This is uucp.info, produced by makeinfo version 4.1 from uucp.texi. START-INFO-DIR-ENTRY * UUCP: (uucp). Transfer mail and news across phone lines. END-INFO-DIR-ENTRY This file documents Taylor UUCP, version 1.07. Copyright (C) 1992, 1993, 1994, 1995, 2002 Ian Lance Taylor Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "Copying" are included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "Copying" may be included in a translation approved by the author instead of in the original English.  File: uucp.info, Node: The Initial Handshake, Next: UUCP Protocol Commands, Prev: UUCP Protocol, Up: UUCP Protocol The Initial Handshake --------------------- Before the initial handshake, the caller will usually have logged in the called machine and somehow started the UUCP package there. On Unix this is normally done by setting the shell of the login name used to `/usr/lib/uucp/uucico'. All messages in the initial handshake begin with a `^P' (a byte with the octal value `\020') and end with a null byte (`\000'). A few systems end these messages with a line feed character (`\012') instead of a null byte; the examples below assume a null byte is being used. Some options below are supported by QFT, which stands for Queued File Transfer, and is (or was) an internal Bell Labs version of UUCP. Taylor UUCP size negotiation was introduced by Taylor UUCP, and is also supported by DOS based UUPlus and Amiga based wUUCP and UUCP-1.17. The initial handshake goes as follows. It is begun by the called machine. called: `\020Shere=hostname\000' The hostname is the UUCP name of the called machine. Older UUCP packages do not output it, and simply send `\020Shere\000'. caller: `\020Shostname options\000' The hostname is the UUCP name of the calling machine. The following options may appear (or there may be none): `-QSEQ' Report sequence number for this conversation. The sequence number is stored at both sites, and incremented after each call. If there is a sequence number mismatch, something has gone wrong (somebody may have broken security by pretending to be one of the machines) and the call is denied. If the sequence number changes on one of the machines, perhaps because of an attempted breakin or because a disk backup was restored, the sequence numbers on the two machines must be reconciled manually. `-xLEVEL' Requests the called system to set its debugging level to the specified value. This is not supported by all systems. `-pGRADE' `-vgrade=GRADE' Requests the called system to only transfer files of the specified grade or higher. This is not supported by all systems. Some systems support `-p', some support `-vgrade='. UUPlus allows either `-p' or `-v' to be specified on a per-system basis in the `SYSTEMS' file (`gradechar' option). `-R' Indicates that the calling UUCP understands how to restart failed file transmissions. Supported only by System V Release 4 UUCP, QFT, and Taylor UUCP. `-ULIMIT' Reports the ulimit value of the calling UUCP. The limit is specified as a base 16 number in C notation (e.g., `-U0x1000000'). This number is the number of 512 byte blocks in the largest file which the calling UUCP can create. The called UUCP may not transfer a file larger than this. Supported only by System V Release 4 UUCP, QFT and UUPlus. UUPlus reports the lesser of the available disk space on the spool directory drive and the ulimit variable in `UUPLUS.CFG'. Taylor UUCP understands this option, but does not generate it. `-N[NUMBER]' Indicates that the calling UUCP understands the Taylor UUCP size negotiation extension. Not supported by traditional UUCP packages. Supported by UUPlus. The optional number is a bitmask of features supported by the calling UUCP, and is described below. called: `\020ROK\000' There are actually several possible responses. `ROK' The calling UUCP is acceptable, and the handshake proceeds to the protocol negotiation. Some options may also appear; see below. `ROKN[NUMBER]' The calling UUCP is acceptable, it specified `-N', and the called UUCP also understands the Taylor UUCP size limiting extensions. The optional number is a bitmask of features supported by the called UUCP, and is described below. `RLCK' The called UUCP already has a lock for the calling UUCP, which normally indicates the two machines are already communicating. `RCB' The called UUCP will call back. This may be used to avoid impostors (but only one machine out of each pair should call back, or no conversation will ever begin). `RBADSEQ' The call sequence number is wrong (see the `-Q' discussion above). `RLOGIN' The calling UUCP is using the wrong login name. `RYou are unknown to me' The calling UUCP is not known to the called UUCP, and the called UUCP does not permit connections from unknown systems. Some versions of UUCP just drop the line rather than sending this message. If the response is `ROK', the following options are supported by System V Release 4 UUCP and QFT. `-R' The called