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发表于 2004-6-22 11:30:58| 字数 7,504| - 中国–甘肃–兰州 移动
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Note that I am not aware how to disable these if they exist in any
PPP configuration file. Setting them as 0 does not disable them.
If echo is set on in /etc/ppp/options you can not disable them in
/etc/ppp/options.ircomm.
When you debug the connection, you want to add options
debug debug debug
nodetach
To get interactive messages to console. Note that you need
to write debug three times to get enough messages.
To optimize connection, you should add packet size to as large as possible.
GPRS is able to handle 1500 byte packets. Your latency is bad anyhow, so
there is no need to use small packets. (Actually, it caused a lot problems
when the MTU was changed. Don't touch the default before you get the
connection up.)
TBD: what is the best compression combination?
A working chatscript (/etc/chatscripts/gprs) is:
........... (TBD)
A working GPRS peer definition (/etc/ppp/peers/gprs) is:
........... (TBD)
And putting all this together you can call Internet through GPRS cellular
telephone by simply writing "pppd call gprs". You can always check the
connection status by
% ifconfic ppp0
....
Naturally you need plenty of IP parameters right to get connection up but
they are general to any Internet connection. Especially boring is to change
DNS servers in /etc/resolv.conf to those that operator suggests. (Note that
there is a new feature to fetch DNS servers from network inside PPP protocol
(option usepeerdns) but GPRS does not seem to support that.)
PARAMETERS IN ERICSSON R520m GPRS PHONE
Normally, you left all the connection parameters as defaults except APN.
That means that user name and password are empty (and you don't want to send
password at all) and you don't set fixed IP address. Quality of service
parameters are normally "as subscribed".
First, you configure some communication profiles to your GPRS phone. This is
necessary as the profiles will be used as we bring up the gprs connection
later. The profiles are referred to by a number called the CID. Typically we
will use either CID=1 or CID=2, maybe most often the latter as the number 1
may have been reserved for WAP. The most important parameter for every
connection is a string called APN, which identifies the network we want to
connect to. You have to ask from your operator what APN to use to access
public Internet, in our case of the Sonera, it is simply "internet". There
are different strings to access WAP gateway or corporate intranets.
Here's how to set up the profiles for your Ericsson R520m phone. Go to
"Settings" and scroll down to the end of the menu and pick "Data comm.".
Then pick "Data accounts". You might already have a suitable account here,
but if not go ahead and create one. (Typically, a WAP profile would have the
string WAP in its name, and these can't be used.) Creating a new account
happens through pressing "Add account". Here you can simply specify the APN,
the username and password can be left as empty, and everything else to
reasonable defaults. In the case of Sonera, we need to set the APN to
"internet" and the name of the profile should be "INTERNET". As the creation
has been performed, go back to the "Data accounts" menu and pick the account
you just created and press Yes. A menu appears, and you will see at the end
the CID value, typically either 1 or 2. Memorize this.
The init string for the telephone is (from Windows settings file erim520.inf
in associated CD ROM):
AT &F<cr>
AT V1E0S0=0&D2&C1<cr>
AT +CMEE=1<cr>
This looks like more adapted to GSM data connections but we have used the
same one to initialize GPRS connections.
There are some settings where you should set default to GPRS to ensure that
GPRS is used whenever possible. However, they are not critical in PC use.
Note that in this telephone, infrared connection is not on unless you
disable Bluetooth. The only warning is that you have just Bluetooth icon on
the display but not infrared icon (although you have enabled infrared).
The only way to know that the GPRS connection is on is to ask status of the
phone, for example using the volume button on the side of the phone. As the
last line there is a mention on GPRS if it is on. I don't know any way to
find out how much data you have transferred in the current session.
The telephone is able to run on 115200 kbps in infrared interface. There is
no need to limit speed of infrared to lower speed like in some other
cellular telephones.
The speed of connection with these settings is around 3.2 kBps (26kbps).
There may be some other settings to increase speed. (It seems that my
operator Sonera has limited the maximum speed to much lower during 2002!)
