QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/files/packet/misc/netconf.arc/NETCODE.TXT

Text File | 1988-12-10 | 27KB | 521 lines

                    The KA9Q Internet (TCP/IP) Package: A Progress
                                        Report


                                   Phil Karn, KA9Q



                                       _A_B_S_T_R_A_C_T

                     For over  two  years,  the  author  has  led  the
                development  of  C-language  software implementing the
                ARPA  Internet   protocol   suite   (commonly   called
                "TCP/IP").    Intended  for  amateur  radio  use,  the
                software was originally written on and for the IBM  PC
                and  its clones running MS-DOS.  However, the use of a
                de-facto industry standard protocol set  has  resulted
                in  considerable  interest in and contributions to the
                effort by non-amateurs as well.  The software has been
                "ported"  to several different computers and is enjoy-
                ing increasing use in  both  conventional  Local  Area
                Network  (LAN)  environments as well as amateur packet
                radio.

                     This paper describes  the  considerable  progress
                this  effort  has  made, and reflects on the choice of
                TCP/IP now that significant on-air experience has been
                gained.



           _1.  _I_n_t_r_o_d_u_c_t_i_o_n

                At  the  Fourth  ARRL  Amateur  Radio  Computer  Networking
           Conference in March 1985, I proposed that the ARPA Internet Pro-
           tocols be used in amateur packet  radio.  [2]  [3]  Since  then,
           TCP/IP has become a reality on amateur radio.  Many stations now
           run TCP/IP almost exclusively, and it is increasing steadily  in
           popularity.

           _2.  _W_h_a_t "_T_C_P/_I_P" _i_s - _a_n_d _i_s_n'_t: _A _R_e_v_i_e_w

                Unfortunately, the subject of higher level networking  pro-
           tocols  in  amateur  radio  (including,  but not limited to, the
           famous virtual circuit  vs  datagram  debate)  is  still  highly
           controversial  in  certain  circles. Because many misconceptions
           about TCP/IP persist, I will review what it is and is not.

                TCP and IP are only two  elements  (albeit  very  important
           ones)  of  a  larger, modular set of protocols known as the ARPA
           Internet Protocol Suite.  It must be stressed that only  "higher


                                   December 6, 1988








           level" protocols are specified. In ISO jargon, the ARPA Protocol
           Suite begins with the upper half of the network layer (level 3B,
           also  called  the  internet sublayer) and goes all the way up to
           level 7, the application; levels 1, 2 and  3A  are  deliberately
           left  unspecified.  This is in keeping with ARPA's original pur-
           pose: constructing a uniform _i_n_t_e_r_n_e_t_w_o_r_k  out  of  an  existing
           collection  of  dissimilar  links  and even entire networks that
           would otherwise be incompatible with each other.   There  is  no
           "ARPA  Standard Link Level Protocol" because there is no need to
           require only one; they can all coexist yet still interoperate.

                AX.25 Level 2, X.25 and the network layers of NET/ROM, Tex-
           net,  and  even  COSI  fit  into the Internet model very nicely.
           TCP/IP does _n_o_t compete with these developments (except for  the
           level  4  or  transport  level  components in some of them), but
           rather _c_o_m_p_l_e_m_e_n_t_s them all. By filling a very  real  need,  the
           ARPA  suite  is today he de-facto industry standard for computer
           networking when a wide variety of computers and underlying  net-
           working technologies must be interconnected.

           _3.  _W_h_a_t "_H_i_g_h_e_r _L_e_v_e_l _N_e_t_w_o_r_k_i_n_g" _R_e_a_l_l_y _M_e_a_n_s

                In the ISO model, everything above layer 3 is "end-to-end".
           That  is,  layers  4  through  7  exist  _o_n_l_y  in the end users'
           machines (_h_o_s_t_s in ARPA terminology, _e_n_d _s_y_s_t_e_m_s in ISO) not  in
           the  intermediate  packet  switches  (_g_a_t_e_w_a_y_s).  Unfortunately,
           some have used terminology at  variance  with  this  definition,
           causing  considerable  confusion  as  to  the meaning of "higher
           level networking".  For example, the addition of hop-by-hop ack-
           nowledgements  to a network is _n_o_t "level 3 networking", it is a
           level 2 function.  Further, by strict interpretation of the  ISO
           model,  we  already  have  a de-facto datagram-oriented "network
           layer" in the address field that is part of "AX.25 Level 2".  We
           already have a de-facto "transport" protocol running in the TNCs
           that maintains connections on an end-to-end  basis.   Installing
           "real"  level 3 and 4 protocols means pushing AX.25 back down to
           the link layer it was designed for.

