Thanks for reply! > First, the packet is a IP/UDP/RTP packet, so where is the origion > packet from?
>I'm not sure to understand you question. The IP/UDP/RTP packet comes >from any application that generates such a packet: software SIP phone, >PIBX... I means that if these Ip/UDP/RTP packet's headers are constructed by the application itself? can you explain the principle of the iprohc's tunnel to me.I don't understand it well... Thanks 2013/6/1 Didier Barvaux <[email protected]> > Hello 宋鑫, > > > In iprohc reference, it creates a tunnel and a udp socket, if the > > virtual interface get a packet, first it will compress the packet to > > a rohc packet,then tunnel the rohc packet to the udp socket,at last > > use "sendto" to send the rohc packet. but I have some confusions > > about it. > > Not an UDP socket, but a RAW socket. So encapsulation is IP only > instead of IP/UDP. > > > > First, the packet is a IP/UDP/RTP packet, so where is the origion > > packet from? > > I'm not sure to understand you question. The IP/UDP/RTP packet comes > from any application that generates such a packet: software SIP phone, > PIBX... > > > > Second, after compress, the IP/UDP/RTP packet is transformed to a > > rohc packet,but when transport is UDP,using the "sendto" function, it > > adds the IP and UDP header again.If this is not efficient? > > Yes, kind of. It would more efficient to avoid the IP overhead, but you > need it to transport ROHC packets over Internet without help from the > link layer. If you control the link layer on the path between the 2 > ROHC endpoints, you don't need it. > > Back on efficiency, let's compute the IP/ROHC efficiency: > - The original IP/UDP/RTP is composed of 40 bytes of headers. > - The resulting ROHC packet is composed of 1 byte of headers (best > case). > - The IP/ROHC packet is composed of 21 bytes of headers. > - So, we saved 19 bytes of headers per packet, ie. 47% of headers. > - If the RTP payload is short (20 bytes for example), we saved 19 > bytes of a 60-byte packet, ie. 31% of the packet. > > A third of bandwidth is great, but we can do better. Let's pack several > ROHC packets together in one IP packet (as IP/ROHC does). It will save > use a part of the overhead added by the IP encapsulation. > > Let's do the computation with packing set to 5 ROHC packets: > - 5 IP/UDP/RTP/data packets weight 5 * (40 + 20) = 300 bytes. > - 5 ROHC packets weight 5 * (1 + 20) = 105 bytes. > - one IP/(5*ROHC) packet weights 20 + 105 = 125 bytes. > - so, we saved 175 bytes, ie. 58% of the whole packets. > > Saving 58% of bandwidth seems "efficient" to me :) > > Regards, > Didier > > _______________________________________________ > Mailing list: https://launchpad.net/~rohc > Post to : [email protected] > Unsubscribe : https://launchpad.net/~rohc > More help : https://help.launchpad.net/ListHelp > >
_______________________________________________ Mailing list: https://launchpad.net/~rohc Post to : [email protected] Unsubscribe : https://launchpad.net/~rohc More help : https://help.launchpad.net/ListHelp
