Push To Talk CDMA2000® 1X Network Planning and Dimensioning

Dave Anderson, Caroline Chan Nortel Networks

PTT Network Planning and Dimensioning

PG 1 What is Push-To-Talk

• Is typically a Voice over IP data call in a CDMA2000® 1X network • Ideally uses FCH only, no SCH • Is an ‘always on’ PPP session between the terminal and PDSN • Is a group call with 1 person talking, multiple people listening • Phone or Server may buffer early speech to improve call set up latency perception. • Is a data application that runs transparently on CDMA2000® 1X infrastructure • PTT implementation should minimizes the impact on the underlying network

PG 2 PTT Network Planning and Dimensioning Example PTT functionality

MSC / HLR

Talker PTT BSC PDSN / Server FA Router WAN

Mobile on power up creates PPP session for PTT NAI

Mobile registers user id to IP mapping on PTT server via SIP

User Pushes to Talk, Dormant-to-active transition

VoIP traffic sent from originator to PTT server Group

Server replicates packets and sends to all group members

Group receivers go network initiated dormant to active

PG 3 PTT Network Planning and Dimensioning Evolution of Wireless Data Planning

• Voice on Wireless evolved over each technology introduction – Subscribers, Call profile, traffic – BHCA drove equipment demand planning • Data Evolution over Wireless – Circuit switched data mostly until CDMA2000® 1X – SMS – Voice centric evolution to data • Packet Data – What is a typical application usage model ? – Is there an Erlang like equivalent to plan networks ? – How does the application usage model impact each node in the wireless data network ? • Nortel Networks developing / Evolving techniques for data traffic over wireless – Common equipment supports voice and or Data – Optimal solution for range of applications / subscriber usage – Adapting processes, tools, to capture changing service offerings to become more data centric

PG 4 PTT Network Planning and Dimensioning CDMA2000® 1X End to End – Provisioning PTT

MSC / HLR QOSPI PTT Server BSC PDSN / Router FA Router WAN HA Router Internet

• • BSC resource PDSN settings capacity provisioning • PPP duration • MIP • RRM settings • Timers and • WAN throughput • PPP idle timeout •Registration • BTS provisioning Parameter (SCH • PTT Domain •Timers PTT Server thresholds) definition • Addressing (NAT) • Scalability

Dimension-able Network Elements relevant to any data application

PG 5 PTT Network Planning and Dimensioning Push to Talk - Key usage parameters & call model attributes:

• Average Busy Hour PTT originations per subscriber excluding Presence Update or SIP Registration

• Average number of parties, including the originator, per PTT call

• Frequency of Presence Update

• Percentage of PTT subscribers will make one transition from a PTT session to a “normal” data session and back to a PTT session in a busy hour.

• Average Fundamental Channel (FCH) hold time for the PTT presence update message

• PPP session setup and SIP registration call hold time upon power up

PG 6 PTT Network Planning and Dimensioning PTT attributes: Network planning

• Uses the CDMA2000® 1X data channel: VoIP approx: 6-8 kbps – WAN network throughput needs to be dimensioned but is relatively minor • Group size is a key attribute. Has multiplier effect on – IP traffic volume • Wan throughput • BSC throughput • backhaul – BHCA (dormant to active) • MSC capacity • Paging Channel capacity • BSC control node capacity

Presence / STUN frequency – Determines additional hold time of resources and BHCA

PG 7 PTT Network Planning and Dimensioning PTT Group Size Air Interface capacity

2-party PTT Call (from perspective of User 1)

User 2 talks VAF = 1/2 Forward F,2 link Listen Listen Listen

User 1 talks Reverse VAFR,2 = 1/2 link Talk Talk Talk

Fwd. VAF increases 3-party PTT Call (from perspective of User 1)

User 2 talks User 3 talks VAF = 2/3 Forward F,3 link Listen Listen Listen Listen

User 1 talks Reverse VAFR,3 = 1/3 link Talk Talk

PG 8 PTT Network Planning and Dimensioning PTT user per Sector (per group size)

PTT users per sector ( 6 seconds talk, 3 seconds idle)

40 35 30 25 20 15 10 Users per sector 5 0 0 5 10 15 20 25 Group Size

As group size grows users per sector decreases until all FCH are full

PG 9 PTT Network Planning and Dimensioning PTT Attributes & Implications on each node

• Terminal – PTT terminal/client does not require Reverse Supplemental Channel. – Slot cycle index could be set 0 to reduce terminating latency – Terminal PPP establishment procedure should be included in call model • BTS (holding time) – Need to be provisioned for FCH traffic expected, SCH should ideally be 0 – Radio Resource Management set to accommodate projected FCH usage, including group – minimize blocking • BSC (holding time) – BSC buffer settings to eliminate SCH usage (impacts other apps, of course) – Dormant to active timer to improve PTT latency (impacts other applications). • MSC (BHCA) – Need to dimension for Dormant to active transition due to PTT calls including group multiplier • PDSN (sessions) – Simultaneous PPP sessions (tends to be a mostly always on application) – Frequency of subscriber transitioning from PTT to regular CDMA2000® 1X and back. • WAN (throughput) – Aggregate throughput

