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Header compression plugin

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Nicolas Hennion

Header compression plugin

Hi all,

it will be very nice to implement the ROHC (RObust Header Compression, RFC 3095) in a standalone plugin.

IP, UDP and UDP header will be compressed from 40 octets to 3-5 ! A nice optimization for audio and video streaming.

You can find more informations about the ROHC and its open-source librairy: https://launchpad.net/rohc/

The API documentation for compressor and decompressor are available here:

- http://www.tech.viveris.com/docs/rohc/group__rohc__comp.html

- http://www.tech.viveris.com/docs/rohc/group__rohc__decomp.html

Any developper interrested ?

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Vasilis Liaskovitis

Re: Header compression plugin

Hi,

I am interested in helping develop and test a rohc gstreamer plugin. I
am new in both the gstreamer and rohc communities and I 'd appreciate
any comments for the following approach. I think this would involve
implementing 2 new gstelements:

- rohccomp: accepts a packet stream and performs the packet
compression. The input stream would be either in pcap format or
accepted from a virtual interface (tun). Perhaps there are other input
possibilities that I am not aware of.
- rohcdecomp: accepts a compressed packet, decompresses and passes it on.

Some gstreamer properties of both elements would include the rohc
profile chosen and the input format chosen (pcap or reading from a tun
interface)

These 2 gstreamer elements would allow for similar functionality as
the applications test/test.c and apps/tunnel/tunnel.c (from the rohc
source code tree) to be implemented in a gst-launch command line
pipeline.

The pcap input file handling could be similar in principle to the
pcapparse plugin in gst-plugins-bad. E.g to implement
compression/decompression.of pcap packets and pass this rohc flow
through udp we could use these pipelines:

sender / compressor:
gst-launch filesrc location="packets.pcap" ! rohccomp ! udpsink
receiver / decompressor:
gst-launch udpsrc ! rohcdecomp ! filesink location = "packets_otherside.txt"

Rohc_decomp would output raw packets for now, though pcap-output
should be possible in theory.

Reading from a tun/tap interface (e.g. file /dev/net/tun) happens with
a regular unix socket. Is there a gstreamer element that already
implements opening and reading from an arbitrary file? If not, could
this be implemented inside the rohc elements as a mode of input, or
maybe as a separate element?
I am basically asking if elements similar to socketsrc, socketsink in
the following example exist or if it makes sense to have them:

sender / compressor (assuming someone is sending packets to tun0)
gst-launch socketsrc location="/dev/net/tun0" ! rohccomp ! udpsink
receiver / decompressor (assuming someone is reading packets from tun1)
gst-launch udpsrc ! rohcdecomp ! socketsink location = "/dev/net/tun1"

Are there currently other ways in which the rohc library can be used?

The above discussion only deals with UDP packets for now - if there
would be added complexity / issues when using rtp please share.
Does the above description look sufficient? Please feel free to make
other suggestions or comments.
Also let me know if someone else is already working on this off-lists
so that development efforts are not duplicated.
thanks,

- Vasilis

On Mon, Jan 18, 2010 at 8:18 AM, Nicolas Hennion
<[hidden email]> wrote:

> Hi all,
> it will be very nice to implement the ROHC (RObust Header Compression, RFC
> 3095) in a standalone plugin.
> IP, UDP and UDP header will be compressed from 40 octets to 3-5 ! A nice
> optimization for audio and video streaming.
> You can find more informations about the ROHC and its open-source
> librairy: https://launchpad.net/rohc/
> The API documentation for compressor and decompressor are available here:
> - http://www.tech.viveris.com/docs/rohc/group__rohc__comp.html
> - http://www.tech.viveris.com/docs/rohc/group__rohc__decomp.html
> Any developper interrested ?
>
>
> ----
> Le sage ne dit pas ce qu'il sait, le sot ne sait pas ce qu'il dit.
> ----
>
> ------------------------------------------------------------------------------
> Throughout its 18-year history, RSA Conference consistently attracts the
> world's best and brightest in the field, creating opportunities for
> Conference
> attendees to learn about information security's most important issues
> through
> interactions with peers, luminaries and emerging and established companies.
> http://p.sf.net/sfu/rsaconf-dev2dev
> _______________________________________________
> gstreamer-devel mailing list
> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/gstreamer-devel
>
>

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Nicolas Hennion

Re: Header compression plugin

In reply to this post by Nicolas Hennion

Hi Vasilis, nice to find a person interrested by this challenge !

