3G mobile service provider traffic analysis using KPIs of CSSR and CDR in Circuit Switched and Packet Switched network

Prepared by: Almontaser bellah faisal Mohamed hussien

almontaserbellahhussien@gmail.com

Abstract The Next Generation Wireless Networks (NGWN) will be

heterogeneous in nature where the different Radio Access Technologies (RATs) operate together. The most important feature of 3G mobile cellular network is introduction of voice data integrated service under multilayered cell environment to support overflow traffic of lower layered cells by upper ones.

This paper first introduces the architecture of general 3G communication system in both parts; packet switched (PS) and circuit switched (CS) networks and then applies statistical analysis to Key Performance Indicators (KPI) monitored from network entities in PS and CS network to guide the long term capacity planning and better coverage for the network by introducing a 3G network optimization cycle phases to analysis the problems from the KPIs and propose the suitable solution for these problems, our methodology is applied to a case study of a cellular communications service provider company report for UTRAN performance in a month. This UTRAN consist of two RNCs and 622 NodeBs. This report is proposed as an example of this case study and it's generated according to the proper UTRAN deployment company formulas; which is Huawei in this case.

Introduction At present, dissimilar wireless access networks including 2.5G,3G,

Bluetooth, WLAN and Wi-MAX coexist in the mobile computing environment, where each of these Radio access technologies offer complementary characteristics and features in terms of its coverage area, data rate, resource utilization and power consumption. With all these there are constant improvements in the existing technologies offering better performance at lesser cost [1]. This is beneficial in both the end users and service provider's perspective.

In the service provider part these user's calls is the most important thing in which represent the traffic of the network, traffic in a telecommunications network is traditionally classified as voice and data but the present technology advances promise and video services in the near future over broadband channels[2]. Moreover land wire communications networks will integrate new mobile services. Recently

great attention has been paid to these mobile services, especially in cellular systems which will soon cover urban areas.

This traffic is moving from simple voice and SMS to multimedia. UMTS can bring more attractive applications and better experience to subscribers, and provide a higher efficient network and faster roll-out capability of new services to operators.

The instantaneous traffic intensity in a pool of resources is the number of busy resources at a given instant of time. The pool of resources may be a group of servers, e.g. trunk lines. The statistical moments of the traffic intensity may be calculated for a given period of time.

Erlang is the basic unit of telecom traffic intensity. Strictly speaking, an erlang is what mathematicians call a "dimensionless unit," representing continuous use of one circuit. However, since a single circuit used continuously carries 60 minutes of calling in one hour, one erlang is usually defined as 60 minutes of traffic. If you receive 300 two-minute calls in an hour, then you received 600 minutes, or 10 erlangs of traffic in that hour.

1. General 3G communication system architecture

Packet Switched (PS) domain and Circuit Switched Domain compose the Core Network (CN) of a 2G Global Systems for Mobile Communications (GSM) or a 3G UMTS network. Whether in 2G or 3G phase, the CN plays an essential role in the mobile network system to provide such important capabilities as mobility management, call and session control, switching and routing, charging and billing, and security protection.

In R99 version, the first version of 3G UMTS network, the CN domain still consists of the same network entities (NE) and the same network architecture as that in GSM phase. However, there is a change in the circuit switched domain of R4, the second version of UMTS, which supports a networking mode where bearer is separated from control. Meanwhile multiple bearer modes such as ATM/IP/TDM are supported by CN. Consequently the Mobile Switching Center (MSC) in GSM/UMTS R99 is split into two NEs: MSC Server (MSS) and Media Gateway (MGW). We should note that no changes happen in packet switched domain from R99 to R4 except for a new Iu-PS interface which is used to connect PS domain with 3G radio access network (RAN).

Fig.1 UMTS topology CN of PS and CS domain

The CN in UMTS is logically classified into the circuit switched domain (CS) and packet switched domain (PS). The CS domain includes such logical NEs as MSC Server, MGW, Visitor Location Register (VLR) integrated in MSC Server physically, Home Location Register (HLR), Authentication Center (AUC), and Equipment Identity Register (EIR). The packet switched domain (PS) includes Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). More specifically, PS domain consists of data service NEs: SGSN and GGSN as well as auxiliary NEs like Charging Gateway (CG), Border Gateway (BG) and Domain Name System Server (DNS), and different service platforms attached to PS domain. Figure 1 displays the topology of UMTS CN with the logical NEs mentioned above.

