Inside Ethernet switch source code

Story

July 20, 2007

Duncan Young

GE Intelligent Platforms, Inc.

The U.S. Navy has been using Ethernet for many years in combat systems, but many other types of platforms are also turning to Ethernet for its ease and economy of implementation, its wealth of hardware support, and its performance.

Many military platforms are adopting GbE as their backbone intraplatform network.
The U.S. Navy has been using Ethernet for many years in combat systems, but
many other types of platforms are also turning to Ethernet for its ease and
economy of implementation, its wealth of hardware support, and its performance.
Some of these new adopters are satisfying requirements for the Global Information
Grids (GIGs) IPv6 mandate, but many are adopting Ethernet purely on its merits.
Ethernet switches are essential elements of a network and are readily available
in stand-alone or embeddable formats, covering the complete spectrum of environmental
requirements from the benign office to the harshest military specifications.

The choice of network or switched fabric for a particular
application is complex, and more than one type may be employed on a platform
to achieve optimum performance. The characteristics of the primary contenders
can be summarized:

Serial RapidIO – High performance,
high data integrity, low-latency switched fabric for interconnection of
many ports within a chassis. Typically
Serial RapidIO is used in multicomputing environments for DSP applications.
Fibre Channel -– Supports concurrent
protocols such as SCSI and IP on the same network. It has flexible topologies
and for small systems can be configured without a switch. The
use of fibre at the physical level offers inherent protection from electromagnetic
effects, making it suitable for military applications. The
primary commercial use of Fibre Channel is in Storage Area Networks (SANs).
PCI Express – High-performance,
scalable, serial connection using PCI-like memory mapping; often used for
connection to high-speed peripheral devices or sensors; similar
to PCI as it has a single master that controls access.
Ethernet – High-performance
network with 1 Gbps readily available now, 10 Gbps being introduced; synonymous
with the Internet and IP. It can be used as an interconnect
at many levels from board to board, between chassis, between systems, as
an intraplatform private network and, of course, extending to the Internet
or the military’s GIG.

Key to the performance and interoperability of switches
is the onboard software, including protocol, management, and operating system.
The functions of a switch are controlled by IEEE standards for the physical
and signaling levels and by Request for Comments (RFCs) published by the
Internet Engineering Task Force (IETF) for the switching, routing, and management
of the switch. Vendors of switches often make use of off-the-shelf,
real-time operating systems and commercially produced protocol software to
provide a complete packaged product for their customers. However
this is not always the ideal solution for long-running military programs where
the customer may want to “freeze” at a particular revision of software
and still receive support, or have the ability to pass on limited rights to
the source code to their end customer.

When Ethernet is used in real-time intraplatform networks,
there can be timing and response parameters that can be modified for performance
or determinism just for that platform, requiring easy access to the source
code for modification and its subsequent long-term support. An example of
this is the Spanning Tree Protocol (STP), which is used to determine the
optimum routing of messages through a network. When any new connection is
made, it must first listen and learn the applicable routing of the network
before establishing its normal operation. A root bridge (switch)
is elected, and the STP then creates paths through the network from switch
to switch, using the shortest routes in a tree structure. Without
STP, this routing might create loops resulting in broadcast storms from switch
to switch. STP can take a matter of minutes to establish new
routing before a device can become active on the network. To
address this delay, Rapid Spanning Tree Protocol (RSTP) was introduced to provide
a more rapid convergence of the tree, but there are specific cases in critical
networks where yet faster reconvergence is needed.

An intraplatform network, such as might be implemented
on an armored fighting vehicle, an Unmanned Aerial Vehicle (UAV), or a naval
vessel’s combat
system, is essentially a closed private network. The network
will have been designed with many redundant paths to provide enhanced survivability
in the event of battle damage. Waiting many seconds for the
RSTP to reestablish network routing if active paths are lost would be unacceptable,
but within the closed network environment, it is possible to change the parameters
of the RSTP outside its normal limits to provide much faster response to path
failures. By reducing the time to detect failures and reestablish
network routing, an intraplatform network can be tailored to suit the criticality
requirements of a specific platform yet still retain the economy and ease of
use that Ethernet offers.

Access to switch source code and the ability to make rapid
changes to suit particular customer requirements are both essential ingredients
of success in tailoring commercial technologies to suit the sometimes unique
requirements of military programs. Recognizing this, GE Fanuc has introduced
OpenWare, a switch management package configured from a mix of modules written
in-house and from open source to provide the complete protocol, management,
and operating system suite for their new range of NETernity Ethernet switches
supporting both IPv4 and IPv6. The RM922C, a 24-port switch
in 6U VME format, is shown in Figure 1.

Figure 1: The RM922C, a 24-port switch in 6U VME format

Leveraging the best that the commercial technology base
has to offer has many advantages for military programs. It translates into
lower development costs, faster time-to-deployment, and less risk. However,
there are times when the best needs to be better in order to meet the most
stringent military requirements. Ethernet switches use tried
and tested technology that can be improved on where safety, time-sensitivity,
and fail-safe operation are more critical than their commercial counterparts.
But this requires the access and capability to modify a switch’s source
code. Providing this will only serve to enhance Ethernet’s adoption
into a broader range of critical and strategic military platforms, many of
which continue to use proprietary solutions today.

To learn more, e-mail Duncan at
young.duncan1@btinternet.com.