North American Network Operators Group

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Re: IPv6 news

  • From: John Dupuy
  • Date: Tue Oct 18 12:38:20 2005

At 07:36 AM 10/18/2005, Andre Oppermann wrote:
[... items deleted ...]

To summarize the differences between PSTN and Internet routing:

 o  PSTN ports numbers only within regions/area codes
 o  PSTN routes the return path along the forward path (symetric)
 o  PSTN calls have pre-determined characteristics and performance (64kbit)
 o  PSTN has static routing with periodic sync from porting database
 o  PSTN pays the routing table lookup only once when doing call setup
 o  PSTN call forwarding and peering is not free or zero settlement

Largely true; influenced by history and the difference between circuit-switched networks and packet-switched networks. LNP is more like DNS than multihoming. Sort of. Imagine TCP using domain names rather than IP addresses.

I should note however, that in the U.S., Number Portability (LNP) rarely uses call forwarding anymore. Except in legacy rural areas, the LNP dip occurs before reaching the host office and is thus shunted to the correct carrier earlier up in the stream. At minimum it is done by the N+1 switch. However, it is common for the IXCs (LD Carriers) and CLECs do it even earlier to avoid paying the local ILEC database lookup fees. In that scenario, it routes perfectly to the correct carrier.

BTW, telephone networks are generally do not multihome and are very fragile. Node (Switch) failure brings down large sections of the network. They instead concentrate on 99.99%+ uptime for the switches themselves. In other words, they concentrate on internal component redudancy and same-destination route redundancy rather than handling an outage of the entire switch. The SS7 network has removed some of this fragility, but not all. Not by a long shot.

Describing this in a picture:

Internet way: "route around problems"

A - B - C
\ /

The Telco way: "try to make problems never happen"


Where the AA in the Telco model is essentially the same equipment in the same room with redundant components.

Anyway, ... TCP using DNS rather than IP?... Interesting thought.