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FTSC FIDONET TECHNICAL STANDARDS COMMITTEE
**********************************************************************
Publication: FTS-1024
Revision: 1
Title: Raw ifcico mail transfer protocol
Author: Michiel Broek, 2:280/2802
Issue Date: 27 August 2003
Review Date: 27 August 2005
----------------------------------------------------------------------
Status of this document
-----------------------
This document is a Fidonet Technical Standard (FTS), issued by the
FTSC for the benefit of the Fidonet community.
This document is released to the public domain, and may be used,
copied or modified for any purpose whatever.
Abstract
--------
This specification defines raw ifcico - a protocol to handle a
session between two Fidonet Technology systems over a reliable
connection.
Assumption that the connection is reliable makes possible to
eliminate error-checking.
Table of contents
-----------------
1. Background
2. Definitions
3. Protocol Overview
4. Frame Format
5. Protocol Commands and Their Arguments
6. Protocol States
1. Finite State Machine Notation
2. Send files batch
3. Receive files batch
7. License
8. Glossary
9. References
10. Acknowledgements
A. Author Contact Data
B. History
---------------------------------------------------------------
1. Background
-------------
The raw ifcico protocol is in use for a long time, and was
developed for Eugene G. Crossers ifmail package by Stanislav
Voronyi <stas@uanet.kharkov.ua>.
This document attempts to document the current practice for
communication between two Fidonet systems via a reliable channel,
provide technical reference for Fidonet software developers and
eventually improve Fidonet connectivity.
2. Definitions
--------------
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT" and "MAY"
in this document are to be interpreted as specified in [FTA-0006].
However, for readability, these words may sometimes not appear in
all uppercase letters in this specification. Although it should not
impact minimal realization of raw ifcico protocol, it must be noted
that Protocol Extensions may override, update or obsolete
requirement levels indicated by the above keywords in chapters from
3 to 6 inclusive.
Calling party in this document is referred to as the Originating
side and called party is referred to as the Answering side.
Originating side here is the party that initiates the connection
between two systems.
Mailer in this document is a software that implements the protocol.
Words "frame", "packet", and "block" when used in this document
refer to raw ifcico frames, unless explicitly stated otherwise.
Other definitions that are not local to this document can be found
in the Glossary.
3. Protocol Overview
--------------------
The raw ifcico protocol can only be started when two mailers
initiate a EMSI protocol handshake and the called system presents
the TCP EMSI compatibility code. If the calling system also
supports the raw ifcico protocol it will transmit the TCP
compatibility code to the calling system to initiate the raw
ifcico session. Mailers should only present the EMSI TCP
compatibility code when the connection is made over data
transparent bi-directional channels with reliable transmission.
Whenever TCP/IP socket is used, the unregistered port number for
raw ifcico 60179 SHOULD be used.
After a successfull EMSI handshake, the calling system starts
sending all files to the called system. When all files are sent,
the calling system receives all files from the called system.
If the calling system allowes requests made by the called system
and the called system made file requests, then the calling system
will send all requested files to the called system. Normally this
will not happen because the calling system does not accept requests
during outbound sessions.
4. Frame Format
---------------
Raw ifcico is defined in terms of sending and receiving
specifically formatted data blocks. We call them frames.
Command frames carry protocol commands and may change protocol
state. Data frames are usually appended to files being received by
mailers or may be discarded, depending on the protocol state.
The particular way of mapping an octet stream or a datagram stream
of the transport layer into raw ifcico frames may depend on the
underlying protocol suite. At this time, we define such mapping for
TCP/IP socket connection which can also be used for similar
transports as well.
The socket stream is being split into raw ifcico frames in the
following manner:
76543210 76543210 76543210 76543210 76543210
+--------+--------+--------+--------+---- ...... ----+--------+
| 0xc6 | Type | MSBlen | LSBlen | DATA | 0x6c |
+--------+--------+--------+--------+---- ...... ----+--------+
|<- Frame header ->|<- frame data ->|<- end->|
upto 2048 octets
If Type is 0x87, this is a command frame.
