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dmine45

AT&T Tandem thoughts (4ESS, N4E, etc.)

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I go all over the US for work and vacation, and when I do I like to see how the local network homes on various tandems (AT&T, MCI, Sprint) when I can. I like to do it from landlines and cellphones since both route differently.

 

I also do this with VOIP carriers since often times they dump you on the POTS network at various places, and this can either be static or dynamic. (Can you say Tandem round robin?)

 

Often times calls from landline, cellular or VOIP go to the newer "edge switches" that are in the format of NPA-xL (like 412-9L). I believe most of these are 5ESS based. But most of the time you can reach a 4ESS in the format of xxx-T.

 

Anyhow, I was in a very rural place in Wyoming in May while on vacation. It was a rest stop in the middle of nowhere. The rest stop used to have a pay phone (you can tell it was there and removed), but they did have a microcell for Verizon Wireless (obviously fed by DSL).

 

Doing my test for AT&T, it did the round robin as I suspected (some sort of VOIP backhaul) and I came up on 088-T a few times. That *used* to be the AT&T tandem for San Diego. They retired the 4ESS a few years ago, but now it comes up in the "new" voice that AT&T is using for the new generation "N4E" system.The N4E uses the old 4ESS software hosted in a virtual environment in newer hardware (lot smaller footprint and more in tune with modern packet switching).

 

Sure enough, I was in San Diego last week and tried it from a COCOT. Yup, they do have a new N4E and has the new voice on the trailer.

 

So I'm wondering how many of the existing 4ESS systems will be replaced by N4E systems?

 

I also wonder how many 4ESS and N4E systems are out there. I found a N4E in Scottsdale, AZ (NPA 480) not too long ago. Haven't explored what else is new out there recently.

 

 

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037T was just converted from old 4E to N4E dialed from Indonesia.

 

038T as of a few days ago has not been converted.

 

Both of those tandems are located in Houston, TX, where I live.

037T.flac

Edited by ramsaso
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On 7/25/2017 at 7:47 AM, ramsaso said:

037T was just converted from old 4E to N4E dialed from Indonesia.

 

Interesting. That's one of the tandems in Houston, TX. Mind if I ask you what you dialed to reach it?

 

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So I'm wondering how many of the existing 4ESS systems will be replaced by N4E systems?

 

They put in a couple every year. They don't all (but typically do) replace one when they're installed. Given the sluggish time frame, how many they're going to install is probably a question of how AT&T's politics work out for them in the long term. The current band of executives has been responsible for some borderline irrational decisions in the past, like grandfathering all non-IP services on their CLEC divisions in 2013. No, seriously. Their CLEC network was then and still is, aside from a few Sonuses, pretty much all circuit switches, and much of their voice over IP traffic is hauled to the customer over T1 circuits. It's like a halfbaked version of Apple's decision to remove the floppy drive/audio output/whatever else from their products.

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I'm curious, why are the phone companies replacing the 4ESS like that? Are the originals getting too old?

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Only AT&T operates them right now; they were a bunch of LECs that bought them for intra-LATA switching, but those were replaced with DMS-200s. My guess as to why those were replaced is there was limited expertise available to run them, and a lot of collective, expensive headscratching.

 

For AT&T, it's a little different; they developed the 4ESS with Western Electric/Nokia/whatever from the ground up to be a good toll switch; feature-wise, the software gives it a leg up over the DMS family for that. I'm guessing less so for local operations considering AT&T-owned local carriers like Pacific Bell phased them out years ago,

 

But to answer your question, well, maybe. The older 4ESSes are pretty damn old, but in the world of circuit switching, that doesn't mean a whole lot. All the hardware is on easily replaceable cards, so you can replace stuff as needed; it's not like PCI or anything. You can just disable a card, yank it out, and shove something else in it's place. The processors are redundant, so you can do this with them too. A switch that was installed thirty, forty years ago has probably had most of it's earlier cards replaced with updated versions at some point, so it's not like running a car that old. But the last 4ESS was installed in 1999. Assuming nothing is interchangeable with the 5ESS (it very well could be; you'll see design decisions like that sometimes), it's possible the manufacturer is trouble finding components for repairs and new cards. Though considering Nokia currently holds pretty much all knowledge about it, top to bottom, I'd find it hard to believe they couldn't just do a limited run of more parts if they were up against the wall. They have a good enough business relationship with AT&T that they'd definitely do this if it was a problem. Considering Nokia end of lifed the 4ESS, my guess is AT&T specifically made some decision to phase it out.

