Dear Carles,
On 20.10.19 17:54, Carles Gomez Montenegro wrote:
Dear Alexander,
Dear Carles,
On 20.10.19 15:37, Carles Gomez Montenegro wrote:
Dear Alexander,
Thanks for your responses.
To some extent, I see similarities between the environment you are
considering (CAN) and MS/TP. Few years ago, the 6Lo WG produced RFC
8163,
which specifies IPv6 over MS/TP.
The main difference I see between CAN and MS/TP is the packet/frame
size. MS/TP satisfies the minimal requirements of 1500 octets minimal
MTU where CAN only has 8 octets of payload per frame. 6LoCAN therefore
defines a fragmentation an reassembly.
Your draft proposes using a subset of ISO-TP for fragmentation and
reassembly.
Clarifying question: is ISO-TP part of the CAN protocol (stack)?
The CAN specification does only define the data-link-layer. ISO-TP is an
ISO-Standard (ISO 15765-2:2016). It defines a transport protocol and
network layer services. 6LoCAN uses the fragmentation/reassembly and
flow-control mechanism defined in this standard. Flow-control is only
applied on unicast packets.
I understand that using header compression reduces the amount of IPv6
packets that will require fragmentation. Also, it provides a more
efficient use of the bus. Interesting!
IPHC helps to reduce the number of frames needed to send an IPv6 packet.
Nevertheless, sending an IPv6 packet in a single frame is only possible
for CAN-FD (up to 64 bytes payload). Classical CAN always needs
fragmentation and reassembly.
I see. Anyway, there is the need to comply with the 1280-byte IPv6 MTU
requirement, but it is already satisfied in your draft.
In my opinion, 6LoCAN is the right WG because it defines a
"6lo-adaption-layer". It specifies a fragmentation and reassembly as
other 6lo technologies do.
I actually mentioned MS/TP and the (6Lo-produced) RFC 8163 to emphasize
the potential similarities with CAN (and 6LoCAN), since the 6Lo WG has
also dealt with technologies with somewhat different characteristics (e.g.
wireless, mesh topologies, energy-constrained devices, etc.).
[1] https://en.wikipedia.org/wiki/ISO_15765-2
--
Alexander Wachter, BSc
Student of Information and Computer Engineering
Graz University of Technology
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