Re: [Roll] Review of draft-ietf-roll-urban-routing-reqs-01

Dear all,

Thanks to Jean-Philippe for this thorough review. Please find a first
shot of personal comments inline, but I'll let my fellow co-authors
further elaborate accordingly.

	[CJ] [snip] 
	Abstract
	#######
	s/ for a wireless ROLL solution to be useful the protocol(s)
ought to be energy-efficient, scalable, and autonomous/ the routing
solution ought to be energy-efficient, scalable and autonomous.

	JP> You may want to use a different word than "Autonomous". Do
you refer to the "self configuration" property ?
	[CJ] We chose "autonomous" because it was generic enough, while
I think "self configuration" is too restrictive: it's not only a matter
of configuration, it's also a matter of making (forwarding) decisions,
self-healing capabilities, etc. Another word I would suggest is
"self-organizing", if this is more specific. 

	Section 1
	#######
	* "Section 6 discusses the routing requirements for networks
comprising
	   such constrained devices in a U-LLN environment.  These
requirements
	   may be overlapping requirements derived from other
application-
	   specific requirements documents or as listed in
	   [I-D.culler-rl2n-routing-reqs]."

	JP> Please remove this reference (ID abandoned) and insert
reference to
http://www.ietf.org/internet-drafts/draft-ietf-roll-home-routing-reqs-02
.txt
<http://www.ietf.org/internet-drafts/draft-ietf-roll-home-routing-reqs-0
2.txt> ,
http://www.ietf.org/internet-drafts/draft-ietf-roll-indus-routing-reqs-0
1.txt
<http://www.ietf.org/internet-drafts/draft-ietf-roll-indus-routing-reqs-
01.txt>  and
http://www.ietf.org/internet-drafts/draft-martocci-roll-commercial-routi
ng-reqs-00.txt
<http://www.ietf.org/internet-drafts/draft-martocci-roll-commercial-rout
ing-reqs-00.txt> .
	[CJ] OK. 

	* s/ Section 7 provides an overview of security considerations/
Section 7 provides an overview of routing security considerations 
	[CJ] OK. 

	Section 2
	########

	* S/ ROLL: Routing over Low power and Lossy networks/ ROLL:
Routing Over Low power and Lossy networks
	[CJ] OK. 

	* Schedule:  An agreed execution, wake-up, transmission,
reception,
	         etc., time-table between two or more field devices.
	The definition is a little bit too vague. If used in the generic
sense, no need to add it to the terminology section. Otherwise, it ought
to be more specific.
	[CJ] Schedule is indeed very generic, but I think the sue of the
word makes perfect sense in the context of U-WSN networks. Being more
specific would mean elaborating on use cases where schedule information
is taken into account by field devices to perform some specific action.
If this proposal makes sense, I'm not sure the terminology section is
appropriate for such elaboration and would therefore suggest we (1) keep
the "schedule" definition in this section and (2) further elaborate on a
use case that illustrates the use of schedule information in section 5
of the draft. 

	Section 3.1.1
	###########
	* S/ pre- planned location/ pre-planned location
	[CJ] OK. 

	* What you refer to as a repeater is in fact a router. What I
would suggest here is to reword this paragraph to indicate that some
nodes are simple routers whereas other nodes are routers and lso perform
sensing/actuating task. Insert this paragraph after the Actuators and
Sensors paragraphs.
	[CJ] So you're suggesting to (1) remove section 3.1.2 (not
3.1.1, actually), and (2) indicate that some nodes are routers (not
"simple", btw :-), others also perform sensing/actuating tasks, right?
I'm fine with this suggestion, but I'd like to hear the feedback from my
colleagues. It's also worth mentioning that a "repeater" has a very
specific meaning in "classical" networking environments, remembering the
old days of FOIRL and the like...that may be another reason to avoid the
use of this notion within the roll context.

	* "Actuators may generally be mobile but are likely to be static
in the majority of near-future roll-outs": seems a bit contradictory.
Don't you want to simply say that in a near-future the majority will be
static?
	[CJ] Not quite, because actuators can be devices used by people
who move from one place to another to check how the sensor network is
doing. I think both cases are valid, and would therefore stick to the
current wording. 

