[Search] [txt|xml|pdf|bibtex] [Tracker] [Email] [Nits]

Versions: 00                                                            
Benchmarking Methodology Working Group                         G. Lencse
Internet-Draft                               Szechenyi Istvan University
Intended status: Informational                                  K. Shima
Expires: November 18, 2021                      IIJ Innovation Institute
                                                            May 17, 2021


  Benchmarking Methodology for Stateful NATxy Gateways using RFC 4814
                       Pseudorandom Port Numbers
               draft-lencse-bmwg-benchmarking-stateful-00

Abstract

   RFC 2544 has defined a benchmarking methodology for network
   interconnect devices.  RFC 5180 addressed IPv6 specificities and it
   also provided a technology update, but excluded IPv6 transition
   technologies.  RFC 8219 addressed IPv6 transition technologies,
   including stateful NAT64.  However, none of them discussed how to
   apply RFC 4814 pseudorandom port numbers to any stateful NAT (NAT44,
   NAT64, NAT66) technologies.  We discuss why using pseudorandom port
   numbers with stateful NAT gateways is a hard problem and recommend a
   solution.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 18, 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of



Lencse & Shima          Expires November 18, 2021               [Page 1]


Internet-Draft       Benchmarking Stateful Gateways             May 2021


   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Pseudorandom Port Numbers and Stateful Translation  . . . . .   3
   3.  Test Setup and Terminology  . . . . . . . . . . . . . . . . .   4
   4.  Recommended Benchmarking Method . . . . . . . . . . . . . . .   5
     4.1.  Restricted Port Number Ranges . . . . . . . . . . . . . .   5
     4.2.  Preliminary Test Phase  . . . . . . . . . . . . . . . . .   6
     4.3.  Control of the Connection Tracking Table Entries  . . . .   7
     4.4.  Measurement of the Maximum Connection Establishment Rate    8
     4.5.  Real Test Phase . . . . . . . . . . . . . . . . . . . . .   8
     4.6.  Writing and Reading Order of the State Table  . . . . . .   9
     4.7.  Peculiarities of Stateful Testing . . . . . . . . . . . .  10
       4.7.1.  Timeout Budget  . . . . . . . . . . . . . . . . . . .  10
       4.7.2.  Special Warning Against Non-zero Frame Loss Testing .  10
   5.  Implementation and Experience . . . . . . . . . . . . . . . .  10
   6.  Limitations of using UDP as Transport Layer Protocol  . . . .  11
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  13
     A.1.  00  . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   [RFC2544] has defined a comprehensive benchmarking methodology for
   network interconnect devices, which is still in use.  It was mainly
   IP version independent, but it used IPv4 in its examples.  [RFC5180]
   addressed IPv6 specificities and also added technology updates, but
   declared IPv6 transition technologies out of its scope.  [RFC8219]
   addressed the IPv6 transition technologies, including stateful NAT64.
   It has reused several benchmarking procedures from [RFC2544] (e.g.
   throughput, frame loss rate), it has redefined the latency
   measurement, and added further ones, e.g. the PDV (packet delay
   variation) measurement.




Lencse & Shima          Expires November 18, 2021               [Page 2]


Internet-Draft       Benchmarking Stateful Gateways             May 2021


   However, none of them discussed, how to apply [RFC4814] pseudorandom
   port numbers, when benchmarking stateful NATxy (NAT44, NAT64, NAT66)
   gateways.  We are not aware of any other RFCs that address this
   question.

   First, we discuss why using pseudorandom port numbers with stateful
   NATxy gateways is a hard problem.

   Then we recommend a solution.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Pseudorandom Port Numbers and Stateful Translation

   In its appendix, [RFC2544] has defined a frame format for test frames
   including specific source and destination port numbers.  [RFC4814]
   recommends to use pseudorandom and uniformly distributed values for
   both source and destination port numbers.  However, stateful NATxy
   (NAT44, NAT64, NAT66) solutions use the port numbers to identify
   connections.  The usage of pseudorandom port numbers causes different
   problems depending on the direction.

   o  As for the private to public direction, pseudorandom source and
      destination port numbers could be used, however, this approach
      would be a denial of service attack against the stateful NATxy
      gateway, because it would exhaust its connection tracking table.
      To that end, let us see some calculations using the
      recommendations of RFC 4814:

      *  The recommended source port range is: 1024-65535, thus its size
         is: 64512.

      *  The recommended destination port range is: 1-49151, thus its
         size is: 49151.

      *  The number of source and destination port number combinations
         is: 3,170,829,312.

      We note that section 12 of [RFC2544] also requires testing with
      256 destination networks, which further increases the number of
      connection tracking table entries.




