Tag Archives: cable

Tried to replace the PSTN lately?

A great challenge for the current US wireline telephone companies is how to replace the voice telephone network (aka Public Switched Telephone Network or PSTN), build up over 80+ years by the Bell System and its progeny. Same concern applies to the cable companies that built their own version of voice service networks over the past 20 years. Though these have different origins, they share the issue of technology obsolesce (with increasing risk of outages, and higher on-going expenses), all while voice revenues are declining; making the business case for replacement extremely difficult. Over the past 29 years I’ve seen multiple attempts at replacement strategies and many different business justifications.

I had someone argue the first “PSTN replacement” was actually the installation of the SS7 network during the 1980s, which removed inter-office signaling from in-band (where it could be and was hacked!) to an out-of-band separate data network using X.25 technology (actually SS6 did this first, but was not fully deployed). If so, then this was the last “successful” replacement! Every attempt I know of since then has ‘failed’. First there was Integrated Services Digital Network (ISDN), which had a strong start in the late 80s, but has only had long-term success at the interface between public and private switches (PBXs). The residential form of ISDN, known as the Basic Rate Interface (BRI), re-used the existing twisted pair of cooper wires, yet was capable of carrying two digital voice channels and a very low bandwidth 16kbps switched data channel (2B+D). The voice channels could alternatively be used for 56kbps data as well. At the time there were no browsers, no webservers; mostly just FTP, email and private BBSs.  This was long before the World Wide Web became the runaway application of the Internet. In the 90s when the WWW came to be, ISDN BRI was not up that task and was quickly forgotten.

A really massive attempt to replace the PSTN was the Pacific Bell Consumer Broadband Network, which I was involved in from 1993-1996. The plan was to supply 500,000 homes in California (and elsewhere) a combination of voice, data and TV services, based on an exciting (to me, the engineer) mix of technologies from the telco world, but using cable’s hybrid fiber coax architecture. The big issue, though, was that it required running new fiber to each neighborhood and new cable drops to each of those houses. All that digging up of streets, or even stringing aerial, is disruptive and expensive. Being California, there were regulatory issues too (this was pre Telecom Act of 1996). But the final nail was when the Internet started to become a big deal [remember those dialup 56kbps modems?], but the data capabilities were based on ISDN…so this one failed too.

Not long after that the cable industry started deploying broadband cable modems to carry IP-based data, and the telcos followed with Digital Subscriber Line (DSL) services (and later, with IPTV using an upgraded DSL service). The key for both of these was that the implementation was scalable and an incremental overlay on the existing networks (coax or twisted pair), rather than a voice network replacement. No massive digging up of the neighborhoods. Well…, except for Verizon’s FiOS where the fiber is brought to every house directly using PON technology. That’s still a lot of digging, and a lot of expense to put electronics with a backup battery in every home. And so, having already deployed its most economical neighborhoods, Verizon has discontinued any further plans to grow the FiOS coverage areas. Interestingly though, FiOS still carries voice services via the same old Class 4/5 POTS switches in use since the late 1970s and 80s [their plans for IMS still pending].

Most recently? Look at the offer from Verizon Wireless (and AT&T also) to have the wireless network provide voice connectivity for your home phonesets, for only $20/month (on par or cheaper than most basic wireline services), … added to your existing mobile smartphone service, of course.

So what are the takeaways here?

  1. The Bell System (R&D by Bell Labs) did many things well. And that equipment has lasted. Yet, I also have to say, that won’t carry the telcos much longer…
  2. Data has been a growing theme in all these network changes. It’s clear that data (with video via that data) service is now the primary residential service. Not voice, nor linear TV. [It’s also clear that Bell Labs was spectacularly not good a predicting consumer demand for data services!]
  3. Incremental change is a lot easier than wholesale replacement, both in technology and economically. Don’t try to shallow the whole thing in one gulp; cut it up into smaller chucks, especially ones that can be justified in other ways…
  4. Mobile networks are taking over… at least for the 98ish% of the US population area where 4G will be fully built out. [And I didn’t discuss VoIP, except via implication…]
  5. Economically, it’s all about the bundle!, regardless of whether measured in lines, ARPU or RGU!
  6. And lastly, it’s also about moving away from heavily regulated domains [but we’ll save deeper discussion of that topic for a future post].