Hi Tom, Thank you for the clarification.
In telecom there are also "shelves" mounted on racks. A shelf is a metal frame with PSU and slots that can contain other cards. It is usually 1U-9U in height. So it looks to me that a shelf is a type of chassis. Now, there are usually subtended shelves that sit next to a main shelf and connected by external cables. A subtended shelf (or subshelf) is also a metal frame with PSU and slots, but it does not have its own control units and instead is managed directly by the main shelf. If a subshelf is also considered as a type of chassis, then it means that a chassis (shelf) could contain another chassis (subshelf) as its child, and a subshelf has a shelf as its parent. Alternatively, it could be modeled by using a "stack" to group these chassises together, but then to capture the parent-child relationship between a shelf and a subshelf, it needs to create a stack that contains both the main shelf and another stack which contains the subshelf. It sounds a little redundant to me. Thoughts are much appreciated. Thanks, Aihua On Wed, Oct 20, 2021 at 8:51 AM <[email protected]> wrote: > The confusion appears to stem from the exclusion of "chassis" in the first > part of this sentence: > > "Any class of physical component, except a stack, may be contained within > a chassis; a chassis may only be contained within a stack." > > It takes a rather pedantic read of the text to suggest that "any class of > physical component" may also include a chassis, but perhaps it is worth > updating the text to specifically state "Any class of physical component, > except a stack or a chassis, may be contained within a chassis". > > Nesting a chassis within a chassis I don't see being useful to permit in > practice/practically useful. > > Nested stacking sounds plausible. 'A stack of stacks' reminds me of a few > designs I've seen in the past (4-way Cisco VSS, perhaps?) > > Regards, > > Tom > > My sincere apologies for Outlook. > > -----Original Message----- > From: netmod <[email protected]> On Behalf Of tom petch > Sent: 20 October 2021 12:10 > To: Aihua Guo <[email protected]>; [email protected] > Subject: Re: [netmod] Clarification on the description for chassis and > stack in RFC 8348 > > From: netmod <[email protected]> on behalf of Aihua Guo < > [email protected]> > Sent: 13 October 2021 20:17 > > Hi All, > > RFC 8348 defines chassis and stack as two identities for networking > equipment. The description for chassis says that "Any class of physical > component, except a stack, may be contained within a chassis; a chassis may > only be contained within a stack." First statement of this sentence seems > to suggest that a chassis (which is a component) can also be contained > within a chassis, while the next statement, "a chassis may only be > contained within a stack." seems to suggest that a chassis can be only > contained within a stack and not within another chassis, which seems to > contradict with the previous statement. So, which statement is correct? > > <tp> > I do not know what the authors had in mind but to me a chassis is clearly > a chassis and a stack a stack:-) > > A chassis is a frame, usually metal, often with PSU and perhaps > managements functions into which blades can be slotted. Without at least > one blade it is usually not good for much except testing the management > module although that may well be a blade and not integral with the > chassis. A multi-protocol switch would be a likely example. I have not > seen a chassis within a chassis. > > By contrast, a stack is made up of stackable elements, each of which is > complete in itself and could be used by itself as a one element stack but > which also have in/out sockets which enable multiple elements to be > integrated into a single functional element. A LAN hub where each element > supports 16 ports and eight can be stacked to form a 128 port hub would be > an example. If the elements are all connected together, I see a stack. If > they are physically co-located but function as several separate entities > then I see several stacks but not a stack within a stack. > > HTH > > Tom Petch > > > Another point to clarify is that in the description for stack, "...a stack > may be contained within another stack. Only chassis components should be > contained within a stack." Is it correct to understand that a stack can > contain either another stack or a chassis, or both, but nothing else? > > I would appreciate the clarification. > > Thanks, > Aihua > > > > > > > _______________________________________________ > netmod mailing list > [email protected] > > https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Fmailman%2Flistinfo%2Fnetmod&data=04%7C01%7Ctom.2.hill%40bt.com%7Ceceaf59456654bcbc2cb08d993ba4469%7Ca7f356889c004d5eba4129f146377ab0%7C0%7C0%7C637703250499568112%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=hdfDrlNtUJpN%2FddyjlDwn5tjHDosdORIC0qa%2BmCA2fc%3D&reserved=0 > > _______________________________________________ > netmod mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/netmod >
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