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Delay analysis of PoC service solutions for Public Safety communications over LTE networks DELAY ANALYSIS OF PUSH-TO-TALK OVER CELLULAR (POC) SERVICE SOLUTIONS FOR PUBLIC SAFETY COMMUNICATIONS OVER LTE NETWORKS Author: Chengsui Lu Date: 27 August, 2012 Abstract – In this master thesis, the concept of public safety communication solutions over modern commercial cellular systems is presented, and the delay analysis for Puch-to-Talk over Cellular (PoC) service is provided especially for the LTE and IMS networks. Firstly, the motivations and requirements of public safety communications using commercial cellular technology are studied and introduced. Secondly, the 3GPP IMS-based public safety communication network architecture and the PoC service are described in details. Thirdly, we make a survey of the PoC delay targets for modern emergency communication networks. Finally, the call set-up delay and end to end delay calculations are done by dividing into latency components of each network entities. Our analysis shows that typical call set-up time and end to end delay are within 275 milliseconds and 250 milliseconds respectively, and the mainstream LTE cellular technology can be designed to satisfy the stringent time constraints for public safety purpose, making LTE a promising option for public safety communications. Key words: Public Safety communication networks; delay analysis; LTE; call setup time; end to end latency; IMS. 1/48
Delay analysis of PoC service solutions for Public Safety communications over LTE networks TABLE OF ACRONYMS Acronym Description 3G Thirrd Generation 3GPP 3rd Generation Partnership Project AKA Authentication and Key Agreement AMR Adaptive Multi-Rate APCO Association of Public-safety Communications Officials-International ARPU Average Revenue Per User B3G Beyond 3G BLER Block Error Rate BTS Base Transceiver Station CAI Common Air Interface CAPEX CAPital EXpenditure CDMA Code Division Multiple Access CN Core Network CPC Continuous Packet Connectivity CSCF Call Session Control Function DHS Department of Homeland Security DMO Direct Mode Operation DnD Do-not-Disturb EPC Evolved Packet Core EPS Evolved Packet System ETSI European Telecommunications Standards Institute E-UTRAN Evolved-UMTS Terrestrial Radio Access Network FCC Federal Communications Commission FMO Future Mode of Operation GGSN Gateway GPRS Support Node GLMS Group and List Management Server GoS Grades of Service GoTa Global open Trunking architecture 2/48
Delay analysis of PoC service solutions for Public Safety communications over LTE networks GPRS General packet radio service GSM Global System of Mobile communication H-ARQ Hybrid-Automatic Repeat reQuest HSS Home Subscriber Server HTTP HyperText Transfer Protocol IA Information Assurance I-CSCF Interrogating-Call Session Control Function iDEN integrated Digital Enhanced Network IETF Internet Engineering Task Force IM Instant Messages IMS IP Multimedia Subsystem IP Internet Protocol IP-CAN IP Connectivity Access Network IPSec IP Security ITU International Telecommunications Union LTE Long Term Evolution MBMS Multimedia Broadcast/Multicast Services MESA Mobility for Emergency and Safety Applications MITM Man-In-The-Middle attacks MME Mobility Management Entity MS Mobile Station MTSI Multimedia Telephony Service over IMS NPSTC National Public Safety Telecommunications Council OMA Open Mobile Alliance OPEX OPerating EXpense OSI Open Systems Interconnection PCC Policy and Charging Control P-CSCF Proxy-Call Session Control Function PDA Personal Digital Assistant PDN GW Packet Data Network GateWay PMO Present Mode of Operation 3/48
Delay analysis of PoC service solutions for Public Safety communications over LTE networks PMR Professional Mobile Radio PoC Push to talk over Cellular PS Packet Switch PSS Public Safety and Security PTT Push To Talk PWS Public Warning Systems QCI QoS class identifier QoS Quality of Service RAN Radio Access Network RF Radio Frequency RNC Radio Network Controller RNS Radio Network System RRM Radio Resource Management RTCP Real-time Transport Control Protocol RTP Real-time Transport Protocol RTT Round-Trip Time SA Security Associations SAE System Architecture Evolution S-CSCF Serving-Call Session Control Function SCTP Stream Control Transmission Protocol SGSN Serving GPRS Support Node S-GW Serving GateWay SIB System Information Block SIP Session Initiation Protocol SMS Short Message Service TIA Telecommunications Industry Association TCO Total Cost of Ownership TCP Transmission Control Protocol TETRA TErrestrial TRunked Radio TISPAN Telecommunications and Internet converged Services and Protocols for Advanced Networking TTI Transmission Time Interval 4/48
