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Top1. Introduction
Our research on ATM model is based on the ATM model that we built in our research paper. The model is explained in-depth below. Figure 1 shows the fundamentals of VoIP protocol stack architecture to implement a VoIP network system over WLANs (Chong & Matthews, 2004; Lindgren, Almquist, & Schelen, 2002). Voice packets are transmitted over IP-based networks. VoIP is a real-time application and transmits the voice on a Real-Time Transport Protocol (RTP), User Datagram Protocol (UDP) and Internet Protocol (IP) over networks (Cai, Ling, Shen, Mark, & Cai, 2009). Each voice packet is small in size and the voice packet has the headers: RTP (12 bytes), UDP (8 bytes), and IP (20 bytes) headers. The data-link layer Medium Access Control (MAC) has a (34 bytes) header. All these headers sum up to 74 bytes of overhead in the VoIP application. The Session Initiation Protocol (SIP) was considered to handle a multimedia call setup and H.323 is considered by ITU to allocate IP-based phones on the public telephone network to talk to a PC-based phone over IP-based networks (Ehlert, Zhang, & Magedanz, 2008). It is a standard that specifies the components, protocols and procedures for multimedia communication services such as real-time audio, video and data communications over IP-based packet networks (Hasbullah, Nisar & Said, 2009; Nisar, Said & Hasbullah, 2010)
Figure 1. Internal view of the “NorthWest” subnet
Figure 1 shows the components and subsequent layout of the NorthWest subnet. Each of the subnets has identical components and layout as that of the Northwest subnet. Each has 2 ATM Voice client workstations, 2 ATM Video client workstations, 2 ATM Data (Email & FTP) client workstations, a central ATM cross connection switch, and an ATM server. Each client is connected individually to the central switch; and so is the server. These links are also all full-duplex ATM connection links. The central switch is then also connected to the network outside of the subnet. As stated each subnet is connected to a switch, so the central switch inside the subnet thus is connected to one of the central switches outside of the subnet (E.g. CentralWest switch). This connection is also made via a bidirectional ATM link. Thus, altogether, there are 8 links being utilised within a subnet.
Figure 2 shows the high-level perspective of the ATM model that was produced in research Lab. The model consists of 8 main components: 2 central ATM cross connection switches, 4 subnets, an application config and a profile config.
Figure 2. High level view of the ATM network model
As shown in Figure 2, the subnets are each connected to one of the cross connection switches (NorthWest & SouthWest to the CentralWest switch; SouthEast & NorthEast to the CentralEast switch). Both central switches are then connected to each other; utilising a total of 5 links altogether. These links are all full-duplex (bidirectional) ATM connection links. The application config “Applications” houses the definitions for all the applications that will be used in our model. In our research Lab ATM model three definitions have already been setup; these are definitions for Email, FTP, Voice and Video. The profiles config “Profiles” houses the rules and settings for applications. So in this case there will be four profiles – one for each application definition outlined in the application config.
Top2. Node Configuration (Station, Switch, Server)
In this model, there are a total of 34 nodes. The categorical breakdown of them is as follows in Box 1.
Table 1. Average voice packet delay variance (sec)
| Average Delay Variance (sec) |
| Segment Size (bytes) | 20 | 2,000 | 64,000 | 100,000 | Overall |
| Average (sec) | 0.0000018 | 0.0000018 | 0.0000018 | 0.0000018 | 0.0000018 |