Carriergrade vs. Internet VoIP

1
Carrier-grade vs. Internet VoIP

• Henning Schulzrinne
• (with Wenyu Jiang)
• Columbia University
• FCC Technical Advisory Council III
• Washington, DC October 20, 2003

2
Overview

• Previous talk interactive communication services
• signaling media
• Now focus on overall architecture
• network service availability
• signaling services SIP, H.323
• supporting services DNS, DHCP, LDAP,
• network transport
• network quality-of-service
• packet loss, delay, jitter

3
Overview

• (on-going work, preliminary results, still
  looking for measurement sites, )
• Service availability
• Measurement setup
• Measurement results
• call success probability
• overall network loss
• network outages
• outage induced call abortion probability

4
Service availability

• Users do not care about QoS
• at least not about packet loss, jitter, delay
• rather, its service availability ? how likely is
  it that I can place a call and not get
  interrupted?
• availability MTBF / (MTBF MTTR)
• MTBF mean time between failures
• MTTR mean time to repair
• availability successful calls / first call
  attempts
• equipment availability 99.999 (5 nines) ? 5
  minutes/year
• ATT (2003)
• Sprint IP frame relay SLA 99.5

5
Availability PSTN metrics

• PSTN metrics (Worldbank study)
• fault rate
• should be less than 0.2 per main line
• fault clearance ( MTTR)
• next business day
• call completion rate
• during network busy hour
• varies from about 60 - 75
• dial tone delay

6
Example PSTN statistics
Source Worldbank
7
Measurement setup
8
Measurement setup

• Active measurements
• call duration 3 or 7 minutes
• UDP packets
• 36 bytes alternating with 72 bytes (FEC)
• 40 ms spacing
• September 10 to December 6, 2002
• 13,500 call hours

9
Call success probability

• 62,027 calls succeeded, 292 failed ? 99.53
  availability
• roughly constant across I2, I2, commercial ISPs

10
Overall network loss

• PSTN once connected, call usually of good
  quality
• exception mobile phones
• compute periods of time below loss threshold
• 5 causes degradation for many codecs
• others acceptable till 20

11
Network outages

• sustained packet losses
• arbitrarily defined at 8 packets
• far beyond any recoverable loss (FEC,
  interpolation)
• 23 outages
• make up significant part of 0.25 unavailability
• symmetric A?B ?? B?A?
• spatially correlated A?B ? ? A?X?
• not correlated across networks (e.g., I2 and
  commercial)

12
Network outages
13
Network outages
14
Outage-induced call abortion probability

• Long interruption ? user likely to abandon call
• from E.855 survey Pholding e-t/17.26 (t in
  seconds)
• ? half the users will abandon call after 12s
• 2,566 have at least one outage
• 946 of 2,566 expected to be dropped ? 1.53 of
  all calls

15
Conclusions from measurement

• Availability in space is (mostly) solved ?
  availability in time restricts usability for new
  applications
• initial investigation into service availability
  for VoIP
• need to define metrics for, say, web access
• unify packet loss and no Internet dial tone
• far less than 5 nines
• working on identifying fault sources and
  locations
• looking for additional measurement sites

16
Whats next?

• Existing SLAs are mostly useless
• too many exceptions
• wrong time scales month vs. minutes
• no guarantees for interconnects
• Existing measurements similarly dubious
• Limited ability to learn from mistakes
• what are the primary causes of service
  unavailability?
• what can I do to protect myself multi-homing
  via same fiber? diverse access mechanisms?
• Consumers of services have no good ways to
  compare service availability
• only some very large customers may get access to
  carrier-internal data
• Thus, market failure
• Need published metrics
• similar to switch availability reporting