why I was concerned about IP header cksum

Craig Partridge <craig@aland.bbn.com> Mon, 16 October 1995 20:21 UTC

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Subject: why I was concerned about IP header cksum
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From: Craig Partridge <craig@aland.bbn.com>
Date: Mon, 16 Oct 95 12:53:25 -0700
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Hi folks:

When I posted notes about a month ago about IP header checksum issues,
I got some queries about what I was building.  The press release that explains
what I'm up to went out last week and is appended.

Regarding the IP header checksum, I can now explain a bit more about what
the issue is.  We are using off the shelf components (the boards are custom
designed, but none of the chips or processors are).  And the core of the
forwarding process is a workstation-class processor (e.g., Pentium, Alpha,
PowerPC) that examines each header, modifies it and decides where to send
the packet affiliated with the header (along with the updated header).

The instruction budget, as you might imagine, is tight.  We're doing several
million datagrams per second per processor, so the total instruction budget
(for an "average" datagram including device driver) is in the neighborhood
of 50 to 100 instructions.  That's feasible.  (As a check, I took VJ's fastest
IP forwarding code plus our proposed device driver interface and hand compiled
it for an older model Alpha, yielding 60 instructions in 46 clock cycles --
the Alpha was memory bound rather than software bound -- I couldn't load and
store the header plus SNMP variables any faster).

For some RISC processors, summing 10 16-bit words is painful (even if you use
larger word sizes) due to the lack of a carry bit, so the instruction count can
easily get to 10 or 15 instructions (which added to 50 instructions total,
is a real performance killer...)




Press Contacts:

Donna Lane						Paul Davis		
BBN 								For BBN		
(617) 873-2559 						(617) 494-9500		                 
Internet: dlane@bbn.com 			pdavis@fitzcomm.com

BBN Wins Contract to Develop Multigigabit Router

Two-Year Pact will Result in Development of High Speed IP Router  25
Times Faster than Current Commercial Products

CAMBRIDGE, Mass., October 10, 1995. BBN (NYSE:BBN) today announced that
it has been awarded a contract by the Department of Defense's Advanced
Research Projects Agency (ARPA) to develop an ultra high-speed Internet
Protocol (IP) router that will enable breakthrough levels of traffic to
be routed among wide-area and local-area (LAN) networks.  Under terms of
the contract, BBN Systems and Technologies will deliver a prototype
multigigabit router in late 1997.  The base contract is valued at $4.8
million, with options totaling $2.1 million. 
  BBN Systems and Technologies was the developer of the ARPANET, the
forerunner to today's global Internet.  

Routers are communications devices that are critical components of IP
networks, such as the Internet.  Routers interconnect multiple networks
and work by forwarding information from one network to another,
dynamically determining the best path to any destination.  Scheduled for
delivery in 1997, the BBN multigigabit router is intended to provide
router performance for IP data that far exceeds current transmission

"Without a doubt, the demand for higher Internet speeds and capacities
is readily predictable," said Dr. Vinton Cerf, senior vice president for
data architecture, MCI Data Services Division.  "This research effort is
a natural next step in the evolution of the Internet and, if successful,
will provide a much-needed capability for future growth of this exciting
new telecommunications infrastructure."  Dr. Cerf is the co-inventor of
the Internet's Transmission Control Protocol/Internet Protocol (TCP/IP).   

"The work we plan to do under this contract will enable ARPA to
continue to use IP networks and routers to connect to more expansive,
complex networks in the future," said David Campbell, president of BBN
Systems and Technologies.  "The router points the way toward extremely
fast backbone and hub routers, which will be capable of forwarding large
amounts of data with extremely low delay.  It also enhances our ability
to experiment with and operationally use multigigabit networks.
  "In addition, the router will have significant relevance to government
agencies, especially for military applications.  The multigigabit
router's ability to transmit large, high-resolution digital images
quickly will enable US military analysts to access minutes-old data for
more efficient and accurate decision-making," Campbell said.

The contract calls for BBN to develop a prototype of the router that
supports two 622 megabits-per-second Asynchronous Transfer Mode (ATM)
interfaces, with an option to build 2.4 gigabit-per-second interfaces to
work on the same prototype.

"The technology developed for this prototype can provide the basis for
a more powerful router that supports dozens of interfaces," said Dr.
Craig Partridge, BBN's technical leader for the multigigabit router
project.  "The multigigabit router, with an aggregate data transfer rate
of 50 gigabits per second, will be 25 times faster than currently
available commercial routers, and will be able to handle the combined
traffic of nearly 500 FDDI rings."

An FDDI ring is a 100 megabit-per-second LAN.  A router of this
performance level is capable of interfacing with new gigabit-per-second
and faster networking technologies, such as ATM, High-Performance
Parallel Interface (HIPPI) and Fibre Channel.

BBN Systems and Technologies is a pioneer of many of today's
leading-edge technologies, including the global Internet.  The company
conducts research and development in computer, communications and
information sciences, and develops advanced technology products, systems
and application software that help people work and learn together.  

Headquartered in Cambridge, Mass., BBN (Bolt Beranek and Newman Inc.,
NYSE:BBN) is a leading provider of internetworking technologies, data
analysis software and collaborative systems and services for commercial
customers, government agencies and educational institutions.  The
company posted revenue of $215 million for its fiscal year ended June
30, 1995.

Further information about BBN products and customers may be obtained
through BBN's Internet Web site at http://www.bbn.com.

# # #

- --------
Joan L. Irons
Corporate Communications
BBN Corporation
150 CambridgePark Drive
Cambridge, MA 02140

(617) 873-3514 Voice
(617) 873-6899 Fax
JIrons@bbn.com Internet