Page 90 - From GMS to LTE

76 From GSM to LTE-Advanced Pro and 5G

Table 2.1 Selected GPRS multislot classes from 3GPP (3rd Generation Partnership Project) TS 45.002
Annex B1 [1].

Multislot class Max. timeslots downlink Uplink Sum

8 4 1 5
10 4 2 5
12 4 4 5
32 5 3 6

seen in the table, multislot class 10 supports four timeslots in the downlink direc-
tion and two in the uplink direction. This means that the speed in the uplink direc-
tion is significantly less than in the downlink direction. For applications like web
browsing, it is not a big disadvantage to have more bandwidth in the downlink than
in the uplink direction. The requests for web pages that are sent in the uplink
direction are usually quite small, whereas web pages and embedded pictures
require faster speed in the downlink direction. Hence, web browsing benefits from
the higher datarates in the downlink direction and does not suffer very much from
the limited uplink speed. For applications like e‐mail with file attachments or mul-
timedia messaging service (MMS) messages with large pictures or video content,
two timeslots in the uplink direction are a clear limitation and increase the trans-
mission time considerably.
Also important to note in Table 2.1 is that for most classes the maximum number of
timeslots used simultaneously is lower than the combined number of uplink and down-
link timeslots. For example, for GPRS class 32, which is widely used today, the sum is six
timeslots. This means that if five timeslots are allocated by the network in the downlink
direction, only one can be allocated in the uplink direction. If the network detects that
the mobile device wants to send a larger amount of data to the network, it can reconfig-
ure the connection to use three timeslots in the uplink and three in the downlink, thus
again resulting in the use of six simultaneous timeslots. During a web‐browsing session,
for example, it can be observed that the network assigns two uplink timeslots to the
subscriber when the web page request is initially sent. As soon as data to be sent to the
subscriber arrives, the network quickly reconfigures the connection to use five times-
lots in the downlink direction and only a single timeslot, if required, in the uplink
direction.
In order for the network to know how many timeslots the mobile device supports,
the device has to inform the network of its capabilities. This so‐called mobile station
classmark also contains other information such as ciphering capabilities. The class-
mark information is sent every time the mobile device accesses the network. It is then
used by the network together with other information such as available timeslots to
decide how many of them can be assigned to the user. The network also stores the
classmark sent in the uplink direction and is thus able to assign resources in the
downlink direction immediately, without asking the mobile device for its capabili-
ties first.