Cisco Systems 7920 IP IP Phone User Manual
Contents
1. A A w aoBoBHoB8o2o8Haos3383 interface interface id description 11m Towards Wireless Access Point no ip address mls qos monitor dscp 0 10 18 26 34 46 48 56 Service policy output EGRESS POLICING Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 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 lt xx yy gt switchport mode access spanning tree bpduguard enable spanning tree bpdufilter enable no channel protocol spanning tree portfast vlan vlan id auto qos voip trust Connecting APs to the Catalyst 2950 SI 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 lt xx yy gt switchport mode access spanning tree bpduguard enable spanning tree bpdufilter enable no channel protocol spanning tree portfast vlan vlan id Using Cisco Emergency Responder for E911 calls with the Cisco 7920 The Cisco Emergency Responder proactive2. network The highlighted sections show the data that is relevant for the packet sizes of VoIP traffic G 711 and G 729 Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone Parameters long Shot Theoretical Maximum Throughput in Bits Second Preamble usec 144 72 1 l Fender Cur T i 31 ESI I 18 3 4 length 55 1 0 2 1 jSir Qusec tO 64 amp 8608733 857 623 317517 2 5364 513 3 990 809 1 731 102 916030 6 788 795 705 057 514 056 Not Applicable 4201 417 2 972 816 1 469 153 Not Applicable 6080 431 3 859 516 1 693 961 Not Applicable 7 086 106 4 263 015 1 780 415 Not Applicable LLL LLL usi S CTS no frag eq 1000000 Preamble Hea der Leng 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 calculations below a VoIP call has the following characteristics 1 The packets are made up of a 20 byte IP header an 8 byte UDP header a 12 byte RTP header and the RTP data 2 The RTP data is a 20ms voice sample For G 729 this is 20 bytes For G 711 this is 160 bytes 3 The total VoIP packet is 200 bytes
3. 9 Layer 2 ROAMING ues epe DR e E EGO ERE tees RR IURE TUR ER DE TNR RAE 10 layer 3 ROamimng nei Ge trt eo ttc m t debo fe deeds cati t e es adeestddages 12 AB URS Er HII M M 13 WIEAN QOS for VoIP 6 nei ren era VR at 14 Interconnecting WLANS to Cisco Campus Infrastructure ceeccecsseceesceeececeseeeeeeeeaeceeaeceeaeeenaees 18 Connecting APs to the Catalyst 3550 SMI or EMIL sees nennen 19 Connecting APs to the Catalyst 2950 EL e eene eene tenente enne 20 Connecting APs to the Catalyst 2950 SL enne ennt nennen 20 Using Cisco Emergency Responder for E911 calls with the Cisco 7920 ssuss 20 Caveats and Limitations 3 21 erro rete esce egere eet rr Le beers ER a oatacdeapesawsosasaees 21 CallvAdmission COnttol 5 4312 4 eei dee rere ret e te eR eerie ert ete tete te edd deed 22 Designing Around the Lack of Layer 3 Roaming eese 22 Other Caveats and Limitations ein a aa aa aaa a s a a aa aai hie 22 Related Information doe e et iee a i a E e eet be reete ea e a R a a aeiee 23 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 Phones per AP Numbers
4. PSAP personnel to identify that the caller is using a wireless device by using a code or abbreviation in the Automatic Location Information ALD or switch port location field This is important information for first responders because it means that adjacent floors hallways rooms and even buildings may need to be searched to locate an unconscious or incapable caller The following image is an example of the Cisco Emergency Responder s configuration Graphical User Interface GUI isco Em For Cisco IP Telephony Solutions 4 Onsite Alert Settings ERL Configuration Find Details of ERLs Where ERL Name contains x where CER Group is Ecs cc xj Find To list all items click Find without entering any search text Configure Default GEL Add New ERL Status Ready Click on record to view edit Matching Record s 1to 3 of 3 Default 3010 40833300 mamal Security WestTasmznDrive cisco ca Ch E Milpitas 20911 4082220 Security SanCalaveras Milpitas ca T B vie Building 10911 4081110 Security Tasmantrive cisco ca x B ow Page 1 of 1 Configure Default ERL Add New ERL Caveats and Limitations Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 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 accomp
5. Port mark down to 0 Ensures appropriate treatment of high priority traffic including soft phones and prevents users from consuming excessive bandwidth by re configuring their PCs Connecting APs to the Catalyst 3550 SMI or EMI 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 lt xx yy gt switchport mode access spanning tree bpduguard enable spanning tree bpdufilter enable no channel protocol spanning tree portfast vlan vlan id mls qos auto qos voip trust ls qos map cos dscp 0 10 18 26 34 46 48 56 ls qos aggregate police AGG POL 5M DEFAULT 5000000 8000 exceed action drop lass map match any EGRESS DSCP 0 tch ip dscp 0 lass map match any EGRESS DSCP 10 tch ip dscp 10 lass map match any EGRESS DSCP 56 tch ip dscp 56 lass map match any EGRESS DSCP 26 tch ip dscp 26 lass map match any EGRESS DSCP 18 tch ip dscp 18 lass map match any EGRESS DSCP 48 match ip dscp 48 policy map EGRESS POLICING class EGRESS DSCP 0 police aggregate AGG POL 5M DEFAUL class EGRESS DSCP 10 police aggregate AGG POL 5M DEFAUL class EGRESS DSCP 18 police aggregate AGG POL 5M DEFAUL class EGRESS DSCP 34 police aggregate AGG POL 5M DEFAUL class EGRESS DSCP 48 police aggregate AGG POL 5M DEFAUL class EGRESS DSCP 56 police aggregate AGG POL 5M DEFAUL I w
6. This is especially true for upstream traffic since there is no queuing among clients on the 802 11b side of the AP The simplest way to accomplish this is to stay within the guidelines for the number of WLAN clients per AP Exceeding this creates additional opportunities to introduce packet delay and jitter For more details about deploying QoS in WLAN networks refer to the Wireless Quality of Service Deployment Guide Interconnecting WLANs to Cisco Campus Infrastructure This section contains pre tested recommended configurations This helps you to quickly and simply build and deploy a Cisco approved network design using Catalyst 3550 and 2950 series Intelligent Ethernet Switches By following the information in this section you can create a Cisco AVVID Network Infrastructure to run converged voice video and data network over IP with due consideration for QoS bandwidth latency and high performance in demand by Cisco AV VID Network Infrastructure solutions The AP template should be configured when a single AP is attached to a port This template adds all the baseline security and resiliency features of the standard desktop template but for the Catalyst 3550 it also optimizes the performance of the attached AP Ethernet switch ports can transmit and receive at 100Mbps However APs depending on the type 802 11b only have a practical throughput of 6Mbps or less This throughput mismatch means that with a burst of traffic the
