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RFC 1030 - On testing the NETBLT Protocol over divers networks


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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

   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.

   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,
   another throughput measurement is more useful for analyzing NETBLT's
   performance.  The "steady-state throughput" is the rate at which data
   is transmitted as the transfer size approaches infinity.  It does not
   take into account connection setup time, and (more importantly), does
   not take into account the time spent recovering from packet-loss
   errors that occur after the last buffer in the transmission is sent
   out.  For NETBLT transfers using networks with long round-trip delays
   (and consequently with large numbers of outstanding buffers), this
   "late" recovery phase can add large amounts of time to the
   transmission, time which does not reflect NETBLT's peak transmission
   rate.  The throughputs listed in the test cases that follow are all
   steady-state throughputs.

4. Implementation Performance

   This section describes the theoretical performance of the IBM PC/AT
   NETBLT implementation on both the transmitting and receiving sides.
   Theoretical performance was measured on two LANs: a 10 megabit-per-
   second Proteon Token Ring and a 10 megabit-per-second Ethernet.
   "Theoretical performance" is defined to be the performance achieved
   if the sending NETBLT did nothing but transmit data packets, and the
   receiving NETBLT did nothing but receive data packets.

   Measuring the send-side's theoretical performance is fairly easy,
   since the sending NETBLT does very little more than transmit packets
   at a predetermined rate.  There are few, if any, factors which can
   influence the processing speed one way or another.

   Using a Proteon P1300 interface on a Proteon Token Ring, the IBM
   PC/AT NETBLT implementation can copy a maximum-sized packet (1990
   bytes excluding protocol headers) from NETBLT buffer to NETBLT data
   packet, format the packet header, and transmit the packet onto the
   network in about 8 milliseconds.  This translates to a maximum
   theoretical throughput of 1.99 megabits per second.

   Using a 3COM 3C500 interface on an Ethernet LAN, the same
   implementation can transmit a maximum-sized packet (1438 bytes
   excluding protocol headers) in 6.0 milliseconds, for a maximum
   theoretical throughput of 1.92 megabits per second.

   Measuring the receive-side's theoretical performance is more
   difficult.  Since all timer management and message ACK overhead is
   incurred at the receiving NETBLT's end, the processing speed can be
   slightly slower than the sending NETBLT's processing speed (this does

   not even take into account the demultiplexing overhead that the
   receiver incurs while matching packets with protocol handling
   functions and connections).  In fact, the amount by which the two
   processing speeds differ is dependent on several factors, the most
   important of which are: length of the NETBLT buffer list, the number
   of data timers which may need to be set, and the number of control
   messages which are ACKed by the data packet.  Almost all of this
   added overhead is directly related to the number of outstanding
   buffers allowable during the transfer.  The fewer the number of
   outstanding buffers, the shorter the NETBLT buffer list, and the
   faster a scan through the buffer list and the shorter the list of
   unacknowledged control messages.

   Assuming a single-outstanding-buffer transfer, the receiving-side
   NETBLT can DMA a maximum-sized data packet from the Proteon Token
   Ring into its network interface, copy it from the interface into a
   packet buffer and finally copy the packet into the correct NETBLT
   buffer in 8 milliseconds: the same speed as the sender of data.

   Under the same conditions, the implementation can receive a maximum-
   sized packet from the Ethernet in 6.1 milliseconds, for a maximum
   theoretical throughput of 1.89 megabits per second.

5. Testing on a Proteon Token Ring

   The Proteon Token Ring used for testing is a 10 megabit-per-second
   LAN supporting about 40 hosts.  The machines on either end of the
   transfer were IBM PC/ATs using Proteon P1300 network interfaces.  The
   Token Ring provides high bandwidth with low round-trip delay and
   negligible packet loss, a good debugging environment in situations
   where packet loss, packet reordering, and long round-trip time would
   hinder debugging.  Also contributing to high performance is the large
   (maximum 2046 bytes) network MTU.  The larger packets take somewhat
   longer to transmit than do smaller packets (8 milliseconds per 2046
   byte packet versus 6 milliseconds per 1500 byte packet), but the
   lessened per-byte computational overhead increases throughput
   somewhat.