	* "Similar to the access points, actuator nodes do not suffer
from any long-term resource constraints." what about battery-operated
actuators ?
	[CJ] I'll leave that one to my colleagues :-) 

	Section 3.1.4
	###########
	* "pollution data, such as polluting gases (SO2, NOx, CO,
Ozone),
	 heavy metals (e.g.  Mercury), pH, radioactivity, etc;" =>
please expand acronym when first used.
	[CJ] Hmmm...I don't see too many acronyms in that sentence,
actually. This is chemistry stuff, unless you're suggesting we provide
the "lettered" designation of these substances like carbon oxyde, etc.?
I wouldn't go that way... 

	* "These meters will be capable of
	   advanced sensing functionalities such as measuring quality of
	   service, providing granular interval data, or automating the
	   detection of alarm conditions."
	You may want to more accurately define the term "quality of
service" since as you know, we used that term of other purposes in IETF
documents.
	[CJ] Agreed. Since this is a list of examples, I would suggest
something like "measuring the quality of the water provided to the
customers".

	* In addition they may be capable of
	   advanced interactive functionalities such as remote service
	   disconnect or remote demand reset." => in this case, they are
also acting as actuators.
	[CJ] Agreed. 

	Section 3.2 
	#########

	* s/ between one other/between each other
	[CJ] OK. 

	* "The network MUST be capable of supporting the organization of
	   a large number of sensing nodes into regions containing on
the order
	   of 10^2 to 10^4 sensing nodes each."
	JP> Thanks to make this "MUST" routing-specific and move it to
the requirements section.
	[CJ] Agreed - would suggest this should be the introductory
sentence of section 6.1. 

	Section 3.3
	#########

	* RFID: expand acronym (Radio Frequency IDentification) and add
to the terminology section
	[CJ] OK. 

	* s/battery-powered nodes/battery powered nodes
	[CJ] OK. 
	"Sensor nodes are capable of forwarding data." In other words,
they can act as routers. No need to repeat this here.
	[CJ] Fair enough. 

	Section 3.4
	#########

	* "2.  packet errors due to medium access control;" JP> It is
not really "packet error" here.
	[CJ] Do you mean "transmission erros"? If so, I would agree with
you that this wording is better, but then I guess it should be used for
first three cases, right? 

	* Some available protocols may cause packets of neighbouring
nodes to collide and hence cause a link outage." JP> You may want to be
more specific "Some" ?
	[CJ] Do you mean examples, because the previous sentence
mentions the L2 protocols this sentence refers to?

	* "if ISM bands are to be used.  For instance, if the 2.4GHz ISM
band is
	   used to facilitate communication between U-LLN nodes, then
heavily
	   loaded WLAN hot-spots become a detrimental performance factor
	   jeopardizing the functioning of the U-LLN."
	JP> Please expand acronym when first used and add to the
terminology section (ISM, WLAN, ...)
	[CJ] OK. 

	* Don't you want to say a few words about the varying BER
leading to potentially even higher packet error loss ratio?
	[CJ] Expand the acronym ;-) I agree, bit error rate
considerations should deserve a couple of sentences in this section. 

	Section 4.1
	#########

	* "Pre-programmed MAC": expand acronym
	[CJ] OK. 

	* "the autonomous organization" => self-organizing?
	[CJ] Much better indeed. 

	* "For example, nodes in urban sensor nodes SHOULD be able to:"
=> Several of the requirements that follow are nor routing specific. You
may either want to change the SHOULD for a "should" or just focus on the
routing aspects and move them to the routing requirements section.
	[CJ] They may not be routing specific, but I think they do
affect how routing policies are enforced. I woudl therefore suggest we
stick to the proposed wording. 

	* "o  Dynamically compute, select and possibly optimize the
(multiple)
	      path(s) that will be used by the participating devices to
forward
	      the traffic towards the actuators and/or the access point
	      according to the service-specific and traffic-specific
QoS,
	      traffic engineering and security policies that will have
to be
	      enforced at the scale of a routing domain (that is, a set
of
	      networking devices administered by a globally unique
entity), or a
	      region of such domain (e.g. a metropolitan area composed
of
	      clusters of sensors)."
	JP> You list important and stringent requirements here. Do you
really need a routing algorithms capable of computing a path on a per
QoS/service specific/... Basis ?
	[CJ] I don't read this sentence as you do. What I meant here is
that entities that operate urban sensor networks specify their own
policies (routing, te, security, QoS, etc.), which may be
service-specific. The requirement suggests that the devices involved in
the enforcement of such policies should behave accordingly, that is,
compute, select, establish and maintain paths whose characteristics
comply with these policies. But I agree this is a strong requirement,
but not stronger than, say, the self-organization requirement.