Ping latencies with GPRS are typically 1.5 to 4 seconds.
ERICSSON T39
There is a problem in Ericsson T39 telephone and current pppd software
in Linux. Telephone does not do framing right and it breaks the PPP
protocol in Linux. There is an easy way to circumvent the problem:
add the following line to /etc/modules.conf:
options ppp_async flag_time=0
This information is from Zoltan Nagy <rnzoli@axelero.hu>. The previous patch
by Tommi Linnakangas (Tommi.Linnakangas@iki.fi) that slowed down the PPP
negotiation is not needed any more.
CAN I CONNECT TWO GPRS TELEPHONES TOGETHER?
Unfortunately no. All the connections must be started from the
telephone. You must use servers in the network.
At theory there could be some proxy that could help here but we
are not aware of such an application.
SECURITY PROTOCOLS WITH GPRS
Likely all operators use network address translation or NAT
to change your IP address on the edge of the network. This
means that standard IPsec protocol does not work with GPRS.
There are extensions that allow that but still they do not
interoperate between different IPsec implementations. Most
vendors do not support it yet.
SSH works with GPRS but it is quite useless in interactive
use. All security protocols use challenge-response authentication
that requires several roundtrips. If packets are lost, timeouts
affect badly performance. Starting SSH connection requires tens
of secons.
COMBINING GSM DATA AND GPRS DATA WITH THE SAME SETUP
(I am interested in hearing if somebody manages to do that.)
ROAMING ABROAD
When you roam abroad, all the settings should remain the same.
Especially, APN should be globally unique.
With our Sonera connection, roaming to Norway should work but
we have not tried it (yet). Follow the Sonera links for more
info.
SOME GPRS TERMS
Here are some important GPRS terms. Some of there are not used in this
howto to keep things simple. However, you need these if you read any GPRS
descriptions - writers of that kind of material love acronyms. Here are two
groups of terms: important ones for this scenario and less important ones
(network internal terms).
Important terms:
GPRS
General Packet Radio Service
APN
Access Point Name. Name of the ISP, Operator WAP gateway or
company intranet.
GGSN
Gateway GPRS Service Node. Node that relays IP packets to ISP,
Operator WAP gateway or Company intranet. APN actually identifies
one interface in one GGSN.
PDP context
This is synonym for your IP tunneling connection to ISP
ISP
Internet Service Provider. That operator that gives you
general Internet connectivity, DNS services, email services
and even your IP address. Often the same as your GPRS operator
but not necessarily.
MS
Mobile Station. Your cellular telephone.
MT
Mobile Terminal. Your PC.
Less important terms:
PDP
Packet Data Protocol. (IP in this case.)
IMSI
International Mobile Subscriber Identity. Your subscription
and identity information related to subscription. There is no
special GPRS IMSI but it is the same as your GSM IMSI.
GTP
GPRS Tunneling Protocol. The protocol used to tunnel IP packets
from your location (SGSN) to GGSN.
SNDCP
Subnetwork Dependent Convergence Protocol. The protocol used to
tunnel IP packets from your terminal to your location server (SGSN).
SGSN
Serving GPRS Service Node. The node that keeps track of you when
you are on it's location area.
GPRS LINKS
http://www.etsi.org
http://mobileinternet.ericsson.com
http://www.3gpp.org
http://www.mobilegprs.com
OPERATOR LINKS
http://www.qindel.com/gprs
Contains instructions (in Spanish!) how to set up connection to Spanish
cellular operators.
http://www.sonera.fi/gprsasetukset
Contains instruction (in Finnish!) how to set up connection to Finnish
cellular operator Sonera.
DISCLAIMER
Note that although we both work for Ericsson we have not used or even
received any information from Ericsson for this HOWTO. We just happened to
be among the lucky ones to receive Ericsson R520m telephones among the first
ones and wanted to share the experience. Terminology used in this howto is
meant for more clarity than accuracy. Esa is not affiliated with the
Finnish operator DNA - the mail address dna.fi is the older Domestic Network
Association, the operator is dnafinland.fi. |
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