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ISBN: 978-972-8939-25-0 © 2010 IADISfor better understanding the impact caused by traffic pattern. The topology is detailed in the Section 0. Theprotocols are grouped in distinct pairs for the simulation turns, for a better perception of the fairness propertyof each protocol, as follows: (i) CTCP versus DCCP CCID2, (ii) CTCP versus DCCP CCID3, (iii) CUBICversus DCCP CCID2, (iv) CUBIC versus DCCP CCID3, (v) CUVIC versus CTCP, and (vi) DCCP CCID2versus DCCP CCID3.3.1 Simulation ScenariosWe consider a topology (see Figure 1) in which 4 local area networks (LAN) are interconnected by theirR1 , R2,R3,R4L = L1 , L2,L3,L4, in a typical corporative scenariorespective routers R = { } and adjacent links { }of a set of subsidiaries. In each local area network, we dispose sending nodes, i N : Si = { S1 , S 2,...,S 48}target (i.e., receiving) nodes, i Ν : Ti = { T1 , T 2,...,T 48}∈ and∈ in sufficient quantity and individual throughput sothat the links L 1 , L2,L3,L4are saturated, and contention occurs forthwith. Hence, for each simulation turn,the respective protocol pair fights for the shared link bandwidth.Figure 1. Simulation topologyLANs are configured with internal bandwidth links of 10 Mbps with a latency of 1 ms. L1 , L2,L3,L4have1 Mbps of bandwidth with a latency of 20 ms. VoIP transmissions occupy a small amount of bandwidth,therefore we place 96 nodes uniformly spread over the 4 LANs, with 12 sending nodes and 12 target nodesper local area network. Each sending node in a LAN has a corresponding target node in the opposite LAN.Let S 1 be the sender node 1 of the LAN connected to R 1 , S 1 will send packets towards T1in the LANconnected to R3 (i.e., opposite LAN). Similarly, as S 48 is placed in the LAN connected to R 4 , T 48 is placedin the LAN connected to R 2 . As a result, packets generated in a LAN must traverse two links and anintermediate router to reach the target LAN. The packet queues among routers have the sizes adjusted to 300packets and DropTail policy. The protocols are arranged in pairs for each simulation turn, as follows: (a)CTCP versus DCCP CCID2, (b) CTCP versus DCCP CCID3, (c) CUBIC versus DCCP CCID2, (d) CUBICversus DCCP CCID3, (e) CUBIC versus CTCP, and (f) DCCP CCID2 versus DCCP CCID3.VoIP traffic is simulated by the Exponential Traffic Application (NS-2). As recommended by ITU-T(1993) and Bouras et al. (2007) for a simulated VoIP traffic, the mean ON-time (i.e., talking time) of 1.004 s,the mean OFF-time (i.e., silence time) of 1.587 s, sending rate of 80 Kbps, and packet size of 160 bytes. TheVoIP ON/OFF time ratio is relevant because we have spread many sender nodes among LANs. The expectedbehavior is that not all the senders are talking at same time. CBR packet size is configured to 1,000 bytes andthe sending rate of 800 Kbps, for each sender. CBR senders may generate data packets in a configurablesending rate, therefore in the simulations with traffic pattern CBR we employ only 8 nodes, with 1 sendingnode and 1 target node per LAN. To avoid the phase effect, CBR senders start at timet ∈ Ν, δ ∈R : t = 0 + δ ,0 ≤ δ ≤ 75 , whereδ is random. The adopted simulation time for a turn is 900 s.3.2 Simulation ResultsPlotted results represent the mean value of 10 rounds of simulation. The values in parenthesis represent theconfidence interval, with confidence of 95%. Metrics are represented by a mean value of the transmissionsfor a simulation turn.214