If Type is 0xe1, this is a data frame.
16 bits marked MSBlen and LSBlen carry the size of the DATA part
in octets with the LSBlen marked being the least significant.
That is, the actual length of a raw ifcico data frame is SIZE+5.
The size of the DATA part may vary between 1 and 2048 octets. A
correct realization should never set SIZE to 0. Upon receiving of a
packet header with the SIZE field set to 0, the total length of the
incoming packet must be treated as 5, this packet must be dropped,
and the event should be logged. The standard implementation uses
data blocks of 1024 octets.
Command frames carry command arguments. Command arguments are an
arbitrary symbol string that may be null-terminated. Treating of a
null character in the middle of a command depends on realization
(with the options being "treat as whitespace" or "treat as
end-of-line"). The terminating null character (if any) is either
stripped or used by mailers internally as an end-of-line marker.
Because reliable connections can be slow, the receiver should use
a very relaxed timeout on the data to receive.
The receiver should wait for each character of a frame for 120
seconds.
5. Protocol Commands and Their Arguments
----------------------------------------
The following commands are defined:
S <filename> <size> <timestamp%2>
This is transmitted by the party that is in sendfiles mode to give
the information about the file to transmit. The command arguments
are separated by spaces. The filename is a 8.3 filename. The size
is a unsigned long integer that represents the filesize in bytes.
The timestamp is a Unix timestamp in seconds since 1 januari 1970
and is rounded up to even seconds. This is to make it compatiblei
with DOS file systems that cannot store the file timestamp odd
seconds.
RS
In response to the send file command, the receiving system can send
this command (Receive Skip) to indicate that this file is already
received and must be skipped.
RN
In response to the send file commmand, the receiving system can
send this command (Receive Not), to refuse this and any further
files. The session should be terminated.
ROK [<offset>]
In response to the send file commmand, the receiving system should
send this command (Receive OK) to tell the sender to start sending
the file. The optional parameter offset can be given with an offset
from which point to start sending the file. If no offset is given,
the offset must be assumed zero, start from the begin of file.
EOF
This command should be send to the receiver to indicate End Of
File, no more file datablocks will follow.
FOK
This command is transmitted in response to the EOF command by the
receiving system to indicate that the transmitted file was received
without errors.
FERROR
This command is transmitted in response to the EOF command by the
receiving system to indicate that the transmitted file was received
with errors. The sending system must mark the file as not
transmitted so it can be send in another session.
SN
This command is transmitted by the sending system to indicate that
the last file is send and no more files will follow.
RN
This command is transmitted by the receiving system to acknowledge
the SN command.
6. Protocol States
------------------
6.1 Finite State Machine Notation
---------------------------------
.-----+---------+----------------------+----------------------+----.
|State| State | Predicate(s) | Action(s) |Next|
| # | Name | | | St |
|-----+---------+----------------------+----------------------+----|
| fnn*| | | | |
`-----+---------+----------------------+----------------------+----'
State # - Number of this state (e.g. R13).
f - FSM initial (Window, Sender, Receiver, ...)
nn - state number
* - state which represents a lower level protocol
which is represented by yet another automation.
State Name - Descriptive name of this state.
Predicate(s) - Conditions which terminate the state. If predicates
are non-exclusive, consider them ordered.
