26 Jun
2022
26 Jun
'22
8:19 a.m.
From: Paul Ruizendaal
it would seem to me that Sandy had figured out a core
problem some 30
years before the TCP/IP world would come up with a similar solution. I
would not even be surprised if I learned that modern telco routers
transparantly set up virtual circuits for tcp traffic.
To fully explore this topic would take a book, which I don't have the energy
to write, and nobody would bother to read, but...
Anyway, I'm not upon the latest and greatest high-speed routers: I saw some
stuff from one major vendor under NDA about a decade ago, but that's my most
recent - but at that point there was nothing that looked even _vaguely_ like
virtual circuits. (The stuff Craig was alluding to was just about
connectivity for getting bitts from _interface_ to _interface_ - if you don't
have a giant crossbar - which is going to require buffering on each input
anyway - how exactly do you get bits from board A to board Q - a single
shared bus isn't going to do it...)
A problem with anything like VC's in core switches is the growth of per-VC
state - a major high-speed node will have packets from _millions_ of TCP
connections flowing through it at any time. In the late-80's/early-90's - well
over 30 years ago - I came up with an advanced routing architecture called
Nimrod (see RFC-1992, "The Nimrod Routing Architecture"; RFC-1753 may be of
interest too); it had things called 'flows' which were half way between pure
datagrams (i.e. no setup - you just stick the right destination address in the
header and send it off) and VCs (read the RFCs if you want to kow why), and it
went to a lot of trouble to allow flow aggregation in traffic going to core
switches _precisely_ to limit the growth of state in core switches, which
would have traffic from millions of connections going through them.
I have barely begun to even scratch the surface, here.
Noel