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RFC 1385

EIP: The Extended Internet Protocol

Pages: 17
Obsoleted by:  6814

ToP   noToC   RFC1385 - Page 1
Network Working Group                                            Z. Wang
Request for Comments: 1385                     University College London
                                                           November 1992

                  EIP: The Extended Internet Protocol
           A Framework for Maintaining Backward Compatibility

Status of this Memo

   This memo provides information for the Internet community. It does
   not specify an Internet standard. Distribution of this memo is


   The Extended Internet Protocol (EIP) provides a framework for solving
   the problem of address space exhaustion with a new addressing and
   routing scheme, yet maintaining maximum backward compatibility with
   current IP. EIP can substantially reduce the amount of modifications
   needed to the current Internet systems and greatly ease the
   difficulties of transition. This is an "idea" paper and discussion is
   strongly encouraged on


   The Internet faces two serious scaling problems: address exhaustion
   and routing explosion [1-2]. The Internet will run out of Class B
   numbers soon and the 32-bit IP address space will be exhausted
   altogether in a few years time.  The total number of IP networks will
   also grow to a point where routing algorithms will not be able to
   perform routing based a flat network number.

   A number of short-term solutions have been proposed recently which
   attempt to make more efficient use of the the remaining address space
   and to ease the immediate difficulties [3-5].  However, it is
   important that a long term solution be developed and deployed before
   the 32-bit address space runs out.

   An obvious approach to this problem is to replace the current IP with
   a new internet protocol that has no backward compatibility with the
   current IP. A number of proposals have been put forward: Pip[7],
   Nimrod [8], TUBA [6] and SIP [14].  However, as IP is really the
   cornerstone of the current Internet, replacing it with a new "IP"
   requires fundamental changes to many aspects of the Internet system
   (e.g., routing, routers, hosts, ARP, RARP, ICMP, TCP, UDP, DNS, FTP).

   Migrating to a new "IP" in effect creates a new "Internet".  The
ToP   noToC   RFC1385 - Page 2
   development and deployment of such a new "Internet" would take a very
   large amount of time and effort. In particular, in order to maintain
   interoperability between the old and new systems during the
   transition period, almost all upgraded systems have to run both the
   new and old versions in parallel and also have to determine which
   version to use depending on whether the other side is upgraded or

   Let us now have a look at the detailed changes that will be required
   to replace the current IP with a completely new "IP" and to maintain
   the interoperability between the new and the old systems.

   1) Border Routers: Border routers have to be upgraded and to provide
      address translation service for IP packets across the boundaries.
      Note that the translation has to be done on the outgoing IP
      packets as well as the in-coming packets to IP hosts.

   2) Subnet Routers: Subnet Routers have to be upgraded and have to
      deal with both the new and the old packet formats.

   3) Hosts: Hosts have to be upgraded and run both the new and the
      old protocols in parallel. Upgraded hosts also have to determine
      whether the other side is upgraded or not in order to choose the
      correct protocol to use.

   4) DNS: The DNS has to be modified to provide mapping for domain
      names and new addresses.

   5) ARP/RARP: ARP/RARP have to be modified, and upgraded hosts and
      routers have to deal with both the old and new ARP/RARP packets.

   6) ICMP: ICMP has to be modified, and the upgraded routers have to
      be able to generate both both old and new ICMP packets.  However,
      it may be impossible for a backbone router to determine
      whether the packet comes from an upgraded host or an IP host but
      translated by the border router.

   7) TCP/UDP Checksum: The pseudo headers may have to be modified to
      use the new addresses.

   8) FTP: The DATA PORT (PORT) command has to be changed to pass new

   In this paper, we argue that an evolutionary approach can extend the
   addressing space yet maintain backward compatibility.  The Extended
   Internet Protocol (EIP) we present here can be used as a framework by
   which a new routing and addressing scheme may solve the problem of
   address exhaustion yet maintain maximum backward compatibility to
ToP   noToC   RFC1385 - Page 3
   current IP.

   EIP has a number of very desirable features:

   1) EIP allows the Internet to have virtually unlimited number of
      network numbers and over 10**9 hosts in each network.

   2) EIP is flexible to accommodate most routing and addressing
      schemes, such as those proposed in Nimrod [8], Pip [7], NSAP [9]
      and CityCodes [10]. EIP also allows new fields such as Handling
      Directive [7] or CI [11] to be added.

