? What are Metacard's UDP (datagram) Limits

[andu]

Sparticus Zarris, Cross Country Communications wrote:

> I'm trying to see what the limit is for UDP "packets" sent from Metacard using the form:
> 
> open datagram socket to <socketID>
> write <myData> to socket <socketID>
> 
> 
> Keep in mind this is for UDP packets (datagram).
> 
> 
> I set up a sender and a listener using the MetaCard stack "chat.mc" as the shell.
> 
> 
> 
> Here's the problem.
> 
> I thought there would be a limit of some sort on the packet size -- probably associated with the size of Ethernet frames on my network, or a multiple of that size.
> 
> I sent 32K of data, and got it out the other end, exactly.
> 
> I then assumed there was no problem, maybe there was NO limit.
> 
> Then I wrote a simple app that assumed there was NO limit.
> 
> My simple app wouldn't work.
> 
> My simple app was sending blocks of about 64K.
> 
> I re-tested using the "chat.mc" shell.
> 
> 
> Turns out, I can send any amount of data, any kind of data, but no more than EXACTLY 65,507 bytes.
> 
> 
> If I sent 65,508 bytes, NO PART OF THE DATA IS SENT.  NO ERROR IS REPORTED.
> 
> 
> WHY, is this a MetaCard limit?  I'm sure Scott will explain this away as a feature, so it would be nice to understand the rationale, and if this is identical across all platforms
> 
> What kind of a limit is 65,507 bytes.  It is NOT a power of 2.  But is sure dang close.
> 
> What does it mean.
> 
> Is it yet another flaw in MC.


I'm curious what other flows you have in mind but from my experience 
with tcp + sockets the limitations are in the OS, amount of traffic, 
type of connection, etc., generally nothing particularly related to 
Metacard.
Also from what I know, udp only allows for limited size packets, maybe 
you just found that limit.
I'd look for more info on udp on the internet, an rfc or something.


> 
> Has anyone else ever run into this.  Is this a hard-and-fast limit across all platforms?
> 
> Is this this way because of some underlying API (like maybe a limit in BerkeleySockets, or some such API that Meta is using).
> 
> Or maybe that he is setting a buffer size some place, and it should be set to another value??
> 
> 
> I am using PowerPC Macintosh on OS 9.04, and 8.5.1  and MC 2.4.1
> 
> Why can't I find this documented anywhere?
> 
> Clues?
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> 


-- 
____________________
Regards, Andu Novac