CSD » History » Version 1
laforge, 11/20/2022 07:24 PM
1 | 1 | laforge | {{include(MacroNotImplementedYet)}} |
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3 | h1. Circuit Switched Data (CSD) |
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5 | CSD is a way to transport user data over circuit-switched GSM calls. It is the cellular equivalent of the use of analog modems or ISDN TA over wired telephony networks: You dial a number, the usual call control protocol for signaling creates a dedicated, circuit switched connection to the destination. If they answer the call, a transparent communication channel is established between both sides. |
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7 | GSM CSD implements both synchronous and asynchronous bearer services. |
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9 | h2. Facsimile / Telefax |
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11 | CSD is also what is used to implement Facsimile (Telefax) services over GSM. |
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13 | h2. Interworking |
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15 | When CSD services (sync/async/fax) are used between two GSM subscribers, no interworking is required. The data is passed transparently end-to-end. |
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17 | However, when interworking with the wired network is required, an interworking function (IWF) is required. |
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19 | h3. Interworking with ISDN data calls |
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21 | This is the situation where a GSM mobile subscriber is establishing a CSD call to a native ISDN subscriber. |
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23 | In this case, the V.110 signal is rate-adapted at the IWF to the 64kBps of the ISDN bearer chanel. |
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25 | h3. Interworking with analog modems in POTS or ISDN |
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27 | In this case, the IWF terminates the V.110 from the GSM RAN and implements a modem towards the external POTS/ISDN subscriber. |
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29 | h3. Interworking with analog Telefax in POTS or ISDN |
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31 | This is similar to the analog modem situation above. |