Re: [802.21] [DNA] Prefix information for link identification in DNA
On Fri, Oct 07, 2005 at 10:41:03AM +0200, zze-Seamless PERESSE M ext RD-RESA-REN wrote:
> Peretz,
>
> from the definitions in the communication model, I guess I was more referring to the R1 (or R3) interface: because in my example the MIH is in the PoA (the PoA is a PoS)...
>
> ...maybe it's a good idea to try to integrate the new definitions Andrea gave to the proposed communication model ?
I think it's a great idea.
Yoshihiro Ohba
>
>
> Mathieu
>
> ________________________________
>
> De : Peretz Feder [mailto:pfeder@LUCENT.COM]
> Envoy¸«± : vendredi 7 octobre 2005 01:24
> ¸Ŗ¢ : STDS-802-21@LISTSERV.IEEE.ORG
> Objet : Re: [802.21] [DNA] Prefix information for link identification in DNA
>
>
> Mathieu:
>
> You are describing the R6 interface in the proposed communication model
>
> http://www.ieee802.org/21/sept05_meeting_docs/21-05-0365-02-0000-communication_model_text_(draft).doc
>
> Peretz Feder
>
> On 10/4/2005 12:00 PM, zze-Seamless PERESSE M ext RD-RESA-REN wrote:
>
>
> Alright, so here is another example:
>
> If the PoA is co-located with the PoS, although it is clear that L2 transport of MIH messages is prefered, L3 transport could be used in cases where L2 transport is not available.
>
> For instance, imagine an AP that has a 802.11 firmware that has no "802.21 functionnalities" (no upgrade available from the manufacturer). Thus it cannot use 802.11 TG? functionnalities that are required for 802.21 to work at L2.
> To provide PoS functionnalities, MIH software would still have to be added in the AP OS , but then the only way to exchange MIH messages would be through L3 transport.
>
>
> UE----------------- AP (PoA & PoS)
> 802.11
> MIH<---------------->MIH
> L2 or L3
>
> Regards,
>
> Mathieu
>
> -----Message d'origine-----
> De : Andrea Francini [mailto:francini@LUCENT.COM]
> Envoy¸«± : mardi 4 octobre 2005 16:16
> ¸Ŗ¢ : STDS-802-21@listserv.ieee.org
> Objet : Re: [802.21] [DNA] Prefix information for link identification in DNA
>
> Hello Mathieu,
>
> As Yoshihiro already pointed out for the other "conclusive" statement I had in my previous message, my choices of "may" and "must" were most likely premature.
>
> I think it is now a good time to start identifying all situations that may apply to the transport of MIH information between the UE and the MIH PoS depending on the placement of the MIH PoS. Examples like the one provided by Yoshihiro on the possible use of LLC for MIH transport (see below) offer an excellent start for such a discussion.
>
> Regards,
>
> Andrea
>
>
> Yoshihiro's example:
> -------------------
>
> I think the "must" in last sentence might be "may" for the following reason.
>
> In the example below, I think the UE could still use an L2 transport for exchanging MIH information with the MIH PoS if the MIH transport is defined on top of LLC (which is still L2) and the MIH PoS supports the L2 transport. The non-PoA MIH PoS may be implemented on the particular Ethernet interface of an IP-capable or IP-incapable node.
>
> 802.11 link Ethernet link
> UE --------------------- AP ------------------- non-PoA MIH PoS
>
>
>
> zze-Seamless PERESSE M ext RD-RESA-REN wrote:
>
>
> Hi Andrea,
>
> Thanks for your new definitions, those sound perfectly right to me as well.
>
> Just one comment:
>
>
>
> The UE may use L2 transport for exchanging MIH information with an MIH PoS that is co-located with a PoA.
>
>
> With the use of "may", are you implying that the UE may use L3 transport as well ? If so, shouldn't that be explicitely stated ?
