Question

Programming the protocol stack for GPRS/WLAN interconnection

Asked by: rcamaren

Hi all,

I'm pursuing my Master in Communications and trying to decide on my thesis. I´m trying to establish a seamless roaming between GRPS and WLAN in a laptop (of course I would have a Wi-Fi card and a GPRS PCMCIA card). I mean, the laptop could access internet/email/... from both networks without loosing the session when roaming bw them.

I have read several docs in IEEE and 3GPP and think the best solution is to use a tight coupling approach, the WLAN acts as another RAN on the GPRS network. To achieve this, a IEEE document recommends to add a protocol called WAF (Wireless Adaptation Function) in the middle of the LLC and RLC/MAC layers. The WAF signals the activation of WLAN interface when entering a WLAN area. It also signals the change of RA to GMM, supports the paging procedure. etc.

I have read all the questions/answers posted here. Very helpful.

Some my questions are:
1. I haven't found a PCMCIA card for GPRS, anyone knows about one comercially available ?
2. Since I need to add the WAF layer, I could not use a current phone (because I cannot modify the protocol stack) so I need a internal GPRS modem so I can modify the stack of protocols in the laptop. Any recommendation about the best environment to do this I mean to use Linux (this way I only have to introduce my code for the WAF layer) or use some Active X alredy developed?
3. How does the IP assigment work in GPRS? Does my IP change when moving to another Routing Area or do I have the same IP all the time moving to other cells, Routing Areas?
4. This is becoming a big project, do you know any company, university or people working on this?

Any help is very welcomed.

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Asked On
2004-02-03 at 15:04:26ID20872351
Tags

gprs

,

programming

,

stack

,

protocol

Topic

General Packet Radio Service (GPRS)

Participating Experts
2
Points
500
Comments
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Answers

 

by: SimonTayPosted on 2004-02-14 at 08:18:04ID: 10361254

1) TDK Systems used to make a GPRS card, there are a few around http://www.premierelect.co.uk/gsmstart.html
2) You'll be lucky! - any approved GSM/GPRS card will NOT allow you access to the GPRS layer as this would nullify R&TTE approvals.  You'll be limited to the AT command interface ETSI07.07.
3) Most networks are dynamic leased IP addresses, although a few will give you a fixed IP for an additional fee.  Most networks will also disconnect the IP address after a short time of sending no data (30 seconds sometimes).
4) Only possibly the manufacturers of GSM/GPRS - see 2).

Simon

 

by: drelectroPosted on 2004-02-17 at 03:49:18ID: 10381186

1/ Nokia D211 or Sony Ericsson GC75

2/ Forget it, see the previous comment, if you're going to do this it will have to be at the application layer, regardless of approvals no-one is going to give you the source code to thier module. Reading your question a bit closer you imply that you can't use a regular phone to do this for exactly this reason, Unfortunatly a PC-Card phone or external modem works exactly the same way as any other phone, IE all the smarts are in the card none of the GPRS stack is implemented in the PC.

3/ As per the other poster but in Australia you don't get dropped for inactivity that quickly.

4/
If you've not yet done so have a look at Mobile IP, you might like to start here:-

http://www.computer.org/internet/v2n1/perkins.htm

This set of protocols does exactly what you're looking to do.

I've never heard of it being implemented on a GPRS network though (but it could be).
I have personally implememented it for a CDMA 1x terminal device.

 

by: rcamarenPosted on 2004-02-17 at 08:04:09ID: 10383431

Your comments have been very valuable to me and the links. Thanks a lot. I had considered the Mobile IP approach, but I wanted to explore another alternatives in the short term because Mobile IP is the slowest in terms of handover latency. But anyway I think Mobile IPv6 will arrange this problem once direct tunneling (instead of triangular routing) could be implemented (and be secure of course).

I just don't get clear about number 3 and unfortunatly I haven't found the answer on the resources I have. How does the roaming works on GPRS regarding the IP address? Do you know if the IPaddress is changed when I move to another Routing Area (RA)?

I have found that a routing area is similar to a Location Area for circuit switched services, but RA is typically smaller and for packet switches services of course. As far as I know, IP address is left unchanged while being inside the RA, but what happens when it changes to another??

Thanks again for your help...

 

by: drelectroPosted on 2004-02-17 at 13:55:14ID: 10386703

In my experience the assigned IP address is valid for the entire session and does not get changed, in fact there is no real mechanism in PPP (which is used by GPRS modems at the serial link layer) to allow the assigned IP to be changed once the session is established.
This implies that if the IP address were to change when roaming from RA to RA the session would need to be terminated and re-established, in my experience this does not happen.

20120131-EE-VQP-002

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