North American Network Operators Group
Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

Re: IPv6 news

  • From: Andre Oppermann
  • Date: Tue Oct 18 10:20:04 2005 
Paul Jakma wrote:

On Tue, 18 Oct 2005, Andre Oppermann wrote:

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

However, it can be confined to that arbitrary area.

Yes, but it's a very cumbersum process.  You have to track this stuff
for all regions and countries.  They all vary how they do it.  For
example your ComReg publishes a couple of tables now and then with
new/changed information.  (Look for ComReg 04/35, 03/143R, etc.)
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.)
SS7 over IP is quite popular these days.  However call routing != SS7
message routing.
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.
IP routing is not symmetric whereas circuit switching is.  In a case
of individual IP address portability the return traffic always goes
back to the ISP who has that particular prefix.  No matter who 'opened'
the connection.  If I port my static dial-up IP to my new super FTTH
ISP then suddenly up to 100Mbit of return traffic have to pass from
Dial-Up ISP to FTTH ISP.  I'd say this screws the Dial-Up ISP pretty
royally.  And you too because he most likely doesn't have that much
capacity.


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

Uhm, sure it is.

Nope, it's not.  Can you name a phone prefix routing protocol?
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 ;) ).
That works differently.  In the PSTN you always have multiple routes
to a destination.  If you have a direct trunk between two CO's then
it will fill that first.  When the direct trunk is full, the local
switch has got an overflow route towards a neighboring or higher
switch.  It can have multiple overflow routes with different priorities.
You can replace full trunk with dead trunk to get your redundancy.

However there is no dynamic call routing as we know it from BGP or
OSPF.  At least not directly.  Some switch vendors have developed
call optimization software which runs in some sort of central intelligence
center in the network and tries to optimize the trunk usage and priorities
based on statistical and historical data.


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.
The stumbling block is that all IP packets return to the prefix
holder (the old ISP) and the end-user bandwidth is not fixed.


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.
$RIR making allocations that way is not sufficient.  It would need
regulatory backing to enforce IP address portability.  Every established
carrier is not very interested in porting IP addresses to competitors.


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

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

IP is asymmetric and PSTN is symmetric.  There you have the first
major problem with IP in this szenario.
o PSTN calls have pre-determined characteristics and performance (64kbit)
No bearing on routing.

Very much so.  See my Dial-Up vs. FTTH ISP example.


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).
The differences are far greater.  See my description of call routing
above.


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. ;)
As you can see in the Dial-Up vs. FTTH ISP case as new ISP you don't
have a chance to differentiate yourself through better routing or
performance or QOS or whatever from anyone else.  If the performance
at the old ISP was lousy before it is lousy after porting the IP
address because it's still the shitty bandwidth of that old ISP.

--
Andre