7. VLAN Port VLAN ID PVID is not tagged Each VLAN is then mapped to a unique SSID on the AP Users or IP phones can then be assigned to VLANs based on either static configuration of SSID or dynamically though the use of RADIUS authentication Each VLAN can use a different security mechanism although only one can be unencrypted open The following is an example of configuring VLANs on VxWorks based APs AP350 or AP1200 det x ti o Di GQ Beach e Gem JD 2 0 J Actress 4 rtp 10 01 2 2524 SetPr ok AN abri rewae Marie 2 afar ari jot Par aga rot c AN aberit 110 01 2 242 5ebup ehm eco Urbs API200 ac436b VLAN ID 2 Cisco Systems Cisco 1200 Series AP 1201T Moe tinie VLAN Name VLAN Enable Detwit Prony De fudt Poly Group Enhanced MIC venficatnion for WEP Temporal Key Integrity Protoccl WEP Key Rotation Interval Alen WEP Key l WEP Rey WEP Kep r i n WEP Key 4 Eater AD bit WEP keye ac LO hexadecimal digite MP e or A F Entes 128 8 WEP keys e 26 hexedecinal dts 05 af or A F Apply Ox Cancel Restore Deteuhs Map Login Hei 20 Come AP nor vec 2 Cus Penes Be cauta ll Core O itens The following is an example of configuring VLANs on Cisco IOS Software based APs AP1100 or AP1200 Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone Doso 105 Series AP Services TLAN Microsoft Bry Be pr Favortes Iocs thp KJ deme gt O A Il Dee Gu
8. followed to accommodate the roaming nature of 802 11b phones Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 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 Catalyst switches for the MAC addresses of the Cisco 7920 phones Cisco Emergency Responder groups devices into Emergency Response Locations ERL so they can be identified by a physical location such as building floor or region of floor Depending on how the power levels are configured on the Cisco APs it is possible that the signal could propagate to floors above or below the actual AP that the Cisco 7920 is associated with Using antennas that propagate RF signal in a more horizontal pattern helps alleviate this but emergency personnel within a building should be made aware of this when organizing their searches for the individual or device that initiated the emergency call An E911 coverage policy is an individual decision that each company needs to make and adapt it to their physical locations It is recommended that each AP been assigned to its own ERL or minimally grouping a couple of adjacent APs into one ERL This has the benefit of allowing on site and potentially
9. of IPX UDP RTP headers RTP data The 802 11 header Layer 2 MAC is 24 bytes long so the total packet is 224 bytes 4 RTP data is transmitted at 50 packets per second pps in each direction or 100pps for a full duplex conversation Looking at the 11Mb column of the chart we can make the following calculations for G 711 e 256 byte packet size 2 596 588 bits per second 324 573 bytes per second Theoretical packet rate 100 packets per second 224 bytes per packet 22 400 bytes per second Bandwidth of a G 711 VoIP call e 324 573 22 400 14 489 calls Theoretical maximum VoIP capacity per 802 11b channel e 14 489 6 8 69 calls Theoretical maximum number of VoIP calls 60 percent of the bandwidth Note Sixty percent of the bandwidth is used to calculate the number of VoIP calls which allows for the following It allows bandwidth to be available for data traffic It provides bandwidth consideration for 802 11b management traffic and acknowledgements The design consideration for G 711 calls is not to exceed seven concurrent VoIP calls per AP This number has been proven in lab testing to provide acceptable voice quality The design consideration for G 729 calls is not to exceed eight concurrent VoIP calls per AP This number has been proven in lab testing to provide acceptable voice quality Note The following information affects Voice Activity Detection VAD configuration Cisco Wireless IPT Design Guide f
10. of 802 11b Phones per Layer 2 Subnet or VLAN Understanding Layer 2 and Layer 3 Roaming Understanding Roaming Terminology Layer 2 Roaming Layer 3 Roaming VLANs WLAN QoS for VoIP Interconnecting WLANs to Cisco Campus Infrastructure Connecting APs to the Catalyst 3550 SMI or EMI Connecting APs to the Catalyst 2950 EI Connecting APs to the Catalyst 2950 SI Using Cisco Emergency Responder for E911 calls with the Cisco 7920 Caveats and Limitations Call Admission Control Designing Around the Lack of Layer 3 Roaming Other Caveats and Limitations Related Information Introduction This document provides design guidelines and deployment recommendations for customers adding the Cisco 7920 IP Phone to an existing Architecture for Voice Video and Integrated Data AVVID network The assumption is made that you have either an existing AVVID network for wired IP phones or that you have previously read the AVVID design guides It is not assumed that you have previous Wireless LAN WLAN experience This document makes reference to several existing design guides for 802 11 IP Telephony and campus network design Prerequisites Requirements Readers of this document should be knowledgeable of the following Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 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
11. the data rates that traffic is supported e Since all WLAN traffic is seen by all other WLAN devices within range additional security considerations need to be taken to ensure that traffic is not captured or manipulated by intruders RF Overview Site Surveys and Design Recommendations Before getting started with any WLAN deployment the first activity that every network administrator should undertake is a complete site survey of the environment where the WLAN devices are deployed The site survey should be performed to understand the number of APs required to provide Radio Frequency RF coverage It should take into consideration which types of antennas provide the best coverage as well as where sources of RF interference exist An important factor to keep in mind is that rarely do two physical environments have the same RF characteristics Because of this the sections of this document that are RF specific are generalized Network administrators may need to adjust those parameters to their specific RF environment and requirements While you may have already performed RF site surveys for an initial WLAN deployment it is important to Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 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 cha