UUCP knows how to restart failed file transmissions. `-ULIMIT' Reports the ulimit value of the called UUCP. The limit is specified as a base 16 number in C notation. This number is the number of 512 byte blocks in the largest file which the called UUCP can create. The calling UUCP may not send a file larger than this. Also supported by UUPlus. Taylor UUCP understands this option, but does not generate it. `-xLEVEL' I'm not sure just what this means. It may request the calling UUCP to set its debugging level to the specified value. If the response is not `ROK' (or `ROKN') both sides hang up the phone, abandoning the call. called: `\020Pprotocols\000' Note that the called UUCP outputs two strings in a row. The protocols string is a list of UUCP protocols supported by the caller. Each UUCP protocol has a single character name. These protocols are discussed in more detail later in this document. For example, the called UUCP might send `\020Pgf\000'. caller: `\020Uprotocol\000' The calling UUCP selects which protocol to use out of the protocols offered by the called UUCP. If there are no mutually supported protocols, the calling UUCP sends `\020UN\000' and both sides hang up the phone. Otherwise the calling UUCP sends something like `\020Ug\000'. Most UUCP packages will consider each locally supported protocol in turn and select the first one supported by the called UUCP. With some versions of HDB UUCP, this can be modified by giving a list of protocols after the device name in the `Devices' file or the `Systems' file. For example, to select the `e' protocol in `Systems', airs Any ACU,e ... or in Devices, ACU,e ttyXX ... Taylor UUCP provides the `protocol' command which may be used either for a system (*note Protocol Selection::) or a port (*note port File::). UUPlus allows specification of the protocol string on a per-system basis in the `SYSTEMS' file. The optional number following a `-N' sent by the calling system, or an `ROKN' sent by the called system, is a bitmask of features supported by the UUCP package. The optional number was introduced in Taylor UUCP version 1.04. The number is sent as an octal number with a leading zero. The following bits are currently defined. A missing number should be taken as `011'. `01' UUCP supports size negotiation. `02' UUCP supports file restart. `04' UUCP supports the `E' command. `010' UUCP requires the file size in the `S' and `R' commands to be in base 10. This bit is used by default if no number appears, but should not be explicitly sent. `020' UUCP expects a dummy string between the notify field and the size field in an `S' command. This is true of SVR4 UUCP. This bit should not be used. `040' UUCP supports the `q' option in the `S', `R', `X', and `E' commands. After the protocol has been selected and the initial handshake has been completed, both sides turn on the selected protocol. For some protocols (notably `g') a further handshake is done at this point.  File: uucp.info, Node: UUCP Protocol Commands, Next: The Final Handshake, Prev: The Initial Handshake, Up: UUCP Protocol UUCP Protocol Commands ---------------------- Each protocol supports a method for sending a command to the remote system. This method is used to transmit a series of commands between the two UUCP packages. At all times, one package is the master and the other is the slave. Initially, the calling UUCP is the master. If a protocol error occurs during the exchange of commands, both sides move immediately to the final handshake. The master will send one of five commands: `S', `R', `X', `E', or `H'. Any file name referred to below is either an absolute file name beginning with `/', a public directory file name beginning with `~/', a file name relative to a user's home directory beginning with `~USER/', or a spool directory file name. File names in the spool directory are not absolute, but instead are converted to file names within the spool directory by UUCP. They always begin with `C.' (for a command file created by `uucp' or `uux'), `D.' (for a data file created by `uucp', `uux' or by an execution, or received from another system for an execution), or `X.' (for an execution file created by `uux' or received from another system). All the commands other than the `H' command support options. The `q' option indicates that the command argument strings are backslash quoted. If the `q' option appears, then any backslash in one of the arguments should be followed by either a backslash or three octal digits. The backslash quoting is interpreted as in a C string. If the `q' option does not appear, backslashes in the strings are not treated specially. The `q' option was introduced in Taylor UUCP version 1.07. * Menu: * The S Command:: The S Command * The R Command:: The R Command * The X Command:: The X Command * The E Command:: The E Command * The H Command:: The H Command  File: uucp.info, Node: The S Command, Next: The R Command, Prev: UUCP Protocol Commands, Up: UUCP Protocol Commands The S Command ............. master: `S FROM TO USER -OPTIONS TEMP MODE NOTIFY SIZE' The `S' and the `-' are literal characters. This is a request by the master to send a file to the slave. FROM The name of the file to send. If the `C' option does not appear in OPTIONS, the master will actually open and send this file. Otherwise the file has been copied to the spool directory, where it is named TEMP. The slave ignores this field unless TO is a directory, in which case the basename of FROM will be used as the file name. If FROM is a spool directory filename, it must be a data file created for or by an execution, and must begin with `D.'