ATOMIC-2
		Going the Last Meter for Gigabit LANs
			 (abstract - GBN'96)
	Joe Touch, Ted Faber, Annette DeSchon, Avneesh Sachdev
		  USC/Information Sciences Institute
				   
    The ATOMIC LAN is a 640-Mbps supporting 33 workstations for ISI's
HPCC Division, in operation for over a year. The ATOMIC-2 project is
investigating ways to make that "Gbps" bandwidth effective for
everyday workstation use. Replacing an Ethernet LAN with the ATOMIC
LAN provides higher aggregate network bandwidth, but does not
necessarily increase the bandwidth available to each user.  ATOMIC-2
is focused on how to bring gigabits that last meter between the LAN
and the user.
    We have identified five research areas in breaking the last-meter
bandwidth barrier: file system performance, application protocol
performance, security performance, gateway development, and
fault-tolerant network management. In each area, we have identified
systems reorganizations that can alleviate the corresponding
bottleneck.  We are currently implementing generalizable solutions to
these challenges.
    Distributed file system performance is usually optimized to reduce
network load, increase local caching, and alleviate server load.  When
a gigabit LAN is available, some of this current tuning impedes
throughput. SunOS NFS is limited by synchronous RPCs, and per-process
parallelism in the BIODs (block I/O daemons). We provided an alternate
asynchronous, pipelined RPC with at-most-once semantics, implemented
inside a single process. The raw RPC throughput increased by 40%; we
have currently seen an overall 10% increase at the file system level,
and work continues.
    Application protocol performance is limited by copying data across
the user/kernel protection boundary, unwieldy 'mbufs', and multiple,
serial copies of the same data. We are currently implementing a
user-space protocol that avoids the kernel-crossing and does not use
mbufs. We kept multiple copies to retain socket send/receive semantics
(with reusable buffers), and pipeline the copies by overlapping
programmed I/O and DMA copying.
    We analyzed the performance of security protocols, which must be
end-to-end, and thus are implemented inside the last-meter boundary.
Our implementation of IPv4 Authentication Headers (AH) in SunOS
indicated that the additional encapsulation had a small impact on
performance (10%). The authentication algorithm itself, MD5, reduces
overall throughput by 75%. Our analysis of the MD5 algorithm showed
that individual packet processing could not be internally
parallelized.  We have developed an Alternate Hash Algorithm that is 3
times faster than MD5, although cryptographically weaker.
    We have implemented ATOMIC to ATM and fast-Ethernet gateway using
a Sun SPARC with host interfaces, and shown it can support OC-3
bandwidths (unidirectional). Higher bandwidths or bi-directional use
overloads the host bus. We plan to re-implement the gateway using
peer-to-peer DMA, transferring packets directly between the host
interfaces, avoiding system RAM and reducing the system bus
utilization. Using host interfaces allows our gateway to follow the
technology curve more closely, rather than requiring subsequent
revision of router interfaces.
    The ATOMIC LAN also requires fault-tolerant routing. ATOMIC is a
switched LAN, where switches are usually distributed throughout the
LAN infrastructure.  This architecture provides multiple points of
failure. We provide a backup Ethernet LAN to avoid service
interruptions, and increase user confidence.