 

As I said before, the current executive leadership at AT&T has gone through a pretty huge ideological change. They've decided the only way for the company to survive is to make a frantic rush towards IP telephony, a very significant change with how they were run before. They've tried replacing the 4ESS with all sorts of things over the last couple decades; 5ESSes, DMS-250s, even some sort of weird custom switch in the nineties. For whatever reason though, that never panned out. In line with "everything needs to be IP right now" thinking, this is probably the best answer they could come up with.

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From what I heard several years ago, the later 4ESS switches that were installed in the mid to late 90s were of a newer generation than those from 1976 to the late 80s.

 

And yes, some of these switches are 40 years old!! But as TP said, over time I bet most of the guts have been replaced (though I do wonder about the announcement machines - some of which are quite broken!).

 

But I think to say relevant, AT&T like a lot of other telcos are going VoIP. I know Verizon basically runs it's old school POTS TDM network and a VoIP network in parallel with gateways to cross connect the two worlds as necessary.

 

Yeah, AT&T has introduced DMS-250, 5ESS, etc. into the long distance network, but the venerable 4ESS is still the backbone. Just curious what their strategy is to play in a mixed TDM and IP environment moving forward.

 

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Please tell me they run these VOIP links over their existing physical trunk network and not the greater public Internet...

Why "N4E"/"New 4ESS"? Wouldn't "4AESS" have better followed convention?

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Please tell me they run these VOIP links over their existing physical trunk network and not the greater public Internet...

 

The N4Es specifically have media gateways, so they could just use existing TDM trunks. I don't know what they're run over, but with things that are very clearly running over IP like the 4E-APS redesigns (notice in areas like Los Angeles and New York, the 800-223-1104 ANAC has a different voice. They don't seem to be actively adding these at the moment), I just sorta assume they're at least reachable on the public internet. Occasionally they'll have the sort of staggering packet loss that would imply a bunch of people trying to attack it or something.

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With AT&T's large fibre + MPLS backbone, it's gonna be MPLS w/ traffic engineering.

 

So likely unreachable via the public internet.

 

Notable factoids:

 

1). MPLS DOES provide a private network

2). MPLS doesn't include/provide encryption

3). They have a high likelihood of using a protocol called IS-IS for route distribution (tell that to your neocon relatives!)

 

Able to be tapped by LEOs and TLAs, more than likely.

Edited by gewt
Clarification
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Replying to my own old thread...

 

Looks like more 4ESSes have been replaces with N4E systems. Found this link that used Mark Cuccia's old 4ESS list and is being updated. I need to add a few to this list myself.

 

https://pastebin.com/Q67S9WNB

 

 

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Finally was able to do some AT&T tandem testing from an old school POTS line (getting really rare these days)

 

So here's what I've come up with: A number of old 4ESS switches are still in the network, but they are fast being replaced with N4E switches. At the same time, a number of N4E switches are being installed where they never had a switch, or maybe a 5ESS as an edge switch.

 

Either way, this makes for an interesting list. Some of these are guesses based upon my knowledge of the network, etc. These were all tested with the infamous NPA-959-69xx method, with the switch 144-T (Monrovia, MD) as the basis. Eventually I'd like to try some of these from other entry points into the network.

 

And in a number of cases, the announcement machines are broken and all you get is reorder. Sadly they're just not caring and maintaining the old 4ESSes since they're slated for retirement.

