Apologies for being off-topic Taking it slightly broader (PDP-11 instead of V7), there is a lot of discussion about that on Mike Meuss’ TCP-digest mailing list: https://ftp.ripe.net/rfc/museum/tcp-ip-digest/ There is a 1985 index of available implementations as well ( https://ftp.ripe.net/rfc/museum/tcp-ip-implementations.txt.1 ). It includes the following options for PDP-11 systems: 1.7.5. UNIX 2.9BSD DESCRIPTION: 2.9BSD TCP/IP is an adaptation of Berkeley's original VAX TCP/IP (running under BSD 4.1B UNIX) which in turn is an offshoot of BBN's VAX TCP/IP. 2.9BSD TCP/IP runs on PDP-11/44s and PDP-11/70s. The 2.8 version from SRI was adapted by Bill Croft (formerly at SRI), then Tektronix adapted it for 2.9. Berkeley took over modification of the software and brought it back to SRI where Dan Chernikoff and Greg Satz adapted it for a later release of 2.9. In addition to TCP/IP, UDP, ARP and the raw packet interface is available. ICMP redirects are not supported. User software implementations include Telnet and FTP, plus Berkeley-developed local net protocols, RWHO, RSH, RLOGIN, and RCP. 2.9BSD with TCP/IP support could probably be made to run on smaller PDP-11s although the address space would be very tight and might present problems. 1.7.6. Venix/11 TCP/IP DESCRIPTION: This is based on the "PDP-11/45" implementation available from the MIT Laboratory for Computer Science. It has been ported to a V7 UNIX system, in particular VenturCom's Venix/11 V2.0. As little of the processing as possible takes place in the kernel, to minimize the code space required. It fits comfortably on I&D machines, but is almost hopeless on the smaller machines. The kernel includes a proNET device driver, IP fragment reassembly, IP header processing, local-net header processing, and simple routing. The rest of the IP processing, and all of the UDP and TCP functions, are in user libraries. The psuedo-teletype driver is also in the kernel, and is used by Server TELNET. User programs handle ICMP processing; User and Server TELNET, SMTP, TFTP, Finger, and Discard. There are User programs for Nicname and Hostname. IEN-116 nameservers are used by all programs, and an IEN-116 nameserver is also provided. The TCP used is very simple, not very fast, and lies about windows. No FTP is available, nor is one currently planned. 1.7.8. BBN-V6-UNIX DESCRIPTION: This TCP/IP/ICMP implementation runs as a user process in version 6 UNIX, with modifications obtained from BBN for network access. IP reassembles fragments into datagrams, but has no separate IP user interface. TCP supports user and server Telnet, echo, discard, internet SMTP mail, and FTP. ICMP generates replies to Echo Requests, and sends Source-Quench when reassembly buffers are full. 1. Hardware - PDP-11/70 and PDP-11/45 running UNIX version 6, with BBN IPC additions. 2. Software - written in C, requiring 25K instruction space, 20K data space. Supports 10 connections (including "listeners"). 3. Unimplemented protocol features: - TCP - Discards out-of-order segments. - IP - Does not handle some options and ICMP messages. 1.7.9. v 3COM-UNET DESCRIPTION: UNET is a communication software package which enables UNIX systems to communicate using TCP/IP protocols. UNET will utilize any physical communications media, from low speed links such as twisted pair RS-232C to high speed coaxial links such as Ethernet. All layers of the UNET package are directly available to the user. The highest layer provides user programs implementing ARPA standard File Transfer Protocol (UFTP), Virtual Terminal Protocol (UVTP), and Mail Transfer Protocols (UMTP). These programs in turn utilize the virtual circuit services of the TCP. The TCP protocol is implemented on top of the IP. Finally, IP can simultaneously interface to multiple local networks. UNET implements 5 of the 7 layers of the International Standards Organization Open Systems Interconnection Reference Model, layers 2 through 6: Link, Network, Transport, Session, and Presentation. Features of TCP 6 not yet implemented are Precedence and Security, End-of-Letter, and Urgent. Feature of IP 4 not yet implemented is Options. Of these, we have 2.9BSD and (a forerunner of) BBN-V6-Unix available on the TUHS Unix Tree. The Venix/11 source and the 3COM source appear lost. These (unfortunately) are the ones that were implemented on top of V7. Also, BBN back-ported the TCP/IP code of BBN VAX-TCP to V7 for their C/70 Unix.