To be a call setup protocol of VoIP service, latency for session initiation should be the first consideration that decides the quality of the service. However, introduced overheads for maintaining correctness of system are unavoidable if a well quality of service is required to be provided. So the tradeoff between call setup latency and maintenance overhead would the key points for performance of systems. In our simulations, we observe the variation of call setup latency and maintenance overhead while being in different environments.
We do not measure the effect of physical network because of the emphasis of the performance in architectures. Instead, we calculate the hop counts and number of messages needed for call setup and maintenance overhead. Followings are the results and analysis of performance.
1. Comparison with different numbers of online nodes
We vary the number of online nodes from 1000 to 10000 and explore the scalability of each approach.
In Figure 5 and Figure 6, we measure the average of call setup latency in different proportions of buddies to non-buddies such that that we can know the practicability of systems. In which, these line segments go curving following the increasing of numbers of online nodes and with a trend toward an upper bound in both approaches. The diagrams present the convergence properties owned in both approaches and these have been proved in [3, 7]. Besides, we can see that with larger proportion of calls to buddies costs less latency in establishing sessions and the performances of both approaches are similar. That is because there is already cached and tracked information in buddy list by invoking the presence policy [8] such that users can directly connect the sessions to buddies. Else, call setup with larger proportion of calls to non-buddies mostly relies on the performance of search mechanisms in the approaches and essentially costs more latency. It’s clear to see that latency needed in
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UP2P SIP approach is all the time lower than P2P SIP over Chord approach.
In Figure 7, it shows how much maintenance overhead needed to provide such quality of call setup services above. We can see both curves are arising exponentially following the increasing number of online nodes. But it’s obviously that the requirement of maintenance overhead in UP2P SIP approach are all the time slower than in P2P SIP over Chord approach.
P2P SIP over Chord
0 1 2 3 4 5 6 7 8 9 10
0 2000 4000 6000 8000 10000 12000
# of Nodes
Latency (Hops)
Buddy (10%) & Non-buddy (90%) Buddy (50%) & Non-buddy (50%) Buddy (90%) & Non-buddy (10%)
Figure 5: The variation of call setup latency while varying the number of online nodes in P2P SIP over Chord approach.
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UP2P SIP
0 1 2 3 4 5 6 7 8 9 10
0 2000 4000 6000 8000 10000 12000
# of Nodes
Latency (Hops)
Buddy (10%) & Non-buddy (90%) Buddy (50%) & Non-buddy (50%) Buddy (90%) & Non-buddy (10%)
Figure 6: The variation of call setup latency while varying the number of online nodes in UP2P SIP approach.
0 2000 4000 6000 8000 10000 12000 14000 16000
0 2000 4000 6000 8000 10000 12000
# of nodes
Maintenance Overhead (msg/sec)
P2P SIP over Chord UP2P SIP
Figure 7: The variation of maintenance overhead needed to provide such quality of call setup service above.
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2. Comparison with different numbers of mobile nodes
In the section, we try out to know the effect of mobility by changing the number of mobile nodes in the network, i.e. mobile rate.
In figure 8, it illustrates that the increasing of mobile rate follows the longer latency with no exception of different proportions of callee when call initiation in P2P SIP over Chord approach. This is because with more mobile users comes with larger opportunity to churn the network. This phenomenon results in more staled finger tables lengthening routing paths while call initiation.
On the contrary, we can see the latency remains steady in UP2P SIP approach in Figure 9.
This is because the unstructured P2P network we adopt suffers less from the effect of mobility.
Even several nodes moving out the network simultaneously, the relaying nodes can still flood the request to other existed neighbors and buddies. Besides, a low-diameter P2P network is constructed and in which each node seems to be arranged in the center of the network such that the call setup messages can be relayed along near shortest path.
