Hi Pascal
Draft "draft-ietf-6lo-fragment-recovery" seem to assume that the size of the
compressed header stay fix while traveling the RPL domain.
For example:
"In this specification, the size and offset of the fragments are expressed on
the compressed packet."
"The last fragment for a datagram is recognized when its fragment_offset and
its fragment_size add up to the datagram_size."
However, fields HLIM [RFC6282], CmprI and CmprE [RFC6554] may have an impact on
the compressed header size if the maximum compression is applied at each hop.
Is this problem addressed in the draft?
Are you aware of other IPv6 fields or options which can cause this issue?
How this issue should be addressed?
I tried to illustrate this problem in the example bellow:
IPv6 packet
- IPv6 packet header
- Hop limit = 66 (elided)
- Source Address = FE80 0000 0000 0000 0201 4200 0000 0000 (elided)
- Destination Address = FE80 0000 0000 0000 0214 7700 0000 0001 (elided)
- RPL routing header
- CmprI = 15
- CmprE = 9
- Addresses = FE80 0000 0000 0000 0214 7700 0000 0002, FE80 0000 0000 0000
0214 7700 0000 0003, FE80 0000 0000 0000 0200 0C00 0000 0004
IPv6 packet
- IPv6 packet header
- Hop limit = 65 (elided)
- Source Address = FE80 0000 0000 0000 0201 4200 0000 0000 (elided)
- Destination Address = FE80 0000 0000 0000 0214 7700 0000 0002 (elided)
- RPL routing header
- CmprI = 15
- CmprE = 9
- Addresses = FE80 0000 0000 0000 0214 7700 1234 0001, FE80 0000 0000 0000
0214 7700 1234 0003, FE80 0000 0000 0000 0201 42AB CDEF 0004
IPv6 packet
- IPv6 packet header
- Hop limit = 64 (in line)
- Source Address = FE80 0000 0000 0000 0201 4200 0000 0000 (elided)
- Destination Address = FE80 0000 0000 0000 0214 7700 0000 0003 (elided)
- RPL routing header
- CmprI = 9
- CmprE = 9
- Addresses = FE80 0000 0000 0000 0214 7700 1234 0001, FE80 0000 0000 0000
0214 7700 0000 0002, FE80 0000 0000 0000 0201 42AB CDEF 0004
IPv6 packet
- IPv6 packet header
- Hop limit = 63 (elided)
- Source Address = FE80 0000 0000 0000 0201 4200 0000 0000 (elided)
- Destination Address = FE80 0000 0000 0000 0200 0C00 0000 0004 (elided)
- RPL routing header
- CmprI = 9
- CmprE = 9
- Addresses = FE80 0000 0000 0000 0214 7700 1234 0001, FE80 0000 0000 0000
0214 7700 0000 0002, FE80 0000 0000 0000 0214 7700 0000 0003
Regards,
Michel
From: Pascal Thubert (pthubert) <[email protected]>
Sent: Monday, January 21, 2019 6:58 AM
To: Michel Veillette <[email protected]>; Dario Tedeschi
([email protected]) <[email protected]>
Cc: [email protected]
Subject: RE: draft-ietf-6lo-fragment-recovery maximum fragment size too small
Works for me Michel :
So we need answers from the list. The choice on the table is either to reduce
the datagram_tag field to 256 as illustrated below or to use a 4 bytes unit for
links with large MTUs (more than 127 octets).
What do people think is more appropriate to their needs?
Pascal
From: Michel Veillette
<[email protected]<mailto:[email protected]>>
Sent: jeudi 17 janvier 2019 18:56
To: Pascal Thubert (pthubert) <[email protected]<mailto:[email protected]>>;
Dario Tedeschi ([email protected]<mailto:[email protected]>)
<[email protected]<mailto:[email protected]>>
Cc: [email protected]<mailto:[email protected]>
Subject: RE: draft-ietf-6lo-fragment-recovery maximum fragment size too small
Hi Pascal
I'm sorry, the propose format in my last email doesn't fix the datagram total
length limitation.
32 fragments of 512 bytes still limit the datagram to 16 kB.