                These distinctions are not just semantic  quibbling.   They
           affects  one's entire view of how the pieces should fit together
           in the network and how it should appear to the users.

           _4.  _C_o_m_p_u_t_e_r _N_e_t_w_o_r_k_i_n_g _v_s _T_e_r_m_i_n_a_l _N_e_t_w_o_r_k_i_n_g

                It should now be apparent that the purpose of higher  level
           protocols  is  to  connect _c_o_m_p_u_t_e_r_s, not just terminals, and to
           use the capabilities of those computers effectively.  (Running a
           "terminal  program"  on a PC is _n_o_t using it effectively.)  True
           networking is much more  than  just  providing  "virtual  wires"
           between dumb terminals[1] or even a dumb terminal and a bulletin
           _________________________
             [1] The term _d_u_m_b _t_e_r_m_i_n_a_l was originally a trademark
           of  Lear Siegler Corporation for their ADM-3 CRT termi-



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           board system.  While packet's use of faster modems,  addressing,
           error  detection and retransmission does provide channel sharing
           and error-free communications, without  higher  level  protocols
           running on the user's computers the result is _q_u_a_l_i_t_a_t_i_v_e_l_y lit-
           tle different than ordinary radio teletype  (RTTY).[2]  In  con-
           trast, _t_r_u_e networking involves one or more high level (applica-
           tion, presentation and transport) protocols plus a multi-tasking
           operating  system  running in the end-user's machine, performing
           end-to-end functions automatically on  behalf  of  human  users.
           For  example,  a  single  system  might respond automatically to
           remote requests for file, accept remotely sent files  and  elec-
           tronic  mail  for  storage,  and  initiate similar operations on
           other computers in response to local commands -- all  simultane-
           ously,  with  minimal  operator  intervention.  In the following
           sections I will review the major ARPA protocols and describe the
           implementation  of  those in the KA9Q Internet software package,
           starting with the top layers and working down.

           _5.  _I_n_t_e_r_n_e_t _S_o_f_t_w_a_r_e _C_o_m_p_o_n_e_n_t_s

                A major goal of the KA9Q Internet package was that multiple
           network  activities  should  go on simultaneously.  This greatly
           increases the usefulness of  the  system,  and  alleviates  many
           other  potentially  troublesome  problems.   For example, "stuck
           connections" caused by the other station  abruptly  disappearing
           are  only  a minor annoyance, as the only resources wasted are a
           few bytes of RAM. The  system  can  still  be  used  by  others;
           keepalive timers aren't necessary.

                Since MS-DOS is not a multitasking system, all of the  pro-
           tocols  were combined in a single MS-DOS program called net.exe,
           and a very simple form of multitasking is  performed  internally
           by a "commutator loop" mechanism.[3] The main loop of  the  pro-
           gram  sequentially  polls  various  routines to see if they need
           service. For example, the keyboard is checked  for  input,  then
           the serial input buffer is checked for characters, then the Eth-
           ernet receiver is checked for packets, then the timer is checked
           to see if a tick occurred, and so on.
           _________________________
           nal. The term quickly became generic, referring to  any
           keyboard/display  (or printer) combination lacking pro-
           grammability and local file storage.  Only recently has
           it  really  become pejorative, since many complete per-
           sonal computers now cost significantly less  than  dumb
           terminals.
             [2] Some call  conventional  packet  operation  "RTTY
           packet".
             [3] This is somewhat similar to the multitasking form
           of FORTH known  as  IPS,  or  Interpreter  for  Process
           Structures.  IPS  was developed by DJ4ZC for use in the
           AMSAT Phase 3 satellites.