In the case of maintenance overhead, Figure 10 shows the results that both systems pay additional penalty to handle the dynamics of network with increasing proportion of mobile users inside. But the costs paid in both approaches are scarcely comparable. Maintenance overhead in P2P SIP over Chord approach is a great quantity more than that in UP2P SIP approach. The reason is that nodes in P2P SIP over Chord has to maintain a logical overlay which is unstable due to frequent churns, especially caused by nodes moving. Nodes in which spend huge effort updating the staled finger tables periodically. In contrast, nodes in UP2P SIP approach master plenty connections for routing simultaneously and have no inflexible necessary correcting few entries which are staled in neighbor table.
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P2P SIP over Chord Buddy (10%) & Non-buddy (90%) Buddy (50%) & Non-buddy (50%) Buddy (90%) & Non-buddy (10%)
Figure 8: The variation of call setup latency while varying the proportion of mobile users in P2P SIP over Chord approach.
UP2P SIP Buddy (10%) & Non-buddy (90%) Buddy (50%) & Non-buddy (50%) Buddy (90%) & Non-buddy (10%)
Figure 9: The variation of call setup latency while varying the proportion of mobile users in UP2P SIP approach.
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0 2000 4000 6000 8000 10000 12000 14000
0 20 40 60 80
Mobile Rate (%)
Maintenance Overhead (msg/sec)
100 P2P SIP over Chord UP2P SIP
Figure 10: The variation of maintenance overhead while varying the proportion of mobile users in both approaches.
3. Comparison with different period of stabilization
Nodes in P2P network achieve gradual search relying on distributed routing tables (e.g.
finger tables and neighbor tables), unfortunately, while are usually staled by network dynamics. Therefore, how long one node updates its routing table is a critical factor affecting performance of system. In this session, we wish to realize the difference of both performances by decreasing the period of stabilization in P2P SIP over Chord approach from 5 minutes to 1 minute. In Figure 11, among the curves represented P2P SIP over Chord approach, we can see any with shorter period cost less latency than the others with longer period. The more frequent stabilization comes with less latency while initiating a SIP call. However, the range of advance is finite that the performance is limited by the routing mechanism so that it can not cost latency as less as in our approach.
On the other hand, a great amount of maintenance overhead is introduced while increasing the frequency of stabilization. In Figure 12, we observe that the additionally increasing effect to handle staled tables is out of scale with the incoming benefit on call setup.
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0 2 4 6 8 10 12
0 20 40 60 80
Mobile Rate (%)
Latency (Hops)
100 P2P SIP over Chord_stable period=300 sec P2P SIP over Chord_stable period=240 sec P2P SIP over Chord_stable period=180 sec P2P SIP over Chord_stable period=120 sec UP2P_stable period=300 sec
Figure11: The comparison of latency between P2P SIP over Chord approaches with different periods of stabilization and UP2P approach.
0 5000 10000 15000 20000 25000
0 20 40 60 80
Mobile Rate (%)
Maintenance Overhead (msg/sec)
100 P2P SIP over Chord_stable period=300 sec P2P SIP over Chord_stable period=240 sec P2P SIP over Chord_stable period=180 sec P2P SIP over Chord_stable period=120 sec UP2P_stable period=300 sec
Figure12: The comparison of overhead between P2P SIP over Chord approaches with different periods of stabilization and UP2P approach
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V. Conclusions
Recently there are several P2P approaches proposed for telephony using SIP, however, they are not concerned about mobility which are evolved from the popularity of wireless technology. Increasing of mobile users comes with more frequent churns and DHT-base architectures cannot suffer these dynamics emerged in great numbers. As a result, call setup latency and maintenance traffic are first and deep to be affected.
In the study, we propose an approach with unstructured P2P for telephony using SIP.
In which, nodes directly connect to those with particular relationships, such as buddies, and not only shortens the latency when call setup but also decreases the overhead spent on maintaining the burdensome loading. Besides, to the non-buddy call initiation, we additionally build a low-diameter network ensuring any session can be rapidly connected.
Finally we demonstrate through simulations. The simulation result shows that whether increasing the number of online users or increasing the proportion of mobile users in the network, our approach is more suitable being applied in mobile environment than DHT-base approaches.
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References
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