   The fastest single-outstanding-buffer transmission rate was 1.49
   megabits per second, and was achieved using a test case with the
   following parameters:

      transfer size   2-5 million bytes

      data packet size
                      1990 bytes

      buffer size     19900 bytes

      burst size      5 packets

      burst interval  40 milliseconds.  The timer code on the IBM PC/AT
                      is accurate to within 1 millisecond, so a 40
                      millisecond burst can be timed very accurately.

   Allowing only one outstanding buffer reduced the protocol to running
   "lock-step" (the receiver of data sends a GO, the sender sends data,
   the receiver sends an OK, followed by a GO for the next buffer).
   Since the lock-step test incurred one round-trip-delay's worth of
   overhead per buffer (between transmission of a buffer's last data
   packet and receipt of an OK for that buffer/GO for the next buffer),
   a test with two outstanding buffers (providing essentially constant
   packet transmission) should have resulted in higher throughput.

   A second test, this time with two outstanding buffers, was performed,
   with the above parameters identical save for an increased burst
   interval of 43 milliseconds.  The highest throughput recorded was
   1.75 megabits per second.  This represents 95% efficiency (5 1990-
   byte packets every 43 milliseconds gives a maximum theoretical
   throughput of 1.85 megabits per second).  The increase in throughput
   over a single-outstanding-buffer transmission occurs because, with
   two outstanding buffers, there is no round-trip-delay lag between
   buffer transmissions and the sending NETBLT can transmit constantly.
   Because the P1300 interface can transmit and receive concurrently, no
   packets were dropped due to collision on the interface.

   As mentioned previously, the minimum transmission time for a
   maximum-sized packet on the Proteon Ring is 8 milliseconds.  One
   would expect, therefore, that the maximum throughput for a double-
   buffered transmission would occur with a burst interval of 8
   milliseconds times 5 packets per burst, or 40 milliseconds.  This
   would allow the sender of data to transmit bursts with no "dead time"
   in between bursts.  Unfortunately, the sender of data must take time
   to process incoming control messages, which typically forces a 2-3
   millisecond gap between bursts, lowering the throughput.  With a
   burst interval of 43 milliseconds, the incoming packets are processed

   during the 3 millisecond-per-burst "dead time", making the protocol
   more efficient.

6. Testing on an Ethernet

   The network used in performing this series of tests was a 10 megabit
   per second Ethernet supporting about 150 hosts.  The machines at
   either end of the NETBLT connection were IBM PC/ATs using 3COM 3C500
   network interfaces.  As with the Proteon Token Ring, the Ethernet
   provides high bandwidth with low delay.  Unfortunately, the
   particular Ethernet used for testing (MIT's infamous Subnet 26) is
   known for being somewhat noisy.  In addition, the 3COM 3C500 Ethernet
   interfaces are relatively unsophisticated, with only a single
   hardware packet buffer for both transmitting and receiving packets.
   This gives the interface an annoying tendency to drop packets under
   heavy load.  The combination of these factors made protocol
   performance analysis somewhat more difficult than on the Proteon
   Ring.

   The fastest single-buffer transmission rate was 1.45 megabits per
   second, and was achieved using a test case with the following
   parameters:

      transfer size   2-5 million bytes

      data packet size
                      1438 bytes (maximum size excluding protocol
                      headers).

      buffer size     14380 bytes

      burst size      5 packets

      burst interval  30 milliseconds (6.0 milliseconds x 5 packets).

   A second test, this one with parameters identical to the first save
   for number of outstanding buffers (2 instead of 1) resulted in
   substantially lower throughput (994 kilobits per second), with a
   large number of packets retransmitted (10%).  The retransmissions
   occurred because the 3COM 3C500 network interface has only one
   hardware packet buffer and cannot hold a transmitting and receiving
   packet at the same time.  With two outstanding buffers, the sender of
   data can transmit constantly; this means that when the receiver of
   data attempts to send a packet, its interface's receive hardware goes

   deaf to the network and any packets being transmitted at the time by
   the sender of data are lost.  A symmetrical problem occurs with
   control messages sent from receiver of data to sender of data, but
   the number of control messages sent is small enough and the
   retransmission algorithm redundant enough that little performance
   degradation occurs due to control message loss.

