CSD » History » Version 5
laforge, 11/21/2022 10:54 AM
| 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 | 3 | laforge | GSM CSD (in its single-slot variants, excluding HSCSD) implements |
| 8 | 1 | laforge | |
| 9 | 3 | laforge | |_.22.002 Bearer Service|_.22.003 Teleservice|_.43.010 model|_.Description| |
| 10 | |BS20T|?|2b|transparent synchronous data| |
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| 11 | |BS30T|?|1b|transparent asynchronous data. first converted aysnc->sync, then treated like sync| |
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| 12 | |BS20NT|?|3b|non-transparent asynchronous data. Uses RLP (ARQ) protocol for less erros, but creates variable delay.| |
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| 13 | |?|TS62T|5a|transparent facsimile group 3| |
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| 16 | 1 | laforge | h2. Facsimile / Telefax |
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| 18 | CSD is also what is used to implement Facsimile (Telefax) services over GSM. |
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| 20 | h2. Interworking |
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| 22 | 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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| 23 | |||
| 24 | However, when interworking with the wired network is required, an interworking function (IWF) is required. |
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| 26 | h3. Interworking with ISDN data calls |
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| 27 | |||
| 28 | This is the situation where a GSM mobile subscriber is establishing a CSD call to a native ISDN subscriber. |
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| 30 | 4 | laforge | In this case, the [[retronetworking:V110|V.110]] signal is rate-adapted at the IWF to the 64kBps of the ISDN bearer chanel. |
| 31 | 1 | laforge | |
| 32 | h3. Interworking with analog modems in POTS or ISDN |
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| 34 | 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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| 36 | h3. Interworking with analog Telefax in POTS or ISDN |
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| 37 | |||
| 38 | This is similar to the analog modem situation above. |
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| 39 | 2 | laforge | |
| 40 | h2. Implementation Status |
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| 42 | 1 | laforge | We currently don't implement these features yet, but we are aiming at implementing them in 2023. For details, see "all Issues tagged with CSD":https://osmocom.org/issues?f%5B%5D=tags&f%5B%5D=status_id&fields%5B%5D=tags&fields%5B%5D=status_id&op%5Bstatus_id%5D=o&op%5Btags%5D=%3D&operators%5Bstatus_id%5D=o&operators%5Btags%5D=%3D&set_filter=1&v%5Bstatus_id%5D%5B%5D=&v%5Btags%5D%5B%5D=ASCI&values%5Bstatus_id%5D%5B%5D=&values%5Btags%5D%5B%5D=CSD |
| 43 | 3 | laforge | |
| 44 | h2. Relevant specifications |
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| 45 | |||
| 46 | |_.Number|_.Description| |
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| 47 | |3GPP TS 22.002|CS Bearer Services| |
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| 48 | |3GPP TS 22.003|CS Teleservices| |
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| 49 | |3GPP TS 43.010|Decription of connection types. Note particularly Table 4 + section 6.4| |
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| 50 | |3GPP TS 43.045|Fax G3| |
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| 51 | 5 | laforge | |3GPP TS 44.021|Rate adaptation on MS-BSS interface; RA0; RA1/RA1' single-slot| |
| 52 | 3 | laforge | |3GPP TS 44.022|RLP protocol (for non-transparent async)| |
| 53 | |3GPP TS 27.001|TA functions in MS| |
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| 54 | |3GPP TS 27.002|TA functions for async bearers| |
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| 55 | 1 | laforge | |3GPP TS 27.003|TA functions for sync bearers| |
| 56 | 5 | laforge | |3GPP TS 48.020|Rate adaptation on BSS-MSC interface; RA1/RA1' multi-slot, RA1''| |
| 57 | |3GPP TS 48.060|TRAU frame format for classic E1 BTS (Section 5.3, 5.5.3, 6.7)| |
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| 58 | 3 | laforge | |3GPP TS 29.007|Interworking between PLMN and ISDN| |