SGSN is responsible for the delivery of data packets from and to MSs within its serving area. Its tasks include packet routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions. Its interfaces include Iu-Ps interface connecting to RNC, Gn/Gp interface to GGSN, Gr interface to HLR, Gs interface to MSC Server or MSC, Gd interface to Short Message Center (SMC), and Ga interface to Charging Gateway.

GGSN is a gateway between UMTS PS/GPRS network and external data networks (e.g. Internet). It performs such functions as routing and data encapsulation between a MS and external data network, security control, network access control and network management. From UMTS PS/GPRS aspect, a MS selects a GGSN as its routing device between itself and external network in the activation process of PDP

context in which Access Point Name (APN) defines the access point to destination data network. From external data network aspect, GGSN is a router that can address all MS IPs in UMTS PS/GPRS network. GGSN provides Gc interface to connect with HLR, Gn/Gp interface with SGSN, Gi interface with external data networks, and Ga interface with CG.

Charging Gateway is the billing unit for PS domain. Sometimes coupled together with SGSN, it collects, merges, filters and stores the original Call Detail Record (CDR) from SGSN and communicates with billing center, and then transfers sorted CDR to billing center.

HLR is responsible for storing, updating, revising or deleting subscriber related information, covering the basic service subscription information, supplementary service subscription information and location information of subscribers. In addition, it also implements the function of subscriber security management. From physical connection aspect, HLR provides D interface to connect with VLR in MSC Server, C interface to connect with MSC Server or MSC in GSM CN, Gr interface with SGSN, and Gc interface with GGSN. The type of signaling message delivered from and to HLR is Mobile Application Part (MAP) [5].

In UMTS circuit switched domain, MSC Server is a functional entity that implements mobile call service, mobility management, handover, and other supplementary services. Due to the philosophy of separation of control function from bearer function in UMTS CN, it is actually a controller of MGW to establish call routes between Mobile Stations (MS) via Mc interface. MSC Server also physically integrates with a VLR to hold subscriber's data. MSC Server provides the optional Gs interface with SGSN.

In addition, a MGW in a UMTS implements bearer processing functions between different networks. It implements UMTS voice communication, multimedia service, CS domain data service, and interworking between PSTN and UMTS CN and between GSM CN and UMTS CN. MGW provides Iu-CS interface to connect with the Radio Network Controller (RNC) in the Radio Access Network (RAN), Nb interfaces with its peer MGW, E interfaces with 2G MSC, Mc interfaces with MSC Server, A interface with BSC, and Ai interface with Public Switched Telephone Network (PSTN)[5].

2. Huawei solutions for 3G networks:

Huawei SingleRAN is a radio access network (RAN) technology offered by Huawei that allows mobile telecommunications operators to support multiple mobile communications standards and wireless

telephone services on a single network[1]. The technology incorporates a software-defined radio device, and is designed with a consolidated set of hardware components, allowing operators to purchase, operate and maintain a single telecommunications network and set of equipment, while supporting multiple mobile communications standards.[2]

High Speed Packet Access (HSPA) is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), that extends and improves the performance of existing 3rd generation mobile telecommunication networks utilizing the WCDMA protocols[3]. A further improved 3GPP standard, Evolved HSPA (also known as HSPA+), was released late in 2008 with subsequent worldwide adoption beginning in 2010. The newer standard allows bit-rates to reach as high as 337 Mbit/s in the downlink and 34 Mbit/s in the uplink. However, these speeds are rarely achieved in practice. [4]

With the deployment of HSDPA, much more transmission bandwidth is required. In order to meet the customer's requirements to reduce the cost of transmission with the same quality, Huawei provides a Hybrid IP transmission solution with the principle that voice and other services demanding conversational QoS are carried on high QoS network (eg. E1) and Best Effort packet data services are carried on low QoS network (eg. ADSL). It is also a stepping stone to All IP RAN solution.

Fig.2 Huawei hybrid IP transmission solution

The Radio Network Controller (or RNC) is a governing element in the UMTS radio access network (UTRAN) and is responsible for controlling the Node Bs that are connected to it. The RNC carries out radio resource management, some of the mobility management functions and is the point where encryption is done before user data is sent to and from the mobile. The RNC connects to the Circuit Switched Core Network through Media Gateway (MGW) and to the SGSN (Serving GPRS Support Node) in the Packet Switched Core Network.