   When the burst interval was lengthened from 30 milliseconds per 5
   packet burst to 45 milliseconds per 5 packet burst, a third as many
   packets were dropped, and throughput climbed accordingly, to 1.12
   megabits per second.  Presumably, the longer burst interval allowed
   more dead time between bursts and less likelihood of the receiver of
   data's interface being deaf to the net while the sender of data was
   sending a packet.  An interesting note is that, when the same test
   was conducted on a special Ethernet LAN with the only two hosts
   attached being the two NETBLT machines, no packets were dropped once
   the burst interval rose above 40 milliseconds/5 packet burst.  The
   improved performance was doubtless due to the absence of extra
   network traffic.

7. Testing on the Wideband Network

   The following section describes results gathered using the Wideband
   network.  The Wideband network is a satellite-based network with ten
   stations competing for a raw satellite channel bandwidth of 3
   megabits per second.  Since the various tests resulted in substantial
   changes to the NETBLT specification and implementation, some of the
   major changes are described along with the results and problems that
   forced those changes.

   The Wideband network has several characteristics that make it an
   excellent environment for testing NETBLT.  First, it has an extremely
   long round-trip delay (1.8 seconds).  This provides a good test of
   NETBLT's rate control and multiple-buffering capabilities.  NETBLT's
   rate control allows the packet transmission rate to be regulated
   independently of the maximum allowable amount of outstanding data,
   providing flow control as well as very large "windows".  NETBLT's
   multiple-buffering capability enables data to still be transmitted
   while earlier data are awaiting retransmission and subsequent data
   are being prepared for transmission.  On a network with a long
   round-trip delay, the alternative "lock-step" approach would require
   a 1.8 second gap between each buffer transmission, degrading
   performance.

   Another interesting characteristic of the Wideband network is its
   throughput.  Although its raw bandwidth is 3 megabits per second, at
   the time of these tests fully 2/3 of that was consumed by low-level
   network overhead and hardware limitations.  (A detailed analysis of

   the overhead appears at the end of this document.)  This reduces the
   available bandwidth to just over 1 megabit per second.  Since the
   NETBLT implementation can run substantially faster than that, testing
   over the Wideband net allows us to measure NETBLT's ability to
   utilize very high percentages of available bandwidth.

   Finally, the Wideband net has some interesting packet reorder and
   delay characteristics that provide a good test of NETBLT's ability to
   deal with these problems.

   Testing progressed in several phases.  The first phase involved using
   source-routed packets in a path from an IBM PC/AT on MIT's Subnet 26,
   through a BBN Butterfly Gateway, over a T1 link to BBN, onto the
   Wideband network, back down into a BBN Voice Funnel, and onto ISI's
   Ethernet to another IBM PC/AT.  Testing proceeded fairly slowly, due
   to gateway software and source-routing bugs.  Once a connection was
   finally established, we recorded a best throughput of approximately
   90K bits per second.

   Several problems contributed to the low throughput.  First, the
   gateways at either end were forwarding packets onto their respective
   LANs faster than the IBM PC/AT's could accept them (the 3COM 3C500
   interface would not have time to re-enable input before another
   packet would arrive from the gateway).  Even with bursts of size 1,
   spaced 6 milliseconds apart, the gateways would aggregate groups of
   packets coming from the same satellite frame, and send them faster
   than the PC could receive them.  The obvious result was many dropped
   packets, and degraded performance.  Also, the half-duplex nature of
   the 3COM interface caused incoming packets to be dropped when packets
   were being sent.

   The number of packets dropped on the sending NETBLT side due to the
   long interface re-enable time was reduced by packing as many control
   messages as possible into a single control packet (rather than
   placing only one message in a control packet).  This reduced the
   number of control packets transmitted to one per buffer transmission,
   which the PC was able to handle.  In particular, messages of the form
   OK(n) were combined with messages of the form GO(n + 1), in order to
   prevent two control packets from arriving too close together to both
   be received.

