My comments are enclosed.
Thanks and regards,
Radhika R. Roy AT&T
From: Tom-PT Taylor[SMTP:Tom-PT.Taylor.taylor@NT.COM] Reply To: Mailing list for parties associated with ITU-T Study Group 16 Sent: Thursday, August 20, 1998 2:16 PM To: ITU-SG16@MAILBAG.INTEL.COM Subject: Re: Contribution (Inter-GK Communications)
The comments below convey one or two valid points, but are marred by failure to recognize that different functions within H.323 have different message routing requirements. The valid points are:
- efficient handling of LRQs is tricky (but getting around that is what a
good bit of the Annex G work is all about) [Radhika: It depends what kind of solutions we are looking for. If one has to get around that, something will be lost in the pocess. So, there can be different kinds of solutions. One model can get around that, while the other one should not. We need to work for all options.]
- if a call crosses several administrative domains, each domain has to
have a chance to authorize the use of the resources to be consumed by the call. [Radhika: Yes, you are right. Now the question is where the resource information resides. At zone level, the resource information resides at the GK level.Therefore, to abstract the resource information for all zones, all zones need to be involved. One way of doing is that we can use the "inter-zone" model as proposed in AT&T contribution. For adm part, the zone level info can abstracted to the domain. The bottom line is that a GK of a given zne is the repository for all information in H.323. How to abstract is is a different matter.]
My further comments are interspersed with those of Mr. Roy.
Tom Taylor
-----Original Message----- From: Roy, Radhika R, ALTEC [SMTP:rrroy@ATT.COM] Sent: Thursday, August 20, 1998 12:35 AM To: ITU-SG16@MAILBAG.INTEL.COM Subject: Re: Contribution (Inter-GK Communications)
Hi Everyone:
Here are my comments on APC-1422 Hierarchical Model Based VideoServer's Proposal:
It is appreciable that Mr. Santo Wiaryman, VideoServer, presented an addressing scheme that ranges from multiple zones to multiple domains. The basic idea of the addressing scheme related to the zone and the domain
is
the core of the proposal, and is applicable in other situations as well
no
matter whether the architectural model is hierarchical or non-hierarchical. The opportunities and problems that are presented are real. This contribution has increased our understanding related to the addressing scheme in the context of zones and domains.
However, the addressing scheme has been applied using the model
specified
in APC-1422 that uses hierarchical architecture using the border GKs. In
this
context, the following comments will reveal the fundamental aspects of
the
model proposed in APC-1422 considering the insights that have provided
by
this proposal:
It appears that a sort of routing scheme(s) needs to be used forsending the addressing information from a source zone GK through a
series
of hierarchical border GKs up to the root border GK, and from the root
border
GK through a series border GKs to the destination zone GK. 2. No mechanism is proposed in the signaling messages to protect against routing loops when the "abstraction" of routing is made between the source zone GK , a series of hierarchical border GKs, and the
destination
zone GK.
[Taylor, Tom [CAR:B318-I:EXCH]] First valid point: handling ofLRQs or their functional equivalent is tricky. Your proposal to add time-to-live to LRQs seems to have been accepted. [Radhika: TTL is not sufficient. I guess that 'pathValue' parameter has been proposed to get around that problem. The question is whether or not the model proposed in APC-1422 should be kept in a "limited environment" so that more flexible models need to be evolved later for both hierarchical and non-hierarchical model.]
Is there any inter-GK protocol messages (e.g., resourceavailability) needed between the zone GK and the border GK and between
the
border GKs other than the zone messages considering the (networking) configurations of the GKs? 4. It appears that a root border GK needs to be defined. Who will decide the root GK from which a hierarchy will be establsihed? Is it any international organization like IANA? 5. The path between the source and the destination GK is the pre-specified hierarchical logical path, and may not be optimal between the source-destination GK.
[Taylor, Tom [CAR:B318-I:EXCH]] Postulating such a path, it isused only to distribute addressing information. Call signaling and media packet routing do not need to follow the same path, and in fact most of the routing decisions are made at the transport rather than the application level. [Radhika: My discusssion has been limited to the RAS signaling messages only (not the media path) because the GKs will be handling the mandatory RAS signaling messages. So, the signaling messages will always follow the per-defined hierarchical logical path between the GKs. The routing decision between the GKs will be made at the GK level, whereas the rotuing decison btween the two GKs (e.g., there may be many routers/switches between the two GKs) will be made at the network level.]