                                   December 6, 1988








                When events occur, calls are made to the  appropriate  rou-
           tines;  incoming data triggers the appropriate link level proto-
           col modules, which in turn call the higher  level  modules,  and
           eventually  the  applications  are  called.  This is known as an
           _u_p_c_a_l_l or _p_s_e_u_d_o-_i_n_t_e_r_r_u_p_t mechanism,  and  has  been  used  for
           other  small  networking  packages  such  as MIT's PC/IP.  It is
           important to note that there  is  no  conventional  sleep/wakeup
           mechanism;  each application must provide functions to be called
           asynchronously by the system. These functions  cannot  block  or
           hog  the  processor;  they must respond to the event and return.
           The applications must therefore be structured as state  machines
           driven by upcalls.  While this is a somewhat unusual environment
           for a programmer, it isn't too hard to get used to it.  In fact,
           it  encourages  the programmer to think about what should happen
           for every possible combination of state and event; it's easy  to
           get  sloppy about this in a conventional environment by assuming
           that only the desired event can occur in a certain state.

                I do not mean to imply that the commutator loop approach is
           superior. I originally chose it as a simple expedient, and since
           then I've been surprised by how much I've been able to do with a
           very  small  amount  of  memory.  The  entire executable program
           net.exe, containing all of the protocols about to be  described,
           is  only about 60K bytes. In comparison, the popular PC terminal
           program "Procomm" is almost three times as large![4]  One  major
           drawback of the upcall structure, however, is the lack of appli-
           cation portability. Future developments may include a true  mul-
           titasking   kernel  so  that  a  more  conventional  programming
           environment may be supplied as well.

                The user interface is simple, but functional.  Commands  to
           invoke  each of the applications are provided, along with others
           primarily useful for monitoring and statistics gathering.  Up to
           ten  client  "sessions"  may exist at any one time, and the user
           may switch between them at will.   There  is  no  limit  on  the
           number  of server sessions that may exist at one time other than
           the memory available on the machine for buffering and housekeep-
           ing.

           _5._1.  _T_e_l_n_e_t, _F_T_P _a_n_d _S_M_T_P _A_p_p_l_i_c_a_t_i_o_n_s

                While many application protocols have been built for packet
           networks, three are most useful: remote login, file transfer and
           mail transfer.  This is reflected in the "big three" ARPA Inter-
           net  application  protocols:  Telnet, FTP and SMTP respectively.
           Each application protocol is further broken down into _c_l_i_e_n_t and
           _s_e_r_v_e_r  halves. Clients act on behalf of local users by initiat-
           ing communication with remote servers that passively await their
           requests.
           _________________________
             [4] I do admit that net.exe lacks  certain  essential
           features, e.g., exploding windows and sound effects.




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                Clients and servers for all three protocols  are  presently
           in  the  software,  although the telnet server does nothing more
           than route an incoming connection to the console  for  keyboard-
           to-keyboard chatting.  (MS-DOS isn't a timesharing system, so it
           wasn't possible to provide conventional  telnet  service).   FTP
           supports  both  ASCII  (default) and binary file transfers, with
           passwords protecting against unauthorized file access.  SMTP  is
           presently  functional  but  it  does  not  have  the features of
           mailers found on larger systems such as mailing lists and  mail-
           level  forwarding.   Two  miscellaneous  application servers are
           also provided: echo and discard.  They are intended  mainly  for
           testing.

           _5._2.  _T_C_P _a_n_d _U_D_P _T_r_a_n_s_p_o_r_t _P_r_o_t_o_c_o_l_s

                The applications just described all use TCP, the  Transmis-
           sion  Control Protocol.  TCP is a transport/session layer (level
           4 and 5) protocol that provides virtual circuit services  on  an
           end-to-end  basis.   The  use  of TCP is not mandatory, however.
           Some important applications prefer not to use virtual  circuits,
           so  an alternative is supplied: UDP, the User Datagram Protocol.
           UDP is important for routing algorithms, information  broadcast-
           ing  and  transaction-oriented  applications such as the Network
           File System (NFS).[5]

                The TCP was the first module written for the package and is
           now quite mature.  Three upcalls are provided to the application
           layer: receive, send and protocol  state  change.   The  receive
           upcall  indicates  that  data has arrived which may be read from
           the receive queue by the application.  The send upcall indicates
           that  outgoing  data  has  been  acknowledged, freeing up buffer
           space that may now be used for  additional  transmissions.   The
           protocol  state  change  upcall  indicates  when connections are
           opened and closed, and applications use these to drive their own
           state  machines  and  to determine end of file.  Much effort has
           gone into tuning the TCP retransmission algorithms for efficient
           operation   across  amateur  packet  radio,  including  a  novel
           approach to measuring round trip times accurately during periods
           of high packet loss.  [6]

                The UDP module is much simpler than  TCP.  Only  a  receive
           data upcall is provided.

