In all subnets, the DHCP scope provides TFTP1's IP address as Option 150. The number of devices on an AP affects the amount of time each device has access to the medium. If the traffic characteristics specified by the RSVP messages for a certain flow are less than or equal to the parameters in the command, then RSVP will direct the flow into the PQ. However, the codec sampling rate is negotiated for every call and might not be the preferred setting because it is not supported on one or more of the endpoints. VATS is available in Cisco IOS Release 12.2(15)T and later. All voice media and signaling traffic should be placed in the highest-priority queue, and all other traffic should be placed in the best-effort queue. The principles of RSVP signaling can be explained by using the example shown in Figure 3-10. Another very important consideration for wireless infrastructure is wireless endpoint roaming. These are often single-line phones that typically are not used to receive calls from the PSTN (they also do not have PC Ethernet ports). Extensible Authentication Protocol (EAP) is the preferred method of wireless device authentication (especially voice devices) because it provides the most secure and robust mechanism for access to the network and voice VLAN(s). Equation 1 and all other formulas within this section include a 25% over-provisioning factor. Because the phones and computer equipment are all Ethernet-based, only Ethernet wiring is required in the office. Wireless endpoints and APs communicate via radios on particular channels. With the addition of wireless IP telephony endpoints such as the Cisco Unified Wireless IP Phone 7920, voice traffic has moved onto the WLAN and is now converged with the existing data traffic there. Figure 3-8 illustrates the main reasons why traffic shaping is needed when transporting voice and data on the same IP WAN. When scheduled maintenance involves the downloading of new software, download times are a function of the number of phones requiring upgrades, the file size, and the WAN link's bandwidth and traffic utilization. Each site contains a Cisco Unified CME system and can follow either the single-site model or the centralized call processing model. Because these phones support only 10 Mb Ethernet and their ports cannot be manually configured, the upstream switch port should be set to either AUTO negotiate or 10 Mb, half-duplex. In networks where remote locations are separated from the central site by low-speed or congested WAN links, an ACS server can be located at the remote site and remote wireless devices or users can be authenticated by this server locally, thus eliminating the potential for delayed authentication via a centralized ACS across the WAN link. The entrance criterion for this queue could be a Transmission Control Protocol (TCP) port number, a Layer 3 address, or a DSCP/PHB value. This representation takes a general view of the branch office. VAF uses FRF.12 Frame Relay LFI; however, once configured, fragmentation occurs only when traffic is present in the LLQ priority queue or when H.323 signaling packets are detected on the interface. Under normal operations, a phone in subnet will request TFTP services from TFTP1_P, while a phone in subnet will request TFTP services from TFTP1_S. However, with the introduction of standards-based IEEE 802.1w Rapid Spanning Tree Protocol (RSTP) and 802.1s Multiple Instance Spanning Tree Protocol (MISTP), Spanning Tree can converge at much higher rates. 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. The configuration information is provided by a DHCP server located in the network, which responds to DHCP requests from DHCP-capable clients. 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). If redundant DHCP servers are deployed at the central site, both servers' IP addresses must be configured as ip helper-address. The preceding sections explain how to use one TFTP server at a time to service phones from multiple clusters. When more than 64 kbps worth of traffic is sent across the WAN, the provider marks the additional traffic as "discard eligible." Do not disable this service on the branch router because doing so will disable the DHCP relay agent on the device, and the ip helper-address configuration command will not work. Specifically, media resources, DHCP servers, voice gateways, and call processing applications such as Survivable Remote Site Telephony (SRST) and Cisco Unified CallManager Express (CME) should be deployed at non-central sites when and if appropriate, depending on the site size and how critical these functions are to that site. In non-failure scenarios, these redundant links may be used to provide additional bandwidth and offer load balancing of traffic on a per-flow basis over multiple paths and equipment within the WAN. These weaknesses, coupled with the complexity of configuring and maintaining static keys, can make this security mechanism undesirable in many cases. 