Document: FSC-0039
Version: 04
Date: 29-Sep-90
A Type-2 Packet Extension Proposal
Mark A. Howard 1:260/340@FidoNet
Status of this document:
------------------------
This FSC suggests a proposed protocol for the FidoNet(r) community,
and requests discussion and suggestions for improvements. Distribution
of this document is unlimited.
Fido and FidoNet are registered marks of Tom Jennings and Fido Software.
FTS-0001 is a copyrighted work of Randy Bush.
Introduction
------------
This document serves two major purposes. The first is an attempt to define
and document the Type-2 packet which is widely in use in FidoNet today.
Although FTS-0001 defines the structure of a Type-2 packet, the natural
evolution of our network, mostly with regards to addressing methodology,
has made it necessary to utilize hitherto unused portions of the header
to insert Zone and Point information. Also, it has become apparent that
some of the existing fields are not large enough to accomplish their
original tasks.
The second is to propose a simple mechanism to allow FidoNet to begin to
utilize advanced mail packing techniques. It is quite apparent that while
Type-2 has served us faithfully for some time now, the evolution of our
network in terms of technical and physical complexity has caused us to
consider more efficient and functional ways to pack mail.
It should be made clear that with the exception of the Capability Word,
Capability Word Validation Copy, ProductCode(hi), and Revision(minor),
which are proposed extensions to the Type-2 packet header, this FSC is
an attempt to correctly document existing practices with regards to the
insertion of zone and point info by at least three mail processors in
use today.
The Type-2 Header (Where's the Zone?)
-------------------------------------
Although FTS-0001 has recently been updated to reflect the use of some of
the areas in the packed message header for zone data, at least two other
methods for inserting the zone information have been adopted, making it
necessary to provide support for both formats in all of the zone aware mail
processors. The end result is more code, and redundant information in the
packet header.
This has presented a problem in logistics, as it is difficult to consider
the project of updating mail processors using one type to use the other.
As sufficient indentification is provided, in the form of the product code,
to determine the expected location of the zone information, and because
code already exists in most of the mail processors to overcome this, this
proposal does not attempt to suggest that one method be used over the
other, rather the intent is to attempt to document the extensions in use,
and the products involved.
See the accompanying chart and cross-reference.
The Product Code
----------------
Based upon the current rate of requests for product codes from the FTSC,
it is probable that the Product Code byte will not be large enough to
accomodate all of the codes required. While it is not reasonable to
expect that all Type-2 processors will eventually check the hi-order byte
proposed here, it is likely that 'current' mail processors will. This
can be nothing but benefical, as it will force users to upgrade their
mail processors to a product which will as a minimum, support Type-2
with Zone and Point extensions, and quite possibly, processors that will
utilize more advanced mail packing techniques, making Type-2 extinct once
and for all.
The Capability Word (How do we GET there from here?)
-----------------------------------------------------
Everybody would like to see more efficient and functional ways to pack and
exchange mail. Several Type-3 message bundle proposals exist, but none
really address a problem which must be solved first. The problem is that
since FidoNet is a hobbyist network, no demands can be placed on any one
sysop to upgrade or change their bundling software. Because of this, it
is necessary to consider strategies which allow for the existence of Type-2
bundlers in the network topology.
Considerable advantages can be realized, however, between systems that
consent to use advanced bundling techniques. One way to do this is to
simply send netmail to all of your connecting systems, saying "Hey, I've
got a Type-3 bundler now, how about you?" This could become quite
tiresome, and does not represent much of an improvement on the current
situation.
What would be desirable is a network that would 'upgrade itself'. Given a
situation where mail processors of various capabilities will exist in a
network topology, the goal is to provide a mechanism whereby two links can
determine and utilize the most efficient bundling method to use, in a
manner transparent to the sysop.
For instance, let's say that the FTSC releases the Type-7 All New Singing
and Dancing bundle format. Well, your current version of SlingToss can
only support Types 2, 3, and 5. One of your downlinks gets a new version
of MailMangle which can support Types 2, 3, 4, and 7. Well, it is quite
obvious that since you and he are exchanging 4 megs of mail each night,
and it's an overseas call, that it would be in your interest to obtain a
new version of SlingToss which can support Type 7.
Note that this is *optional*. Because both processors can support Type-3,
they will continue to exchange Type-3 mail quite happily, even though
MailMangle is happily advertising the availability of Type-7. Even your
downlinks which are still using stone-age Type-2 processors will be fine,
as SlingToss will always export Type-2 bundles when no higher capability
can be determined.
