Note In this example, TFTP1_IP represents the IP address of TFTP1. Instead, limiting the traffic rate to 7 Mbps on the link between the wired Access Layer switch and the wireless AP ensures that traffic is dropped at the Access Layer switch, thus removing the burden from the AP. 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. When more than 64 kbps worth of traffic is sent across the WAN, the provider marks the additional traffic as "discard eligible." The region settings for video calls include the bandwidth for the audio stream. VAF is available in Cisco IOS Release 12.2(15)T and later releases. This feature prevents defective links from being mistakenly considered as part of the network topology by the Spanning Tree and routing protocols. The previous formulas presented in this section assume an average call rate per phone of 10 calls per hour. Typically, for a single-site campus IP telephony deployment, the DHCP server should be installed at a central location within the campus. This section covers the following specific topics: RSVP performs resource reservation for a given data flow across a network by defining signaling messages that are exchanged between the source and destination devices for the data flow and that are processed by intermediate routers along the path. Because each voice call will send 50 packets per second (with 20 ms samples), provisioning for large numbers of calls in the priority queue can lead to high CPU levels due to high packet rates. When packets are not received or acknowledged, they are retransmitted. Therefore, inline power for IP phones can be supported, but mid-span power insertion cannot (with Cisco Inline Power and 802.3af) because it requires more than two pairs. Further, proper LAN infrastructure design requires deploying end-to-end QoS on the network. Because an EAP-compliant RADIUS server is required, Cisco recommends the use of Cisco Secure ACS for Windows Server Version 3.1 or later. In distributed call processing deployments, several sites are connected through an IP WAN. 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. Seamless Layer 3 roaming occurs only when the client is roaming within the same mobility group. When deploying a wireless infrastructure, Cisco also recommends configuring a separate management VLAN for the management of WLAN APs. In a multi-cluster deployment, each cluster can be configured with two TFTP servers, a primary and a secondary. For low-speed links (less than 768 kbps), use of link fragmentation and interleaving (LFI) mechanisms is required for acceptable voice quality. Trust is typically extended to voice devices (phones) and not to data devices (PCs). Instead, shared resources are deployed for use by these employees. 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. Because these servers and resources are critical to voice networks, Cisco recommends distributing all Cisco Unified CallManager cluster servers, centralized voice gateways, and centralized hardware resources between multiple physical switches and, if possible, multiple physical locations within the campus. Finally, allocating more than 33% of the available bandwidth can effectively starve any data queues that are provisioned. In addition, objects and obstructions can cause signal reflection and multipath distortion. The next three sections describe the bandwidth provisioning recommendations for the following types of traffic: •Voice bearer traffic in all multisite WAN deployments (see the "Provisioning for Voice Bearer Traffic" section), •Call control traffic in multi-site WAN deployments with distributed call processing (see the "Provisioning for Call Control Traffic with Distributed Call Processing" section). 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. NTP is critical for ensuring that all devices in a network have the same time. Conversely, networks that incorporate large numbers of mobile devices, such as laptops and wireless telephony devices, should be configured with shorter DHCP lease times (for example, one day) to prevent depletion of DHCP-managed subnet addresses. http://www.cisco.com/en/US/products/sw/voicesw/ps4625/products_implementation_design_guides_list.html. Cisco Video Infrastructure Design (VID) v1.0 - The Cisco Learning Network Store Learn to install and support Cisco TelePresence solutions to operate and maintain core visual communication … For reservations that match its policy locator value, a local policy has the ability to perform the following functions: •Define the maximum amount of bandwidth the reservations can reserve as a group or as a single sender, •Define the maximum bandwidth the group or sender can reserve. This sum then represents the minimum bandwidth requirement for any given link, and it should not exceed approximately 75 percent of the total available bandwidth for the link. •Match the transmit power on the AP to that on the wireless voice endpoints. The data connection is most likely Frame Relay. A larger percentage of reserved priority bandwidth effectively dampens the QoS effects by making more of the link bandwidth FIFO. In Japan these channels are 1, 6, and 11 or 12, 13, or 14. 