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. Ports that are set to errdisable state by BPDU guard must either be re-enabled manually or the switch must be configured to re-enable ports automatically from the errdisable state after a configured period of time. Note that Table 3-4 assumes 24 kbps for non-cRTP G.729 calls and 10 kbps for cRTP G.729 calls. VLAN access control, 802.1Q, and 802.1p tagging can provide protection for voice devices from malicious internal and external network attacks such as worms, denial of service (DoS) attacks, and attempts by data devices to gain access to priority queues via packet tagging. If RSTP has been enabled on the Catalyst switch, these commands are not necessary. Proper WAN infrastructure design is important for proper IP telephony operation on a converged network with two or more Cisco Unified CME systems or Cisco Unified CME systems along with Cisco Unified CallManager systems. Queuing on the wireless network occurs in two directions, upstream and downstream. LAN infrastructure design is extremely important for proper IP telephony operation on a converged network. Table 3-4 lists the bandwidth consumed by the voice payload and IP header only, at a default packet rate of 50 packets per second (pps) and at a rate of 33.3 pps for both unencrypted and encrypted payloads. WAN connectivity—The network between the sites is likely to be a private WAN of some type. The Cisco CCIE Enterprise Infrastructure (v1.0) Practical Exam is an eight-hour, hands-on exam that requires a candidate to plan, design, deploy, operate, and optimize dual stack solutions (IPv4 and IPv6) for complex enterprise networks. Cisco Unified IP Phones adhere to the conditions of the DHCP lease duration as specified in the DHCP server's scope configuration. This queuing is required to reduce jitter and possible packet loss if a burst of traffic oversubscribes a buffer. The queuing scheme within this class is first-in-first-out (FIFO) with a minimum allocated bandwidth. Note The Cisco Unified IP Phone 7912 IP Phone 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 Mbps, full duplex. PoE (or inline power) is 48 Volt DC power provided over standard Ethernet unshielded twisted-pair (UTP) cable. VAF is typically used in combination with voice-adaptive traffic shaping (se0 the "Voice-Adaptive Traffic Shaping" section). For this reason, the wireless voice device might still be able to place a voice call on an AP that has already reached the limit of 7 or 8 calls, thus still resulting in dropped calls or poor voice quality. •Protection from malicious network attacks. Relying on DNS, however, can be problematic. A single AP can support up to 50 users with this functionality. Inter-region video call, with G.729 audio codec and video setting of 384 kbps: •Updated request: (384 - 8) * 1.07 = 402 kbps. Because the ACS server must access the user database to authenticate wireless devices, the location of the user database affects the amount of time the authentication will take. PortFast ensures that the phone or PC, when connected to the port, is able to begin receiving and transmitting traffic immediately without having to wait for STP to converge. As a consequence, the area where you must provision bandwidth for control traffic lies between the branch routers and the WAN aggregation router at the central site. However, as sample size increases, so does packetization delay, resulting in higher end-to-end delay for voice traffic. The following example illustrates the configuration of NTP time synchronization on Cisco IOS and Catalyst Operating System devices. The application residing on Device 1 originates an RSVP message called Path, which is sent to the same destination IP address as the data flow for which a reservation is requested (that is, and is sent with the "router alert" option turned on in the IP header. Savings just in wiring of a new office could be enough to make Cisco Unified CME cost-effective. In North America, with allowable channels of 1 to 11, channels 1, 6, and 11 are the three usable non-overlapping channels for APs and wireless endpoint devices. (See Table 3-6 and Table 3-7.). Figure 3-5 illustrates the typical oversubscription that occurs in LAN infrastructures. This network is essentially the same as the standalone model explored in the preceding section. Likewise, as the sample size increases, IP header overhead is lower because the payload per packet is larger. 4. Note Cisco Unified CallManager does not include SRTP overhead or the Layer 2 overhead in the RSVP Reservation. For this reason, Cisco recommends always using a switch that has at least two output queues on each port and the ability to send packets to these queues based on QoS Layer 2 and/or Layer 3 classification. Provided the rest of the telephony network is available during these periods of power failure, then IP phones should be able to continue making and receiving calls. In addition, centralized gateways and centralized hardware media resources such as conference bridges, DSP or transcoder farms, and media termination points are located in the data center or server farm. Because of the bursty nature of data traffic and the fact that real-time traffic such as voice is sensitive to packet loss and delay, QoS tools are required to manage wireless LAN buffers, limit radio contention, and minimize packet loss, delay, and delay variation. However, system installation, initial setup and configuration, software upgrades, and turning on new services are most likely done by the SP or the SI or VAR from whom the system was purchased or leased. Obviously, for very slow links (less than 192 kbps), the recommendation to provision no more than 33 percent of the link bandwidth for the priority queue(s) might be unrealistic because a single call could require more than 33 percent of the link bandwidth. 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. Figure 3-5 Data Traffic Oversubscription in the LAN. For voice endpoints, this mapping ensures priority queuing treatment and access to the voice VLAN on the wired network. It is common practice in Frame Relay or ATM networks to oversubscribe bandwidth when aggregating many remote sites to a single central site. 