rfc1986.txt

来自「中、英文RFC文档大全打包下载完全版 .」· 文本 代码 · 共 1,180 行 · 第 1/4 页

   before, see RFC 1030 [6]. These test results in Tables 13 and 14,
   "ETFTP Performance," were gathered from files transferred across the
   network and LST-5C TACSAT radios.  The radios were connected together
   via a coaxial cable to provide a "clean" link. A clean link is
   defined to a BER of 10e-5. The throughput rates are defined to be the
   file size divided by the elapsed time resulting in bits per second
   (bps).  The elapsed time is measured from the time of the "get" or
   "put" command to the completion of the transfer. This is an all
   inclusive time measurement based on user perspective. It includes the



Polites, Wollman & Woo        Experimental                     [Page 16]

RFC 1986                         ETFTP                       August 1996


   connection time, transfer time, error recovery time, and disconnect
   time. The user concept of elapsed time is the length of time it takes
   to copy a file from disk to disk. These results show only the average
   performances, including the occasional packet re-transmissions. The
   network configuration was set as:

   ETFTP Parameters:

   Filesize                101,306 bytes
   Radiodelay      2 seconds
   Buffersize      16,384-131,072 bytes
   Packetsize      512-2048 bytes
   Burstsize               8-16 packets/burst

   Gracilis PackeTen Parameters:

   0 TX Delay      400 milliseconds
   1 P Persist     255 [range 1-255]
   2 Slot Time     30 milliseconds
   3 TX Tail               300 milliseconds
   4 Rcv Buffers   8 2048 bytes/buffer
   5 Idle Code     Flag

   Radio Parameters:

   Baudrate                16,000 bps
   Encryption      on


   Table 13: ETFTP Performance at 8 Packets/Burst in Bits/Second

   +-----------+-----------+-----------+-----------+-----------+
   |buffersize |packetsize |packetsize |packetsize |packetsize |
   |(bytes)    |2,048 bytes|1,448 bytes|1,024 bytes|512 bytes  |
   +-----------+-----------+-----------+-----------+-----------+
   |    16,384 |     7,153 |     6,952 |     6,648 |     5,248 |
   +-----------+-----------+-----------+-----------+-----------+
   |    32,768 |     7,652 |     7,438 |     7,152 |     4,926 |
   +-----------+-----------+-----------+-----------+-----------+
   |    65,536 |     8,072 |     8,752 |     8,416 |     5,368 |
   +-----------+-----------+-----------+-----------+-----------+
   |   131,072 |     8,828 |     9,112 |     7,888 |     5,728 |
   +-----------+-----------+-----------+-----------+-----------+








Polites, Wollman & Woo        Experimental                     [Page 17]

RFC 1986                         ETFTP                       August 1996


   Table 14: ETFTP Performance at 16 Packets/Burst in Bits/Second

   +-----------+-----------+-----------+-----------+-----------+
   |buffersize |packetsize |packetsize |packetsize |packetsize |
   |(bytes)    |2,048 bytes|1,448 bytes|1,024 bytes|512 bytes  |
   +-----------+-----------+-----------+-----------+-----------+
   |    16,384 |     5,544 |     5,045 |     4,801 |     4,570 |
   +-----------+-----------+-----------+-----------+-----------+
   |    32,768 |     8,861 |     8,230 |     8,016 |     7,645 |
   +-----------+-----------+-----------+-----------+-----------+
   |    65,536 |     9,672 |     9,424 |     9,376 |     8,920 |
   +-----------+-----------+-----------+-----------+-----------+
   |   131,072 |    10,432 |    10,168 |     9,578 |     9,124 |
   +-----------+-----------+-----------+-----------+-----------+

2.7 PERFORMANCE CONSIDERATIONS

   These tests were performed across a tactical radio link with a
   maximum data rate of 16000 bps. In testing ETFTP, it was found that
   the delay associated with the half duplex channel turnaround time was
   the biggest factor in throughput performance. Therefore, every
   attempt was made to minimize the number of times the channel needed
   to be turned around. Obviously, the easiest thing to do is to use as
   big a buffer as necessary to read in a file, as acknowledgments
   occurred only at the buffer boundaries. This is not always feasible,
   as available storage on disk could easily exceed available memory.
   However, the current ETFTP buffersize is set at a maximum of 524,288
   bytes.

   The larger packetsizes also improved performance. The limit on
   packetsize is based on the 1500 byte MTU of network store and forward
   devices. In a high BER environment, a large packetsize could be
   detrimental to success. By reducing the packetsize, even though it
   negatively impacts performance, reliability is sustained. When used
   in conjunction with FEC, both performance and reliability can be
   maintained at an acceptable level.

