YAPP(tm) protocol for Packet Radio binary file transfer
(c) 1986, Jeff Jacobsen - WA7MBL
Revision 1.1 06/23/86
----------------------------------------------------------
YAPP PACKET TYPES
Size of packet data ranges from 2-258 bytes.
len = length of following bytes (not including len)
RR Rcv_Rdy ACK 01
RF Rcv_File ACK 02
AF Ack_EOF ACK 03 [1.1]
AT Ack_EOT ACK 04 [1.1]
SI Send_Init ENQ 01
HD Send_Hdr SOH len (Filename) NUL (File Size in ASCII) NUL
(Opt)
DT Send_Data STX len (Data) {if len=0 then data length = 256}
EF Send_EOF ETX 01
ET Send_EOT EOT 01
NR Not_Rdy NAK len (Optional Reason in ASCII)
RE Resume NAK len R NULL (File size in ASCII) NULL
CN Cancel CAN len (Optional Reason in ASCII)
CA Can_Ack ACK 05
{Following are for use in Server mode}
RI Rcv_Init ENQ 02 len (Filespec requested - wildcard allowed)
TX Text DLE len (ASCII text for display) {to send text from
server}
{Unimplement - Reserved for Server Commands}
UU Comands ENQ 03
ENQ 04
ENQ 05
...
ENQ FF
STATE TABLES for SEND
State Send Pkt Upon Next State
S (Send) SI RR SH
RF SD
NR Start/Done
First few timeouts S
RI S
Other/Timeout Abort
SH (Hdr) HD RF SD
NR Start/Done
IF (RESUME) RE Move file position
then SD
Other/Timeout Abort
SD (Data) DT (Not EOF) SD
(EOF) SE
SE (EOF) EF AF (More files) SH
AF (No More Files) ST
Other/Timeout Abort
ST (EOT) ET AT Start/Done
Other/Timeout Start/Done
STATE TABLES for RECEIVE
State On If Do Send Pkt Next State
R (Rec) SI (ready) RR RH
SI (opt)* open file RF RD
SI (not ready) NR Start/Done
NR Start/Done
Other/Timeout Abort
(opt)* If header info not desired it is ok to
open file and indiate ready for file
RH (Hdr) HD open file RF RD
HD (no room) NR Start/Done
IF (RESUME)
HD Already open file for RE RD
have file! append at -256
byte from EOF
ELSE HD Already have file!! NR Start/Done
SI RH
ET AT Start/Done
Other/Timeout Abort
RD (Data) DT store data RD
EF close file AF RH
Other/Timeout Abort
OTHER STATE
Any State On CN Send CA Start/Done
except CW
CW (Can_Wait) On CA Start/Done
On CN Send CA CW
Timeout Display Err Msg Start/Done
Abort Send CN CW
--------
Starting States
For 2 users not using Remote Server
Sender goes to State S, Receiver to State R after manually
exchanging file names. Since File Name is known, Recevier
may optionally send RF from state R and bypass file header.
Sender should give Receiver ample time to get into Receive
State.
For Remote Server Mode
USER (Start) Next State
User wishing to Send S
User wishing to Receive Send RI R
Other Server Request Send COMMAND Start
SERVER (Start)
Gets SI R
Gets RI (file fnd) S
(no file) Send NR Start
Gets COMMAND (Do Command) Start
---------------------------------------------------------
All states except Send Data should timeout if nothing is heard
for a period of time Tc (Crash timer). Send Data isn't expecting
any input and if it should receive some it must be a Cancel, or
a TX (text) packet, otherwise Abort.
--------
Revision 1.1 - Added AF & AT to acknowledge End of File and
End of Transfer. This allows an automated sender to know that
a file was received successfully. It also helps get past a
problem in the TNC-2 code by requiring the sender to wait for the
Ack-EOT before switching from transparent mode back to converse
mode.
RESUME
--------------
The new state introduced from FC1EBN in TPK are explained and is
inserted in
state table for recieve and send a file.
Note that it's valid only if RESUME is true. This will implie or not
the cancellation of file in case of transfer abort.
This metode is ok for resume a file transfert but it have some limit if
the two station hasn't the same RESUME state ON or OFF or not!
1st example:
A is a sender with RESUME OFF and B is receiver with RESUME ON.
A initiate transfer with B and at certain time this will abort.
In this case B (RESUME ON) don't erase the file and retry to download
from A.
Now the transfer always abort because B that already have a part of file
request the resume that A interpret as Abort.
2nd example:
A is a sender and B is receiver both with resume ON.
Today B download PINCO.ZIP (1st version, 10KByte) from A.
Tomorrow in A there is the same filename but with lenght changed due a
new version of program (PINCO.ZIP 2nd version, 11Kbyte).
If B never delete the previous version of PINCO.ZIP from download
directory
the last 1000 byte of new file are append to the 10000 of the old one
make
simply caos!!
This because Yapp never check if it is the same file (eg comparing
filedate
and time).
YappC extension introduced in F6FBB BBS 5.14
--------------------------------------------
When a user request a resume of a previuos file transfer, every Yapp
frame
long pklen byte is followed from a simple checksum byte.
So during a resume a Yapp Send_Data frame is:
STX len (Data) chksum
If len = 0 then data lenght = 256, note that len not include chksum byte
and
this is the checksum of Data byte.
21/5/92
Extensions to the Yapp protocol used in TPK v 1.65a and FBB v 5.14
------------------------------------------------------------------
HEADER extension:
-----------------
The header now carry the DATE and TIME of the file being transmitted.
[SOH] [Len] [Filename] [NUL] [File Size] [NUL] [Date] [Time] [NUL]
Date and Time are the values reported by DOS, coded in 4 hexadecimal
characters and sent in ASCII.
Receiver has the choice to use extended Yapp with checksum or normal
Yapp.
- Normal Yapp reply is RF as before and the receiver can keep the
date and time information .
- Extended Yapp reply is : RT Receive_TPK
and is coded : [ACK] [ACK]
If receiver reply is RT the protocol used will be what i have called
YappC
for Yapp with checksum. When sender get this packet he MUST use YappC.
Data Packets extension:
-----------------------
If receiver reply is RT the protocol used will be YappC. The checksum
allow
detection of packets corrupted along the link, particularly on the RS232
lines where there is no error control or correction (or very poor !)....
Data packets : [STX] [Len] [Datas] [Checksum]
Checksum is the sum of all datas bytes on 8 bits like Xmodem.
If checksum is bad receiver must send a Cancel and go in the CW state.
Transfer Resuming:
------------------
A new field has been added to the resume reply to tell sender if
receiver
can use YappC or not.
- Resume reply for Yapp: (as used before by TPK and FBB)
[NAK] [Len] [R] [NUL] [Received Length] [NUL]
I I I
I I +-- in ASCII as in the header
I +-- as Resume !
I
+------- len of the following bytes
- Resume reply for YappC:
[NAK] [Len] [R] [NUL] [Received Length] [NUL] [C] [NUL]
I
Tell sender i can go in YappC -----+
When sender get this packet he must use YappC.
Pr4Win by Bernd M. Stroj (OE8DJK), last updated on May 7, 1998.