Re: [802.21] [DNA] Prefix information for link identification in DNA
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.
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.
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
> > > > >
> > > > > ________________________________
> > > > >
> > > > > From: ext Peretz Feder [mailto:pfeder@LUCENT.COM]
> > > > > Sent: Fri 9/30/2005 10:06 AM
> > > > > To: STDS-802-21@listserv.ieee.org
> > > > > Subject: Re: [802.21] [DNA] Prefix information for link
> > identification in DNA
> > > > >
> > > > > "I do not understand how any one would conclude that
> > the MIH services are only between UE and the AP/BS."
> > > > >
> > > > > The discussion is PoA and not services. The 1st PoA
> > could be L2 for IS and CS. With no PoA at L2, the poor UE
> > will have no MIH services until IP is established. The
> > performance will be very different, not to mention a UE with
> > a bridging only attributes, such as 802.16 terminal with only
> > Ethernet CS (no IP CS).
> > > > >
> > > > > Nobody is saying MIH services are strictly between UE
> > and BS. Performance will be better when PoA L2 MIH is established.
> > > > >
> > > > > Peretz
> > > > >
> > > > > On 9/30/2005 10:50 AM, Srinivas.Sreemanthula@nokia.com wrote:
> > > > >
> > > > > The MIIS is provisioned between MIH in UE to a
> > network counter part any
> > > > > where in the network. This network node can
> > either act as a proxy info
> > > > > server or an info server. We also identified
> > MIIS requires L3 and hence
> > > > > the WG went through the exercise of identifying
> > all the UL requirements
> > > > > and establish coordination with IETF. However,
> > in that discussion, there
> > > > > was no reference to whether the AP/BS was MIH
> > or non-MIH capable.
> > > > >
> > > > > Even if we leave out the info services from the
> > discussion, I do not
> > > > > understand how any one would conclude that the
> > MIH services are only
> > > > > between UE and the AP/BS.
> > > > >
> > > > >
> > > > >
> > > > > -----Original Message-----
> > > > > From: ext Peretz Feder
> > [mailto:pfeder@lucent.com]
> > > > > Sent: Friday, September 30, 2005 9:39 AM
> > > > > To: Sreemanthula Srinivas (Nokia-NRC/Dallas)
> > > > > Cc: STDS-802-21@listserv.ieee.org
> > > > > Subject: Re: [802.21] [DNA] Prefix
> > information for link
> > > > > identification in DNA
> > > > >
> > > > > Are you indicating attaching to a non
> > MIH enabled AP/BS and
> > > > > receiving MIH IS over R4 from a remote
> > MIH info server?
> > > > >
> > > > >
> > > > > On 9/30/2005 10:27 AM,
> > Srinivas.Sreemanthula@nokia.com wrote:
> > > > >
> > > > >
> > > > >
> > > > > Did we miss the whole
> > discussion of MIH information services?
> > > > >
> > > > >
> > > > > ________________________________
> > > > >
> > > > > From: ext Peretz Feder
> > [mailto:pfeder@LUCENT.COM]
> > > > > Sent: Friday, September
> > 30, 2005 9:16 AM
> > > > > To:
> > STDS-802-21@LISTSERV.IEEE.ORG
> > > > > Subject: Re: [802.21]
> > [DNA] Prefix information for link
> > > > >
> > > > >
> > > > > identification
> > > > >
> > > > >
> > > > > in DNA
> > > > >
> > > > >
> > > > > "you have first to be
> > very clear about what you're attaching"
> > > > >
> > > > > I would think that in
> > 802.21, we first attach the UE's
> > > > >
> > > > >
> > > > > MIH to a BS/AP
> > > > >
> > > > >
> > > > > that supports MIH capability.
> > > > >
> > > > > On 9/30/2005 8:55 AM,
> > Stefano M. Faccin wrote:
> > > > >
> > > > >
> > > > > Mike, well said!
> > > > > Stefano
> > > > >
> > > > >
> > ________________________________
> > > > >
> > > > > From: ext Mike
> > Moreton [mailto:mm2006@MAILSNARE.NET]
> > > > > Sent: Fri
> > 9/30/2005 3:09 AM
> > > > > To:
> > STDS-802-21@listserv.ieee.org
> > > > > Subject: Re:
> > [802.21] [DNA] Prefix information for link
> > > > > identification in DNA
> > > > >
> > > > >
> > > > >
> > > > > To extend (I
> > think!) Stefano's point, before
> > > > >
> > > > >
> > > > > determining what the PoA
> > > > >
> > > > >
> > > > > is, you have first to be very
> > clear about what you're
> > > > >
> > > > >
> > > > > attaching. Just
> > > > >
> > > > >
> > > > > saying "the terminal" makes no
> > sense, because different layers in the
> > > > > terminal's protocol stack
> > attach to different places in the network.
> > > > >
> > > > > For example,
> > the PHY layer attaches to the AP,
> > > > >
> > > > >
> > > > > but the TCP layer
> > > > >
> > > > >
> > > > > attaches to the destination host.
> > > > >
> > > > > Mike.
> > > > >
> > > > >
> > > > >
> > > > >
> > -----Original Message-----
> > > > > From:
> > Stefano M. Faccin
> > > > > [mailto:stefano.faccin@NOKIA.COM]
> > > > > Sent:
> > Friday, September 30, 2005 1:08 AM
> > > > > To:
> > STDS-802-21@listserv.ieee.org
> > > > >
> > Subject: Re: [802.21] [DNA] Prefix
> > > > >
> > > > >
> > > > > information for link
> > > > >
> > > > >
> > > > >
> > identification in DNA
> > > > >
> > > > >
> > > > > Yoshihiro,
> > > > > I'm not
> > sure why should restrict the
> > > > >
> > > > >
> > > > > term PoA to have only a
> > > > >
> > > > >
> > > > > L2
> > meaning as you suggest below. I
> > > > >
> > > > >
> > > > > think we should
> > > > >
> > > > >
> > > > >
> > distinguish clearly between L2 PoA and L3 PoA.
> > > > > For me, the L3
> > > > > PoA is
> > where the terminal gets IP conenctivity.
> > > > > E.g. for GPRS
> > > > > the L3
> > PoA is the IP link on which the
> > > > >
> > > > >
> > > > > GGSN is located. In
> > > > >
> > > > >
> > > > > L2, PoA
> > is the point where the access-specific
> > > > > L2 connection
> > > > >
> > terminates (e.g. an AP in 802.11).
> > > > > Stefano
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
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> > > >
> >