12. AP needs to do packet drops which adds an excessive processor burden to the unit and affects performance By taking advantage of the Catalyst 3550 policing and rate limiting capabilities the task of dropping excessive packets is removed from the AP This template rate limits the port to the practical throughput of 6M and guaranteeing 1 Mbps for high priority voice and control traffic Because of this prioritization this template can be used with wireless IP telephones The 3550 24 PWR in line power switch can be used to provide power to the AP This template helps create a secure and resilient network connection with the following features Return Port Configurations to Default Prevents configuration conflicts clearing any pre existing port configurations This allows you to start with a clean slate Disable Dynamic Trunking Protocol DTP Disables trunking which is not needed for a connection to an AP Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 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 other data voice and management VLANs thereby isolating traffic and ensuring greater control of traffic Enable QoS and Do not Trust the
13. Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone Table of Contents Wireless IPT Design Guide for the Cisco 7920 IP Phone ccsscssssscsssscsssscssssssssscsssscssssscssssssesssssessesecees 1 IntrOdUctohD noie Re Pe ee 1 Pr requis Srii easier eo eeeh e t Oei ee e eee ie dede lade devudbacteuah EE E 1 Jus IW SHIT HT sovecsecesduand oubaceducdelatiavsseda vive deeevbastieashedeve 1 Components Used 1 4 careo nel Geis ad ea OE MIR P EPI ge 2 ConventloBs 3 nitor eve tite Lis ES rette RRR ROE OEE 2 Cisco 7920 IP Phon OYerVIe Wiz de tei ette eerie rera pes dan belre e bk tane Cae une esee ao Deae Lesage anexo 2 MISATNSOVOEVIGW dere croco reete enean eoe de ue PEU UE PARE XE T Eve YER FORCE e debel a ve be ERU NV 2 RF Overview Site Surveys and Design Recommendations sssseeeeeeene 2 VOIB QOS adieu etm eden potet es rn de eren ERE 3 Security for the Cisco 7920 and WLAN Networks ccecccceecceceseeesecesaeceaceceeneeceeeecsaeceeaeeeaeeceeeeeees 5 Network SIZ PIENE naia A e e E aaa a era aA E aA Ee A AAA A EED aa 6 Number of 802 11b Devices per ABl Eeee Ea AE anaE R EEE EEEE E aai aal 6 Number of 802 116 IP Phones per APriora EE EEEa a e aa a i aa 6 Numbers of 802 11b Phones per Layer 2 Subnet or VLAN eene 8 Understanding Layer 2 and Layer 3 Roaming esesssessessseeeeeeneeeeeee ener enne 9 Understanding Roaming Terminology rennen ennt
14. EAP Cisco Light Extensible Authentication Protocol LEAP for authentication and data encryption When either encryption model is used both the signaling Signaling Connection Control Part SCCP and media RTP are encrypted between the Cisco 7920 and AP Static WEP requires that a 40 or 128 bit key be manually entered on all of the Cisco 7920s as well as the APs It performs AP based authentication based on the device such as the Cisco 7920 having a matching key LEAP allows devices such as the Cisco 7920 and the AP to be mutually authenticated Cisco 7920 gt AP AP gt Cisco 7920 based on a username and password Upon authentication a dynamic key is used between the Cisco 7920 and the AP to encrypt traffic If LEAP is used a LEAP compliant RADIUS server such as the Cisco Secure ACS for Windows is required to provide access to the user database The ACS server can either store the username and password database locally or it can access that information from an external Microsoft Windows directory Note While it is a valid configuration option it is not recommended that an external off ACS database be used to store the username and password credentials for Cisco 7920 phones Because the ACS server must be queried whenever the Cisco 7920 roams between APs the unpredictable delay to access this external database could cause excessive delay and poor voice quality The placement of the ACS server should be considered when depl
15. The calling ratio used to determine active versus non active calls This is often determined using Erlang calculators Based on these factors and normal business class Erlang ratios 3 1 through 5 1 it is recommended not to exceed 450 to 600 Cisco 7920s per Layer 2 subnet or VLAN Note The limitation of 30 APs per subnet or VLAN is introduced due to new functionality added to Cisco WLAN clients such as PCs and Cisco APs The functionality is called Secure Fast Roaming and introduces a new WLAN architecture that reduces the amount of time it takes a WLAN client to roam between APs The Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 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 more than 30 APs of coverage can disable the WDS or Secure Fast Roaming functionality on the APs This eliminates the limitation of 30 APs in the subnet or VLAN In the future as WDS functionality is migrated to faster processing devices within the network the 30 AP per subnet limitation will be expanded or removed For more information on this refer to Cisco Structured Wireless Aware Network SWAN Overview Understanding Layer 2 and Layer 3 Roam
16. alling patterns of individual customers Erlang ratios Cisco Enterprise Solutions Engineering ESE recommends no more than seven calls concurrent using G 711 or eight calls concurrent using G 729 Beyond that number of calls when background data is present the voice quality of all calls becomes unacceptable Packetization rates for this testing were done with 20ms sample rates This generates 50pps in each direction VAD was disabled during the testing Using large sample sizes such as 40ms could result in a larger number of simultaneous calls but it also increases the end to end delay of the VoIP calls These testing results come from the creation of traffic simulating normal desktop traffic for 15 to 20 users such as HTTP FTP Simple Mail Transfer Protocol SMTP Point of Presence POP Telnet 3270 TN3270 and then adding incremental Cisco 7920 phones The number of Cisco 7920s phones added with active calls stopped when the Mean Opinion Scores MOSs dropped below the average MOS for G 711 or G 729 calls on the wired network Numbers of 802 11b Phones per Layer 2 Subnet or VLAN The number of 802 11b phones that should be deployed per Layer 2 subnet or VLAN is dependent on the following factors No more than 30 APs should be deployed per Layer 2 subnet or VLAN This is the recommendation to optimize memory and performance on the APs No more than seven G 711 or eight G 729 active calls should be deployed per AP
