TThhee BBeerrkkeelleeyy UUNNIIXX((RR))
               TTiimmee SSyynncchhrroonniizzaattiioonn PPrroottooccooll

    _R_i_c_c_a_r_d_o _G_u_s_e_l_l_a_, _S_t_e_f_a_n_o _Z_a_t_t_i_, _a_n_d _J_a_m_e_s _M_. _B_l_o_o_m
              Computer Systems Research Group
                 Computer Science Division
 Department of Electrical Engineering and Computer Science
             University of California, Berkeley
                     Berkeley, CA 94720



IInnttrroodduuccttiioonn

     The  Time  Synchronization  Protocol  (TSP)  has   been
designed for specific use by the program _t_i_m_e_d, a local area
network clock synchronizer for  the  UNIX  4.3BSD  operating
system.  Timed is built on the DARPA UDP protocol [4] and is
based on a master slave scheme.

     TSP serves a dual purpose.  First, it supports messages
for  the  synchronization of the clocks of the various hosts
in a local area network.  Second, it supports  messages  for
the  election that occurs among slave time daemons when, for
any reason,  the  master  disappears.   The  synchronization
mechanism and the election procedure employed by the program
timed are described in other documents [1,2,3].

     Briefly, the synchronization software, which works in a
local area network, consists of a collection of _t_i_m_e _d_a_e_m_o_n_s
(one per machine) and is based on a master-slave  structure.
The  present  implementation keeps processor clocks synchro-
nized within 20 milliseconds.  A _m_a_s_t_e_r _t_i_m_e _d_a_e_m_o_n measures
the  time  difference  between  the  clock of the machine on
which it is running and those of all  other  machines.   The
current  implementation uses ICMP _T_i_m_e _S_t_a_m_p _R_e_q_u_e_s_t_s [5] to
measure the clock difference between machines.   The  master
computes  the  _n_e_t_w_o_r_k _t_i_m_e as the average of the times pro-
vided by nonfaulty clocks.1 It then sends to each _s_l_a_v_e _t_i_m_e
-----------
This  work  was  sponsored by the Defense Advanced
Research Projects Agency (DoD), monitored  by  the
Naval  Electronics  Systems Command under contract
No. N00039-84-C-0089, and  by  the  Italian  CSELT
Corporation.   The views and conclusions contained
in this document are  those  of  the  authors  and
should not be interpreted as representing official
policies, either  expressed  or  implied,  of  the
Defense  Research  Projects Agency, of the US Gov-
ernment, or of CSELT.
  1 A clock is considered to be  faulty  when  its









SMM:12-2     The Berkeley UNIX Time Synchronization Protocol


_d_a_e_m_o_n  the correction that should be performed on the clock
of its machine.   This  process  is  repeated  periodically.
Since  the  correction  is  expressed  as  a time difference
rather than an absolute time,  transmission  delays  do  not
interfere with synchronization.  When a machine comes up and
joins the network, it starts a slave time daemon, which will
ask  the  master  for  the  correct  time and will reset the
machine's clock before any user  activity  can  begin.   The
time  daemons  therefore  maintain  a single network time in
spite of the drift of clocks away from each other.

     Additionally, a time daemon on gateway machines may run
as  a  _s_u_b_m_a_s_t_e_r.   A  submaster  time daemon functions as a
slave on one network that already has a master and as master
on  other networks.  In addition, a submaster is responsible
for propagating broadcast packets from one  network  to  the
other.

     To ensure that service provided is continuous and reli-
able, it is necessary to  implement  an  election  algorithm
that  will elect a new master should the machine running the
current master crash, the  master  terminate  (for  example,
because of a run-time error), or the network be partitioned.
Under our algorithm, slaves are able  to  realize  when  the
master  has  stopped  functioning  and to elect a new master
from among themselves.  It is important to note  that  since
the  failure  of the master results only in a gradual diver-
gence of clock values, the election need not  occur  immedi-
ately.

     All the communication occurring among time daemons uses
the TSP protocol.  While some messages need not be sent in a
reliable way, most communication in TSP requires reliability
not provided by the  underlying  protocol.   Reliability  is
achieved  by  the use of acknowledgements, sequence numbers,
and retransmission when message losses occur.  When  a  mes-
sage  that requires acknowledgment is not acknowledged after
multiple attempts, the time daemon that has sent the message
will  assume that the addressee is down.  This document will
not describe the details of how reliability is  implemented,
but will only point out when a message type requires a reli-
able transport mechanism.

     The message format in TSP is the same for  all  message
types;  however,  in  some instances, one or more fields are
not used.  The next section describes  the  message  format.
The following sections describe in detail the different mes-
sage types, their use and the contents of each field.  NOTE:
The message format is likely to change in future versions of
-----------
value  is  more  than  a  small specified interval
apart from the  majority  of  the  clocks  of  the
machines  on the same network.  See [1,2] for more
details.









The Berkeley UNIX Time Synchronization Protocol     SMM:12-3


timed.



MMeessssaaggee FFoorrmmaatt

     All fields are based upon 8-bit bytes.   Fields  should
be sent in network byte order if they are more than one byte
long.  The structure of a TSP message is the following:

1)   A one byte message type.