. TO The name to give the file on the slave. If this field names a directory the file is placed within that directory with the basename of FROM. A name ending in `/' is taken to be a directory even if one does not already exist with that name. If TO begins with `X.', an execution file will be created on the slave. Otherwise, if TO begins with `D.' it names a data file to be used by some execution file. Otherwise, TO should not be in the spool directory. USER The name of the user who requested the transfer. OPTIONS A list of options to control the transfer. The following options are defined (all options are single characters): `C' The file has been copied to the spool directory (the master should use TEMP rather than FROM). `c' The file has not been copied to the spool directory (this is the default). `d' The slave should create directories as necessary (this is the default). `f' The slave should not create directories if necessary, but should fail the transfer instead. `m' The master should send mail to USER when the transfer is complete. `n' The slave should send mail to NOTIFY when the transfer is complete. `q' Backslash quoting is applied to the FROM, TO, USER, and NOTIFY arguments. *Note UUCP Protocol Commands::. This option was introduced in Taylor UUCP version 1.07. TEMP If the `C' option appears in OPTIONS, this names the file to be sent. Otherwise if FROM is in the spool directory, TEMP is the same as FROM. Otherwise TEMP may be a dummy string, such as `D.0'. After the transfer has been succesfully completed, the master will delete the file TEMP. MODE This is an octal number giving the mode of the file on the master. If the file is not in the spool directory, the slave will always create it with mode 0666, except that if (MODE & 0111) is not zero (the file is executable), the slave will create the file with mode 0777. If the file is in the spool directory, some UUCP packages will use the algorithm above and some will always create the file with mode 0600. This field is ignored by UUPlus, since it is meaningless on DOS; UUPlus uses 0666 for outgoing files. NOTIFY This field may not be present, and in any case is only meaningful if the `n' option appears in OPTIONS. If the `n' option appears, then, when the transfer is successfully completed, the slave will send mail to NOTIFY, which must be a legal mailing address on the slave. If a SIZE field will appear but the `n' option does not appear, NOTIFY will always be present, typically as the string `dummy' or simply a pair of double quotes. SIZE This field is only present when doing Taylor UUCP or SVR4 UUCP size negotiation. It is the size of the file in bytes. Taylor UUCP version 1.03 sends the size as a decimal integer, while versions 1.04 and up, and all other UUCP packages that support size negotiation, send the size in base 16 with a leading 0x. The slave then responds with an `S' command response. `SY START' The slave is willing to accept the file, and file transfer begins. The START field will only be present when using file restart. It specifies the byte offset into the file at which to start sending. If this is a new file, START will be 0x0. `SN2' The slave denies permission to transfer the file. This can mean that the destination directory may not be accessed, or that no requests are permitted. It implies that the file transfer will never succeed. `SN4' The slave is unable to create the necessary temporary file. This implies that the file transfer might succeed later. `SN6' This is only used by Taylor UUCP size negotiation. It means that the slave considers the file too large to transfer at the moment, but it may be possible to transfer it at some other time. `SN7' This is only used by Taylor UUCP size negotiation. It means that the slave considers the file too large to ever transfer. `SN8' This is only used by Taylor UUCP. It means that the file was already received in a previous conversation. This can happen if the receive acknowledgement was lost after it was sent by the receiver but before it was received by the sender. `SN9' This is only used by Taylor UUCP (versions 1.05 and up) and UUPlus (versions 2.0 and up). It means that the remote system was unable to open another channel (see the discussion of the `i' protocol for more information about channels). This implies that the file transfer might succeed later. `SN10' This is reportedly used by SVR4 UUCP to mean that the file size is too large. If the slave responds with `SY', a file transfer begins. When the file transfer is complete, the slave sends a `C' command response. `CY' The file transfer was successful. `CYM' The file transfer was successful, and the slave wishes to become the master; the master should send an `H' command, described below. `CN5' The temporary file could not be moved into the final location. This implies that the file transfer will never succeed. After the `C' command response has been received (in the `SY' case) or immediately (in an `SN' case) the master will send another command.  File: uucp.info, Node: The R Command, Next: The X Command, Prev: The S Command, Up: UUCP Protocol Commands The R Command ............. master: `R FROM TO USER -OPTIONS SIZE' The `R' and the `-' are literal characters. This is a request by the master to receive a file from the slave. I do not know how SVR4 UUCP or QFT implement file transfer restart in this case. FROM This is the name of the file on the slave which the master wishes to receive. It must not be in the spool directory, and it may not contain any wildcards. TO This is the name of the file to create on the master. I do not believe that it can be a directory. It may only be in the spool directory if this file is being requested to support an execution either on the master or on some system other than the slave. USER The name of the user who requested the transfer. OPTIONS A list of options to control the transfer. The following options are defined (all options are single characters): `d' The master should create directories as necessary (this is the default). `f' The master should not create directories if necessary, but should fail the transfer instead. `m' The master should send mail to USER when the transfer is complete. `q' Backslash quoting is applied to the FROM, TO, and USER arguments. *Note UUCP Protocol Commands::. This option was introduced in Taylor UUCP version 1.07. SIZE This only appears if Taylor UUCP size negotiation is being used. It specifies the largest file which the master is prepared to accept (when using SVR4 UUCP or QFT, this was specified in the `-U' option during the initial handshake). The slave then responds with an `R' command response. UUPlus does not support `R' requests, and always responds with `RN2'. `RY MODE [SIZE]' The slave is willing to send the file, and file transfer begins. The MODE argument is the octal mode of the file on the slave. The master treats this just as the slave does the MODE argument in the send command, q.v. I am told that SVR4 UUCP sends a trailing SIZE argument. For some versions of BSD UUCP, the MODE argument may have a trailing `M' character (e.g., `RY 0666M'). This means that the slave wishes to become the master. `RN2' The slave is not willing to send the file, either because it is not permitted or because the file does not exist. This implies that the file request will never succeed. `RN6' This is only used by Taylor UUCP size negotiation. It means that the file is too large to send, either because of the size limit specifies by the master or because the slave considers it too large. The file transfer might succeed later, or it might not (this may be cleared up in a later release of Taylor UUCP). `RN9' This is only used by Taylor UUCP (versions 1.05 and up) and FSUUCP (versions 1.5 and up). It means that the remote system was unable to open another channel (see the discussion of the `i' protocol for more information about channels). This implies that the file transfer might succeed later. If the slave responds with `RY', a file transfer begins. When the file transfer is complete, the master sends a `C' command. The slave pretty much ignores this, although it may log it. `CY' The file transfer was successful. `CN5' The temporary file could not be moved into the final location. After the `C' command response has been sent (in the `RY' case) or immediately (in an `RN' case) the master will send another command.  File: uucp.info, Node: The X Command, Next: The E Command, Prev: The R Command, Up: UUCP Protocol Commands The X Command ............. master: `X FROM TO USER -OPTIONS' The `X' and the `-' are literal characters. This is a request by the master to, in essence, execute uucp on the slave. The slave should execute `uucp FROM TO'. FROM This is the name of the file or files on the slave which the master wishes to transfer. Any wildcards are expanded on the slave. If the master is requesting that the files be transferred to itself, the request would normally contain wildcard characters, since otherwise an `R' command would suffice. The master can also use this command to request that the slave transfer files to a third system. TO This is the name of the file or directory to which