IPv6 news

Tue Oct 18 13:31:08 UTC 2005

On Tue, 18 Oct 2005, Andre Oppermann wrote:

> No.  Within a region.  Normally area codes are a region. 
> Sometimes entire country codes are a region in this sense. 
> Depends on the size of the region/country though.  In some cases 
> there is even more than one area code for the same region.

Ah, yes, that I know.

I thought maybe you were referring to number -> GSM SIM IMSI mapping 
within a telco, or whatever is the equivalent for fixed-line. (How 
roaming is done is really interesting btw).

<snip interesting details>

> said default carrier.  On top of this forwarding doesn't come for 
> free.

Of course not.

> the call routing tables on my switches with that registry.  In a 
> very competitive area this lead to 30-50% of all numbers being 
> ported and thus showing up in my routing table.

Yep. Any geographic solution must consider that disaggregation will 
always tend towards 100%.

> As we know from the Internet DFZ the routing table becomes very 
> large.

However, it can be confined to that arbitrary area.

> That's why number portability is normally only offered within the 
> same area code or region.  So you can't take your NY fixed line 
> phone number to LA.  Unless of course you have someone picking up 
> the call in NY and transporting it to you in LA.

Yep, obviously ;).

> You can forget that X.25 stuff.  It's only used for SS7 message 
> routing and doesn't have anything to do with call routing as such.

Ah, it was used for everything in that network actually - but that 
was a very very specialised telco network. (And they had started 
moving to IP when I last worked with them.)

>>> Outgoing are not affected because the TDM network always sets up parallel 
>>> in/out path's. The return channel for your outgoing call doesn't come back 
>>> through your former mobile operator.

> Sure.  However this is the main difference between the TDM network 
> and the Internet.  Due to this fact many things work on the phone 
> network like carrier pre-selection, phone number portability, etc., 
> that do not work on an IP network.

I'm not source how assymetric paths affect portability etc. Also, IP 
is well capable of that, and makes life easier.

> On the phone network the prefix information is not dynamically 
> exchanged.

Uhm, sure it is.

> There are number portability registries whose data you can download 
> every night or so and then dump it into your own switch or IN 
> platform.

The number portability registries can be updated infrequently, yes.

The telco prefix routing information however most definitely *is* 
routed dynamically. Maybe you don't have to participate in this 
routing (your not a telco?), but between the telcos - most definitely 
;).

(If not, we were scammed for a fortune for dynamically routed 
redundancy of calls across a set of exchanges ;) ).

>> 2. Providers must be prepared to carry other providers traffic into
>>    the area
>
> Only one of them.  The 'default' carrier.  There are many phone networks
> and carriers carrier who do not have 100% coverage.

Let me restate that:

2. One or more providers must be prepared to carry any
    providers traffic into the area

Same thing.

The incentive for providers to announce such an area-prefix to as 
many other providers outside of the area as possible would be to 
reduce settlement fees within the area for the smaller providers, and 
for the big ones -> make money.

>> 2a. The providers within the area have to figure out how to bill for
>>     the difference of this traffic.
>
> No.  Usually the tariff is set by the regulator based on some fixed
> interconnection charge and network element usage.

How they figure it out (with or without a regulator) doesn't matter. 
It just has to be figured out. We don't have IP regulators, so for IP 
providers would have to figure it out all by themselves obviously. ;)

That'd be the stumbling block I suspect.

> Well, we can learn from them that circuit switched networks are 
> different than packet switched networks.  Beyond that not much.

If you want to focus on the differences between IP and POTS/GSM, 
sure, they're completely different. However, the point is to examine 
the abstract model for how telcos manage to achieve number 
portability without global-scope exchange of subscriber information 
and see what, if any, techniques could apply to IP.

> To summarize the differences between PSTN and Internet routing:
>
> o  PSTN ports numbers only within regions/area codes

We're discussing what would be possible with area (rather than 
provider) assigned IP addresses. Ie, this is as possible for IP as 
PSTN, if $RIR decides to make some allocations in this way.

> o  PSTN routes the return path along the forward path (symetric)

I thought you said it didn't? No matter, IP is assymmetric.

> o  PSTN calls have pre-determined characteristics and performance (64kbit)

No bearing on routing.

> o  PSTN has static routing with periodic sync from porting database

The important point is that information to describe number->provider 
is exchanged betweeen providers in the area only. Whether it's done 
by dynamic protocols, email or post is an irrelevant detail, all that 
matters is that we have a way to do same in IP (we do: BGP).

> o  PSTN pays the routing table lookup only once when doing call setup

Well, that's simply a fundamental difference between packet and 
circuit switching ;).

> o  PSTN call forwarding and peering is not free or zero settlement

Indeed, I thought I had emphasised that working out the billing would 
be a major component of area-allocated IP. ;)

regards,
-- 
Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
Fortune:
QOTD:
 	"There may be no excuse for laziness, but I'm sure looking."