When implementing the IEXCNA model for VoIP service, the traffic load and network dimension can be analyzed based on the traffic parameters provided in the operator networks. After collecting the traffic information from existing operator network as input data, the traffic loading and bandwidth requirement is calculated for VoIP service.
The results are analyzed for both IEXCNA and NON-IEXCNA model of network inter-connections for VoIP service. The function models of IEXCNA and NON-IEXCNA are derived according to the tele-traffic theory (Freeman, 1984; Lawson, 1983) described in 5.1.7 and 5.2.1. The Bandwidth Saving Parameter (BSP) and Bandwidth Efficiency Function is generated from the outcome of the differences between IEXCNA model and NON-IEXCNA model implemented for VoIP service.
5.1 Traffic Load Calculation and Bandwidth Dimensioning
To analyze the traffic load, the input data of traffic model is provided according to call scenarios and traffic volume. The VoIP service traffic of the operators including Type 2 operator A, Type 2 operator B and Type1 PSTN are analyzed based on different call situations and traffic volume generated.
5.1.1 Traffic Input Data
When there are only two Type 2 operators A and B, both Type 2 operator A and operator B generate VoIP traffic to and from Type 1 PSTN. The Type 2 operator A and Type 2 operator B traffic model have the following traffic parameters.
a. 50 thousand subscribers registered in Type 2 operator A and 50 thousand subscribers registered in Type 2 operator B
b. Attached Rate10% of the subscribers using VoIP service.
c. Average holding time per call is 3 minutes.
d. 12Kbps per call which stands for each VoIP channel capacity requirement e. The call probability is variable and 0.1 is selected for the normal case
f. Type 2 to Type 2 calls 70% and Type 2 to Type 1 call 30% of total traffic volume g. Blocking Rate (Grade of service) = 0.01
h. One E1 transmission link supports 30 Channels in the physical layer for ISUP calls and 150 Channels for SIP calls in the physical layer for standard conditions
5.1.2 Traffic Dimensioning for VoIP Service
The traffic volume between Type 2 operator A and Type 2 operator B and the traffic generated by Type 2 operator A and Type 2 operator B onto Type 1 PSTN is calculated as below. When call probability = 10% for VoIP subscribers in average.
The traffic load is equal to 15000 minutes = 15000/60 = 250 Erlang (Mina, 1974).
Where Type 2 call 70% = 250 * 0.7 = 175 Erlang
By Erlang B formula (Freeman, 1984; Lawson, 1983), 175 Erlang is equal to 196 SIP channels, The transmission requirement of 196/150 = 1.3 E1
Type 2 operators onto Type 1 call 30% = 250 * 0.3 = 75 Erlang
By Erlang B formula, it is equal to 91 ISUP channels, The transmission requirement of 91/30 = 3E1
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According to Erlang B theory (Freeman, 1984; Lawson 1983; Rey, 1984), when the traffic load is 175 Erlang with blocking rate 0.01, the required bandwidth is 196 channels.
5.1.3 Bandwidth Requirement for Non-IEXCNA model
Therefore for NON-IEXCNA model, the traffic bandwidth required is shown as below.
And it requires 10E1 bandwidth for VoIP traffic.
Type 2A toward Type 1 PSTN = 3E1 Type 2B toward Type 1 PSTN = 3E1
Type 2A toward Type 2B = CEILING(1.3,1) = 2E1 Tyep 2B toward Type 2A = CEILING(1.3,1) = 2E1 Total traffic bandwidth for VoIP = 3 + 3 + 2 + 2 = 10
.
Figure 5.1-1 The bandwidth requirement for NON-IEXCNA model of VoIP service
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5.1.4 The Traffic Volume Generated for IEXCNA Model,
The traffic between Type 2 operator A and Type 2 operator B will be processed by IEXCNA system. The traffic generated between Type 1 PSTN and Type 2 operator A and operator B are aggregated into IEXCNA system before routed and transferred into the destination shown as Fig. 5.1-2.
