2. Changing the Dynamics of Network Analysis J. Scott Haugdahl CTO, WildPackets, Inc. scott@wildpackets.com www.wildpackets.com

3. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara What’s Changing about Network Analysis? Unlike data protocols, VoIP is sensitive to –Delays –Congestion –Jitter –Buffering at the receiver Convergence can affect performance Analysis is highly dependent on where the data is gathered 802.11 compounds VoIP analysis challenges

4. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara VoIP Packet Analysis Invaluable for granular VoIP analysis –Packet variance analysis (jitter), check for dropped packets at selected points in the path, late packet arrivals, out of sequence packets, examine RTCP reports, derive MOS scores, etc. VoIP signaling analysis –Can involve multiple protocols and IP addresses –Filtering can be tricky, capture at end-user VoIP voice stream analysis –RTP streams are two-way and independent –Filter at end-points by IP, then selectively analyze each direction

5. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara Quality of Experience (QoE) Check for consistent packet delivery and verify QoS policies such as 802.11e as well as prioritization of packets sourced from layer 3 devices For wireless, analyze impact of hand-off between access points Compare derived MOS scores for overall voice quality Playback captured VoIP RTP voice streams –Analysis close to listener is best –Listening to independent (i.e. one-way) streams is best –Ability to vary the jitter buffer during playback assists in determining the optimal jitter buffer size

6. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara...................... Jitter Jitter is the variance in packet delivery intervals to the listener Jitter buffer adds additional delay to voice reaching the ear piece in case other packets need to catch up Packets are buffered and delayed at the Receiver The “jitter” buffer releases a G.711 packet every 20 ms A G.711 packet sent every 20 ms Packets delayed more than the buffer delay (100 ms as an example) are dropped Packet jitter and drops    

7. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara VoIP Jitter Analysis Good thing we have that jitter buffer! G.711 every 20 ms is good 2.9 ms recovery – not bad

8. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara End-to-end Voice Quality Analysis HQ user IP Remote user IP … note the decrease in quality at the other end The call goes through the network and…

9. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara RTP Control Protocol (RTCP) Defines RTP Sender and Receiver Report (combined) –Found in the same RFC as RTP, RFC 3550, which obsoletes RFC 1889 –Contains total packet and byte counts, packet loss, and jitter information –Optional, but all VoIP end-nodes should implement it! Enhanced by RTCP Extended Report (XR) –RFC 3611 –Can be sent by non-recipients such as PSTN gateways –Defines multiple report blocks with detailed information such as Loss RLE Report – Similar to RTCP RR but noting specific RTP packets that were lost Duplicate Packet RLE Report Packet Receipt Times Report Detailed jitter, loss rate, discard rate, computed MOS scores, echo, noise, and other information as end-node capable

10. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara Example RTCP Packet

11. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara Cause: Competition with data protocols Packets Get There But In Time?

12. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara 802.11 Wireless VoIP Analysis is Essential Diagnose pre- and post-deployment problems using expert events such as –Excessive wireless retransmissions –Recovery and data rate changes during RTP sessions –Excessive jitter –VoIP protocol signaling errors –Late packet arrival analysis at end-points Use an analyzer either side of an access point to perform call and quality analysis for converged networks –Full seven layer analysis including encrypted packets on the wireless using phone WEP keys; 802.11 media analysis is always available regardless of encryption

13. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara A VoIP over WLAN Problem Cause: Excessive environmental interference on channel 11.

14. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara “Hidden” Wireless Errors are Costly Lowering the data rate on a retry may get the data through but… –It’s very inefficient Retries at same speed and then lowered are even worse Sender can bounce up and down We need detailed operational WLAN analysis to see this and determine the impact and to help optimize our physical environment, AP and client settings, etc. Frame at 11 MbpsSame Frame at 5.5 Mbps Over 3x bandwidth wasted to send one voice packet No 802.11 Ack

15. www.voipdeveloper.com August 8-10, 2006 Santa Clara, California Hyatt Regency Santa Clara J. Scott Haugdahl CTO, WildPackets, Inc. scott@wildpackets.com www.wildpackets.com