Performance of data services in GERAN networks V. Wille and M. Kok The performance of data based services such as Internet browsing and e-mailing in GSM EDGE Radio Access Networks (GERAN) is described. Results from networks around the world show that quite significant performance differences exist, despite the fact that all systems are based on the same technical standard.
Introduction: GERAN systems were launched around 1992 when the primary load was circuit-switched voice traffic. Since the introduction of General Packet Radio Service (GPRS) during 2001, based on Release 97, and Enhanced GPRS (EGPRS) in 2003, based on Release 99, GERAN systems are also able to offer services which are based on packet-switched traffic. Owing to the widespread use of GERAN networks it is useful for industry regulators, network operators and equipment vendors to have a good understanding of the performance of data services in these systems. The performance expected from both GPRS and EGPRS has been extensively analysed in network simulations [1]. In such simulations ‘idealised’ data rates for the airinterface are normally quoted, e.g. a maximum data rate of 59.2 kbit=s per time slot (TSL) is stated for EGPRS and 11.2 kbit=s for GPRS when using coding scheme 2. Converting simulation based data rates into the performance experienced by users of real applications in actual networks is not straightforward since simulations are based on various assumptions, e.g. in simulations it is common to assume regularly spaced site locations and uniform antenna heights. But such assumptions are not reflected in actual networks. Frequency planning imperfections might also lead to interference conditions, which are worse than those considered in the simulations. Adjacency planning issues and cell congestion might have a similarly detrimental effect on application performance. The interaction between application protocols and network conditions is also likely to reduce performance. High interference levels, for example, might cause a high ratio of data retransmission, which in turn will lead to further reductions in data rates owing to the nature of the TCP=IP protocol. In addition, network peculiarities such as the number of available frequencies and the quality of the transmission network will also have a significant performance impact. Furthermore, most network simulations focus heavily on assessing the air-interface performance and, for simplicity sake, pay little attention to the non-radio part. For packet-based applications, however, the core network will also have a significant performance impact. Any imperfections in this domain will lead to performance degradations. Hence the data rates achievable in actual networks might be below those observed in simulations. To determine the actual performance of packet-switched data services in GERAN networks a large-scale measurement campaign was carried out.
500 kB size, respectively), HTTP browsing (downloading information from a proprietary Internet site), e-mail sending and receiving (8 kB size), as well as sending and receiving 25 kB Multimedia Messaging Services (MMS). In addition the performance of Short Message Services (SMS) was investigated. Furthermore GPRS Attach (putting the mobile into the ‘ready’ state) and PDP Context Activation (being able to transmit data) were also investigated. Of these eight services, only six are truly usable by the end-user; GPRS Attach and PDP Context Activation rather characterise important technical performance aspects of GPRS. In addition, SMS is not a packet-switched service, but has been included as it is a data service. For all these ‘services’ the analysis focuses on two key performance aspects: reliability of the service and how speedily it is performed. Discussion of results: A total of over 156000 transactions were carried out during the entire measurement campaign. The division of these transactions between the eight services can be seen in Table 1. The performance of each network for each of the 16 performance criteria is described by the median value observed during the measurement surveys. Performance differences between networks are highlighted by displaying the best, median and worst performance value of the median values from the individual networks. In addition, the performance value of the best 20% and the worst 20% of all networks is also shown. Thus a total of five key points are highlighted on the performance distribution for each service.