The signaling message only passes through the source and thedestination zone GK, and other hierarchical GKs. As a result, if a call
is
established between the source-destination path, the call may have to
pass
through many "intermediate zones" in addition to the source and destination zone. Consequently, the intermediate zone GKs will be completely unable
to
play any roles.
[Taylor, Tom [CAR:B318-I:EXCH]] There is a kernel of truth here,the second valid point I noted above. However, the RAS messages you list below are designed for communication between the endpoint and its Gatekeeper. There are other solutions to the authorization problem (e.g. use of RADIUS/DIAMETER) besides propagation of these messages. Moreover, authorization will not typically be done by the Gatekeeper itself, but by an authorization server which it consults. It will be more efficient fto communicate with the authorization server for each administrative domain directly wherever possible rather than invoke a chain of Gatekeepers to do it indirectly.[Radhika: Please note that H.323 also envisions there may be multiple GKs between the endpoints. Now the communications in multiple-GK environment have not been addressed adequately. That is why, we are working so deligently to solve the inter-GK communications problems. The authorization level can be made abstracted from each zone-GK level to the administrative level as well if needed for intra-domain communications, and/or there can be a central adm server for the domain as you have envisioned. It depends how an architecture is created. Again, in H.323, all information resides in the GK level.]
For example, bandwidth/QOS resources that are supposed to be allocated in each zone by each GK between the source-destination path before placing the call cannot be done. The RAS messages such as ARQ/ACF/ARJ, BRQ/BCJ/BRJ, URQ/UCF/URJ, DRQ/DCF/DRJ, RAI/RAC, and others may not be
able
to play proper roles for all zones between the source-destination path through which a call is established. 7. Is there any solution provided by the model described in
APC-1422
if the zone boundaries become logical instead of physical?
[Taylor, Tom [CAR:B318-I:EXCH]] Not clear how a zone as definedin H.323 is anything but logical. [Radhika: Logical zone boundary means that physical boundaries of the H.323 entities may be the same (may even the same network and the same physical space), but the H.323 entities may belong to different GKs. An analogy can be shown in the case of "Virtual LAN" and other model.]
This simple example presented by VideoServer using the proposed APC-1422 model can also lead to a very high-level comparison between the hierarchical and non-hierarchical model. The following table may provide a high-level summary of comparison between the two models:
Table 1: High Level Summary of Comparsion
Description Hierarchical Model: APC-1422/Example VideoServer
Proposal
Non-Hierarchical Model: AT&T's Proposal Remarks
Routing between the GKs Routing is needed:
Static routing through the pre-specified logical pathNo scope for path optimizationNo mechanism for avoiding loops Routing is needed:Dynamic routing between the source-destination GKsPath is optimizedMechanism is provided to avoid loops(Static routing can also be done if needed) Non-hierarchicalmodel appears to be much superior ARQ/ACF/ARJ Bandwidth/QOS allocation cannot be confirmed because the signaling message does not pass through all zones between the source-destination path. Bandwidth/QOS allocation can be
confirmed
because the signaling message passes through all zones between the source-destination path Non-hierarchical model appears to be much
superior
BRQ/BCJ/BRJ Bandwidth/QOS change cannot be confirmed because the signaling message does not pass through all zones between the source-destination path. Bandwidth/QOS change can be confirmed because the signaling message passes through all zones between the source-destination path Non-hierarchical model appears to be much
superior
All RAS signaling messages that may have implications for all zones between the source-destination path of the call Signaling messages cannot pass through the intermediate zones Signaling messages can pass through all zones between the source-destination path Non-hierarchical model appears to be much superior Root-GK A root-GK needs to be defined (does it mean to have an international authority like IANA?) No need to define a root-GK Non-hierarchical model appears to be much superior Logical zone boundary Probably cannot be defined (may be limited to physical zone boundaries only) Can be defined (in addition to physical one) Non-hierarchical model appears to be much superior
If you have any questions, please let me know.
Thanks and regards,
Radhika R. Roy AT&T, USA Tel: +1 732 949 8657 Email: rrroy@att.com