[lwip-users] Re: PPP negotiate process

[yueyue papa]

Based on the PPP spec: 

Address: 
In HDLC this is the address of the destination of the frame. But in 
PPP we are dealing with a direct link between two devices, so this field 
has no real meaning. It is thus always set to “11111111” (0xFF 
or 255 decimal), which is equivalent to a broadcast (it means “all 
stations”).

After the GPRS module CHAP negotiate

#####################

fsm_sdata(IPCP): Sent code 1,1,22.
IPCP: sending Configure-Request, id 1
IPCP: open state 2 (LS_CLOSED) -> 6 (LS_REQSENT)
Read 10 bytes:
7e 80 21 01 00 00 04 67 c3 7e                       ~.!....g.~
#######################

The address changed to 80.

Whether it will impact the fcs  check?

On Tue, Apr 7, 2009 at 2:35 PM, yueyue papa <address@hidden> wrote:

from the log the major problem is after CHAP success.

Request peer address, and got a fcs error.
#######################

pppInProc[0]: got 10 bytes
pppInput[0]: IPCP len=4
fsm_input(IPCP):1,0,4
fsm_rconfreq(IPCP): Rcvd id 0 state=6 (LS_REQSENT)
ipcp_reqci: Requesting peer address
ipcp_reqci: returning Configure-NAK
pppWrite[0]: len=18
Written 18 bytes:
7e ff 03 80 21 03 00 00 0a 03 06 00 00 00 00 a0     ~...!...........
3d 7e                                               =~

fsm_sdata(IPCP): Sent code 3,0,10.
Read 29 bytes:
7e 80 21 03 01 00 16 03 06 0d 0a 44 09 82 81 06     ~.!........D....
d3 88 70 32 83 06 d3 88 14 cb bc a0 7e              ..p2........~

pppInProc[0]: got 29 bytes
pppInProc[0]: Dropping bad fcs 0xAD6A proto=0x8021

#########################


#########################

fsm_sdata(IPCP): Sent code 1,2,14.
IPCP: sending Configure-Request, id 2
Read 21 bytes:
7e 80 21 04 02 00 0e 01 0d 0a 00 00 00 00 00 00     ~.!.............
00 00 66 f7 7e                                      ..f.~

pppInProc[0]: got 21 bytes
pppInProc[0]: Dropping bad fcs 0xFC02 proto=0x8021

#########################

I got many 29 and 21 bytes fcs error. 

How could I confirm this is really FCS error, or some other protocol ?

Lee