   Performance degradation from dropped control packets was also
   minimized by changing to a highly redundant control packet
   transmission algorithm.  Control messages are now stored in a single
   long-lived packet, with ACKed messages continuously bumped off the
   head of the packet and new messages added at the tail of the packet.
   Every time a new message needs to be transmitted, any unACKed old
   messages are transmitted as well.  The sending NETBLT, which receives

   these control messages, is tuned to ignore duplicate messages with
   almost no overhead.  This transmission redundancy puts little
   reliance on the NETBLT control timer, further reducing performance
   degradation from lost control packets.

   Although the effect of dropped packets on the receiving NETBLT could
   not be completely eliminated, it was reduced somewhat by some changes
   to the implementation.  Data packets from the sending NETBLT are
   guaranteed to be transmitted by buffer number, lowest number first.
   In some cases, this allowed the receiving NETBLT to make retransmit-
   request decisions for a buffer N, if packets for N were expected but
   none were received at the time packets for a buffer N+M were
   received.  This optimization was somewhat complicated, but improved
   NETBLT's performance in the face of missing packets.  Unfortunately,
   the dropped-packet problem remained until the NETBLT implementation
   was ported to a SUN-3 workstation.  The SUN is able to handle the
   incoming packets quite well, dropping only 0.5% of the data packets
   (as opposed to the PC's 15 - 20%).

   Another problem with the Wideband network was its tendency to re-
   order and delay packets.  Dealing with these problems required
   several changes in the implementation.  Previously, the NETBLT
   implementation was "optimized" to generate retransmit requests as
   soon as possible, if possible not relying on expiration of a data
   timer.  For instance, when the receiving NETBLT received an LDATA
   packet for a buffer N, and other packets in buffer N had not arrived,
   the receiver would immediately generate a RESEND for the missing
   packets.  Similarly, under certain circumstances, the receiver would
   generate a RESEND for a buffer N if packets for N were expected and
   had not arrived before packets for a buffer N+M.  Obviously, packet-
   reordering made these "optimizations" generate retransmit requests
   unnecessarily.  In the first case, the implementation was changed to
   no longer generate a retransmit request on receipt of an LDATA with
   other packets missing in the buffer.  In the second case, a data
   timer was set with an updated (and presumably more accurate) value,
   hopefully allowing any re-ordered packets to arrive before timing out
   and generating a retransmit request.

   It is difficult to accommodate Wideband network packet delay in the
   NETBLT implementation.  Packet delays tend to occur in multiples of
   600 milliseconds, due to the Wideband network's datagram reservation
   scheme.  A timer value calculation algorithm that used a fixed
   variance on the order of 600 milliseconds would cause performance
   degradation when packets were lost.  On the other hand, short fixed
   variance values would not react well to the long delays possible on
   the Wideband net.  Our solution has been to use an adaptive data
   timer value calculation algorithm.  The algorithm maintains an
   average inter-packet arrival value, and uses that to determine the

   data timer value.  If the inter-packet arrival time increases, the
   data timer value will lengthen.

   At this point, testing proceeded between NETBLT implementations on a
   SUN-3 workstation and an IBM PC/AT.  The arrival of a Butterfly
   Gateway at ISI eliminated the need for source-routed packets; some
   performance improvement was also expected because the Butterfly
   Gateway is optimized for IP datagram traffic.

   In order to put the best Wideband network test results in context, a
   short analysis follows, showing the best throughput expected on a
   fully loaded channel.  Again, a detailed analysis of the numbers that
   follow appears at the end of this document.

   The best possible datagram rate over the current Wideband
   configuration is 24,054 bits per channel frame, or 3006 bytes every
   21.22 milliseconds.  Since the transmission route begins and ends on
   an Ethernet, the largest amount of data transmissible (after
   accounting for packet header overhead) is 1438 bytes per packet.
   This translates to approximately 2 packets per frame.  Since we want
   to avoid overflowing the channel, we should transmit slightly slower
   than the channel frame rate of 21.2 milliseconds.  We therefore came
   up with a best possible throughput of 2 1438-byte packets every 22
   milliseconds, or 1.05 megabits per second.