Call admission control is one of the radio resource management technique plays instrumental role in ensure the desired QoS to the users

working on different applications which have diversified QoS requirements from the wireless networks.

3. Key Performance Indicators KPIs

Key Performance Indicators (KPIs) are a valuable tool for improving overall business operations. The problem is that somewhere along the line the burden imparted by gathering and compiling month-end KPIs has become greater than the value these sometimes "outdated" numbers represent. How much effort, custom coding, and cost must go into compiling and calculating these measures?

Successful KPI implementation depends on the organization's ability to quickly gather and distribute this key business information without becoming beholden to large, complex, relational databases and applications. Traditional systems can't provide real-time information and require far too much effort and money. KPIs should work for the business without requiring that half the entire organization work for groups that make, maintain, and feed these KPI systems.

Key performance indicators (KPIs) in GSM, UMTS, HSPA and LTE are defined through the definition and measurement of key parameters of input and output of internal network system and/or maintenance & operation progress of mobile network operations.

Key Performance Indicators are a set of quantifiable measures used in GSM, UMTS, HSPA, and LTE networks to gauge or compare performance in terms of meeting mobile network's strategic and operational goals. KPIs vary between management, marketing, operations and network engineering people depending on their priorities, perspectives or performance criteria sometimes referred to as "key success indicators (KSI)".

Fig.3 Huawei 3G KPIs Architecture

3.1. Huawei RAN KPIs

As purposed in this document is to describe the RAN KPI performance monitoring and analysis of problems that bad KPI values indicate. The following analysis contains a list of the most common KPIs used in Huawei networks. These KPIs are monitored constantly. When the value of a KPI goes below the defined threshold, then detailed analysis should be performed in order to identify the reasons of this deterioration. Once the reasons are found, proper solutions will be proposed and implemented.

This document focuses more in the analysis of failure causes rather than the KPI monitoring itself. The most common use cases for monitoring and analysis of bad KPI values are presented for 3G RAN.

3.1.1. "3G" Performance Analysis Use Cases

We had choose some of cases that are available to study from the report, these cases are:

o Low Call Setup Success Rate for Voice o Low Call Setup Success Rate for PS o High Call Drop Rate for AMR o High Call Drop Rate for PS o Low HSUPA Throughput

3.1.2. General Methodology:

1. Define RAN KPI class required (Accessibility, Retainability, Mobility, Resource Usage).

2. Define KPI per service (AMR, Video Call, R99 PS, HSDPA,HSUPA).

3. Define KPI formulas.

4. Define target or guaranteed KPI values.

5. Assess weekly average PLMN/RNC KPI performance in order to identify KPIs below target.

6. Assess RNC/Area level performance in order to check if bad performance occurs across network or only in specific areas.

7. Analyze bad performing KPIs in cell level in order to identify failure causes.

8. Use TopN cell approach to identify the worst performers. Identify top 20 worst cells.

9. Look at failure distribution in network topology (urban, rural, motorway, RNC border, etc.).

10. Propose solution to improve KPI value.

UTRAN KPI analysis is a major method for RAN maintenance engineers and network optimization engineers to evaluate network performance. Comparing with drive tests, call detail logs, and alarms, KPI analysis can be used to monitor network operation directly and conveniently. To better locate network problems and optimize network KPI, abnormal indices, call detail logs, tracked messages, and drive tests can be used together.

4. RAB & RRC requests:

In evaluation or diagnosing network KPI performance, RAB and RRC are two of the most important concepts because they are responsible for all the negotiation involved in those calls.

Fig.4 RRC request establishment.

- RRC setup procedure is the process that establishes the L3 connection between UE and RNC that is used for signaling traffic only.

- After RNC receives the RRC CONNECTION REQUEST, processes it and allocates relevant resources on L1, L2 and L3 of the air interface for this signaling connection.

- The RNC notifies the UE for the prepared configuration with the RRC CONNECTION SETUP message.

- The UE reports its capabilities to the RNC with the RRC CONNECTION SETUP COMPLETE.

Fig.5 RAB request establishment.

- RAB setup procedure is the process that establishes the higher-layer connection between UE and CN that is used to transfer the user data only (not signaling).