17. ates received by the Cisco AP in beacon messages using the QBSS element Based on this information the Cisco 7920 can determine if the load on a given AP is excessive and if it should attempt to associate with a less congested AP in order to preserve the QoS of an IP Telephony call The following is an example of configuring the QBBS element in beacons on VxWorks based APs deti xx Dek 9o 2 lt Diew Groote Grete J D 5 gw Auderess 4E rito 110 01 2 25z 5etQu5002 L ahn fedes DR arere http f L c ce we zl AP1200 ac436b AP Radio Interna Quality of Service Cisco Systems Cisse 1200 Series AP 12417 Map Hele Uptins 45 days 20 2100 ge 0 Best Effort dethutt i zss x 3 Excellent Effort 255 4 Controlled Load ps j fess 5 Interactive Video hs a fes z 6 Interactme Voice sz n a 7 Network Control gt 127 Alioured untoer Sor CO Wmin and CWrnwe we 1 3 7 15 31 65 127 255 511 and 1023 CWiminm must be less than or equa to CWmax Apply Ox Cancel Restore Detours Map ihowniitstp vidt DKA Ceca ms oc tanita li Core Doreen Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone The following is an example of configuring the QBBS element in beacons on Cisco IOS Software based APs ADVANCED Enable Dicsble Beyond just having queuing and setting packets with the correct DiffServ markings delay and jitter need to be taken into consideration
18. chnique similar to IEEE 802 11e called Enhanced DCF EDCF EDCF is a model that allows end devices that have delay sensitive multimedia traffic to modify their aCWmin and aCWmax values to allow for statically greater and more frequent access to the medium The following is an example of how EDCF works on Cisco WLAN devices DIFS DIFS_ i IFS Station X Voice 1 Frame a a 3H Best Effort 12 om eigo e mo ghee oec gh Sf tet n a oi Fame i i wn Best Effort 2 mm pp EIN Eachoffime J Eackottimeremaning E By default end points usually have aCWmin and aCWmax values of 31 and 255 respectively for all data traffic For VoIP traffic Cisco APs and Cisco 7920s set the aCWmin and aCWmax to values of 3 and 31 respectively This is equivalent to CoS of 6 Cisco IOS Software based APs can also vary the IFS in addition to the aCWmin and aCWmax Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 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 e Based on the VLAN Based on the dynamic registration of devices such as the Cisco 7920 IP Phone Although eight queues are supported on the AP it is recommended to only have two
19. d the AP e Can only provide limited admission control Unlike networks with dedicated bandwidth WLAN networks have to consider traffic direction when discussing QoS Traffic needs to be considered as either upstream or downstream from the point of view of the AP as shown in the following example Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone carens Cows Downstream QoS only Bi Directional QoS 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 transmit as soon as the medium is free WLAN devices use a CA mechanism to prevent multiple stations from sending at the same time The model used for WLAN data transmission is called Distributed Coordination Function DCF The following image is an example of 802 11b DCF Station E E Bachofftime S Bachofftime remaining DCF ensures that the following events occur when the end points try to transmit data 1 After the previous frame has been transmitted and detected by the other end points each end point waits for a period of time called Inter Frame Space IFS 2 There are the following three potential values for IFS Short IFS SIFS The shortest interva
20. he AP coverage for another Layer 2 network L3 Roaming Mobile IP L2 Roaming IAPP Layer 2 Roaming Layer 2 Roaming occurs when a WLAN device for example the Cisco 7920 physically moves enough that its radio associates to a different AP The original and the updated AP offer coverage for the same IP subnet so that the WLANs client are still valid after the roam The Cisco 7920 performs an Layer 2 roam for the following reasons e When the Cisco 7920 initially boots this is considered a roaming event because it is associating with a new AP The Cisco 7920 does not receive beacons from the associated AP and therefore believes that the AP is no longer available If three consecutive beacons are not received by the Cisco 7920 and its unicast packet to the AP is not acknowledged the Cisco 7920 begins the roaming process to another AP The Cisco 7920 periodically scans for better APs Because the initial startup is considered to be a roaming event all client stations have roamed at least once After the roam process has completed the client station maintains the list of eligible roam targets When all AP information is received channel update current AP update the phone evaluates its current AP with the list of eligible roam targets If conditions change on the current AP RSSI low or QBSS high so that one of the APs in the client s stored list now appears to be a better choice than the current AP the phone starts a handoff
21. in an RF coverage area The Cisco 7920 attempts to associate with the AP that has the highest RSSI value and matching authentication or encryption Type QBSS This is a beacon Information Element IE that allows the AP to communicate the Channel Utilization CU to the Cisco 7920 The Cisco 7920 uses the QBSS value to determine if it should attempt to roam to another AP as APs with high CU may not be able to effectively handle VoIP traffic When roaming the Cisco 7920 uses the following model to determine which AP should be used as the handoff candidate 1 Determine which APs are advertising QBSS in their beacons These should be considered handoff candidates before APs that are not advertising QBSS If any of these meet the threshold criteria begin the roaming process 2 If no APs advertise QBSS or those advertising do not meet the threshold criteria look for APs that are not advertising QBSS but have acceptable RSSI levels The amount of time it takes for the Cisco 7920 to roam between APs is dependent on the security model used average times e Layer 2 roaming with static WEP less than 100ms e Layer 2 roaming with LEAP local ACS authentication 200 to 400ms Note Delay times with LEAP could be longer than 200 to 300ms if the ACS server is heavily used by other applications such as remote access dial up or VPN or TACACS authentication Layer 2 roaming time is the time between the last RTP packet seen on AP1 and the firs