   Because of possible software bugs in either the Butterfly Gateway or
   the BSAT (gateway-to-earth-station interface), 1438-byte packets were
   fragmented before transmission over the Wideband network, causing
   packet delay and poor performance.  The best throughput was achieved
   with the following values:

      transfer size   500,000 - 750,000 bytes

      data packet size
                      1432 bytes

      buffer size     14320 bytes

      burst size      5 packets

      burst interval  55 milliseconds

   Steady-state throughputs ranged from 926 kilobits per second to 942
   kilobits per second, approximately 90% channel utilization.  The

   amount of data transmitted should have been an order of magnitude
   higher, in order to get a longer steady-state period; unfortunately
   at the time we were testing, the Ethernet interface of ISI's
   Butterfly Gateway would lock up fairly quickly (in 40-60 seconds) at
   packet rates of approximately 90 per second, forcing a gateway reset.
   Transmissions therefore had to take less than this amount of time.
   This problem has reportedly been fixed since the tests were
   conducted.

   In order to test the Wideband network under overload conditions, we
   attempted several tests at rates of 5 1432-byte packets every 50
   milliseconds.  At this rate, the Wideband network ground to a halt as
   four of the ten network BSATs immediately crashed and reset their
   channel processor nodes.  Apparently, the BSATs crash because the ESI
   (Earth Station Interface), which sends data from the BSAT to the
   satellite, stops its transmit clock to the BSAT if it runs out of
   buffer space.  The BIO interface connecting BSAT and ESI does not
   tolerate this clock-stopping, and typically locks up, forcing the
   channel processor node to reset.  A more sophisticated interface,
   allowing faster transmissions, is being installed in the near future.

8. Future Directions

   Some more testing needs to be performed over the Wideband Network in
   order to get a complete analysis of NETBLT's performance.  Once the
   Butterfly Gateway Ethernet interface lockup problem described earlier
   has been fixed, we want to perform transmissions of 10 to 50 million
   bytes to get accurate steady-state throughput results.  We also want
   to run several NETBLT processes in parallel, each tuned to take a
   fraction of the Wideband Network's available bandwidth.  Hopefully,
   this will demonstrate whether or not burst synchronization across
   different NETBLT processes will cause network congestion or failure.
   Once the BIO BSAT-ESI interface is upgraded, we will want to try for
   higher throughputs, as well as greater hardware stability under
   overload conditions.

   As far as future directions of research into NETBLT, one important
   area needs to be explored.  A series of algorithms need to be
   developed to allow dynamic selection and control of NETBLT's
   transmission parameters (burst size, burst interval, and number of
   outstanding buffers).  Ideally, this dynamic control will not require
   any information from outside sources such as gateways; instead,
   NETBLT processes will use end-to-end information in order to make
   transmission rate decisions in the face of noisy channels and network
   congestion.  Some research on dynamic rate control is taking place
   now, but much more work needs done before the results can be
   integrated into NETBLT.

I. Wideband Bandwidth Analysis

   Although the raw bandwidth of the Wideband Network is 3 megabits per
   second, currently only about 1 megabit per second of it is available
   to transmit data.  The large amount of overhead is due to the channel
   control strategy (which uses a fixed-width control subframe based on
   the maximum number of stations sharing the channel) and the low-
   performance BIO interface between BBN's BSAT (Butterfly Satellite
   Interface) and Linkabit's ESI (Earth Station Interface).  Higher-
   performance BSMI interfaces are soon to be installed in all Wideband
   sites, which should improve the amount of available bandwidth.

   Bandwidth on the Wideband network is divided up into frames, each of
   which has multiple subframes.  A frame is 32768 channel symbols, at 2
   bits per symbol.  One frame is available for transmission every 21.22
   milliseconds, giving a raw bandwidth of 65536 bits / 21.22 ms, or
   3.081 megabits per second.