   3) EIP can substantially reduce the amount of modifications to
      current systems and greatly ease the difficulties in transition.
      In particular, it does not require the upgraded hosts and subnet
      routers to run two set of protocols in parallel.

   4) EIP requires no changes to all assigned IP addresses and subnet
      structures in local are networks.  and requires no modifications
      to ARP/RARP, ICMP, TCP/UDP checksum.

   5) EIP can greatly ease the difficulties of transition.  During the
      transition period, no upgrade is required to the subnet routers.
      EIP hosts maintain full compatibility with IP hosts within the
      same network, even after the transition period.  During the
      transition period, IP hosts can communicate with any hosts in
      other networks via a simple translation service.

   In the rest of the paper, IP refers to the current Internet Protocol
   and EIP refers to the Extended Internet Protocol (EIP is pronounced
   as "ape" - a step forward in the evolution :-).

Extended Internet Protocol (EIP)

   The EIP header format is shown in Figure 1 and the contents of the
   header follows.
ToP   noToC   RFC1385 - Page 4
       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      |Version|  IHL  |Type of Service|          Total Length         |
      |         Identification        |Flags|      Fragment Offset    |
      |  Time to Live |    Protocol   |         Header Checksum       |
      |                Source Host Number                             |
      |              Destination Host Number                          |
      |     EIP ID    | EIP Ext Length|   EIP Extension (variable)    |

                    Figure 1: EIP Header Format

   Version:  4 bits

     The Version field is identical to that of IP. This field is set
     purely for compatibility with IP hosts. It is not checked by EIP

   IHL:  4 bits

     Internet Header Length is identical to that of IP. IHL is set to
     the length of EIP header purely for compatibility with IP. This
     field is not checked by EIP hosts.  see below the EIP Extension
     Length field for more details)

   Type of Service:  8 bits

     The ToS field is identical to that of IP.

   Total Length:  16 bits

     The Total Length field is identical to that of IP.

   Identification:  16 bits

     The Identification field is identical to that of IP.

   Flags:  3 bits

     The Flags field is identical to that of IP.
ToP   noToC   RFC1385 - Page 5
   Fragment Offset:  13 bits

     The Fragment Offset field is identical to that of IP.

   Time to Live:  8 bits

     The Time to Live field is identical to that of IP.

   Protocol:  8 bits

     The Protocol field is identical to that of IP.

   Header Checksum:  16 bits

     The Header Checksum field is identical to that of IP.

   Source Host Number:  32 bits

     The Source Host Number field is used for identifying the
     source host but is unique only within the source network
     (the equivalent of the host portion of the source IP address).

   Destination Host Number:  32 bits

     The Destination Host Number field is used for identifying the
     destination host but is unique only within the destination network
     (the equivalent of the host portion of the destination IP address).

   EIP ID: 8 bits

     The EIP ID field equals to 0x8A. The EIP ID value is chosen
     in such a way that, to IP hosts and IP routers, an EIP appears
     to be an IP packet with a new IP option of following parameters:

       ---- ----- ------ ------ -----------
         1    0     TBD    var

       Option:  Type=TBD

   EIP Extension Length: 8 bits

        The EIP Extension Length field indicates the total length
        of the EIP ID field, EIP Extension Length field and the
        EIP Extension field in octets. The maximum length that the
        IHL field above can specify is 60 bytes, which is considered
        too short in future. EIP hosts actually use the EIP Extension
        Length field to calculate the total header length:
ToP   noToC   RFC1385 - Page 6
     The total header length = EIP Extension Length + 20.

     The maximum header length of an EIP packet is then 276 bytes.

   EIP Extension: variable

     The EIP Extension field holds the Source Network Number,
     Destination Network Number and other fields. The format
     of the Extension field is not specified here. In its simplest
     form, it can be used to hold two fixed size fields as the
     Source Network Number and Destination Network Number as the
     extension to the addressing space. Since the Extension
     field is variable in length, it can accommodate almost any
     routing and addressing schemes. For example, the Extension
     field can be used to hold "Routing Directive" etc specified
     in Pip [7] or "Endpoint IDs" suggested in Nimrod [8], or the
     "CityCode" [10]. It can also hold other fields such as the
     "Handling Directive" [7] or "Connectionless ID" [11].

   EIP achieves maximum backward compatibility with IP by making the
   extended space appear to be an IP option to the IP hosts and routers.

