In addition to the LFI mechanisms mentioned above, voice-adaptive fragmentation (VAF) is another LFI mechanism for Frame Relay links. DHCP is used by hosts on the network to obtain initial configuration information, including IP address, subnet mask, default gateway, and TFTP server address. If the TFTP server receives a request for a file that it does not have (such as a configuration file created and maintained by the TFTP server of a different cluster), it will search for that file in a list of alternate file locations. •QoS trust boundary extension to voice devices. Table 3-5 does not include Layer 2 header overhead and does not take into account any possible compression schemes, such as compressed Real-Time Transport Protocol (cRTP). In addition to using no more than 75% of the total available bandwidth for data, voice, and video, the total bandwidth configured for all LLQ priority queues should typically not exceed 33% of the total link bandwidth. In addition, if more than one type of traffic is provisioned in the priority queue (for example, voice and video), this configuration defeats the purpose of enabling QoS because the priority queue essentially becomes a first-in, first-out (FIFO) queue. Note If Cisco Catalyst 4000 Series switches are used as Layer 3 devices at the distribution layer, a minimum of a Supervisor Engine 2+ (SUP2+) or Supervisor Engine 3 (SUP3) module is required. HSRP should also be configured in such a way as to load-balance traffic between both HSRP routers. LAN infrastructure design is extremely important for proper IP telephony operation on a converged network. Figure 3-11 shows the difference between these two approaches from the perspective of a Cisco IOS router. Whether roaming at Layer 2 or Layer 3, device downtime decreases from 300-400 ms to 100 ms or less. These bandwidth numbers are based on voice payload and IP/UDP/RTP headers only. By using the passive-interface command on all interfaces facing the access layer, you prevent routing updates from being sent out on these interfaces and, therefore, neighbor adjacencies are not formed. At the default packetization rate of 20 ms, SRTP VoIP packets have a 164-byte payload for G.711 or a 24-byte payload for G.729. This feature prevents defective links from being mistakenly considered as part of the network topology by the Spanning Tree and routing protocols. Equation 1 and all other formulas within this section include a 25% over-provisioning factor. The app-id is not a single piece of information but multiple variable-length strings. This method requires only that the wireless device be configured with the proper SSID for the wireless VLAN to which the device wishes to connect. Properly designing a WLAN requires, first and foremost, ensuring that the existing wired network is deployed in a highly available, fault-tolerant and redundant manner. Recommended Hardware and Software Combinations, Application ID Call Admission Control Model, How Cisco Unified CallManager Uses the Application ID, Cisco Unified Wireless IP Phone 7920, page 21-30. In this case, we assume that both policy and admission control are successful on 10.50.50.50, which means that the bandwidth provided by the Tspec in the path state for this session is reserved on the outgoing interface (in the same direction as the data flow, that is from Device 1 to Device 2), and a corresponding "reservation state" is created. Example 3-7 illustrates both methods of configuring the NTP.conf file. Properly designing a WAN requires building fault-tolerant network links and planning for the possibility that these links might become unavailable. Furthermore, it is always a good idea to provide a local ACS or an on-AP RADIUS server at remote sites to ensure that remote wireless devices can still authenticate in the event of a WAN failure. It should also be noted that, beginning in Cisco IOS Release 12.2(13)T, cRTP can be configured as part of the voice class with the Class-Based cRTP feature. Local policies based on Application ID are applied to an interface using the ip rsvp policy local identity command. This 75% rule assumes that some bandwidth is required for overhead traffic, such as routing and Layer 2 keep-alives. Figure 3-5 Data Traffic Oversubscription in the LAN. The section describes bandwidth provisioning for the following types of traffic: As illustrated in Figure 3-15, a voice-over-IP (VoIP) packet consists of the payload, IP header, User Datagram Protocol (UDP) header, Real-Time Transport Protocol (RTP) header, and Layer 2 Link header. The following sections examine the required infrastructure layers and network services: WAN deployments for voice networks must follow a hub-and-spoke topology, with a central hub site and multiple remote spoke sites connected into the central hub site. It could also be a virtual private network (VPN) using the public Internet as the transport, but as such it is not QoS-enabled and, therefore, is not a good fit for deploying VoIP traffic. If call admission control is not desired on an interface, set the bandwidth value to 75% of the interface bandwidth. Time synchronization is also important for other devices within the network. For low-speed links (less than 768 kbps), use of link fragmentation and interleaving (LFI) mechanisms is required for acceptable voice quality. This new feature provides compression statistics and bandwidth status via the show policy interface command, which can be very helpful in determining the offered rate on an interface service policy class given the fact that cRTP is compressing the IP/RTP headers. I am going to design and build an LAN network under a tunnel underground with long distance between the switches. Typical access layer switches include the stackable Cisco Catalyst 2950, Cisco Catalyst 3500XL, Cisco Catalyst 3550, and Cisco Catalyst 3750, and also the larger, higher-density Catalyst 4000 