[lwip-users] Porting the lwip TCP/IP/PPP stack, hints for debugging needed, avoiding pitfalls

[Wagner Hans-Jörg]

Hi

I am a very novice with lwip and porting to embedded system. I'm planning to port the lwip to the OSE delta from ENEA running (4.5.1 quite old version) on a MPC555 as a diploma thesis.

It's for a gsm based dial up connection to a Windows based PPP-server (perhaps client) to have a cheap independent m2m connection with a reliable TCP/IP based error correction retransmission mechanism (we dont want to need our customers IT infrastructure, if it has any because it could be a blocking issue for the customers to buy our support package). Sorry if I lack some theoretical basics. I know a little bit TCP/IP but not PPP.

At the moment the requirements are not already clear, if the the connection will be established from the embedded system side or from the windows PC side. Would the lwIP stack provide both capabilities to initiate a PPP link (this would be in the role as client I guess) or to accept a PPP connection from the PC (in the role as a server I guess).
I browsed shortly through the lwip sources. I found some client state definitions in the chap & pap modules as well as some server state definitions. However I only found a pppInput call in the PPP state machine of ppp.c. I'm wondering if lwip can only act as a PPP server, or am I wrong.

BTW do you know a good PPP tutorial (not RFC like style) with detailed explanations of the link establish phases with the PPP control headers used. perhaps in a diagram style (some sort of request response arrows from left to right and right to left).

Are the roles of TCP server and client completely independent of the roles of PPP server and client on the underlying layer. E.g. the device initiated a PPP connection as a client starts now a TCP server for accepting. Would that be possible?

Is there the possibility to establish a PPP connection between the embedded device and the PC without using a modem dial up, just with a direct cable connection to make first trials and debuggings?
Can I start a PPP client or server on a w2k or xp platform without configuring this dial-up or ras things? Are there tutorials to do this?
I already did some socket programming in JDK1.5 for windows. As soon as there is a PPP link do both sides have a IP address for the com port? Do I have to configure it for the PC if it acts as a server (how)? Can I use the socket programming in Java on the PC for this PPP connection as I would do it for an ethernet connection?

Sorry for the basic questions. But as the time is limited, I cannot investigate in every details and I therefore need some starting point.

Kind regards
Hans-Joerg