[Ns-developers] tag rework for next release
tomh at tomh.org
Wed Jun 3 23:01:30 PDT 2009
The below message revisits my previous comments, with a couple more.
Mathieu Lacage wrote:
> On Fri, 2009-04-03 at 11:04 -0700, Tom Henderson wrote:
>> One thing that I noticed is that packet tags are left out of the
>> Packet::Serialize() process (while byte tags are included). This is a
>> bit subtle, but it basically means that packets that are sent to another
>> node via an ns-3 channel will retain packet tags but if that ns-3
>> channel happens to utilize a real IP tunnel (in a distributed simulation
>> use case) the packet tags will be stripped.
>> It seems like we ought to support packet tags in Serialize, but is there
>> a reason why not?
> Lazyness: I can fix this late next week but feel free to beat me to it.
What is the status of serializing tags? I see this in the code:
// write tags
//reserve = m_tags.GetSerializedSize ();
//m_tags.Serialize (buffer.Begin (), reserve);
// aggregate byte buffer, metadata, and tags
Buffer tmp = m_buffer.CreateFullCopy ();
>> We ought to document somewhere the interaction between application-level
>> tags and NSC, while this is not yet fixed for NSC.
> I doubt it will ever be really fixed in nsc.
this would be nice to document somewhere in NSC, tracker, and/or manual.
If a packet enters an nsc stack with tags, should some log message be
raised? Do you have a suggestion on how to document this?
>> samples/main-packet-tag.cc could be enhanced with a byte example and
>> more commenting. I would volunteer to contribute this patch if you want.
> please, do.
Since I suggested it previously, I will volunteer to do this and fix the
manual before the release.
>> Also, in udp-echo-server.cc:
>> NS_LOG_INFO ("Received " << packet->GetSize() << " bytes
>> from " <<
>> - packet->RemoveAllTags ();
>> + packet->RemoveAllPacketTags ();
>> NS_LOG_LOGIC ("Echoing packet");
>> socket->SendTo (packet, 0, from);
>> Why not remove all byte tags also? Conceptually, this is a new packet
>> that is being echoed; i.e., it should behave the same as if the packet
>> were freed and a new one generated.
> Yes, this makes sense.
the above still needs fixed.
\packetperf Doxygen is stale; it would be nice also to include some
brief comment about the performance implication of enabling metadata,
and the two different types of tags
There is a distinction between packet and byte tags in terms of removal
that could be more explicit in the doxygen. Namely, packet tags can be
removed one-by-one, while byte tags must all be removed. So, maybe
document that byte tags are assumed to have a lifetime of a packet and
not removed until the packet is conceptually freed, while packet tags
added somewhere should be removed by the consumer of the tag (such as a
cross-layer tag internal to a node that should be stripped before
sending on an ns-3 channel).
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