wegrzyn@encore.UUCP (Chuck Wegrzyn) (02/25/85)
I am posting this over the network because I believe that
others are interested in knowing the protocols of UUCP.
Below is listed all the information that I have acquired
to date. This includes the initial handshaking phase, though
not the login phase. It also doesn't include information
about the data transfer protocol for non-packet networks
(the -G option left off the uucico command line). But, just
hold on - I am working on that stuff.
For a point of information : the slave is the UUCP site being
dialed, and the master is the one doing the calling up. The
protocols listed in the handshaking and termination phase are
independent of any UUCP site : it is universal. The stuff in
the work phase depends on the specific protocol chosen. The
concepts in the work phase are independent of protocol, ie. the
sequences are the same. It is just the lower level stuff that
changes from protocol to protocol. I have access only to level
g and will document it as I begin to understand it.
Most of the stuff you see here is gotten from the debug phase
of the current BSD UUCP system.
I hope this is useful. Maybe this will get some of the real
'brains' in UUCP to get off their duffs and provide some real
detail. In any case, if you have any questions please feel
free to contact me. I will post any questions and answers over
the network.
Chuck Wegrzyn
{allegra,decvax,ihnp4}!encore!wegrzyn
(617) 237-1022
UUCP Handshake Phase
====================
Master Slave
------ -----
<----- \020Shere\0 (1)
(2) \020S<mastername> <switches>\0 ----->
<----- \020RLCK\0 (3)
\020RCB\0
\020ROK\0
\020RBADSEQ\0
<----- \020P<protos>\0 (4)
(5) \020U<proto>\0 ----->
\020UN\0
(6) ...
(0) This communication happens outside of the packet communication that
is supported. If the -G flag is sent on the uucico line, all
communications will occur without the use of the packet
simulation software. The communication at this level is just
the characters listed above.
(1) The slave sends the sequence indicated, while the master waits for
the message.
(2) The slave waits for the master to send a response message. The message
is composed of the master's name and some optional switches.
The switch field can include the following
-g (set by the -G switch on the
master's uucico command line.
Indicates that communication
occurs over a packet switch net.)
-xN (set by the -x switch on the
master's uucico command line.
The number N is the debug level
desired.)
-QM (M is really a sequence number
for the communication.)
Each switch is separated from the others by a 'blank' character.
(3) The slave will send one of the many responses. The meanings appear to
be :
RLCK
This message implies that a 'lock' failure occurred:
a file called LCK..mastername couldn't be created since
one already exists. This seems to imply that the master
is already in communication with the slave.
RCB
This message will be sent out if the slave requires a
call back to the master - the slave will not accept a
call from the master but will call the master instead.
ROK
This message will be returned if the sequence number that
was sent in the message, attached to the -Q switch, from
the master is the same as that computed on the slave.
RBADSEQ
Happens if the sequence numbers do not match.
(Notes on the sequence number - if a machine does not keep
sequence numbers, the value is set to 0. If no -Q switch
is given in the master's line, the sequence number is
defaulted to 0.
The sequence file, SQFILE, has the format
<remotename> <number> <month>/<day>-<hour>:<min>
where <remotename> is the name of a master and <number>
is the previous sequence number. If the <number> field
is not present, or if it is greater than 9998, it is
set to 0. The <number> field is an ascii representation
of the number. The stuff after the <number> is the time
the sequence number was last changed, this information
doesn't seem important.)
(4) The slave sends a message that identifies all the protocols that
it supports. It seems that BSD supports 'g' as the normal case.
Some sites, such as Allegra, support 'e' and 'g', and a few
sites support 'f' as well. I have no information about these
protocols. The exact message sent might look like
\020Pefg\0
where efg indicates that this slave supports the e,f and g
protocols.
(5) The slave waits for a response from the master with the chosen
protocol. If the master has a protocol that is in common the
master will send the message
\020U<proto>\0
where <proto> is the protocol (letter) chosen. If no protocol
is in common, the master will send the message
\020UN\0
(6) At this point both the slave and master agree to use the designated
protocol. The first thing that now happens is that the master
checks for work.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
UUCP Work Phase
===============
Master Slave
------ -----
(a) Master has UUCP Work
(1) X file1 file2 ----->
<----- XN (2)
XY
When the master wants the slave to do a 'uux' command
it sends the X message. If the slave can't or won't
do it, the slave will send an XN message. Otherwise
it will send an XY message.
