Affects of Queuing Mechanisms on RTP Traffic Comparative Analysis of Jitter, End-to- End Delay and Packet Loss

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1 Comparative Analysis of Jitter, End-to- End Delay and Packet Loss Gregory Epiphaniou 1 Carsten Maple 1 Paul Sant 1 Matthew Reeves 2 1 Institute for Research in Applicable Computing University of Bedfordshire 2 Modern Networks Hitchin, United Kingdom ARES Conference, 2010

2 Outline 1 Aim and Objectives 2 Some facts on VoIP implementation VoIP Impairments Queuing Mechanims 3 First-In-First Out Random Early Detection Differentiated Services 4 5

3 Aim and Objectives Investigate VoIP traffic behaviour under burst traffic conditions Illustrate precise effects of queuing mechanisms to VoIP and compare results Find the most appropriate mechanism to be used in the case of unelastic traffic DropTail (FIFO), RED and DiffServ, and their effects on real-time voice traffic Extract measurements on e2e delay, jitter and packet loss rates for each mechanism examined The NS-2 simulator has been used

4 Some facts on VoIP implementation VoIP Impairments Queuing Mechanims Some facts on VoIP implementation IP telephony (IPTel) refers to the technology to transport real-time media over an IP network Converging voice and data into a best-effort service network demands preferential handling of traffic QoS assurance has increased due to the enormous growth of users accessing networks Voice coders contribute to end-to-end delay due to sample accumulation delays and look-ahead delays VoIP must reach the QoS that a Public Switched Telephone Network (PSTN) provides Best-effort service networks has resulted in many technical challenges regarding traffic engineering and shaping

5 Some facts on VoIP implementation VoIP Impairments Queuing Mechanims VoIP Impairements Jitter and E2E Delay Jitter can be effectively described as the unwanted variation in the inter-arrival packet time Jitter = (T i T i 1 ) (T si T si 1 ) (1)

6 Some facts on VoIP implementation VoIP Impairments Queuing Mechanims VoIP Impairements Jitter and E2E Delay Jitter can be effectively described as the unwanted variation in the inter-arrival packet time Jitter = (T i T i 1 ) (T si T si 1 ) (1) End-to-end delay is one of the most important threats to perceived QoS H ( ) L H D k = = qk i L = + d k i (2) C i C i C i i=1 i=1

7 Some facts on VoIP implementation VoIP Impairments Queuing Mechanims VoIP Impairements Packet Loss Rate and NIST Recommendations Packet loss may occur at any stage of a network transmission Plr ij = pkts lost pkts received = pkts sent i pkts receivedj pkts receivedj (3) PLR ij 0.05 Pkts senti (4) The ITU-T (International Telecommunication Union) recommends that for one way transmission the actual end-to-end delay limits are: 0 to 150ms: Acceptable for most network hosted applications. 150 to 400ms: International or satellite connections. > 400ms: Unacceptable for general network purposes.

8 Some facts on VoIP implementation VoIP Impairments Queuing Mechanims VoIP Impairements Media Path Additional Delays Packetisation Delay Serialisation Delay Propagation Delay T DP = P s C bw (5) D s = P s + H L L s (6) D pr = L u (7) Figure: VoIP media path [?]

9 Some facts on VoIP implementation VoIP Impairments Queuing Mechanims Queuing Mechanisms - FIFO In FIFO all packets are treated equally and served at the same order in which they were placed in the queue Figure: FIFO Queue Computationaly inexpensive Predictable queue behaviour since no packet re-ordering takes place Minimum queuing delay at the intermediate hops Does not support traffic clasification Linear relationship between aggregation of incoming traffic and mean queuing delay Benefits UDP flows

10 Some facts on VoIP implementation VoIP Impairments Queuing Mechanims Queuing Mechanisms - RED Figure: RED Queue Counts the dropping probability of a packet Decisions are made based on Max/Min queue length threshold If the avg queue length is greater than max threshold the packets are marked The average queue size does not exceed the maximum threshold High throughput and low avg delay for high speed networks with TCP connections

11 DiffServ Aim and Objectives Some facts on VoIP implementation VoIP Impairments Queuing Mechanims Figure: IPv4 ToS byte Figure: DiffServ code point field Achieves division of packets into classes by using a 6-bit DSCP Define the policies for the level of service for each flow Performs packet marking and traffic shaping based on the policies Core routers forward packets based on their marking

12 Simulation Parameters First-In-First Out Random Early Detection Differentiated Services Elastic and unelastic traffic examined (RTP and TCP) Pareto ON/OFF model has been used to mimick VoIP traffic G.711 (64kbps), burst time 20ms, idle time 10ms and rate 87.4kbps Default payload size of 160 bytes Total simulation time 62sec No crtp/multiplexing mechanisms Table: Link characteristics nodes Propagation Delay [ms] Link capacity [Mb] n 0 - n n 1 - n n 2 - n n 3 - n n 3 - n

13 FIFO Results and Discussion First-In-First Out Random Early Detection Differentiated Services 0.09 Figure: Simulation Model FIFO Delay variation for RTP traffic with FIFO [sec] Traffic sent Dropped TCP RTP Simulation time [sec] Figure: Jitter for RTP traffic with FIFO

14 FIFO e2e delay Aim and Objectives First-In-First Out Random Early Detection Differentiated Services RTP OWD for RTP traffic with 50pkts buffer size [sec] Simulation time [sec] RTP OWD for RTP traffic with 25pkts buffer size [sec] Simulation time [sec] Figure: Simulation Model FIFO: RTP One Way Delay with buffer size of 50pkts and DropTail Figure: Simulation Model FIFO: RTP One Way Delay with buffer size of 25pkts and DropTail

15 RED Results and Discussion First-In-First Out Random Early Detection Differentiated Services 0.08 Delay Variation for RTP traffic with RED [sec] Simulation time [sec] Figure: Simulation Model RED Figure: Simulation Model RED: Delay Variation for RTP traffic against simulation time

16 RED e2e delay and packet loss First-In-First Out Random Early Detection Differentiated Services Total RTP packets dropped with RED Simulation time [sec] Figure: Simulation Model RED: RTP packet drop rate against simulation time RTP OWD with RED [sec] Simulation time [sec] Figure: Simulation Model RED: RTP One Way Delay with buffer size of 50pkts against simulation time

17 DiffServ Results and Discussion First-In-First Out Random Early Detection Differentiated Services 0.08 Figure: Simulation Model DiffServ Delay variation for RTP traffic with DiffServ Traffic Sent Dropped TCP RTP Simulation time [sec] Figure: Jitter for RTP traffic against simulation time

18 First-In-First Out Random Early Detection Differentiated Services DiffServ e2e delay and packet loss Total RTP packets dropped with DiffServ RTP OWD with DiffServ Simulation time [sec] Simulation time [sec] Figure: Simulation Model DiffServ: RTP packet drop rate against simulation time Figure: Simulation Model DiffServ: RTP One Way Delay with buffer size of 50pkts against simulation time

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