 

I'll also attach a file that shows more detail and depth of the testing. ("Local" means I got my local 4ESS recording, in my case 144-T)

 

But here's the short list of what I've been able to verify during my test that took place between January to March 2020:

 

Area Code    ST    Tandem    N4E/4ESS
310    CA    ?    Reorder (4ESS)
312    IL    ?    Reorder (4ESS)
209    CA    ?    Reorder (4ESS)
860    CT    ?    Reorder (4ESS)
909    CA    ?    Reorder (4ESS)
912    GA    ?    Reorder (4ESS)
708    IL    ?    Reorder (4ESS)
505    NM    002-T    Reorder (4ESS)
404    GA    007-T    N4E
512    TX    008-T    4ESS
410    MD    010-T    Reorder (4ESS)
205    AL    011-T    Reorder (4ESS)
704    NC    015-T    Reorder (4ESS)
304    WV    016-T    4ESS
216    OH    017-T    4ESS
803    SC    018-T    4ESS
614    OH    019-T    Reorder (4ESS)
719    CO    020-T    Reorder (4ESS)
609    NJ    022-T    Reorder (4ESS)
515    IA    024-T    N4E
303    CO    027-T    Reorder (4ESS)
908    NJ    030-T    local
508    MA    031-T    4ESS
817    TX    032-T    N4E
616    MI    033-T    4ESS
910    NC    034-T    Reorder (4ESS)
713    TX    037-T    N4E
601    MS    040-T    Reorder (4ESS)
423    TN    042-T    4ESS
816    MO    043-T    N4E
517    MI    044-T    4ESS
502    KY    047-T    4ESS
501    AR    048-T    N4E
915    TX    050-T    4ESS
901    TN    051-T    4ESS
603    NH    052-T    4ESS
615    TN    058-T    N4E
504    LA    060-T    silence (4ESS)
201    NJ    061-T    Reorder (4ESS)
718    NY    065-T    N4E
405    OK    069-T    Reorder (4ESS)
510    CA    070-T    Reorder (4ESS)
402    NE    071-T    N4E
309    IL    073-T    4ESS
215    PA    074-T    4ESS
602    AZ    075-T    Reorder (4ESS)
503    OR    077-T    4ESS
702    NV    081-T    Reorder (4ESS)
219    IN    082-T    4ESS
916    CA    083-T    N4E
818    CA    084-T    4ESS
801    UT    086-T    4ESS
619    CA    088-T    N4E
415    CA    089-T    4ESS
408    CA    090-T    4ESS
217    IL    091-T    4ESS
413    MA    091-T    Reorder (4ESS)
509    WA    093-T    4ESS
314    MO    094-T    N4E
206    WA    095-T    Reorder (4ESS)
315    NY    096-T    Reorder (4ESS)
813    FL    097-T    4ESS
419    OH    098-T    4ESS
918    OK    099-T    4ESS
914    NY    104-T    silence
414    WI    105-T    4ESS
212    NY    111-T    Reorder (4ESS)
520    AZ    114-T    Reorder (4ESS)
203    CT    119-T    4ESS
706    GA    126-T    Reorder (4ESS)
954    FL    131-T    Reorder (4ESS)
608    WI    132-T    4ESS
928    AZ    149-T    N4E - Flagstaff?
239    FL    151-T    N4E - Fort Myers/Cape Coral?
213    CA    152-T    N4E - Los Angeles (replacement? addition?)
781    MA    153-T    N4E - Boston suburbs?
432    TX    154-T    N4E - Odessa?
480    AZ    155-T    N4E - Scottsdale?
904    FL    157-T    N4E - Jacksonville?
714    CA    158-T    N4E - Anaheim? (replacement? addition?)
610    PA    159-T    N4E - Allentown?
612    MN    no ID    N4E - Minneapolis?
301    MD    no ID    N4E - Not exactly sure (DC suburbs?)

 

Area Codes for AT&T Tandem Testing March 2020.xls

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