1. Feasibility study of IP Multimedia Subsystem(IMS) based Push to Talk over Cellular(PoC) for Public Safety and Security communications By Sanjay Kanti Das Insrtuctor: Lic.Tech. Michael Hall Supervisor: Prof. Sven-Gustav Häggman Master’s Thesis Presentation Espoo,8th of August,2006

2. Acknowledgements  Professor Sven-Gustav Häggman  Lic.Tech. Michael Hall  Parents and friends This Thesis has been done in Communication Laboratory,Dept.of Electrical and Communications Engineering,Helsinki University of Technology(HUT)

3. Agenda Introduction PSS communication requirements What is PoC and Technology behind PoC PoC over GPRS implementations and Challenges Improvement proposals Emergency capacity increase for packet data traffic in GSM/GPRS cell Feasibility study summary Case study: analogue PSS network vs possible PoC over commercial network Conclusions

4. Introduction Public safety professionals rely on PMR networks, most which are analogue Motivation to find an alternative is to save CAPEX and OPEX and benefited from the advanced services Feasibility is analyzed considering the requirement of PSS communication Both day-to-day routine work and emergency situation handling capability are considered Study has done based on technical specification documents and related literature Technical Information and factual data are collected from technical papers, reports and news articles posted in the internet. According to a study in June ’01 by IMS Research

5. PSS communications requirements With time, PSS usage scenarios as well as the requirements of the PSS professionals have changed a lot. In addition to the voice service other types of communication are also required to ease the operation of the PSS professionals in different scenarios Broadly categorized as Interactive voice communication Non-interactive voice communication Interactive data communication Non-interactive data communication A Modern PSS network Telephony Video Phone Video conferencing Push to Talk functionality Group call function Location based services Instant messaging........ PSS network Intranet /Internet access GPS

6. PSS communications requirements continued Resilience of the network Single node failure does not hamper the operation. Power backup &Transmission redundancy Capacity to handle extral load during emergency situation handling Security Nation-wide coverage irrespective of geographical nature of land. Seamless roaming-minimum service interruption time during cell change. Fast call setup time-in sub-second range. Specialized group call functionality Dynamic group formation Late entry Rejoin Priority and pre-emption settings Good voice quality Data communication Interworking with other PLMN, PSTN or ISDN network.

7. What is PoC? Half duplex voice communication that provides 1-to-1 and 1-to-N walkie-talkie type communication. VoIP in cellular network environment RTP, UDP and IP protocols for Media tranport One person can talk at a time and others listen Other participants can request for floor to talk when one’s talk bursts finish Contention of the Right-to-Speak is managed through Floor Control mechanism Receiver- Auto Answer or Manual Answer mode IMS in the core network AMR Payload (Voice Data)RTPUDPIP RTP media packet

8. PoC Architecture UE has the PoC client software, communicates with PoC server over the It interface PoC server responsible for floor control,tear down of session, media duplication and forwarding. IMS core is responsible for routing, charging and finding the called user. IMS gets presence information of a user through Ips interface. GLMS server maintains group and list of PoC users. Core network and Access network elements provide the required connectivity services between UE & PoC server. Is ItIt PoC Client UE ACCESSNETWORKACCESSNETWORK IMS CORE PoC Server Rem ote Netw ork GMLS Presenc e Server In If Ik Im Ips Ipl

9. PoC services One-to-one personal call One-to-many group call Pre-defined group call Ad-hoc group call Instant group chat Dynamic group formation Instant messaging Auto answer and manual answer mode. Personal alert: that tells the called user to call back to the calling user. Presence information of individual group members Access/Reject list etc. Works among different operators PoC Roaming across the boarder Ease of use PoC over GPRS Network User C User D User B

10. PoC over GPRS Northstream study concludes that the GPRS network, if tuned correctly, meets the PoC technical demands According to Northstream study PoC over GPRS is 5 times more efficient that PoC over CS GSM network Efficient use of radio resources Always on GPRS Network SG SN GG SN Radio Access Network IMS based PoC core UEUE Chat Session

11. Challenges of PoC over GPRS network Impact of mibility PSS professionals need to move frequently Cell reselection causes service interruption time from 1-2 seconds to several seconds depending on the channel availability and traffic load of the target cell Incident or overload handling Extra resource are not kept reserved before hand in commercial network During any incident traffic increase drastically CS voice call pre-empted the PS call Situation would be worse in rural areas Setup time PSS communication requires call setup time in the sub-second range Still it is not available RA1 SA1 RA3 SA2 RA2 SA1

12. Challenges continued Delay in speech Best effort GPRS network does not gurantee the end to end QoS Reciepient in congested cell will possibly receive the data packet later and may ask for repetation Which certainly hamper the smooth PSS operation Voice quality Best effort GPRS network does not gurantee contanst bit rate Voice quality can be deteriorated due congestion in the cell or bad radio condition Effect of unicasting Based on Unicasting. PoC server duplicates the data and one copy for each recepient is sent over transport and core network. It will create an extra load to the transport and radio network when PoC user increases. Po C Ser ver Core Netw ork BSC/R NC BTSBTS

13. Improvement Proposals  Radio resource allocation scheme Radio resource allocation exclusively to GPRS PS data traffic for the sake of blocking of CS voice calls To overcome pre-emption by CS voice traffic and reduce delay due to contention for resources. Shows better performance  Use of early media settings in the network  Limiting the number of PoC or packet switched users per PDCH helps to maintain a higher bit rate per user  A jitter buffer at the receiving side can handle small delay variations or jitter caused by the GPRS access network

14. Improvement proposals continued The NACC feature in the PS domain significantly reduces the service interruption time due to cell reselection. The NACC feature is included in 3GPP Release ‘99 and Release 4 The NACC feature is included in 3GPP Release ‘99 and Release 4

15. Emergency Capacity increase in GSM/GPRS cell Intermediate solution to handle overload Assign traffic channel to PS domain by commands from OSS Increase capacity for packet data traffic as well as for PoC traffic blocking CS traffic for the time being. BS C OS S

16. Summary of Technical Feasibility Analysis Key findings in favour of PoC over commercial GSM/GPRS network Radio coverage Data services Interworking with other networks Roaming accross the nation boarder Presence information Easy integration of new IMS based services etc. Improvement Areas: Call setup time Prioritization of PoC traffic Cell change time etc. Acceptable level

17. Case study: Bangaldesh PSS communication depends on over-aged analogue technology Coverage & Capacity: local coverage around police station and wide area coverage only big cities 6 (six) cellular operators and out of them 4 has nation wide coverage Largest operator GrameenPhone(GP) covered almost 88% of the whole country. It has been seen that most police officiers use mobile phone for their personal and official communications.

18. Summary and Conclusions Finally, it is concluded that, given the demanding requirements for public safety and security users, PoC over commercial GSM/GPRS networks needs proper dimensioning and tuning of the access network and some modification in the core network part. Taking into account the suggested measures, PoC over a public network can be a good alternative to a legacy analogue PMR network

19. Thank you! Any questions?