[Info-vax] booting vaxstation off alpha

[Johnny Billquist]

On 2013-02-12 16:20, Stephen Hoffman wrote:
> On 2013-02-12 07:48:22 +0000, Hans Vlems said:
>
>> On 12 feb, 01:31, Johnny Billquist <b... at softjar.se> wrote:
>>> On 2013-02-11 13:44, Stephen Hoffman wrote:
>>>
>>>
>>>
>>>
>>>
>>>> On 2013-02-11 07:54:11 +0000, Hans Vlems said:
>>>
>>>>> DECnet over DSSI works fine, provided you get the incantations right.
>>>>> All I tried was CTERM and FAL and both worked as expected (reliable
>>>>> albeit slow).
>>>>> Another example of an undocumented, unsupported feature that works
>>>>> alright.
>>>
>>>> Not that there is even a remote chance of seeing DSSI gear around, nor
>>>> any likelihood of IP over FC nor connections, but...
>>>
>>>> If you ran any tests[1] with that, how well does that "albeit slow"
>>>> connection perform as compared with slow Ethernet?  CI wasn't known for
>>>> its network performance, as compared with DECnet over even then-current
>>>> 10 Mb Ethernet, and usual recommendations back then had CI at higher
>>>> cost as a backup connection.  I can't see DSSI being much better in
>>>> that
>>>> regard.
>>>
>>> That sounds weird. Do you know why?
>
> Read up on the (complexity) of the CI controller, and decide for
> yourself <http://lazowska.cs.washington.edu/p130-kronenberg.pdf>

Thanks. I don't see much complexity, really, though. I do notice that at 
least in their tests, they definitely achieved way higher transfer rates 
than at all possible with thick ethernet. (I do have a long standing 
item on my todo-list to implement CI communication for NetBSD, but I 
don't know when I'll ever have the time...)

>>> I mean, CI was after all two redundant full duplex 70 Mbit/s channels,
>>> compared to the half-duplex 10Mbit/s ethernet. Not to mention the fact
>>> that the MTU of CI is much larger.
>
> 70 Mb dual-channel, not duplex.

Ok. But with dual-channel, you implicitly get full duplex. One channel 
can send, while the other one receives. Admittedly, with 16 nodes, not 
all can send and receive at the same time, but the CI controller as such 
can deal with it. Just that you need a free cable to do any transmits.

>> Yes, I know what you mean Johnny. I don't think the CI was full duplex
>> though.
>
> Correct.  Some later-vintage CI controllers could use both channels in
> parallel.

Um. The paper you referenced to above, points out that all CI 
controllers do this, and did from day 1. Page 131, second chapter, 
second paragraph.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol