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7. Inter-operator SMS MessagesSuppose 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 MessagesThe 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:
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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