Seq Number and Ack Number in TCP stack

[puppie7777]

Hi, There!
i have built in a tcp stack which uses the ported tcp for CCS from Microchip TCP/IP stack. my pic now works as client, it works fine just except one "small" problem, if anyone has the simalar encounters as the following i will be very appreciated if he/she can share the experience!

The whole protocol stack which includes TCP/IP PPP stack works fine, but the connection keeps running for long time, my pic suddently "dont care about" any following incoming packets when pic side sending out a packet missing. (if the GPRS traffic is smooth, it will run for quite long time, maybe can transmit 10 thousand plus packets), and every time in this case, the program will "jump out" due to the sequence number and the ACK number not match. (my crc-16 checksum caculation in ppp layer works fine!).

Any suggestion will be highly appriciated!

[Guest]

Same experiences. Currently I'm working on this (ppp and ported tcp/ip stack) over PSTN. Sometimes I can upload huge files to an FTP server and sometimes it lacks after a couple 100 bytes.
Note that I have assigned an inactivity timer to the ip stack to disconnect (close the socket, disconnect ppp and then disconnect modem). It is not a solution for the problem just helps to keep phone charges as low as possible

[puppie7777]

Hi, there!

Now i have found out the reason, it is because my pic directly connect to GPRS modem (i m not using NIC), so there is not a "retransmit" mechanism on the virtural MAC layer to retransmit the data if no ACK received.

Actually in the TCPTick() function from Microchip TCP/IP stack, there is a "retransmit" mechanism, so far seems i can manage to retransmit an ACK packet, but still dont know how to implement on retransmitting data packet. Because the stack "push" this task to the NIC.

does anyone got a direction on that?
Rgds!