Delay analysis of PoC service solutions for Public Safety communications over LTE networks UDP User Datagram Protocol UE User Equipment UHF Ultra High Frequency UMTS Universal Mobile Telecommunications System UPSF User Profile Server Function UTRAN UMTS Terrestrial Radio Access Network VHF Very High Frequency VoIP Voice over IP WiFi Wireless Fidelity XDMS XML Document Management Server XML eXtensible Markup Language 5/48
Delay analysis of PoC service solutions for Public Safety communications over LTE networks TABLE OF CONTENTS 1. INTRODUCTION .10 1.1 TECHNOLOGICAL TRENDS IN PUBLIC SAFETY COMMUNICATION NETWORKS .10 1.2 KEY BENEFITS OF ADOPTING MAINSTREAM CELLULAR TECHNOLOGY .11 1.3 CHALLENGES AND OPPORTUNITIES .12 1.4 OBJECTIVES .12 1.5 RELATED WORKS .13 1.6 THESIS OUTLINE.13 2. TECHNICAL REQUIREMENTS.14 2.1 GENERAL REQUIREMENTS .14 2.1.1 Basic and specialized services .14 2.1.2 Network availability .15 2.1.3 Coverage.15 2.1.4 Capacity .15 2.1.5 Interoperability .15 2.1.6 Secure scheme .15 2.1.7 Call setup time .15 2.1.8 Voice quality .15 2.2 POC OVER LTE REQUIREMENTS .16 3. IMS-BASED PUBLIC SAFETY COMMUNICATION NETWORK SOLUTION .17 3.1 OVERVIEW: IMS CORE AND 3GPP IP-CAN .17 3.2 FUNCTIONAL ENTITIES .18 3.2.1 IM Subsystem .18 3.2.2 IP Connectivity Access Network (IP-CAN).18 3.3 IMS APPLICATIONS .19 3.3.1 PoC services .20 3.3.2 PoC architecture .20 3.3.3 PoC protocols .21 3.3.4 PoC procedures.21 4. DELAY ANALYSIS .24 4.1 POC DELAY TARGETS .24 4.1.1 Delay targets in commercial mobile networks .24 4.1.2 Delay targets for public safety communication networks .27 4.2 POC DELAY ASSUMPTIONS .28 4.3 POC DELAY CALCULATIONS .28 6/48
Delay analysis of PoC service solutions for Public Safety communications over LTE networks 4.3.1 Delay components in EPS (E-UTRAN and EPC) .29 4.3.2 Delay components in IMS and Application layer .32 4.3.3 Latencies in session establishment .32 4.3.4 Floor control latencies .36 4.3.5 End to end latencies.37 4.3.6 Delays between different IMS cores .40 4.3.7 Sensitivity analysis .41 4.3.8 Conclusions .44 5. CONCLUSION .45 6. REFERENCES.46 7/48
Delay analysis of PoC service solutions for Public Safety communications over LTE networks LIST OF FIGURES Figure 1.1: Technological trends of Public Safety Communication Networks in initial stage .11 Figure 1.2: Technological trends of Public Safety Communication Networks in future stage .11 Figure 2.1: Technological requirements of PoC over LTE for public safety .16 Figure 3.1: Architecture of the IMS-based Public Safety Communication Network .17 Figure 3.2: PoC service architecture (figure with modifications based on [30]) .20 Figure 3.3: PoC protocol stack .21 Figure 3.4: PoC emergency call scenario .22 Figure 3.5: PoC instant group talk procedure.23 Figure 4.1: PoC early media session establishment procedure .25 Figure 4.2: PoC late media session establishment procedure.26 Figure 4.3: PoC “Right to speak” and “Start to speak” .26 Figure 4.4: The analytic model for PoC delay calculation .28 Figure 4.5: Control plane latency from idle to connected mode [50].29 Figure 4.6: Paging procedures .30 Figure 4.7: User-plane latency .31 Figure 4.8: Session establishment (early media) delay analysis .33 Figure 4.9: Session establishment (late media) delay analysis.34 Figure 4.10: Group session establishment (early media) delay analysis .35 Figure 4.11: Main delay components in session establishments .36 Figure 4.12: Floor changeover delay analysis .37 Figure 4.13: End to end delay analysis.37 Figure 4.14: Mouth to ear delay analysis .38 Figure 4.15: Turnaround Time analysis .39 Figure 4.16: Session establishment (early media) between different IMS cores .40 Figure 4.17: Sensitivity analysis on the LTE user plane latency .42 Figure 4.18: Sensitivity analysis on the radio C-plane latencies .43 Figure 4.19: Sensitivity analysis on the IMS/Server/Client processing latency.44 8/48
Delay analysis of PoC service solutions for Public Safety communications over LTE networks LIST OF TABLES Table 4.1: PoC delay target values for commercial mobile networks .24 Table 4.2: Delay target values for public safety networks .27 Table 4.3: LTE U-plane transfer delay budget and QCI characteristics, extracted from [54] .31 Table 4.4: Delay components in LTE (E-UTRAN and EPC) .32 Table 4.5: Delay components in IMS and Application layer .32 Table 4.6: Session establishment (early media) delay analysis .33 Table 4.7: Session establishment (late media) delay analysis .34 Table 4.8: Group session establishment (early media) delay analysis .35 Table 4.9: Main delay components in session establishments .36 Table 4.10: Floor changeover delay analysis .37 Table 4.11: End to end delay analysis .37 Table 4.12: Mouth to ear delay analysis.38 Table 4.13: Turnaround Time analysis.39 Table 4.14: Session establishment (early media) between different IMS cores .41 9/48