   Each frame contains two subframes, a control subframe and a data
   subframe.  The control subframe is subdivided into ten slots, one per
   earth station.  Control information takes up 200 symbols per station.
   Because the communications interface between BSAT and ESI only runs
   at 2 megabits per second, there must be a padding interval of 1263
   symbols between each slot of information, bringing the total control
   subframe size up to 1463 symbols x 10 stations, or 14630 symbols.
   The data subframe then has 18138 symbols available.  The maximum
   datagram size is currently expressed as a 14-bit quantity, further
   dropping the maximum amount of data in a frame to 16384 symbols.
   After header information is taken into account, this value drops to
   16,036 symbols.  At 2 bits per symbol, using a 3/4 coding rate, the
   actual amount of usable data in a frame is 24,054 bits, or
   approximately 3006 bytes.  Thus the theoretical usable bandwidth is
   24,054 bits every 21.22 milliseconds, or 1.13 megabits per second.
   Since the NETBLT implementations are running on Ethernet LANs
   gatewayed to the Wideband network, the 3006 bytes per channel frame
   of usable bandwidth translates to two maximum-sized (1500 bytes)
   Ethernet packets per channel frame, or 1.045 megabits per second.

II. Detailed Proteon Ring LAN Test Results

   Following is a table of some of the test results gathered from
   testing NETBLT between two IBM PC/ATs on a Proteon Token Ring LAN.
   The table headers have the following definitions:

      BS/BI           burst size in packets and burst interval in
                      milliseconds

      PSZ             number of bytes in DATA/LDATA packet data segment

      BFSZ            number of bytes in NETBLT buffer

      XFSZ            number of kilobytes in transfer

      NBUFS           number of outstanding buffers

      #LOSS           number of data packets lost

      #RXM            number of data packets retransmitted

      DTMOS           number of data timeouts on receiving end

      SPEED           steady-state throughput in megabits per second

      BS/BI  PSZ    BFSZ   XFSZ   NBUFS  #LOSS  #RXM   DTMOS  SPEED

      5/25   1438   14380  1438   1      0      0      0      1.45
      5/25   1438   14380  1438   1      0      0      0      1.45
      5/30   1438   14380  1438   1      0      0      0      1.45
      5/30   1438   14380  1438   1      0      0      0      1.45
      5/35   1438   14380  1438   1      0      0      0      1.40
      5/35   1438   14380  1438   1      0      0      0      1.41
      5/40   1438   14380  1438   1      0      0      0      1.33
      5/40   1438   14380  1438   1      0      0      0      1.33

      5/25   1438   14380  1438   2      0      0      0      1.62

      5/25   1438   14380  1438   2      0      0      0      1.61
      5/30   1438   14380  1438   2      0      0      0      1.60
      5/30   1438   14380  1438   2      0      0      0      1.61
      5/34   1438   14380  1438   2      0      0      0      1.59
      5/35   1438   14380  1438   2      0      0      0      1.58

      5/25   1990   19900  1990   1      0      0      0      1.48
      5/25   1990   19900  1990   1      0      0      0      1.49
      5/30   1990   19900  1990   1      0      0      0      1.48
      5/30   1990   19900  1990   1      0      0      0      1.48
      5/35   1990   19900  1990   1      0      0      0      1.49
      5/35   1990   19900  1990   1      0      0      0      1.48
      5/40   1990   19900  1990   1      0      0      0      1.49
      5/40   1990   19900  1990   1      0      0      0      1.49
      5/45   1990   19900  1990   1      0      0      0      1.45
      5/45   1990   19900  1990   1      0      0      0      1.46

      5/25   1990   19900  1990   2      0      0      0      1.75
      5/25   1990   19900  1990   2      0      0      0      1.75
      5/30   1990   19900  1990   2      0      0      0      1.74
      5/30   1990   19900  1990   2      0      0      0      1.75
      5/35   1990   19900  1990   2      0      0      0      1.74
      5/35   1990   19900  1990   2      0      0      0      1.74
      5/40   1990   19900  1990   2      0      0      0      1.75
      5/40   1990   19900  1990   2      0      0      0      1.74
      5/43   1990   19900  1990   2      0      0      0      1.75
      5/43   1990   19900  1990   2      0      0      0      1.74
      5/43   1990   19900  1990   2      0      0      0      1.75
      5/44   1990   19900  1990   2      0      0      0      1.73
      5/44   1990   19900  1990   2      0      0      0      1.72
      5/45   1990   19900  1990   2      0      0      0      1.70
      5/45   1990   19900  1990   2      0      0      0      1.72

III. Detailed Ethernet LAN Testing Results

   Following is a table of some of the test results gathered from
   testing NETBLT between two IBM PC/ATs on an Ethernet LAN.  See
   previous appendix for table header definitions.

