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Cisco Systems 7920 IP manual

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Table of contents for the manual

  • Page 1

    Table of Contents Wireless IPT Design Guide for the Cisco 7920 IP Phone ................................................................................1 Introduction .............................................................................................................................................1 Prerequisites ..........................[...]

  • Page 2

    Wireless IPT Design Guide for the Cisco 7920 IP Phone Introduction Prerequisites Requirements Components Used Conventions Cisco 7920 IP Phone Overview WLAN Overview RF Overview  Site Surveys and Design Recommendations VoIP QoS Security for the Cisco 7920 and WLAN Networks Network Sizing Number of 802.11b Devices per AP Number of 802.11b IP Phone[...]

  • Page 3

    AVVID design guides and administration. • Components Used The information in this document is based on the software and hardware versions below: The Cisco 7920 IP Phone. • The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configu[...]

  • Page 4

    remember that the Cisco 7920 has somewhat different roaming characteristics than Cisco Aironet Network Interface Cards (NICs). This includes thresholds on the Cisco 7920 that determine when the phone roams or how much the RF environment needs to change in order to determine when a roaming event should occur. Because of this, it is recommended that [...]

  • Page 5

    Voice traffic can be classified with the following characteristics: Smooth  VoIP packets are sent at consistent intervals with uniform packet sizes. • Benign  VoIP packets only attempt to use the bandwidth necessary to send from end to end. VoIP does not use any windowing to determine data rates. • Packet Loss Sensitive  VoIP traffic i[...]

  • Page 6

    Technical Assistance Center (TAC) (if problems arise) is limited for this situation. Security for the Cisco 7920 and WLAN Networks The Cisco 7920 is supported in the architecture of the Cisco Wireless Security Suite. The architecture is discussed in detail in documents for Wireless LAN Security Solution. The architecture fits into the overall Cisco[...]

  • Page 7

    RADIUS functionality in a small office, but could also be used as a ACS server in case of WAN failure. The following is a step−by−step example of configuring the fallback RADIUS server for LEAP authentication: Configure the Network Access Server (NAS), by issuing the following commands: radius−server local nas 192.168.10.35 key Cisco nas 192.[...]

  • Page 8

    One of the key aspects when calculating network capacity for 802.11b networks is that it is a shared medium. Because of this, consideration must be given for radio contention among the various devices. This means that the back−off algorithms in 802.11b, that allow multiple devices to access the medium, affect the overall throughput. For the VoIP [...]

  • Page 9

    All of the above calculations and design recommendations are based on VAD being disabled on the Cisco 7920 IP Phones. VAD is a mechanism in VoIP where no RTP packets are sent if no speech is occurring during the conversation. VAD can be enabled on the Cisco 7920 phones and provides some bandwidth conservation, typically around 30 percent. With VAD [...]

  • Page 10

    30 AP limit is due to memory and processor constraints on the Wireless Domain Server (WDS), which is AP functionality to provide this enhanced roaming and security. This functionality is introduced into Cisco IOS Software Release 11.2(11)JA on the Cisco APs. Deployments that do not require this functionality, or have a physical area that requires m[...]

  • Page 11

    Note: Any references to roam or roaming throughout the remainder of this document is in the context of mid−call roaming. As it relates to roaming, the Cisco 7920 IP Phone currently only supports Layer 2 roaming. This means that a Cisco 7920 IP Phone can roam between APs that have coverage for a single Layer 2 subnet, but calls are dropped when th[...]

  • Page 12

    this AP. If either the association or authentication fails, it continues to try the next best AP. Note: As a Cisco 7920 roams between APs, it re−authenticates with each new AP. AP B sends a null MAC multicast using the source address of the Cisco 7920. This updates the Content Addressable Memory (CAM) tables in upstream switches and directs furth[...]

