event of a primary-device failure. Additional Router Functionality Beyond simply acting as a connection point to the Internet, routers can provide other functionality, including the following. Firewall Routers can screen incoming and outgoing traffic. Deep Packet Inspection (DPI) You can use DPI to manage internal traffic. See Chapter 1 for more information about DPI. Data Centers and IP Private Branch Exchanges Encryption protocols Routers employ IPsec and other protocols for send- ing packets over the Internet securely. T1 and T3 multiplexers See Chapter 5 for more information about T1 and T3. Video Digital Signal Processor (DSP) This is used for conferencing services. Wi-Fi An increasingly popular capability for branch and small offices, this allows users to connect wirelessly to the router for Internet access. Session Initiation Protocol (SIP) SIP support permits trunking for Uni- fied Communications (UC) functions such as presence and instant messaging with other sites and VoIP calls. Quality of Service (QoS) This prioritizes voice and video in the WAN. Voice and video are assigned tags that classify them with a higher priority than data bits. These services are located on specialized circuit boards, or blades, within the router. In new routers, multiple services can be located on the same blade, which can have more than one processor. Blade servers hold blades that are arranged vertically and housed in racks in data centers. In contrast to horizontal circuit boards, vertical arrange- ments such as this conserve space and can share power supplies, fans, and cabling, thus consuming less energy. In addition, applications can be added or removed without taking the server out of service. IP PRIVATE BRANCH EXCHANGE SYSTEMS FOR INTERNAL USE IP phone systems operate on servers that use industry-standard operating systems and often open-standardized protocols. They don't require a great deal of space and are considered another application in the data center. IP Private Branch Exchange Systems for Internal Use IP for