Contribution (Inter-GK Communications)

Roy, Radhika R, ALTEC rrroy at ATT.COM
Thu Aug 20 00:34:32 EDT 1998


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:

1.      It appears that a sort of routing scheme(s) needs to be used for
sending 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.
3.      Is there any inter-GK protocol messages (e.g., resource
availability) 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.
6.      The signaling message only passes through the source and the
destination 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. 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?

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 path
*       No scope for path optimization
*       No mechanism for avoiding loops Routing is needed:
*       Dynamic routing between the source-destination GKs
*       Path is optimized
*       Mechanism is provided to avoid loops
*       (Static routing can also be done if needed)     Non-hierarchical
model 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 at att.com



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