Delay analysis of PoC service solutions for Public Safety communications over LTE networks 1. Introduction 1.1 Technological trends in Public Safety Communication Networks Public Safety and Security (PSS) services, including fire brigades, police forces, ambulance services, coastguards, etcetera, are a prior subject for citizens and governments. Well functioning communication solutions are an essential element for these public safety agencies to coordinate resources with their command centers as well as other PSS users in the field both during daily routine work and in emergencies. Experience has proven that the mandatory services and facilities required by public safety organizations can only be partially provided on existing commercial communications systems, which even often crash under the burden when catastrophe strikes. Therefore, many agencies and the governments have been investing significant resources in building and funding reliable first responder communication networks to be better prepared. Traditionally public safety entities depend on the analog Professional Mobile Radio (PMR) systems, that use radio-broadcast techniques from short wave to Very High Frequency (VHF), Ultra High Frequency (UHF) and microwave for basic group communication. These systems often only focus on voice communication, and are found to be incapable to keep pace with increasing demands of new features and services, such as transmitting fingerprints and videos of crime scenes. Moreover, the legacy analogue PMR networks have the issue of interoperability as identified in several studies [1],[2] from USA Department of Homeland Security (DHS), because of the incompatibility among agencies, vendors and techniques. In a large fire or disaster, different public safety sectors may be forced to use hand signals or delivering messages as the old Greeks would, on foot. Today many public safety networks evolve to sophisticated digital PMR systems, for example TErrestrial TRunked Radio (TETRA) [3], Association of Public-Safety Communications Officials-International Project 25 (APCO P25) [4], TETRAPOL [5], integrated Digital Enhanced Network (iDEN) [6], Global open Trunking architecture (GoTa) [7], etc. Digital technology helps to improve the quality and security of communication, however, the main drawback of this approach is that, the relatively small and closed market leads to far too high capital and operational expenditure, and short on advanced functionalities due to the increasing complexity of public safety tasks to face nature disasters and terrorist attacks [8] [9], for instance, surveillance video and high-speed data transfers. Modern commercial cellular networks has witnessed an explosive growth of high spectrum efficiency, reduced latency, and improved prioritization of users. As a consequence, currently mobile communication systems have in the past few years been revisited as an option for public safety organizations in many countries to reduce the cost per subscriber and allow improved services [10][15]. Unfortunately, earlier studies [13][14] conclude that the fundamental requirements of low delays and high system capacity for mission critical communities are not met in Universal Mobile Telecommunications System (UMTS) networks. Following the mainstream technology developments of the consumer market, most of the difficulties for public safety communication networks are foreseen to be sorted out in the infrastructure of 3rd Generation Partnership Project (3GPP) Internet Protocol (IP) Multimedia Subsystem (IMS) [16] on top of 3G (Third Generation) / Beyond 3G (B3G) Radio Access Network (RAN). Furthermore, the Federal Communications Commission (FCC) in USA has already launched proceedings on the congressionally mandated National Broadband Plan since 2010, adopting 3G/B3G technologies to boost capabilities for commercial consumers and homeland securities. Recently, National Public Safety Telecommunications Council (NPSTC) [17] in USA provided a starting point from the definition and requirements to support mission critical voice with the latest B3G wireless technology of Long Term Evolution (LTE) [18]. In the rising trend of public safety communication networks, open standardized solutions are preferred, while proprietary PMR systems could still be considered in an early stage. As illustrated conceptually in figure 1.1, LTE broadband network can be deployed for data-intensive services to complement rather than to replace legacy voice-intensive PMR systems in the initial phase. Progressively, the voice-intensive services would be migrated smoothly from previous PMRs to the IP-based networks, 10/48
