Mobile L2TP Technical

An L2TP tunnel is established using the pre-agreed IP addresses, hostname and shared secret. Note that if your LNS rejects the tunnel connection, or fails to respond to the SCCRQ or a subsequent HELLO, then it will be black listed for 5 minutes allowing further connections to go to the fall-back LNSs.

Once the tunnel is established, a session is established for each connecting data SIM.

ICRQ

Attribute		Meaning
Assigned Session ID	14	Session ID
Call Serial Number	15	Present if received from mobile network
Calling Number	22	19 digit ICCID of SIM, starting 8944

ICCN

Attribute		Meaning
Framing Type	19	Always 1 (PPP)
Initial Received LCP CONFREQ	26	As received / negotiated by proxy
Last Sent LCP CONFREQ	27	As sent / negotiated by proxy
Last Received LCP CONFREQ	28	As received / negotiated by proxy
Proxy Authen Type	29	Will always be CHAP
Proxy Authen Name	30	User name from mobile device, typically blank
Proxy Authen Challenge	31	Chap challenge
Proxy Authen ID	32	Chap challenge ID
Proxy Authen Response	33	Chap response hash
Tx connect speed	24	Present if advised by mobile network
Rx connect speed	38	Present if advised by mobile network

Limitations

• Only available on data SIMs.
• Called Number is a fixed APN and not the one entered on the phone, which is ignored.
• Reduced MTU of 1450 is in operation when L2TP is run over the internet. This restriction can be removed to allow full 1500 byte MTU where direct *Baby-jumbo frame links are available from us to your LNS.
• User-Name passed is what is provided by the mobile which is usually blank. Do not use the password 'password' as this will not be passed through.
• IPv6 is not available yet, but is planned for the future if possible.