Lencse & Shima          Expires November 18, 2021               [Page 3]


Internet-Draft       Benchmarking Stateful Gateways             May 2021


   o  As for the public to private direction, the stateful DUT would
      drop any packets that do not belong to an existing connection,
      therefore, the direct usage of pseudorandom port numbers from the
      above-mentioned ranges is not feasible.

3.  Test Setup and Terminology

   Our methodology works with any IP version.  We use IPv4 in the Test
   Setup shown in Figure 1 to facilitate its easy understanding based on
   the well-known stateful NAT44 (also called NAPT: Network Address and
   Port Translation) solution.

                 +--------------------------------------+
        10.0.0.2 |Initiator                    Responder| 198.19.0.2
   +-------------|                Tester                |<------------+
   | private IPv4|                         [state table]| public IPv4 |
   |             +--------------------------------------+             |
   |                                                                  |
   |             +--------------------------------------+             |
   |    10.0.0.1 |                 DUT:                 | 198.19.0.1  |
   +------------>|        Sateful NATxy gateway         |-------------+
     private IPv4|     [connection tracking table]      | public IPv4
                 +--------------------------------------+


       Figure 1: Test Setup for benchmarking stateful NATxy gateways

   As for transport layer protocol, [RFC2544] recommended testing with
   UDP, and it was kept also in [RFC8219].  For the general
   recommendation, we also keep UDP, thus the port numbers in the
   following text are to be understood as UDP port numbers.  We discuss
   the limitation of this approach in Section 6.

   We define the most important elements of our proposed benchmarking
   system as follows.

   o  Connection tracking table: The stateful NATxy gateway uses a
      connection tracking table to be able to perform the stateful
      translation in the public to private direction.  Its size, policy
      and content is unknown for the Tester.

   o  Four tuple: The four numbers that identify a connection are source
      IP address, source port number, destination IP address,
      destination port number.

   o  Initiator: The port of the Tester that may initiate a connection
      through the stateful DUT in the private to public direction.
      Theoretically, it can use any source and destination port numbers:



Lencse & Shima          Expires November 18, 2021               [Page 4]


Internet-Draft       Benchmarking Stateful Gateways             May 2021


      if they do not belong to an existing connection, the DUT will
      register a new connection into its connection tracking table.

   o  Responder: The port of the Tester that may not initiate a
      connection through the stateful DUT in the public to private
      direction.  It may send only frames that belong to an existing
      connection.  To that end, it uses four tuples that have been
      previously extracted from the received test frames and stored in
      its state table.

   o  State table: The Responder of the Tester extracts the four tuple
      from each received test frame and stores it in its state table.
      Recommendation is given for writing and reading order of the state
      table in Section 4.6.

   o  Preliminary test phase: Test frames are sent only by the Initiator
      to the Responder through the DUT to fill both the connection
      tracking table of the DUT and the state table of the Responder.
      This is a newly introduced operation phase for stateful NATxy
      benchmarking.  The necessity of this phase is explained in
      Section 4.2.

   o  Real test phase: The actual test (e.g. throughput, latency, etc.)
      is performed in this phase after the completion of the preliminary
      test phase.  Test frames are sent as required (e.g. bidirectional
      test or unidirectional test in any of the two directions).

4.  Recommended Benchmarking Method

4.1.  Restricted Port Number Ranges

   The Initiator SHOULD use restricted ranges for source and destination
   port numbers to avoid the denial of service attack against the
   connection tracking table of the DUT described in Section 2.  The
   size of the source port number range SHOULD be larger (e.g. in the
   order of a few times ten thousand), whereas the size of the
   destination port number range SHOULD be smaller (may vary from a few
   to several hundreds or thousands as needed).  The rationale is that
   source and destination port numbers that can be observed in the
   Internet traffic are not symmetrical.  Whereas source port numbers
   may be random, there are a few very popular destination port numbers
   (e.g. 443, 80, etc., see [IIR2020]) and others hardly occur.  And we
   have found that their role is also asymmetric in the Linux kernel
   routing hash function [LEN2020].

   The product of the sizes of the two ranges can be used as a
   parameter.  The performance of the stateful NATxy gateway MAY be
   examined as function of this parameter.



Lencse & Shima          Expires November 18, 2021               [Page 5]


Internet-Draft       Benchmarking Stateful Gateways             May 2021


4.2.  Preliminary Test Phase

   The preliminary phase serves two purposes:

   1.  The connection tracking table of the DUT is filled.  It is
       important, because its maximum connection establishment rate may
       be lower than its maximum frame forwarding rate (that is
       throughput).