When call probability = 0.1,The traffic load is equal to 15000 minutes = 15000/60 = 250 Erlang. Where Type 2 call 70% = 250 * 0.7 = 175 Erlang. Type 2 to Type 1 call 30%
= 250 * 0.3 = 75 Erlang.
The traffic load of IEXCNA model for Type 2 operator A is 250 Erlang.
Based on Erlang B theory (Freeman, 1984; Lawson; 1983; Martin, 1972), it requires 273 channels for SIP calls via IEXCNA. The transmission link for SIP traffic is CEILING (273/150,1) = 2
The traffic load of IEXCNA model for Type 2 operator B is 250 Erlang.
Based on Erlang B theory, it requires 273 channels for SIP calls toward IEXCNA.
The transmission link for SIP traffic is CEILING (273/150,1) = 2
Type 2 operators onto Type 1 call is 75 * 2 = 150 Erlang for (Type 2A + Type 2B) via IEXCNA toward Type 1 PSTN.
Based on Erlang B theory, it requires 170 channels for ISUP calls.
The transmission link for ISUP traffic is 170/30 = 5.6 5.1.5 Bandwidth Requirement for IEXCNA model
For IEXCNA model, the traffic bandwidth requirement is 10E1 for VoIP traffic.
(Type 2A + Type 2B) via IEXCNA toward Type 1 PSTN = CEILING(5.6,1) = 6E1 Type 2A via IEXCNA to Type 2B+ Tyep 2B via IEXCNA to Type 2A= 2 + 2 = 4E1 Total traffic bandwidth for VoIP = 6 + 4 = 10. The traffic bandwidth required is shown as below.
Figure 5.1-2 The bandwidth requirement for IEXCNA model of VoIP service
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5.1.6 Multiple Type 2 operators to PSTN Traffic Load Function Model
If the number of Type 2 operators is N, for NON-IEXCNA model, the overall E1 is described as below. No matter how the traffic is distributed, the transmission link between each Type 2 operator needs at least one E1 for minimum.
Non-IEXCNA Model for Bandwidth Requirement Function:
3N + CEILING[ErlangB(175/COMBIN(N,2) *2)/150,1]*COMBIN(N,2) for N≧3 IEXCNA Model for Bandwidth Requirement Function:
Erlang B(75*N)/30 for ISUP traffic when traffic from N Type 2 Operators via IEXCNA to Type 1 PSTN.
For the traffic from each of the Type 2 Operators to IEXCNA is 250 Erlang.
Based on Erlang B theory, it requires 273 channels for SIP calls toward IEXCNA.
The transmission link for SIP traffic is CEILING (273/150,1) = 2 The total transmission links for N Type 2 Operators need 2N E1
Total Traffic load for N type 2 operators to PSTN Type 1 and other Type 2 Operators using IEXCNA Model for Bandwidth Requirement Function is:
CEILING[ErlangB(75*N)/30,1]+2N for N≧3
Bandwidth Efficiency Function is derived as below:
Let the number of Type 2 operators is N
A = 3N + CEILING[ErlangB(175/COMBIN(N,2) *2)/150,1]*COMBIN(N,2), representing Non-IEXCNA Bandwidth Requirement Function.
B = CEILING[ErlangB(75*N)/30,1]+2N, representing IEXCNA Bandwidth Requirement Function.
K = A - B; the Bandwidth Saving Parameter (BSP) γ = K/A
The BSP γ related to Number of Type 2 Operators is shown in Table-5.1-1.
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Table 5.1-1 BSP γ related to Number of Type 2 Operators
N A B K γ
2 10 10 0 0.00%
3 12 15 -3 -25.00%
4 18 19 -1 -5.56%
6 33 28 5 15.15%
8 52 37 15 28.85%
10 75 46 29 38.67%
12 102 55 47 46.08%
14 133 64 69 51.88%
16 168 73 95 56.55%
18 207 82 125 60.39%
20 250 91 159 63.60%
22 297 100 197 66.33%
24 348 109 239 68.68%
26 403 118 285 70.72%
28 462 127 335 72.51%
30 525 136 389 74.10%
32 592 145 447 75.51%
34 663 154 509 76.77%
36 738 163 575 77.91%
38 817 172 645 78.95%
40 900 181 719 79.89%
The result of Table 5.1-1 is plotted in Fig 5.1-3. The transmission investment and operational cost of network management is proportional to the transmission links of bandwidth requirement. The operational cost and transmission investment of Non-IEXCNA model compared to IEXCNA model is shown in Fig. 5.1-4.
