Subject: [nemo] home-network-models grammar & spelling

From: "T.J.Kniveton" <[email-masked]>
Date: Fri, 16 Jul 2004 18:40:23 -0700

Here are some suggestions on grammar and spelling changes to the draft. 
I will just attach my edited version, and you can diff it against the 
existing version. My comments are in [brackets].

General comments:

The document is generally good. However, I find that in parts it is a 
bit vague, and doesn't give enough motivation to help people decide 
which, and more importantly, why, they should choose a particular 
configuration. I tried to make comments in-line in these cases.

Since parts of the draft deal with address management and allocation 
issues, the draft walks a line between Informational and BCP (which I 
find a bit strange, since there are very few, and no commercial, 
deployments at this point from which we could deduce these BCPs. Thus, 
we need some more experience to have a really authoritative document on 
this subject.

Maybe it's just me, but I had a hard time parsing much of the document. 
I had to read certain sections multiple times, and was still left with 
ambiguities in my mind regarding what was meant. Since there are many 
examples of what you "may" do, but not much guidance as to which you 
should pick, I, as an implementor, would have a hard time taking much 
information from the document until *after* I had already figured out 
which type of network to set up at home. By that point, I probably 
wouldn't need the assistance of this document because I would have 
figured it out.

However, I do like the examples you show, and I think they are useful 
in the implementation process.

TJ

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From: Vijay Devarapalli <[email-masked]>
Date: Mon, 19 Jul 2004 12:24:38 -0700

hi TJ,

thanks for reviewing the document. I will try to address a few of
your comments.

> we need some more experience to have a really authoritative document on 

I agree. it is definitely is not a BCP.

> examples of what you "may" do, 

exactly. it describes various way of configuring the home link for
NEMO support. it also suggests "returning home" procedures for each
case.

> but not much guidance as to which you 
> should pick, 

we werent going to do that. just list them all and describe the
pros and cons. do you think we should? it would be very hard to get
WG concensus on that.

>    Virtual Home Network: In this disposition, there is no physical Home
>       Link at all for the Mobile Routers to come back home to. [Then what is there? elaborate.]

it is supposed to say, the home link is virtual. will fix this.

> 
>    Mobile Home Network: In this disposition, there is a bitwise
>       hierarchy of Home Networks. A global Home Network is advertised to
>       the infrastructure by a head Home Agent and further delegated into
>       Mobile Networks of shorter prefix and the same high-order bits. Each subnet is owned by a Mobile Router that
>       registers it using the NEMO protocol and acts as a Home Agent for
>       that network.
> [Isn't the word "subnet" deprecated in IPv6?]

havent heard about this. can you provide a reference to this?
2461bis and 2462bis still talk about "subnets".

> 
>    As an example, say that the aggregation has a global routing prefix
>    of m = 48 bits (A:B:C::/48), with subnet ID size of n = 16 bits ( n +
>    m = 64).
> [Wouldn't this be the *host* ID and not the subnet ID, which is 16 bits? The subnet (prefix) is the 48 bit part.]

in the above example interface ID is 64 bits, subnet ID is 16 bits
and the prefix is 48 bits. the following is from RFC 3513.

   2.5.4 Global Unicast Addresses

      The general format for IPv6 global unicast addresses is as follows:

      |         n bits         |   m bits  |       128-n-m bits         |
      +------------------------+-----------+----------------------------+
      | global routing prefix  | subnet ID |       interface ID         |
      +------------------------+-----------+----------------------------+

> 
>    o  Alternatively, a Mobile Router could also form a Home Address from
>       one of its prefixes and use it to register, performing DAD
>       on its ingress network.
> [I haven't heard the term ingress network before. Can we say ingress interface?]

agreed.

> 4.1 Returning Home
> 
>    In the extended Home Network model, the Home Network is configured on
>    a physical interface of the Home Agent, the Home Link.
> 
>    A Mobile Router returns Home by connecting directly to the Home Link,
>    and dropping the MRHA tunnel. At that point, the MR does not participate in the routing of packets to the Mobile Network; the Home Agent takes over this responsibility.
> 
>    If the Home Address of the Mobile Router is derived from one of its
>    Mobile Networks, then the MR may connect to the Home Link using an
>    egress interface and autoconfigure an address on the Home Link. The
>    MR recognizes the prefix of its Home Agent in order to decide that it
>    is Home. Note that in that case the Home Address does not match the
>    Home Prefix.
> [What is the point of this? Seems overly complicated.]

the NEMO basic support allows the MR to configure a HoA from its
Mobile Network Prefix (NEMO-prefix). the above only tries to
explain the returning home procedure for such a case.

>    Thus, the Home Agent MUST intercept all the packets to MNNs on
>    the registered prefixes [what are "registered prefixes"?]. 

those prefixes that the MR included in the Binding Update to the
Home Agent. but I agree, it needs to be clarified.

>    There are certain advantages to making the Home Link a virtual link:
> 
>       A virtual link may not experience any disruption related to
>       physical maintenance or to hardware problems, so it is more
>       available than a physical link. The high availability of the Home
>       Link is critical for the mobility service.
> 
> [I disagree. A virtual home link is exactly available, in terms of L2 connectivity, as a home link which is broken and down 100% of the time. The only exception is if the OS does not allow prefixes to be assigned to a link that does not have an L1 connection, which are rare.]

I agree. Ryuji, Pascal?

Vijay