PG 10 PTT Network Planning and Dimensioning PTT Call Model Assumptions and Capacity Prediction Tool

PG 11 PTT Network Planning and Dimensioning Sample PTT Call Model

• Average PTT originations per PTT subscriber in the busy hour (excluding the presence update) is expected to be 0.5. • Average number of parties, including the originator, per PTT call is expected to be 2.5. • The timer for PTT presence update is expected to be 15 minutes. • Average number of PTT presence update messages per hour per PTT subscriber is expected to be 4.0. • It is expected that 75 percent of PTT subscribers will make one transition from a PTT session to a “normal” CDMA2000® 1X data session and back to a PTT session in one hour. Therefore, the average number of PPP session setup – teardown pairs per PTT subscriber per hour is expected to be 1.5 (75% * 2).

PG 12 PTT Network Planning and Dimensioning Sample PTT Call Model

• Average PTT (BSC resource) call hold time is 120 seconds. • Average Fundamental Channel (FCH) hold time for the PTT presence update message is 15 seconds. • On power up, PPP session setup (BSC resource) call hold time is expected to be 15 seconds. • A “normal”, non-PTT CDMA2000® 1X data session includes one initial PPP session setup and two dormant-to-active transitions. • Average time duration from last data transfer to active-to-dormant transition is 12.5 seconds.

PG 13 PTT Network Planning and Dimensioning Call Model Prediction Tool

• Given call model for “normal” data, Nortel Networks developed spreadsheet tool predicts new data call model that includes impact of PTT. • Call model tool inputs – PTT subscriber penetration. – Average number of voice calls per non-PTT subscriber per hour. – Call model percentage numbers before PTT subscribers are added. • Call model tool outputs – Frequency of CDMA, , and CDMA2000® 1X voice calls. – Frequency of CDMA2000® 1X data calls. – Frequency of mobile termination in CDMA2000® 1X data calls. – Frequency of mobile origination in CDMA2000® 1X data calls. – Frequency of initial PPP session setup in CDMA2000® 1X data calls.

PG 14 PTT Network Planning and Dimensioning Summary

• Access Nodes – High number of dormant to active transitions per PTT sub will lead to increase in system BHCAs and CDMA2000® 1X data call penetration. – Increased demand on CDMA2000® 1X data call resources due to increased CDMA2000® 1X data call attempts and longer total resources holding time. – Resources blocking and data call downgrade measurements should be monitored closely. • Core – Low throughput requirement – Higher BHCA : • Transition from PTT to CDMA2000® 1X data starts a new data session • Registration, authentication, accounting … • PPP presence update frequency, dormant -> active • Call set up in MSC, accounting … – Longer session duration lead to higher signaling layer activities • More RP handoff • More MIP handoff • More interim accounting messages

PG 15 PTT Network Planning and Dimensioning PTT Engineering Recommendation

PG 16 PTT Network Planning and Dimensioning Capacity Engineering is a key element in service assurance RF Optimization Call Profile Tool Workload Performance Portal data collection Analysis BTS blocks ? Data rate downgrades ? RP throughput? Network Eng App Call Models 100% Capacity Network eng limit Engineering Re-dimensioning Radio

Application Application BSC % Capacity Monitoring Performance Engineering PDSN

0 time

Call Profiling and Monitoring are enablers

PG 17 PTT Network Planning and Dimensioning PTT Engineering Recommendations

PTT Optimization Suggestions: • PTT system – Set Longer Presence Update Interval. – PTT terminals behavior in case of PTT server unreachable – reinitiating flood. – STUN message interval – set as long as acceptable – Combine signaling messages if possible e.g. STUN, Presence Update, Buddy Update, MIP Registration – Delay at the end of PTT calls before the FCH teardown needs to be less than active to dormant timer in BSC to prevent excessive FCH holding time. – A max group size should be considered to limit multiplier impact on all nodes. • CDMA2000® 1X network – Separate PPP session timers in PDSN for PTT domain – Active to dormant timer – optimum setting to balance PTT latency vs network resources. – Radio Resource management settings review – need to set for new average call model with PTT skew. – Provisioning review – revisit overall network design based on PTT forecast. – Revisit SCH thresholds to reduce PTT SCH usage – PPP teardown timers need to be set for always on.

PTT Engineering and Dimensioning Exercises involve Operator, PTT & Infrastructure Vendors

PG 18 PTT Network Planning and Dimensioning PTT Network Planning and Dimensioning

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