GPRS PPP connect failture during LCP negotiation

Question

I did some work to transplant TCP/IP stack to MCU. Through GPRS, MCU can connect internet. However, I met with some trouble during LCP negotiation.The following is my solution referring networking material

1. In order to make MCU PPP simpler.The LCP option request will be respond with rejection.

   Server:7e ff 03 c0 21 01 01 00 14 02 06 00 00 00 00 05 06 b0 70 9c c3 07 02 08 02 54 06 7e
   
   MCU:7e ff 03 c0 21 04 01 00 04 02 06 00 00 00 00 05 06 b0 70 9c c3 07 02 08 02 69 78 7e
   

2. A authentication request is expected in the second step. But i get a none LCP option request.     

   Server:7e ff 03 c0 21 01 02 00 04 b5 5a 7e
       

This means server forces MCU to start LCP negotiation.I am missing.

I send a authentication option request to server so that forcing server to start authentication option negotiation.Server respond me two packets.One is a ACK packet for authentication request.The another still is the none LCP option.

MCU:7e ff 03 c0 21 01 05 00 08 03 04 C0 23 ac 56 7e

Server:7e ff 03 c0 21 02 05 00 08 03 04 C0 23 bd 34 7e
Server:7e ff 03 c0 21 01 02 00 04 b5 5a 7e

After several "none option" request, The negotiation over. What should I do? I am l

(My english is not good .I hope you can understand my means.)

Answer 1

When you respond with Configure-Reject when modem sends Configure-Request. Then modem will send a new modified Configure-Request. See RFC1661 chapter 6.4.

So you should respond with Configure-Ack when Configure-Request contains suitable values for you. So you should send Configure-Ack after the second Configure-Request.