           _5._3.  _I_n_t_e_r_n_e_t _P_r_o_t_o_c_o_l (_I_P)

                The core protocol of the ARPA Internet is called, naturally
           _________________________
             [5] NFS is not implemented in the package (yet) so it
           will not be described here.  However, its popularity is
           mushrooming around the Internet.  On many Ethernet  lo-
           cal  area  networks  (LANs) NFS/UDP traffic now exceeds
           that using TCP.




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           enough, the Internet Protocol (IP).  IP sits  immediately  above
           the  existing lower level networks (_s_u_b_n_e_t_s in ARPA terms). This
           is the only mandatory protocol in the entire suite.  The  higher
           level protocol in use (TCP, etc) need be agreed upon only by the
           hosts involved, but you can't be "on the  Internet"  unless  you
           run IP.

                Since IP is "spoken" by  hosts  and  "interpreted"  by  the
           gateways (packet switches), I found it convenient to split my IP
           into two halves.  The  upper  half  contains  the  parts  of  IP
           relevant  to a host (outgoing packet generation, incoming packet
           demultiplexing, fragment reassembly).  The lower  half  contains
           the  IP packet switching components (routing and fragmentation).
           Every host is also a gateway, i.e., it  will  route  and  switch
           traffic that is just passing through in addition to sourcing and
           sinking its own traffic.  If the code is to be run  on  a  dedi-
           cated gateway, the host functions can be removed to save space.

                The packet routing portion of my IP includes a  generalized
           form  of  _s_u_b_n_e_t_t_i_n_g, the ability to structure the address space
           into a tree-shaped hierarchy. [3]  Each  entry  in  the  routing
           table includes a width field saying how many bits in its address
           field are significant. When packets are  routed,  the  algorithm
           finds  the routing table entry providing the "best match" to the
           leading bits of the  destination  address.   This  allows  large
           blocks of addresses that share a common next hop, e.g., all west
           coast addresses in an east coast switch, to share a single rout-
           ing  table  entry.  This  reduces  the average size of a routing
           table enormously while still allowing arbitrary routes to be set
           up.  Even this relatively complex technique, however, only takes
           about 6 milliseconds to route a packet on the  IBM  PC,  thereby
           refuting the argument that datagram routing "costs" too much.

                No automatic routing algorithm  is  provided  as  yet;  the
           routes  must  be set up manually. Automatic routing is clearly a
           desirable long-term goal, but it is a difficult and  challenging
           problem in any network so I have deferred it.

           _5._4.  _S_u_b_n_e_t _P_r_o_t_o_c_o_l_s

                Link/subnet drivers for AX.25 Level 2, Ethernet  and  asyn-
           chronous  point-to-point  links  are  presently provided. In the
           spirit of the Internet, others  can  be  added  easily  as  they
           become available (e.g., NET/ROM, Texnet and COSI).

                The AX.25 Level 2 driver is at present very simple; each IP
           datagram  is  encapsulated in a single AX.25 UI (connectionless)
           frame.  The KISS TNC [1] was  developed  to  allow  these  "raw"
           packets  to  be  generated.   This  was an expedient for initial
           operation; it is _n_o_t the only way that IP can be run on  top  of
           AX.25.    It   is   entirely  possible  to  use  the  full-blown
           connection-oriented AX.25 protocol  under  IP  if  necessary  to
           improve hop-by-hop reliability; this will have to be done to use
           the internals of NET/ROM to move IP traffic, for example. On the


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           other  hand,  collision-free  backbone channels would do well to
           avoid the extra complexity  and  overhead  of  link  level  ack-
           nowledgements.

                It is incorrect to say that IP cannot be run efficiently on
           noisy poor channels because of its relatively large header size.
           While not done at  present,  the  subnet  or  link  may  perform
           intranet  fragmentation.  That  is,  it  may  chop  up  a single
           datagram into multiple smaller packets and reassemble them tran-
           sparently at the other end of the link before passing them up to
           IP.  This is distinct from the internet level fragmentation done
           by IP, and is preferable for performance reasons when the subnet
           has an unusually small packet size limit.  As for  the  "inordi-
           nate" overhead associated with a 40-byte TCP/IP header, consider
           that even at 1200 baud, 40 bytes  takes  only  a  quarter  of  a
           second  to send.  Many stations spend more than this just keying
           up the transmitter.  As faster modems (e.g., the new  WA4DSY  56
           kbps design) become widespread, header overhead will become even
           more of a non-issue.