22. incorrectly and overall network instability Designs using this should model should be reviewed with your Cisco Systems Engineer before deployment For customers that may eventually be considering extending their Layer 3 networks down to the access switches the model of building large Layer 2 VLANs is no longer valid Other Caveats and Limitations The following are other things to be aware of regarding the Cisco 7920 IP Phone Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone Cisco 7920 does not support network based directories This will be supported in future software releases e 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 Messaging TAC eLearning Solutions Recommended Reading Troubleshooting Cisco IP Telephony Technical Support Cisco Systems All contents are Copyright 1992 2003 Cisco Systems Inc All rights reserved Important Notices and Privacy Statement Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone
23. 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 configuration If your network is live make sure that you understand the potential impact of any command Conventions For more information on document conventions see the Cisco Technical Tips Conventions Cisco 7920 IP Phone Overview The Cisco 7920 IP Phone extends the AVVID family of IP phones from 10 100 Ethernet to 802 11b WLANs The Cisco 7920 provides a multi line appearance with functionality similar to existing Cisco 79xx IP Phones In addition the Cisco 7920 provides enhanced WLAN security and Quality of Service QoS for operation in 802 11b networks Future enhancements to the Cisco 7920 will add support for XML based data access and services as well as Universal Serial Bus USB connectivity for additional data services WLAN Overview 802 11b WLAN networks allow multiple devices to transmit data voice and video at data rates up to 11Mb While WLAN networks allow similar types of traffic to be transmitted over them it does have certain characteristics that differ from wired networks e WLANs operate as a shared medium which means that communication on the WLAN is half duplex and that all devices within a single WLAN share the 11Mb WLAN bandwidth varies based on the distance that a WLAN client is from a WLAN Access Point AP The farther the distance the lower
24. ing One of the obvious benefits of WLAN IP phones over wired IP phones is the ability to physically move from place to place while having a conversation However unlike cellular phone services where coverage areas are usually nationwide or international WLAN IP phones have smaller coverage areas In addition administrators of WLAN IP phone networks need to understand and consider their IP addressing schemes before deploying WLAN IP phones What needs to be considered is how WLAN IP phone coverage overlays with the Layer 2 and Layer 3 addressing within the IP network An Layer 2 network is defined as being a single IP subnet and broadcast domain An Layer 3 network is defined as the combination of multiple IP subnets and broadcast domains Understanding Roaming Terminology When discussing the term roaming it is often good to understand the audience and their understanding of the term For people that mostly work with voice systems they often associate roaming with the concept of physical movement and from where a call can be originated For people that mostly work with 802 11 data networks they also often associate roaming with the concept of physical movement but they often associate this with data connectivity while physically moving To simplify the terminology the following two terms are introduced e Pre Call Roaming This is when a user with a Cisco 7920 physically moves from place to place within a campus or between sites before ma
25. king a voice call This roaming may be within an Layer 2 VLAN or across Layer 3 subnet boundaries If this is within an Layer 2 VLAN the IP address on the Cisco 7920 remains the same If it is across an Layer 3 boundary and Dynamic Host Configuration Protocol DHCP is enabled on the Cisco 7920 the Cisco 7920 recognizes that it is no longer in the previous subnet and uses DHCP to obtain a new IP address Note The process by which the Cisco 7920 recognizes that it is no longer in the correct subnet works as follows 1 The Cisco 7920 does not received SCCP keepalive messages from the Cisco CallManager that it is registered with 30 to 90 seconds 2 It attempts to re register with an alternate Cisco CallManager 30 to 60 seconds 3 It realizes that it cannot reach the Cisco CallManager through the IP address and requests a new IP address using DHCP Mid Call Roaming This is when a user with a Cisco 7920 physically moves from place to place within a campus or between sites while a voice call is active on the phone Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 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 the phone roams into t
26. l It is used by APs to send acknowledgements and management traffic Point Coordination IFS PIFS This is not used by commercial products Distributed IFS DIFS DIFS is the interval used by most other end points 3 After the IFS interval has expired the end points begin their CA procedure This procedure uses two values called aCW min and aCWmax The Contention Window CW determines what additional amount of time an end point should wait after the IFS to attend to transmit a packet The value of the CW used is determined by the following 1 Each end point has the values for aCWmin and aCWmax defined Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 2 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 If the medium is available the end point transmits the packets 4 If the medium is unavailable such as if another device sent a packet the end point waits until the end of the packet transmission from another device and the IFS period In addition it doubles the value chosen in Step 2 and then attempts to transmit The end point continues to double the value from b until it either reached aCWmax or the packet is transmitted W CA The following shows the growth in the random backoff range with retries 1023 1023 1025 For WLAN QoS Cisco APs and Cisco 7920 phones use a te
