draft-masotta-tftpexts-windowsize-opt-00.txt Patrick Masotta/Vercot
Intended status: Proposed Standard
INTERNET-DRAFT March 2012
Expires: Aug 07, 2012
TFTP Windowsize Option
Abstract
The Trivial File Transfer Protocol [1] is a simple, lock-step, file
transfer protocol which allows a client to get or put a file onto a
remote host. One of its primary uses is the booting of diskless
nodes on a Local Area Network. TFTP is used because it is very
simple to implement in a small node's limited ROM space. However,
the choice of a lock-step schema is not the most efficient for use
on a LAN.
This document describes a TFTP option which allows the client and
server to negotiate a windowsize of consecutive blocks to send
as an alternative for replacing the lock-step single block schema.
The TFTP Option Extension mechanism is described in [2].
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FOR A PARTICULAR PURPOSE.
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provisions of BCP 78 and BCP 79.
Distribution of this draft is unlimited. It is intended to become the
new BCP 42 obsoleting RFC 6195. Comments should be sent to the DNS
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Windowsize Option Specification
The TFTP Read Request or Write Request packet is modified to include
the blocksize option as follows. Note that all fields except "opc"
are NULL-terminated.
Patrick Masotta Expires Aug 07, 2012 [Page 1]
Internet Draft TFTP Windowsize Option March 2012
+-------+---~~---+---+---~~---+---+-----~~-----+---+---~~---+---+
| opc |filename| 0 | mode | 0 | windowsize | 0 | #blocks| 0 |
+-------+---~~---+---+---~~---+---+-----~~-----+---+---~~---+---+
opc
The opcode field contains either a 1, for Read Requests, or 2,
for Write Requests, as defined in [1].
filename
The name of the file to be read or written, as defined in [1].
mode
The mode of the file transfer: "netascii", "octet", or "mail",
as defined in [1].
windowsize
The Windowsize option, "windowsize" (case in-sensitive).
#blocks
The number of blocks in a window, specified in ASCII. Valid
values range between "1" and "65464" blocks, inclusive. The
windowsize refers to the number of consecutives blocks
transmited before stop and wait for the reception of the
ack of the last block transmited.
For example:
+-------+--------+---+--------+---+------------+---+------+---+
| 1 | foobar | 0 | binary | 0 | windowsize | 0 | 16 | 0 |
+-------+--------+---+--------+---+------------+---+------+---+
is a Read Request, for the file named "foobar", in binary transfer
mode, with a window size of 16 blocks (as blocksize is not defined
the 512 Bytes per block default applies).
If the server is willing to accept the windowsize option, it sends
an Option Acknowledgment (OACK) to the client. The specified value
must be less than or equal to the value specified by the client.
The client must then either use the size specified in the OACK,
or send an ERROR packet, with error code 8, to terminate the
transfer.
The rules for determining the final packet are unchanged from [1].
The reception of a data window with a number of blocks length less
than the negotiated windowsize is the final window. If the
windowsize is greater than the amount of data to be transfered,
the first window is the final window. If the amount of data to be
transfered is an integral multiple of the windowsize, an extra
data packet containing no data is sent to end the transfer.
Patrick Masotta Expires Aug 07, 2012 [Page 2]
Internet Draft TFTP Windowsize Option March 2012
Proof of Concept
Performance tests were run on the prototype implementation using a
variety of windowsizes and a fixed blocksize of 1456 bytes. The
tests were run on a lightly loaded Gigabit Ethernet, between two
Toshiba Tecra Core 2 Duo 2.2 Ghz, in "octet" mode, on 180MB files.
Seconds |
|
300 +
| windowsize time(s)
| --------- ------
| x 1 257
250 + 2 131
| 4 76
| 8 54
| 16 42
200 + 32 38
| 64 35
|
|
150 +
|
| x
|
100 +
|
| x
|
50 + x
| x
| x x
|
0 +----+-----+-----+-----+-----+-----+-----+--
1 2 4 8 16 32 64
windowsize (blocks of 1456 bytes)
Patrick Masotta Expires Aug 07, 2012 [Page 3]
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The comparisons between transfer times (without a gateway) between
the standard lock-step schema and the negotiated windowsizes are:
1 -0%
2 -49%
4 -70%
8 -79%
16 -84%
32 -85%
64 -86%
As was anticipated, the transfer time decreases with the use of a
windowed schema. The reason for the reduction in time is the
reduction in the number of the required synchronous acknowledgement
exchanged.
Error Handling
In case of an error detection the whole windowsize window is
retransmited.
Security Considerations
The basic TFTP protocol has no security mechanism. This is why it
has no rename, delete, or file overwrite capabilities. This document
does not add any security to TFTP; however, the specified extensions
do not add any additional security risks.
References
[1] Sollins, K., "The TFTP Protocol (Revision 2)", Request for
Comments 1350 (STD 33), October 1992.
[2] Malkin, G., Harkin, A., "TFTP Option Extension", RFC 1782 March
1995.
Authors' Addresses
Patrick Masotta
300 W 11th Avenue, #9A
Denver, CO 80204
EMail: masotta@vercot.com
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