GPRS tips by PA5DD

Updated: 2010-03-14

GPRS (General Packet Radio Services) which is a part of the GSM standard can be an affordable alternative to a proper Internet connection, because only the traffic is charged - not the connection time. Radio amateurs normally require to be constantly online, but does not demand a lot of bandwidth or traffic. GPRS is highly mobile with coverage in almost any part of Europe.

Rates vary a lot across Europe. In Denmark the cheapest rate is 1.34 Euro/MB with a pre-paid SIM. The general roamning charge across Europe appears to be around 7.50 Euro/MB.

Being connected to Shouts, a DX cluster and a chat node will consume from 20kB to 100kB/hr. GPRS is therefore affordable even, with high charging rates per MB. If you for example confine yourself to microwave cluster spots and the microwave chat, you can stay connected for many hours without reaching 100kB of traffic. This requires that you follow some simple rules:

hardware

Be aware that some mobile telephones can handle the GPRS protocol, without offering the use of a GPRS connection to an external terminal (your PC). Personally I have used a combined W-LAN/GRPS PCMCIA card (NOKIA D211) and recently a NOKIA 6230i via a Bluetooth interface to the PC. The GPRS/Bluetooth combination is a big advantage, since the mobile telephone can be placed freely for best coverage. This also solves the problem of the GSM bursts being detected by audio equipment etc.

 

If you connect your phone via an USB port, or if your "phone" is a USB dongle then be aware that all USB ports on your PC with its own controller will create a seperate Windows modem under "Control Panel >Network and Dial-up connections". The modem settings suggested below have to be applied to ALL these GPRS modems:

A tricky situation can arise if you install the connection at home on one USB port, and then connect it to another USB port on location. The PC will probably auto-install, but the modem will then have default settings and will not limit traffic as suggested below. Best pre-caution is to plug the phone into all USB ports one-by-one and install the connection to the phone on all ports. Afterwards change the settings of all the modems as suggested below.

use Telnet

use Telnet rather than HTML to connect to chats & DX clusters. This will generate much less traffic. OZ2M has written a Telnet client using some enhanced messaging allowing the client to offer many of the functions known from the Web browser interface. Other Telnet clients are available from EA6VQ & JA3THL.

OZ2M  EA6VQ   JA3THL

remove unneccesary network bindings

Uncheck all expect TCP/IP under Control Panel>Network and Dial-up connections>Properties (for the GPRS modem )>Networking (and press OK)

use a firewall

Use the ZoneAlarm software firewall (which is for free) to control the programs on your computer that aceess the Internet. Remember to shut down any other software firewalls you might have installed. By setting the program control to only allow your Telnet application to access the Internet, you can safeguard yourself against automatic updaters and the like accessing the Internet, and generating GPRS traffic. Other firewalls with outgoing control might work aswell.

Note that the Windows XP firewall cannot be used to control your programs. This because it only provides incoming protection.

Be sure to test that there is no leaking traffic after setting up the firewall. The way to test it is to shut down the Telnet application and watch for other traffic (Right click connection icon, and choose Status). The initial connection will cost some bytes, but after a minute of so both Sent and Received bytes should stay constant, until you start your Telnet application.

 

Your firewall probably has a logging option to help you identify sniper traffic. The Windows XP firewall has such a logging option.

If you want to use DNS (Domain Name Server) lookup, you will also have to allow "Generic Host Process for Win32 Services" ("svchost.exe") for XP, or "Services and Controller app" ("services.exe") in Win2000.

use IP adresses

By using IP adresses (like 194.146.226.26) rather than domain names (like www.on4kst.info) you make the connection establishment faster and more reliable. Sometimes GPRS latency will make the name lookup fail. Domain names can be resolved to IP adressess by using "nslookup.exe" in the command window on a proper Internet connection in beforehand.

The KST2Me client connects default to the IP adress of the ON4KST server.

do not connect to a DNS

Note: Since all Windows applications normally use Internet domian names, the disabling of the DNS as described here could be used as the only safeguard against excess traffic. In that case no extra firewall is needed. Be careful though if you have set any of your programs up to use IP adresses (things like SKYPE, VPN etc.). The beauty of this solution is that the DNS disabling only applies to the GPRS modem, and therefore a "seemless" switch can be made between for example an Ethernet or W-LAN connection at home, and a GPRS connection in the field. I recommend that you re-start your PC, when switching from a Ethernet to the GPRS connection to avoid any problems with cached DNS values. Also make sure that no other network connections (disable W-LAN) exist that will give the PC access to a real DNS server.

When you establish your GPRS connection, the TCP/IP layer in your modem will nomally attempt to receive a DNS (Domain Name Server) adress from the GPRS server. This will cost you some kBs on every connection. You can save these bytes by entering a DNS server adress in the TCP/IP properties of your GPRS modem connection. Even with a manual set DNS adress, the GPRS connection will try to establish contact with the DNS server on start-up. Again this is costing you traffic on every connect. The solution is to set the DNS server adress to the internal loopback adress of your PC  (127.0.0.1). This way the traffic will not reach the GPRS modem. You should only use the last solution in case you are only using IP adresses (see above). Every connection will still cost around 500B, because the modem need to aquire an IP adress.

The unwanted traffic generated is related to the fact, that the ZoneAlarm firewall does not block traffic on the DNS IP port. If you set your DNS server to 127.0.0.1 you do not need to shut down SKYPE either (see below).

Control Panel>Network and Dial-up connections>Properties (for the GPRS dial-up connection)>Networking>Highlight TCP/IP>click Properties

Click OK in both windows on exit.

shut down SKYPE

SKYPE uses IP adresses and pings the DNS server to detect WAN presence. Shut it down and disable "Start Skype when I start Windows".

filter traffic

Do not subscribe to unneccesary traffic on the chats or the DX clusters. On ON4KST all extra traffic is optional, and have to be switched on. On a DX Spider node you can use some of the following example commands (The settings are remembered, so you only have to do it once):

unset/ann                                             (kill announcements)
unset/wwv                                           (kill WWV messages)
unset/wcy                                            (kill WWV from DK0WCY)
unset/wx                                              (kill weather reports)
accept/spots on 30000/77000000       (only spots above 30MHz)
accept/spots on 1290000/77000000   (only micorwave spots)
accept/spots on 50000/433000 and (by_zone 14,15,16,20,33,34,40 or call_zone 14,15,16,20,33,34,40)  (only European VHF/UHF spots)

Telnet access adresses
adress:port

ON4KST chat   
www.on4kst.info:23000   194.146.226.26:23000

OZ5BBS DXC (DX Spider)
www.oz3fyn.dk:8000  194.192.135.177:8000

PI4CC DXC (DX Spider)
dxc.pi4cc.nl:8000  82.95.254.239:8000