>
> Regards,
>
> Mathieu
>
> -----Message d'origine-----
> De : Andrea Francini [mailto:francini@LUCENT.COM] Envoy¸«± : mardi 4
> octobre 2005 00:03 ¸Ŗ¢ : STDS-802-21@listserv.ieee.org Objet : Re:
> [802.21] [DNA] Prefix information for link identification in DNA
>
> Hi Yoshihiro,
>
> I agree with you that the notion of adjacency I am using also applies, in the case of UE1, to UE2 and UE3 (and not only to the AR). However, the PoA definition also includes a "network-side" qualifier that does not apply to UE2 and UE3 and still allows (if really needed) to distinguish the AR from UE2 and UE3.
>
> I understand you mostly oppose the notions of "L3 PoA" and "L3 link". Let's see if we can get rid of them with the following:
>
> 1. We define "link" and "PoA" in strict L2 sense.
>
> 2. We avoid any link-like or PoA-like definition for L3.
>
> 3. We define the "MIH Point of Service (PoS)" as a network-side counterpart of the UE for the exchange of MIH information, and the "MIH pairing" as the relationship that exists between MIH-enabled UE and MIH PoS when they exchange MIH messages/information.
>
> With the above arrangement:
>
> A UE attaches to a network through a link that terminates at a PoA.
> (No L2 qualifiers needed for "link" and "PoA".)
>
> The UE exchanges MIH information with MIH PoS's. Generally, the MIH PoS resides at an interface on a network node with which the MIH function of the node is registered for MIH services. An MIH PoS may or may not be co-located with a PoA on the same (L2) interface.
>
> It can happen that an interface on an MIH-capable node (i.e., a node that contains an MIH function instance) does not host an MIH PoS because the local MIH function is not registered with that interface for MIH support. However, an MIH PoS may still be found in the same network node at a different interface.
>
> The UE may use L2 transport for exchanging MIH information with an MIH PoS that is co-located with a PoA.
>
> The UE must use L3 transport for exchanging MIH information with an MIH PoS that is not co-located with a PoA.
>
> Thanks,
>
> Andrea
>
> Yoshihiro Ohba wrote:
>
>
> Andrea has a good example of an L3 link that consists of 802.11 link
> and Ethernet link, so let me discuss based on the example.
>
> Obviously there can be multiple UEs attached to the same AP
> something
> like:
>
> 802.11 link Ethernet link
> UE1--------------------- AP ------------------- AR
> / /
> UE2-------------------+ /
> /
> UE3------------------+
>
> Do you call UE2 and UE3 "L3 PoAs of UE1" just because they are
> adjacent nodes for UE1 in terms of L3? I have a problem with
> calling
> UE2 and UE3 as PoAs because UE1 is not really attaching to UE2 and
> UE3. In fact, there is no notion of attaching to a particular node
> in IP (though there is a notion of attaching to a network in DNA
> WG), so I think it is hard to have an agreement on bringing the
> notion of PoA to IP layer which is not defined in the IETF.
>
> Please see my further comment below.
>
> On Mon, Oct 03, 2005 at 12:50:46PM -0400, Andrea Francini wrote:
>
>
> Hi Mike,
>
> I really appreciate your comments. I think they are moving this
> part of the discussion (definitions and their necessity) in a good direction.
>
> As I wrote in earlier messages, I recognize well that the
> definitions I proposed have plenty of room for improvement. Your
> comment points out that now also the notion of adjacency would
> need to be explicitly spelled out for a better common understanding.
>
> So this time, instead of generating another controversial
> definition on top of the previos ones, I'll take a step back and
> try to be more clear with the problem I would like to see solved.
>
> We started with the attempt to converge on a good definition of
> Point of Access (PoA).
>
> Why do we need such a definition?
>
> 1. We need a name for the point in the network from which the UE
> obtains connectivity.
>
> 2. We need a name for the first point in the network with which
> the UE can exchange MIH-related information (for any of the three MIH services).
>
> Can a single definition of PoA address both needs at the same time?
> I don't think so, because a single definition cannot capture all
> possible combinations (in particular, it cannot provide a good
> distinction between the cases where MIH is immediately available
> at the AP/BS and where it is only available deeper inside the network).
