Quoting Mark Wieder <[EMAIL PROTECTED]>: > thierry- > > Thursday, November 18, 2004, 3:28:37 AM, you wrote: > > t> i've read in some technical books that Datagram is not a sure way > t> to send information; means that some transport packets can be lost > t> over the Net. > > t> Can someone tell me if it's still true on a single Win machine with > t> 2 applications talking together with Datagram sockets ? > > t> or pointing some good information on this ? > > It's not an OS thing: TCP is one level up in the OSI network hierarchy > from UDP.
Actually, UDP and TCP are at the same level in the hierarchy - each of them is implemented directly on top of IP (along with ICMP, IGMP and various others). TCP and UDP both provide a transport layer - - TCP provides reliable, warranted (sometime called guaranteed, though that's not strictly true) delivery, where the sequential arrival is guaranteed. - UDP provides non-reliable (i.e. no "guarantee" of arrival), non-sequential-guaranteed delivery. > UDP Datagram packets are the lowest level in which you can > package data and specify a recipient on the network, but there's no > mechanism to define either a packet sequence or a handshake protocol. > Both these things are in the TCP level. If you're comfortable with > some packets possibly arriving out of order (you handle all this > yourself) and are creating your own protocol for determining when > packets have arrived safely then datagrams are *much* faster than TCP > packets. If you're sending individual datagram packets rather than > multi-packet transactions and do some simple handshaking then you're > safe with datagrams. They're used quite a bit for control packets > where small amounts of data need to be sent quickly. > > Do a web search for the OSI network model - here's a quick sample: > http://www.webopedia.com/quick_ref/OSI_Layers.asp > > You'll find datagrams at layer 3 and TCP at layer 4. > > All you need to know about datagrams: > http://www.faqs.org/rfcs/rfc768.html > If you are on a single machine, then (my opinion only) - arrival out of order is theoretically possible - but so unlikely I'd personally ignore it. (unless it happened as a side-effect of the non-arrival test below). - duplicated packet arrival is theoretically possible - but so unlikely I'd ignore it - non-arrival of a packet is also theroetically possible - I'd ignore it for an application for my own personal use, but would not ignore it for a professional app. However, a simple "packet lost - please retransmit" capability would be enough to deal with the very, very small chance of it happening. On Windows you should be able to install TCP/IP provideed there is at least one interface capable of supporting it - needn't be Ethernet, modems can also suport it, as can a loopback interface mentioned in other reponses. -- Alex Tweedly. _______________________________________________ use-revolution mailing list [EMAIL PROTECTED] http://lists.runrev.com/mailman/listinfo/use-revolution
