Why doesn't BGP... -Reply

Sun Nov 17 08:56:29 UTC 1996

Larry J. Plato <ljp at ans.net> wrote:

>Connectionless and Connection oriented both refer to packet switched
>technologies, whereas the phone company uses circuit switched technology.

Yes, this is absolutely correct.

>Circuit switched means that the same wires/timeslots are dedicated to
>a call from the time it starts until the time it finishes.If you do
>not speak, the wires are idle/wasted.  I am sure you understand packet
>switching.  In a packet switched network, connectionless means that each
>packet has no state information, and stands alone, in the IP world we call
>this UDP. Connection oriented would be the equivalent of telnet or
>some other TCP service.

This is a terminological question.  Here the talk was about connectionless
and connection-oriented _network_ layer; not the transport layer.

The connection-oriented packet routing network is a generalized case
of circuit switching -- you can multiplex connections differently.

The fundamental difference between connectionless and connection-oriented
networks is the amount of state necessarily kept by gateways in order
to perform forwarding of the bits.  A gateway of a connectionless network
has only to keep the traffic-independent topological information (this
definition is more generic than just next-hop routing; it includes
source-based routing, semi-flows, etc).  A gateway of a connection-oriented
network has to keep the topological information (in order to be able
to route connections) and the traffic-dependent table of connections.

BTW, by that definition an IP network which supports RSVP _is_ a connection
oriented network.

If gateway has state which is modified by traffic, that state must
necessarily grow with the traffic; in Internet case, exponentially
and at the rate far exceeding Moore law's.

>SS7 (Signalling System 7) is a connectionless packet switched technology
>used to control the setup and teardown of circuit switched calls.
>Originally is was used as a database query technology to make 800
>numbers portable across carriers.  If this did not make sense I can descibe
>it in a little mnore detail offline.

At least that telcos got right.

--vadim