Larry J. Plato <ljp@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
Larry J. Plato <ljp@ans.net> wrote:
Connectionless and Connection oriented both refer to packet switched technologies, whereas the phone company uses circuit switched technology. ...
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 ...
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.
Vadim makes my point better than I did - SS7 etc. make their routing decision OTO once per call (on call setup). IP makes it once per packet. Therefore you can put a lot more effort into finding the correct route if you only have to perform the calculation once. This was an algorthmic point not a network/transport layer point. Alex Bligh Xara Networks
In message <199611171205.MAA02263@diamond.xara.net>, "Alex.Bligh" writes:
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 descib e it in a little mnore detail offline.
Vadim makes my point better than I did - SS7 etc. make their routing decision OTO once per call (on call setup). IP makes it once per packet. Therefore you can put a lot more effort into finding the correct route if you only have to perform the calculation once. This was an algorthmic point not a network/transport layer point.
Alex Bligh Xara Networks
The route computation is made by the routing protocol and is only made when a route changes. Maybe you know of a router implementation where the forwarding code checks the BGP and OSPF paths for every packet, but I don't know of any that work that way. If routers were stable, routers would make all of their routing decisions within minutes of power up and never change those decisions. Forwarding is then based on the table builtbased on those decisions. Call setup happens every time a connection is setup. Even as much as routes flap in the Internet, the load on the routers (ones that actually work, mythical) only affects mostly stable routes by slowing their convergence when they make their very rare bounce. That's why IP routing scales as well as it does and switches using comparable processors have already exceeded call setup rates in limited environments. IP routing has an scaling advantage over call setup. Call setup can take advantage of the lowest loaded path at the time of setup, providing a better chance to load balance (ala PNNI). The VC table has a speed forwarding advantage over the IP radix tree. The radix tree may have a space advantage due to aggregation. That in a nutshell is the IP vs ATM flamewar (did I miss anything - ommisions private mail unless it was major). The interest in IP switching (CSRs, tag switching, IP switching proposal de jour) comes from a desire to combine the best of the two. Curtis
In message <199611171205.MAA02263@diamond.xara.net>, "Alex.Bligh" writes:
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 descib e it in a little mnore detail offline.
Vadim makes my point better than I did - SS7 etc. make their routing decision OTO once per call (on call setup). IP makes it once per packet. Therefore you can put a lot more effort into finding the correct route if you only have to perform the calculation once. This was an algorthmic point not a network/transport layer point.
Alex Bligh Xara Networks
The route computation is made by the routing protocol and is only made when a route changes. Maybe you know of a router implementation where the forwarding code checks the BGP and OSPF paths for every packet, but I don't know of any that work that way.
If routers were stable, routers would make all of their routing decisions within minutes of power up and never change those decisions. Forwarding is then based on the table builtbased on those decisions.
Yes I know - I meant IP has to recalculate whenever its given new information as it makes a forwarding decision once per packet. Apologies for my inablity to write. The original question was "why doesn't BGP respond to changes in line congestion etc. like SS7 does". I supposed my answer assumed that the time between significant changes of congestion "anywhere" on the internet (i.e. time between changes to BGP calc) would be an order of magnitude smaller than length of average telephone call. This may be to do with (possibly unjustified who knows) perception of instabililty of a system with all sorts of types of feedback controlled by disparate groups of varying technical expertise with different hardware etc. etc. Though your point about BGP is accurate, it assumes the amount of flap remains constant. As I would guess most congestion appears within ASes (as opposed to between them), in order for congestion response to be usefully implemented it would have to alter the advertised metric etc. when congestion *within* that AS changed (so if ISPs connection to the Sprint NAP becomes congested it sends the routes with a different metric or something at Sprint and in the opposite direction at MAE-East). This would remove a lot of the isolation between BGP and internal routing protocols that makes BGP stable(ish).
Call setup happens every time a connection is setup. Even as much as routes flap in the Internet, the load on the routers (ones that actually work, mythical) only affects mostly stable routes by slowing their convergence when they make their very rare bounce. That's why IP routing scales as well as it does and switches using comparable processors have already exceeded call setup rates in limited environments.
See point about assuming that the suggestion would have no effect on the amount of withdrawls/announcements. But heh, we are arguing about hypotheticals and counterfactuals as this is a cul-de-sac. You list alternative strategies greater minds than mine have come up with below ...
IP routing has an scaling advantage over call setup. Call setup can take advantage of the lowest loaded path at the time of setup, providing a better chance to load balance (ala PNNI). The VC table has a speed forwarding advantage over the IP radix tree. The radix tree may have a space advantage due to aggregation. That in a nutshell is the IP vs ATM flamewar (did I miss anything - ommisions private mail unless it was major). The interest in IP switching (CSRs, tag switching, IP switching proposal de jour) comes from a desire to combine the best of the two.
Alex Bligh Xara Networks
participants (3)
-
Alex.Bligh -
Curtis Villamizar -
Vadim Antonov