That was the other half of going to Extended Super Frame. Lyle talked about AMI going away below, but didn't mention what replaced it (Binary 8bit Zero Substitution for the kids on the list). I don't know about the other ILECs out there, but I don't know if Verizon will even provision a T1 anymore. I know you can still get a PRI (that's how our phone systems interface with the PSTN), but if we needed a CT1 instead, I don't know that they'd be able (willing) to deliver it. I know you can't get a BRI. We moved offices a few years ago and we basically lost the ability to use our STEs for anything but voice as we couldn't get BRIs delivered to the new space. Speaking of ISDN, I had equipment that would support 56k ISDN, but never saw it provisioned (was that Switch56? Or am I mixing up FR and ISDN?). All of the ISDN circuits I dealt with were standard 2B+D (BRI), or 23B+D (PRI). I think the oldest (and weirdest) piece of gear I personally worked on was a Gandalf ISDN router that was supporting a US Navy site to site connection. Which makes me a newcomer to The Internet compared to a lot of people on this list, I'm sure. -- Jamie Bowden (jamie.s.bowden@raytheon.com) (703) 842-3848 Sr Computer Network Technologist II Raytheon Space and Airborne Systems 1100 Wilson Blvd., Suite 2000 Arlington, VA 22209
-----Original Message----- From: NANOG <nanog-bounces@nanog.org> On Behalf Of Roy Sent: Monday, January 27, 2020 1:39 PM To: nanog@nanog.org Subject: [External] Re: Reminiscing our first internet connections (WAS) Re: akamai yesterday - what in the world was that
Don't forget B8ZS which did way with the need for SFon copper data T1s
On 1/27/2020 10:43 AM, Lyle Giese wrote:
64k vs 56k was the result of changing T1 framing from SF to ESF. SF utilized AMI(Alt Mark Inversion) required for copper T1 lines between Central Offices. SF(Super Frame) robbed bits for signalling and limited each voice channel to 56k. Conversion to fiber between TELCO offices allowed the conversion of SF to ESF, which dropped the AMI requirement and the resultant bit robbing, allowing 64k throughput per voice channel.
In other words, the limitation was in the inter-office T1's and the conversion of to fiber between TELCO offices cleared that hurdle.
Lyle Giese
LCR Computer Services, Inc.