MTNBroadband
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I have seen a number of questions about GSM frequencies and time slots.
MTN is allocated a number of GSM frequencies by the regulator.
Each frequency can support up to eight normal voice calls simultaneously. Each voice call uses one TIMESLOT. This means that eight users are all talking on the same frequency and they take turns to use the frequency.
It is actually a pair of frequencies because there is an uplink and a downlink.
The first two timeslots in a cell are reserved for signalling - or control between the network and the handsets (identifying the cell, sending and receiving SMSs, cell broadcast, paging for a handset when it is called, handing over between cells etc). For a basic cell with one frequency (eg in a small town), there are therefore six timeslots left - ie six people can talk at once. A cell with two frequencies supports these six and has an additional frequency which then allows another eight (so fourteen callers at once), and a third frequency would add another eight to allow 22 callers. For a very large cell with multiple frequencies you would need to allocate additional signal channels.
It is true (as one forumite mentioned) that half rate (HR) voice codecs only occupy half a timeslot.
Circuit switched data (good old) uses one timeslot and gives 9 600 bps (with a good padding of error detection and correction bits). MTN implemented about 5 years ago the ability to send 14 400 bps on the same channel. This service was exclusive and meant that MTN users with capable handsets got 50% faster data even then. This service is charged on duration and the user has exclusive use of the connection so would not be 'bumped off'. However it does not make sense with the new data tariffs to use this for common applications.
MTN also launched HSCSD (high speed circuit switched data) which was circuit switched but would connect on multiple timeslots. The user had exclusive use of one timeslot and would share additional timeslots if they were free. Maximum speed of this was 4 x 14 400 bps = 57 600 bps which was pretty good for wireless in 2000. This is the service that some forumites mentioned. It is more expensive than GPRS with the new tariffs. It is still a popular service and I must say a number of MTN staff still use it because the performance is better overall than GPRS (in a non-EDGE site).
GPRS, GPRS+ and EDGE all work on a different basis. Users are only allocated timeslots when they are actively transferring data. However while they are transferring they have at least one timeslot where they are prioritised as 'voice users'. In other words an active user is not just 'bumped off'. Certainly the connection does not drop under normal circumstances. GPRS specifications allow for multiple users to share this single timeslot. MTN tends to provision so there is very limited sharing of timeslots in this way.
The maximum that handset requests is four timeslots for download or two for upload. I have discussed elsewhere how the timeslots are related to data speeds but here's a re-cap.
Under best radio conditions:-
GPRS supports up to 12 kbps per timeslot
GPRS+ supports up to 20 kbps per timeslot
EDGE supports up to 59.2 kbps per timeslot.
In a site with reasonable data traffic it is possible for MTN to dedicate timeslots exclusively for packet-switched data but this is only one of a number of mechanisms which can be used to maximise the user experience and our engineers have learnt a number of tricks in this regard.
I hope that clarifies some of the timeslot issues
MTN is allocated a number of GSM frequencies by the regulator.
Each frequency can support up to eight normal voice calls simultaneously. Each voice call uses one TIMESLOT. This means that eight users are all talking on the same frequency and they take turns to use the frequency.
It is actually a pair of frequencies because there is an uplink and a downlink.
The first two timeslots in a cell are reserved for signalling - or control between the network and the handsets (identifying the cell, sending and receiving SMSs, cell broadcast, paging for a handset when it is called, handing over between cells etc). For a basic cell with one frequency (eg in a small town), there are therefore six timeslots left - ie six people can talk at once. A cell with two frequencies supports these six and has an additional frequency which then allows another eight (so fourteen callers at once), and a third frequency would add another eight to allow 22 callers. For a very large cell with multiple frequencies you would need to allocate additional signal channels.
It is true (as one forumite mentioned) that half rate (HR) voice codecs only occupy half a timeslot.
Circuit switched data (good old) uses one timeslot and gives 9 600 bps (with a good padding of error detection and correction bits). MTN implemented about 5 years ago the ability to send 14 400 bps on the same channel. This service was exclusive and meant that MTN users with capable handsets got 50% faster data even then. This service is charged on duration and the user has exclusive use of the connection so would not be 'bumped off'. However it does not make sense with the new data tariffs to use this for common applications.
MTN also launched HSCSD (high speed circuit switched data) which was circuit switched but would connect on multiple timeslots. The user had exclusive use of one timeslot and would share additional timeslots if they were free. Maximum speed of this was 4 x 14 400 bps = 57 600 bps which was pretty good for wireless in 2000. This is the service that some forumites mentioned. It is more expensive than GPRS with the new tariffs. It is still a popular service and I must say a number of MTN staff still use it because the performance is better overall than GPRS (in a non-EDGE site).
GPRS, GPRS+ and EDGE all work on a different basis. Users are only allocated timeslots when they are actively transferring data. However while they are transferring they have at least one timeslot where they are prioritised as 'voice users'. In other words an active user is not just 'bumped off'. Certainly the connection does not drop under normal circumstances. GPRS specifications allow for multiple users to share this single timeslot. MTN tends to provision so there is very limited sharing of timeslots in this way.
The maximum that handset requests is four timeslots for download or two for upload. I have discussed elsewhere how the timeslots are related to data speeds but here's a re-cap.
Under best radio conditions:-
GPRS supports up to 12 kbps per timeslot
GPRS+ supports up to 20 kbps per timeslot
EDGE supports up to 59.2 kbps per timeslot.
In a site with reasonable data traffic it is possible for MTN to dedicate timeslots exclusively for packet-switched data but this is only one of a number of mechanisms which can be used to maximise the user experience and our engineers have learnt a number of tricks in this regard.
I hope that clarifies some of the timeslot issues