Action(s) - Action(s) corresponding to predicate(s)
Next State - Subsequent state corresponding to predicate(s)
6.2 Send files batch.
---------------------
tcpsndfiles (Sender)
.-----+---------+----------------------+----------------------+----.
|State| State | Predicate(s) | Action(s) |Next|
| # | Name | | | St |
|-----+---------+----------------------+----------------------+----|
| S0 | Send | | Send 0xaa 0x55 | S1 |
| | sync | | octets | |
|-----|---------|----------------------|----------------------|----|
| S1 | Sync | 1 Received octet 0xaa| wait for next | S2 |
| | wait 1 | 2 Received other | again | S1 |
| | | 3 120 seconds nothing| error | err|
|-----|---------|----------------------|----------------------|----|
| S2 | Sync | 1 Received octet 0x55| send files | S3 |
| | wait 2 | 2 Received other | again | S1 |
| | | 3 120 seconds nothing| error | err|
|-----|---------|----------------------|----------------------|----|
| S3 | Send | 1 more files | Sendfile | S4 |
| | files | 2 all are sent | End of batch | S9 |
|-----|---------|----------------------|----------------------|----|
| S4 | Sendfile| | Send S command | S5 |
| | info | | | |
|-----|---------|----------------------|----------------------|----|
| S5 | Ackfile | 1 Receive RS | skip file | S3 |
| | | 2 Receive RN | fatal error | err|
| | | 3 Receive ROK <offs> | send data | S6 |
|-----|---------|----------------------|----------------------|----|
| S6 | Senddata| 1 End of file | signal EOF | S7 |
| | frame | 2 more datablocks | continue | S6 |
|-----|---------|----------------------|----------------------|----|
| S7 | Send EOF| | wait for ack | S8 |
|-----|---------|----------------------|----------------------|----|
| S8 | Waitack | 1 Receive FOK | next file | S3 |
| | | 2 Receive FERROR | next file | S3 |
|-----|---------|----------------------|----------------------|----|
| S9 | Finsend | | Send SN command | S10|
|-----|---------|----------------------|----------------------|----|
| S10 | Finack | 1 Receive RN | Batch completed | OK |
| | | 2 Timeout | Batch error | err|
`-----+---------+----------------------+----------------------+----'
6.3 Receive files batch.
------------------------
tcprcvfiles (Receiver)
.-----+---------+----------------------+----------------------+----.
|State| State | Predicate(s) | Action(s) |Next|
| # | Name | | | St |
|-----+---------+----------------------+----------------------+----|
| R0 | Send | | Send 0xaa 0x55 | R1 |
| | sync | | octets | |
|-----|---------|----------------------|----------------------|----|
| R1 | Sync | 1 Received octet 0xaa| wait for next | R2 |
| | wait 1 | 2 Received other | again | R1 |
| | | 3 120 seconds nothing| error | err|
|-----|---------|----------------------|----------------------|----|
| R2 | Sync | 1 Received octet 0x55| Wait command | R3 |
| | wait 2 | 2 Received other | again | R1 |
| | | 3 120 seconds nothing| error | err|
|-----|---------|----------------------|----------------------|----|
| R3 | Wait | 1 SN | End of batch | R7 |
| | command | 2 S file command | Receive file | R4 |
| | | 3 Garbage | Report | err|
| | | 4 120 seconds nothing| Report | err|
|-----|---------|----------------------|----------------------|----|
| R4 | Start | 1 File allready rcvd | Send RS command | R3 |
| | receive | 2 Fatal error | Send RN command | err|
| | | 3 Ready for receive | Send ROK <offset> cmd| R5 |
|-----|---------|----------------------|----------------------|----|
| R5 | Receive | 1 Data frame | Append to file | R5 |
| | frame | 2 Command EOF | Received EOF | R6 |
| | | 3 Garbage | Report | err|
| | | 4 120 seconds nothing| Report | err|
|-----|---------|----------------------|----------------------|----|
| R6 | Rcvd | 1 File ok | Send FOK | R3 |
| | EOF | 2 File errors | Send FERROR | R3 |
|-----|---------|----------------------|----------------------|----|
| R7 | Finack | | Send RN command | OK |
`-----+---------+----------------------+----------------------+----'
7. License
----------
Quoted from the ifmail readme:
Copyright (c) 1993-2000 Eugene G. Crosser
THIS SOFTWARE IS PROVIDED AS IS AND COME WITH NO WARRANTY OF ANY
KIND, EITHER EXPRESSED OR IMPLIED. IN NO EVENT WILL THE COPYRIGHT
HOLDER BE LIABLE FOR ANY DAMAGES RESULTING FROM THE USE OF THIS
SOFTWARE.
