Re: [ECOS] Need help for TCP/IP over PPP via GSM modem

[Matt Jerdonek <maj1224 at yahoo dot com>]

We just finished testing TCP/IP over PPP with a GSM
modem.  There was one problem that we encountered that
might explain what you're seeing ...

The eCos PPP stack does not negotiate ACCM.  Our GSM
provider had a bug in their PPP server that caused
their ACCM to default to zero when the peer did not
negotiate ACCM (it should have defaulted to
0xFFFFFFFF).  This would cause the PPP stack in eCos
to think the incoming PPP frames had a bad checksum,
and discard them.  We fixed the problem by turning on
ACCM negotiation in the PPP stack (Set
wo->neg_asyncmap to 1 in lcp_init).  There is a more
complete patch that is submitted to fix this issue,
but it has not yet been committed.

Hope this helps,
-- Matt

--- Weili Yao <weili_yao@trimble.com> wrote:

> Hello, there:
>     I am using Redhat ECOS for our TCP/IP over PPP
> connection via GSM
> modem. The ECOS source was downloaded from CVS about
> two months ago. The
> GSM service provider is Cingular Wireless with GPRS
> enabled. The problem
> is after PPP connection established, I was not able
> to ping or connect
> to anywhere. It failed at recvfrom() with return -1
> when used in the
> ping_host(...) (see ppp_updown.c). The TCP/IP
> connect() API call waits
> forever. But the same source code (only with
> different serial port on
> the device) works with serial cable connected to my
> Linux box. With that
> serial cable attached to Linux, I was able to do
> ping and to call
> connect().
>     Can anybody there help me with this problem? It
> seems to me that
> with wireless modem PPP connection, the TCP/IP code
> does not work. By
> the way, even though it failed at recvfrom() in the
> ping, I do see the
> ICMP echo back in the port driver, and the echo data
> is correct, but
> that incoming data is not used by recvfrom(). Why?
> Look at the routing
> table, the local device IP address is assigned to:
> 10.216.27.198, but
> the remote (at Cingular) IP address is:
> 66.102.185.195. Does this have
> any conflict? These IP addresses are assigned
> automatically during PPP
> connection.
> 
>     The following is the details how to set the PPP
> connection and what
> the routing table is. Please let me know if you need
> more information. I
> really appreciate your help with this problem.
> 
> For the PPP connection, I am using:
>     user name: WAP@CINGULARGPRS.COM
>     password: CINGULAR1
> After using AT commands(baud rate is configured as
> 115200) :
>     AT+CGDCONT=1,"IP","WAP.CINGULAR"
>     ATD*99***1#
> by supplying above user name and password in the
> CHAP, the PPP
> connection has been established. 
>  
> After PPP connection established, I used ECOS API:
> show_network_tables(printf)  to check the network
> information and I got
> the following routing table:
> "Routing tables " 
> 
> "Destination       Gateway          Mask       Flags
>       Interface " 
> 
> 0.0.0.0           66.102.185.195   0.0.0.0      UGS 
>        ppp0 
> 
> 66.102.185.195    10.216.27.198                 UH  
>        ppp0
> 
> 127.0.0.0         127.0.0.1        255.0.0.0    UG  
>        lo0
> 
> 127.0.0.1         127.0.0.1                     UH  
>        lo0
> 
> Interface statistics
> 
> lo0 
> 
>     IP: 127.0.0.1, Broadcast: 127.0.0.1, Netmask:
> 255.0.0.0
> 
>         UP, LOOPBACK, RUNNING, MULTICAST
> 
>     MTU: 16384, Metric: 0 
> 
>        Rx - Packets: 0, Bytes: 0, 
> 
>        Tx - Packets: 0, Bytes: 0
> 
> ppp0 
> 
>      IP: 10.216.27.198, Broadcast: 66.102.185.195,
> Netmask: 255.0.0.0
> 
>          UP, RUNNING, MULTICAST
> 
>      MTU: 1500, Metric: 0, 
> 
>          Rx - Packets: 0, Bytes: 0" 
> 
>          Tx - Packets: 0, Bytes: 0
> 
> ============
> Thank you a lot!
> 
> Weili Yao
> 
> 
> 
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> 
> 



		
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