   When an IP host receives an EIP packets, the EIP Extension field is
   safely ignored as it appears to the IP hosts as an new, therefore an
   unknown, IP option.  As a result, there is no need for translation
   for in-coming EIP packets destined to IP hosts and there is also no
   need for subnet routers to be upgraded during the transition period
   see later section for more details).

   EIP hosts or routers can, however, determine whether a packet is an
   IP packet or an EIP packet by examining the EIP ID field, whose
   position is fixed in the header.

   The EIP Extension field holds the Source and Destination Network
   Numbers, which are only used for communications between different
   networks. For communications within the same network, the Network
   Numbers may be omitted. When the Extension field is omitted, there is
   little difference between an IP packet and an EIP packet.  Therefore,
   EIP hosts can maintain completely compatibility with IP hosts within
   one network.

   In EIP, the Network Numbers and Host Numbers are separate and the IP
   address field is used for the Host Number in EIP. There are a number
   of advantages:

   1) It maintains full compatibility between IP hosts and EIP hosts
      for communications within one network.  Note that the Network
      Number is not needed for communications within one network. A
ToP   noToC   RFC1385 - Page 7
      host can omit the Extension field if it does not need any other
      information in the Extension field, when it communicates with
      another host within the same network.

   2) It allows the IP subnet routers to route EIP packet by treating
      the Host Number as the IP address during the transition period,
      therefore the subnet routers are not required to be updated
      along the border routers.

   3) It allows ARP/RARP to work with both EIP and IP hosts without
      any modifications.

   4) It allows the translation at the border routers much easier.
      During the transition period when the IP addresses are still
      unique, the network portion of the IP addresses can be directly
      extracted and mapped to EIP Network Numbers.

Modifications to IP Systems

   In this section, we outline the modifications to the IP systems that
   are needed for transition to EIP. Because of the similarity between
   the EIP and IP, the amount of modifications needed to current systems
   are substantially reduced.

   1) Network Numbers: Each network has to be assigned a new EIP Network
      Number based on the addressing scheme used. The mapping
      between the IP network numbers and the EIP Network Numbers can
      be used for translation service (see below).

   2) Host Numbers: There is no need for assigning EIP Host Numbers.
      All existing hosts can use their current IP addresses as their
      EIP Host Numbers. New machines may be allocated any number from
      the 32-bit Host Number space since the structure posed on IP
      addressing is no longer necessary. However, during the transition,
      allocation of EIP Host Numbers should still follow the IP
      addressing rule, so that the EIP Host Numbers are still globally
      unique and can still be interpreted as IP addresses.  This will
      allow a more gradual transition to EIP (see below).

   3) Translation Service: During the transition period when the EIP
      Host Numbers are still unique, an address translation service
      can be provided to IP hosts that need communicate with hosts in
      other networks cross the upgraded backbone networks.  The
      translation service can be provided by the border routers.  When a
      border router receives an IP packet, it obtains the Destination
      Network Number by looking up in the mapping table between IP
      network numbers and EIP Network Numbers. The border router then
      adds the Extension field with the Source and Destination Network
ToP   noToC   RFC1385 - Page 8
      Numbers into the packet, and forwards to the backbone networks.
      It is only necessary to translate the out-going IP packets to
      the EIP packets.  There is no need to translate the EIP packets
      back to IP packets even when they are destined to IP hosts.
      This is because that the Extension field in the EIP packets
      appears to IP hosts just an unknown IP option and is ignored by
      the IP hosts during the processing.

   4) Border Routers: The new EIP Extension has to be implemented and
      routing has to be done based on the Network Number in the EIP
      Extension field. The border routers may have to provide the
      translation service for out-going IP packets during the transition

   5) Subnet Routers: No modifications are required during the transition
      period when EIP Host Numbers (which equals to the IP
      addresses) are still globally unique. The subnet routing is carried
      out based on the EIP Host Numbers and when the EIP Host
      IDs are still unique, subnet routers can determine, by treating
      the EIP Host Number as the IP addresses, whether a packet is
      destined to remote networks or not and forward correctly. The
      Extension field in the EIP packets also appear to the IP subnet
      routers an unknown IP option and is ignored in the processing.
      However, subnet routers eventually have to implement the EIP
      Extension and carry out routing based on Network Numbers when
      EIP Host Numbers are no longer globally unique.