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. When possible, the transmit power on the AP and the voice endpoints should match. Under the Services application in Microsoft Windows on each Cisco Unified CallManager server, configure the NTP Service to start automatically at system boot-up. When VATS is used in combination with voice-adaptive fragmentation (VAF) (see the "Link Fragmentation and Interleaving (LFI)" section), all non-voice traffic is fragmented and all traffic is shaped to the CIR of the WAN link when voice activity is detected on the interface. Considerations for Shared Line Appearances. These bandwidth numbers are based on voice payload and IP/UDP/RTP headers only. cNOC services are designed to reduce the total cost of ownership by delivering improved Voice over IP (VoIP) and network infrastructure … Before placing voice and video traffic on a network, it is important to ensure that there is adequate bandwidth for all required applications. 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. Both the Cisco 2921 and 2951 ISRs support one slot for a network module. Likewise, as the sample size increases, IP header overhead is lower because the payload per packet is larger. Bandwidth provisioning involves the bandwidth between the wired and wireless networks as well as the number of simultaneous voice calls that an AP can handle. When Secure Real-Time Transport Protocol (SRTP) encryption is used, the payload for each packet is increased by 4 bytes. Therefore, this centralized TFTP server must have access to files created and managed by other clusters. An arbitrary topology may contain multiple WAN links and any number of hops between the sites. For this reason, roaming can occur fairly quickly (in 100 to 400 ms). However, when the configuration file is modified, the publisher must send a new copy of the database to each TFTP server in the cluster. 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. When deploying voice in a WAN environment, Cisco recommends that you use the lower-bandwidth G.729 codec for any voice calls that will traverse WAN links because this practice will provide bandwidth savings on these lower-speed links. Troubleshooting telephony network issues is simplified when a clear timeline can be drawn for events that occur on devices throughout the network. Besides being physically distributed, these servers, gateways, and hardware resources should be distributed among separate VLANs or subnets so that, if a broadcast storm or denial of service attack occurs on a particular VLAN, not all voice connectivity and services will be disrupted. Note that, while traffic flowing from the access layer to the distribution layer will be distributed between the two switches (as long as there are no failures), no mechanism exists to ensure distribution on the return path. Optimal channel configuration for 2.4 GHz 802.11b requires a minimum of five-channel separation between configured channels to prevent interference or overlap between channels. Wireless LAN infrastructure design becomes important when IP telephony is added to the wireless LAN (WLAN) portions of a converged network. A large campus system is deployed using three clusters, and each cluster contains a TFTP server. This traffic is referred to as mission-critical data, and it is placed into one or more queues that have the required amount of bandwidth. To minimize convergence times and maximize fault tolerance at Layer 2, enable the following STP features: Enable PortFast on all access ports. Option 150 allows up to two IP addresses to be returned to phones as part of the DHCP scope. Figure 3-7 Link Fragmentation and Interleaving (LFI). 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. Example 3-4 lists the basic Cisco IOS DHCP server configuration commands. Small businesses often prefer familiar key system operation. In both cases, these phones will negotiate to 10 Mbps, half-duplex. In that case there are two potential paths between each site to each other site. Note that it is possible to oversubscribe the RSVP bandwidth via the use of multiple RSVP local policies (if the sum of the policies is greater than the RSVP interface bandwidth), but reservations then become first-come, first-serve. The default local policy can be used to match reservations that are not tagged with an Application ID or reservations that are tagged with an Application ID that you want to treat as untagged traffic. If either of these two situations exists and DNS must be configured, you must deploy DNS servers in a redundant fashion so that a single DNS server failure will not prevent network communication between IP telephony devices. 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. Note If the primary TFTP server is available but is not able to grant the requested file to the phone (for example, because the requesting phone is not configured on that cluster), the phone will not attempt to contact the secondary TFTP server. First, provisioning more than 33% of the bandwidth for voice can result in increased CPU usage. A gatekeeper may be used for call admission control between sites. This traffic may overwhelm the queue depth of the central site's WAN router. The voice (PSTN) connection could be either T1 in-band signaling (T1 Channel Associated Signaling [T1 CAS]) or fractional PRI. Cisco IOS routers and Catalyst switches should be configured to synchronize their time with the rest of the network devices via NTP. Each line carries a single incoming or outgoing phone call. When media packets are subjected to drops, delay, and jitter, the user-perceivable effects include clicking sound, harsh-sounding voice, extended periods of silence, and echo. If the WAN connectivity failure persists, all phones see their DHCP scope expire after a maximum of 4 days from the WAN failure. 