ideo. Even though voice quality is generally good in IP systems, the aforementioned problems can occur. Therefore, packets with voice and video are given priority over packets containing bits that are less time-sensitive, such as e-mail. Voice QoS and Security Keeping networks secure is a difficult, ongoing challenge. Security needs to be installed in IP telephony system www.TechnicalPDF.com servers, and in all of the Layer 2 and Layer 3 switches, the routers, and the firewalls. In particular, many IP systems use common protocols. These protocols are wide open in the sense that many hackers know how they work and put a great deal of effort into finding their vulnerabilities. Organizations use the following to ensure voice quality: QoS solutions These solutions mark and prioritize voice and are important to ensure minimal delays for acceptable voice quality. See the upcoming sections "Assessing Network Quality by Using Voice Quality Measurements" and "Prioritizing Voice and Video on a VLAN" for information about voice quality measurements and Virtual LANs (VLANs). Compression Compressing and digitizing voice signals impacts quality. For example, the compression algorithm, Adaptive Multi-Rate Wideband (AMR-WB), based on the G.722.2 standard, is able to compress 16,000 samples of voice per second to rates as low as 12.65 kilobits per second. At this rate, each voice session uses only 12.65KB of bandwidth, but provides better audio than earlier compression standards, including G.711, which required more capacity. G.722.2 provides high-definition (HD) voice and is used for some mobile voice traffic. In addition to the preceding, proxy servers authenticate callers to verify that they are who they say they are before being sent to their destination. Proxy servers, located in gateways and firewalls, serve as intermediaries between callers and applications or endpoints, telephones, and other devices connected to the LAN. Assessing Network Quality by Using Voice Quality Measurements IT staff members can manage VoIP by usin