   6) Hosts: The EIP Extension has to be implemented.  routing has to
      be done based on the Network Number in the EIP Extension field,
      and also based on the Host Number and subnet mask if subnetting
      is used. IP hosts may communication with any hosts within the
      same network at any time. During the transition period when the
      EIP Host Numbers are still unique, IP hosts can communicate with
      any hosts in other network via the translation service.

   7) DNS: A new resource record (RR) type "N" has to be added for EIP
      Network Numbers. The RR type "A", currently used for IP
      addresses, can still be used for EIP Host Numbers. RR type "N"
      entries have to be added and RR type "PTR" to be updated.  All
      other entries remain unchanged.

   8) ARP/RARP: No modifications are required. The ARP and RARP are
      used for mapping between EIP Host Numbers and physical

   9) ICMP: No modifications are required.

   10) TCP/UDP Checksum: No modifications are required. The pseudo
ToP   noToC   RFC1385 - Page 9
       header includes the EIP Source and Destination IDs instead of
       the source and destination IP addresses.

   11) FTP: No modifications are required during the transition period
       when the IP hosts can still communicate with hosts in other
       networks via the translation service. After the transition period,
       however, the "DATA Port (Port)" command has to be modified to
       pass the port number only and ignore the IP address.  A new FTP
       command may be created to pass both the port number and the EIP
       address to allow a third party to be involved in the file

Transition to EIP

   In this section, we outline a plan for transition to EIP.

   EIP can greatly reduce the complexity of transition. In particular,
   there is no need for the updated hosts and subnet routers to run two
   protocols in parallel in order to achieve interoperability between
   old and new systems.  During the transition, IP hosts can still
   communicate with any machines in the same network without any
   changes.  When the EIP Host Numbers (i.e., the 32-bit IP addresses)
   are still globally unique, IP hosts can contact hosts in other
   networks via translation service provided in the border routers.

   The transition goes as follows:

   Phase 0:
        a) Choose an addressing and routing scheme for the Internet.
        b) Implement the routing protocol.
        c) Assign new Network Numbers to existing networks.

   Phase 1:
        a) Update all backbone routers and border routers.
        b) Update DNS servers.
        c) Start translation service.

   Phase 2:
        a) Update first the key hosts such as mail servers, DNS servers,
        FTP servers and central machines.
        b) Update gradually the rest of the hosts.

   Phase 3:
        a) Update subnet routers
        b) Withdraw the translation service.

   The translation service can be provided as long as the Host IDs
   (i.e., the 32-bit IP address) are still globally unique. When the IP
ToP   noToC   RFC1385 - Page 10
   address space is exhausted, the translation service will be withdrawn
   and the remaining IP hosts can only communicate with hosts within the
   the same network. At the same time, networks can use any numbers in
   the 32-bit space for addressing their hosts.

Related Work

   A recent proposal called IPAE by Hinden and Crocker also attempts to
   minimize the modifications to the current IP system yet to extend the
   addressing space [12]. IPAE uses encapsulation so that the extended
   space is carried as IP data. However, it has been found that the 64
   bits IP data returned by an ICMP packet is too small to hold the
   Global IP addresses. Thus, when a router receives an ICMP generated
   by an old IP host, it is not able to convert it into a proper ICMP
   packet. More details can be found in [13].


   EIP does not necessary increase the header length significantly as
   most of the fields in the current IP will be still needed in the new
   internet protocol. There are debates as to whether fragmentation and
   header checksum are necessary in the new internet protocol but no
   consensus has been reached.

   EIP assumes that IP hosts and routers ignore unknown IP option
   silently as required by [15,16].  Some people have expressed some
   concerns as to whether current IP routers and hosts in the Internet
   can deal with unknown IP options properly.

   In order to look into the issues further, we carried out a number of
   experiments over the use of IP option. We selected 35 hosts over 30
   countries across the Internet. A TCP test program (based on ttcp.c)
   then transmitted data to the echo port (tcp port 7) of each of the
   hosts. Two tests were carried out for each host, one with an unknown
   option (type 0x8A, length 40 bytes) and the other without any

   It is difficult to ensure that the conditions under which the two
   tests run are identical but we tried to make them as close as
   possible. The two tests (test-opt and test-noopt) run on the same
   machine a Sun4) in parallel, i.e., "test-opt& ; test-noopt&" and then
   again in the reverse order, i.e., "test-noopt& ; test-opt&", so each
   test pair actually run twice.  Each host was ping'ed before the tests
   so that the domain name information was cached before the name

   The experiments were carried out at three sites: UCL, Bellcore and
   Cambridge University. The tcp echo throughput (KB/Sec) results are
ToP   noToC   RFC1385 - Page 11
   listed in Appendix.