the files should be transferred. This will normally use a UUCP name. For example, if the master wishes to receive the files itself, it would use `master!path'. USER The name of the user who requested the transfer. OPTIONS A list of options to control the transfer. As far as I know, only one option is defined: `q' Backslash quoting is applied to the FROM, TO, and USER arguments. *Note UUCP Protocol Commands::. This option was introduced in Taylor UUCP version 1.07. The slave then responds with an `X' command response. FSUUCP does not support `X' requests, and always responds with `XN'. `XY' The request was accepted, and the appropriate file transfer commands have been queued up for later processing. `XN' The request was denied. No particular reason is given. In either case, the master will then send another command.  File: uucp.info, Node: The E Command, Next: The H Command, Prev: The X Command, Up: UUCP Protocol Commands The E Command ............. master: `E FROM TO USER -OPTIONS TEMP MODE NOTIFY SIZE COMMAND' The `E' command is only supported by Taylor UUCP 1.04 and up. It is used to make an execution request without requiring a separate `X.*' file. *Note Execution File Format::. It is only used when the command to be executed requires a single input file which is passed to it as standard input. All the fields have the same meaning as they do for an `S' command, except for OPTIONS and COMMAND. OPTIONS A list of options to control the transfer. The following options are defined (all options are single characters): `C' The file has been copied to the spool directory (the master should use TEMP rather than FROM). `c' The file has not been copied to the spool directory (this is the default). `N' No mail message should be sent, even if the command fails. This is the equivalent of the `N' command in an `X.*' file. `Z' A mail message should be sent if the command fails (this is generally the default in any case). This is the equivalent of the `Z' command in an `X.*' file. `R' Mail messages about the execution should be sent to the address in the NOTIFY field. This is the equivalent of the `R' command in an `X.*' file. `e' The execution should be done with `/bin/sh'. This is the equivalent of the `e' command in an `X.*' file. `q' Backslash quoting is applied to the FROM, TO, USER, and NOTIFY arguments. *Note UUCP Protocol Commands::. This option was introduced in Taylor UUCP version 1.07. Note that the COMMAND argument is not backslash quoted--that argument is defined as the remainder of the line, and so is already permitted to contain any character. COMMAND The command which should be executed. This is the equivalent of the `C' command in an `X.*' file. The slave then responds with an `E' command response. These are the same as the `S' command responses, but the initial character is `E' rather than `S'. If the slave responds with `EY', the file transfer begins. When the file transfer is complete, the slave sends a `C' command response, just as for the `S' command. After a successful file transfer, the slave is responsible for arranging for the command to be executed. The transferred file is passed as standard input, as though it were named in the `I' and `F' commands of an `X.*' file. After the `C' command response has been received (in the `EY' case) or immediately (in an `EN' case) the master will send another command.  File: uucp.info, Node: The H Command, Prev: The E Command, Up: UUCP Protocol Commands The H Command ............. master: `H' This is used by the master to hang up the connection. The slave will respond with an `H' command response. `HY' The slave agrees to hang up the connection. In this case the master sends another `HY' command. In some UUCP packages the slave will then send a third `HY' command. At this point the protocol is shut down, and the final handshake is begun. `HN' The slave does not agree to hang up. In this case the master and the slave exchange roles. The next command will be sent by the former slave, which is the new master. The roles may be reversed several times during a single connection.  File: uucp.info, Node: The Final Handshake, Prev: UUCP Protocol Commands, Up: UUCP Protocol The Final Handshake ------------------- After the protocol has been shut down, the final handshake is performed. This handshake has no real purpose, and some UUCP packages simply drop the connection rather than do it (in fact, some will drop the connection immediately after both sides agree to hangup, without even closing down the protocol). caller: `\020OOOOOO\000' called: `\020OOOOOOO\000' That is, the calling UUCP sends six `O' characters and the called UUCP replies with seven `O' characters. Some UUCP packages always send six `O' characters.  