7. Inter-operator
SMS Messages
Suppose
you and your friend are using the mobile phone service of wireless
network operator A and wireless network operator B respectively. The
transmission of an SMS message from you to your friend involves two
wireless networks. This SMS message is called an inter-operator SMS
message.
Typically,
the cost for sending an inter-operator SMS message from a mobile
phone is higher than that for sending an intra-operator SMS message.
7.1. Transmission
Process of Inter-operator SMS Messages
The
transmission of an inter-operator SMS message involves one or more
SMS centers. Generally, there are two different ways for the
transmission of inter-operator SMS messages. In the first way,
signaling interconnections are set up between two wireless networks.
When the originator SMS center receives an inter-operator SMS
message, it gets the routing information from the recipient wireless
network and delivers the SMS message to the recipient mobile phone
directly. The following figure illustrates the transmission process:

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The
first way can be used if the two wireless networks involved in the
transmission of the inter-operator SMS message are based on similar
technologies. However, if this is not true, the second way has to be
used. For example, when an SMS message is sent from a GSM network to
a CDMA network. In the second way, the originator SMS center and the
recipient SMS center are interconnected through an SMS gateway or
with a communication protocol that is supported by both SMS centers.
The SMS message first reaches the originator SMS center, which will
then forward the SMS message towards the recipient SMS center. The
recipient SMS center will be responsible for sending the SMS message
to the recipient mobile phone and storing the SMS message if the
recipient mobile phone is offline. The following figure illustrates
the transmission process:
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