	Section 4.2
	#########

	* "After the initialization phase and possibly some operational
time,
	   new nodes may be injected into the network as well as
existing nodes
	   removed from the network.  The former might be because a
removed node
	   is replaced or denser readings/actuations are needed or
routing
	   protocols report connectivity problems. "
	JP> Just to avoid any mis-interpretation when referring to
routing problem, you mean that it may be desirable to inject to node
because connectivity is not sufficient (lack of enough redundant path,
...) and not because of a routing issue per say.
	[CJ] Not necessarily because connectivity is insufficient (new
services, network expansion, node maintenance, etc.), and not
necessarily because there is a routing issue, indeed. 

	* "Differentiation
	   SHOULD be made between node disappearance, where the node
disappears
	   without prior notification, and user or node-initiated
disassociation
	   ("phased-out"), where the node has enough time to inform the
network
	   about its removal."
	JP> Again this is not a routing requirement. Unless you refer to
the ability for the routing protocol to advertise to the rest of the
network that it will be removed in order for the other node to
re-compute their path and avoid traffic disruption (e.g. Similarly to
what we do with the ISIS overload bit for example.) Is it what you mean
? 
	[CJ] This is indeed what we meant (at least that's my reading of
this sentence, but I'll let my colleagues further comment on that). If
so, please clarify and move the routing requirement (SHOULD in capital
letter to the routing requirement section).
	[CJ] OK. 

	* "The protocol(s) hence SHOULD support the pinpointing of
problematic routing areas"
	JP> Could you clarify what you mean by "pinpointing" since it
could be interpreted in many ways? 
	[CJ] Fair enough, we need to be more explicit. Maybe something
like: "the protocol should be able to convey information about
malfunctioning nodes which may affect or jeopardize the overall routing
efficiency, so that self-configuration capabilities of the sensor
network might be solicited to facilitate the appropriate
reconfiguration."

	* The following section also requires some clarification - you
wrote:
	"Furthermore, to inform the
	   access point(s) of the node's arrival and association with
the
	   network as well as freshly associated nodes about packet
forwarding
	   schedules, roles, etc, appropriate (link state) updating
mechanisms
	   SHOULD be supported."
	JP> Are you explicitly requiring a Link State routing protocol
or a routing protocol that provides information about link states or ...
?
	[CJ] We meant "a protocol that can provide information about
link status", indeed. 
	Note that a requirement document should stay solution agnostic
and stay focus on the requirement. 
	[CJ] Fully agreed. 
	Is you requirement that any node needs to have visibility on
other node characteristics with no attempt of aggregation?
	[CJ] Well, yes, presumably depending on design considerations:
cluster head vs. clients within the cluster, for example. I think this
is typical Self Organizing Networking capability.

	Section 4.3
	#########

	* "The protocol(s) hence MUST support a large number of highly
	   directional unicast flows from the sensing nodes or sensing
clusters
	   towards the access point or highly directed multicast or
anycast
	   flows from the nodes towards multiple access points."
	JP> I think that what you mean is that the routing protocol MUST
be optimized for Multipoint-to-Point traffic patterns (from
sensors/actuators to Sink). As written, it is not clear whether you
refer to it as a routing requirement ?
	[CJ] Agreed. 
	This in fact what you wrote in section 6.5: "To this end, the
routing protocol(s) SHOULD support and utilize the fact of highly
directed traffic flow to facilitate scalability and parameter
constrained routing."
	[CJ] Correct. 

	* s/ More generally, entire routing areas may be avoided at e.g.
night but heavily used during the day when nodes are scavenging from
sunlight/ More generally, entire routing areas may be avoided (e.g. at
night) but heavily used during the day when nodes are scavenging from
sunlight.
	JP> Doesn't this translate to the requirement for time-based
routing (some form of policy routing) ?
	[CJ] Correct, but I don't see any harm in providing a practical
example. 

	Section 4.4
	#########

	"However, they are not very stringent where
	   latencies SHOULD simply be sufficiently smaller than typical
	   reporting intervals"
	JP> This is certainly true but not a routing requirement but a
data plane requirement unless you refer to the ability to support QoS
aware routing where each node may want to be able to compute different
paths depending on the traffic requirements?
	[CJ] This is indeed related to the third bullet that appears in
section 4.1. 

