Talk:Systems Network Architecture

The IBM System/360 and System/370 did not act as controllers for peripherals and were not limited to 16 I/O devices per channel. An I/O channel connected to control units, which in turn connected to peripherals^[1]. In the case of DASD, tape and telecommunications, it was normal for one controller to connect to or include multiple peripherals.

Shmuel (Seymour J.) Metz Username:Chatul (talk) 23:05, 20 November 2010 (UTC)

In System/360 and early (large) System/370 models, the channels where separate devices as well. Rbakels (talk) 09:31, 14 March 2014 (UTC)

SDLC and HDLC did not use an ECC; they used a simple Cyclic redundancy check (CRC). Shmuel (Seymour J.) Metz Username:Chatul (talk) 23:16, 20 November 2010 (UTC)

This is better than SLIP, which used nothing. If you have a known, fixed, frame length you can calculate a table of values to reconstruct the original data from the CRC value (of course assuming your CRC transmitted correctly which is pretty silly)... — Preceding unsigned comment added by 203.214.89.130 (talk) 12:05, 28 November 2012 (UTC)

And what if, as I think is the case in most if not all uses of SDLC/HDLC (including SDLC in SNA), you don't have a known, fixed, frame length? Guy Harris (talk) 12:04, 15 December 2020 (UTC)

Dial-up modems faster than 300 bps were available in 1962, well before SNA. Shmuel (Seymour J.) Metz Username:Chatul (talk) 23:31, 20 November 2010 (UTC)

There may have been faster leased-line modems in 1962, but the Bell 103 was the fastest dialup modem in 1962, at up to 300 bps, but perhaps most commonly used with Teletype equipment at up to 110 bps. The next improvement in dialup rates was the Bell 202, which offered dialup rates up to 1200bps half-duplex, with a 75 bps reverse channel. I can't find a reference for the date of introduction of the 202, but I don't think it was before 1964. --Brouhaha (talk) 19:38, 2 October 2011 (UTC)

From Modem:

In the summer of 1960, the name Data-Phone was introduced to replace the earlier term digital subset. The 202 Data-Phone was a half-duplex asynchronous service that was marketed extensively in late 1960. In 1962, the 201A and 201B Data-Phones were introduced. They were synchronous modems using two-bit-per-baud phase-shift keying (PSK). The 201A operated half-duplex at 2,000 bit/s over normal phone lines,

Shmuel (Seymour J.) Metz Username:Chatul (talk) 22:36, 3 October 2011 (UTC)

Thanks for pointing that out. I believe the years claimed in that article are wrong, and will add citation-needed tags to it. --Brouhaha (talk) 23:48, 6 October 2011 (UTC)

While IBM initially only supported SNA in VTAM, they later added SNA support to TCAM 10. Also, as part of the Advanced Communications Function (ACF) announcement they added Multi-System Network Facility (MSNF) to ACF/TCAM and ACF/VTAM. MSNF, APPN and MSI each altered the way routing was done in SNA. In particular, MSNF supported connecting two mainframes with a channel-to-channel adapter (CTCA), but communication line interconnection (remote) was also supported).

Also, should I add any of the relevant manuals to the article? Some are brief summaries and some are highly technical. Shmuel (Seymour J.) Metz Username:Chatul (talk) 15:55, 17 October 2011 (UTC)

ACF/VTAM was historical in the sense that it was the first instance of systems software that was not distributed free of charge by IBM. This is sometimes attributed to anti-trust issues, but those predeate the announcement of ACF/VTAM by many years. The actual reason was the advent of "plug compatible" computers. Originally, IBM software would only run on IBM computers so there was no point in charging it separately, but providing free IBM software for non-IBM computers was not an attractive business for IBM. Rbakels (talk) 09:36, 14 March 2014 (UTC)

Dial-up connection speed was limited to 300 bits per second mainly because faster modulation schemes had not yet been implemented. In those days, a transmissions were at one bit per baud. It was better modulation schemes, which allowed multiple bits per symbol, that provided increased speeds on the same dial-up line.

Also, until the 1968 Carterfone decision, any equipment attached to the public switched telephone network had to be approved by the carrier, i.e., AT&T. And AT&T only supplied 300 bps modems. — Preceding unsigned comment added by 71.191.134.57 (talk) 19:05, 3 April 2012 (UTC)

POTS (PSTN what?) was frequency limited 300 to 3000 Hertz (notable was women with higher pitched voices had communication issues, often poor response at high end). ISDN used to connect to local distribution was 8-16 8KHz data channels to each phone line (3KHz and Nyquist limitations). When I did Tech Support in 1996+ I would get customers in Eastern Washington, Florida panhandle et al that had no touch tone, only pulse dialing. In 1994 a customer returned a modem I installed because ADP would not accept connections faster than 1200bps. In the 90's USWest (now Verizon) upgraded Arizona to a purposely limited 9600bps. Note that most credit card authentication devices contain 300bps modems: the 256 bytes on the magnetic stripe can be processed faster than the time for a faster modem can negotiate a connection (that and most cell and Sat phones had limited bandwidth at 1G or 2G technologies, limited support for Cellular Packet Data). When I sold phone equipment in 1979 (in Seattle), phone company would disconnect customer equipment claiming it was defective and threatening customers not using GTE/USWest equipment. PSTN refers to the Telco infrastructure (c.f ISDN at the time), POTS refers to the customer end: the 48volt 50mA on the red and green wires that powers the carbon microphone and dynamic earpiece. In the 80's, I had a 1200bps modem that fit over a phone handset (not many motels had customer accessible phone jacks let alone ethernet) and not all phone lines would accept the signal (even though couldn't tell from voice quality.) Shjacks45 (talk) 09:37, 27 June 2013 (UTC)

