[e2e] Lost Layer?
Jon.Crowcroft at cl.cam.ac.uk
Tue Feb 11 00:53:13 PST 2014
yes, but for the fact that MOST things now have a net later as well as
a link layer in fact, because most the world is either in a data
center or on a cellular data net, and both have topology that is
manged by routingthat runs below the IP layer and is tech specific -
sure, some peopel call the datacenter (common) case L2 routing, but
its still a network since there are (loads of) switches and topology
maintenance - even more so with cellular - indeed, when you roam,
you're internetworking at the cel layer too so all those recursive
layering lessons come home to roost
the other net layer stuff that happened in the "old days"
when IP ran on complicated interconnects of a single kind
was traffic management (e.g. link layer flow control and reliability
in the x.25 and arpanet cases) which again shows up today in cellular
and data center (where 'orrible 'acks 'ave to be perpertrated with fancy
interframe ethernet delays to solve tcp incast problems)
not that I am saying this is good mecessarily,
just that it keeps re-emergeing -
of course with SDN and NVF stuff, its all moot what is a layer
(it always was, but now its explicit again)
"i am not a layer, nor do i play one on iptv"
might be a sig we could put here..
In missive <20140211041157.7F5E518C0CA at mercury.lcs.mit.edu>, Noel Chiappa typed
>> > From: Joe Touch <touch at ISI.EDU>
>> > I don't at all understand the difference between a "network layer" and
>> > an "internetwork layer".
>>ATM stuff, etc = 'network layer'. (Or, reaching further back, ARPANET stuff.)
>>IPvN = 'internetwork layer'.
>> > I have no idea what a 'network' layer is that is different from what we
>> > currently call the link layer.
>>The thing is that for more complex networks (like ATM, ARPANET, etc) you have
>>'link' layers which are lower/more-local than the system-wide 'network' layer.
>>For example, in the ARPANET example, ISTR that one of the interface modes
>>involved using an HDLC link to talk to the IMP. On top of that one ran 1822
>>headers (with the destination IMP/port, etc); the latter being the 'network'
>>Not all situations include a network layer. Most often (especially these
>>days), the internetwork layer runs directly on top of the link layer. But
>>sometimes there's a network layer sandwiched in there too.
>>Not so much any more, though, because with the increasing prevalence of
>>internetworking protocols, there's no real use for a network layer - it's
>>just replication of functionality, usually. So people just run the
>>internetwork layer directly on top of the link layer, and the functionality
>>that would usually be supplied by the network layer (e.g. path selection
>>across the 'subnetwork', in the older sense of that word - not to be confused
>>with IPvN 'subnets') is supplied by the internetwork layer instead.
More information about the end2end-interest