Multicast and WM 2003

  • Thread starter Thread starter stu
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stu

I'm having an issue getting multicast to work. I have created a simple
sender app and receiver app (separate apps). When I run the receiver
app on the desktop and send from the pda, it works fine. When I send
from the PDA to the desktop the packet never arrives.

setup: The pda is connected to a lan with wifi and the desktop is
connected via wired eth-net. The ap is connected to the same switch as
the desktop. The pda is a dell axim running Windows mobile 2003. The
desktop runs Win xp (sp1a).

As the receiver, I can see igmp exclude requests from the pda when it
joins the group. The ttl value is acceptable. I've tried both the
udpclient class as well as writing the socket code myself, neither of
which worked. I've tried different address and port combos.

Does anyone have any clues on this one? Thanks!

michael =)
 
When I run the receiver
app on the desktop and send from the pda, it works fine. When I send
from the PDA to the desktop the packet never arrives.
Click to expand...

I think these 2 statements talk about the same situation, so which scenario
doesn't work?

Do you have a firewall on a desktop?
 
I did a quick search, but couldn't find anything; mostly what I saw was
stuff on the emu and multicast.

Firewall, no my firewall is turned off. To clarify the other question
pda send to pc = yes
pc send to pda = no

In general, I have a little more info. I got a hold of a pda with ppc
2002 and tried a couple things. I tried the same setup except used the
ppc pda instead of the pc. I got the same result:
ppc2k2 send to wm2k3 = no
wm2k3 send to ppc2k2 = yes

So, it looks like it is an issue with windows mobile 2003. Either that
or I have completely pissed off WM 2k3 somehow. I'm going to see if I
can get another WM 2k3 pda.

Any thoughts on issues with WM 2k3? Thanks!

michael =)
 
A search on "multicast" gets 24 results...

You should check, since you're going through an AP on the wireless leg, that
the AP isn't filtering that sort of message on the way out. If you have
wired Ethernet capability on any of the PPC devices, you might try that, to
eliminate wireless as the problem. In fact, one of the 24 results in this
group indicates this as a likely explanation, so you should eliminate it
before moving on to more aggressive measures.

So, in *all* of these cases, *all* devices involved, whether sending or
receiving, have joined the same multicast group, right? Successfully
(you're checking return values of every socket method you call)?

If you're convinced that your code is right, I'd next move to native code
and do this straight through WinSock, which definitely does work with
Windows CE 4.2-based devices. That takes another layer out of the equation.

Paul T.
 
When I pulled in the 2nd PDA, they were both using wifi, on the same
AP.

The sender doesn't have to be a part of the mutlicast group, but in
this case it does join the group, because it is the only way to adjust
the TTL of the packets being sent to the group. I have thought about
going to native code, but would like to stay in .net land. I'm not
doing anything unusual, so I would be interested as to why things
aren't working.

Yes, the devices can ping each other.

I have been doing exception handling, but not paying much attention to
the return values... I'll check those.

michael =)
 
OK, and the sender should also receive the multicast, then. Do they?

I'm not saying that you should throw away the idea of actually implementing
your program in .NETCF. I'm just saying that, in the process of debugging
network problems, having anything layered on top of WinSock, whether it's
..NETCF, MFC, or whatever, more often then not hides the real source of
problems. Since the problem seems to be "can't receive a multicast packet on
a WM2003 device", dumping all of the stuff that might make you erroneously
think that is a good idea before you just conclude that the OS is broken.

Paul T.
 
This actually turned out to be a wifi issue. I'm in a building pretty
well painted by numerous APs and I was getting crazy packet loss on
multicast packets. How about a round of applause for how 802.11 treats
multicast. Anyway, I switched over to ad hoc mode and things worked
much better.
 
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