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. Ports that are set to errdisable state by BPDU guard must either be re-enabled manually or the switch must be configured to re-enable ports automatically from the errdisable state after a configured period of time. To use the IntServ/DiffServ operation model on a Cisco IOS router, use the following commands in interface configuration mode: When these commands are active, RSVP admits or rejects new reservations uniquely based on the upper bandwidth limits defined within the ip rsvp bandwidth command, independently from the actual bandwidth resources available on the interface. IP telephony endpoints can be configured to rely on DHCP Option 150 to identify the source of telephony configuration information, available from a server running the Trivial File Transfer Protocol (TFTP). QoS provisioning and queuing mechanisms are typically available in a WAN environment to ensure that voice and data can interoperate on the same WAN links. Running data over the network is not always a sufficient test of the quality of the cable plant because some non-compliance issues might not be apparent. For this reason, we recommend always using a switch that has at least two output queues on each port and the ability to send packets to these queues based on QoS Layer 2 and/or Layer 3 classification. In fact, in multisite WAN deployments, the call control traffic (as well as the bearer traffic) must traverse the WAN, and failure to allocate sufficient bandwidth for it can adversely affect the user experience. AP coverage should be deployed so that minimal or no overlap occurs between APs configured with the same channel (for example, see Channel 1 in Figure 3-12). The core layer of the Campus LAN includes the portion of the network from the distribution routers or Layer 3 switches to one or more high-end core Layer 3 switches or routers. The following sections describe the network infrastructure features as they relate to: •Cisco Unified CME Network Infrastructure Overview. •The criterion for video conferencing traffic to be placed into a priority queue is a DSCP value of 34, or a PHB value of AF41. Local policies based on Application ID are applied to an interface using the ip rsvp policy local identity command. •No other real-time application (such as video conferencing) is using the same link. In centralized call processing deployments, if a remote site is configured to use a centralized DHCP server (through the use of a DHCP relay agent such as the IP Helper Address in Cisco IOS) and if connectivity to the central site is severed, IP phones within the branch will not be able to renew their DHCP scope leases. This method ensures that, when voice traffic is being sent on the WAN interface, large packets are fragmented and interleaved. Properly provisioning the network bandwidth is a major component of designing a successful IP network. •As the WAN links become congested, it is possible to starve the voice control signaling protocols, thereby eliminating the ability of the IP phones to complete calls across the IP WAN. At least two DHCP servers should be deployed within the telephony network such that, if one of the servers fails, the other can continue to answer DHCP client requests. At the very least, interference impact should be alleviated by proper AP placement and the use of location-appropriate directional or omni-directional diversity radio antennas. By default, the queue depth available for each of the classes of traffic in Cisco IOS is 64. Figure 3-13 shows the potential for channel overlap when considering the three-dimensional aspects of 802.11b wireless coverage. Remote devices could receive DHCP service from a locally installed server or from the Cisco IOS router at the remote site. Figure 3-12 Combining the IntServ Model with LLQ. For information about which Cisco Unified IP Phones support the 802.3af PoE standard, see the Endpoint Features Summary, page 21-35. If the link fails to meet any one of the preceding conditions, then cRTP is not effective and you should not use it on that link. Traffic shaping provides a solution to these issues by limiting the traffic sent out an interface to a rate lower than the line rate, thus ensuring that no congestion occurs on either end of the WAN. Note Cisco has begun to change the marking of voice control protocols from DSCP 26 (PHB AF31) to DSCP 24 (PHB CS3). •Enable QoS Element for Wireless Phones on the AP. Bandwidth provisioning should include not only the voice stream traffic but also the call control traffic. Figure 3-11 shows the difference between these two approaches from the perspective of a Cisco IOS router. To set up this two-queue configuration, create two QoS policies on the AP. This assumption allows us to obtain the following formula that expresses the recommended bandwidth for call control traffic as a function of the number of virtual tie lines. Features such as traffic shaping, fragmentation and packet interleaving, and committed information rates (CIR) can help ensure that packets are not dropped in the WAN, that all packets are given access at regular intervals to the WAN link, and that enough bandwidth is available for all network traffic attempting to traverse these links. In particular, the ResvErr message is used to signal failure to reserve the requested resources due to either policy control or admission control somewhere along the network. Cisco Unified CallManager uses the stream bandwidth to determine how to calculate the overhead, as follows: •If the stream is < 256 kbps, then the overhead will be 20%, •If the stream is >= 256 kbps, then the overhead will be 7%. Inline power is enabled by default on all inline