Subject: [Last-Call] Iotdir telechat review of draft-ietf-lpwan-schc-over-lorawan-10

From: JADHAV Rahul via Datatracker <[email-masked]>
Date: Sun, 20 Sep 2020 11:45:41 -0700

Reviewer: JADHAV Rahul
Review result: Ready with Issues

Dear authors of schc-over-lorawan,

Thank you for this work.
Following is my review handled as part of IoT-DIR review process:

Section 4:
[RJ] The architecture shows "Join Server" but the section has no explanation
for it.

Section 4:
"The Network Gateway (NGW) is the interconnection node between the Radio
Gateway and the Internet." [RJ] It is mentioned that NGW is the gateway to the
Internet but the SCHC C/D and F/R is handled on the LoRaWAN application server.
How would the compressed packets be sent out to the Internet from NGW? [RJ] In
the last para of the section it is mentioned that "(SCHC gateway) acts as the
first-hop IP router for the device. This means that the NGW is not the
interconnection node between the RGW and the Internet.

Section 4:
[RJ] The terms used in the architecture figure 3 and the document are
different/confusing. For e.g., the figure mentions Application Server which is
referred to as SCHC Gateway in the overall document. The figure mentions
Network Server but is referred to as Network Gateway (NGW) in the overall
document. As a reader, I wanted to use this architecture diagram as a ref but
the terms mentioned in the diagram are different from those used in the draft
elsewhere.

Section 4.1:
"The lower the downlink latency, the higher the power consumption."
[RJ] I didn't understand why lower latency could result in higher power
consumption. I think the intention was to use either downlink frequency or
listen periodicity as a driver for higher power consumption.

Section 4.3/4.4:
[RJ] The terms "frames" and "messages" are used interchangeably. Would be
better to use a fixed term, or else clarify these terms in the document.

Section 4.6:
[RJ] FRMPayload is not defined anywhere.

Section 5.1:
[RJ] I believe the term "fragmented datagram" should be used in place of
"fragmentation datagram" in the whole of this para.

Section 5.1:
"It uses another FPort for data downlink and its associated SCHC control
uplinks, named FPortDown in this document." [RJ] Just for my understanding, the
FPortUp and FPortDown are disjoint sets i.e., an FPort part of FPortUp set
cannot be part of the FPortDown set. Is this correct? If yes, can we make it
explicit in the document?

Section 5.2:
"RuleID = 22 (8-bit) for which SCHC compression was not possible..."
[RJ] I believe RuleID = 22 is provisioned for LoRaWAN messages which are sent
uncompressed i.e., if a device wants to send an uncompressed IPv6 then it can
use this RuleID. Is this correct? If yes, can we state this sample use-case for
RuleID=22?

Section 5.3:
"There is a small probability of IID collision in a LoRaWAN network, if such
event occurs the IID can be changed by rekeying the device on L2 level (ie:
trigger a LoRaWAN join)." [RJ] As I understand, IID collision can be detected
only by the Network Gateway. How would the Network Gateway initiate a LoRaWAN
join? Section 4.4 defines that only the end device can initiate a JoinRequest
frame.

Section 5.6.1:
Please provide a reference to Section 8.2.4 in RFC 8724 for DTag.

Section 5.6.2:
The term Tile is not defined in the document nor is there a ref to RFC 8724.
Better to redefine it here or at least have a ref to RFC 8724.

Section 5.6.3:
The term "applicative uplink" is used in this and subsequent sections. Are you
referring to the application uplink? Not sure of what applicative means in the
context?

Section 5.6.3.5.1:
"LoRaWAN layer will respect the regulation if required."
I believe the local spectrum regulation is what is referred here, but am not
sure.

Section 6: Security Considerations
The section mentions the use of IID for privacy protection and the use of
AES-128 encryption for payload encryption. However, it is not clear to me as to
how the replay protection can be handled i.e. if an attacker replays the data
sent by any other node previously, how can it be protected? I believe this is
handled as part of the LoRaWAN mac layer?

Minor Nits:

Section 3:

Known information are part of the "context".
Known information is of the "context".

This component called SCHC...
This component is called SCHC...

...the RG is called a Gateway...
...the RGW is called a Gateway...

Section 4:

SCHC C/D and F/R are LoRaWAN Application Server;
SCHC C/D and F/R are handled by LoRaWAN Application Server;

Section 4.4:
...contains (amongst other fields) the major network's settings...
...contains (amongst other fields) the network's major settings...

Section 4.7:
...a packet send over LoRaWAN radio link...
...a packet sent over LoRaWAN radio link...

Section 5.2:
In order to improve interoperability RECOMMENDED fragmentation....
In order to improve interoperability, RECOMMENDED fragmentation....

Section 5.6.2:
In that case the device is the fragmentation transmitter, and the SCHC gateway
the fragmentation receiver. In that case, the device is the fragment
transmitter, and the SCHC gateway is the fragment receiver.

Section 5.6.3.1: Figure title
"including LoraWAN FPort"
"including LoRaWAN FPort"

Section 6: Section Title
Security considerations
Security Considerations