File: uucp.info, Node: g Protocol, Next: f Protocol, Prev: UUCP Protocol, Up: Protocols UUCP `g' Protocol ================= The `g' protocol is a packet based flow controlled error correcting protocol that requires an eight bit clear connection. It is the original UUCP protocol, and is supported by all UUCP implementations. Many implementations of it are only able to support small window and packet sizes, specifically a window size of 3 and a packet size of 64 bytes, but the protocol itself can support up to a window size of 7 and a packet size of 4096 bytes. Complaints about the inefficiency of the `g' protocol generally refer to specific implementations, rather than to the correctly implemented protocol. The `g' protocol was originally designed for general packet drivers, and thus contains some features that are not used by UUCP, including an alternate data channel and the ability to renegotiate packet and window sizes during the communication session. The `g' protocol is spoofed by many Telebit modems. When spoofing is in effect, each Telebit modem uses the `g' protocol to communicate with the attached computer, but the data between the modems is sent using a Telebit proprietary error correcting protocol. This allows for very high throughput over the Telebit connection, which, because it is half-duplex, would not normally be able to handle the `g' protocol very well at all. When a Telebit is spoofing the `g' protocol, it forces the packet size to be 64 bytes and the window size to be 3. This discussion of the `g' protocol explains how it works, but does not discuss useful error handling techniques. Some discussion of this can be found in Jamie E. Hanrahan's paper, cited above (*note UUCP Protocol Sources::). All `g' protocol communication is done with packets. Each packet begins with a six byte header. Control packets consist only of the header. Data packets contain additional data. The header is as follows: `\020' Every packet begins with a `^P'. K (1 <= K <= 9) The K value is always 9 for a control packet. For a data packet, the K value indicates how much data follows the six byte header. The amount of data is 2 ** (K + 4), where ** indicates exponentiation. Thus a K value of 1 means 32 data bytes and a K value of 8 means 4096 data bytes. The K value for a data packet must be between 1 and 8 inclusive. checksum low byte checksum high byte The checksum value is described below. control byte The control byte indicates the type of packet, and is described below. xor byte This byte is the xor of K, the checksum low byte, the checksum high byte and the control byte (i.e., the second, third, fourth and fifth header bytes). It is used to ensure that the header data is valid. The control byte in the header is composed of three bit fields, referred to here as TT (two bits), XXX (three bits) and YYY (three bits). The control is TTXXXYYY, or `(TT << 6) + (XXX << 3) + YYY'. The TT field takes on the following values: `0' This is a control packet. In this case the K byte in the header must be 9. The XXX field indicates the type of control packet; these types are described below. `1' This is an alternate data channel packet. This is not used by UUCP. `2' This is a data packet, and the entire contents of the attached data field (whose length is given by the K byte in the header) are valid. The XXX and YYY fields are described below. `3' This is a short data packet. Let the length of the data field (as given by the K byte in the header) be L. Let the first byte in the data field be B1. If B1 is less than 128 (if the most significant bit of B1 is 0), then there are `L - B1' valid bytes of data in the data field, beginning with the second byte. If `B1 >= 128', let B2 be the second byte in the data field. Then there are `L - ((B1 & 0x7f) + (B2 << 7))' valid bytes of data in the data field, beginning with the third byte. In all cases L bytes of data are sent (and all data bytes participate in the checksum calculation) but some of the trailing bytes may be dropped by the receiver. The XXX and YYY fields are described below. In a data packet (short or not) the XXX field gives the sequence number of the packet. Thus sequence numbers can range from 0 to 7, inclusive. The YYY field gives the sequence number of the last correctly received packet. Each communication direction uses a window which indicates how many unacknowledged packets may be transmitted before waiting for an acknowledgement. The window may range from 1 to 7, and may be different in each direction. For example, if the window is 3 and the last packet acknowledged was packet number 6, packet numbers 7, 0 and 1 may be sent but the sender must wait for an acknowledgement before sending packet number 2. This acknowledgement could come as the YYY field of a data packet, or as the YYY field of a `RJ' or `RR' control packet (described below). Each packet must be transmitted in order (the sender may not skip sequence numbers). Each packet must be acknowledged, and each packet must be acknowledged in order. In a control packet, the XXX field takes on the following values: 1 `CLOSE' The connection should be closed immediately. This is typically sent when one side has seen too many errors and wants to give up. It is also sent when shutting down the protocol. If an unexpected `CLOSE' packet is received, a `CLOSE' packet should be sent in reply and the `g' protocol should halt, causing UUCP to enter the final handshake. 