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The Impact of Firewalls on Packet Voice
The Tolly Group, Jan 2001, Pages: 42
Network managers seeking to integrate voice services into their data networks will need to consider the impact that network security has on latency-sensitive packet voice. At a minimum, voice traffic almost certainly will need to traverse firewalls that secure a network from unwanted access. Firewalls, however, may render packet voice useless if they block desired calls from completing or cause additional end-to-end latency, thereby lowering voice quality. Firewall implementations also vary by design and may, therefore, impact end-to-end latency differently.
This issue seeks to understand the impact that different firewall architectures have on the end-to-end latency and quality of voice delivered over a converged network. This issue focused on branch-to-branch and branch-to-remote scenarios that employ H.323 standards-based VoIP technology, and are secured using packet filtering firewalls. The WAN connection between the locations in each scenario was a simulated T1 with no additional jitter or packet loss induced. Furthermore, testing was limited to the impacts of firewall on voice quality in the absence of any traffic shaping or Quality-of-Service mechanisms.
Researchers established two firewall-secured LANs and connected them via a simulated WAN. A series of tests investigated the latency and voice quality differences that result from a firewall actively filtering network traffic and actively translating network addresses.
This issue focused on Perceptual Speech Quality Measure (Psqm), and latency. Primary net production was completed using AltiGen Communications, Inc. Altiserv PBX with built-in H.323 Gateway, AltiWare OE (version 3.5), Netscreen-100 Firewall (an Asic-based firewall implementation) and a Nokia IP650 Firewall with Checkpoint Software (a software-based firewall implementation). Key infrastructure elements consisted of standard Ethernet/Fast Ethernet switch environment using a Nebula 4000 Workgroup Switch, emulated T1 and modem connection using Shunra Software's 'The Cloud' simulation software, Agilent Technologies' Voice Quality Tester and an Acterna DA-360 DominoPlus Chassis (with a DA-362 DominoFE Internetwork Analyzer module).
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