Women with high pitched voices had no problems in making phone calls: the "high C" used in some opera repertoire relates to 10 1046 Hz. Rbakels (talk) 11:56, 15 December 2020 (UTC)

By the 1980's you could get 2400 bps over an acoustic coupler and the 208B 4800 bps modem was bog common in the mainframe world. I'm aware of faster speeds for dialup in the 1980's, but the were too expensive for the sites that I worked at.

Re the acronyms: POTS is Plain old telephone service and PSTN is Public switched telephone network. Shmuel (Seymour J.) Metz Username:Chatul (talk) 20:59, 15 July 2013 (UTC)

I recall that as a rule of thumb, 2400 bps was the maximum for dial-up lines and 9600 bps for fixed lines in the 1970s. For modem developers, it always was a frustration that the Shannon theorem predicted the possibility much higher speeds than they were actually able to achieve. In the early 1980s, IBM developed really faster modems, using advanced algoritims (Trellis). But this has nothing to do with SNA. Rbakels (talk) 09:52, 14 March 2014 (UTC)

That may have been true for asynchronous modems; it certainly wasn't true for synchronous modems. Not only did the Bell 208B run at 4800 bps on a dial line in the 1970's, but ITU approved ITU-T Recommendation V.27 in 1972; my recollection is that the 208B was available in the 1960's.Shmuel (Seymour J.) Metz Username:Chatul (talk) 14:35, 14 March 2014 (UTC)

To answer the question of whether the 3770 is related to the 2780 and 3780, no, it is not. However, there is no separate article on the 3770 and the 2780 article does discuss it, so the link to that article is appropriate unless and until somebody splits the 3770 off into a separate article. Shmuel (Seymour J.) Metz Username:Chatul (talk) 12:47, 27 June 2012 (UTC)

Unfortunately there isn't much 3770 info online (yet). Hopefully there'll be more in a while. Peter Flass (talk) 14:02, 27 June 2012 (UTC)

www.3770-emulation.com/‎ or en.wikipedia.org/wiki/IBM_2780/3780‎ Shjacks45 (talk) 09:46, 27 June 2013 (UTC)

Introduction to IBM 3770 SNA/RJE Communications does give some details, although the reference to emulation is incorrect. However, IBM 2780/3780‎ is the article about which the question was originally asked. Shmuel (Seymour J.) Metz Username:Chatul (talk) 17:32, 27 June 2013 (UTC)

I added some references to the article, but did not cite the manuals for protocol details/ Would those be TMI, or is it reasonable to add them as well? E.g.,

• IBM (June 1989), Systems Network Architecture Formats (PDF), Eleventh Edition, IBM, GA27-3136-10
• IBM (April 1981), Systems Network Architecture - Sessions Between Logical Units (PDF), Third Edition, IBM, GC20-1868-2
• IBM (December 1979), Systems Network Architecture - Introduction to Sessions between Logical Units (PDF), Third Edition, IBM, GC20-1869-2
• IBM (June 1993), Systems Network Architecture: Transaction Programmer's Reference Manual for LU Type 6.2, Sixth Edition, IBM, GC30-3084-05
• IBM (December 1996), Systems Network Architecture Type 2.1 Node Reference, Fifth Edition, IBM, SC30-3422-04
• IBM (October 1996), Systems Network Architecture LU 6.2 Reference: Peer Protocols, Third Edition, IBM, SC31-6808-02

Shmuel (Seymour J.) Metz Username:Chatul (talk) 20:40, 17 July 2013 (UTC)

I'd say that if the article gives those protocol details, it's appropriate to give citations for those details. Guy Harris (talk) 21:24, 17 July 2013 (UTC)

The article currently does not give those details. Shmuel (Seymour J.) Metz Username:Chatul (talk) 18:58, 19 July 2013 (UTC)

Then they wouldn't be references. They might, however, be worth including in "External links" or "Further details" or something such as that. Guy Harris (talk) 21:38, 19 July 2013 (UTC)

The article associates "Advanced Communication Function" with SNA. That is not correct. There was SNA before ACF.

Initially, the mainframe SNA software was called just VTAM, and it was delivered free of charge with the operating system software, like all IBM systems software at the time. The reason was that IBM software ran only on IBM hardware, so the price was effectively included in the hardware price.

With the advent of "plug compatible" computers, computers made by other manufacturers such as Amdahl that ran IBM software, there was a reason to charge systems software separately. The first systems software packages charged separately were VTAM and NCP, now called ACF/VTAM and ACF/NCP. Only later, complete operating systems were charged, like MVS and VSE.

ACF/VTAM was announced in 1976 and shipped in 1978. Rbakels (talk) 11:35, 15 December 2020 (UTC)

The article covers network addressable units, e.g., SSCP, but it does not discuss, e.g., the structure and types of packets, the types of data flow, the mechanics of initiating and terminating sessions. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 20:45, 13 December 2021 (UTC)