      BS/BI  PSZ    BFSZ   XFSZ   NBUFS  #LOSS  #RXM   DTMOS  SPEED

      5/30   1438   14380  1438   1      9      9      6      1.42
      5/30   1438   14380  1438   1      2      2      2      1.45
      5/30   1438   14380  1438   1      5      5      4      1.44
      5/35   1438   14380  1438   1      7      7      7      1.38
      5/35   1438   14380  1438   1      6      6      5      1.38
      5/40   1438   14380  1438   1      48     48     44     1.15
      5/40   1438   14380  1438   1      50     50     38     1.17
      5/40   1438   14380  1438   1      13     13     11     1.28
      5/40   1438   14380  1438   1      7      7      5      1.30

      5/30   1438   14380  1438   2      206    206    198    0.995
      5/30   1438   14380  1438   2      213    213    198    0.994
      5/40   1438   14380  1438   2      117    121    129    1.05
      5/40   1438   14380  1438   2      178    181    166    0.892
      5/40   1438   14380  1438   2      135    138    130    1.03
      5/45   1438   14380  1438   2      57     57     52     1.12
      5/45   1438   14380  1438   2      97     97     99     1.02
      5/45   1438   14380  1438   2      62     62     51     1.09

      5/15   512    10240  2048   1      6      6      4      0.909
      5/15   512    10240  2048   1      10     11     7      0.907
      5/18   512    10240  2048   1      11     11     8      0.891
      5/18   512    10240  2048   1      5      5      9      0.906
      5/19   512    10240  2048   1      3      3      3      0.905
      5/19   512    10240  2048   1      8      8      7      0.898
      5/20   512    10240  2048   1      7      7      4      0.876
      5/20   512    10240  2048   1      11     12     5      0.871
      5/20   512    10240  2048   1      8      9      5      0.874
      5/30   512    10240  2048   2      113    116    84     0.599
      5/30   512    10240  2048   2      20     20     14     0.661
      5/30   512    10240  2048   2      49     50     40     0.638

IV. Detailed Wideband Network Testing Results

   Following is a table of some of the test results gathered from
   testing NETBLT between an IBM PC/AT and a SUN-3 using the Wideband
   satellite network.  See previous appendix for table header
   definitions.

      BS/BI  PSZ    BFSZ   XFSZ   NBUFS  #LOSS  #RXM   SPEED

      5/90   1400   14000  500    22     9      10     0.584
      5/90   1400   14000  500    22     12     12     0.576
      5/90   1400   14000  500    22     3      3      0.591
      5/90   1420   14200  500    22     12     12     0.591
      5/90   1420   14200  500    22     6      6      0.600
      5/90   1430   14300  500    22     9      10     0.600
      5/90   1430   14300  500    22     15     15     0.591
      5/90   1430   14300  500    22     12     12     0.590
      5/90   1432   14320  716    22     13     16     0.591
      5/90   1434   14340  717    22     33     147    0.483
      5/90   1436   14360  718    22     25     122    0.500
      5/90   1436   14360  718    22     25     109    0.512
      5/90   1436   14360  718    22     28     153    0.476
      5/90   1438   14380  719    22     6      109    0.533

      5/80   1432   14320  716    22     56     68     0.673
      5/80   1432   14320  716    22     14     14     0.666
      5/80   1432   14320  716    22     15     16     0.661
      5/60   1432   14320  716    22     19     22     0.856
      5/60   1432   14320  716    22     84     95     0.699
      5/60   1432   14320  716    22     18     21     0.871
      5/60   1432   14320  716    30     38     40     0.837
      5/60   1432   14320  716    30     25     26     0.869
      5/55   1432   14320  716    22     13     13     0.935
      5/55   1432   14320  716    22     25     25     0.926
      5/55   1432   14320  716    22     25     25     0.926
      5/55   1432   14320  716    22     20     20     0.932
      5/55   1432   14320  716    22     17     19     0.934
      5/55   1432   14320  716    22     13     14     0.942

 

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