   The burstsize translates into how long the radio transmitters are
   keyed to transmit. In ETFTP, the ideal situation is to have the first
   packet of a burst arrive in the radio transmit buffer, as the last
   packet of the previous burst is just finished being sent. In this
   way, the radio transmitter would never be dropped for the duration of
   one buffer. In a multi-user radio network, a full buffer transmission
   would be inconsiderate, as the transmit cycle could last for several
   minutes, instead of seconds. In measuring voice communications,
   typical transmit durations are on the order of five to twenty
   seconds.  This means that the buffersize and burstsize could be
   adjusted to have similar transmission durations.



Polites, Wollman & Woo        Experimental                     [Page 18]

RFC 1986                         ETFTP                       August 1996


3.  REFERENCE SECTION

   [1] Clark, D., Lambert, M., and L. Zhang,
       "NETBLT: A Bulk Data Transfer Protocol", RFC 998, MIT,
       March 1987.

   [2] Postel, J., "User Datagram Protocol" STD 6, RFC 768,
       USC/Information Sciences Institute, August 1980.

   [3] Sollins, K., "Trivial File Transfer Protocol", STD 33,
       RFC 1350, MIT, July 1992.

   [4] MIL-STD-2045-44500, 18 June 1993, "Military Standard Tactical
       Communications Protocol 2 (TACO 2) fot the National Imagery
       Transmission Format Standard", Ft. Monmouth, New Jersey.

   [5] Stevens, W. Richard, 1990, "UNIX Network Programming",
       Prentice-Hall Inc., Englewood, New Jersey, Chapter 12.

   [6] Lambert, M., "On Testing the NETBLT Protocol over
       Divers Networks", RFC 1030, MIT, November 1987.

4.  SECURITY CONSIDERATIONS

   The ETFTP program is a security loophole in any UNIX environment.
   There is no user/password validation. All the problems associated to
   TFTP are repeated in ETFTP. The server program must be owned by root
   and setuid to root in order to work. As an experimental prototype
   program, the security issue was overlooked. Since this protocol has
   proven too be a viable solution in tactical radio networks, the
   security issues will have to be addressed, and corrected.




















Polites, Wollman & Woo        Experimental                     [Page 19]

RFC 1986                         ETFTP                       August 1996


5.  AUTHORS' ADDRESSES

   William J. Polites
   The Mitre Corporation
   145 Wyckoff Rd.
   Eatontown, NJ 07724

   Phone: [phone]
   EMail:[e-mail]


   William Wollman
   The Mitre Corporation
   145 Wyckoff Rd.
   Eatontown, NJ 07724

   Phone: [phone]
   EMail:[e-mail]


   David Woo
   The Mitre Corporation
   145 Wyckoff Rd.
   Eatontown, NJ 07724

   Phone: [phone]
   EMail: [e-mail]


   Russ Langan
   U.S. Army Communications Electronics Command (CECOM)
   AMSEL-RD-ST-SP
   ATTN: Russell Langan
   Fort Monmouth, NJ 07703

   Phone: [phone]
   Fax: [phone]
   EMail: [e-mail]













Polites, Wollman & Woo        Experimental                     [Page 20]

RFC 1986                         ETFTP                       August 1996


6.  GLOSSARY

   ATD             Advanced Technology Demonstration
   AX.25           Amateur Radio X.25 Protocol
   BER             Bit Error Rate
   EPLRS           Enhanced Position Location Reporting Systems
   ETFTP           Enhanced Trivial File Transfer Protocol
   FEC             Forward Error Correction
   FTP             File Transfer Protocol
   HF              High Frequency
   LCU             Lightweight Computer Unit
   ms              milliseconds
   MTU             Maximum Transfer Unit
   NETBLT  NETwork Block Transfer protocol
   NITFS           National Imagery Transmission Format Standard
   PC              Personal Computer
   RNC             Radio Network Controller
   SAS             Survivable Adaptive Systems
   SATCOM  SATellite COMmunications
   SCO             Santa Cruz Operations
   SINCGARS        SINgle Channel Ground and Airborne Radio Systems
   SLIP            Serial Line Internet Protocol
   TACO2           Tactical Communications Protocol 2
   TCP             Transmission Control Protocol
   TFTP            Trivial File Transfer Protocol
   UDP             User Datagram Protocol
   UHF             Ultra High Frequency

   * Modification from NETBLT RFC 998.
   * The new packet size is a modification to the NETBLT RFC 998.
   * The new packet size is a modification to the NETBLT RFC 998.




















Polites, Wollman & Woo        Experimental                     [Page 21]