> This is why I thought that it made sense to have a general notion
> of PoA (the first point in the network from which the UE obtains a
> certain service) and then further qualify it with the appropriate
> attributes (L2, L3, and MIH are the ones that I originally
> considered relevant in the
> 802.21 context; TCP can be another one).
>
> Still in general terms, being the PoA the first point in the
> network that the UE can use as a peer for message exchanges
> related to a certain service, defining the entity that exists
> between UE and PoA with respect to that service is the next step. I thought that "link"
> could be a good term, although I realize more and more that "link" has a strong L2 connotation that may not be easy to relax.
>
>
> Whatever term we use, it must convey the notion that the UE and
> the PoA are next to each other on it, otherwise the PoA is no
> longer "the first point in the network". I used "adjacent" in the
> definition of link, with the idea that the adjancency is not
> necessarily physical, but only logical within the same context in which the service obtained from the PoA is defined.
>
> Think for example of a network of routers that is built on top of
> a network of ATM switches. I consider two routers adjacent if they
> are on IP hop away from each other, independently of the number of
> ATM switches that exist in the physical path between them.
> Similarly in 802.21, two L3 entities are adjacent if no other L3
> entity exists in between, independently of the number of L2 segments (or "L2 links") that connect them.
>
> In a situation like the following:
>
>
> 802.11 link Ethernet link
> UE --------------------- AP ------------------- AR
>
>
> how can we capture the fact that the Access Router (AR) is the
> first
> L3 entity in the access network path of the UE?
>
> With the definitions I proposed, the 802.11 and Ethernet links are
> L2 links, the AP includes the L2 PoA for the UE, the AR includes
> the
> L3 PoA for the UE, and an
> L3 link exists between the UE and the AR (of course only after the
> UE has obtained its IP address).
>
> If the 802.11 interface on the AP is MIH-capable, the AP also
> includes the MIH PoA for the UE, independently of the MIH
> capabilities of the AR. If only the Ethernet interface on the AR is MIH-capable, the AR includes the MIH PoA.
>
>
> With the definitions I proposed, every entity of the example gets
> an unambiguous name. I don't have any problem with changing the
> names or the wording of the definitions, but I still want to have
> a name for each of the entities. Any other proposal should pass the same test.
>
>
> I think that unambiguous naming is also possible even if we call the
> immediate L2 link to UE as "link", and the end point of the
> immediate
> L2 link as "PoA", for example:
>
> If the 802.11 interface on the AP is MIH-capable, we can call the AP
> the MIH PoA (or MIH AP) for the UE, independently of the MIH
> capabilities of the
> AR. If only the Ethernet interface on the AR is MIH-capable, we can
> call the AR the MIH AR.
>
> On the other hand, regardless of which direction we take (i.e.,
> defining link and PoA for each layer vs. defining link and PoA for
> L2 only), definition of the "immediate L2 link for the UE" still
> depends on each media, e.g., a PDP context can be the immediate L2
> link for GPRS, and an association between a STA and an AP can be the
> immediate
> L2 link in 802.11, etc. I think this is more important thing to
> consider.
>
>
>
> With respect to your specific concerns:
>
>
>
> I think the link between two adjacent layer 3 entities is actually a layer 2 link. To me, the > purpose of any link at layer N is to provide a PDU transfer service to layer N+1.
>
>
> Do you mean that two layer-3 entities are adjacent only if they
> are connected by a single L2 link, i.e., only if no other L2 node
> exists between the respective
> L2 interfaces? What term could then be applied to the two L2
> interfaces to express the fact that no other L2 node exists between them?
>
> In the IP-over-ATM example, two neighboring routers can be
> attached to ATM nodes that are connected by a single ATM VC or by
> a chain of ATM VC's. With my definition of adjacency, the two
> routers are adjacent in both cases (i.e., neighboring = L3-adjacent). Would it be the same with your definition?
