Iphone

We are using GPRS to connect cars to our mainoffice , we are using Intermec devices , we are confused about which is the best modem to use ? can you please give us an advice about the best modems in the market?
thank you.

Iphone

Most GPRS unit are the same.
However, this is what differentiate them:

Check the GPRS class your unit supports,
and find a vendor which suites your needs.

ETSI GPRS Class definition
A - GPRS and GSM simultaneously
B - Either of GPRS or GSM at any given time
C - GPRS or GSM exclusively
CG - Class-C in GPRS only mode
CC - Class-C in circuit switched only mode (lowest mode)

Class-A handsets will be able to support simultaneous attach,
activation, monitoring, invocation and data transfer in
both GPRS and GSM modes. Calls can be made or received on
both services subject to the QoS parameters.

Class-B will be able to attach to, activate and monitor both
services simultaneously but only be able to support data
transfer on one at a time. Active GPRS virtual circuits are
not cleared down when GSM facilities are in use, but any
attempt to contact the PDP address will result in a “busy or held”
indication. For instance, if an incoming GSM call is answered, the
GPRS connection is put on hold. This may cause problems for some
applications using the GPRS connection, e.g. a file transfer may
be aborted because the transfer protocol timeout expired.

Class-C handsets will only be able to operate exclusively in one
mode at a time, i.e. non-simultaneous attaches. Manually changing
from one mode to the other involves detachment from the previously
selected service.

The AT command AT+CGCLASS will indicate the current mode and
which modes are supported.


The bandwidth available to the GPRS user is dependant upon several
factors. In order to increase the bandwidth per channel, a different
Coding Scheme can be chosen, but this is at the expense of reduced
error protection.

ETSI have defined four coding schemes, from CS1 (highest error correction,
lowest data rate) to CS4 (no error correction, highest data rate).
The high incidence of errors when CS3 and CS4 are used prohibits their
use under most circumstances.

The second way of increasing bandwidth is to utilise multiple timeslots.
Handsets will be described by the maximum number of timeslots that
they can use on the downlink, plus the number of timeslots that they can
use on the uplink, for instance ‘2+1’, ‘4+1’, ‘3+2’. The majority of data will
be received by the handset rather than transmitted by it.

Timeslots will be dynamically allocated according to availability. Up to 8
timeslots are available on any given channel within a cell and the
management of resources will be negotiated between the handset and
the network. GSM will generally take priority over GPRS and so from time
to time availability may be reduced as the number of voice callers
rises. However, the advantage of GPRS is that as soon as a timeslot
becomes available it can benefit many data users.

1 Timeslot
CS1: 9.05 Kbps
CS2: 13.4 Kbps
CS3: 15.6 Kbps
CS4: 21.4 Kbps

2 Timeslots
CS1: 18.1 Kbps
CS2: 26.8 Kbps
CS3: 31.2 Kbps
CS4: 42.8 Kbps

3 Timeslots
CS1: 27.15Kbps
CS2: 40.2 Kbps
CS3: 46.8 Kbps
CS4: 64.2 Kbps

4 Timeslots
CS1: 36.2 Kbps
CS2: 53.6 Kbps
CS3: 62.4 Kbps
CS4: 85.6 Kbps

This table lists the theoretical maximum transmission rates (throughput)
using the different coding schemes and utilising one or more timeslots.
Up to four timeslots may be available for GPRS on a given live cell, but this
may be dynamically adjusted against the requirements of GSM users on
the same cell when the service becomes live.

Under coding scheme 2 (CS2) for example, each timeslot provides
13.4Kbps (K bits per second). This provides a payload of approximately 12Kbps.


Then you need to consider how many bands you need. In example:

For USA - you need a handset which supports GSM 1900
For ASIA - GSM 900
For Europe - GSM 900/1800

Dualband handsets refers to GSM 900/1800 and Tri-Band
for all.


I know that this information doesn't say which handset is the best, but
it should give you some usefull information you should use when you
are looking for a new handset provider.