Subject:
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Re: legOS Network Protocol
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Newsgroups:
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lugnet.robotics.rcx.legos
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Date:
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Wed, 14 Apr 1999 22:00:32 GMT
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Viewed:
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1086 times
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Mike Moran wrote:
> Anyway, I had a look around and I found some references on a protocol
> layered on top of IP called RDP (Reliable Data Protocol). It provides
> a message-based unreliable or reliable (toggled as necessary) service
> on top of IP ie most of the advantages of TCP without all the guff.
Sounds good. Does it provide a stream interface or datagrams only? My
faulty memory suggests that it might be the latter. If the network
implementation supports packet reassembly (packets larger than MTU), there
may not be a need for a stream interface. Unless, maybe, someone fancies
putting a web server on their RCX. <grin>
> I'm still reading through the rfc (rfc908) but one thing I've noticed
> is that it needs a timer per connection. How many timers are available in
> the RCX? Perhaps we could restrict the timer granularity to get more or
> something like that?
I think all of the hardware timers are being used (IR carrier, Serial bit
rate, systime), but there is a system timer (driven by one of the
aforementioned hardware timers) with millisecond granularity (should be
sufficient for network code), and you can implement the functionality of more
timers by periodically comparing respective variables against it, seeing if
systime has become greater. I am not aware of any MCUs with 2^16 timers in
hardware.
> The rfc is definitely worth looking at for implementation ideas. One
> thing to note is that we couldn't possibly support the amount of ports
> it specifies (128 or 256 if I remember correctly) since this would mean
> 128^2 or 256^2 possible live connections.
I think they're talking about an addressing scheme with 16 possible hosts and
16 possible ports. Of course, you don't have to be using all possible
permutations simultaneously. That doesn't even happen on most TCP/IP
machines.
> Anyway, who else is actively interested in this?
Oh, I'm interested in the networking stuff, but I'm probably more helpful
staying out of their way. I've got my hands full with the minutiae of signal
implementation. I'd love to see more discussion of the networking stuff on
the list.
I'll eventually be tackling virtual timer issues when I try to implement the
alarm() function. My needs will dictate that a signal be sent to a specified
pid when the timer expires. What sort of interface will be required for the
RDP timers? Polled? Callback? Signal? I might as well make it general
enough for multiple uses.
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Message has 2 Replies:
 | | Re: legOS Network Protocol
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| This would almost have to be a UDP like protocol just because the RCX has such limited resources and the complexity of adding transmision control to the protocol would be nasty. I really hate news groups, I like having messages sent to me directly. (...) (25 years ago, 15-Apr-99, to lugnet.robotics.rcx.legos)
| | | Re: legOS Network Protocol
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| (...) The interface is specifically datagram only. Dunno about packet reassembly; I doubt it as the philosophy is minimalism. The main advantage I see in it is the ability to change the degree of checking it does on your behalf to ensure packets (...) (25 years ago, 20-Apr-99, to lugnet.robotics.rcx.legos)
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Message is in Reply To:
| | Re: legOS Network Protocol
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| (...) I too may be interested in this, although probably only the higher level stuff ie I'm not too sure how good I'd be at interfacing with the IR. Anyway, I had a look around and I found some references on a protocol layered on top of IP called (...) (25 years ago, 14-Apr-99, to lugnet.robotics.rcx.legos)
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