[asterisk-ss7] IP vs TDM (was TCAP over VPN?)

Kevin P. Fleming kpfleming at digium.com
Wed Jul 14 07:20:12 CDT 2010

On 07/13/2010 08:19 PM, Bryan Scott wrote:
> On Jul 13, 2010, at 7:01 PM, Charl Barnard wrote:
>>> Which at least partially explains the lower cost... there aren't any
>>> TDM
>>> circuits involved.
>> I always suspected the Big Transition to IP was more vendor push than
>> operator pull, so I'm keen to hear why a sharp guy like Kevin would reckon
>> that TDM is inherently more expensive than IP ..
> I don't think it's so much the hardware as it is the transport.
> Some of my SS7 A-Links come to West Wendover, NV from Reno, NV, spanning the ENTIRE state and transiting multiple LECs along the way.  One provider figured they could offer redundant A-Link service to two points in two states over IP for half the cost of one of those existing TDM circuits.

Exactly. If you wanted an A-Link from a provider 2K miles away (not that
uncommon), doing that over TDM would be exorbitantly expensive, but
doing it over IP means either routing over the public Internet (lowest
cost, but not much quality of service) or over an MPLS connection (where
you only have the 'line cost' for the local loop, which could even be
DSL if the traffic volume is low enough).

And there are hardware costs as well; on the provider end, they can
provision one or two GigE ports from an edge router to the network
cloud, and service thousands of customer connections. Even on an
high-end router, those ports might cost $1K each. Doing the same thing
with TDM circuits (even at only one DS-0 per customer) could easily
require one or two OC-3 ports, which cost, umm.. well, a lot more than
$1K each :-)

Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
skype: kpfleming | jabber: kfleming at digium.com
Check us out at www.digium.com & www.asterisk.org

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