           _5._5.  _T_h_e _A_d_d_r_e_s_s _R_e_s_o_l_u_t_i_o_n _P_r_o_t_o_c_o_l (_A_R_P)

                The Internet Protocol provides its own addressing  indepen-
           dent  of that used in the subnetworks. It is therefore necessary
           to map IP addresses into subnet addresses for each  hop.   Some-
           times  this can be done by making the subnet address part of the
           IP address, but frequently this isn't possible because the  sub-
           net address is too big.  This is the case with both Ethernet and
           AX.25, so the Address Resolution Protocol was implemented. [7]

                The ARP module in the package serves both subnet protocols.
           Since  ARP  requires a broadcast facility in the subnet, I chose
           "QST-0" as the AX.25 broadcast  address.   Manual  commands  are
           provided  to  manipulate  the  ARP  translation table, either to
           override the automatic mechanism or to specify  multi-hop  digi-
           peater  paths.  The latter must be done manually since the AX.25
           subnet can no longer provide broadcasting when  digipeaters  are
           involved.

           _6.  _A_v_a_i_l_a_b_i_l_i_t_y

                The entire software package, including executable programs,
           complete   source   code  and  documentation,  is  available  to
           interested amateurs for the cost of copying  only.   It  may  be
           freely  used  and copied for noncommercial purposes only.  Brian
           Lloyd, WB6RQN, handles the distribution on MS-DOS format  floppy
           disks;  send  him  $5  to cover costs and he will provide disks,
           mailers and postage. Persons outside the US should add enough to
           cover higher postage costs.

           _7.  _C_r_e_d_i_t_s

                Many people  have  contributed  in  various  ways  to  this
           effort,  so  what  follows  is  necessarily only a partial list.


                                   December 6, 1988








           Bdale Garbee N3EUA wrote the mail command  _b_m,  and  coordinates
           the integration of software releases.  Mike Chepponis K3MC wrote
           the first KISS software for the TNC-2 and has been  instrumental
           in  encouraging others to support other TNCs (see [1] for a com-
           plete list).  Jon Bloom KE3Z contributed the driver for the HAPN
           HDLC  adapter  card  for  the PC.  Brian Lloyd WB6RQN has widely
           promoted the amateur use of TCP/IP, writing  introductory  maga-
           zine  articles  geared  to the novice user.  When the code first
           became available, Brian organized a local group of users in  the
           Washington  DC area that has since grown to several dozen; their
           feedback, as well as that of other groups around the world,  has
           proven  very useful in improving the package.  Brian also spends
           a considerable amount of time distributing the package on floppy
           disk by mail.

                While I wrote the bulk of net.exe myself, others  supported
           my  efforts  by  patiently answering my many questions about the
           details of the protocols.  Thanks go to Dave Mills W3HCF of  the
           University of Delaware and Jon Postel of the University of Cali-
           fornia Information Sciences Institute.

           _8.  _R_e_f_e_r_e_n_c_e_s


           1.   Chepponis, M., and Karn, P., "The KISS TNC: A simple  Host-
                to-TNC communications protocol," this conference.

           2.   Karn, P., "TCP/IP: A Proposal for Amateur Packet Radio Lev-
                els 3 and 4," Fourth ARRL Amateur Radio Computer Networking
                Conference, San Francisco, March 1985, p. 4.62.

           3.   Karn, P., "Addressing and Routing Issues in Amateur  Packet
                Radio,"  Fourth  ARRL  Amateur  Radio  Computer  Networking
                Conference, San Francisco, March 1985, p. 4.69.

           4.   "For own in-house network, COS selects TCP/IP,"  Data  Com-
                munications magazine, June 1987.

           5.   Bloom, J., "NET.EXE: Beyond the TNC," Gateway  Vol.  3  No.
                12, Feb 6, 1987.

           6.   Karn, P., and Partridge,  C.,  "Improving  Round-Trip  Time
                Estimates   in   Reliable   Transport  Protocols,"  SIGCOMM
                Workshop proceedings, Stowe, Vt., August 1987.

           7.   Plummer, "Address Resolution Protocol," ARPA RFC 826.










                                   December 6, 1988