AT&T Technical Journal Jan 1985/System 75 Tell All, Carrier Switches




In 1984, AT&T started to market their new digital (fully digital that is) PBX called the System 75. The System 75 was a fully new system that could handle infinite technologies such as ISDN, PRI, T-1, and later IP and packet switching. AT&T also marketed the System 85, which was a Band-Aid code version of the Dimension. The System 85 ran on whatever stored software that used for the Dimension, but it shared hardware compatibilities with the System 75. In fact the System 85 had some interesting features such as AUDIX “Unified Messaging”, ports could max out to over 30,000 extensions and support up to 40 attendant consoles. Well, not the 302 console I posted earlier, but a boxy one that was used for the Dimension.

Another system called the System 25 was based almost entirely on the Merlin system with the code, and features. The System 25 is much comparable to a Merlin Magix or Legend system of today, which eventually replaced this odd setup.

What was common with all the cards and the type of carriers is the boards were cross compatible and hardware for phone lines and trunks could be interchanged during a cutover to a larger system. There was a reason why there was color coded labels on the boards, back in those days System x5 systems required tone clocks, processors and auxiliary connections  to be together, line cards and those alike could be free floating if the customer chose so. Later versions of the Definity system would not have color coded labels and the cards could go in whatever fashion.

system75 8


This cabinet can weigh as much as a stainless steel refrigerator, about an 800 pound voice gorilla and can support up to 700 lines.

It’s kinda strange how the power unit is located right next to the processor and tape unit…wouldn’t that cause problems?

To the left and right of each shelf  has a power supply, for each row, it uses two sources of power. What’s interesting in this first version they all have power on and off (or kill switches.)  Newer versions had power in only.

The bottom area was changed to support battery backups, the power supply and it’s tone generator in later years of the Definity/MultiVantage/Communication Manager systems.

It’s safe to say the System 75 scaled horrifically in the beginning again with that 700 port limit. However with creative integrators, you could theoretically have thousands of extensions using multiple System 75 (or even 85) PBXes and link the systems with a Distributed Communications System which would allow feature transparency through multiple of mediums (microwave, fiber, copper, CO, etc.) The New York State Government was a classic example where their Albany network had about 80,000 or so ports/extensions/lines and this was their original setup when commissioning this type of systems in the late 80s, according to Network World. DCS gets lot of mentions in this tell all as this would be a selling point to sell this system to other customers.

AT&T Technical Journal Jan 1985/System 75 Tell All, Attendant Console



Some things don’t change. Sometimes familiarity you shouldn’t mess around with.

In this case, the operator switchboard or Attendant Console as remained mostly the same since 1984, first released for the System 75 PBX. This model # was 302 series, but rarely is branded as such, only in the administrative terminal sessions to add stations and alike. There were 4 different series of 302s, suffixed with letters

A was the model shown below, very Merlin looking, and used button caps similar to Nortels, but more smaller.

B had a different display, with a white instead of metallic.

C replaced the button caps and supported 2 wiring environments. Prior to 302C, you needed the full 8 wires of copper to connect the console. C also introduced modular connections for the hand or headset. Prior to C, the console automatically logged in operators if they plugged in that dual 1/4″ jack into the console. Because of the change of jacks, the operator would had to press a few buttons to log them in.

302D was introduced around the turn of the century and required 2 wire environments only. 302C could work in ether/or environment


At some point, as of this writing in 2015, the 302 Series is officially dead and is no longer sold as new by Avaya as many operators have evolved to administrative assistants doing multiple things and split the calls between those groups, or in some operator environments have been replaced by s0ftware based sets. Operator sets don’t come cheap, and including its Direct Extension Selection or DXS can cost about $1,100 new!