   2.  The state table of the Responder is filled with valid four
       tuples.  It is a precondition for the Responder to be able to
       transmit frames that belong to connections exist in the
       connection tracking table of the DUT.

   Whereas the above two things are always necessary before the real
   test phase, the preliminary phase can be used without the real test
   phase.  It is done so, when the maximum connection establishment rate
   is measured (as described in Section 4.4).

   A preliminary test phase MUST be performed before all tests performed
   in the real test phase.  In this phase, the following things happen:

   1.  The Initiator sends test frames to the Responder through the DUT
       at a specific frame rate.

   2.  The DUT performs the stateful translation of the test frames and
       it also stores the new combinations in its connection tracking
       table.

   3.  The Responder receives the translated test frames and updates its
       state table with the received four tuples.  The responder
       transmits no test frames during the preliminary phase.

   When the preliminary test phase is performed in preparation to the
   real test phase, the applied frame rate and the duration of the
   preliminary phase SHOULD be carefully selected so that:

   o  The applied frame rate be safely lower than the maximum connection
      establishment rate.

   o  The initial transient of the filling of the connection tracking
      table of the DUT be finished.

   o  Enough four tuples be stored in the state table of the Responder
      so that it can generate frames with the proper distribution of the
      four tuples.





Lencse & Shima          Expires November 18, 2021               [Page 6]


Internet-Draft       Benchmarking Stateful Gateways             May 2021


   o  The connections do not time out in the DUT even during the
      beginning of the real test phase.

4.3.  Control of the Connection Tracking Table Entries

   The number of the entries in the connection tracking table of the DUT
   MAY be controlled by using all different source port number
   destination port number combinations.

   Let NF and NC denote the number of test frames to send and the number
   of all possible source port number destination port number
   combinations, respectively.

   1.  If NF and NC are in the same order of magnitude, then the all
       different source port number destination port number combinations
       may be computing efficiently generated by preparing a random
       permutation of the previously enumerated all possible source port
       number destination port number combinations using Dustenfeld's
       random shuffle algorithm [DUST1964].

   2.  If NF is at least an order of magnitude less than NC, then a
       simpler solution may be used: the Initiator registers in a table
       and then it checks if a given source port number destination port
       number combination was already used (and if yes, then it MUST
       generate a new one).

   3.  If NF is at least two orders of magnitude less than NC, then
       mostly different source port number destination port number
       combinations can be generated without any specific provision.

   Important warning: in normal router testing, the port number
   selection algorithm (whether it is pseudo-random or enumerated) does
   not affect final results.  However, our experience with iptables
   shows that if the connection tracking table is filled using port
   number enumeration in increasing order, then the maximum connection
   establishment rate of iptables degrades significantly compared to its
   performance using pseudorandom port numbers [LEN2021].

   [RFC4814] REQUIRES pseudorandom port numbers, which we believe is a
   good approximation of the distribution of the source port numbers a
   NATxy gateway on the Internet may face with.

   The enumeration of the source port number destination port number
   combinations in increasing order MAY be used as an additional
   measurement to discover worst case performance.






Lencse & Shima          Expires November 18, 2021               [Page 7]


Internet-Draft       Benchmarking Stateful Gateways             May 2021


4.4.  Measurement of the Maximum Connection Establishment Rate

   The maximum connection establishment rate is an important
   characteristic of the stateful NATxy gateway and its determination is
   necessary for the safe execution of the preliminary test phase
   (without frame loss) before the real test phase.

   The measurement procedure of the maximum connection establishment
   rate is very similar to the throughput measurement procedure defined
   in [RFC2544].

   Procedure: The Initiator sends a specific number of test frames using
   all (or mostly) different source port number destination port number
   combinations at a specific rate through the DUT.  The Responder
   counts the frames that are successfully translated by the DUT.  If
   the count of offered frames is equal to the count of received frames,
   the rate of the offered stream is raised and the test is rerun.  If
   fewer frames are received than were transmitted, the rate of the
   offered stream is reduced and the test is rerun.

   The maximum connection establishment rate is the fastest rate at
   which the count of test frames successfully translated by the DUT is
   equal to the number of test frames sent to it by the Initiator.

   Notes:

   1.  All different source port number destination port number
       combinations SHOULD be used, if the results of the measurement
       are published.  Mostly different source port number destination
       port number combinations MAY be used, if the results of the
       measurement are not published, but they are used only to
       determine a good enough frame rate for the preliminary test phase
       preparing the test system for the real test phase.

   2.  In practice, we RECOMMEND the usage of binary search.

   3.  As for the successful translation, the Responder MAY (or SHOULD?)
       check that the source IP address is different than the original
       source IP address set by the Initiator.

