I am the assigned Gen-ART reviewer for this draft. For background on
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Please resolve these comments along with any other Last Call comments
you may receive.
Document: draft-ietf-6lo-btle-13.txt
Reviewer: Elwyn Davies
Review Date: 2015/06/01
IETF LC End Date: 2015/06/09
IESG Telechat date: (if known) -
Summary:
Major issues:
Minor issues:
s2.2: As I read this section, it seems to imply (but doesn't make it
totally clear) that a peripheral would only connect to a single central
over IPv6 at a time. Is this true? Mesh networking being out of scope
would appear to be another issue that would not necessarily preclude a
peripheral from having multiple interfaces to different centrals -
provided it was capable of handling the multiple interfaces - but would
not need to act as a router. OK, this might not be something that would
be an everyday event in the IoT but it would be good to make it clear
what the specification implies in this area.
s3.2, para 5: [This is just fractionally more than editorial] The
selection of the multilink subnet model is important and deserves a
(sub-sub-)section to itself. I suggest moving the second and subsequent
sentences of para 5 of s3.2 to a new s3.2.1 and renumbering the
remaining sub-sub-sections, thus:
OLD:
Bluetooth LE connections used to build a star topology are point-to-
point in nature, as Bluetooth broadcast features are not used for
IPv6 over Bluetooth LE (except for discovery of nodes supporting
IPSS). As the IPv6 over Bluetooth LE is intended for constrained
nodes, and for Internet of Things use cases and environments,
multilink model's benefits are considered to overweight multilink
model's drawbacks described in RFC 4903 [RFC4903]. Hence a multilink
model has been chosen, as further illustrated in Section 3.3.
Because of this, link-local multicast communications can happen only
within a single Bluetooth LE connection, and thus 6LN-to-6LN
communications using link-local addresses are not possible. 6LNs
connected to the same 6LBR has to communicate with each other by
using the shared prefix used on the subnet. The 6LBR ensures address
collisions do not occur (see Section 3.2.2) and forwards packets sent
by one 6LN to another.
After the peripheral and central have connected at the Bluetooth LE
level, the link can be considered up and IPv6 address configuration
and transmission can begin.
3.2.1. Stateless address autoconfiguration
...
NEW:
Bluetooth LE connections used to build a star topology are point-to-
point in nature, as Bluetooth broadcast features are not used for
IPv6 over Bluetooth LE (except for discovery of nodes supporting
IPSS).
After the peripheral and central have connected at the Bluetooth LE
level, the link can be considered up and IPv6 address configuration
and transmission can begin.
3.2.1. IPv6 Subnet Model
In the Bluetooth LE piconet model (see Section 2.2) peripherals each
have a separate link to the central and the central acts as an IPv6
router rather than a link layer switch. As discussed in [RFC4903],
conventional usage of IPv6 anticipates IPv6 subnets spanning a single
link at the link layer. As IPv6 over Bluetooth LE is intended for
constrained
nodes, and for Internet of Things use cases and environments, the
complexity of implementing a separate subnet on each peripheral-central
link and routing between the subnets appears to be excessive. In the
Bluetooth LE case, the benefits of treating the collection of
point-to-point
links between a central and its connected peripherals as a single
multilink
subnet rather than a multiplicity of separate subnets are considered to
outweigh the multilink model's drawbacks as described in RFC 4903
[RFC4903].
Hence a multilink model has been chosen, as further illustrated in
Section 3.3.
Because of this, link-local multicast communications can happen only
within a single Bluetooth LE connection, and thus 6LN-to-6LN
communications using link-local addresses are not possible. 6LNs
connected to the same 6LBR have to communicate with each other by
using the shared prefix used on the subnet. The 6LBR ensures address
collisions do not occur (see Section 3.2.3) and forwards packets sent
by one 6LN to another.
3.2.2. Stateless address autoconfiguration
....
END
Nits/editorial comments:
General: Prefer 'octet' to 'byte'.
General: Consistent use of 'link layer' or 'link-layer' - both are used
in a somewhat aribitrary fashion.