The DXS has evolved, but the  general idea hasn’t changed. In fact the Merlin looking industrial designed remained in tact right to the EOS. The first generation had 8 buttons on the very bottom acting as “Hundreds groups select”. Simply put, if you have dial plan from 4000 to 6000, the bottom 8 buttons would be labeled “40”, “41”, “42” and “53”, “54”. etc. So if you want to call extension 5138, you would hit the bottom “51” key from hundreds group, then  press “38” in the 100 array keys. You can monitor a group of hundreds at a time and in later models as the System 75 evolved from supporting a few hundred extension into the behemoth of the Definity PBX supporting tens of thousands of lines, the Hundreds group keys maxed to 20, so you could monitor a couple thousands of lines if you had that model.




This picture is interesting because its very rare for any AT&T/Avaya Red publication to show exploded views of any of their equipment. This was standard operating procedure for Nortel if someone wanted to replace a part in a console or a set, however it was the job of AT&T to Lucent to Avaya to let this type of work be done by them or vendors.

AT&T Technical Journal Jan 1985/System 75 Tell All, Wiring Panel





This is one of the figure pictures in the AT&T Technical Journal, and the tell all of the System 75 PBX. What’s interesting about the wiring is modular, I’m not sure if the RJ45 jacks come from Amphenol to the cross connect or the voice drops.  I thought most System 75 setups in those days (and probably in the mid 90s) were 66 blocks where you’d take an Amphenol from the PBX and ether splice the wires to a 66 block or plug in it if the block had a female Amp adaptor.

system75 3

Unboxing my “New” Definity CMC/csi PBX

Good Morning!

I taped this on the day I received my Definity system from one of my followers, Jason. He offered me his old switch and decided why not take advantage of an offer, despite my relationship status is beyond repair with Avaya.

The Compact Modular Carrier, or CMC is similar to the Meridian Option 11. It’s bigger than a KSU, but it’s still wall mountable or sit on a floor and can stack up to 5 modules totaling to about 700 extensions, depending on your configuration given you have 60 circuit cards you can add.

For the record, apologies for some of the video quality, needed to compress from a multi gigabyte video file to under a 100mb, well it got too compressed. I still have my Final Cut file, and I’ll re-export it with some less compression.

Happy Saint Patrick’s Day, part two


Here is a short video featuring the aforementioned telephone posted earlier today. I recorded this video yesterday in my office tied to a Definity CMC/csi/small carrier PBX. The set was programmed as a 500 so it could pulse dial. If you are near any Definity switch and hear clicking, it is most likely coming from the relays on the analog boards. 500 and rotary telephones are no longer supported in the age of Voice over IP as such technology requires parts like relays and such to delay dialing and stuff like that.

The Avaya 8434 Office Telephone

We’re going back the Definity PBX theme, I wanted to continue post pictures of my own phone stuff.

I bought this Avaya/Lucent/AT&T 8434 Digital Voice Terminal on eBay as a little birthday present to myself back early this year. (Well it was around my birthday.) I explain the reasoning later on.


Whether or not you have know about the system, you see this phone in lots of places, in the America’s Newsroom in the basement level at the Fox News Channel, many of  operations at NBC in the next block over in NYC have tons upon tons of 8434 users that if you tune to your TV ether on MSNBC or the local affiliate there have these decades old terminals. This model the perfect phone for secretaries, war rooms, and as I had shown earlier, in legislative halls like in Albany, New York to the Governor’s Office in Boston, Mass.

There’s no doubt why these are still in existence in many locations, regardless if its technically an antique –  you have 34 buttons for speed/auto dial, line appearances, etc and a wonderful backlit display.


This model was introduced to the Definity ecosystem by AT&T’s Information Systems Unit around 1990. The 8434 was one of the 8 various 8400 Series models, such as the 8403, 8405, 8410, and 8411. There were sub variants such as two way speakerphone and display abilities, but I’ll leave that technical stuff out.* These terminals were reverse compatible, so if you had a shop that still was running as a System 85 or 75, the thing would be able to be “ailased” as a 7400 series telephones. The system would think this as a 7444 but on the desktop it was clearly an 8434.