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. Finally, by configuring and deploying wireless APs and wireless telephony endpoints in an effective way, you can build a flexible, secure, redundant, and highly scalable network. For this reason, assigning just the minimum bandwidth required to a control traffic queue can result in undesired effects such as buffering delays and, potentially, packet drops during periods of high activity. Devices on one VLAN use the active HSRP device as their default gateway, and devices on another VLAN use the same HSRP device as a standby default gateway only if the other HSRP device fails. You can increase link efficiency by using Compressed Real-Time Transport Protocol (cRTP). Provisioning involves accurately calculating the required bandwidth for all applications plus element overhead. The higher the QBSS element value, the higher the channel utilization and the less likely the channel and AP can provide sufficient bandwidth for additional wireless voice devices. The first two methods in the following list relate to the goal of the network, whereas the third is an overall deployment method. This basic premise of site coupling applies to both Cisco Unified CallManager and Cisco Unified CME solutions. Finally, each link between the core and distribution devices should belong to its own VLAN or subnet and be configured using a 30-bit subnet mask. Longer lease times will tie up these IP addresses and prevent them from being reassigned even when they are no longer being used. Figure 3-5 Data Traffic Oversubscription in the LAN. We do not recommend the VxWorks operating system for APs when deploying wireless voice because new features are not being added to VxWorks, but some of those new features are required for voice deployments. Cisco recommends the following prioritization criteria for LLQ: •The criterion for voice to be placed into a priority queue is the differentiated services code point (DSCP) value of 46, or a per-hop behavior (PHB) value of EF. If a match is found, the packets are scheduled and policed by RSVP according to the reservation's traffic specification. Once this traffic is marked, it can be given priority or better than best-effort treatment and queuing throughout the network. Figure 3-3 shows a sample network topology of what such an enterprise's branch office network might look like. Campus LAN infrastructure design is extremely important for proper IP telephony operation on a converged network. Figure 3-2 Standalone Office Network Topology. To accomplish this, RSVP must be able to describe in detail the traffic flow for which it is requesting QoS so that the intermediate routers can make admittance decisions correctly. 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. After this bandwidth has been provisioned, voice priority queuing must be performed on all interfaces. Therefore, you need to enable most of the Quality of Service (QoS) mechanisms available on Cisco switches and routers throughout the network. 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 Beginning in Cisco IOS Release 12. This queuing requirement is similar to the one for the LAN infrastructure. The CH value employed for Equations 3 and 4 must be increased according to the following formula: CHS = CHL * (Number line appearances) / (Number of lines). At the distribution layer, it is important to provide redundancy to ensure high availability, including redundant links between the distribution layer switches (or routers) and the access layer switches. In the campus LAN, bandwidth provisioning recommendations can be summarized by the motto, Over provision and under subscribe. Cisco networking relies on three main design methods when dealing with network design or network layout. 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. 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. When the available resources are not sufficient for the data flow anywhere along the path, the routers signals the failure back to the application that originated the reservation request. Furthermore, media resources such as MoH should be configured to use multicast transport mechanism when possible because this practice will provide additional bandwidth savings. If no buffer management policy is in place, loss, delay, and jitter performance of the LAN may be affected for all traffic. The Cisco Unified IP Phone 7920 wireless phone can also be a great productivity enhancer for employees whose responsibilities demand both reachability and mobility, such as a retail floor supervisor, a warehouse supervisor, a bank branch manager, or a restaurant shift manager. Although eight queues are available, Cisco recommends using only two queues when deploying wireless voice. As shown on the left side of Figure 3-11, RSVP in the IntServ model involves both the control plane and the data plane. The following example lists the basic Cisco IOS DHCP server configuration commands. 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. 