2 `RJ' or `NAK' The last packet was not received correctly. The YYY field contains the sequence number of the last correctly received packet. 3 `SRJ' Selective reject. The YYY field contains the sequence number of a packet that was not received correctly, and should be retransmitted. This is not used by UUCP, and most implementations will not recognize it. 4 `RR' or `ACK' Packet acknowledgement. The YYY field contains the sequence number of the last correctly received packet. 5 `INITC' Third initialization packet. The YYY field contains the maximum window size to use. 6 `INITB' Second initialization packet. The YYY field contains the packet size to use. It requests a size of 2 ** (YYY + 5). Note that this is not the same coding used for the K byte in the packet header (it is 1 less). Most UUCP implementations that request a packet size larger than 64 bytes can handle any packet size up to that specified. 7 `INITA' First initialization packet. The YYY field contains the maximum window size to use. To compute the checksum, call the control byte (the fifth byte in the header) C. The checksum of a control packet is simply `0xaaaa - C'. The checksum of a data packet is `0xaaaa - (CHECK ^ C)', where `^' denotes exclusive or, and CHECK is the result of the following routine as run on the contents of the data field (every byte in the data field participates in the checksum, even for a short data packet). Below is the routine used by an early version of Taylor UUCP; it is a slightly modified version of a routine which John Gilmore patched from G.L. Chesson's original paper. The `z' argument points to the data and the `c' argument indicates how much data there is. int igchecksum (z, c) register const char *z; register int c; { register unsigned int ichk1, ichk2; ichk1 = 0xffff; ichk2 = 0; do { register unsigned int b; /* Rotate ichk1 left. */ if ((ichk1 & 0x8000) == 0) ichk1 <<= 1; else { ichk1 <<= 1; ++ichk1; } /* Add the next character to ichk1. */ b = *z++ & 0xff; ichk1 += b; /* Add ichk1 xor the character position in the buffer counting from the back to ichk2. */ ichk2 += ichk1 ^ c; /* If the character was zero, or adding it to ichk1 caused an overflow, xor ichk2 to ichk1. */ if (b == 0 || (ichk1 & 0xffff) < b) ichk1 ^= ichk2; } while (--c > 0); return ichk1 & 0xffff; } When the `g' protocol is started, the calling UUCP sends an `INITA' control packet with the window size it wishes the called UUCP to use. The called UUCP responds with an `INITA' packet with the window size it wishes the calling UUCP to use. Pairs of `INITB' and `INITC' packets are then similarly exchanged. When these exchanges are completed, the protocol is considered to have been started. Note that the window and packet sizes are not a negotiation. Each system announces the window and packet size which the other system should use. It is possible that different window and packet sizes will be used in each direction. The protocol works this way on the theory that each system knows how much data it can accept without getting overrun. Therefore, each system tells the other how much data to send before waiting for an acknowledgement. When a UUCP package transmits a command, it sends one or more data packets. All the data packets will normally be complete, although some UUCP packages may send the last one as a short packet. The command string is sent with a trailing null byte, to let the receiving package know when the command is finished. Some UUCP packages require the last byte of the last packet sent to be null, even if the command ends earlier in the packet. Some packages may require all the trailing bytes in the last packet to be null, but I have not confirmed this. When a UUCP package sends a file, it will send a sequence of data packets. The end of the file is signalled by a short data packet containing zero valid bytes (it will normally be preceeded by a short data packet containing the last few bytes in the file). Note that the sequence numbers cover the entire communication session, including both command and file data. When the protocol is shut down, each UUCP package sends a `CLOSE' control packet.  