4.5.  Real Test Phase

   As for the traffic direction, there are three possible cases during
   the real test phase:

   o  bidirectional traffic: The Initiator sends test frames to the
      Responder and the Responder sends test frames to the Initiator.




Lencse & Shima          Expires November 18, 2021               [Page 8]


Internet-Draft       Benchmarking Stateful Gateways             May 2021


   o  unidirectional traffic from the Initiator to the Responder: The
      Initiator sends test frames to the Responder but the Responder
      does not send test frames to the Initiator.

   o  unidirectional traffic from the Responder to the Initiator: The
      Responder sends test frames to the Initiator but the Initiator
      does not send test frames to the Responder.

   If the Initiator sends test frames, then it uses pseudorandom source
   port numbers and destination port numbers from the restricted port
   number ranges.  The responder receives the test frames, updates its
   state table and processes the test frames as required by the given
   measurement procedure (e.g. only counts them for throughput test,
   handles timestamps for latency or PDV tests, etc.).

   If the Responder sends test frames, then it uses the four tuples from
   its state table.  The reading order of the state table may follow
   different policies (discussed in Section 4.6).  The Initiator
   receives the test frames, and processes them as required by the given
   measurement procedure.

   As for the actual measurement procedures, we RECOMMEND to use the
   updated ones from Section 7 of [RFC8219].

4.6.  Writing and Reading Order of the State Table

   As for writing policy of the state table of the Responder, we
   RECOMMEND round robin, because it ensures that its entries are
   automatically kept fresh and thus there is no need to handle timeout.

   The Responder can read its state table in various orders.  We
   RECOMMEND one of the following ones:

   o  round robin

   o  pseudorandom (with restriction!)

   o  random permutation (no position is repeated until all positions
      are used).

   Pseudorandom reading order of the state table MAY NOT be used with
   unidirectional traffic from the Responder to the Initiator, because
   if a four tuple is not used until timeout time, then its connection
   is deleted from the connection tracking table of the DUT and a later
   use of the given four tuple will cause frame loss.  There is no such
   problem, when bidirectional traffic is used, because then the state
   table of the Responder is periodically refreshed.




Lencse & Shima          Expires November 18, 2021               [Page 9]


Internet-Draft       Benchmarking Stateful Gateways             May 2021


   We do not see any problem in the round robin reading order, because
   the state table is filled using pseudorandom port numbers.

4.7.  Peculiarities of Stateful Testing

   Stateful testing involves some issues not present in stateless
   testing.

4.7.1.  Timeout Budget

   Even though we do black box testing, one MUST consider timeout and
   carefully manage timeout budget.  For example, if the frame rate is
   high enough, then every single entry of the state table of the
   Responder is refreshed within timeout time and it prevents frame
   sending with a stale four tuple.  If the entries of the state table
   are not refreshed (due to testing with single directional traffic
   from the Responder to the Initiator) then using all four tuples
   within timeout time can keep all connection tracking table entries of
   the DUT alive.

   Special care should be taken for the lower frame rate in the
   preliminary phase.

   If the binary search (or the decreasing of the applied frame rates
   during the frame loss rate test) results in a frame rate that is too
   low to keep alive the connection tracking table entries, then it
   results in the failure of the consecutive tests (the binary search of
   the throughput test counts down to zero).

4.7.2.  Special Warning Against Non-zero Frame Loss Testing

   Several network performance tester vendors include a parameter called
   "Loss Tolerance" (or similar) for the throughput test and several
   benchmarking professionals actually use nonzero values [TOL2001].  If
   frames are lost during stateful testing (especially if it happens
   during a test with unidirectional traffic from the Responder to the
   Initiator) the refreshing of the corresponding connection tracking
   table element is not ensured and it may result in the loss of further
   frames (not due to the low performance of the DUT, but due to using a
   stale four tuple).

5.  Implementation and Experience

   The "stateful" branch of siitperf [SIITPERF] is a partial
   implementation of this concept.

   Our experience is documented in a paper currently under review
   [LEN2021].



Lencse & Shima          Expires November 18, 2021              [Page 10]


Internet-Draft       Benchmarking Stateful Gateways             May 2021


6.  Limitations of using UDP as Transport Layer Protocol

   Stateful NATxy solutions handle TCP and UDP differently, e.g.
   iptables uses 30s timeout for UDP and 60s timeout for TCP.  Thus
   benchmarking results produced using UDP do not necessarily
   characterize the performance of a NATxy gateway well enough, when
   they are used for forwarding Internet traffic.  As for the given
   example, timeout values of the DUT may be adjusted, but it requires
   extra consideration.