- When the RNC receives the RAB ASSIGNMENT REQUEST allocates the necessary resources for the requested service, after successful call admission. Resources include Codes, CE, Power, IUB bandwidth.

- Then the RB is setup which is the UTRAN part of the RAB. - Upon successful completion of the RB setup, the RNC responds to

the CN with the RAB ASSIGNMET RESPOND message.

Call Drop Rate:

The Call Drop Rate (CDR) is the fraction of the telephone calls which, due to technical reasons, were cut off before the speaking parties had finished their conversation and before one of them had hung up (dropped calls), this fraction is usually measured as a percentage of all calls.

This KPI describes the ratio of RAB release requests related to the number of successful RAB establishment (per CS/PS domain). Drops are derived from "IU Release Request" and "RAB Release Request" messages sent from UTRAN to the CN as calculated by the formula:

Type = Є {Conv, Strm, Intact, Bgrd}.

RAB.SuccEstabPSNoQueuing: No. of successfully established RABs for PS domain in which a queuing process has not been involved.

RAB.SuccEstabCSNoQueuing: No. of successfully established RABs for CS domain in which a queuing process has not been involved.

RAB.SuccEstabPSQueuing: No. of successfully established RABs for PS domain in which a queuing process has been involved.

RAB.SuccEstabCSQueuing: No. of successfully established RABs for CS domain in which a queuing process has been involved.

RAB.RelReqPS: No. of RABs release requests to release UTRAN for PS domain.

RAB.RelReqCS: No. of RABs release requests to release UTRAN for CS domain.

RAB.NbrIuRelReqCS: Number of RAB related to the Iu release request for CS domain.

RAB.NbrIuRelReqPS: Number of RAB related to the Iu release request for PS domain.

This KPI reflects the user (UE) point of view, since the user may complain about a connection which is released unexpectedly.

Call Setup Success Rate:

The Call Set up Success Rate (CSSR) is one of the most important Key Performance Indicators (KPIs) used by all mobile operators. The CSSR in general is a term in telecommunications denoting the fraction of the attempts to make a call which result in a connection to the dialed number. However there is no standard measurement possible for this parameter. Therefore the different operators can measure it differently.

This KPI describes the ratio of successful call establishments. It is based on the Successful RRC Connection Establishment Rate for call setup purposes and the RAB Establishment Success Rate for all RAB types. Both KPIs are multiplied. Since RRC counters are measured per cell object, the sum over all cells within one RNC needs to be built, in order to get this rate on RNC level.

Cause: - Originating Conversational Call. - Originating Streaming Call. - Originating Interactive Call. - Originating Background Call. - Terminating Conversational Call. - Terminating Streaming Call. - Terminating Interactive Call. - Terminating Background Call.

RRC.AttConnEstab: No. of RRC connection establishment attempts for each establishment cause.

RRC.SuccConnEstab: No. of successful RRC establishments for each establishment cause.

RabEstabSR: RAB establishment success rate, This KPI describes the ratio of all successful RAB establishments related to the total number of RAB establishment attempts.

RAB.AttEstabCS = No. of requested RAB in establishment attempts for CS domain. RAB.AttEstabPS = No. of requested RAB in establishment attempts for PS domain. Network KPI parameters Optimization methodology:

Parameter optimization is an important step after RF Optimization. It improves service quality and utilization of network resources; also it's a

complicated procedure and needs parameter and algorithm knowledge, but when combined with other optimization activities makes network better.

Fig.6 KPI analysis optimization cycle flowchart

Related work:

The WCDMA based 3G cellular standards have a great flexibility and a variety of logical and transport channels defined for different types of traffic classes, An access control protocol was proposed for an integrated voice, video and non real-time data traffic on the forward link (cell-site to mobile). The QoS of voice for mobile users in the mixed traffic environment was estimated in [6].

The data services in a third generation mobile telecommunication networks characterize the mix of several traffic types for capacity and quality of service (QoS) planning. The analysis of QoS parameters of a mobile network, such as channel occupation time, handoff, new call blocking probabilities and traffic in Erlangs were described in [7].

In [8] the performance of three video traffic models in predicting the number of data packets that were scheduled at the next time slot was discussed.

