A Study of VoIP Gateway Selection Techniques

1
A Study of VoIP Gateway Selection Techniques

• Matthew Caesar, Dipak Ghosal, Randy Katz
• mccaesar, randy_at_cs.berkeley.edu
• ghosal_at_cs.ucdavis.edu

2
Motivation/Goals

• Goals
• Few blocked calls
• Good Quality of Service (QoS)
• Preferential QoS to high priority users
• Methods
• Advertising gateway congestion
• Monitoring and recording call QoS
• Call redirection
• Questions
• Is it feasible to route based on dynamic
  congestion information?
• How best to redirect calls with congestion and
  QoS sensitivity?

3
System Architecture
Example Call Setup
Example Advertisement
4
Assumptions

• ADs cooperate to provide service.
• Use IETFs TRIP architecture to support
  interoperability.
• Number of Gateways is small enough to store
  per-ITG routing information at the LS.
• Cost of multi-gateway-hop routes (e.g.
  IP-PSTN-IP) will be prohibitively expensive.
• Majority of QoS degradation is inter-AD, not
  intra-AD.

5
Redirection Techniques

• Local Redirection
• Random Redirection
• CS Redirection
• QoSS Redirection
• Hybrid Redirection (CSQoSS)
• cost alphaC(1-alpha)QoS
• Price Sensitive Schemes
• Also varied setsize
• Perform random redirection over the set

6
Evaluation Metrics

• Number of blocked calls
• Average call QoS
• Used Mean Opinion Score (MOS) based on RTP loss
  rate
• Economic efficiency
• Ratio of service tier to QoS achieved
• Stability Variance in gateway utilization
• Over time
• Over the set of gateways
• Overhead
• Advertisement bandwidth consumption

7
System Performance

• Results Call QoS
• More congestion sensitivity decreases quality
• Small setsizes offer best quality

• Results Blocking Probability
• More congestion sensitivity decreases blocking
  probability
• Small setsizes cause few blocked calls

8
System Performance

• Results Background Traffic
• QoS sensitivity minimizes effects of cross
  traffic
• Even a little sensitivity to QoS vastly improves
  call quality

• Results System Stability
• More congestion sensitivity decreases blocking
  probability
• Small setsizes cause few blocked calls

9
Effect of Flash Crowd

• Change from 0.1 to 4.0 offered load in 1
  simulated hour
• Some randomization is necessary to improve the
  call blocking rate
• Randomization not required for smaller flash
  crowds

10
Conclusions

• QoS sensitivity necessary for best-effort
  Internet
• Suffers from load oscillations
• Congestion sensitivity necessary for limited
  gateway resources
• Chooses poor-QoS paths
• Hybrid scheme is very effective
• Good QoS, low blocking probability
• Resilient to flash-crowds, background traffic
• Future work
• Price sensitive schemes
• Multi-class user model
• Effective admission control