*OK, here’s the technical stats: There are 3 suffixes on the 8400 model numbers, B means basic, no display; + means a two way speakerphone (the ones that have a B can only listen only), D is obvious, it means it has a built in display and DX had improved speakerphones and changes on the fixed button features, etc.

This model I have is a DX. I forget the differences between the original, but my model has a jack for external speakerphone/headset and a sidecar jack designed exclusively for the 8434.


I had an XM24 sidecar to my 6424 telephone but it got fried last year, so I thought in theory (since the IP Office shares the same number of features and appearances like its Definity-like cousin) that the 8434 could work. I thought it would work with my Avaya IP Office digital phone system. Turns out it works only for testing and selecting a ringtone, but it doesn’t function beyond that because the switch is too damn smart. I thought given it uses a common proprietary signaling  known as the Digital Communications Protocol or DCP.

What really sucks whether if its an incompatibility issue or if its dead is it Vacuum Florescent Display which has a glowing green colored LED like display. It be very cool to see it function

Regardless its deemed to be incompatible.

That’s all for now!

Office Telephones: Avaya 2420 – Mount Washington Hotel, Bretton Woods, NH

The Mount Washington Hotel, in Bretton Woods, NH has a lot of history. The Mount Washington Hotel was the first Hotel to have an in house phone service. This place was the homebase for the International Monetary Fund or IMF after World War II, and was 3 season hotel up until a change of ownership in the late 1990s.

The place now is an all year round hotel, including other nearby hotels and resorts, and has been partially sold to the Omni Hotel Group, whom of which did major changes to the hotel, such as upgrading the old Centrex network to a modern Avaya PBX.

I’ve stayed at the hotel on a number of ocassions for a local conference, and I can attest the Centrex system sucked. I tried to call room service one time, and the call was staticy. The Bellman and front desk had ISDN terminals from Mitel (unmarked models) and Nortel (5300s) In 2010 I noticed they went to an Avaya CM PBX, and its not IP based. The hotel can’t handle Cat 5 wiring throughout the hotel, so most Internet traffic is done through WiFi, and the wiring for the phones is 2 pair, hence 2420s being installed for the bellman, front desk and the restaurants and bars within.


Avaya 8410 Digital Voice Terminal

This was taken in April of 2010, after a surgery done at Boston Medical Center. This place appears to have been users dating from the System 75 or System 85 PBX systems because I had seen 7410s, 8410s and 6400s and everything in between. This complex also houses the Boston University Medical School, which uses the Boston Medical’s network. I don’t know how many ports this place has – but its a big hospital compared to what I have seen where I live. Could be in the low tens of thousands.

a picture of an 8410 telephone from Avaya


the phone appears to not be working. You may ask why? Well other than the screen now showing any information, the second sign, is the first left hand button should have a red light indicating that line (or “call appearance”) is ready to be used and is in idle state.

[Really] Private Systems: Massachusetts State House

These sets of pictures were taken in 2009 at the Massachusetts State House. The government of Commonwealth of Massachusetts have been long time Avaya users dating back to the late 1980s.  If you are a native to that state, you should be proud that your tax dollars were at work from upgrading to the latest and greatest office telephones. However, as of these exposures, I would highly assume they are still use the 6400 series telephones.

An Avaya 6424 and a 6408 Digital telephone at the House Chambers of the Massachusetts State House.

I do not have any clue what is in the backend of the Boston area telephone network. Its a Definity based system but that’s all I know. I don’t know how many nodes, how many unique PBX systems that are located throughout the Boston area. Unlike the state that borders far west,  the Commonwealth is often tight lipped about telling anyone anything about the government. I do know Massachusetts has a headcount of maybe just north of 50,000 employees – yeah that’s a lot for a government sector.

This news footage shows a lady making a phone call on ether an AT&T/Avaya 7405 or a 7434 terminal with a florescent screen adjunct in 1991. From  YouTube user: MSTS1

Another unknown is how their dialing plan works. I remember going into one of the elevators was a 7 digit telephone number to reach the campus security. The  Commonwealth does not publish a government directory, nor do they have an online directory. Nor their western counterpart  publishes even a  guide to learn their telephones. They are very secretive in that state, and there is no such thing as public knowledge (don’t say its a security issue – that’s an excuse!)

