After taking into account the half-duplex nature of the wireless medium and the overhead of wireless headers, the practical throughput on the 802.11b wireless network is about 7 Mbps. 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. Once this authentication occurs, traffic to and from the wireless device is encrypted using TKIP or WEP. Note The preceding information applies to large-scale networks. •Multicast packets on the WLAN are unacknowledged and are not retransmitted if lost or corrupted. However, this chapter addresses many issues related to larger enterprise-sized networks. 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. To give the user as much flexibility as possible in matching application policy locators to local policies, the RSVP local policy command line interface (CLI) accepts application ID match criteria in the form of Unix-style regular expressions for the policy locator. cRTP operates on a per-hop basis. A VoIP-capable WAN is most likely either privately owned or provided as a single service to all the sites of the enterprise by a SP. •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. (See Table 3-7. The WAN links that connect each of the spoke sites to the hub site are normally provisioned to accommodate different types of traffic (for example, data, voice, and video). The phone goes through this process once per software upgrade. The IP phone marks its voice control signaling and voice RTP streams at the source, and it adheres to the values presented in Table 3-2. This distribution of resources ensures that, given a hardware failure (such as a switch or switch line card failure), at least some servers in the cluster will still be available to provide telephony services. When compared to the RSVP bandwidth value, the priority queue must be over-provisioned. After packets have been marked with the appropriate tag at Layer 2 (CoS) and Layer 3 (DSCP or PHB), it is important to configure the network to schedule or queue traffic based on this classification, so as to provide each class of traffic with the service it needs from the network. Enable these features where appropriate to ensure that, when changes occur on the Layer 2 network, STP converges as rapidly as possible to provide high availability. Limiting bandwidth per application requires that an RSVP local policy matching the application bandwidth limit be applied to the router interface and that each reservation request flag the application to which it belongs so that it may be admitted against the appropriate bandwidth limit. The RSVP Local Policy provides the mechanism for controlling a reservation based on an Application ID. The business model and size of the office dictate whether the office might prefer key system operation (Line1, Line2, and so on appear on the buttons of each phone) or PBX-like operation with typically a single extension per phone and DID service from the CO. Downstream queuing concerns traffic traveling from the wired network to the AP and down to the wireless endpoint. The following sections examine the infrastructure layers and network services: Note For more information on campus design, see the Gigabit Campus Network Design white paper at http://www.cisco.com/warp/public/cc/so/neso/lnso/cpso/gcnd_wp.pdf. The policy maps define the traffic that is admitted into each queue. This practice eliminates topological loops at Layer 2, thus avoiding temporary flow interruptions due to Spanning Tree convergence. Traffic returning from the core layer and destined for the access layer will follow the shortest and/or least costly routed path. •The call control signaling, which consists of packets belonging to one of several protocols, according to the endpoints involved in the call (for example, H.323, MGCP, SCCP, or (J)TAPI). When Secure Real-Time Transport Protocol (SRTP) encryption is used, the payload for each packet is increased by 4 bytes. This amount should be sufficient for most large enterprise deployments. As mentioned previously, redundant DHCP servers should be deployed. To control wireless network channels and eliminate channel overlap, it is important to configure a channel number manually on each AP based on its location. Sometimes voice mail is still deployed for these employees (again, accessed from a common phone or break room) for human resources or training purposes. Note With the introduction of RSTP 802.1w, features such as PortFast and UplinkFast are not required because these mechanisms are built in to this standard. Once a highly available, fault-tolerant, multi-layer campus network has been built, network services such as DNS, DHCP, TFTP, and NTP can be deployed. The entire usable bandwidth (75% of the link speed) can be assigned to LLQ classes, as shown in Figure 3-13, as it normally is today. As with VAF, exercise care when enabling VATS because activation can have an adverse effect on non-voice traffic. Instead, shared resources are deployed for use by these employees. This DHCP client Request, once acknowledged by the DHCP server, will allow the IP phone to retain use of the IP scope (that is, the IP address, default gateway, subnet mask, DNS server (optional), and TFTP server (optional)) for another lease period. This means that the call admission control function is separate from the scheduling and policing functions, which can be performed by the Low Latency Queuing (LLQ) algorithm according to predefined class maps, policy maps, and service policies. It also is connected via a single Ethernet cable to a LAN switch that provides inline power to the phones. The Tspec, as described in RFC 2210, contains the following attributes to describe the traffic flow in detail: •Token Bucket Rate [r] — The average traffic rate in bytes per second, •Token Bucket Size [b] — The maximum burst of a flow in bytes, •Peak Data Rate [p] — The peak traffic rate in bytes per second. Next, an understanding of wireless technology is required. This oversubscription, coupled with individual traffic volumes and the cumulative effects of multiple independent traffic sources, can result in the egress interface buffers becoming full instantaneously, thus causing additional packets to drop when they attempt to enter the egress buffer. The survey should include verifying non-overlapping channel configurations, AP coverage, and required data and traffic rates; eliminating rogue APs; and identifying and mitigating the impact of potential interference sources. Computer equipment can be plugged into the back of the phone, and virtual LAN (VLAN) technology can be used to provide virtual separation (and therefore security) of voice from data traffic. To ensure proper NTP time synchronization on routers and switches, it may be necessary to configure time zones using the clock timezone command (in Cisco IOS software) and/or set timezone command (in Catalyst Operating System). While useful, this average does not show the congestion peaks on a campus interface. Figure 3-9 Link Fragmentation and Interleaving (LFI). Compressed Real-Time Transport Protocol (cRTP). •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. Without using an app-id, there is only one bandwidth value that is configurable per interface in RSVP. Another important aspect of the RSVP protocol is that it adopts a soft-state approach, which means that for each session both the path state and the reservation state along the network need to be refreshed periodically by the application by sending identical Path and Resv messages. Inter-region call with audio codec set to G729: •Initial request: 40 kbps, using a 10 ms worst-case scenario, •Updated request: 24 kbps, using the preferred sample size of 20 ms. Inter-region call with audio codec set to G711: •Initial request: 96 kbps, using a 10 ms worst-case scenario, •Updated request: 80 kbps, using the preferred sample size of 20 ms. As with the audio stream, the initial reservation for the video stream will rely on the region settings because the endpoint codec capabilities will not be fully negotiated at the time of the reservation. The use of IBM Cabling System (ICS) or Token Ring shielded twisted-pair type 1A or 2A cabling is supported for IP Communications under the following conditions: •Cable lengths should be 100 meters or less. Furthermore, only a single Ethernet wire or jack is required to each employee location or desktop. This indicates to the requesting application that an end-to-end reservation has been established and that bandwidth has been set aside for this data flow in all RSVP-enabled routers across the network. DNS server(s) deployed within a network provide a database that maps network services to hostnames and, in turn, hostnames to IP addresses. This amount of overlap ensures smooth roaming for wireless endpoints as they move between AP coverage cells. (This arrangement is called key-system or square-keyswitch type of deployment.). The combined non-RSVP and RSVP admission control mechanisms must not use more bandwidth than is allocated to ensure that the priority queue is never over-subscribed. Figure 3-11 illustrates this mechanism with a generic example, where R is the rate with traffic shaping applied. Note There are some new QoS mechanisms for DSL and cable technologies that can provide guaranteed bandwidth; however, these mechanisms are not typically deployed by service providers, and these services are still significantly oversubscribed. Routing protocols at the core layer should again be configured and optimized for path redundancy and fast convergence. The Resource Reservation Protocol (RSVP) is the first significant industry-standard protocol for dynamically setting up end-to-end QoS across a heterogeneous network. In other words, these links and topologies are unable to provide guaranteed bandwidth, and when traffic is sent on these links, it is sent best-effort with no guarantee that it will reach its destination. Attendant consoles can also be software based consoles from Cisco-certified third-party vendors. This amount of overlap ensures smooth roaming for wireless endpoints as they move between AP coverage cells. Note We have begun to change the marking of voice control protocols from DSCP 26 (PHB AF31) to DSCP 24 (PHB CS3). Once a highly available, fault-tolerant, multi-layer campus network has been built, network …