So, after dashing off the check to the author, your new version of
SlingToss comes in the mail! You rush over to your system, and install it.
The next time SlingToss exports mail to the MailMangle system, it says
"Hey! I can now support Type 2, 3, 5, and 7! So, whattya got?" This is
no skin off MailMangle's nose, he's had Type-7 for quite a while, and he
begins to export Type-7 bundles to SlingToss. "It's about time.", he says.
Now, this scenario is made possible by implementing a 'Capability Word' in
the present and future packet headers. The Capability Update mechanism
depends on several assumptions:
1) Any Advanced Capability Bundler *MUST* be capable of receiving and
faithfully processing Type-2 bundles. Hopefully, the inbound packets
will be in the new format proposed by this document, but then again,
this is not an exact science. What this means is that it is likely
that some packets may arrive with the Capability Word (CW) set to 0.
In this case, Type-2 is assumed, assuring compatibility. The only
caveat is that it is conceivable that some obscure mail processor
uses the location proposed for the CW for other arcane purposes. This
| can detected through the CWValidation Copy, which is byte-swapped and
| compared with the CW at that time. If a mismatch is found, a CW of
| type 0 is assumed, and a Type-2 bundling method is used.
2) An Advanced Capability Bundler, hereafter referred to as a Type-N
Bundler, must have a method to store and maintain the node-by-node
capability information. This can be done many ways, and in fact
several processors already have begun to maintain node information
outside of that found in AREAS.BBS, mostly to implement pre-arranged
alternate compression methods. In a text configuration file, you
might see the following:
; Address Comp Send LastCW ; Comments
Node 1:260/340 ZIP Auto 7 ; Auto detect & upgrade
Node 1:135/20 LZH 3 2,3,7 ; Always send Type-3
Node 1: ARC 2 0 ; Stone-Age processor
Node 1:135/4 --- Auto 7 ; Sent me netmail
Node 1: --- 0 0 ; Don't send CW
In this example, the fields are:
Address - downlink address. Note that this is not necessarily
relative to echomail, only, it is possible to append
information to the node database as netmail packets are
receieved from different addresses.
Comp - desired mail compression method.
Send - Auto - automatically determined maximum common packing
method to use. Automatically update to LastCW
when packing.
LastCW - Last CW received from remote system.
3) A Type-N Bundle will always advertise it's capabilities in the CW
regardless of the type being sent. As shown in the above example,
it allows Type-N processors to automatically track the capability
of your system. Again, in cases where a stone-age processor is
being used, this field will be ignored, and in the unusual event
that it is not ignored, and is somehow harmful to the far system,
the Type-N processor can be configured to send a CW of 0.
The format of the Capability Word is designed to support up to 15 future
bundle types, and is bit-mapped to facilitate the easy determination of
the maximum common level supported between two nodes:
msb Capability Word lsb
Node Supports ------------FTSC Type Supported----------------
U 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2
2, 3, and 7 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 1
2, 3, and 5 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 1
2 (this FSC) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
Stone Age** 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
^
+--- Indicates UseNet RFC-822 capability
** - a mismatch in the CWValidation Copy also
produces a CW=0.
In this example, the Type-N bundler would first compare the remote CW
| and the byte-swapped remote CWValidation Copy, and check for a mismatch.
Prior to the compare, the MSB of the CW's are masked, as this bit is
reserved to indicate whether the mail processor is capable of also
accepting UseNet RFC-822 bundles. Following the MSB mask, and bit
comparison, if they do not match, a remote CW of 0 is assumed. If they
match, the Type-N processor would AND the local and remote CW words,
obtaining a CW expressing the Types which are in common to both systems.
The most significant Type will be used, by default, but note that this
assumes that new bundling Types will be increasingly more efficient or
in some way more beneficial.
Because this may not always be the case, there should be a method provided,
as illustrated above, to override the automatic upgrade should this become
the case.
The MSB of the CW is used to indicate whether the mail processor can accept
UseNet RFC-822 bundles or not. It is a separate indicator, and not intended
to be used as a part of the above comparison, however can be used to also
advertise RFC-822 capability to other systems. Since RFC-822 is 'set in
stone', there is no need to assign more than one capability bit.
It might seem somewhat limiting to only consider the possibility of 15
different future bundling methods, but it is my opinion that the careful
use of a 'Sub-Type' byte in the packet header can allow for the variations
on a single theme, and that proposals for new formats should be evaluated
by the FTSC to determine whether sufficient benefit can be realized in
the implementation of the given format, prior to assigning a new type
code.