This is Open Source(tm) software. Except for the modules borrowed
from other packages (which may be subject to different licensing
policy), you may use this software for any purpose, commercial or
noncommercial, including, but not limited to, modifying it and
distributing with or without fee modified or unmodified copies,
provided that the above copyright notice is retained.
8. Glossary
-----------
Many entries in this glossary are provided courtesy of Butterfly
Glossary of Internet and Data Communication terms and RFC-1983.
connection-oriented
Data communication method in which communication proceeds
through three well-defined phases: connection
establishment, data transfer, connection release. TCP is a
connection-oriented protocol.
data link layer
The OSI layer that is responsible for data transfer across
a single physical connection, or series of bridged
connections, between two Network entities.
flow control
A technique for ensuring that a transmitting entity does
not overwhelm a receiving entity.
IP
(Internet Protocol). The Internet Protocol, defined in STD
5, RFC 791, is the network layer for the TCP/IP Protocol
Suite. It is a connectionless, best-effort packet switching
protocol.
network layer
Layer 3 of the OSI reference model. Layer 3 is the layer at
which routing, addressing and connection management take
place.
OSI (Open Systems Interconnection) Reference Model
A seven-layer structure designed to describe computer
network architectures and the way that data passes through
them. This model was developed by the ISO (International
Organization for Standardization) in 1978 to clearly define
the interfaces in multivendor networks, and to provide
users of those networks with conceptual guidelines in the
construction of such networks.
port
A port is a transport layer demultiplexing value. Each
application has a unique port identifier associated with
it.
physical layer
The OSI layer that provides the means to activate and use
physical connections for bit transmission. In plain terms,
the Physical Layer provides the procedures for transferring
a single bit across a Physical Media.
reliable transmission
a type of transport service that:
* recovers from errors by retransmitting errored frames
* delivers frames in correct sequence (also known as
stream-oriented)
* usually is used in connection-oriented mode
session layer
Layer 5 of the OSI reference model. Coordinates session
activity between applications, including application-layer
error control, dialog control, and remote procedure calls.
socket
Software structure operating as a communications and point
within a network device.
TCP
Transmission Control Protocol. An Internet Standard
transport layer reliable protocol defined in STD 7, RFC
793. It is connection-oriented and stream-oriented.
TCP/IP protocol suite
Transmission Control Protocol over Internet Protocol. This
is a common shorthand which refers to the suite of
transport and application protocols which runs over IP.
transport layer
Layer 4 of the OSI reference model. The transport layer is
responsible for reliable network communication between end
nodes. It implements flow and error control and often uses
virtual circuits to ensure reliable data delivery.
unixtime
number of seconds elapsed since 00:00:00 UTC, Jan. 1, 1970.
9. References
-------------
[FTS-0001]
A Basic FidoNet(r) Technical Standard, Revision 16. Randy
Bush, Pacific Systems Group, September 30, 1995. FTS-0001.
[FTS-0008]
Extending FTS-0001 to include Bark requests, Revision 3.
[FSC-0056]
Joaquim H. Homrighausen, EMSI/IEMSI protocol definition.
May 3, 1991. FSC-0056.
[FSC-0088]
Compatibility and Link Qualifier Extensions for EMSI
Sessions, Revision 1. Robert Williamson.
[FTA-1006]
Key words to indicate requirement levels, Fidonet Technical
Standards Committee administrative. FTA-1006.
10. Acknowledgements
--------------------
This document is partially based on extracts from RFCs and FTSC
publications too numerous to be acknowledged individually.
Ifcico is written by Eugene G. Crosser <crosser@average.org>;
2:5020/230@fidonet
The raw ifcico protocol is written by Stanislav Voronyi
<stas@uanet.kharkov.ua>
B. History
----------
Rev.1, 20030810:
Initial release.