R1,
>>can you point me to where I can find out about
SS7-wireless connections? actually what I want to know is
how is IP-T handled via satellite networks?<<
I'm glad you clarified that, Byron, since SS7 related
wireless, in the sense of cellular and PCS, could take us
quite some time to unravel. Maybe we'll get into that some
other time, when mobile base stations and roaming
capabilities begin playing a greater role in VoIP
applications. That should be lottsa fun. <g>
Where satellite trunks on the Global Switched Telephone
Network or GSTN (or equivalent) are concerned, SS7 is
generally applied the same way as it is for terrestrially-
based switched trunks. In fact, trunks may be intermixed,
in the order of sequence in which they are selected,
alternately being submarine cable or satellite. Echo
suppression in older systems, and echo cancellation in
newer ones, make up the difference for traditional voice
circuits.
Let's see if I understand your question. Does it have to do
with application of VoIP algorithms in TCP/IP delivery
over these satellite facilities? Or does it have to do with
sending switched services over the satellite facilities that
will be connected eventually with VoIP links on the
ground. There's a difference.
As for latency, in rough numbers you can depend on at
least a quarter of a second, sometimes more, in pure
propagation times for each of the uplink and downlink
paths, i.e., 0.5 to 0.6 seconds round trip if you were to
measure it through a hardwired loopback arrangement,
without considering any of the latencies of the VoIP
engines or gateways, routers, etc., or "tail circtuis"
to subscribers through ordinary telco providers networks,
and certainly without considering the latency of the
Internet itself.
For this reason, I've been very cautious about passing
judgments about ventures whose platforms depend on the
use of satellites in the VoIP space. Overall latencies can
easily exceed a half second under good conditions,
when you tally all of the factors in the equation.
>>how do we send a wireless signal up then back down
onto and off of an IP-T network{i.e. the conversion of
signal process(magic box)? and what are the latency's and
is the compression(packeting) enough to take care of the
delay?<<
Again, if the satellite section of the call path is "switched"
then it takes on a personality of any ordinary switched
circuit, only it has more delay.
If the satellite portion is actually an extension of the IP
cloud, using TCP/IP, then there are added complications
which emerging protocols out of the IETF are attempting to
solve, due to the very nature of the IP protocol which has to
do with estimating route costs as a function of absolute
delay, router resources, as well as other forms of link
"costs," and what will be placed over them. But these are,
at best, suited for certain forms of non-time- critical data
applications at this time, and not optimally suited for the
delivery of real time voice and real time video, under
normal circumstances.
Of course, it also makes a difference if the satellite
portion of the network is dedicated to a private IP
backbone, or if it is one of many potential paths on the
open Internet.
For some good insights into the issues surrounding the
interactions of TCP/IP, the Internet, and satellites, go
to the following Business Communications Review abstract
on the subject from their April, 1997 issue:
bcr.com
>> btw, I was just @ GRIC and noticed that INDOSAT=JV
partner of DGIV, is part of the GRIC network DUH, <<
Just as multinational banks must clear and settle in a variety
of settlement schemes using geographically dictated
clearinghouses, carriers in the new order (ITSPs) will find
themselves increasingly using multiple forms of settlement
until a global order is established. This brings to mind the
press release the other day concerning the Open Settlement
Protocol (OSP) which 3Com, Cisco, GRIC, iPass, and
TransNexus agreed to support, with additional support from
the ETSI TIPHON initiative. See:
Message 5657731
[[BTW, did anyone notice the conspicuous absence here of
Tom Evslin's ITXC in this announcement? What's up
there? Anyone?]]
Something on the order of what the ITU now has in place
for accounting rates and settlements, I'd imagine, although
it would need to be drastically updated and modified, not to
mention the mechanics that would need to be put in place
to make it work across the board. I'm not holding my
breath. So, the fact that one ITSP (DGIV) has hooks into
multiple consortia isn't too alarming, if you think about it.
I don't quite understand where you are coming from with
the following question. Please elaborate for me:
>>that answers a lot but I still need to understand a bit
more I also think that comparable to SS7-Nortel's 250
should also do the trick no?<<
Regards, Frank Coluccio |