In [9] the performance of the dedicated channel for WWW traffic was investigated. Performance of the UMTS MAC on dedicated channel

for web traffic had been studied through simulation models in terms of throughput, transfer delay, collision probability.

The results were compared with the performance obtained by deploying a scheduling scheme based on weight. The scheme was simulated with different number of users. The results showed that the scheme improved the system capacity while maintaining the acceptable end-to-end delay.

Results:

Fig.7 CS traffic in Erlang

Fig.8 CS CSSR rate vs CDR rate

Fig.9 PS CSSR rate vs DCR rate

Fig.10 HSPA throughput (MB)

Conclusion:

From these results analysis of pad KPI is done and the following procedure summary for causes probabilities and KPI optimizations are suggested for better network performance:

Call drop is a Radio Network KPI in Retainability KPIs category

Causes: Poor coverage, High interference, Poor UL coverage, Poor dominance, Pilot pollution, Missing neighbors and Fast change of RF conditions usually causes drop calls, e.g. turning a corner. Optimizations:

- Scrambling code planning adjustment - System/handover parameter tuning (Intra-freq, Inter-RAT) - Neighbors list optimization - RF optimization

Pilot pollution optimizations: - Antenna adjustment (e.g. azimuth or down tilt). - Pilot power optimization

Call Setup Success Rate is a Radio Network KPI in Accessibility

KPIs category .

Increasing the call setup success rate as much as practical and affordable In mobile networks this is achieved by improving radio coverage, expanding the capacity of the network and optimizing the performance of its elements, all of which may require considerable effort and significant investments on the part of the network operator. Causes and optimizations:

- Transmission problem: following counters indicate transmission issue on Iub interface; check relative alarms to identify faults on the transmission path or the transmission boards of RNC/NodeB.

- Radio resource congestion: following counters indicate lack of radio resources or Iub bandwidth. Check the Admission Control thresholds. Take appropriate measures to relieve congestion, e.g. activate LDR (Load Reshuffling), OLC (Overload Control) algorithms, and to increase capacity.

- RF problem: following counter indicate failure due to RF issue. Check coverage in the failure points. Check if most failures occur in cell border (most probably they are). Check FACH power. Check DL interference in the cell: is there a pilot pollution issue? Check UL interference in the cell.

- RNL related problem: following counters indicate that the failure is due to a RNL (Radio Network Layer) procedure problem; includes congestion counters.

- Congestion problem: following counters indicate lack of radio recourses or Iub bandwidth. Check the Admission Control thresholds. Take appropriate measures to relieve congestion, e.g. activate LDR, OLC algorithms, and to increase capacity.

References

[1] Wikipedia (2014) Huawei SingleRAN, Available at: http://en.wikipedia.org/wiki/Huawei_SingleRAN (Accessed: 24th December 2014).

[2] Huawei.com "How do you suit all needs with one simple solution?" Huawei. Retrieved 21 October 2011. http://www.huawei.com/ilink/en/solutions/expand-broadband/HW_077174

[3] 3GPP TS 25.306 version 11.8.0 Release 11 "Universal Mobile Telecommunications System (UMTS); UE Radio Access capabilities". ETSI. January 2014. Retrieved March 4, 2014.

[4] Ei Ko Sei Del. "Technology of High Speed Packet Access ( HSPA)"(white paper). 2008.

[5] Ye Ouyang and M. Hosein Fallah. "An Analysis of Traffic and Throughput for UMTS Packet Core Networks" Howe School of Technology Management, Stevens Institute of Technology, NJ, USA,(2012).

[6] N. Sulaiman, R. Carrasco and G. Chester, "Estimating Quality of Service of Mixed Traffic in 3G Networks", International Conference on Intelligent and Advanced Systems, Vol. No. 1, pp. 427-429, 2007.

[7] Aloizio P Silva, Geraldo R. Mateus, "Performance Analysis for Data Service in 3G Network", Vol. No 3 pp. 1-27, 2003.

[8] Yat Hong Chan et.al, "Traffic Prediction Based Access Control Using Different Video Traffic Models in 3G CDMA High Speed Data Networks," School of Engineering Science Simon Fraser University, ISBN:1-59593-306-9, 2006.

[9] Munju Sarvugyu, Ratnam V. Raju Kumar, "Performance Analysis of the UMTS system for web traffic over dedicated channels", Department of Electrical Communication Engineering, pp. 414417, 2005.

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