Abstract: s/is standardized since the revision/has been standardized
since revision/
Abstract: The 6LoWPAN acronym needs to be expanded.
s1: To be consistent with the abstract it would be best if the
connection (equivalence) between Bluetooth Smart and Bluetooth LE was
reiterated in the first sentence and noted that Bluetooth LE is used in
the rest of the document.
s1, para 1: To avoid jargon s/coin cell/very low capacity (e.g., "coin
cell")/
s1, para 2: Suggest s/ideal protocol/ideal protocol for communication
with such devices/ to make it clear what it is ideal for.
s1, para 3: 802.15.4 needs a reference. Should this be to the updated
2011 version ( RFC 4944 refers to the 2003 standard)?
IEEE Computer Society, "IEEE Std. 802.15.4-2011 IEEE Standard for Local
and metropolitan area networks--
Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs)", June 2011.
s1, para 3: The general connection to 6LoWPAN mentioned in the last
sentence of the Abstract ought to be repeated at the start of para 3;
OLD:
RFCs 4944, 6282, and 6775 [RFC4944][RFC6282][RFC6775] specify the
transmission of IPv6 over IEEE 802.15.4.
NEW:
This document describes how IPv6 is transported over Bluetooth Smart
(also known as
Bluetooth LE) low power connections using IPv6 over Low power
Wireless Personal Area
Networks (6LoWPAN) techniques. RFCs 4944, 6282, and 6775
[RFC4944][RFC6282][RFC6775]
developed for 6LoWPAN specify the transmission of IPv6 over IEEE
802.15.4.
END
s1.1, para 2: Please include the expansions of the acronyms 6LN, 6LR and
6LBR here.
s2, para 1:
Bluetooth LE is designed for transferring small amounts of data
infrequently at modest data rates at a very low cost per bit.
Presumably this is energy cost? Maybe better:
s/at a very low cost/with a very small energy expenditure/
s2, para 2: s/published/published the/,
s/includes/includes the/,
s/link-layer/a link-layer/
s2, para 2: To be clear 'newer' (presumably) applies to both BT 4.1 and
IPSP 1.0:
s/newer/more recent versions of either specification to provide
necessary capabilities/
s2, para 3:
OLD:
which will include Bluetooth 4.1 chipsets
NEW:
that incorporate chipsets implementing Bluetooth 4.1 or later
END
s2, para 3: The standard cannot guarantee presences of Bluetooth LE:
s/will also be included/is also expected to be included/
s2.1, para 1:
The device internal Host Controller Interface (HCI)
I don't think the qualifier 'device internal' really helps here and
could be usefully omitted.
The nature of the interface is explained in the following text.
s2.2, para 1: 'but since Bluetooth 4.1' is a bit ambiguous. After some
thought, I assume it is supposed to mean that the capability to connect
to multiple centrals at once started only with BT 4.1. How about:
OLD:
but since Bluetooth 4.1 can also connect to multiple centrals.
NEW:
but with versions of Bluetooth from 4.1 onwards it can also connect to
multiple centrals at the same time.
END
s2.2, para 1: s/i.e. a Bluetooth/i.e., a Bluetooth/
s2.3, para 1: Hope the device isn't running on AC!!
OLD:
This typically happens at every power cycle of a device.
NEW:
New addresses are typically generated each time a device is powered on.
END
s2.4, title: s/packets sizes/packet sizes/
s2.4: s/Optimal/The optimal/,
s/Default MTU/The default MTU/,
s/exclusing L2CAP/excluding the L2CAP/,
s/protocol data/a protocol data/,
s/link layer fragmentation/a link layer fragmentation/,
s/provides MTU/provides an MTU/
s/single link-layer MTU value/an equal link layer MTU for the
two directions/
s3, para 1: s/due Bluetooth LE's/due to Bluetooth LE's/
s3, para 2: s/both star and mesh topology/both star and mesh topologies/,
s/inter- peripheral/inter-peripheral/ [Space removed]
s3, para 4: s/Bluetooth SIG/the Bluetooth SIG/
s3, last sentence: This duplicates the statement made in s2 (subject to
the mod proposed above). It could be omitted. However, if repeating it
is thought worthwhile, it might be better right at the start of s3.
s3.1: s/IPv6 stack/the IPv6 stack/,
s/GATT stack/the GATT stack/,
s/Bluetooth LE/the Bluetooth LE/,
s/GATT/The GATT/
s/Internet/The Internet/
s3.2, para 1: s/The concept of/The distinct concepts of the/,
s/needs/need/, s/the relationship/their relationship/
s3.2, para 2: s/6LoWPAN/the 6LoWPAN/,
s/use of 1280 byte/use of a 1280 byte [octet] MTU/
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