Re: [802.21] [DNA] Prefix information for link identification in DNA
Hi Andrea,
I don't see much value in defining L3 and MIH entities as PoAs, as
connectivity to appropriate L3 and MIH entities will be established
once an L2 link is selected and the UE establishes L2 connectivity on
the selected L2 link as a result of a handover decision. In other
words, definition of PoA should be associated with what we choose (L2
link) in the process of handover decision making.
Yoshihiro Ohba
On Fri, Sep 30, 2005 at 05:55:16PM -0400, Andrea Francini wrote:
> Hi Yoshihiro,
>
> > By definition, this will make any IP neighbor (a host and a router) on
> > the same IP link an L3 PoA. But what is the meaning of defining L3
> > node as PoA from handover perspective while I would be mostly
> > interested in choosing an L2 link to attach?
>
> Based on the definitions, the UE may have at the same time an L2 PoA, an L3 PoA,
> and an MIH PoA. One PoA does not exclude the others. When attached to an 802.16
> network, for example, the UE may have the L2 PoA in the serving BS, the L3 PoA
> in an access router deeper inside the network, and the MIH PoA either in the BS
> (L2 MIH PoA) or in the access router (L3 MIH PoA).
>
> Regards,
>
> Andrea
>
>
> Yoshihiro Ohba wrote:
> >
> > Hi Andrea,
> >
> > Thanks for the detailed definition. Please see my comments below.
> >
> > On Fri, Sep 30, 2005 at 03:40:43PM -0400, Andrea Francini wrote:
> > > Hi Yoshihiro,
> > >
> > > I definitely don't mean to contradict what I wrote yesterday. I still think of
> > > the PoA as a link endpoint.
> > >
> > > Your comment rightly brings up the necessity of providing a clear definition of
> > > "link" since link and PoA are tightly inter-related.
> > >
> > > With a generic definition of PoA as a link endpoint, defining "L2 PoA", "L3
> > > PoA", and "MIH PoA" implies corresponding definitions of "L2 link", "L3 link",
> > > and "MIH link".
> > >
> > > I assume from now on that a layer-agnostic notion of link is accepted and that
> > > "link" is not strictly a Layer-2 notion. The group can debate if this is a valid
> > > assumption. If not (i.e., the group prefers to assign a strong L2 flavor to
> > > "link"), we can find a better term (e.g., "connection", or "relationship") and
> > > base on the new term both the generic and the specific definitions of PoA. In
> > > this latter case, "link" would be synonymous of "L2 connection" (or "L2
> > > relationship", or whatever other term the group may identify).
> > >
> > > I can think of the following generic definition for a layer-agnostic link:
> > >
> > > "Communication relationship for the exchange of messages between adjacent peer
> > > protocol entities."
> > >
> > > Where:
> > >
> > > "Peer protocol entities" always belong to the same protocol layer (e.g., L2, L3,
> > > MIH).
> > >
> > > "Adjacent" emphasizes that there is no other interposed peer entity between the
> > > ones that terminate the link (e.g., there cannot be another L3 entity between
> > > the endpoints of an L3 link; if such entity is present, there are two and not
> > > one L3 links). This does not prevent a link from having more than two endpoints:
> > > in a multicast link, for example, all endpoints are adjacent to each other and
> > > none of them is necessary to enable connectivity between others.
> > >
> > > The layer-specific definitions easily follow:
> > >
> > > L2 link: "Communication relationship for the exchange of L2 messages between
> > > adjacent L2 entities."
> > >
> > > L3 link: "Communication relationship for the exchange of L3 messages between
> > > adjacent L3 entities."
> > >
> > > MIH link: "Communication relationship for the exchange of MIH messages between
> > > adjacent MIH entities."
> > >
> > > Having the notions of "L2 link", "L3 link", and "MIH link" in place, the PoA
> > > definitions I previously proposed can easily be mapped as follows:
> > >
> > > L2 PoA: network-side endpoint of L2 link involving the UE
> > > L3 PoA: network-side endpoint of L3 link involving the UE
> > > MIH PoA: network-side endpoint of MIH link involving the UE
> > >
> > > As for identifying the endpoint entity as part of a network node:
> > >
> > > The L2 PoA is an L2 interface on the network node, identified by an L2 address.
> > >
> > > The L3 PoA is an L3 interface on the network node, identified by an L3 address
> > > (on a router, the same physical interface can co-locate L2 and L3 interfaces).
> >
> > By definition, this will make any IP neighbor (a host and a router) on
> > the same IP link an L3 PoA. But what is the meaning of defining L3
> > node as PoA from handover perspective while I would be mostly
> > interested in choosing an L2 link to attach?
> >
> > >
> > > The MIH PoA is an MIH interface on the network node, i.e., an interface (either
> > > L2 or L3) with which the MIH function of the network node is registered for any
> > > of the MIH services. When referring to both transport and MIH capabilities of
> > > the interface, we may have an "L2 MIH PoA" or an "L3 MIH PoA".
> >
> > Similar question: What is the meaning of defining MIH as PoA from
> > handover perspective while I would be mostly interested in choosing an
> > L2 link to attach?
> >
> > >
> > > The main purpose of the endpoint vs. node distinction in the PoA definition is
> > > to avoid ambiguities when the same network node can terminate multiple links and
> > > present for each of them different capabilities and behaviors (i.e., MIH
> > > capability can be activated on one interface and not on another, or the node can
> > > be a hybrid L2/L3 box with both L2 ports and L3 ports). Defining the PoA with
> > > respect to a specific link (or connection) brings the focus of the PoA
> > > definition on the functionality that the corresponding UE can obtain from that
> > > point in the network, without requiring any unnecessary assumptions on the
> > > overall nature of the network node that includes it.
> > >
> > > While I am sure that the wording for the definitions I am proposing can be
> > > dramatically improved, I am convinced of the absolute necessity to single out
> > > the respective entities and provide clear definitions for each of them.
> > >
> > > Thanks,
> > >
> > > Andrea
> > >
> >
> > Regards,
> >
> > Yoshihiro Ohba
>