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IEXCNA Model BSP Curve
-40.00%
-20.00%
0.00%
20.00%
40.00%
60.00%
80.00%
100.00%
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
Type 2 Operators
Figure 5.1-3 BSP of IEXCNA model related to N of Type 2 Operators
The operational cost of IEXCNA model compared to NON-IEXCNA model is shown as Fig 5.1-4.
non-IEXCNA vs IEXCNA
0 100 200 300 400 500 600 700 800 900 1000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Type 2 operaotrs
Cost Index
non-IEXCNA cost index IEXCNA cost index Figure 5.1-4 Non-IEXCNA model operational cost compared to IEXCNA model operational cost
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5.1.7 Erlang B Formula
one E1=2Mbps; 2Mbps÷ 12Kbps=166
one E1 can support 166Voice channels; considering overhead and packet loss, it should be 150 channels for normal condition.
Blocking rate also called Quality of Service or Grade of Service. If blocking rate En(a)=0.01, based on
Erlang B formula (Freeman, 1984),
The Erlang B table of channel requirement is shown in the table 3 for different input of blocking rate and traffic load. N is the required bandwidth number of channel.
Table 5.1-2 Erlang B Table
Erlang B Loss Probability n
0.001 0.010 0.1
15 6.077 8.108 12.484
30 16.684 20.337 28.113 45 28.447 33.342 44.165
60 40.795 46.95 60.401
90 66.484 74.685 93.146 100 75.242 84.064 104.11
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The overall traffic load calculation for Type 2 A operator and Type 2 B operator are shown in the Table 4.
Table 5.1-3 Overall traffic load and bandwidth dimensioning
subscriber call probability holding time (minutes) usage
(minutes) Erlang Channel No
50000 0.40 3 60000 250 273
50000 0.35 3 52500 375 400
50000 0.30 3 45000 500 527
50000 0.25 3 37500 625 657
50000 0.20 3 30000 750 779
50000 0.15 3 22500 875 904
50000 0.10 3 15000 1000 1029
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5.2 Overall IEXCNA Model for Commercial VoIP Service
Based on the traffic load calculation and bandwidth dimensioning, the practical example of network architecture based on IEXCNA model for VoIP service is described in the Fig.
5.2-1.
Figure 5.2-1 The practical example of network architecture based on IEXCNA model for VoIP service
5.2.1 New Business Opportunity for VoIP Service
Wireless VoIP (Voice over Internet Protocol) technology has just started to make an impact in the telecommunication space. Most of the industry pundits consider Wireless VoIP as the application that is going to revolutionize the whole telecommunication market (Salsano and Veltri, 2002). Even though there are numerous challenges in supporting VoIP over Wi-Fi (Wireless Fidelity) telephony, the present infrastructure is well equipped to handle VoIP over Wi-Fi calls (Butler, 2006).
Issues like security, handoffs and QoS (Quality of Service) have been addressed by various standards that have emerged over the last couple of years. With large shipments of VoIP over Wi-Fi devices already out there, one could easily predict that next big thing in telecom space is Wireless VoIP technology. Access Points, WLAN (Wireless Local Area Network) Switches/Mobility Controllers, 802.11 Chipsets and Wireless handsets that support VoIP are being shipped in large volumes in all parts of the world.
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Wireless VoIP will be more powerful when IMS based IEXCNA system is introduced into the infrastructure. The Interoperability between wireless and cellular infrastructure is a tough technical challenge at present. The hand-off and roaming in the Cellular/VoIP over Wi-Fi convergence arena, is more complex than the simple handoff challenges from one Acess point to another. The IMS based IEXCNA system can provides wireless-cellular convergence for VoIP service operators (Butler, 2006).