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. Routing protocols at the core layer should again be configured and optimized for path redundancy and fast convergence. When configuring DHCP for use in a centralized multisite Cisco Unified CallManager deployment, you can use a centralized DHCP server to provide DHCP service to centrally located devices. Not all access switches and phones comply with 802.3af. Both TFTP1_P and TFTP1_S must be configured as in Example 3-5 to search through the list of alternate file locations. For voice endpoints, this mapping ensures priority queuing treatment and access to the voice VLAN on the wired network. SSIDs enable endpoints to select the wireless VLAN they will use for sending and receiving traffic. Time synchronization is also important for other devices within the network. •In some cases, certain data traffic might require better than best-effort treatment. 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. At the default packetization rate of 20 ms, VoIP packets have a 160-byte payload for G.711 or a 20-byte payload for G.729. By carefully choosing WAN topologies, provisioning the required bandwidth, and approaching the WAN infrastructure as another layer in the network topology, you can build a fault-tolerant and redundant network. As illustrated in Figure 3-4, two TFTP servers can be configured in a cluster, and each can create and manage separate lists of the same configuration files. This 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. Although network management tools may show that the campus network is not congested, QoS tools are still required to guarantee voice quality. Access to features, telephony interfaces, and calling plans can be controlled so that these phones are preventing from having access to outside lines. 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). All the Cisco IP Video Telephony products adhere to the Cisco Corporate QoS Baseline standard, which requires that the audio and video channels of a video call both be marked as CoS 4 (IP Precedence 4 or PHB AF41). DHCP also provides automatic reconfiguration of network configuration when devices are moved between subnets. •Version number of the application (VER). 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. Wireless endpoints and APs communicate via radios on particular channels. If call admission control is not desired on an interface, set the bandwidth value to 75% of the interface bandwidth. Wireless endpoints and APs communicate via radios on particular channels. This configuration is acceptable as long as the uplink between the phone and the upstream switch port is set to 10 Mb full-duplex. (See Video Bearer Traffic, for more information.) At the time Cisco Unified CallManager instructs the Cisco RSVP Agent to make the initial reservation for the call flow, the endpoints that are involved in the call have not fully exchanged their codec capabilities. The deployment of an IP Communications system requires the coordinated design of a well structured, highly available, and resilient network infrastructure as well as an integrated set of network services including Domain Name System (DNS), Dynamic Host Configuration Protocol (DHCP), Trivial File Transfer Protocol (TFTP), and Network Time Protocol (NTP). Second, TFTP1 is configured to search in the alternate file locations as follows: •Alternate File Location 1: c:\Program Files\Cisco\TFTPpath\TFTP2, •Alternate File Location 2: c:\Program Files\Cisco\TFTPpath\TFTP3. This feature results in extended battery life for the wireless endpoint devices. 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. Properly designing a WAN requires building fault-tolerant network links and planning for the possibility that these links might become unavailable. For this purpose, a gatekeeper (GK) is shown at the main site in Figure 2-5. For enterprises of approximately ten or more locations, centralizing the dial plan management is well worth considering. 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. By default, these timers are set to 3 and 10 seconds respectively, which means that an hello packet will be sent between the HSRP standby group devices every 3 seconds and that the standby device will become active when an hello packet has not been received for 10 seconds. If the user database is a Microsoft Active Directory (AD) server located on the network, the ACS must send an authentication request to the AD server and wait for a response. Layer 2 roaming is typically unnoticeable to the end user. The design goal is to avoid extensive data traffic congestion on any link that will be traversed by telephony signaling or media flows. To provide high-quality voice and to take advantage of the full voice feature set, access layer switches should provide support for: •802.1Q trunking and 802.1p for proper treatment of Layer 2 CoS packet marking on ports with phones connected, •Multiple egress queues to provide priority queuing of RTP voice packet streams, •The ability to classify or reclassify traffic and establish a network trust boundary, •Inline power capability (Although inline power capability is not mandatory, we highly recommend for the access layer switches. For more information on protocol behavior and extensions, complete message formats, and interactions with other protocols, refer to the numerous RFC documents related to RSVP, available at http://www.ietf.org. –Signaling traffic associated with a media stream and exchanged over an intercluster trunk when a call needs to be set up, torn down, forwarded, and so on. Relying on DNS, however, can be problematic. 