Delay analysis of PoC service solutions for Public Safety communications over LTE networks as shown in figure 1.2, where group communications are deployed on IP-based services platforms and supported over LTE connectivity plus IP-based service control functions provided by IMS. Figure 1.1: Technological trends of Public Safety Communication Networks in initial stage Figure 1.2: Technological trends of Public Safety Communication Networks in future stage In an envisioned future, IMS-based public safety communication solution is promising to be deployed to minimize the Total Cost of Ownership (TCO) of the corporate and government entities, and provide advanced functionality, while maintaining the priority features and demanded security levels. 1.2 Key benefits of adopting mainstream cellular technology The IMS-based group communication network studied in this thesis will benefit the public safety users and system operators in a number of ways: · Utilize mainstream cellular technology and packet switched transmission [10]. The new system uses 3GPP IMS and LTE infrastructure, which is the most spectrally efficient at present, and their global open standards vastly help to increase the interoperability with other parallel networks. As for the long term, it is designed to migrate with commercial mobile networks as well. · Capture and retain profitable corporate customers, and driven by the professionals. In the same manner, the IMS-based group communication system is in favour to be adopted by local, regional, and county governments [11], and utilities and industries, e.g. transit, airports, petroleum, and chemical companies that rely on mission critical communications and interoperate with public safety departments in emergencies. They are able to participate in 3GPP standardization process, defining and prioritizing user requirements for possible standards. Normally the enterprise customer on average makes a higher monthly Average Revenue Per User (ARPU) than the general ones. · Offer high performance group communication and a variety of features and services in the new PMR networks. Premium features are supported as trunked operation in high-density locations by enabling resource efficiencies [14]. Besides, conventional operation serves cost-effective communications in 11/48
Delay analysis of PoC service solutions for Public Safety communications over LTE networks low-density and routine cases. Communications could be in clear form or secured with encryption, key management, and mutual authentication. · Capitalize on the complete set of investments of edge and core applications already made. On one hand, modern commercial wireless networks have the key assets, i.e. network, spectrum and backoffice, to deliver the IMS-based group radio solution. On the other hand, it provides Common Air Interfaces (CAI) to be compatible and coexist with legacy PMR networks [11]. Hence the proposed system offers an excellent way to make use of these resources and efforts to meet public safety users. · Leverage a combined strength of cellular and PMR vendors. 70 years of private group radio’s experience and over one hundred years’ development of commercial equipment manufacturers and service providers in the marketplace add to a large portfolio of products and competitions, which continue to enhance technology evolution and innovation. 1.3 Challenges and opportunities Correspondingly, the next generation public safety communication networks have the following challenges to overcome: (1) Service availability. As the most important point, it is a critical task for the civil wireless infrastructure to ensure a high level of “five nines”, that is 99.999% probability of Quality of Service (QoS), service continuation and network reliability, which is consisted of equipment failure, equipment redundancy, bandwidth reservation, network segmentation and bandwidth optimization. (2) Mobility of forces [14]. When the public safety personnel quickly move to a new mission site, fluctuating communication load must be supported as for the whole perspective. (3) Advanced services. Increasingly sophisticated functionality should be provided [11], e.g. call pre-emption, group video calls, Public Warning Systems (PWS), data collaboration (share maps or tactical data), and the network is