Subject: Summary Re: [nemo] comments on "Tree Discovery" draft

From: "Fan Zhao" <[email-masked]>
Date: Thu, 26 Aug 2004 18:14:27 -0700 (PDT)

Hi, Pascal, Alex and all,

I have followed this long discussion and want to sort of make a summary.
Hope it helps. 

Problem statement:
When one MR moves to a (nested) NEMO network and wants to connect to the 
Internet, we need to have an efficient and scalable mechanism for MR to 
choose which AR to attach to as fast as possible. Note that this problem 
may share some similarity with others in different scenarios. We need to 
know whether there is something specific to NEMO here or a more efficient 
solution works well with this problem in NEMO only but not in other 
scenarios.
 
There are several possible solutions to this problem.
1. Routing protocol: Routing protocol is running on each MR in order to 
propagate the connectivity information. However it is heavy in terms of 
the routing table and slow to propagate and converge when the topology 
changes.

2. Detection solution: MR may use BU to discover the usable AR to the 
Internet. Firstly, without any helpful metrics, MR has to randomly select 
one AR from (maybe) multiple ARs. MR has no idea about AR and may end up 
with a “bad” (according to its preference) AR even though a better AR is 
available. Secondly, MR has to start the BU procedure and wait until 
either BAck arrives or an error is detected. 

3. TD is efficient because MR just needs to make a decision based on the 
received RA and its preference. No state or routing table is needed. 
However, this doesn’t guarantee the connectivity to the Internet (No one 
does). MR at least needs to wait until the BU procedure succeeds before 
sending the data packet. A “shadow” tree may reduce the length of the 
routing path inside the nested NEMO, but the resulting tree can be any 
shape because it is totally up to the decision of MR.

Do I miss something here?

Fan

---

From: Alexandru Petrescu <[email-masked]>
Date: Fri, 27 Aug 2004 13:53:39 +0200

Thanks for summarizing, some aspects have been overlooked.

Fan Zhao wrote:
> Problem statement: When one MR moves to a (nested) NEMO network and 
> wants to connect to the Internet, we need to have an efficient and 
> scalable mechanism for MR to choose which AR to attach to as fast as
>  possible. Note that this problem may share some similarity with 
> others in different scenarios. We need to know whether there is 
> something specific to NEMO here or a more efficient solution works 
> well with this problem in NEMO only but not in other scenarios.

Also one would check DNA BoF about Dynamic Network Attachment.

> There are several possible solutions to this problem. 1. Routing 
> protocol: Routing protocol is running on each MR in order to 
> propagate the connectivity information. However it is heavy in terms
>  of the routing table and slow to propagate and converge when the 
> topology changes.

Here heaviness depends on how many routing tables are there to be
modified.  A small aggregation of MR's like 10 MR's where only one
extreme MR moves will _not_ induce any large modifications to routing
tables.

>  Internet. Firstly, without any helpful metrics, MR has to randomly 
> select one AR from (maybe) multiple ARs.

DNA stuff?

> Secondly, MR has to start the BU procedure and wait until either BAck
>  arrives or an error is detected.

MR should advertise itself as a default router only if it actually is
connected to the Internet, that is, to its HA (not only to AR).

> 3. TD is efficient because MR just needs to make a decision based on
>  the received RA and its preference. No state or routing table is 
> needed.

"Efficiency" can be defined only if we know requirements and see what
tradeoffs can be made.  TD is not efficient because the deeper the
network, the larger RA's will be.  With a tree of height (or depth) 100,
there'll presumably 100 TIO's in the leaf RA's.  If this is so, TD is
nor scaleable nor efficient.

> A “shadow” tree may reduce the length of the routing path inside the
>  nested NEMO, but the resulting tree can be any shape because it is 
> totally up to the decision of MR.

You mean the "shallow" TD term (having little depth)?  Because we also
have a "shadow" routing table where a dynamic routing protocol puts its
routes when MR is not at home.

Thanks,

Alex

---

From: Alexandru Petrescu <[email-masked]>
Date: Fri, 27 Aug 2004 21:05:28 +0200

Alexandru Petrescu wrote:

>>  scalable mechanism for MR to choose which AR to attach to as fast
>> as possible. Note that this problem may share some similarity with

Sorry its Detecting Network Attachment and it's a WG...

Alex