	* Move "U-LLN network devices SHOULD support unicast and
multicast routing capabilities" to the routing requirement section. You
may want to leave the sentence here (without a SHOULD).
	[CJ] OK. 

	* You use the term "anycast" that has been discussed in the
past, in particular in the context of the Home routing requirement
document. I would suggest to define this term in the document, refer to
RFC4291 or RFC1546, ...
	[CJ] Fully agreed. 

	Section 4.5
	#########

	* "An alarm is likely being
	   registered by a plurality of sensing nodes where the delivery
of a
	   single alert message with its location of origin suffices in
most
	   cases."
	Then you provide the example of toxic gas level. This is one
example where it might be desirable not to perform data
aggregation/fusion and get multiple copies of the same message from
different source to perform "triangulation" and better localize the
incident.
	[CJ] Agreed, but I think this example precisely illustrates the
issue. 

	* "Routing within urban sensor networks SHOULD require the U-LLN
nodes
	   to dynamically compute, select and install different paths
towards a
	   same destination, depending on the nature of the traffic.
>From this
	   perspective, such nodes SHOULD inspect the contents of
traffic
	   payload for making routing and forwarding decisions: 

	JP> This clarifies my previous question; you do refer to ability
to compute different paths (with different characteristic). Note that
the path selection process performed by the sender and potentially
routers along the path is not strictly speaking a routing requirement.
	Move this requirement to the requirement section. 
	[CJ] OK. 

	* "for example, the analysis of the traffic payload SHOULD be
derived into aggregation
	   capabilities for the sake of forwarding efficiency."
	JP> Can you clarify what you mean here?
	[CJ] The analysis of the payload of several packets should help
in making forwarding decisions that will spare network resources.

	* "Delays and latencies are
	   important; however, again, deliveries within seconds SHOULD
suffice
	   in most of the cases."
	JP> Clearly not a routing requirement!
	[CJ] Agreed. 

	Section 5
	########

	* "The network SHOULD take into consideration that different
application
	   traffic may require different priorities when traversing the
network,
	   and that some traffic may be more sensitive to latency."
	JP> If by priorities you mean different routes with different
characteristics then this is fine and already covered. If you refer to
packet marking to provide different QoS in the data plane, this is not a
routing requirement.
	[CJ] Agreed - the former is the correct interpretation. 

	* "An U-LLN SHOULD support occasional large scale traffic flows
from
	   sensing nodes to access points, such as system-wide alerts. "
and "A node MUST be able to send its own alerts toward an access
	   point while continuing to forward traffic on behalf of other
devices
	   who are also experiencing an alert condition.  The network
MUST be
	   able to manage this sudden large traffic flow."
	JP> Not routing requirements. Unless ... You require the ability
to compute multiple paths and use all of them (symmetrical or
asymmetrical routing ???) to spread out the traffic and limit network
delays ?
	[CJ] I think this is a kind of causality effect: the routing
protocol must be able to accommodate traffic bursts by dynamically
computing and selecting multiple paths towards the same destination. 

	* You make an interesting reference to Smart Grid and DR/DSM.
That said, you wrote "The network SHOULD support internetworking, while
giving attention to security implications of interfacing, for example, a
home network with a utility U-LLN."
	JP> Don't you mean that the routing protocol must be able to
potentially interact via potential route redistribution with other
routing protocol used in the Internet, should these two protocols not be
identical ?
	[CJ] Correct. 

	Section 6
	#########

	* S/Current urban roll-outs are composed of sometimes more than
a hundred nodes/ Current urban roll-outs are composed of sometimes more
than one hundred nodes
	[CJ] OK. 

	* " The routing protocols(s) SHOULD support the organization of
a large number of nodes into regions of to-be-specified size."
	JP> It will be difficult (or too easy ;-)) to be compliant with
that SHOULD with a to-be-specified size. Or did you mean "configurable"
?
	[CJ] Configurable is indeed much better. 

	* "To this end, the routing protocol(s) MUST support parameter
	   constrained routing, where examples of such parameters (CPU,
memory
	   size, battery level, etc.) have been given in the previous
paragraph."
	JP> Please use the term "node constrained based routing"
	[CJ] I'm not sure I agree here, because "node-constrained"
sounds more fuzzy to me. "environment-constrained"? 