2)   A one byte version number, specifying the protocol ver-
     sion which the message uses.

3)   A  two  byte sequence number to be used for recognizing
     duplicate  messages  that  occur  when   messages   are
     retransmitted.

4)   Eight  bytes  of packet specific data.  This field con-
     tains two 4 byte time values, a one byte hop count,  or
     may be unused depending on the type of the packet.

5)   A  zero-terminated string of up to 256 ASCII characters
     with the name of the machine sending the message.

     The following charts describe the message  types,  show
their  fields, and explain their usages.  For the purpose of
the following discussion, a time daemon can be considered to
be  in  one of three states: slave, master, or candidate for
election to master.  Also, the term _b_r_o_a_d_c_a_s_t refers to  the
sending of a message to all active time daemons.



AAddjjttiimmee MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                SSeeccoonnddss ooff AAddjjuussttmmeenntt                 |
  +------------------------------------------------------+
  |             MMiiccrroosseeccoonnddss ooff AAddjjuussttmmeenntt               |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_ADJTIME (1)










SMM:12-4     The Berkeley UNIX Time Synchronization Protocol


     The master sends this message to a slave to communicate
the difference between the clock of the slave and  the  net-
work  time  the  master  has  just computed.  The slave will
accordingly adjust the time of its  machine.   This  message
requires an acknowledgment.



AAcckknnoowwlleeddggmmeenntt MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_ACK (2)


     Both  the  master  and  the slaves use this message for
acknowledgment only.  It is used in several  different  con-
texts, for example in reply to an Adjtime message.



MMaasstteerr RReeqquueesstt MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_MASTERREQ (3)











The Berkeley UNIX Time Synchronization Protocol     SMM:12-5


     A  newly-started time daemon broadcasts this message to
locate a master.  No other action is implied by this packet.
It requires a Master Acknowledgment.



MMaasstteerr AAcckknnoowwlleeddggeemmeenntt
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_MASTERACK (4)


     The master sends this message to acknowledge the Master
Request message and the Conflict Resolution Message.



SSeett NNeettwwoorrkk TTiimmee MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |               SSeeccoonnddss ooff TTiimmee ttoo SSeett                 |
  +------------------------------------------------------+
  |             MMiiccrroosseeccoonnddss ooff TTiimmee ttoo SSeett              |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_SETTIME (5)


     The master sends this message to slave time daemons  to
set  their  time.  This packet is sent to newly started time
daemons and when the network date is changed.   It  contains









SMM:12-6     The Berkeley UNIX Time Synchronization Protocol


the  master's  time as an approximation of the network time.
It requires an  acknowledgment.   The  next  synchronization
round will eliminate the small time difference caused by the
random delay in the communication channel.



MMaasstteerr AAccttiivvee MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_MASTERUP (6)


     The master broadcasts this message to solicit the names
of the active slaves.  Slaves will reply with a Slave Active
message.



SSllaavvee AAccttiivvee MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_SLAVEUP (7)












The Berkeley UNIX Time Synchronization Protocol     SMM:12-7


     A slave sends this message to the master in answer to a
Master Active message.  This message is also sent when a new
slave starts up to inform the master that  it  wants  to  be
synchronized.



MMaasstteerr CCaannddiiddaattuurree MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_ELECTION (8)


     A  slave  eligible  to  become a master broadcasts this
message  when  its  election  timer  expires.   The  message
declares that the slave wishes to become the new master.



CCaannddiiddaattuurree AAcccceeppttaannccee MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_ACCEPT (9)












SMM:12-8     The Berkeley UNIX Time Synchronization Protocol


     A slave sends this message to accept the candidature of
the time daemon that has broadcast an Election message.  The
candidate  will add the slave's name to the list of machines
that it will control should it become the master.



CCaannddiiddaattuurree RReejjeeccttiioonn MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_REFUSE (10)


     After a slave accepts the candidature of a time daemon,
it  will  reply  to  any election messages from other slaves
with this message.  This rejects any candidature other  than
the first received.



MMuullttiippllee MMaasstteerr NNoottiiffiiccaattiioonn MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_CONFLICT (11)











The Berkeley UNIX Time Synchronization Protocol     SMM:12-9


     When two or more masters reply to a Master Request mes-
sage, the slave uses this message to inform one of them that
more than one master exists.



CCoonnfflliicctt RReessoolluuttiioonn MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_RESOLVE (12)


     A  master  which  has been informed of the existence of
other masters broadcasts this message to determine  who  the
other masters are.



QQuuiitt MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_QUIT (13)


     This  message  is sent by the master in three different
contexts: 1)  to  a  candidate  that  broadcasts  an  Master









SMM:12-10    The Berkeley UNIX Time Synchronization Protocol


Candidature  message,  2) to another master when notified of
its existence, 3) to another master if a loop  is  detected.
In all cases, the recipient time daemon will become a slave.
This message requires an acknowledgement.