   The results show that the IP option was dealt with properly and there
   is no visible performance difference under the test setup.


   [1] Chiappa, N., "The IP Addressing Issue", Work in Progress, October

   [2] Clark, D., Chapin, L., Cerf, V., Braden, R., and R. Hobby,
       "Towards the Future Architecture", RFC 1287, MIT, BBN, CNRI, ISI,
       UCDavis , December 1991.

   [3] Solensky, F. and F. Kastenholz, "A Revision to IP Address
       Classifications", Work in Progress, March 1992.

   [4] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Supernetting: an
       Address Assignment and Aggregation Strategy", RFC 1338, BARRNet,
       cisco, Merit, OARnet, June 1992.

   [5] Wang, Z., and J. Crowcroft, "A Two-Tier Address Structure for the
       Internet: a solution to the problem of address space exhaustion",
       RFC 1335, University College London, May 1992.

   [6] Callon, R., "TCP and UDP with Bigger Addresses (TUBA), a Simple
       Proposal for Internet Addressing and Routing", RFC 1347, DEC,
       June 1992.

   [7] Tsuchiya, P., "Pip: The 'P' Internet Protocol", Work in Progress,
       May 1992

   [8] Chiappa N., "A New IP Routing and Addressing Architecture", Work
       in Progress, 1992.

   [9] Colella, R., Gardner, E., and R. Callon, "Guidelines for OSI NSAP
       Allocation in the Internet" RFC 1237, NIST, Mitre, DEC, July

  [10] Deering, S., "City Codes: An Alternative Scheme for OSI NSAP
       Allocation in the Internet", Work in Progress, January 1992.

  [11] Clark, D., "Building routers for the routing of tomorrow", in his
       message to, 14 July 1992.

  [12] Hinden, R., and D. Crocker, "A Proposal for IP Address
       Encapsulation (IPAE): A Compatible Version of IP with Large
       Addresses", Work in Progress, July 1992.
ToP   noToC   RFC1385 - Page 12
  [13] Partridge, C., "Re: Note on implementing IPAE", in his message to, 17 July 1992.

  [14] Deering, S., "SIP: Simple Internet Protocol", Work in Progress,
       September 1992.

  [15] Braden, R., Editor, "Requirements for Internet Hosts
        -- Communication Layers", RFC 1122, ISI, October 1989.

  [16] Almquist, P., Editor, "Requirements for IP Routers", Work in
       Progress, October 1991.


       Throughput Test from UCL (

      Destination Host          test-noopt     test-opt
      -------------------        ----------     ---------          1.128756      1.285345          1.063096      1.239709          0.094336      0.043917          0.075681      0.057120              2.090622      2.228181              1.781374      1.692740                1.937596      2.062579                1.928313      1.936784              11.064797     11.724055              10.861720     10.840306               2.463790      0.810133               1.619088      0.860198                   1.565320      1.983795                   1.564788      1.921803            9.903805     11.335920            9.597806     10.678098                     9.897876      9.382925                    10.487118     11.023745                 5.851407      5.482946                 5.992257      6.243283               0.758044      0.844406               0.784532      0.745606        28.341705     29.655824        24.804125     23.240990             1.045922      1.115802             1.330429      0.978184                10.546733     11.500778                 9.624833     10.214136             1.747777      1.702324             1.676151      1.716435
ToP   noToC   RFC1385 - Page 13                    4.449559      4.145081                    6.431675      5.520443            1.199810      1.374546            0.508642      0.993261          3.626448      3.249590          3.913777      4.094849           1.913925      1.795235           1.154936      1.114775               2.299561      0.599665               1.219282      0.873672              0.252704      0.254199              0.236196      0.172367            1.398777      1.243588            0.876177      0.602964             0.531153      0.803387             0.773935      0.557798                 7.813556      6.764543                 7.969203      6.657325       2.321197      2.402477       2.400196      2.695016             0.545775      0.434672             0.284124      0.266017      2.734685      2.857545      1.168154      1.462789           2.552804      2.897286           3.839141      2.407945                    0.294196      0.403697                    0.236260      0.388755            0.465066      0.515361            0.358646      0.511985                  0.484372      0.816722                  0.705733      1.109228              0.899529      0.822544              1.150058      0.881713          1.438481      1.993749          1.325041      1.833999
ToP   noToC   RFC1385 - Page 14
         Throughput Test from Bellcore (