and 6000 switches. Further, proper LAN infrastructure design requires deploying end-to-end QoS on the network. The following link efficiency techniques improve the quality and efficiency of low-speed WAN links. With Cisco IOS releases prior to 12. When an external connection to an NTP server is not available, Cisco IOS software can be used as a reference server for other devices so that all devices including phones use the same time reference. DNS server(s) deployed within a network provide a database that maps hostnames to IP addresses. The policy maps define the traffic that is admitted into each queue. Just as QoS is necessary for LAN and WAN wired network infrastructure in order to ensure high voice quality, QoS is also require for wireless LAN infrastructure. Deploying inline power-capable switches with uninterruptable power supplies (UPS) ensures that IP phones continue to receive power during power failure situations. Bandwidth provisioning should include not only the bearer traffic but also the call control traffic. For example, if a distribution switch fails, all traffic flows will be reestablished through the remaining distribution switch. Shorter lease times require more frequent renewal of the DHCP configuration and increase the amount of DHCP traffic on the network. •Enable QoS Element for Wireless Phones on the AP. In addition to the LFI mechanisms mentioned above, voice-adaptive fragmentation (VAF) is another LFI mechanism for Frame Relay links. Personal calls are probably made from a public payphone in the break room or from a small number of phones set aside in a shared employee space that employees can access during their breaks. •Other voice services—When a small number of sites (such as five or fewer) are interconnected, the on-net dial plan is often simple enough to be implemented directly at each site. If the IP telephony deployment also incorporates remote branch telephony sites, as in a centralized multisite Cisco Unified CallManager deployment, a centralized server can be used to provide DHCP service to devices in the remote sites. How quickly HSRP converges when a failure occurs depends on how the HSRP hello and hold timers are configured. A gatekeeper can be used for keeping dial-plans consistent and easily manageable between sites. Downstream queuing concerns traffic traveling from the wired network to the AP and down to the wireless endpoint. Properly designing a WLAN requires, first and foremost, ensuring that the existing wired network is deployed in a highly available, fault-tolerant and redundant manner. These sites tend to be better candidates for DID service. •Internet connectivity—This is provided via a DSL or a similar type of uplink to the local ISP, which also might host the company's e-mail services. When deploying wireless voice, observe the following specific AP configuration requirements: •Enable Address Resolution Protocol (ARP) caching. Another QoS requirement for wireless networking is the appropriate provisioning of bandwidth. Remote databases have unknown response times and can adversely affect authentication times. With the IntServ/DiffServ model, it is therefore possible to add RSVP call admission control to a network that is already using a Differentiated Services approach to QoS. The following sections discuss these requirements: Properly designing a LAN requires building a robust and redundant network from the top down. Figure 3-8 Optimized Queuing for VoIP over the WAN. It is important, when using VATS, to set end-user expectations and make them aware that data applications will experience slowdowns on a regular basis due to the presence of voice calls across the WAN. The network inFigure 3-2 has the following components: •Employee desktop—Cisco 7960 IP Phones are provided for employees who work at a desk with a computer. While the ingress Ethernet port on the AP can receive traffic at 100 Mbps, the maximum throughput on an 802.11b wireless network is 11 Mbps. Mobile devices typically use IP addresses for short increments of time and then might not request a DHCP renewal or new address for a long period of time. Note The Cisco Unified IP Phone 7912 should not be used with Category 3 cable when a PC is attached because the switch and PC ports on this phone cannot be forced to 10 Mb, full duplex. Configuring the maximum 11 Mbps data rate ensures the best level of throughput for voice devices and the largest number of active calls per AP. Properly provisioning the network bandwidth is a major component of designing a successful IP network. For the same reasons, redundant devices and network links that provide quick convergence after network failures or topology changes are also important to ensure a highly available infrastructure. For example, there may be multiple remote sites that connect to the WAN with a T1 interface, yet the central site has only a single T1 interface. AP and wireless endpoint devices use acknowledgements on the link layer to ensure reliable delivery. You can reduce the affects of multipath distortion by eliminating or reducing interference sources and obstructions, and by using diversity antennas so that only a single antenna is receiving traffic at any one time. At the default packetization rate of 20 ms, SRTP VoIP packets have a 164-byte payload for G.711 or a 24-byte payload for G.729. While useful, this average does not show the congestion peaks on a campus interface. For links speeds of 768 kbps or lower, video conferencing traffic should be placed in a separate class-based weighted fair queue (CBWFQ). Wireless voice RSVP ), and traffic to and from the source to the one for the two main signaling. Leap requires the wireless endpoint roaming in extended battery life for the LAN the! Bandwidth allocation authenticates across the tunnel using a user name and password authenticate! 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