Hi Pascal, > Le 10 juin 2015 à 15:25, Pascal Thubert (pthubert) <[email protected]> a > écrit : > > Dear all: > > This looks like the problem of local namespaces, which is the reason why > MPLS switches labels. > The user may access a limited set of resources from a number of servers, and > servers are read by many users. > You cannot ensure that you have a single alias space that satisfies them all.
Great analogy! And yes, sadly you cannot satisfy them all, at least not with all devices. > > So ,what if the user had its own set of aliases and the server also had its > own set of aliases? > > The aliases could be mapped in a table like a uSAP and a pSAP are mapped > across layers. Broadly: > - First time a user requests a resource in a server, it comes with a tuple > (userid, useralias, fullname) > - The server responds with (serverid, serveralias, userid, user alias). Actually, I think that this could be worked out in CoMI also. Instead of fullname you could provide the YANG id (module ID + data node ID) and do the mapping. User alias would be the special aliased YANG id. User ID, however, could be a little bit more tricky - how do we ensure that it is consistent? Use the IP address of the client could be doable, but we’ll have to include the UDP port just in case someone runs two clients on the same machine. > > After that, if the server is a constrained device then the user talks to the > server with (serverid, serveralias) and the user maintains a switching table > for the resource it uses on various servers. > If the user is the constrained device and the server is not, the user could > talk with (userid, useralias) and the server maintains a switching table. > > For large servers, the server may allocate aliases dynamically based on what > it is being asked. We’d then need to talk about alias update or revocation, > probably in terms of session and lifetime. > > Does that look usable? You are pointing out an interesting question. I would think (but maybe I’m mistaken), that the client should have the leading role in figuring out what’s happening. The idea is the following: The client checks if the server supports aliasing, with the possible options: S1) no aliasing S2) static/server-defined aliasing S3) dynamic/single alias mapping S3.1) mapping already defined S3.2) no mapping defined S4) dynamic/per client alias mapping Then, the client can take action, depending on its own capabilities and the response of the server. E.g. a unconstrained client could obtain the alias mapping if it is static (or if there is a single alias mapping in place) and cache it locally. So, there will be the following correspondence : Given: C1) constrained client C2) unconstrained client We have: C1 + S1) no aliasing, nothing to do C1 + S2) and C1 + S3.1) if the alias mapping is known, use it. otherwise, ignore C1 + S3.2) and C1 + S4) define alias mapping C2 + S1) no aliasing, nothing to do C2 + S2) and C2 + S3.1) if the alias mapping is known, use it. otherwise, learn it C2 + S3.2) and C2 + S4) define alias mapping I would say that the analogy you made with MPLS corresponds quite a lot to the C2+S4 case. Personally, I would be most interested into having one client configure one alias mapping to all servers in the network (e.g. the managing entity), which will profit most from saving several bytes on each message exchange. Everyone else could use the standard IDs, which we’ve already managed to shrink significantly. Indeed, with structured module ID + data node ID (20 bits + 10 bits), YANG URI compression, and long form/short form, we’ll have quite a lot of gain. Reserving module ID = 1 for aliases and maybe writing a short draft on how the aliasing is implemented seems feasible, where we can cover the exact mechanism of alias definition, and client/server interaction. Alexander > > Pascal > > From: 6tisch [mailto:[email protected]] On Behalf Of Andy Bierman > Sent: vendredi 5 juin 2015 20:55 > To: Michel Veillette > Cc: [email protected]; Alexander Pelov; [email protected] > Subject: Re: [6tisch] Reserve space for aliases > > > > On Fri, Jun 5, 2015 at 11:41 AM, Michel Veillette > <[email protected] > <mailto:[email protected]>> wrote: > Hi Alexander > > I have some concerns about allowing CoMI client(s) the control of the list of > aliases. > This approach work fine for the first CoMI application (e.g. 6TiSCH) but what > do we do with the subsequent CoMI application? > > One possible solution is that each CoMI client send a list of (alias, data > node ID) to the CoMI server. In this case, the CoMI client might receive an > error if one or multiple of these aliases are already reserved. > > A second possible solution is that each CoMI client send a list of (data node > ID) and get a list of (alias, data node ID) from the CoMI server. In this > case, CoMI clients will have to deal with a mix population of aliases. > > The proposed solution need to scale to a multi-vendors, multiple applications > environment. > With this is mind, do you have any alternative solutions to propose? > > > > Does this approach allow each client to have a different set of aliases, > so the server has to maintain a configured mapping for each client? > This seems like a lot of overhead and NV-storage requirements > on the server. > > Changing the schema identifiers based on which client is > sending the request seems like a complicated design change > from RESTCONF, NETCONF, or SNMP, where there is only > 1 schema tree which is not dependent on the client identity. > > > Andy > > > > > <image001.jpg> > Michel Veillette > System Architecture Director > Trilliant Inc. > Tel: 450-375-0556 ext. 237 > [email protected] <mailto:[email protected]> > www.trilliantinc.com <http://www.trilliantinc.com/> > > > From: Alexander Pelov [mailto:[email protected] > <mailto:[email protected]>] > Sent: 5 juin 2015 12:03 > To: Michel Veillette > Cc: Andy Bierman; [email protected] <mailto:[email protected]>; [email protected] > <mailto:[email protected]> > Subject: Re: Reserve space for aliases > > Hi Michel, > > > Le 5 juin 2015 à 17:17, Michel Veillette <[email protected] > <mailto:[email protected]>> a écrit : > > Hi Alexander > > In your presentation at 6TiSCH, you propose the following data node ID > structure. > > • 32 bits YANG ID > – 20 bits for module ID (assigned by IETF) > – 10 bits for data node ID (generated deterministically) > > Based on this structure, we can reserve module ID zero for aliases. > > > I was just summarizing what was discussed on the discussion in CoMI. > Actually, it is 30 bits YANG ID, but that’s for purposes to be consistent > with the YANG hash and I don’t mind keeping it 30 bits. > > > > If we want to minimize both the network an node resources require by this > alias mechanism, we can map an entire module to this space. > This can be implemented by a single integer resource (e.g. leaf > alliassedModule { type uint32 } ) > This approach require 4 bytes per CoMI server accessed. > > > It is possible to map an entire module to the alias space and this is up to > the operator. However, if you load two modules which redefine the same alias > you will loose the benefit from it. Maybe it would be interesting to be able > to specify that you want the aliases from THIS specific module to be used. > > If the /mg/0 alias is reserved for managing the aliases, this could be simply > saying: > POST /mg/0 > { > "source_uri" : "/mg/BAA" > } > > where /mg/BAA is the YANG id of the module (20 bits module ID + 10 bits set > to 0). This way, the server will know: OK, get the alias mapping from the > YANG scheme of module with ID = B (as defined by the IETF). > > Or, you can dynamically configure the mapping: > POST /mg/0 > { > YANG_id : alias, > YANG_id : alias, > YANG_id : alias > } > > > If we want a more complex but more flexible aliases mechanism, your proposed > map of (allias, YANG ID) seem the solution. > However, we have to consider that this structure can be as large as 1250 > bytes per CoMI server accessed if limited to 256 aliases. > > This is assuming you need a separate mapping for each server. I would suppose > that in a network you’ll have a single alias mapping (maybe two?) - after > all, you’re trying to optimize the management of your devices (servers). So, > typically you’d map all 6tisch devices with aliases 1-10 (channel, slot, > etc.) and use that on them, and on all other you’d access the full ID. > > Best, > Alexander > > > > <image001.jpg> > Michel Veillette > System Architecture Director > Trilliant Inc. > Tel: 450-375-0556 ext. 237 > [email protected] <mailto:[email protected]> > www.trilliantinc.com <http://www.trilliantinc.com/>
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