      Destination Host          test-noopt     test-opt
      ------------------        ----------     ---------          1.820014      2.128104          1.979981      1.866815          0.099289      0.035877          0.118627      0.103763              0.368476      0.694463              0.443269      0.644050                0.721444      0.960068                0.713952      0.953275               2.989907      2.956766               2.100563      2.010292               2.487185      3.896253               1.944085      4.269323                   2.401733      2.735445                   2.950990      2.793121            4.094820      3.618023            2.952650      2.245001                     6.703408      5.928008                     7.389722      5.815122                 2.094152      2.450695                 5.362362      4.690722               0.092698      0.106880               0.496394      0.681994         2.632951      2.631322         3.717170      1.335914             0.684029      0.921621             0.390263      1.095265                 3.186035      2.325166                 3.053797      3.081236             0.154405      0.124795             0.120283      0.105825                   12.588979     12.957880                   13.861733     12.211125            1.280217      1.112675            0.243205      0.631096          6.249789      5.075968          3.387490      4.583511           2.089536      2.233711           2.476758      2.249439               0.653974      0.866246               0.739127      1.130521              1.541682      1.312546              0.906632      1.042793            0.101496      0.091456            0.054245      0.101585
ToP   noToC   RFC1385 - Page 15             1.044443      0.369528             0.596935      0.870377                 9.530348      8.999789                 8.941888      6.075660       1.619418      1.569645       1.156780      1.158000             0.353632      0.416126             0.221522      0.155505      3.433901      3.272839      3.408975      3.130188           5.367756      6.325031           4.828718      5.676571                    0.301120      0.362481                    0.253222      0.519892            0.364221      0.480789            0.456882      0.580778                  0.246523      1.199412                  0.423476      0.630833              0.748642      0.607284              0.716781      0.643030          2.197595      2.072601          2.489748      2.186684
ToP   noToC   RFC1385 - Page 16
          Throughput Test from Cam U (

      Destination Host          test-noopt     test-opt
      ------------------        ----------     ---------           1.128756       1.285345           1.063096       1.239709           0.031218       0.031221           0.034405       0.034925               0.568487       0.731320               0.558238       0.581415                 1.064302       1.284707                 0.852089       1.025779                7.179942       6.270326                5.772485       6.689160                1.661248       1.726725                1.557839       1.428193                    0.600616       0.926690                    0.772887       0.956636             3.645913       4.504969             1.853503       2.671272                      4.190147       3.421110                      2.270988       3.789678                  1.361227       0.993901                  1.977774       2.415716                1.173451       1.298421                1.151376       1.184210        269.589141     238.920081        331.203020     293.556436              0.343598       0.492202              0.582809       0.930958                  1.529277       1.470571                  0.896041       0.894923              0.131180       0.142239              0.137697       0.148895                     1.330794       0.453590                     0.856476       0.714661             0.094793       0.099981             0.167257       0.151625           0.154681       0.178868           1.095814       0.871496            0.454272       0.384484            0.705198       0.690708                0.149511       0.150021                0.071125       0.077257               0.721184       0.549511               0.250285       0.296195             0.519284       0.491745             0.990174       1.009475
ToP   noToC   RFC1385 - Page 17              0.360751       0.418554              0.344268       0.326605                  4.247430       3.305592                  3.139251       2.945469        0.480731       0.782631        0.230471       0.292273              0.239624       0.334286              0.586156       0.419485       3.630623       3.607504       1.743162       2.994665            5.897946       4.650703            5.118200       5.622022                     0.338358       0.225206                     0.113328       0.112637             0.224967       0.359237             0.452945       0.472345                   2.549709       2.037245                   2.229093       2.469851               0.713586       0.810107               0.612278       0.731705           1.438481       1.993749           1.325041       1.833999

Security Considerations

   Security issues are not discussed in this memo.

Author's Address

   Zheng Wang
   Dept of Computer Science
   University College London
   London WC1E 6BT, UK