supposed to easily integrate new and evolving services. (4) Network security. Due to the sensitive nature of government and defence communications, specific layer of Information Assurance (IA) is strictly stipulated to be integrated [10], with respect to availability, integrity, authentication, confidentiality, and non-repudiation. (5) Smooth updating. Particular public safety segments need the flexibility to keep the existing PMR systems and choose its own technology and economic phase to migrate from Present Mode of Operation (PMO) to Future Mode of Operation (FMO). In addition to the newly proposed IMS-based group radio technology itself, the external market presents unprecedented opportunities at the threshold of this new era: · Save PMR network cost of ownership [10], [15]. Public safety officials are looking for ways to take place of the rising CAPital EXpenditure (CAPEX) and OPerating EXpense (OPEX) to maintain its trunked system, especially in the current financial climate. · Take advantage of the evolutionary power of cellular technology, which turns to be a hot topic in today’s wireless consumer market, and is future proved with continuous improvements of features and services [11], [14]. · Exploit the development of handset diversity. Commercial portable devices already supply a wide variety of data applications with user friendly interfaces, and directly support the advanced services for public safety forces. 1.4 Objectives The objective of this thesis is to analyze the feasibility of applying IMS-based mobile broadband networks to provide tactical group voice services for public safety purpose. More specifically, we contribute to: · outline the concept of IMS-based public safety communication network using commercial cellular technology, and describe its Push To Talk (PTT) over Cellular (PoC) solution; · evaluate the performance of the PoC over 3G/B3G RANs, especially on the aspect of the delay requirements analysis of PoC over LTE. 12/48
Delay analysis of PoC service solutions for Public Safety communications over LTE networks 1.5 Related works For 2G telecommunications, TETRA Association analyzed the potential of GPRS and Code Division Multiple Access (CDMA) networks for mission critical use [13]. They can support cost effective radio coverage for digital services in densely populated areas. But 2G technologies have the problem of 100% rural area coverage, none Direct Mode Operation (DMO) or base station fallback for network outages, slow set up time of VoIP protocols, lack of efficient priority and pre-emptive mechanisms. The study concludes that commercial networks have not been yet considered being properly able to serve the law enforcement user segments by that time. Afterwards, IMS-based PoC service on top of GPRS system for public safety purpose is further scrutinized [14]. This solution still has difficulties to fulfill the needs about call set up time, priority and pre-emptive options. Nevertheless, it provides sufficient performance in the advanced aspects of data/video applications, group call functionality, roaming, interoperability, and user friendliness. With minor modification, some requirements of coverage, voice quality, operation continuity, network resilience, security and privacy may meet the acceptable level. Moreover, it is observed that most of the challenges are caused by the GPRS access network. This study already points out, by means of proper radio network dimensioning and network upgrades, that IMS-based PoC over commercial mobile systems could become a good alternative to the legacy analogue PMR network. In 3G and B3G times, IMS PoC with UMTS / CDMA2000 [11], [19] and HSPA / LTE [10], [15] come with premium features and higher performances than before. Low latency, extended coverage, talk around supports, scalable architecture, well developed priority and pre-emptive schemes are achieved to solve the remaining issues from previous cellular networks. Moreover, novel concepts such as link adaptation and MBMS (Multimedia Broadcast/Multicast Services) are introduced to improve the system capacity. [15] examines the capacity limit of a LTE network, and optimizes the speech codec to further increase its capacity. Therefore, the ne
Delay analysis of PoC service solutions for Public Safety communications over LTE networks 1/48 DELAY ANALYSIS OF PUSH-TO-TALK OVER CELLULAR (P OC) SERVICE SOLUTIONS FOR PUBLIC SAFETY COMMUNICATIONS OVER LTE NETWORKS Author: Chengsui Lu Date: 27 August, 2012 Abstract - In this master thesis, the concept of public safety communication solutions over modern
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