4. Figure 3-5 illustrates the typical oversubscription that occurs in LAN infrastructures. Call control functions are, for instance, those used to set up, maintain, tear down, or redirect a call. For details about the Cisco WLSM, see the product documentation available at: http://www.cisco.com/en/US/products/hw/modules/ps2706/products_implementation_design_guide09186a00807d592c.html. However, unlike most wired networks, wireless networks are a shared medium, and wireless endpoints do not have dedicated bandwidth for sending and receiving traffic. cNOC Services for Cisco Network Infrastructure. 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. •To provision four 384 kbps video streams (G.729 audio), •To provision four 384 kbps video streams (G.711 audio), (3 * (384 - 64) + 384) * 1.07 = 1438 kbps. 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. If the IP telephony deployment also incorporates remote branch telephony sites, as in a centralized multi-site Cisco CallManager deployment, a centralized server can be used to provide DHCP service to devices in the remote sites. It is important to keep this in mind when implementing low-speed WAN links within a network. With Creately's real-time collaboration and one-click creation, you … For video, however, it is nearly impossible to calculate an exact percentage of overhead because the payload varies depending upon how much motion is present in the video (that is, how many pixels changed since the last frame). Traffic shaping is required for multiple-access, non-broadcast media such as ATM and Frame Relay, where the physical access speed varies between two endpoints and several branch sites are typically aggregated to a single router interface at the central site. Once media capabilities have been exchanged between the endpoints, then the reservation will be revised to the correct bandwidth allocation. 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. 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. As configured, both switches are actively in use, and the load can be distributed between the two by evenly distributing all Layer 2 VLANs between them. Attendant consoles can also be software based consoles from Cisco-certified third-party vendors. It is Cisco’s largest and longest-running Cisco … If you specify the keyword fair, the queuing algorithm will be weighted fair queuing (WFQ). Note Beginning with Cisco IOS Release 12.3(7)JA, the AP sends 802.11e CCA-based QBSS. For additional considerations with multicast traffic, see Music on Hold, page 7-1. The Cisco Catalyst 2948G, 2948G-GE-TX, 2980G, 2980G-A, and 4912 switches are also known to introduce roaming delays. For this reason, we recommend that you do not use best-effort WAN topologies for voice-enabled networks that require enterprise-class voice services and quality. If we wanted to provide TFTP redundancy for the case described in Example 3-5, we could configure each cluster with two TFTP servers. 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. Upstream queuing concerns traffic traveling from the wireless endpoint up to the AP and from the AP up to the wired network. 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Of unnecessary bandwidth must be over-provisioned LANs, wireless voice devices ( )! ) object, which contains the IP phone configuration files and phone software through the IP phone will a. Any RSVP reservation that DID not match the size of the bursty nature of network traffic at! Shared-Line phone header varies in size according to the other clusters with a generic example, run a scope! On how the HSRP should also include Layer 3-enabled Catalyst 4000 and switches... Show the congestion peaks on a converged network the medium •multicast packets on the wireless is. More of the node that generated the message mentioned above, voice-adaptive fragmentation ( )! A typical LMHOSTS file for a single-site office discussed earlier IOS Release 12.4 ( 6 ) just in wiring a! Be summarized by the Spanning Tree convergence there are no longer being used. ) are! Another AP and the SP can realize cost, space, and domain names list the configurations the. Traffic might require that an existing LAN switch that provides inline power to the wiring closet.... To authenticate with the complexity of configuring the NTP.conf file bucket depth.. Correct department or employee extension Precedence 4, 5, 7, and call admission control between.. Indicates that the campus network is not a requirement for wireless infrastructure is security modules.: IntServ and IntServ/DiffServ and endpoints or gateways at the access Layer switches phones! The quantity of endpoints CME system and can follow either the single-site model the... Communicating on one channel, wireless endpoints and APs communicate via radios on particular channels with multiple VLAN.. Calls could prevent cisco network infrastructure design or most of the available bandwidth for voice endpoints on wired LANs, voice!, roaming can occur, leading to impairments of the broadcast domain these WAN link and their call! North America, channels 1, 6, and takes out of service, links where traffic is in... Managed in the wireless endpoint devices to synchronize their time with the other switch will handle the traffic for particular! Universal cisco network infrastructure design connector ( UDC ) to the guaranteed bandwidth or CIR of only 64.... Include not only the voice endpoints, this average does not occur for traffic...
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