Re: [802.21] [DNA] Prefix information for link identification in DNA
Hello Andrea,
Thank you the general statement. I totally agree with you.
Yoshihiro Ohba
On Thu, Sep 29, 2005 at 06:19:04PM -0400, Andrea Francini wrote:
> Hello Yoshihiro,
>
> I would like to make a general statement regarding the definition of PoA.
>
> I believe that the application of the PoA definition to an AP/BS/Switch/Router
> (i.e., to a network node) is not appropriate and may generate confusion. The PoA
> definition should instead be tightly associated with the notion of "link": the
> PoA is in fact a particular case of link endpoint, or, even better, one endpoint
> on a particular type of link ("a link that has a UE as one of its endpoints"). A
> given network node may contain multiple link endpoints, some of which are PoA's
> while others are not.
>
> After establishing that a PoA is a link endpoint and not a network node, the
> group can find it easier to determine if the PoA definition should only apply to
> the L2 case (i.e., PoA is intrinsically an L2-link endpoint, no matter if
> residing in a BS, AP, switch, or router) or generically to both L2 and L3 cases
> (so that "L2 PoA" and "L3 PoA" must be used to identify the specific case being
> considered). This way the forwarding capabilities of the network node (L2 switch
> or L3 router) become orthogonal to the definition of PoA (although it remains
> true that no L3 PoA can be found in an L2 switch).
>
> Thanks,
>
> Andrea
>
>
> Yoshihiro Ohba wrote:
> >
> > IETF and IEEE have different notion of "link". I think the IETF DNA
> > WG discussion below is for link identification for "IP link", whereas
> > I believe that IEEE 802.21 WG is interested in identifying "L2 link"
> > (i.e., a connection between UE and AP/BS/Switch/Hub).
> >
> > Speaking about the latter, as I presented in the .21 WG last session,
> > an L2 link can be identified with a pair of PoA type and PoA
> > identifier, where a PoA is an L2 point of attachment such as
> > AP/BS/Switch. RADIUS NAS-Port-Type can be used as a PoA type. A
> > string that is unique within the PoA type (e.g., BSSID) can be used as
> > the PoA identifier. A special case would be that the UE is connected
> > to Ethernet via a hub which may not have any MAC address. In this
> > case, the PoA identifier can be null.
> >
> > Also, we have to agree on the definition of PoA since the term PoA is
> > used in many places in the draft text. Some people are talking about
> > "L3 PoA" such as an access router, but I think this is confusing and
> > should not be considered. If we are interested in "L2 link", then the
> > definition of PoA should be the one (L2 PoA) that is more associated
> > with "L2 link" than IP link. Of course, an AP/BS/Switch may also have
> > the functionality of router, but even in this case we should not call
> > it L3 PoA.
> >
> > Yoshihiro Ohba
> >
> > On Thu, Sep 29, 2005 at 10:26:00AM -0700, Michael G. Williams wrote:
> > > Colleagues,
> > >
> > > Within IEEE 802.21 WG last session, there was some discussion of how to
> > > identify or name a "link" for use in remote scope/remote references if
> > > necessary. This issue was also raised in the "link indications" paper in
> > > progress from Bernard Aboba. Let's have some email list discussion on if
> > > there is any relation or synergy possible with the thread below.
> > >
> > > Best Regards,
> > > Michael
> > >
> > > -----Original Message-----
> > > From: owner-dna@ecselists.eng.monash.edu.au
> > > [mailto:owner-dna@ecselists.eng.monash.edu.au] On Behalf Of ext Bernard
> > > Aboba
> > > Sent: Thursday, September 29, 2005 10:02 AM
> > > To: brett.pentland@eng.monash.edu.au; dna@eng.monash.edu.au
> > > Subject: RE: [DNA] Prefix information for link identification in DNA
> > >
> > > >He thought that it is questionable to assume that:
> > > >
> > > > 1) Every network has a router.
> > > > 2) you can name a network using one of its prefixes.
> > >
> > > There are certainly adhoc networks in which there is no router.
> > > However,
> > > detecting attachment to such a network is quite difficult, because nodes
> > > may join and leave and therefore there is no L3 invariant. That is why
> > > the
> > > DNAv4 reachability test cannot be used to detect attachment to adhoc
> > > networks, but rather adhoc attachment is concluded after failiure of all
> > > other approaches (reachability test, DHCPv4, etc.)
> > >
> > > I would also agree that there are situations in which a network cannot
> > > be named using one of its prefixes. In DNAv4, a private network is not
> > > suitable for identification because it is not unique.
> > >
> > > >So if a link has no router and no prefixes except the link-local prefix
> > >
> > > >(which will be the same for all links) we have a problem.
> > >
> > > I would say that a "problem" only occurs if DNA somehow makes the
> > > situation worse. If a link has no router and no prefixes except
> > > link-local, then the best that can be achieved is for a host to utilize
> > > the link-local address.
> > > Unless DNA somehow impedes that, it may not do any good, but it also
> > > does no harm.
> > >
> > > >I'm not sure what we can reasonably do at layer 3 if there is(are) no
> > > >router(s) present on the link to help the hosts identify the link.
> > > >(Any ideas?)
> > >
> > > The best you can do at L3 is to use a link-local address.
> > >
>