Table 1: Performance of data services in GERAN systems for selected applications Total number of transactions
Worst
20%
Median
80%
Best
GPRS attach success [%]
25.4
91.2
97.2
98.7
100.0
GPRS attach delay [s]
7.5
3.9
2.9
2.1
1.2
PDP context success [%]
56.4
96.1
98.6
PDP context delay [s]
7.9
2.0
1.6
1.3
1.1
FTP success UL [%]
75.9
96.6
98.6
99.6
100.0
FTP throughput UL [kbit=s]
7.5
15.1
17.3
22.3
33.8
FTP success DL [%]
30.4
93.5
97.6
99.0
100.0
FTP throughput DL [kbit=s]
12.2
23.8
26.9
39.1
58.6
HTTP browser success [%]
64.9
94.7
98.0
99.3
100.0
Download time [s]
102.9
63.8
50.7
35.0
21.0
E-mail success [%]
75.9
96.2
98.6
100.0 100.0
E-mail throughput [kbit=s]
2.0
5.2
6.7
31233
17788 100.0 100.0
14207
14883
14173
29188 7.7
9.5
22098
Measurement campaign and analysis methodology: To sample a wide variety of different system implementations under a range of regulatory conditions, it was deemed necessary to conduct the measurement campaign in several networks around the world. A drive-test based approach was selected in order to be able to determine the performance seen by ordinary subscribers from a mix of geographical areas such as urban, sub-urban, as well as rural environments. During the course of the measurement campaign a total of 38 surveys were carried out in 23 countries, covering 84 different networks. In large countries such as the USA, several surveys of the same network were performed in different geographical locations. The total length of all drive routes was about 30000 km. All surveys were conducted during working hours on five consecutive weekdays without the knowledge of the operators. This ‘clandestine’ approach was selected to eliminate the opportunity for operators to ‘tune’ the network for the survey. For brevity sake it is not possible to describe the measurement setup in detail. But it is worth noting that standard multi-slot, class 6, mobiles (Nokia 6220) with local Subscriber Identification Modules were used to experience the performance of local subscribers. Commercially available software was deployed to control the measurement system and the call activity. To enable fair comparison of the results, the same analysis methodology was applied to the data from all surveys. Eight different ‘services’ were investigated, these are: file transfer using the FTP protocol (upload and download of data files of 100 and
SMS success [%]
3.0
98.8
99.5
100.0 100.0
SMS delivery time [s]
70.0
17.1
15.7
14.3
11.4
29.0
88.2
92.0
97.7
100.0
5997.0 126.3
95.4
79.5
61.0
13132 MMS success [%] MMS delivery time [s]
Table 1 displays the results obtained during the measurement campaign using the above-mentioned 16 indicators and five performance values. For example, it can be seen in Table 1 that the GPRS Attach success rate varies greatly between networks. In the best network, 100% of all Attach attempts succeeded. In half of the networks 97.2% of all attempts succeeded, while in the worst network this value was only 25.4%. In the worst 20% of all networks the GPRS Attach success rate was 91.2%, while in the best 20% of all networks the respective value was 98.7%. In terms of GPRS Attach delays, mobiles in the best network are attached to GPRS within 1.2 s. In the worst performing network, the respective value is 7.5 s. When evaluating the results in Table 1, it is useful to bear in mind that both GPRS and EGPRS networks are included in the survey. EGPRS networks benefit from higher residual data rates compared to GPRS systems. This impact would be most noticeable for the throughput or delivery aspects of services such as FTP, HTTP, e-mail and MMS. Issues such as the success rates of all investigated services or the
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delays of GPRS Attach and PDP Context Activation will be less susceptible to the use of GPRS or EGPRS as here only small sets of data are being transferred. The throughput difference between UL FTP and DL FTP is because the mobile can use more TSLs in the DL than in the UL direction. The observed throughput differences between e-mail and FTP are due to the differences in transfer protocol (SMTP against FTP). The most reliable service is SMS. Here the median success rate of all operators is 99.5%. The worst one is MMS, where the corresponding value is just 92.0%. This observation indicates that the higher the technical complexity of delivering a service the lower its reliability. Although not visible from Table 1, in each of the 16 categories a different network displayed the worst performance. This means that although a network might be performing well for one service, its performance for another might be rather poor. For networks that display good performance in one of the investigated services, it is likely that the air-interface is performing well. Hence problems in network-elements associated solely with a particular service are responsible for the observed performance degradation. It can also be seen that the performance of the best networks is rather satisfying. For example, for all services there are networks with a success rate of 100%. However the performance of the worst 20% of networks is normally very poor compared to the other networks. It is believed that poor performance might be due to network specific factors such as the available spectrum. But some of the performance degradation might well be due to planning or implementation mistakes.
Conclusions: GERAN systems can provide packet-data based services very reliably to ordinary subscribers. However, such a reliable service is not provided by all operators of GERAN networks. Large reliability differences exist between networks for all of the investigated services. Similarly there are also quite significant performance differences between the best networks and worst networks in terms of delivery delays and throughput rates. It is believed that the performance of some of the networks can be enhanced via network optimisation. # IEE 2006 Electronics Letters online no: 20063245 doi: 10.1049/el:20063245
10 September 2005
V. Wille and M. Kok (Nokia Networks, Ermine Business Park, Huntingdon, PE28, United Kingdom) E-mail:
[email protected] Reference 1
Halonen, T., Romero, J., and Melero, J.: ‘GSM, GPRS and EDGE performance’ (John Wiley & Sons, 2003, 2nd edn.)
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