Re: [802.21] [DNA] Prefix information for link identification in DNA
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