On testing the NETBLT Protocol over divers networks
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(November 1987; No errata)
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Network Working Group M. Lambert
Request for Comments: 1030 M.I.T. Laboratory for Computer Science
November 1987
On Testing the NETBLT Protocol over Divers Networks
STATUS OF THIS MEMO
This RFC describes the results gathered from testing NETBLT over
three networks of differing bandwidths and round-trip delays. While
the results are not complete, the information gathered so far has
been very promising and supports RFC-998's assertion that that NETBLT
can provide very high throughput over networks with very different
characteristics. Distribution of this memo is unlimited.
1. Introduction
NETBLT (NETwork BLock Transfer) is a transport level protocol
intended for the rapid transfer of a large quantity of data between
computers. It provides a transfer that is reliable and flow
controlled, and is designed to provide maximum throughput over a wide
variety of networks. The NETBLT protocol is specified in RFC-998;
this document assumes an understanding of the specification as
described in RFC-998.
Tests over three different networks are described in this document.
The first network, a 10 megabit-per-second Proteon Token Ring, served
as a "reference environment" to determine NETBLT's best possible
performance. The second network, a 10 megabit-per-second Ethernet,
served as an access path to the third network, the 3 megabit-per-
second Wideband satellite network. Determining NETBLT's performance
over the Ethernet allowed us to account for Ethernet-caused behaviour
in NETBLT transfers that used the Wideband network. Test results for
each network are described in separate sections. The final section
presents some conclusions and further directions of research. The
document's appendices list test results in detail.
2. Acknowledgements
Many thanks are due Bob Braden, Stephen Casner, and Annette DeSchon
of ISI for the time they spent analyzing and commenting on test
results gathered at the ISI end of the NETBLT Wideband network tests.
Bob Braden was also responsible for porting the IBM PC/AT NETBLT
implementation to a SUN-3 workstation running UNIX. Thanks are also
due Mike Brescia, Steven Storch, Claudio Topolcic and others at BBN
who provided much useful information about the Wideband network, and
M. Lambert [Page 1]
RFC 1030 Testing the NETBLT Protocol November 1987
helped monitor it during testing.
3. Implementations and Test Programs
This section briefly describes the NETBLT implementations and test
programs used in the testing. Currently, NETBLT runs on three
machine types: Symbolics LISP machines, IBM PC/ATs, and SUN-3s. The
test results described in this paper were gathered using the IBM
PC/AT and SUN-3 NETBLT implementations. The IBM and SUN
implementations are very similar; most differences lie in timer and
multi-tasking library implementations. The SUN NETBLT implementation
uses UNIX's user-accessible raw IP socket; it is not implemented in
the UNIX kernel.
The test application performs a simple memory-to-memory transfer of
an arbitrary amount of data. All data are actually allocated by the
application, given to the protocol layer, and copied into NETBLT
packets. The results are therefore fairly realistic and, with
appropriately large amounts of buffering, could be attained by disk-
based applications as well.
The test application provides several parameters that can be varied
to alter NETBLT's performance characteristics. The most important of
these parameters are:
burst interval The number of milliseconds from the start of one
burst transmission to the start of the next burst
transmission.
burst size The number of packets transmitted per burst.
buffer size The number of bytes in a NETBLT buffer (all
buffers must be the same size, save the last,
which can be any size required to complete the
transfer).
data packet size
The number of bytes contained in a NETBLT DATA
packet's data segment.
number of outstanding buffers
The number of buffers which can be in
transmission/error recovery at any given moment.
M. Lambert [Page 2]
RFC 1030 Testing the NETBLT Protocol November 1987
The protocol's throughput is measured in two ways. First, the "real
throughput" is throughput as viewed by the user: the number of bits
transferred divided by the time from program start to program finish.
Although this is a useful measurement from the user's point of view,
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