eli@chipcom.com (08/15/89)
I spoke with my US Sprint college pal again. He had some interesting
comments about the "call progress / billing problems" which have been
talked about in previous Digests. He also had some comments on ATT's
fourth quarter 88 posted financial loss.
>From regular equal access (feature group D) -- both destination &
source phone numbers are sent through a CO to an "access tandem" and
then to long distance carrier. In this case, hardware call progress
supervision is available on the destination CO/trunk/line and there is
no chance for error. 99.8% of all long distance calls use this
method, or something called feature group B, so there is no chance for
billing error. An example of a feature group B call would be one that
went through the "950" local access numbers for the long distance
carriers. Before equal access, these 950 numbers were required in
order to provide hardware supervision (and access) with feature group B.
In primitive/podunk exchanges (feature group A), the receiving CO will not
indicate back to the source CO whether someone has picked up the phone.
In this case, software supervision is used. Here there is a nonzero
probability for a billing error. ATT is not susceptible to this type of
error, as some readers have pointed out, because...
ATT calls are terminated on the trunk side of the telco instead of the
line side of the telco, and in this case, ATT uses feature group C,
which is not available to "alternative" long distance carriers due to
the vagaries of how ATT built their network before equal access.
Group C bypasses a few switch steps, which was one of the reasons why
ATT calls used to get completed faster than Sprint's. (This part of
the explanation went over my head a bit; clearly my buddy limited his
comments here so he could get back to work without spending too much time
explaining this "feature group C" setup.)
99.8% of all long distance traffic use hardware supervision, hence the
"billing on unanswered call argument" is mostly a non-issue. In the
.2% which are forced to use software supervision, there can be a false
"off-hook" signal sent back to the originating switch in as few as 6
rings, usually more like 15-20 rings. So, the bottom line is not to
let the destination phone ring or busy for very long -- IF YOU ARE CALLING A
PODUNK EXCHANGE.
Regarding call setup/completion time, he said that Sprint and ATT
are within 2 tenths of a second in call completion time.
He also commented about ISDN and how US Sprint is ready for ISDN,
whereas ATT is behind, and MCI is way behind. Sprint already has
CCS7 (switching something-or-other), a fiber network, and 100% digital
transmission. ATT is accelerating the depreciation of their equipment
because they have to modernize their network in order to support ISDN,
and to keep up with the competition -- in this case, US Sprint.
-- Steve Elias
-- eli@spdcc.com, eli@chipcom.com
-- voice mail: 617 239 9406pvf@houdi.att.com (Paul V Flynn) (08/18/89)
In article <telecom-v09i0297m06@vector.dallas.tx.us> eli@chipcom.com writes: >ATT calls are terminated on the trunk side of the telco instead of the >line side of the telco, and in this case, ATT uses feature group C, >which is not available to "alternative" long distance carriers due to >the vagaries of how ATT built their network before equal access. >Group C bypasses a few switch steps, which was one of the reasons why >ATT calls used to get completed faster than Sprint's. (This part of >the explanation went over my head a bit; clearly my buddy limited his >comments here so he could get back to work without spending too much time >explaining this "feature group C" setup.) I've never heard this one before. Feature Group C access (used by AT&T) and Feature Group D access (used by the others) are both trunk-side connections. What difference between Feature Group C and Feature Group D allows AT&T to have a shorter call setup time than the other common carriers? US Sprint makes heavy use of access tandems, while we tend to connect directly to a local exchange carrier's end office, but that is a business decision on US Sprint's part, not something they are forced to do because of Feature Group D. Can your buddy at US Sprint explain to us what Feature Group C vs. Feature Group D has to do with call setup time? Paul Flynn AT&T Bell Laboratories, Holmdel, NJ