SSeett DDaattee MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |               SSeeccoonnddss ooff TTiimmee ttoo SSeett                 |
  +------------------------------------------------------+
  |             MMiiccrroosseeccoonnddss ooff TTiimmee ttoo SSeett              |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_SETDATE (22)


     The program _d_a_t_e(1) sends this  message  to  the  local
time daemon when a super-user wants to set the network date.
If the local time daemon is the  master,  it  will  set  the
date; if it is a slave, it will communicate the desired date
to the master.



SSeett DDaattee RReeqquueesstt MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |               SSeeccoonnddss ooff TTiimmee ttoo SSeett                 |
  +------------------------------------------------------+
  |             MMiiccrroosseeccoonnddss ooff TTiimmee ttoo SSeett              |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_SETDATEREQ (23)










The Berkeley UNIX Time Synchronization Protocol    SMM:12-11


     A slave that has received a Set Date message will  com-
municate  the desired date to the master using this message.



SSeett DDaattee AAcckknnoowwlleeddggmmeenntt MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_DATEACK (16)


     The master sends this message to a slave in acknowledg-
ment  of  a  Set  Date Request Message.  The same message is
sent by the local time daemon to the program _d_a_t_e_(_1_) to con-
firm that the network date has been set by the master.



SSttaarrtt TTrraacciinngg MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_TRACEON (17)


     The  controlling  program  _t_i_m_e_d_c sends this message to
the local time daemon to start the  recording  in  a  system









SMM:12-12    The Berkeley UNIX Time Synchronization Protocol


file of all messages received.



SSttoopp TTrraacciinngg MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_TRACEOFF (18)


     _T_i_m_e_d_c  sends  this message to the local time daemon to
stop the recording of messages received.



MMaasstteerr SSiittee MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_MSITE (19)


     _T_i_m_e_d_c sends this message to the local time  daemon  to
find out where the master is running.












The Berkeley UNIX Time Synchronization Protocol    SMM:12-13


RReemmoottee MMaasstteerr SSiittee MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_MSITEREQ (20)


     A local time daemon broadcasts this message to find the
location of the master.  It then  uses  the  Acknowledgement
message to communicate this location to _t_i_m_e_d_c.



TTeesstt MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_TEST (21)


     For  testing  purposes,  _t_i_m_e_d_c sends this message to a
slave to cause its election timer to expire.  NOTE: _t_i_m_e_d is
not normally compiled to support this.














SMM:12-14    The Berkeley UNIX Time Synchronization Protocol


LLoooopp DDeetteeccttiioonn MMeessssaaggee
               |             |             |
     BByyttee 11    |   BByyttee 22    |   BByyttee 33    |   BByyttee 44
  +------------+-------------+-------------+-------------+
  |   TTyyppee     | VVeerrssiioonn NNoo.. |       SSeeqquueennccee NNoo..        |
  +------------+-------------+---------------------------+
  | HHoopp CCoouunntt  |               (( uunnuusseedd ))                |
  +------------+-----------------------------------------+
  |                     (( uunnuusseedd ))                       |
  +------------------------------------------------------+
  |                    MMaacchhiinnee NNaammee                      |
  +------------------------------------------------------+
  |                        .. .. ..                         |
  +------------------------------------------------------+



Type: TSP_LOOP (24)


     This packet is initiated by all masters occasionally to
attempt to detect loops.  All submasters forward this packet
onto  the  networks over which they are master.  If a master
receives a packet it sent out initially,  it  knows  that  a
loop exists and tries to correct the problem.

RReeffeerreenncceess

1.   R.  Gusella  and  S.  Zatti, _T_E_M_P_O_: _A _N_e_t_w_o_r_k _T_i_m_e _C_o_n_-
     _t_r_o_l_l_e_r _f_o_r _D_i_s_t_r_i_b_u_t_e_d _B_e_r_k_e_l_e_y  _U_N_I_X  _S_y_s_t_e_m,  USENIX
     Summer  Conference  Proceedings,  Salt  Lake City, June
     1984.

2.   R. Gusella and S. Zatti,  _C_l_o_c_k  _S_y_n_c_h_r_o_n_i_z_a_t_i_o_n  _i_n  _a
     _L_o_c_a_l _A_r_e_a _N_e_t_w_o_r_k, University of California, Berkeley,
     Technical Report, _t_o _a_p_p_e_a_r.

3.   R. Gusella and S. Zatti, _A_n _E_l_e_c_t_i_o_n  _A_l_g_o_r_i_t_h_m  _f_o_r  _a
     _D_i_s_t_r_i_b_u_t_e_d  _C_l_o_c_k  _S_y_n_c_h_r_o_n_i_z_a_t_i_o_n _P_r_o_g_r_a_m, University
     of California, Berkeley, CS Technical Report #275, Dec.
     1985.

4.   Postel,  J.,  _U_s_e_r _D_a_t_a_g_r_a_m _P_r_o_t_o_c_o_l, RFC 768.  Network
     Information Center, SRI International, Menlo Park, Cal-
     ifornia, August 1980.

5.   Postel, J., _I_n_t_e_r_n_e_t _C_o_n_t_r_o_l _M_e_s_s_a_g_e _P_r_o_t_o_c_o_l, RFC 792.
     Network Information Center,  SRI  International,  Menlo
     Park, California, September 1981.