To be honest, i am not a ROHC specialist too... But what i understand from this protocol is that it will be able to compress the IP, UDP (or TCP) and RTP header. In your pipeline exemple, you write:

sender / compressor:
# gst-launch filesrc location="packets.pcap" ! rohccomp ! udpsink
receiver / decompressor:
# gst-launch udpsrc ! rohcdecomp ! filesink location = "packets_otherside.txt"

In this exemple, the header compression is done before the UDP encapsulation, only the RTP hrader will be compressed and not the UDP. I think that the best way to implement the ROHC is to fork the udpsink and udpsrc by addind a new tag (rohc="false|true").

sender / compressor:
# gst-launch filesrc location="packets.pcap" ! udpsink rohc="true"
receiver / decompressor:
# gst-launch udpsrc rohc="false" ! filesink location = "packets_otherside.txt"

Any comments ?

Nicolas

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Vasilis Liaskovitis

Re: Header compression plugin

Hi Nicolas,

On Thu, Jan 28, 2010 at 7:31 AM, Nicolas Hennion
<[hidden email]> wrote:

> Hi Vasilis, nice to find a person interrested by this challenge !
>
> To be honest, i am not a ROHC specialist too... But what i understand from
> this protocol is that it will be able to compress the IP, UDP (or TCP) and
> RTP header. In your pipeline exemple, you write:
>
> sender / compressor:
> # gst-launch filesrc location="packets.pcap" ! rohccomp ! udpsink
> receiver / decompressor:
> # gst-launch udpsrc ! rohcdecomp ! filesink location =
> "packets_otherside.txt"
>
> In this exemple, the header compression is done before the UDP
> encapsulation, only the RTP hrader will be compressed and not the UDP. I

right, my example only did compression for the encapsulated pcap
frames, not for the UDP frames. Both the examples I 've seen in the
source code deal with compressing headers of packets that are later
encapsulated by another packet flow

> think that the best way to implement the ROHC is to fork the udpsink and
> udpsrc by addind a new tag (rohc="false|true").
> sender / compressor:
> # gst-launch filesrc location="packets.pcap" ! udpsink rohc="true"
> receiver / decompressor:
> # gst-launch udpsrc rohc="false" ! filesink location =
> "packets_otherside.txt"
>
> Any comments ?

I assume you mean that in your example pipeline would compress the
whole udp flow. Actually this is a question for the rohc library
developers: Since the library is a userspace implementation, can we
compress headers for the entire packet flow? I think there would be at
least one packet flow being created in the normal kernel stack, and we
need some kernel mechanism e.g. a module to handle the compression of
headers for that network flow within the networking code. So my
question is: can we compress the whole network flow from startpoint to
endpoint? Without a kernel module, I think we 'd always leave some
uncompressed frames on the table.

Perhaps there is a way to directly access all header flow with libpcap
and CONFIG_PACKET_MMAP=y ( a kernel option)? But I am not sure if this
needs to be exposed in a gstreamer element. Currently udpsink and
udpsrc just use regular sockets for the packet flow, no pcap
capabilities are exposed are far as I know.

Apart from that, I think It should be possible to implement the rohc
compression / decompression with an element derived from
udpsrc/udpsink, is that what you mean by forking? The rohc=true/false
setting would be a property of the element. Actually I am not clear on
why you used "rohc=true" in your compressor and "rohc=false" in the
decompressor. DId you mean to say that the properties of the element
are "rohc=compress" and "rohc=decompress"?

In short, this pipeline makes sense in theory. But as I mentioned
udpsrc/udpsink use normal sockets to receive/transmit datagrams and I
don't know if we can have the full header information available for
compression at this layer. I apologize if I am missing something
obvious in the librohc implementation

comments & suggestions are very welcome.

thanks,

- Vasilis

>
> Nicolas
>
> ----
> Ce n'est pas l'appareil qui prend la photo.
> Ce sont les yeux, le coeur, le ventre, tout ça...
> -+- Jacques-Henri Lartigue -+-
> ----
> ------------------------------------------------------------------------------
> The Planet: dedicated and managed hosting, cloud storage, colocation
> Stay online with enterprise data centers and the best network in the
> business
> Choose flexible plans and management services without long-term contracts
> Personal 24x7 support from experience hosting pros just a phone call away.
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> _______________________________________________
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>
>