Mailers
-------
It is quite clear to me that should this concept take hold, that the
logical place to store node capability data is in the local nodelist
database, or an index-associated data file. As above, it is necessary
to generate Type-2 packets for whatever purpose, unless it is known
by prior association, that the far mailer can accept other types of
packets. It is also quite reasonable to assume that a nodelist flag
could be assigned to advertise the CW for a given node, which the
native mailer nodelist compiler could then immediately determine the
preferred bundling method for any given node in FidoNet.
Another possibility would be to pass a capability advertisement in the
extensible portion of a handshake protocol, which may or may not already
exist in FidoNet.
The approach suggested previously in this document suggests the use of
a text configuration file, but it is quite obvious that many benefits
can be realized through the use of the nodelist, including the use of
additional flags to indicate the preferred compression method, etc.
Summary
-------
This document has been created in an attempt to define a method to allow
the future expansion and enhancement of FidoNet technology mail processors
and mailers, and in a way that is the least disruptive to existing mail
operations. The intent is to provide for an environment that is as open,
and extensible as possible.
The mechanism described should allow many different types of processors
(FTSC-registered) to exist in the network at once, and to provide an
environment which is designed to operate at it's maximum efficiency
wherever possible or practical.
Revision 2 of this document was produced to implement suggestions made
primarily by Jan Vroonhof, who suggested the use of the CW Validation
Copy. Jan presented this idea in his FSC-0048, along with other concepts
relating to the correct indentification and handling of zone and point
addressing. This document sanctions the improvements to the CW as
recommended, but does not address or support the other extensions
recommended in FSC-0048.
Thanks
------
To Ward Christensen, creator of XModem and BYE.
Tom Jennings, who started this whole mess.
Joaquim Homrighausen, for lots of good ideas, and motivation. Here's
another Lamborghini to work on.
Wynn Wagner, Oliver McDonald, Roeland Meyer, Andrew Farmer, Claude
Warren, Jan Vroonhof, Bob Hartman, and Vince Perriello, who all
contributed in some way to the creation of this document, mostly
through their messages in NET_DEV.
Type-2 Packet Format (proposed, but currently in use)
-----------------------------------------------------
Field Ofs Siz Type Description Expected value(s)
------- --- --- ---- -------------------------- -----------------
OrgNode 0x0 2 Word Origination node address 0-65535
DstNode 2 2 Word Destination node address 1-65535
Year 4 2 Int Year packet generated 19??-2???
Month 6 2 Int Month " " 0-11 (0=Jan)
Day 8 2 Int Day " " 1-31
Hour A 2 Int Hour " " 0-23
Min C 2 Int Minute " " 0-59
Sec E 2 Int Second " " 0-59
Baud 10 2 Int Baud Rate (not in use) ????
PktVer 12 2 Int Packet Version Always 2
OrgNet 14 2 Word Origination net address 1-65535
DstNet 16 2 Word Destination net address 1-65535
PrdCodL 18 1 Byte FTSC Product Code (lo) 1-255
* PVMajor 19 1 Byte FTSC Product Rev (major) 1-255
Password 1A 8 Char Packet password A-Z,0-9
* QOrgZone 22 2 Int Orig Zone (ZMailQ,QMail) 1-65535
* QDstZone 24 2 Int Dest Zone (ZMailQ,QMail) 1-65535
Filler 26 2 Byte Spare Change ?
| * CapValid 28 2 Word CW Byte-Swapped Valid Copy BitField
* PrdCodH 2A 1 Byte FTSC Product Code (hi) 1-255
* PVMinor 2B 1 Byte FTSC Product Rev (minor) 1-255
* CapWord 2C 2 Word Capability Word BitField
* OrigZone 2E 2 Int Origination Zone 1-65535
* DestZone 30 2 Int Destination Zone 1-65535
* OrigPoint 32 2 Int Origination Point 1-65535
* DestPoint 34 2 Int Destination Point 1-65535
* ProdData 36 4 Long Product-specific data Whatever
PktTerm 3A 2 Word Packet terminator 0000
* - extensions to FTS-0001
Ofs, Siz are in hex, other values are decimal.
Zone/Point Aware Mail Processors (probably a partial list)
----------------------------------------------------------
Prod
Code Name - Uses QOrg/QDstZone Orig/DestZone Orig/DestPoint
---- ----------- ------------- ------------- --------------
0x0C FrontDoor Reads/Updates Yes Yes
0x1A DBridge ????? Yes Yes
0x45 XRS Reads/Updates Yes Yes
0x29 QMail Yes ????? Not point-aware
0x35 ZMailQ Yes ????? Not point-aware
0x3F TosScan Reads/Updates Yes Yes
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