Re: Why doesn't BGP... -Reply
Routing does not use an exponential NP-Complete algorithm (like the travelling salesman). The travelling salesman problem tries to solve the cheapest way in which a salesman can visit every one of a set of cities. In fact, routing can be done in order (n) with a bounded metric and bounded distance, since it really is only trying to find the cheapest way to get to a single destination.
What I don't know, is why is it that SS7, the telephone routing protocol, can do some of the things that are required, like load sharing across unequal paths, for example. Does anyone have any insight into this?
--Neal
Quick comment: You're looking at the computing of routes wrt one router. I'm suggesting that perhaps we should consider the set of all routers since we're concerned about spreading load due to the quick communication from one router to many of every best external-path changing. But no, I'm not familiar with SS7, and I've not even been thinking deeply about other routing algorithm possibilities. I was just suggesting that people are encouraged to do so... Avi
Quick comment: You're looking at the computing of routes wrt one router. I'm suggesting that perhaps we should consider the set of all routers since we're concerned about spreading load due to the quick communication from one router to many of every best external-path changing.
Some people are concerned with that and others are concerned with end-node (or close to it) routers where this is not an issue. I suspect nanog has a good mix with many who run both types.
What I don't know, is why is it that SS7, the telephone routing protocol, can do some of the things that are required, like load sharing across unequal paths, for example. Does anyone have any insight into this?
I *believe* one main difference is that telco sig is connection oriented whereas IP is pretty much collectionless (interesting comparison to netflow switching though); hence telephony switching protocols can afford to wait tenths of seconds finding a route whereas this would not be an acceptable per packet switching overhead. Another is that signalling between switches is carried out-of-band (i.e. is not itself affected by line congestion) which is the bane of many routing protocols. Also note that esp on intl circuits there is still manual preening activity. (prepares flame-suit for telco interconnect guru attack) Alex Bligh Xara Networks
What I don't know, is why is it that SS7, the telephone routing protocol, can do some of the things that are required, like load sharing across unequal paths, for example. Does anyone have any insight into this?
I *believe* one main difference is that telco sig is connection oriented whereas IP is pretty much collectionless (interesting comparison to netflow switching though); hence telephony switching protocols can afford to wait tenths of seconds finding a route whereas this would not be an acceptable per packet switching overhead. Another is that signalling between switches is carried out-of-band (i.e. is not itself affected by line congestion) which is the bane of many routing protocols. Also note that esp on intl circuits there is still manual preening activity.
(prepares flame-suit for telco interconnect guru attack)
Alex Bligh Xara Networks
Alex, Connectionless and Connection oriented both refer to packet switched technologies, whereas the phone company uses circuit switched technology. 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. 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. Larry Plato ANS CO+RE Systems
Larry J. Plato wrote:
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.
Contributing to the information/misinformation of the Universe: These "high speed 56k links" that carry the SS7 traffic and database queries also handle the number portability stuff, since a portable number has to be looked up in similar databases. Of course, now, portable numbers are all the rage. Hmmm. Sounds like the current IP routing situation, only the phone company can't say no because of something called the public service commission. -- allan chong allan@bellsouth.net formerly Bellsouth.net network engineering currently vacationing/looking for work away from East coast.
At 3:25 PM -0500 11/17/96, Allan Chong wrote:
allan chong allan@bellsouth.net
formerly Bellsouth.net network engineering currently vacationing/looking for work away from East coast.
How far away from the east coast? (i.e. Ohio or Colorado or California?) What kinds of things do you want to do? We talk to customers all the time that are looking for help. dave
participants (6)
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Alex.Bligh -
Allan Chong -
Avi Freedman -
dave o'leary -
jon＠branch.net -
Larry J. Plato