(b) Master wants to send a file
(1) S file1 file2 user options ----->
<----- SN2 (2)
SN4
SY
<---- <data exchanged>----> (3)
<----- CY (4)
CN5
If the master wishes to send a file to the slave, it will
send a S message to the slave. If the slave can or will do
the transfer, it sends a SY message. If the slave has a
problem creating work files, it sends a SN4 message. If
the target file can't be created (because of priv's etc)
it sends a SN2 message.
The file1 argument is the source file, and file2 is the
(almost) target filename. If file2 is a directory, then
the target filename is composed of file2 concatenated
with the "last" part of the file1 argument. Note, if the
file2 argument begins with X, the request is targeted to
UUX and not the normal send.
The user argument indicates who, if anyone, is to be notified
if the file has been copied. This user must be on the slave
system.
I am not sure what the options argument does.
After the data has been exchanged the slave will send one of
two messages to the master. A CY message indicates that every-
thing is ok. The message CN5 indicates that the slave had
some problem moving the file to it's permanent location. This
is not the same as a problem during the exchange of data : this
causes the slave to terminate operation.
(c) Master wishes to receive a file.
(1) R file1 file2 user ----->
<----- RN2 (2)
RY mode
(3) <---- <data exchanged> ---->
(4) CY ----->
CN5
If the master wishes the slave to send a file, the master sends
a R message. If the slave has the file and can send it, the
slave will respond with the RY message. If the slave can't find
the file, or won't send it the RN2 message is sent. It doesn't
appear that the 'mode' field of the RY message is used.
The argument file1 is the file to transfer, unless it is a
directory. In this case the file to be transferred is built
of a concatenation of file1 with the "last" part of the file2
argument.
If anything goes wrong with the data transfer, it results in
both the slave and the master terminating.
After the data has been transferred, the master will send an
acknowledgement to the slave. If the transfer and copy to the
destination file has been successful, the master will send the
CY message. Otherwise it will send the CN5 message.
(d) Master has no work, or no more work.
(1) H ----->
<----- HY (2)
HN
(3) HY ----->
<---- HY (4)
(5) ...
The transfer of control is initiated with the master sending
a H message. This message tells the slave that the master has
no work, and the slave should look for work.
If the slave has no work it will respond with the HY message.
This will tell the master to send an HY message, and turn off
the selected protocol. When the HY message is received by the
slave, it turns off the selected protocol as well. Both the
master and slave enter the UUCP termination phase.
If the slave does have work, it sends the HN message to the
master. At this point, the slave becomes the master. After
the master receives the HN message, it becomes the slave.
The whole sequence of sending work starts over again. Note,
the transmission of HN doesn't force the master to send any
other H messages : it waits for stuff from the new master.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
UUCP Termination Sequence
=========================
Master Slave
------ -----
(1) \020OOOOOO\0 ----->
<----- \020OOOOOOO\0 (2)
At this point all conversation has completed normally.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
UUCP Data Transfers
===================
After the initial handshake the systems send messages in one
of two styles : packet and not packet. A Packet protocol is
just raw data transfers : there is no protocol or acknowledgements;
this appears to assume that the lower level is a packet network
of some type. If the style is not Packet, then extra work is
done. I am still working on this stuff.guy@rlgvax.UUCP (Guy Harris) (02/28/85)
> I have access only to level g and will document it as I begin to > understand it. In an issue of ";login:" a couple of years ago, there was a summary of a talk given by Lauren Weinstein on UUCP at USENIX which gave some useful information on the "g" protocol. > (4) The slave sends a message that identifies all the protocols that > it supports. It seems that BSD supports 'g' as the normal case. > Some sites, such as Allegra, support 'e' and 'g', and a few > sites support 'f' as well. I have no information about these > protocols. The "protocol" layer is actually two layers: the actual link-level protocol, and a simple encapsulation of data. The "e" protocol is, I believe, an encapsulation intended to run on top of protocols like TCP/IP - it does regular UNIX reads and writes to the descriptor, under the assumption that the kernel is providing all the flow control and error recovery needed. The 4.3BSD UUCP provides a "t" protocol for the same purpose (UUCP over the ARPANET or over an Ethernet is kind of neat). The "f" protocol assumes a flow-controlled, mostly reliable, 7-bit data path - it was intended for use over X.25 lines using PADs on both ends assembling 7-bit ASCII into X.25 packets and disassembling them at the receiving end. System V's UUCP also has an "x" protocol that runs on top of the BX.25 code that they "supply" in the form of zero-length source files with standard System V. Guy Harris {seismo,ihnp4,allegra}!rlgvax!guy