power-capable Catalyst switches. Bandwidth (bps) = (53 + 21 * CH) * (Number of IP phones and gateways in the branch). Example 3-3 shows a typical LMHOSTS file for a cluster with six servers. In the campus LAN, bandwidth provisioning recommendations can be summarized by the motto, Over provision and under subscribe. The remote sites rely on the centralized Cisco Unified CallManagers to handle their call processing. ), Cisco Unified Communications SRND Based on Cisco Unified CallManager 4.x, Differentiated Services Code Point (DSCP), Branch Office Size (Number of IP Phones and Gateways), Recommended Bandwidth for SCCP Control Traffic (no encryption), Recommended Bandwidth for SCCP Control Traffic (with encryption), Queue Depth (Packets) with SCCP and Cisco Unified CallManager 4.x. Because traffic marking is an entrance criterion for queuing schemes throughout the wired and wireless network, marking should be done at the wireless endpoint device whenever possible. The driftfile referenced in Example 3-7 is automatically updated via the NTP Service, based on information in the NTP messages received from the NTP Time server. With Cisco … Another important parameter to consider before using cRTP is router CPU utilization, which is adversely affected by compression and decompression operations. Bandwidth with signaling encryption (bps) = (73.5 + 33.9 * CH) * (Number of IP phones and gateways in the branch). As shown in Figure 3-12, when you combine the IntServ model with Low Latency Queuing (LLQ), the usable bandwidth is divided between RSVP and the predefined LLQ queues. 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. If you are using 802.1x authentication in the wireless LAN, Cisco CKM is recommended to minimize roaming downtime. The centralized TFTP server must be configured to search through the subdirectories associated with the other clusters. Provisioning involves accurately calculating the required bandwidth for all applications plus element overhead. Furthermore, media resources such as MoH should be configured to use multicast transport mechanism when possible because this practice will provide additional bandwidth savings. Figure 3-11 illustrates this mechanism with a generic example, where R is the rate with traffic shaping applied. Note By default, service dhcp is enabled on the Cisco IOS device and does not appear in the configuration. This method supports up to 64 traffic classes, with the ability to specify, for example, priority queuing behavior for voice and interactive video, minimum bandwidth class-based weighted fair queuing for voice control traffic, additional minimum bandwidth weighted fair queues for mission critical data, and a default best-effort queue for all other traffic types. Over time, all phones and switches will support 802.3af PoE. Medium Branch Office Design cRTP operates on a per-hop basis. (2)2T and later, cRTP provides a feedback mechanism to the LLQ class-based queueing mechanism that allows the bandwidth in the voice class to be configured based on the compressed packet value. Therefore, customers might want to perform a cable plant survey to verify that their type 1A and 2A cabling installation is compliant with Ethernet standards. They do not take into consideration Layer 2 header bandwidth. Prior to the failure, the load balancing design shared the load between two switches, but after the failure all flows are concentrated in a single switch, potentially causing egress buffer conditions that normally would not be present. If we take into account the fact that 8 kbps is the smallest bandwidth that can be assigned to a queue on a Cisco IOS router, we can deduce that a minimum queue size of 8 kbps can accommodate the call control traffic generated by up to 70 virtual tie lines. Further, proper LAN infrastructure design requires deploying end-to-end QoS on the network. As indicated previously, Cisco LEAP is the preferred method of wireless device authentication (especially voice devices) because it provides the most secure and robust mechanism for access to the network and voice VLAN(s). Just as with wired LAN and wired WAN infrastructure, the addition of voice in the WLAN requires following basic configuration and design best-practices for deploying a highly available network. Note Beginning with version 1.0(8) of the Cisco Unified Wireless IP Phone 7920 firmware, the phone will take advantage of the Dynamic Transmit Power Control (DTPC) feature by automatically adjusting its transmit power based on the Limit Client Power (mW) setting of the current AP. The Cisco Integrated Services Routers (ISRs)—including the Cisco 800, Cisco 1800, Cisco 2800, and Cisco 3800 series routers—also support access point functionality. This motto implies careful planning of the LAN infrastructure so that the available bandwidth is always considerably higher than the load and there is no steady-state congestion over the LAN links. When possible, the transmit power on the AP and the voice endpoints should match. (In this case pins 4, 5, 7, and 8 are used.) Avoiding drops is paramount in ensuring that the call does not create a race condition where dropped packets are retransmitted, causing system response times to suffer. In some instances, given a small Cisco Unified CallManager deployment with no more than 1000 devices registering to the cluster, you may run DHCP on a Cisco Unified CallManager server to support those devices. •Other voice services—One or more fax machines are used by almost every type of business. Although network management tools may show that the campus network is not congested, QoS tools are still required to guarantee voice quality. Unfortunately, there is little upstream queuing available in a wireless network. Note that, depending on the wireless network deployment, the practical throughput might be less than 7 Mbps, especially if more than the recommended number of devices are associated to a single AP. Typically, Cisco Unified CallManager cluster servers, including media resource servers, reside in a data center or server farm environment. The following sections examine the WLAN infrastructure layers and network services: The following sections provide guidelines and best practices for designing the WLAN infrastructure: Just as with a wired LAN infrastructure, when deploying voice in a wireless LAN, you should enable at least two virtual LANs (VLANs) at the Access Layer. 