Based on the following constraints:
* Up to 256 active datagram
* Up to 32 fragments
* Up to 64kB datagram
* Up to 2kB fragment (32 fragments of 2 kB = 64 kB datagram)
I recommend the following Dispatch type formats.
Alternatively, the original format with a 4 bytes unit will work for us but
doesn't seem to address all potential issues.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 1 0 0|X| datagram_tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| sequence| fragment_size | fragment_offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 1 0 1 Y| datagram_tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RFRAG Acknowledgment Bitmap (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Regards,
Michel
From: Michel Veillette
Sent: Wednesday, January 16, 2019 9:04 PM
To: 'Pascal Thubert (pthubert)'
<[email protected]<mailto:[email protected]>>; Dario Tedeschi
([email protected]<mailto:[email protected]>)
<[email protected]<mailto:[email protected]>>
Cc: [email protected]<mailto:[email protected]>
Subject: RE: draft-ietf-6lo-fragment-recovery maximum fragment size too small
Using a 4 bytes unit for size and offset doesn't seem to fully solve all
issues, this solution is still limited to 8 kB datagram.
About the dual formats proposal, I'm not convinced this problem is such we
can't find a single format acceptable for everyone.
If maintaining an overhead of 6 bytes is a must, the solution below might be
the best compromise.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 1 0 0| fragment_size |X|E| sequence| datagram_tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fragment_offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 1 0 1 0|Y| Reserved | datagram_tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RFRAG Acknowledgment Bitmap (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Regards,
Michel
From: Pascal Thubert (pthubert) <[email protected]<mailto:[email protected]>>
Sent: Wednesday, January 16, 2019 9:59 AM
To: Michel Veillette
<[email protected]<mailto:[email protected]>>
Cc: [email protected]<mailto:[email protected]>
Subject: RE: draft-ietf-6lo-fragment-recovery maximum fragment size too small
Hello Michel
I have not seen a strong argument against saying that the unit for size and
offset is 4 bytes if the MTU is larger than 127 bytes. This keeps classical
802.15.4 with 1 octet and allows fragments of 512 with 802.15.4g. that would be
the simplest and most economical way of doing it. The only issue is that the
last fragment might be less than the fragment_size, but that can be found based
on the frame size. This seems to be the best tradeoff to me.
As an alternate we could define both of the formats that you copied below, one
as 1 1 1 0 1 0 and the other as 1 1 1 0 1 1 as follows:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 1 0 0|X| datagram_tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| sequence| fragment_size | fragment_offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 1 0 1 Y| datagram_tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RFRAG Acknowledgment Bitmap (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
vs.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 1 1 0|X| datagram_tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| sequence| fragment_size | fragment_offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 1 1 1 Y| datagram_tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RFRAG Acknowledgment Bitmap (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
what do you think?
Pascal
From: Michel Veillette
<[email protected]<mailto:[email protected]>>
Sent: mardi 15 janvier 2019 20:14
To: Pascal Thubert (pthubert) <[email protected]<mailto:[email protected]>>
Subject: RE: draft-ietf-6lo-fragment-recovery maximum fragment size too small
Hi Pascal
Did we reach any consensus about the RFRAG Dispatch type format?
See the last two formats proposed bellow.
Regards,
Michel
From: Michel Veillette
Sent: Tuesday, January 8, 2019 2:28 PM
To: Pascal Thubert (pthubert) <[email protected]<mailto:[email protected]>>
Cc: [email protected]<mailto:[email protected]>
Subject: RE: draft-ietf-6lo-fragment-recovery maximum fragment size too small
Hi Pascal
A 8 bits "datagram_tag" is a strict minimum in our case and peoples might have
good arguments to keep this field aligned with RFC4944.
I also don't see how to implement a 10 bits or 12 bits "datagram_tag" without
adding an octet.
I can go either way but my preference are:
- 16 bits datagram_tag
- 10 bits fragment_size
- 16 bits fragment_offset
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 1 0 0|X| datagram_tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| sequence| fragment_size | fragment_offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 1 0 1 Y| datagram_tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RFRAG Acknowledgment Bitmap (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
vs.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 1 0 0|X| datagram_tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| sequence| fragment_size | fragment_offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 1 0 1 Y| datagram_tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RFRAG Acknowledgment Bitmap (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Regards,
Michel
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