a wide range of military platforms, including
aircraft, land-based vehicles and ships. Now, commercially available
technology, most notably Fibre Channel, has far surpassed the capabilities
of 1553.
1553 has been a good fit for military and defense applications. Its
attributes include:
• Minimal requirements for cabling, because of its
linear topology.
• Support for intelligent and non-intelligent nodes
such as sensors and actuators.
• Fault tolerance when configured with
redundancy.
• Electrical isolation of individual nodes to reduce the possibility of
electrical damage to other terminals on a 1553 network.
• Guaranteed real-time predictability.
Unfortunately, these positive characteristics are beginning to be
outweighed by 1553’s limited serial data transmission speed of only 1
Mbps (128 KB/s). This is too slow for many of today’s military
applications which require the transmission of multimedia information like
video, audio, graphics, and highly dense data.
Today, there are alternative commercial technologies to the aging 1553
bus. These alternative buses have data rates upwards of one gigabit per
second (Gbps) and greater. Thus, it is not unrealistic for defense planners
to expect that the next-generation military data bus will have transmission
speeds far beyond 1553’s 1 Mbps.
A leading contender to replace 1553 is Fibre Channel, which is a standard
of the American National Standards Institute (ANSI). Although its name
might imply fiber optics as a medium, Fibre Channel transists numerous
protocols on both fiber optic and copper media. Fibre Channel’s serial data
transmission speeds, which range from 133 Mbps to 4 Gbps (16.8 MB/s to
0.5 MB/s), is certainly well within the requirements of future military
applications.
Fibre Channel Basics
Unlike other networking technologies, Fibre Channel is not limited by a
single topology—it actually was designed to support a number of standard
topologies. Fibre Channel systems can be configured as point-to-point
links, an arbitrated loop, or a switch-based networking fabric. The
point-to-point topology, as old as the computer industry itself, consists of a
simple direct connection between two Fibre Channel ports.
A Fibre Channel environment is a closed system in which each port logs in
with each other port and trades information on attributes, characteristics
and other parameters. Only then do these ports decide if they can work
together and communicate across the Fibre Channel topology. The
topologies that might be used include circuit switching, active hubs, or a
loop, but it doesn’t matter to the ports that are communicating. The fabric
itself is responsible for maintaining the topology while the ports
communicate.
In embedded military and defense applications, Fibre Channel will likely be
implemented in an arbitrated-loop
(FC-AL) configuration. This topology delivers many of the characteristics
required to operate in harsh environments.
An arbitrated loop system can support as many as 127 nodes without
concentrators or repeaters. Such a configuration provides high bandwidth
communications connections with very low latency. When guaranteed,
deterministic performance is required, point-to-point Fibre Channel
connections can be combined with the arbitrated-loop configuration.
A model of a Fibre Channel network for military use as an avionics
system is under development by the Fibre Channel Avionics Environment
(FCAE) working group. Much of the group’s work involves creating a set
of real-time constructs for the deterministic performance and guaranteed
communication bandwidth needed for certain mission-critical military
applications. The group’s goal is to develop Fibre Channel’s deterministic
behavior capabilities on a par with those of 1533, but to do so with data
transmission speeds in the range of 1 Gbps.
Fibre Channel Switch Fabrics
The third basic topology possible with Fibre Channel technology is a
switch-based networking fabric, which is similar to a telephone network in
that each port that has access to the fabric also has multiple paths
available, so it can reach every other port on the fabric. These multiple
moderate-speed paths provide high aggregate system bandwidth. For
example, an eight-by-eight cross-point switching fabric with 25 MB/s
paths has an aggregate bandwidth for the fabric of 400 MB/s.
A Fibre Channel switching fabric has several different classes of
communications, including circuit-switched mode, which is similar to a
private telephone line and frame-switched mode, which provides a
connectionless link.
In circuit-switched mode, a dedicated path through the fabric is
established before data transfers can commence. The data transfer
continues until the path is broken by either of the communicating ports.
Network designers often opt for this mode when they are seeking low
circuit set-up times or short message transmission delays. The
circuit-switched mode is also effective when the traffic consists mostly of
long data transfers.
In frame-switching mode, bandwidth is dynamically allocated on a
link-by-link basis and the data transmission is in frames. Based on
adaptive routing within the fabric, individual frames between the same pair
of ports are independently switched and may take alternate paths to reach
their destinations. As an alternative, a frame-switching fabric can be set
up so that frames arrive in the proper order at their destinations. In a
frame-switching fabric, buffering is needed to provide link-level flow
control between the connected ports.
Defense and Commercial Applications
In the commercial world, Fibre Channel has been implemented by most of
the major vendors of personal computers and workstations, including IBM,
Sun Microsystems, Hewlett-Packard and Compaq. Interphase
Corporation has emerged as one of the leading suppliers of Fibre Channel
technology to defense contractors and commercial original equipment
manufacturers (OEMs). Interphase offers a complete line of Fibre
Channel host bus adapters (HBAs) for embedded and commercial
applications, as well as an easy-to-use Fibre Channel management tool,
FibreView-Enterprise.
In the military and defense arena, Fibre Channel has already been
selected on a number of projects, such as the F/A-18 Hornet
fighter-bomber, the AWACS Extend Sentry and the B-1 Lancer strategic
bomber. It is also being evaluated for the high-speed interconnections
among the subsystems on the US/UK tactical Joint Strike Fighter (JSF).
Embedded FC for Defense
Interphase has developed several Fibre Channel HBAs that are well
suited to embedded defense or military applications. The 6526 HBA is a
single-port Fibre Channel adapter for CompactPCI-based systems. The
3U 6526 offers the high performance of Fibre Channel and PCI, yet is
very durable because of its gas-tight, high-density pin-and-socket
connectors.
If the application requires more than one Fibre Channel port, the
Interphase 6546 CompactPCI HBA (shown in the photo on p.75) can be
configured with as many as four Fibre Channel ports in a 6U formfactor.
The base 6546 HBA has two Fibre Channel ports and two PMC sites for
mezzanine cards that can be implemented as two additional Fibre Channel
ports or other technologies. When fully configured with four Fibre Channel
ports, the 6546 can deliver up to 4 Gbps of performance with redundancy.
Interphase Corporation
13800 Senlac
Dallas, TX 75234
(800)327-8638 |