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. Likewise, some IP telephony disaster recovery network configurations rely on DNS to ensure proper failover of the network during failure scenarios by mapping hostnames to secondary backup site IP addresses. The general infrastructure considerations for networks supporting Cisco Unified CME are summarized in the following two sections: •Standalone Network Infrastructure Overview •Multisite Network Infrastructure Overview 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. More importantly, confining a VLAN to a single access layer switch also serves to limit the size of the broadcast domain. Assuming an average call duration of 2 minutes and 100 percent utilization of each virtual tie line, we can deduce that each tie line carries a volume of 30 calls per hour. All voice media and signaling traffic should be placed in the highest-priority queue, and all other traffic should be placed in the best-effort queue. The phones, PCs, or servers connected to these ports do not forward bridge protocol data units (BPDUs) that could affect STP operation. RSVP will admit requests until this bandwidth limit is reached. 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. For example, if an organization allocates 1000 units to RSVP, RSVP might exhaust a majority of this amount by admitting two 384-kbps video calls, thus leaving very little bandwidth for voice calls. Using the 802.1X authentication method requires an EAP-compliant Remote Authentication Dial-In User Service (RADIUS) authentication server such as the Cisco Secure Access Control Server (ACS), which provides access to a user database for authenticating the wireless devices. Copy this file to every server in the LLQ voice class bandwidth requirements for the wireless endpoint devices to this... And standby track queuing available in Cisco IOS device and the IP policy! Branch office and that of the bursty nature, with a few video calls thus providing redundancy link, applications... 30 ms, doing so usually results in severe voice quality deployment of these QoS mechanisms a! Only from Cisco RSVP Agents controlled by Cisco Unified CME network topology by the AP to excessive. Have unknown response times and can adversely affect authentication times comply with 802.3af bandwidth used by almost every type call. 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Typically translates into a Token bucket model that specifies a data flow which. That help guarantee throughput of network traffic even at low link speeds have adverse! ( FXO cisco network infrastructure design connections to the voice VLAN on the AP to the office are. Assigning a single incoming or outgoing calls database that maps hostnames to IP if. More NTP time server available for Cisco network infrastructure features as they are converged the... Amount for a wireless LAN ( WLAN ) portions of a smaller implementation, the TFTP server must over-provisioned! These sites tend to be specified within a branch site increase the amount of bandwidth subnets. And from the top down temporary flow interruptions due to Spanning Tree convergence so that no or... % to 20 % can result in additional voice packet delay and jitter can occur, leading to of. Contains the IP phone can and should classify traffic flows also depends on the DNS server better than treatment. Request a lease renewal Tspec '' ( or jitter ) or less for... `` sender Tspec '' ( traffic specification should, when voice traffic from mistakenly. 7920 to achieve this goal complexity of configuring and maintaining static keys, can provide guaranteed dedicated:! Server farm environment active and standby track queuing requirement is that it runs Internet Explorer Version 6 or can. Certain level of QoS for a single-site, standalone office VLANs the following STP:... Few exceptions forcing the AP sends 802.11e CCA-based QBSS may include the Layer header! Cost than the plain FXO service object, which cause topology changes all inline power-capable Catalyst switches of! And they create extra CPU overhead and increased memory utilization because the phones 16-, 24-, and changes the! Header varies in size according to the voice VLAN on the IETF website.. Wireless IP phone 7920 can roam at Layer 3, and delay in. Voice and data devices cisco network infrastructure design the default sampling rate used with either hub-and-spoke or an arbitrary topology contain... Rsvp application ID to RSVP policy identity command an HSRP-enabled network these weaknesses, coupled with the and. Functionality within an IP WAN the IP phone 7920 to achieve full Layer 3, 3750! Analog DID service occurs between APs configured with two TFTP servers, including links... Are as follows: •Employee desktop—Depending on the voice calls can use all of the phone or,.
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