Is USSD Hungry For SS7? (The Answer is No)

 When launching choice facilities, mobile operators are often concerned if these facilities will inhibit existing facilities or infrastructure. In particular, USSD facilities are often below suspicion to exhaust radio channel knack and to induce voice channel investigate. It is evident that a promote exposing operator's primary asset to a risk should be deliberately examined in the to the front commencement.

This article will discuss these concerns and attainable risks.

Following USSD facilities are technologically realizable:

USSD Phase 1 (GSM 02.90) alleviate - a abet launched by a mobile subscriber (phone initiated session or USSD Pull)

USSD Phase 2 (GSM 03.90) encourage - launched by a mobile subscriber or initiated by network (USSD Pull & Push)

Both USSD Phase 1 and 2 facilities can happen simultaneously as soon as a phone call (Call Related USSD Services) or without voice relationship (Call Independent USSD Services).

Call Related USSD services use FACCH (Fast Associated Control Channel) for data transfer, Call Independent USSD services use SDCCH (Stand Alone Dedicated Control Channel).

USSD supports a maximum of 160 bytes of devotee data per notice (the upper limit can be less than 160 bytes depending as regards the order of the underlying protocol enlargement).

The eagerness of the FACCH channel is in this area 140 bytes per second and that of the SDCCH channel is a propos 83 bytes per second.

Thus, any USSD message can be delivered in less than 2 seconds.

Call Related USSD messages are less appealing for statement use early it is most unlikely that the fanatic will be both calling and using USSD. It is doable, however, that a USSD network-initiated proclamation is delivered even if the subscriber is talking. Nonetheless, the risk of a voice channel psychiatry is minimal that is supported by a fact that FACCH is not a dedicated channel but an associated one that means that it is implemented by stealing bits from the joined speech channel if one exists. If such bit stealing is allowed frequently and for long periods of grow pass, it will intensely demean speech feel to some extent but will not prevent the subscriber from speaking. In the battle of a significant deterioration of speech vibes, the thing can be bigger concerning the subject of the side of operator by rearranging FACCH channel utilization priorities.

The matter is more obscure in the warfare of Call Independent USSD services. It is actually a channel resource used for many purposes. These insert establishing calls (including authentication), terminating calls, location updates, informing the network that the subscriber is yet within the advance place. Accordingly, without a forgive SDCCH channel a mobile phone is not dexterous to entry mobile services (i.e. the subscriber is not clever to benefit a call).

Furthermore, Short Message Service (SMS) and USSD messages are as well as communicated more than SDCCH investigative channels. With the above said, an in leisure takeover use of resources of SDCCH logical channel is crucial for obedient and efficient mobile communication.

According to GSM 05.02 guidelines one cell can have going on to 8 SDCCH channels. A typical cell configuration has 4 or 8 SDCCH channels.

One USSD session utilizes one SDCCH channel. It means that 8 simultaneous USSD sessions exhaust SDCCH channel power of one cell. Therefore, accumulation subscribers served by this enormously cell would not be lithe to comport yourself calls or send / get sticking together of SMS messages.

It seems following a earsplitting hardship to the use of USSD services. But it is not; in legal simulation this have emotional impact does not happen.

A proof can be found in a German research paper "Performance Evaluation of GSM Signaling Protocols approximately USSD". According to the paper, it is more probable that additional call initiations would block existing SDCCH channels rather than substitute USSD sessions. It is supported by our 4 year long experience of USSD services gone MTS - we actually never had problems of the simple.

Troubles can actually arise by now enhancement-use of USSD in a geographically limited location, i.e. once further requests are concentrated in a little number of cells. This could happen within a network-initiated advertising disturb upon a stadium, for example.

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Such situations require totaling attention upon the side of the operator. First, all operator is adept to fall USSD session timeouts and consequently decline the probability of simultaneous sustain peak plenty. One transaction within a dialog session is limited to 30 seconds and overall session length is limited to 600 seconds (it can actually differ upon various hardware platforms), thus there is some space to reorganize these parameters. Timeout timers are defined in GSM 09.02.

Second, it is doable to intensify priorities for network services. Thus phone calls may endure the highest priority even if SMS/USSD services may have a belittle priority.