27. lished by a finite number of DSO channels In wired Ethernet AVVID networks this is provided by an interaction between the Cisco CallManager regions and Cisco H 323 gatekeepers However these mechanisms only address CAC for the initial setup of IP Telephony calls They do not address CAC when the underlying network is changing for the IP phone throughout the call This is the case when a Cisco 7920 roams between two APs While the Cisco APs does send out QBSS information about the CU and the Cisco 7920 can utilize this information to determine the best AP to associate with this does not provide a 100 percent guarantee that calls retain proper QoS during a roam between APs One example of when this degraded QoS could occur is an event that causes more than seven or eight active Cisco 7920s to roam into an area served by a single AP thus exceeding the guidelines for calls per AP If the CU is above the CU threshold the call is not setup and the phone displays a network busy message If the CU of the candidate handoff AP is above the threshold the Cisco 7920 remains associated to the existing AP for as long as possible Once the current AP is lost no probe response or beacons received the Cisco 7920 handsoff to the candidate AP regardless of the CU A beep is heard before this happens so the user can go back toward the current AP or stop and finish the conversation Another area of admission control that needs to be considered with the Cisco 7920 i
28. ly queries Cisco CallManager for new phone and user login registration events In response to these events Cisco Emergency Responder automatically searches known Cisco Catalyst switches in the network and finds the location of the phone and the user based on the switch port to which the phone is attached through CDP or the MAC address This information is then updated in a Cisco Emergency Responder location database and is used to identify a callers location when an E911 call is placed With this solution users can move within a campus or between sites wherever and whenever they want without any administrative intervention from the IT organization This eliminates the administrative costs associated with relocating phones or users while maintaining accurate and updated location information for E911 state and safety mandates Cisco Emergency Responder makes informed inbound and outbound call routing decisions based on the location of emergency callers and provides crucial location information to emergency operators in Public Safety Answering Points PSAPs Outbound emergency calls are directed to a gateway associated with the PSAP that is nearest to the caller and in the event of an unintentional call disconnect or need for additional information inbound calls from a PSAP are returned to the original caller For more information refer to product literature for the Cisco Emergency Responder For Cisco 7920 phones several guidelines should be
29. nd it PMIP is currently supported on Cisco APs but it is currently not supported for VoIP applications The Cisco 7920 does not currently support native Layer 3 roaming using MIP In addition the current lack of VLAN support on the Cisco APs when using PMIP prevents the Cisco 7920s from being deployed for Layer 3 roaming The use of VLANs to create isolated voice and data traffic is required by Cisco AVVID design guidelines Note In multistory WLAN deployments where the WLANs on each floor have different subnets particular care needs to be taken in the RF site survey to ensure that stations on one floor do not roam to WLANs on floors above or below Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone VLANs VLANs are used by WLAN networks to provide two distinct functions e 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 guide states that separate VLANs should be created for voice and data traffic This allows appropriate QoS to be provided to different classes of traffic as well as addressing issues such as IP addressing security and network dimensioning Cisco AP350 AP1100 and AP1200 support up to 16 VLANs Cisco APs can be connected to Cisco Catalyst switches through 802 1q trunks hybrid mode native
30. nge in order to determine when a roaming event should occur Because of this it is recommended that a secondary site survey be performed for the Cisco 7920s This gives you the opportunity to tune the APs to ensure that the Cisco 7920s have enough RF coverage and bandwidth to provide proper voice quality The design recommendation is that the Received Signal Strength Indication RSSD level in the RF network is at least 20 throughout the network This provides the Cisco 7920 with the minimum signal coverage to be able to not only initiate a new call but also roam properly between APs The design recommendation is that the QoS Basis Service Set QBSS level on the APs is kept lower than 40 If the Cisco 7920 attempts to initiate a call and the QBSS element in the beacon is more than 40 the call will fail with a network busy tone to the user The power levels of the APs vary from network to network and need to be adjusted to meet site specific requirements On the APs the coverage area increases as the power levels increase But this does not necessarily mean that all the APs should be set to 50 or 100mW This could potentially create an RF environment where the Cisco 7920s roam too frequently because of RF coverage overlap Frequent roams could potentially cause interruptions in the overall voice quality On the Cisco 7920 another tradeoff to consider is that the higher the power level the shorter the battery life VoIP QoS While Voice o
31. onfigure the Network Access Server NAS by issuing the following commands radius server local nas 192 168 10 35 key Cisco nas 192 168 10 45 key Cisco 2 Configure the user database by issuing the following commands radius server local user BM AP1200 one SCM password Cisco user BM AP1100 two SCM password Cisco user testuser password Cisco 3 Configure the local RADIUS server in the APs RADIUS server list by issuing the following commands aaa group server radius rad eap server 192 168 10 45 auth port 1812 acct port 1813 radius server host 192 168 10 45 auth port 1812 acct port 1813 key Cisco 4 Configure the RADIUS server timeouts by issuing the following commands radius server deadtime 10 5 Disable client holdoff by issuing the following command no dotl11 holdoff time Network Sizing Outside of normal IP Telephony design guidance for sizing such as a Public Switched Telephone Network PSTN gateway ports transcoders and WAN bandwidth there are several 802 11b specific considerations to address Number of 802 11b Devices per AP Between 15 to 25 802 11b devices per AP is recommended Normal caveats apply in terms of traffic types usages patterns and physical space coverage Number of 802 11b IP Phones per AP Before any discussion about network planning can take place it helps to understand the basics of the overall network capacity The chart below shows the theoretical maximum throughput of an 802 11b WLAN
