A potential reason for the difference could be if Asterisk uses UDP (which I think that I've read somewhere it does). TCP is a protocol that demands that transmitted packets are numbered and that the receiver both request the re-send of packets that appear to be missing and order any packets that are received out of order (the frame header includes a frame number). In this way, there is a fairly reasonable chance that the data sent will be received. After all, where would this message be (which will be sent and received using TCP) if sme of th chractrs wer misig.
By comparison, UDP was designed for use in environments where the transmission control is not so important. By reducing or removing the need for transmission control, more frames can be squeezed into the available bandwidth potentially providing higher data rates. However, as data can be lost UDP is only suitable for use in applications where the loss of some data is not likely to be materially important. An example is voice transmission. Others include video or web conferencing. This is why SIP phones include features like missing packet interpolation. So I'd guess that Asterisk uses UDP, that Hylafax uses TCP and that sending a TIF image via Asterisk is asking for trouble unless Asterisk can, under prescribed circumstances, use TCP. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Lee Howard Sent: September 14, 2004 7:29 PM To: Asterisk Users Mailing List - Non-Commercial Discussion Subject: Re: [Asterisk-Users] Clarification - FAX on local network On 2004.09.14 11:10 Marty Mastera wrote: > Ok, ok, I know there has been plenty of discussion on asterisk and fax > - > from this I understand: > > 1) First and foremost, use g.711 ulaw Yes, the codec must be lossless. > 2) Packet loss, etc...makes faxing over the internet unreliable I'm not sold on this theory yet. I don't think that it's so much a matter of packet loss (this shouldn't occur regularly), but rather of latency. Transmitting packets over a network, and in particular the internet, can result in latency delays that could, in theory, pose a problem for FoIP, but I've heard of so many people successfully doing FoIP with equipment other than Asterisk (i.e. using Cisco VoIP equipment), that I tend to believe that the reliability factor is more a consequence of SIP or the equipment used (Asterisk and, in my case, a Sipura SP-2000). I have used a HylaFAX system connected to an SP-2000 for both sending and receiving faxes. The fax call comes in to an FXO on the Asterisk server, which directs it over a small LAN to the Sipura. This arrangement works tolerably well, but it's quite noticeably less-reliable than when the HylaFAX server is connected directly to the PSTN. I don't know if the Sipura is to blame or if it's Asterisk, or if it's SIP design. Although I've used a number of IAXys for voice, I haven't tried using one instead of the Sipura for fax. (Testing that would be able to eliminate or isolate SIP+Sipura.) Lee. _______________________________________________ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users _______________________________________________ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