   Other differences in handling UDP or TCP are also possible.  Thus we
   recommend that further investigations are to be performed in this
   field.

7.  Acknowledgements

   The authors would like to thank ... (TBD)

8.  IANA Considerations

   This document does not make any request to IANA.

9.  Security Considerations

   We have no further security considerations beyond that of [RFC8219].
   Perhaps they should be cited here so that they be applied not only
   for the benchmarking of IPv6 transition technologies, but also for
   the benchmarking of stateful NATxy.

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2544]  Bradner, S. and J. McQuaid, "Benchmarking Methodology for
              Network Interconnect Devices", RFC 2544,
              DOI 10.17487/RFC2544, March 1999,
              <https://www.rfc-editor.org/info/rfc2544>.

   [RFC4814]  Newman, D. and T. Player, "Hash and Stuffing: Overlooked
              Factors in Network Device Benchmarking", RFC 4814,
              DOI 10.17487/RFC4814, March 2007,
              <https://www.rfc-editor.org/info/rfc4814>.




Lencse & Shima          Expires November 18, 2021              [Page 11]


Internet-Draft       Benchmarking Stateful Gateways             May 2021


   [RFC5180]  Popoviciu, C., Hamza, A., Van de Velde, G., and D.
              Dugatkin, "IPv6 Benchmarking Methodology for Network
              Interconnect Devices", RFC 5180, DOI 10.17487/RFC5180, May
              2008, <https://www.rfc-editor.org/info/rfc5180>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8219]  Georgescu, M., Pislaru, L., and G. Lencse, "Benchmarking
              Methodology for IPv6 Transition Technologies", RFC 8219,
              DOI 10.17487/RFC8219, August 2017,
              <https://www.rfc-editor.org/info/rfc8219>.

10.2.  Informative References

   [DUST1964]
              Durstenfeld, R., "Algorithm 235: Random
              permutation",  Communications of the ACM, vol. 7, no. 7,
              p.420., DOI 10.1145/364520.364540, July 1964,
              <https://dl.acm.org/doi/10.1145/364520.364540>.

   [IIR2020]  Kurahashi, T., Matsuzaki, Y., Sasaki, T., Saito, T., and
              F. Tsutsuji, "Periodic observation report: Internet trends
              as seen from IIJ infrastructure - 2020",  Internet
              Infrastructure Review, vol. 49, Dec 2020,
              <https://www.iij.ad.jp/en/dev/iir/pdf/
              iir_vol49_report_EN.pdf>.

   [LEN2020]  Lencse, G., "Adding RFC 4814 Random Port Feature to
              Siitperf: Design, Implementation and Performance
              Estimation",  International Journal of Advances in
              Telecommunications, Electrotechnics, Signals and Systems,
              vol 9, no 3, pp. 18-26., DOI 10.11601/ijates.v9i3.291,
              2020, <http://www.hit.bme.hu/~lencse/
              publications/291-1113-1-PB.pdf>.

   [LEN2021]  Lencse, G., "Design and Implementation of a Software
              Tester for Benchmarking Stateful NAT64 Gateways: Theory
              and Practice of Extending Siitperf for Stateful
              Tests",  under review in Computer Commuications,  may be
              revised or removed without notice, 2021,
              <http://www.hit.bme.hu/~lencse/publications/SFNAT64-
              tester-for-review.pdf>.







Lencse & Shima          Expires November 18, 2021              [Page 12]


Internet-Draft       Benchmarking Stateful Gateways             May 2021


   [SIITPERF]
              Lencse, G. and Y. Kadobayashi, "Siitperf: An RFC 8219
              compliant SIIT (stateless NAT64) tester written in C++
              using DPDK",  source code,  available from GitHub, 2019,
              <https://github.com/lencsegabor/siitperf>.

   [TOL2001]  Tolly, K., "The real meaning of zero-loss testing",  IT
              World Canada, 2001,
              <https://www.itworldcanada.com/article/kevin-tolly-the-
              real-meaning-of-zero-loss-testing/33066>.

Appendix A.  Change Log

A.1.  00

   Initial version.

Authors' Addresses

   Gabor Lencse
   Szechenyi Istvan University
   Egyetem ter 1.
   Gyor  H-9026
   Hungary

   Email: lencse@sze.hu


   Keiichi Shima
   IIJ Innovation Institute
   Iidabashi Grand Bloom, 2-10-2 Fujimi
   Chiyoda-ku, Tokyo  102-0071
   Japan

   Email: keiichi@iijlab.net
















Lencse & Shima          Expires November 18, 2021              [Page 13]