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SMS and remote controls SMS (Short Message Service) came as a present with GSM and nobody in the telecom industry thought about it as a profit generator. Today is provides important revenues to the telecom industry, higher than most much hyped other services. This means that it must be reliable or a lot of youngsters will be very upset... SMS and remote controls by Massimo Portolani (2002) SMS revenues are today important figures for telecom operators. SMS have a lot of advantages for operators: they don't actually use bandwith as they travel on the signaling layer, for this reason they can be sent even if all channels in a cell are busy (this happens when you try to place a call and get a Network Busy message on your phone). I am focusing on the importance of SMS for operators because this means that they will do the best they can to have SMS service running all the time (that is what unfortunately doesn't happen with GPRS today, for lack of customers). What is paramount when you wish to set up a remote control system is to be more or less sure that the bearer will work well. The best way to be sure of this is to know that it is an important bearer for the telecom company. An SMS allows the delivery of 140 bytes (=8bit) of data, that can become 160 7 bit ASCII characters (140/7*8=160). For this reason usually one refers to SMS as 160 characters. Delivery advantages: delivery is not direct but relays through a SMSC (Short Message Service Center) that are computers within the operator's network that receive the messages and route them to the recipient with some flexibility. Infact usually an SMS is sent immediately but if the recipient phone is switched off or unreachable is kept for delivery even for 24 hours, that means that it is stored by the operator and sent whenever the recipient telephone registers to the network. This is very useful for a remote device that has to send an alarm message before something (or somebody) breaks it or before power fails. Imagine this poor device (one of our TCS boards I hope) trying to place a call without being able to find a free channel or maybe finding the recipient phone busy! With an SMS this cannot happen, even if all channels in the cell are busy, still the SMS will go, because it travels on the signaling layer, and even if the telephone that should receive the alarm is busy, still the SMS will reach it because SMS arrive even if you are on a call. Multiple recipients: Another advantage is that the same message can be sent once and delivered to many users. So our TCS board, even in a difficult alarm situation, can send an alarm in seconds and be certain that many people will receive it even if the board will shutdown immediately after. SMS works well also in poor coverage areas: If your TCS board (or the recipient telephone) is in a area poorly covered by the GSM network, it is very usual not to be able to establish a connection. On the contrary an SMS will work, even with the lowest possible signal. Speed: if you have to send a small amount of data, it is much faster to do it with an SMS than with a data call, as the latter needs an initial modem handshaking procedure that may take up to 15 seconds. An SMS normally travels in 5 seconds. Drawbacks: Of course nothing is perfect, so where are the problems of SMS? In theory no operator will ever guarantee that the service will always work and they don't even guarantee the delivery of messages! Mamma mia! as we say in Italy, so what? As a matter of fact we never had real problems with the SMS service. On the contrary we had a lot of problems trying to place normal voice calls in moments of high traffic and we had a lot of problems placing data calls as well. You should remember that the priority for operators is to serve the maximum amount of customers as they want to maximize their profits (as economists teach us), so they will sacrify some data channel if there are no channels available for voice transmission. Conclusions: Sometimes it is better to rely on what is good in practice rather than thinking what is good in theory. And remember that if the SMS system will be down even for a while, millions of teen-agers will complain and their voices, that will be heard more than yours, will serve your purpose.

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