>
> I'm not trying to say that they should necessarily be called
> adjacent, but to understand how your definition would apply to the example.
>
>
>
> If you took your definitions as they are, then the layer 3 link coming up would not allow TCP > or UDP to flow - you'd still have to wait for IP address assignment - and that sounds wrong to > me.
>
>
> I think it should be implicit to have IP addresses in place before
> an L3 link can exist. If the implication is not clear, an explicit
> statement can be easily added.
>
>
> For IP, just having an IP address is not sufficient to claim that
> there is L3 connectivity between an UE and an IP node on the same IP
> link. In IPv6 Neighbor Discovery protocol (RFC 2461), at least
> there must be a neighbor cache entry for the communicating node with
> "REACHABLE" state to *roughly* claim that the node is reachable
> (within ten seconds ago).
>
> Regards,
>
> Yoshihiro Ohba
>
>
>
> Thanks,
>
> Andrea
>
>
> Mike Moreton wrote:
>
>
> Andrea,
>
> I really like these definitions - I think they are clear and precise, which gives a good basis to argue from.
>
> Which is what I'm going to do!
>
> I think the link between two adjacent layer 3 entities is actually a layer 2 link. To me, the purpose of any link at layer N is to provide a PDU transfer service to layer N+1.
>
> If you took your definitions as they are, then the layer 3 link coming up would not allow TCP or UDP to flow - you'd still have to wait for IP address assignment - and that sounds wrong to me.
>
> Mike.
>
>
>
> -----Original Message-----
> From: Andrea Francini [mailto:francini@LUCENT.COM]
> Sent: Friday, September 30, 2005 8:41 PM
> To: STDS-802-21@listserv.ieee.org
> Subject: Re: [802.21] [DNA] Prefix information for link
> identification in DNA
>
>
> 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).
>
> 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".
>
> 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
>
>
> Yoshihiro Ohba wrote:
>
>
> Andrea,
>
> The PoA definition below is going to the direction that the
>
>
> notion of
>
>
> PoA is less associated with the notion of "link", as opposed
> to what you made in your previous general statement which I
> have
>
>
> fully agreed.
>
>
> Or you may be introducing a new definition of "link" as "a
> specific type of communication relationship", which seems to
> be too
>
>
> ambiguous.
>
>
> Yoshihiro Ohba
>
> On Fri, Sep 30, 2005 at 11:25:04AM -0400, Andrea Francini wrote:
>
>
> Trying to finalize one part of the ongoing discussion:
>
>
> the PoA definition.
>
>
> I have the impression that some people consider the
>
>
> capability of supporting MIH
>
>
> as part of the definition of PoA, while other people
>
>
> don't, giving it only a
>
>
> network connectivity value.
>
> What about the following:
>
> 1. General definition of PoA:
>
> a. "PoA is the first point in the network that acts as
>
>
> the UE counterpart for a
>
>
> specific type of communication relationship (e.g., L2, L3, MIH)."
>
>
> 2. Accordingly, the following three specific definitions
>
>
> could be added:
>
>
> b. "L2 PoA is the network-side endpoint of the L2 link by
>
>
> which the UE connects
>
>
> to the network."
>
> c. "L3 PoA is the closest network counterpart for the UE
>
>
> that requires an L3
>
>
> address to be identified in UE-generated messages."
>
> d. "MIH PoA is the closest network counterpart of the UE
>
>
> for MIH exchanges."
>
>
> Thanks,
>
> Andrea
>
>
> "Stefano M. Faccin" wrote:
>
>
> Peretz, nobody denies that. The issue here is that what
>
>
> you have been saying doe not allow for deployments that do not
> use any MIH services at L2. Even if you may not believe these
> deployments will happen, there are vendors and operators that
> do believe that their networks will only use MIH services at
> L3, at least for the initial deployments.
> Thjerefore our model and definitions must allow for this. In
> this model, there is no MIH @ L2, and the PoA is in the subnet
> where the UE gets its IP address.
>
>
> Stefano
>
> ________________________________
>
>
>
>
>
>
>