  • Page 13

    Layer 2 roaming with both static WEP and LEAP has been shown to provide acceptable QoS using either G.711 or G.729. If LEAP is being used, it is recommended that users are defined locally on the ACS server. This is because using off−box databases have potentially unknown response times, which could adversely effect overall QoS during Layer 2 roam[...]

  • Page 14

    VLANs VLANs are used by WLAN networks to provide two distinct functions: Segment traffic into distinct broadcast domains (IP subnets). • Create separate security domains for different security models (such as open, WEP, LEAP, Protected Extensible Authentication Protocol (PEAP), EAP Transport Layer Security (EAP/TLS)) • The Cisco AVVID design gu[...]

  • Page 15

    For more details on deploying VLANs in WLAN networks, refer to the Wireless Virtual LAN Deployment Guide. WLAN QoS for VoIP As mentioned earlier, WLANs operate as a shared medium. This means that QoS on WLAN networks are more difficult than wired networks because end points do not have dedicated bandwidth for sending and receiving traffic. The foll[...]

  • Page 16

    Before discussing how WLAN QoS works, you must first understand how end points transmit data on WLAN networks. Similar to wired Ethernet networks, 802.11b WLANs employ Carrier Sense Multiple Access (CSMA). However, instead of using Collision Detection (CD), WLANs use Collision Avoidance (CA). This means that instead of each station trying to transm[...]

  • Page 17

    After the IFS expires, the end point selects a value between 0 and aCWmin. The end point waits the length of this value and determines if the medium is available to transmit. 2. If the medium is available, the end point transmits the packets. 3. If the medium is unavailable (such as if another device sent a packet), the end point waits until the en[...]

  • Page 18

    Cisco Aironet APs support a QoS similar to EDCF as of Cisco IOS Software Release 12.0T SW. This provides up to eight queues for downstream (toward the 802.11b clients) QoS. These queues can be allocated in the following ways: Based on ToS or DiffServ settings of packets. • Based on Layer 2 or Layer 3 Access Control Lists (ACLs). • Based on the [...]

  • Page 19

    The following is an example of configuring the QBBS element in beacons on Cisco IOS Software−based APs: Beyond just having queuing and setting packets with the correct DiffServ markings, delay and jitter need to be taken into consideration. This is especially true for upstream traffic since there is no queuing among clients on the 802.11b side of[...]

  • Page 20

    Disable Port Aggregation Protocol (PagP) − PagP is enabled by default, but it is not needed for user−facing ports. • Enable Port Fast  Allows a switch to quickly resume forwarding traffic if a Spanning Tree Protocol (STP) link goes down. • Configure Wireless VLAN  Creates a unique wireless VLAN that isolates wireless traffic from othe[...]

  • Page 21

    wrr−queue cos−map 4 5 priority−queue out Connecting APs to the Catalyst 2950 EI The following configuration is a reference template for use on Catalyst switch ports that are connected to Cisco APs. It provide the required configurations for security, QoS, and STP: default interface <xx/yy> switchport mode access spanning−tree bpduguar[...]

  • Page 22

    Cisco Emergency Responder can query for IP Phones through either CDP (on the Catalyst switches) or the MAC address. Since CDP is sent as a link−layer multicast and is used by the Cisco AP to determine the QoS settings for the Cisco 7920, it is not propagated up to the Catalyst switch. This means that Cisco Emergency Responder should query the Cat[...]

  • Page 23

    Call Admission Control Call Admission Control (CAC) provides the mechanism that prevents the presence of the next voice call to interrupt or provide poor QoS for all existing voice calls. Regarding Time−Division Multiplex (TDM), this is accomplished by a finite number of DS0 channels. In wired Ethernet AVVID networks, this is provided by an inter[...]

  • Page 24

    Cisco 7920 does not support network−based directories. This will be supported in future software releases. • Cisco 7920 does not support XML−based applications. This will be supported in future software releases. • Related Information Voice Technologies • Voice, Telephony and Messaging Devices • Voice Software • Voice, Telephony and M[...]