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VB Forum / General 2 / April 2005Winsock Question
Can anyone tell me how much data can be fetched on each Data Arrival event in Winsock. What happens if the limit is exceeded and how do you cater for such cases were the data being fetched is larger than the max if there is one. I've written a program which steers through a Menu on an external device normally controlled by keyboard inputs in a Telnet session. When I send an input to the external device some of the information being received is missing because I think it is too long. Also characters which I'm transmitting to steer the menu on the external device appear in the Data Arrival event routine. I was under the impression that the TX and RX are to separate paths. I forgot to mention that I'm using TCP mode in Winsock. Thanks to anyone who can give me any advise of were I'm going wrong :-) Ray how much data can be fetched on each Data Arrival event : This is determined by the network but is approximately 1,500 bytes. What happens if the limit is exceeded? With TCP/IP the message is split into pieces and reassembled at the other end. TCP/IP is a stream and does not send packets of data (UDP does send packetized data) TX and RX are separate. With TCP/IP you need a buffer in which to reassemble the passed message and the message should contain start and end bytes so you can find it in the stream. I don't quite understand your statement "TCP/IP is a stream and does not send packets ". TCP/IP is all packet based isn't it? A computer might send/receive a message via a Winsock socket, but the data is broken down into packets for transmission over the internet. TCP/IP is reliable and UDP is not. I guess maybe this depends on the programming mechanism one is using for communications. Direct Winsock usage will result in data appearing in the receive buffer one packet at a time, or are you simply stating Winsock will perform the packet assembly? I am not a Winsock jock, just a lowly Winsock newbie who has used Winsock for some UDP packet send/receive programming.  SignatureBest regards, Kyle | how much data can be fetched on each Data Arrival event : | This is determined by the network but is approximately 1,500 bytes. [quoted text clipped - 8 lines] | and the message should contain start and end bytes so you can find it | in the stream. In response to the post: On Fri, 29 Apr 2005 15:36:11 -0500, "Kyle" <me@privacy.net> stated...and I replied: >I don't quite understand your statement "TCP/IP is a stream and does >not send packets ". TCP/IP is all packet based isn't it? A computer [quoted text clipped - 6 lines] >assembly? I am not a Winsock jock, just a lowly Winsock newbie who >has used Winsock for some UDP packet send/receive programming. Yes, when you get down to the nuts and bolts of HOW WinSock transmits the data across the internet, it is in Packet form...how else could it be in the Packet based World of TCP. But, when your program is presenting the data to WinSock for transmission, it is sent all at one time (even if you break it up into chunks, which I suggest if it is in total bigger than say 10K). Let's say you have a 50Mb file to send (this is huge on a dial-up connection and will take a LONG time to send). You take the original file, break it up into segments of 10K each. When you send each segment you preceed it with a header that tells the receiver what segment number it is, it's start byte and end byte followed by the actual data. As each 10K segment is dropped onto WinSock, it breaks it up further into say 1K byte chunks, sends it to the reciever's Winsock using TCP, where it is internally reassembled into the 10K segment and presented to the receiving program as a stream of data in the Receive event. The program strips the header and holds the data, or writes it out to disk, or somehow retains it for reassembly into the original 50Mb file. Therefore: To your program, WinSock is a Stream protocol. To WinSock, TCP is a Packet protocol. There can be confusion due to this. Hope this helps, Shell |
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