Re: [SWMP] My understanding so far
Roland Weber <ossfwot@dubioso.net> Fri, 10 August 2007 16:49 UTC
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Date: Fri, 10 Aug 2007 18:49:27 +0200
From: Roland Weber <ossfwot@dubioso.net>
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Subject: Re: [SWMP] My understanding so far
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Hello all, my name is Roland Weber. I've subscribed to this list out of a purely academic interest. I intend to invest a slice of my private time on following the discussions, throwing in my two cents once in a while. This looks like a good occasion to start with that. I'm not familiar with 3D graphics, except for having read through a VRML spec about 10 years ago. I am familiar with HTTP and have some understanding of communication protocols in general. My time will not allow for installing and experimenting with software, nor for much background reading. My apologies if some of my comments are already addressed in the referenced paper, I didn't read it yet. So here are my thoughts on reading the summary... ASSUMPTIONS: 2) maybe mention explicitly that the protocol is meant for one-to-one communication. That is not obvious from assumption 1, but implicit in assumption 2 and the rest of the summary. Given the popularity of P2P networks, many people will associate P2P with many-to-many communication. 4) I associate byte encoding more with message size rather than latency. Maybe mention both? 6,7,9) Nodes have a name, where the name is unique across the hierarchy. Fields have a name and identifier, where the name is not unique across the hierarchy. Maybe the terminology is inherited from other specifications, but I suggest to give the nodes an identifier instead of a name. Then identifiers are unique across the hierarchy for both nodes and fields, while names are not. Control MESSAGES: For one-to-one communication, these messages look sufficient. For many-to-many communication, I would expect some mechanism to exchange information about peers. In that context, the id in the HELLO message would become significant. It could also gain significance in content messages, for example to identify the originator of a change in notification messages. BYE is a good idea. It could implicitly cancel all subscriptions, assuming that subscriptions are non-persistent. The arguments in the COMM message are the sender's address, indicating where the receiver of the message should send it's hello to. The tickets of the primary channel will be used on all secondary channels, too? Content MESSAGES: I assume there will be a mechanism to send groups of these messages, for example in a single UDP packet. There could be cases where for example several fields of a node have to be updated simultaneously to avoid an inconsistent intermediate state. If messages have sequence numbers, will those be on the group level or on the message level? In the first case, FAILNOTIFY could not use the message sequence number alone as the request id. The GETNODEREPLY can become large, if there are many fields and/or children to the node. This looks like a candidate for finer grained scoping in the request. For example, only the fields or only the children. Or only a subset of the children. In the latter case, order of children could become relevant for subset selection. Or only fields and children that have changed since a particular time, using the lastId trick of SUBSCRIBE. The dumping of subtree state in response to a SUBSCRIBE has even more potential to generate a lot of data in replies. In one-to-one communication, there is probably no way to avoid it (many-to-many could engage other peers to send some of the dump). Are there cases where somebody could want a subtree dump without a subscription, snapshot-like? other thoughts regarding subscriptions: The lastId based on message sequence numbers seems OK for one-to-one communication. How about a scenario where a 3D world is hosted in parallel on several servers? A client could have a session with server X at one time, and choose server Y for the next session. Would the client have to get a full dump? Would the servers be supposed to synchronize their message sequence numbers? Should there be a world-specific lastId rather than one based on message sequence numbers? Another solution could be structured IDs, so that the client sends "server X, sequence number whatever" to server Y. Can subscriptions run out of sync between peers? A request GETSUBSCRIPTIONS with corresponding reply could help to recover from that. Again, a case where the response may be large. I hope you find some of my suggestions useful. best regards, Roland Weber _______________________________________________ SWMP mailing list SWMP@ietf.org https://www1.ietf.org/mailman/listinfo/swmp
- Re: [SWMP] Re: faster field messages john_patterson
- [SWMP] My understanding so far john_patterson
- Re: [SWMP] My understanding so far Roland Weber
- Re: [SWMP] My understanding so far Jay C. Weber
- Re: [SWMP] My understanding so far john_patterson
- RE: [SWMP] My understanding so far Tony Parisi
- [SWMP] semantic layers Jay C. Weber
- [SWMP] field-creation semantics Jay C. Weber
- [SWMP] introducing RPC to an asynchronous protocol Jay C. Weber
- [SWMP] Re: semantic layers john_patterson
- [SWMP] faster field messages Jay C. Weber
- [SWMP] Re: field-creation semantics john_patterson
- [SWMP] Re: introducing RPC to an asynchronous pro… john_patterson
- RE: [SWMP] introducing RPC to an asynchronous pro… Tony Parisi
- RE: [SWMP] semantic layers Tony Parisi
- [SWMP] Re: faster field messages john_patterson
- [SWMP] Re: faster field messages Jay C. Weber
- [SWMP] Re: faster field messages john_patterson
- [SWMP] Re: faster field messages Jay C. Weber
- [SWMP] Re: faster field messages john_patterson
- RE: [SWMP] introducing RPC to an asynchronous pro… john_patterson
- RE: [SWMP] introducing RPC to an asynchronous pro… Tony Parisi
- Re: [SWMP] Re: faster field messages Roland Weber
- Re: [SWMP] My understanding so far Roland Weber
- Re: [SWMP] Re: faster field messages Roland Weber
- Re: [SWMP] My understanding so far john_patterson
- Re: [SWMP] My understanding so far Roland Weber
- Re: [SWMP] My understanding so far Jay C. Weber
- Re: [SWMP] My understanding so far Roland Weber