On May 28, 2014, at 12:17 AM, Peter Lothberg <roll at Stupi.SE> wrote:
On May 27, 2014, at 3:17 PM, Bob Armstrong <bob at jfcl.com> wrote:
in Phase IV the hello timer value is sent in the hello message
and that value times 3 (or 2) is used for the listen timer
=20
That would explain why having LEGATO send hello messages more often
doesn't make any difference=85
If you send hellos more often, you time out sooner; either way, you time ou=
t if you lose 3 hellos in a row (or, probably just barely, if you lose two =
in a row). The assumption is that no LAN is that badly broken.
The way to run DECnet over a flaky long distance network is to use point to=
point mode with a data link layer that deals with packet loss. DDCMP is a=
n example of such a data link layer; X.25 is also (after a fashion). That=
=92s what the DECnet design intended.
paul
Putting a PTP DECnet link in TCP would do the same as DDCMP/X.25/Lapb
-P
The earlier DMC emulation in SIMH 3.9 (payload only, not DDCMP) was essentially point to point over TCP. Yes, that gives you what DDCMP does. It s better than X.25/LAPB because those suffer from having a two way rather than three way handshake.
paul
On May 28, 2014, at 12:18 AM, Peter Lothberg <roll at Stupi.SE> wrote:
Do anyone run any links using TCP?
You can tell Multinet to use TCP instead of UDP.
That s the theory, but I have been unable to find any description of what the protocol would look like in that case. If anyone can describe the protocol I would be grateful, then I can implement in in DECnet/Python.
paul
On May 27, 2014, at 3:17 PM, Bob Armstrong <bob at jfcl.com> wrote:
in Phase IV the hello timer value is sent in the hello message
and that value times 3 (or 2) is used for the listen timer
=20
That would explain why having LEGATO send hello messages more often
doesn't make any difference=85
If you send hellos more often, you time out sooner; either way, you time ou=
t if you lose 3 hellos in a row (or, probably just barely, if you lose two =
in a row). The assumption is that no LAN is that badly broken.
The way to run DECnet over a flaky long distance network is to use point to=
point mode with a data link layer that deals with packet loss. DDCMP is a=
n example of such a data link layer; X.25 is also (after a fashion). That=
=92s what the DECnet design intended.
paul
Putting a PTP DECnet link in TCP would do the same as DDCMP/X.25/Lapb
-P
On May 27, 2014, at 4:04 PM, Johnny Billquist <bqt at softjar.se> wrote:
On 2014-05-27 21:48, Bob Armstrong wrote:
The way to run DECnet over a flaky long distance network is to use point
to point mode with a data link layer that deals with packet loss.
Probably a good idea, but we don't have that option on HECnet.
Well, HECnet is not a static piece of equipment. Anything is possible...
My bridge emulates a simple ethernet segment. Good enough many times, but if we have a link like yours, that sometimes seems to drop packets, then maybe some other alternative should be considered.
Now, the question then becomes, what can we do in this case.
As far as I understand, links using Multinet are more broken, and still use UDP. The same would appear to possibly be the case for Cisco as well?
Do anyone run any links using TCP?
That would work. DDCMP over UDP would work.
GRE bridging of Ethernet packets is reasonable because that bridges a datagram service over a datagram service. Usually the Internet is good enough for that to work. Multinet is a much worse option, because it tunnels what it pretends is a point to point link over UDP, without actually implementing any datalink protocol to cope with the mismatch.
DDCMP in a user mode router would not be all that big a job. In Python, even less. Time to accelerate that effort.
paul
On 2014-05-27 21:48, Bob Armstrong wrote:
The way to run DECnet over a flaky long distance network is to use point
to point mode with a data link layer that deals with packet loss.
Probably a good idea, but we don't have that option on HECnet.
Well, HECnet is not a static piece of equipment. Anything is possible...
My bridge emulates a simple ethernet segment. Good enough many times, but if we have a link like yours, that sometimes seems to drop packets, then maybe some other alternative should be considered.
Now, the question then becomes, what can we do in this case.
As far as I understand, links using Multinet are more broken, and still use UDP. The same would appear to possibly be the case for Cisco as well?
Do anyone run any links using TCP?
Johnny
On May 27, 2014, at 3:48 PM, Bob Armstrong <bob at jfcl.com> wrote:
The way to run DECnet over a flaky long distance network is to use point
to point mode with a data link layer that deals with packet loss.
Probably a good idea, but we don't have that option on HECnet.
Bob
The latest SIMH has this (DDCMP, in the DMC/DMR/DMP/DMV emulation).
paul
The way to run DECnet over a flaky long distance network is to use point
to point mode with a data link layer that deals with packet loss.
Probably a good idea, but we don't have that option on HECnet.
Bob
On May 27, 2014, at 3:17 PM, Bob Armstrong <bob at jfcl.com> wrote:
in Phase IV the hello timer value is sent in the hello message
and that value times 3 (or 2) is used for the listen timer
That would explain why having LEGATO send hello messages more often
doesn't make any difference
If you send hellos more often, you time out sooner; either way, you time out if you lose 3 hellos in a row (or, probably just barely, if you lose two in a row). The assumption is that no LAN is that badly broken.
The way to run DECnet over a flaky long distance network is to use point to point mode with a data link layer that deals with packet loss. DDCMP is an example of such a data link layer; X.25 is also (after a fashion). That s what the DECnet design intended.
paul
in Phase IV the hello timer value is sent in the hello message
and that value times 3 (or 2) is used for the listen timer
That would explain why having LEGATO send hello messages more often
doesn't make any difference...
Bob
