1 Resource Management in IP Telephony Networks Matthew Caesar, Dipak Ghosal, Randy H. Katz {mccaesar,

2 Motivation What is IP Telephony? Packetized voice over IP PSTN access through Internet Telephony Gateway (ITG) Benefits: Improved network utilization Next generation services (POTS  PANS) Growth: Revenues $1.7 billion in 2001, 6% of international traffic was over IP, growing [Frost 2002] [Telegeography 2002] Standardized, deployed protocols (TRIP, SIP, H.323)  Requires scalable architecture to limit congestion.

3 Goals High quality, economically efficient telephony over the Internet. Low blocking probability Provide preferential treatment, high QoS Questions: How to perform call admission control? How best to route calls through converged network?

4 Approach Mechanisms Congestion sensitive call admission control ITG selection Techniques Awareness of ITG congestion Path quality between important points in network Distance ITG Utilization * * ** * **

5 Overview IP Telephony Networks Pricing-based Admission Control Redirection Techniques Experimental Design Results Future Work

6 System Architecture ITG LS Example Call Setup Example Advertisement Gateway (ITG) IP Terminal Location Server (LS) Internet Admin. Domain (AD) Example Call Session ITG LS

7 Scope of Study 1. All calls are net-to-phone 2. ADs cooperate to provide service. 3. Use IETF’s TRIP architecture to support interoperability. 4. Disregard degradation in access network. 5. Prices determined at start of call. 6. ITGs offer equal PSTN reachability.

8 Pricing PSTN distance pricing time of day pricing IP Telephony richer user interface allows for more dynamic pricing schemes Baseline: Flat-rate Admission Control (FAC)

9 Congestion Sensitive Call Admission Control (CAC) Goal: prevent system overload and generate revenue Price of call function of number of voice ports in use rises when highly utilized More dynamic than PSTN

10 Price-Congestion Function Used M/M/m/m (m- server loss system) responsive server loss system discouraged arrivals Found price-congestion function that maximized revenue with respect to  m-1 m      m-1   mm

11 Congestion Pricing Analysis Exponential function generates most revenue Stepwise linear function almost as good Maximum system price charged early Approximation to function minimizes price fluctuations

12 Redirection Problem: finding the “best” ITG Approach: tradeoffs between quality and load Method: LS maintains Average measured path quality Number voice ports in use Algorithms: Random Redirection (RR) (baseline) QoS Sensitive Redirection (QR) Congestion Sensitive Redirection (CR) Hybrid Scheme (CQR)

13 Redirection Schemes QoS Sensitive Redirection (QR) Different paths provide different service Technique: Use RTCP RRs to monitor path congestion Route over best paths Congestion Sensitive Redirection (CR) Unbalanced load causes call blocks Technique: Use TRIP advertisements to estimate ITG utilization Route to least utilized ITG

14 Hybrid Redirection (CQR) Choosing nearby ITG improves call quality, but can unbalance load. Algorithm: Compute Rdm =  *M i +(1-  )*Q i M i is utilization, Q i is loss rate Select randomly from k ITGs with lowest Rdm Tradeoffs: Use  to trade off call quality and load balance Use k to vary flash crowd protection Price Sensitive CQR (PCQR) Decrease  for higher bids

15 Overview IP Telephony Networks Pricing-based Admission Control Redirection Techniques Experimental Design Results Future Work

16 Experimental Method Modified ns-2 Ran for 1.5 simulated hours Eliminated first half-hour User Model Bid uniformly distributed Voice traffic on-off Markov process Self-similar cross-traffic Data points stable across several time scales

17 Evaluation: Metrics Blocking Probability Average call QoS Used Mean Opinion Score (MOS) based on RTP loss rate Economic efficiency Ratio of service tier to QoS achieved

18 Admission Control: Blocking Probability Flat pricing unnecessarily blocks many callers Congestion pricing changes system price dynamically with load

19  Redirection: Blocking Probability Congestion sensitivity decreases blocking probability Small k  few blocked calls Congestion Sensitive Redirection (CR) improves balance over Random Redirection (RR)

20 Redirection: Background Traffic Effects  QoS sensitivity minimizes effects of cross traffic  Small amount of sensitivity vastly improves call quality

21 Summary Admission Control Schemes: Congestion sensitive pricing decreases unnecessary call blocking, increases revenue, and improves economic efficiency Derived exponential price-congestion function that maximizes revenue Redirection Schemes: Hybrid scheme achieves “best of both worlds” Price sensitivity improves economic efficiency

22 Future Work Realistic workload Improve user model Develop price-congestion function for real users Study flash-crowd effects ITG Placement Competitive Network

23 Resource Management in IP Telephony Networks Matthew Caesar, Dipak Ghosal, Randy H. Katz {mccaesar,