5.2.2 Business Service Market of Various VoIP Services The VoIP Business Service Market will be growing and driven by:
– Expiration of existing business circuit switched equipment, and its replacement with VoIP equipment
– Lower costs of VoIP calls
– Massive growth of the telecoms market
– Businesses reaping the efficiencies of carrying voice and data traffic over one high quality network
– Realisation that integrating voice functionality into business critical IT applications will improve business productivity
Figure 5.2-2 Business Service Market for VoIP Revenues
Different business users will obtain their VoIP connectivity in different ways:
– Very small businesses will utilise either business broadband services or fully hosted VoIP services
– Some small and medium businesses will replace their key systems with small IP-PBX servers
– Larger enterprises will either adopt fully managed hosted VoIP solutions from service providers, or replace their existing circuit switched internal networks with IP-PBX technologies running over high quality converged voice and data networks
– Many users will explore and adopt peer-to-peer VoIP services, either as a primary or
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secondary way of connecting to partners, colleagues and customers at little cost.
– Business users will increasingly connect their VoIP infrastructures through low cost VoIP peering and interconnect services, bypassing established telco PSTN infrastructures entirely. Such connectivity is only just becoming established but is likely to prove very popular.
However, there will remain for some time, a legacy business customer base which will not want to replace their circuit switched services with VoIP services, and these businesses will continue to be serviced by existing service providers, even if such providers have migrated their own core networks to VoIP.
5.2.3 The Impact of VoIP on Telecom Operators Revenues
Whilst deregulation and competition in the telecoms industry have led to price and revenue erosion across many markets around the world, this trend is being exacerbated by the increasing penetration of VoIP into the telecoms environment.
Although by 2010, it is anticipated business VoIP services will generate US$18 billion in revenues, this will be at the expense of lost circuit switched business voice revenues of US$54 billion, a net loss to the industry of US$36 billion. Combined with further losses incurred in the residential and mobile markets, the combined losses will significantly impact upon both existing traditional telecom's operators, and state treasuries (Butler, 2006).
Figure 5.2-3 VoIP Impact on Net Industry Business
The only way telecom's operators can avoid being driven into bankruptcy, is by either refocusing their activities on alternative revenues streams, or by driving costs out of their voice businesses. If voice is almost going to ‘go for free’, then it must cost virtually nothing to provide – it must in effect be just an application, which happens to use the same common infrastructure as other communications applications. This is the rationale for telco’s investing in next generation all-IP based networks.
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Voice over IP (VoIP) technologies have, over the last few years, become an increasingly credible option for delivering voice connectivity to business users. Services based upon broadband connectivity, hosted VoIP managed services, peer-to-peer technologies and converged network solutions in enterprises, combine to fuel a new market which has now crossed the marketing chasm, and has penetrated the early mass market for business communications voice connectivity.
The opportunities and benefits to businesses of adopting VoIP for voice services include:
– Lower call charges, reductions in mobile telephone calls and costs for roaming users – Convergence of voice and data onto a single network, along with reduced network
management costs
– Simplification of deployments including the cost and organisational impacts of moves and changes, location independence of end-users and ease of extending networks to new sites
– Integration with other applications and the ability to easily add multimedia functionality to VoIP terminals
Barriers do, however, remain to the adoption of VoIP within businesses:
– Cultural - the overall conservative nature of many large and small enterprises towards new technologies, cultural and organisational issues surrounding the convergence of voice and data facilities and concerns about the negative impact on performance and capacity if new deployments do not go well
– Technology – the challenges of deploying a sufficiently high quality-of-service capable network, security and meeting power requirements
– Connectivity - for small companies, non-availability of broadband
Nonetheless, by the end of the decade, it will be the exception for large and small companies not to connect using VoIP technologies in some form or another. Entwined with other substantive changes in the telecoms industry, including massive fibre capacity, penetration of broadband access, increasing speed of routers, open-source technologies, deregulation and privatization, VoIP is helping to redefine business communications and its associated costs.
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