32. or the Cisco 7920 IP Phone 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 enabled on the Cisco 7920 it does not use VAD for transmit Tx packets but it understands what to do on the receive Rx side if VAD is being used by the remote device such as understanding the Service ID SID bit VAD is a global parameter on Cisco CallManager for all phones registered with a specific server or cluster And the general design guidance for wired AV VID networks is to disable V AD because it can provide better overall voice quality This means that unless the Cisco 7920 phones are going to register to a separate Cisco CallManager server than wired Cisco 79xx IP Phones the VAD setting must be the same for all Cisco 79xx phones Beyond determining how much bandwidth is needed for an 802 11b VoIP call consideration must also be made for the overall radio contention for a particular RF channel The general rule is that no more than 15 to 25 802 11b end points should be deployed per AP As more end points are added to an AP the amount of overall bandwidth is reduced and transmission delays potentially increase The number of phones per AP is dependent on c
33. overall QoS during Layer 2 roaming Layer 3 Roaming Layer 3 roaming occurs when a client moves from an AP that covers IP subnet A to an AP that covers IP subnet B At this point the client would no longer have an IP address or default gateway that is valid within the new IP subnet Since the clients IP address and default gateway are no longer valid its existing data sessions or VoIP calls fail since the remote client can no longer reach the local client There are the following ways that clients can work in an environment where they are roaming across Layer 3 boundaries Obtain a new IP address or default gateway in the new subnet through DHCP While this is supported on some operating systems it is not an effective model for VoIP since it would break all existing calls signaling and media Mobile IP MIP is a mechanism where routers within the network allow end points to keep their existing IP address or default gateway and the routers handle rerouting packets to the clients on their new IP subnet MIP requires Home Agent and optionally Foreign Agent functionality on the routers as well as a MIP client on the end points This functionality is not supported on the Cisco 7920 Proxy MIP PMID provides similar functionality to MIP except that the end points do not have to have an embedded MIP client The MIP client is contained in a network device such as an AP and that device acts as a MIP proxy for the end points that reside behi
34. oying LEAP This is because LEAP authentication is required every time a Cisco 7920 roams between APs and RTP traffic voice does not flow until the LEAP authentication is completed Reducing the amount of delay such as router hops and WAN links between APs and the ACS significantly improves the overall voice quality when Cisco 7920 users are roaming The three options for deploying the ACS functionality are as follows Centralized ACS server All users access the ACS server in a central location within the network Remote ACS server For remote offices that have slow speed WAN links or congested WAN links that might delay LEAP processing a ACS server could be deployed locally in the office Local and Fallback RADIUS server functionality in a Cisco AP In Cisco IOS Software Release 12 2 11 JA the Cisco AP supports the ability to authenticate LEAP users without having to access an external ACS server This functionality supports up to 50 users and is supported for EAP Cisco LEAP only This functionality does not interact with a centralized or remote ACS server in terms of database synchronization This functionality is designed to be used as the primary Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 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 1 C
35. procedure to associate with the AP e The Service Set Identifier SSID or encryption type on the Cisco 7920 has changed Once one of the events above occurs the Layer 2 roaming process proceeds as follows 1 The Cisco 7920 looks at its list of eligible roam targets APs with a matching SSID or encryption type and chooses the best candidate The Cisco 7920 then attempt to associate and authenticate to Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 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 2 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 further LAN traffic for the Cisco 7920 to AP B and not AP A 3 AP B sends a MAC multicast using its own source address telling the old AP that AP B now has the client associated to it AP A receives this multicast and removes the client MAC address from its association table This message uses the Inter AP Protocol LAPP In trying to determine potential candidate APs for Layer 2 roaming the Cisco 7920 uses several variables to determine the best AP to associate with The variables are RSSI and QBSS Definitions of these terms follow RSSI This is used by the Cisco 7920 to determine the signal strength and quality of available APs with
36. queues for traffic on the AP to ensure the best possible voice QoS Voice RTP and signaling SCCP traffic should be placed into the highest priority queue All data traffic should be placed into a best effort queue While 802 11b EDCF does not guarantee that voice traffic is protected from data traffic using this queuing model should provide the best statistical results for voice QoS The Cisco 7920 IP Phones support a QoS similar to EDCF for upstream toward the AP traffic In additional the Cisco 7920 dynamically announces its presence with the Cisco Aironet AP to ensure its downstream traffic is placed into the high priority queue on the AP This dynamic announcement is done through Cisco Discovery Protocol CDP The CDP packets are sent from the Cisco 7920 to the AP and identify the phone so that the AP can place all traffic to the phone in the high priority queue The SCCP signaling messages are marked with DiffServ Assured Forwarding AF 31 and RTP packets are marked with DiffServ Expedited Forwarding EF This matches the DiffServ markings of Cisco wired Ethernet IP phones and allows the QoS settings to be consistent from LAN to WLAN environments In addition to setting the DiffServ markings correctly and supporting a QoS similar to EDCF the Cisco 7920 also supports an intelligent mechanism to determine the QoS that can be provides by a given AP It does this based on an algorithm that takes into consideration RSSI and RF CU based on upd
