Hello, In addition to François answer, the max packet size is something you may change in tcp settings at system level.
Usually the packet size (called "MTU") has a 1500 byte default size. If you try to send a 2500 byte packet then this packet will probably be fragmented into 2 packets as you wireshark dump showed. I recommend you to use TCPOptimizer from http://www.speedguide.net/downloads.php This tool will show your actual System level TCP settings and MTU size and eventually change it. Default should be 1500 but you may increase this size but think that this may have some side effects especially if the machine also need to communicate over Internet as packet fragmentation may not be managed very well (web page don't show up, POP3 may not receive full mail...). TCP Optimizer also have a function to test largest packet you can send to destination ("MTU/Latency" tab and then "Largest MTU" button). You may also manually do this test by sending non-fragmented pings with forced size to detect if your destination can fully receive "big" packet. example : ping -4 -f -l 1472 192.168.0.1 This will do a ping to IP 192.168.0.1 with 1472 packet size (1500 - 16 of ethernet encapsulation) and "-f" say "no packet fragmentation allowed". This basic test should work but you may set bigger packet (try the packet size you need +16). regards. FS> Thanks François for your help ! FS> I will try this tomorrow... Just to be sure I'm not asking in the FS> wrong direction, this already worked with my program a few weeks FS> ago... And now without changing anything (or nothing consciously FS> at least !) it doesn't work anymore. FS> Attached just 2 wireshark captures (at the time it worked !), you FS> can see the length of the data is 2114 in one capture and 2348 in FS> the other one. Today I cannot go over 1500 (the rest comes then in FS> another chunk) The problem is that the hardware at the other end, FS> takes this as several answers. Of course this is also a problem on FS> this hardware but I cannot change it, and again it has already FS> worked... FS> Can the network topology (different switches or hub) give FS> different results about this ? FS> Thanks FS> Best regards FS> Frédéric SCHENCKEL FS> * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * FS> cab technologies FS> za Nord du val de Moder FS> 67350 Niedermodern FS> Tél: + 33 3 88 72 25 01 / Fax: +33 3 88 72 25 02 FS> Notre site en Français: www.cab-technologies.fr FS> Adresse support: supp...@cab-technologies.fr FS> * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * FS> -----Message d'origine----- FS> De : twsocket-boun...@elists.org [mailto:twsocket-boun...@elists.org] De la part de François Piette FS> Envoyé : mercredi 20 février 2013 17:54 FS> À : 'ICS support mailing' FS> Objet : Re: [twsocket] TWSocket and data packet length >>I need to send a data packet in one chunck. >>Today the datas are splitted in two chunks, one of 1500 (the MTU limit) >>and FS> another one for the rest. >> I'm not able to go over this 1500 limit. I know it's possible because >> I FS> have another program how does it like this FS> What you ask is to use Jumbo Frames which is available on some gigabit ethernet systems. Jumbo frames are handled by the OS, not Winsock API (TWSocket make use of Winsock API of course). FS> Altough not tested, you should probably do the following: FS> - Set SocketSndBufSize to some large value FS> - Set BufSize to at least the same large value FS> - Send your data as usual. FS> -- FS> francois.pie...@overbyte.be FS> Embarcadero MVP FS> http://www.overbyte.be FS> http://francois-piette.blogspot.com FS> -- FS> To unsubscribe or change your settings for TWSocket mailing list FS> please goto http://lists.elists.org/cgi-bin/mailman/listinfo/twsocket FS> Visit our website at http://www.overbyte.be -- To unsubscribe or change your settings for TWSocket mailing list please goto http://lists.elists.org/cgi-bin/mailman/listinfo/twsocket Visit our website at http://www.overbyte.be