ISDN - Protocol Wars#

Leonardo Rizzi

• Why: A deliberately different pick — a retrocomputing talk that is actually a compressed history of the protocol wars that shaped today's Internet: circuit vs packet, virtual circuits vs datagrams, X.25/OSI vs TCP/IP. Those same debates recur in modern dress (SDN's central control, deterministic networking, SR's source-routed paths), which makes the historical grounding worth an hour.
• What: A tour from the 1973 ARPANET (1822/NCP, IMP maps, DS0 uplinks) through the circuit-vs-packet and VC-vs-datagram arguments (state, congestion control, failure behavior — laid out in a clean comparison table), the Internet-vs-OSI outcome, and then ISDN itself: TDM/E1 framing, BRI/PRI channel architecture, Italy's 1991–1994 "Rete Intelligente" rollout, and an inflation-adjusted 1993 price comparison across European countries (Italian PRI at ~13,800 EUR/yr MCR).
• How: The living part of the talk is OCTOI — the Osmocom community's TDM/ISDN/SS7 network over IP, where retrocomputing enthusiasts interconnect real TDM equipment worldwide, using devices like the icE1usb (dual E1 + GPS-DO + USB, on an iCE40 FPGA). An EWSD switch was even installed at 38C3.
• Where applicable: Not operational — but the datagram-vs-VC argument table is genuinely useful framing for anyone reasoning about connection-oriented revivals in modern fabrics, and the community-TDM-over-IP network is a quirky demonstration that legacy circuit infrastructure can be virtualized over packet networks.