37. reste prede C Le cR IO 0 amp lgie Pete MA 120 144 172 ap service n Cw LL eL Current native VLAN Management VLAN 1 Current VLAN List Create VLAN lt NEW gt vani fe 1 2995 Native VLAN Dolot T Esabin Public Secure Packet Forwarding ssip mrami z Deine som Aeply j Cancel View Information for VLAN 2 7 Fasththereet Packets Fuydio0 902 118 Packets ancoivod 4 4 o Traum bet o 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 following is a list of characteristics of a wired VoIP QoS e Dedicated access per user or device switched ethernet Point to Point P2P WAN Packets marked with 802 1p and IP Type of Service ToS or Differentiated Services DiffServ e Can provide hard QoS e QoS can be applied to upstream or downstream traffic e Can provide hard admission control The following is an example of characteristics of WLAN VoIP QoS e Shared access to bandwidth Packets marked with 802 1p and IP ToS or DiffServ Provides soft QoS QoS is currently available to downstream traffic from the AP but few devices other than the Cisco 7920 provide upstream QoS towar
38. s when a user takes the Cisco 7920 from one location to another such as campus to branch When the Cisco 7920 re registers with the Cisco CallManager there is no mechanism that updates which Cisco CallManager region or gatekeeper zone the Cisco 7920 is associated with This means that it is possible that calls to or from that Cisco 7920 would not properly be accounted for across a WAN link and could cause poor voice quality to phones that are registered in that region Designing Around the Lack of Layer 3 Roaming For customers that require roaming support for a large area such as between floors of a buildings large Layer 2 VLANs spanning across access switches can be created to eliminate the Cisco 7920s crossing an Layer 3 boundary when roaming The following guidelines need to be considered for customers that are looking to deploy large Layer 2 VLANs Cisco ESE guidelines do not recommend that data VLANs span multiple access switches e An Layer 2 VLAN should not cross a building boundary If this is required then an additional overlay Layer 2 core needs to be built to avoid creating instability and excessive traffic in the traditional Layer 3 core Both the voice VLAN and the native VLAN on the AP need to be trunked across the large Layer 2 VLAN This is required to allow both voice traffic and IAPP traffic between the APs e Having Layer 2 VLANs span multiple access switches creates the possibility of STP loops if configured
39. t Effort VoIP sends Real Time Protocol RTP packets using UDP UDP does not have a mechanism to retransmit lost packets The network guidelines defined by Cisco AV VID for proper VoIP operation are as follows Delay Not to exceed 150 ms one way Delay Variation Jitter Not to exceed 30ms Packet Loss Not to exceed 1 percent Note While isolated testing may show that VoIP calls could operate in a network outside of these guidelines deploying a VoIP network under those conditions cannot be predictably engineered Support from the Cisco Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone 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 SAFE security architecture For more information refer to Cisco SAFE Wireless LAN Security in Depth Note The Cisco 7920 does not support Cisco Temporal Key Integrity Protocol TKIP or Cisco Message Integrity Check MIC in the initial software release Future versions of the Cisco 7920 software will add support for TKIP and MIC as well as Wi Fi Protected Access WPA The Cisco 7920 supports both static Wired Equivalency Protocol WEP 802 1 and Extensible Authentication Protocol
40. t RTP packet seen on AP2 It also includes the times it takes to re authenticate and reassociate with AP2 The following image shows a sample trace of a Cisco 7920 roaming to a new AP and the LEAP messaging that is between the Cisco 7920 and the AP Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone Paket Soute Destination SSID Protocol Data kate Ch Signal FL Size Dela Time Felatie Time 1972 AP1200 w0 setchao MAC 4P1200 tTo EAP Request L0 Li 16 i 00 000000 1974 satchoo MC AEL2OC two iP1200 tro EAP Response 10 Lk Sa 00 0538 00 006001 1976 AP1200 tw0 setchao MC 4P1200 tro EAP Request 1 0 Li XX B 00 009895 00 036216 1903 satchao MC AEL2MC two iP1200 tro EAP Response L0 Li A 9 00 052917 00 009153 906 21200 tut Sttcheo BAC aP1200 tro EAP Success LQ Ls 9 B 00 0613 00 10534 1909 satchao MC ArL20 tw0 i1200 tro EAP Request 10 1 10s 6 00 04045 00 109309 1992 4P1200 two sttchzo MAC 4P1200 tTo EAP Response L0 Li 3s B 00 0485 00 1938 1994 AP1200 two sttchao MC iP1200 tro EAP L Key L0 L9 M 00 001268 00 195200 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
41. ver IP VoIP does convert voice signals into IP data packets and converge them with data traffic the requirements of voice and data are very different when transmitted over an IP network Data traffic can be classified with the following characteristics Bursty Traffic can be sent in large or small bursts depending on the application Bandwidth Greedy Transmission Control Protocol TCP applications attempt to use as much bandwidth as the network allows Packet Loss Insensitive The retransmission capabilities of TCP allow data to continue to work correctly even with packet loss on the network Delay Insensitive Most TCP applications can handle some packet delay without effecting overall performance Cisco Wireless IPT Design Guide for the Cisco 7920 IP Phone Bursty Greedy Drop Insensitive Delay Insensitive TCP Retransmits Voice traffic can be classified with the following characteristics e 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 is extremely sensitive to packet loss Excessive loss degrades overall voice quality Delay Sensitive While VoIP can tolerate some amount of delay excessive delay or excessive delay variation jitter degrade overall voice quality User Datagram Protocol UDP Bes
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