File: uucp.info, Node: f Protocol, Next: t Protocol, Prev: g Protocol, Up: Protocols UUCP `f' Protocol ================= The `f' protocol is a seven bit protocol which checksums an entire file at a time. It only uses the characters between `\040' and `\176' (ASCII `space' and `~') inclusive, as well as the carriage return character. It can be very efficient for transferring text only data, but it is very inefficient at transferring eight bit data (such as compressed news). It is not flow controlled, and the checksum is fairly insecure over large files, so using it over a serial connection requires handshaking (XON/XOFF can be used) and error correcting modems. Some people think it should not be used even under those circumstances. I believe that the `f' protocol originated in BSD versions of UUCP. It was originally intended for transmission over X.25 PAD links. The `f' protocol has no startup or finish protocol. However, both sides typically sleep for a couple of seconds before starting up, because they switch the terminal into XON/XOFF mode and want to allow the changes to settle before beginning transmission. When a UUCP package transmits a command, it simply sends a string terminated by a carriage return. When a UUCP package transmits a file, each byte B of the file is translated according to the following table: 0 <= B <= 037: 0172, B + 0100 (0100 to 0137) 040 <= B <= 0171: B ( 040 to 0171) 0172 <= B <= 0177: 0173, B - 0100 ( 072 to 077) 0200 <= B <= 0237: 0174, B - 0100 (0100 to 0137) 0240 <= B <= 0371: 0175, B - 0200 ( 040 to 0171) 0372 <= B <= 0377: 0176, B - 0300 ( 072 to 077) That is, a byte between `\040' and `\171' inclusive is transmitted as is, and all other bytes are prefixed and modified as shown. When all the file data is sent, a seven byte sequence is sent: two bytes of `\176' followed by four ASCII bytes of the checksum as printed in base 16 followed by a carriage return. For example, if the checksum was 0x1234, this would be sent: `\176\1761234\r'. The checksum is initialized to 0xffff. For each byte that is sent it is modified as follows (where B is the byte before it has been transformed as described above): /* Rotate the checksum left. */ if ((ichk & 0x8000) == 0) ichk <<= 1; else { ichk <<= 1; ++ichk; } /* Add the next byte into the checksum. */ ichk += B; When the receiving UUCP sees the checksum, it compares it against its own calculated checksum and replies with a single character followed by a carriage return. `G' The file was received correctly. `R' The checksum did not match, and the file should be resent from the beginning. `Q' The checksum did not match, but too many retries have occurred and the communication session should be abandoned. The sending UUCP checks the returned character and acts accordingly.  File: uucp.info, Node: t Protocol, Next: e Protocol, Prev: f Protocol, Up: Protocols UUCP `t' Protocol ================= The `t' protocol is intended for use on links which provide reliable end-to-end connections, such as TCP. It does no error checking or flow control, and requires an eight bit clear channel. I believe the `t' protocol originated in BSD versions of UUCP. When a UUCP package transmits a command, it first gets the length of the command string, C. It then sends `((C / 512) + 1) * 512' bytes (the smallest multiple of 512 which can hold C bytes plus a null byte) consisting of the command string itself followed by trailing null bytes. When a UUCP package sends a file, it sends it in blocks. Each block contains at most 1024 bytes of data. Each block consists of four bytes containing the amount of data in binary (most significant byte first, the same format as used by the Unix function `htonl') followed by that amount of data. The end of the file is signalled by a block containing zero bytes of data.  File: uucp.info, Node: e Protocol, Next: Big G Protocol, Prev: t Protocol, Up: Protocols UUCP `e' Protocol ================= The `e' protocol is similar to the `t' protocol. It does no flow control or error checking and is intended for use over networks providing reliable end-to-end connections, such as TCP. The `e' protocol originated in versions of HDB UUCP. When a UUCP package transmits a command, it simply sends the command as an ASCII string terminated by a null byte. When a UUCP package transmits a file, it sends the complete size of the file as an ASCII decimal number. The ASCII string is padded out to 20 bytes with null bytes (i.e. if the file is 1000 bytes long, it sends `1000\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0'). It then sends the entire file.  File: uucp.info, Node: Big G Protocol, Next: i Protocol, Prev: e Protocol, Up: Protocols UUCP `G' Protocol ================= The `G' protocol is used by SVR4 UUCP. It is identical to the `g' protocol, except that it is possible to modify the window and packet sizes. The SVR4 implementation of the `g' protocol reportedly is fixed at a packet size of 64 and a window size of 7. Supposedly SVR4 chose to implement a new protocol using a new letter to avoid any potential incompatibilities when using different packet or window sizes. Most implementations of the `g' protocol that accept packets larger than 64 bytes will also accept packets smaller than whatever they requested in the `INITB' packet. The SVR4 `G' implementation is an exception; it will only accept packets of precisely the size it requests in the INITB packet.