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Re: [Ccrtp-devel] IPv6 support in ccRTP


From: David Sugar
Subject: Re: [Ccrtp-devel] IPv6 support in ccRTP
Date: Thu, 05 Oct 2006 08:01:50 -0400
User-agent: Thunderbird 1.5.0.7 (X11/20060913)

When I look into the case of OutgoingDataQueue, I was thinking maybe in that particular case, we can have a CCXX_IPV6 wrapped OutgoingDataQueueIPV6 which inherits from the existing OutgoingDataQueue. It could re-implement just those methods that deal with addresses with new methods that use the IPV6Host objects, cap the v4 virtual with a dummy method, and offer a new v6 virtual of it's own. We could then feed OutgoingDataQueueIPV6 to the upper level template. That might be ugly, but it could work without breaking a lot of existing code or writing all that much new code. The same could probably be done for the other two classes.

I would like to see some feedback on this before doing this :).

David Sugar wrote:
More than likely the IPV6Host... method handlers wrapped in CCXX_IPV6
defines in the other classes are missing.  One of the unfortunate
effects of the way we do address objects is that we have to have
separate methods for ipv4 and ipv6.  If you add pure IPV6 virtuals for
OutgoingDataQueue, etc, however, that will mean the RTPSession (ipv4)
will need then fake ipv6 handlers.

The other ugly possibility is to also have a separate
OutgoingDataQueueIPV6 class, etc...

Let me think about how we got here and what we should do...

Gabor Ivan wrote:
Dear ccRTP developers,

I tried to use ccRTP over an IPv6 protocol stack. If I'm not mistaken,
the only main change (compared to IPv4) is that the class
"RTPSessionIPV6" has to be used instead of "RTPSession". I tried to
create an instance of the class "RTPSessionIPv6":

RTPSessionIPV6 * socket = new RTPSessionIPV6 (IPV6Host("localhost"), port);

and the compiler gave the following errors:

error: cannot allocate an object of abstract type 'ost::RTPSessionIPV6',
because the following virtual functions are pure within
'ost::RTPSessionIPV6':
/usr/include/ccrtp/oqueue.h: virtual void
ost::OutgoingDataQueue::setControlPeer (const ost::IPV4Address&,
ost::tpport_t)
/usr/include/ccrtp/oqueue.h: virtual void
ost::OutgoingDataQueue::setDataPeer (const ost::IPV4Address&, ost::tpport_t)
/usr/include/ccrtp/iqueue.h: virtual void
ost::IncomingDataQueue::recvData (unsigned char *, size_t, const
ost::IPV4Address&, ost::tpport_t&)
/usr/include/ccrtp/cqueue.h: virtual void
ost::QueueRTCPManager::recvControl (unsigned char *, size_t,
ost::IPV4Address&, ost::tpport_t&)

The functions mentioned above are pure virtual functions, making e.g.
the class "OutgoingDataQueue" an abstract class, which cannot be
instantiated. As RTPSessionIPV6 does not implement these fucntions
either, it also becomes an abstract class.

So, the problem is that RTPSessionIPV6 does not implement the functions
mentioned above; instead it implements _almost_ the same functions, but
with "IPV6Host&"-type addresses (and not "IPV4Address&"). Unfortunately
these count as a whole new function in C++, so I assume this to be the
cause of the errors.

The solution could probably be to append the class "RTPSessionIPV6" with
a "fake implementation" of the above mentioned functions, _and_ also
adding the already implemented functions from "RTPSessionIPv6" (which
get the IP address in an  "IPV6Host"-type parameter) as a virtual
function of the classes "OutgoingDataQueue", "IncomingDataQueue",
"QueueRTCPManager".

Sure that mine is not a very nice solution, and, as I'm not quite
familiar with ccRTP yet, it could possibly not work. That's why I'm
asking Your advice: do you consider this a real bug in ccRTP library? If
yes, what solution would You suggest? How is it possible to use ccRTP over an IPv6-based protocol stack?

Thanks,

Gabor Ivan






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