Paul, I can date it a little I suspect, although not as precisely as you might like.  I arrived at UCB in late August/Early September '81 to be a grad student.  Sam had arrived earlier that spring to work for wnj in the CSRG team. I had known Sam before I went to UCB.   [We actually had played rugby against each other in eastern PA many years before he went off to Case and me to CMU].  Anyway, when I arrived Sam was one of the people I already knew and we socialized a lot together in that fall in particular.

We also know the first 'Alpha' kit of 4.1a was not a thing until the next summer.  Plus, during the winter was the arguments with ARPA steering committee about the features that needed to be added. The key item is that vestigial select(2) does not show up until at least 6-9 months after I arrived and it seems like it was part of 4.1a.   As I said, I have memories of discussing all of the networking interfaces, CMU Accent, et al with Sam in particular during that time. So, I would bet Joy did the basic work winter/spring of 82; but I can not be more precise than that.

FWIW: Since I had been working networking at both CMU and Tek before I came to UCB, one of the first things I did when I arrived in fall '81 was to install the Gurwitz BBN IP/TCP stack on 4.1 so we could run Ethernet between the 3 CAD machines in Cory Hall to replace the use of BerkNet over 9600 baud serial links (IIRC Eric Cooper, was involved with that hack also).   When I had arrived, few machines at UCB were on LANS and the need for ARPAnet style networking >>besides<< email was still limited.  The way people connected to systems was their terminal was to connect over serial links and we had a giant 'plugboard' that allowed you patch your terminal into one of the systems [I wonder if there are pictures of these somewhere in the UCB archives - it was quite something].

We had three 780s in the CAD group in Cory and really did not like the plugboard scheme. From my previous experience, I wanted something like telnet or supdup, like we had been messing with at CMU and Tek.  Hence my push to put the BBN code on the CAD systems and use an ethernet.    Eric, please fill me in.   You must have been running the BBN code then also, since Ing70 and then IngVax were the ArpaNet connection (via a VHDH to the LBL IMP - UCB did not yet have its own IMP).   But I know the CAD systems 4.1 networking stuff was done by me.

Its a little fuzzy now, but memory is that Bob Kriddle had run a Xerox 3 Meg cable in Cory, from my machine room over to the Ingres machine room also; but I've forgotten the details.  BerkNet (i.e. serial links) allowed email to flow on campus, but I'm thinking we were trying to make that both more efficient and allow telnet/ftp [which might not have happened until after the C/30 IMP was installed in Evan later).   [Since all ARPAnet email followed through IngVax, Eric's history of dealing with the header file format of the month in the old delivermail program would force his writing sendmail - said history has been repeated here and elsewhere previously].

But this thread got me thinking a little bit.   I've forgotten actual LAN topology we had a UCB now. I know from the CAD hosts, we could talk to the other hosts in our lab in Cory for sure, I want to say we could talk to a few other hosts in Evans and Cory; as I know Sam would give me code usually via some type of network connection, although sneaker-net with 9-track tapes used a great deal too.   I want to say the connection was over Kriddle's 3M Xerox cable (Eric do you remember what you had in IngVax in those days).  I know we also a had real 10Meg cable in floor our lab in Cory, plus at least one Xerox board on one of the systems, another had a DEC interface in it, and Interlan boards in at least two others another.   We must have even had a 3Com board in the third system; as I remember hacking both the Interlan and 3Com drivers (I had written a 3Com driver at Tek previous for VMS.  The Interlan board was new, as was the DEC board; but I've forgotten what we got when).     The original CAD 780 ('Coke')  must have had multiple interfaces in it, but I really don't remember.

FWIW: I spent a good bit of time with Sam in those days. CSRG was using 750s for most of their development, and the couple of 780's in Evan's had a lot of non-DEC equipment in them.   But we had the one large undoctored and max configuration VAX 785 ('Pepsi'), that was fully tricked out with a real DEC I/O equipment in it†  So when CRSG (i.e. Sam) wanted to test things on a 'pure DEC' system with things like TU78's, real RP07's, RMxx drives;  he would give me something and I would debug it late at night on it.  Once it was stable, it might become the system we ran.

While I can not date select(2) more precisely.  I can date routed(2) as being that spring, but after 4.1a's alpha code.   Sam has seen the Xerox routed system at PARC.   The BBN code was a not friendly to sub-nets and we had already started to proliferate them between Evans and Cory Hall.   He decided to create something like the Xerox code for us (as well as the r* commands). routed was created in a couple of weeks after Sam got the idea from Xerox and first place it ran was on the 10 Meg LAN in the CAD group.

Hope this helps,

Clem