	* "For the latter, the protocol(s) MUST support multi- and
	   any-cast addressing.  The protocol(s) SHOULD also support the
	   formation and identification of groups of field devices in
the
	   network."
	JP> You may want to more accurately define the term "anycast" 
	[CJ] Would the couple of references you righfully mentioned
earlier be sufficient?

	* " To mandate fully interoperable implementations, the routing
	   protocol(s) proposed in U-LLN MUST support different devices
and
	   underlying technologies without compromising the operability
and
	   energy efficiency of the network."
	JP> This requires clarification here. Do you mean that the
routing protocol MUST support node constrained based routing? If so, it
is already stated above. The support of different L1/L2 is a given
(route over).
	[CJ] I would agree with Jean-Philippe, and suggest we remove
this wording...but I'll let the co-authors further comment. 

	* Section 6.8, as written, is not related to routing but data
plane. Let me be more specific:

	* "To this end, the routing protocol(s) SHOULD support minimum
latency
	   for alert reporting and time-critical data queries."
	JP> The support of minimum latency path (data plane !) or the
support for different metric path (control plane) ?
	[CJ] As written, I read it as the former interpretation and
would suggest we remove the text. 

	* "For regular data
	   reporting, it SHOULD support latencies not exceeding a
fraction of
	   the smallest reporting interval.  "
	JP> Not a routing requirement. Even if you are referring to a
bound on the total path metric (the metric reflecting the delay in this
case), this is an implementation issue.
	[CJ] Correct. 

	* "Due to the different latency requirements, the routing
protocol(s) SHOULD support the ability of dealing with different latency
requirements.  The routing protocol(s) SHOULD also support the ability
to route according to different metrics (one of which could e.g. be
latency)."
	JP> yes these are routing requirements although I would suggest
to remove the first sentence, the requirement being captured in the
second sentence.
	[CJ] Agreed. 

	Section 7
	#########

	* "As every network, U-LLNs are exposed to security threats that
MUST be addressed."
	JP> You cannot put a MUST here unless you list the routing
security threats.
	[CJ] OK. 

	* s/ potential security threats/ potential routing security
threats => JP> Please use the term "routing security" in place of
"security" throughout the section. 
	[CJ] OK. 

	* "U-LLN networks SHOULD support mechanisms to preserve the
	   confidentiality of the traffic that they forward.  The U-LLN
network
	   SHOULD NOT prevent an application from employing additional
	   confidentiality mechanisms."
	JP> I do agree with the requirement but this is not a routing
requirement. 
	[CJ] Fair enough. 
	Could you focus on the routing security issues ? Or are you
referring to the routing traffic confidentiality ?
	[CJ] No, this wording referred to the traffic forwarded by the
network.  
	This is what you do right after:
	[CJ] Correct. 
	" The U-LLN MUST be protected against attempts to inject false
or
	   modified packets.  For example, an attacker SHOULD be
prevented from
	   manipulating or disabling the routing function by
compromising
	   routing update messages.  Moreover, it SHOULD NOT be possible
to
	   coerce the network into routing packets which have been
modified in
	   transit.  To this end the routing protocol(s) MUST support
message
	   integrity."
	JP> I do not see any reference to the type of routing attacks
that could be performed on such networks because of the typical P2MP
traffic pattern, extensive use of wireless links, ... 
	[CJ] OK, but does that mean we should not consider such
requirement? I don't think so, afaic. 
	JP> What I would suggest is to re-focus on the routing security
issues with the Security expert that will get appointed.
	[CJ] OK. 

	Reference section
	###############

	The current reference section reads:
	11.2.  Informative References

	   [I-D.brandt-roll-home-routing-reqs]
	              Brandt, A., "Home Automation Routing Requirement
in Low
	              Power and Lossy Networks",
	              draft-brandt-roll-home-routing-reqs-01 (work in
progress),
	              May 2008.

	JP> Please update to draft-ietf-roll-home-routing-reqs and add
the reference to draft-ietf-roll-indus-routing-reqs
	[CJ] OK. 

	   [I-D.culler-rl2n-routing-reqs]
	              Vasseur, J. and D. Cullerot, "Routing Requirements
for Low
	              Power And Lossy Networks",
	              draft-culler-rl2n-routing-reqs-01 (work in
progress),
	              July 2007.

	JP> This one can be removed.
	[CJ] OK. 

	Last comment: please check that you expand acronyms when first
used.
	[CJ] OK.

	Cheers,

	Christian. 

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