Some pictures taken in 2010 when I visited there in October with some better quality of images of their super-private of private systems.

Another shot of the press office with very dated key telephones.

That’s all for now!

Private Systems – The New York State Government – Albany, NY

This post focuses on Private Branch Exchanges and one of the largest PBX network using Avaya’s PBX solution.

I thought the larger governments would had been Nortel users, and many of the New York State buildings and agencies do use Nortel, but a few years ago, I didn’t realize that their buildings in the city of Albany and the other communities were in fact users of Avaya systems (or the largest single site users from the best of my own knowdlege…)

The story begins back in the late 80s, the government agencies for the State of New York started a large project known as Empire Net. The project included all telecommunications improvement, one was for the services from the Bell company, second was a large scaled microwave network, and third their private phone systems. AT&T’s Information Systems unit was picked through a bid and installed the NYS Government – a hugge, huuuggee PBX network consisting with multiple System 85 switches with 13 unique PBX systems in the Capital Region of New York! This humble network would replace the existing Centrex service that the NYS government was using prior to.

Connecting these switches, were ether using TIE trunks and/or later with the magic of the Distributed Communications System (DCS), these systems can talk to one another as if they were one big happy voice family. At the time in the late 80s, there were other multivendor systems used statewide. DCS was or is a proprietary protocol that is kinda like the “cloud” of the modern days for the System 85/Definity systems. Some of the buildings had talked via microwave links and now its virtually all fiber.

If you guessed about 20,000 terminals* that was installed here, you sir guessed too conservatively – you were off about 60,000! Yes, 80,000 lines and/or terminals through this almost exclusive single vendor private phone system! I was quite surprised to see such number because no individual traditional Definity PBX could handle no less than 20,000 ports to begin with! This information is courtesy in part of the IT agency of New York as they mention this on their website. I don’t think any other company or even another corporation could brag about such  port count! Granted AT&T never made their own carrier class PBX like Nortel did with their amped up SL-100 (now Communications Server 2100) PBX so to see such customer and the creativity of the old AT&T is pretty awesome to see.

*the average for most enterprises.

While being commissioned originally as a System 85, and various names such as the Definity, etc. the folks in the NYS Government had called their system collectively the CAPNET (for the Capital Region Network) however they do have a Centrex type service with the same name.  Its highly believable this network or system went though the respective upgrades over the years from the original systems into the Generic 3 RISC (G3r formerly the System 75) Definity platform, and may have changed the cabinets to rack mount media gateways and servers with the respective software upgrades and might had gone to IP Telephony or IP trunking, not sure. I don’t know much other than the References listed at the end of this post. The legendary voice messaging system known as AUDIX is withheld from mention, and its known as the CAPNET voice mail service.

I went to Albany in April of 2011, and I grabbed a few pictures. I was not going to blog about this beast without placing images of various phones.

unused desk with ether a 7405 or 7434 terminal

This unused desk shows a pair of ether a 7405 or 7434 terminal that is probably as old as me.

Security Guard Officer near Governors Hall with a 6424 terminal and a XM24 sidecar

The next one shows a security guard at the Governors Hall with a newer 6424 terminal with a lone sidecar adding 24 more buttons.

This one was rather interesting, just because they have a big PBX, doesn’t mean that smaller offices could be using a different system. This Aastra terminal was spotted in the Assembly Chambers. These should not to be confused with the first generation IP phones made by Cisco (or Celius.)  They appear to not be an IP Phone

The Senate Chambers has 8400 types, including the power user 8434 which can handle up to 50 something programmed lines or features with an additional sidecar.

And a random 50 pair ampthenol cable I spotted inside that NYS Capital

Sources: Network World: October 17th, 1988 (Pgs.1& 55) Google Book link New York State Office For Technology, Telephony bureau (