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Deploying NetLink Wireless Telephones
Best Practices
White Paper
Version 1.0
May 2004
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White Paper 1.0 Introduction Wi-Fi telephony is the convergence of wireless voice and data applications using a common Wi-Fi wireless LAN. Wi-Fi telephony bridges traditional telecommunications, data communications, and mobile technologies. A Wi-Fi wireless telephone is a wireless LAN client device, using the same network technology as wireless laptops and PDAs, and sharing the same medium. A Wi-Fi wireless telephone is also functionally equivalent to a wired telephone, requiring co
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White Paper One of the most critical issues in deploying NetLink Wireless 2.1 Coverage Telephones is ensuring sufficient wireless coverage. Often enterprise Wi-Fi networks are designed only for data applications and may not provide adequate coverage for wireless telephone users. Quite often these networks are designed to cover only areas where data terminals will be used, and do not include coverage in other areas such as stairwells, bathrooms, building entrances, or lobby areas wh
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White Paper voice is an application on the wireless LAN because the coverage area of the AP will be greatly reduced. If a site requires configuring the APs to only negotiate at the higher rates, the layout of the wireless LAN must account for the reduced coverage and additional APs will be required to ensure seamless overlapping coverage at the higher rates. 2.1.2 Wireless Bridges Wireless bridges are used to connect Ethernet LANs or extend the range of existing wireless LANs. Such d
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White Paper and provides consistent coverage. Performing a site survey can minimize the possibility of dead spots. The 2.2.1 Site Surveys AP equipment provider can usually perform a site survey. While many tools exist that allow customers to perform their own assessment, SpectraLink recommends that every site employ a professional site survey to ensure optimum coverage and minimize interference. Site surveys are a necessity for large or complex facilities. An extensive site surv
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White Paper The network capacity requirements also factor into the number of APs 2.3 Capacity required, although in most cases the coverage area is the primary factor. Data traffic is very bursty and sporadic, but data applications can tolerate network congestion with reduced throughput and slower response times. On the other hand, voice traffic cannot tolerate unpredictable delays, but at least the bandwidth requirements are constant and consistent for every phone call. Also, te
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White Paper The maximum number of simultaneous telephone calls an AP can support is determined by dividing the total available bandwidth by the percentage of bandwidth used for each individual call. Approximately 20- 40% of the AP bandwidth is reserved for channel negotiation and association algorithms, so 60-80% of the total available bandwidth should be used for calculating the maximum call capacity per AP. Lower overall bandwidth is available when there are a greater number of d
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White Paper 2.3.2 Push-to-Talk The push-to-talk (PTT) mode of the NetLink i640 Wireless Telephone uses SpectraLink’s proprietary SpectraLink Radio Protocol (SRP) Multicasting ADPCM encoding. If a PTT broadcast is active (i.e. a user presses the Considerations PTT button), the feature will use the bandwidth as indicated in the table above for the single transmitting i640 Wireless Telephone and one half of the bandwidth for all of the receiving i640 Wireless Telephones. The data rate u
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White Paper User Calling Intensity Light Moderate Heavy Erlangs per User 0.10 0.15 0.20 Max Active Calls per AP Users Supported per AP (1% Blocking Probability) 1 1 1 1 2 2 2 2 3 4 3 3 4 8 6 4 5 13 9 7 6 19 13 10 7 25 17 13 8 31 21 16 9 37 25 19 10 44 30 22 11 51 34 26 12 58 39 29 Users Supported per Access Point Areas where more Wireless Telephone usage is expected, such as cafeterias and auditoriums, can be provided with additional capacity to support more users b
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White Paper 3.0 Network Infrastructure Considerations The NetLink Wireless Telephone infrastructure components should 3.1 Physical connect to the facility’s local area network (LAN) using Ethernet Connections switches, as opposed to Ethernet hubs, to provide adequate bandwidth and limit traffic collisions. Ethernet switches should be configured to negotiate the connection requirements automatically. NetLink Telephony Gateways require 10Base-T, half-duplex transmission and the NetLi
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White Paper Gateways, a separate TFTP server must be provided. Also, the NetLink SVP Server requires a separate TFTP server for software updates. The NetLink Telephony Gateway cannot be used as a TFTP server for the NetLink SVP Server code. NetLink Telephony Gateways receive software updates only through an FTP server. Page 10
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White Paper 4.0 Quality of Service Quality of Service (QoS) is a means of guaranteeing a level of service 4.1 SpectraLink that will result in a network connection of adequate quality. Typically this Voice Priority results in providing different levels of service for different applications, (SVP) depending on their requirements. When data and voice are competing for bandwidth it is necessary to have a prioritization method that provides a controlled preference to voice packets. Th
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White Paper data transmission rate of 2 Mb/s. A NetLink SVP Server is required for applications using an IP telephony server or using more than four NetLink Telephony Gateways. A NetLink SVP Server can also be used with four or fewer NetLink Telephony Gateways to allow a maximum data transmission rate of 11 Mb/s. A single NetLink SVP Server supports 120 simultaneous calls when used with NetLink Telephony Gateways, or 80 simultaneous calls with an IP telephony server. Multiple NetLink
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White Paper 5.0 Security Security provisions are critical for any enterprise Wi-Fi network. 5.1 Security Wireless technology does not provide any physical barrier to the Concerns network, since radio waves penetrate walls and can be monitored and accessed from outside a facility. The extent of security measures utilized are typically proportional to the value of the information accessible on the network. The security risk for Wi-Fi telephony is not limited to the typical wired t
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White Paper 5.1.3 Emerging Recognizing the need for stronger security standards, the IEEE is developing the 802.11i standard, which is expected to be ratified in late Security 2004. The 802.11i standard includes stronger encryption, key Standards management, and authentication mechanisms. An interim solution endorsed by the Wi-Fi Alliance is Wireless Protected Access (WPA), which is a subset of the 802.11i standard. SpectraLink is committed to industry standards and will implement
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White Paper the IP telephony protocol used on the telephony switch interface. The telephony switch vendor should be able to supply the port numbers used by the protocol. The NetLink Wireless Telephones, NetLink Telephony Gateways, and NetLink SVP Server use TCP and UDP and other common IP protocols from time to time. These include DHCP, DNS, WINS, TFTP, FTP, Telnet, ARP, and ICMP. SpectraLink uses proprietary UDP channels between the infrastructure components that use UDP ports 5454
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White Paper Virtual Private Networks are secured private network connections. 5.5 Virtual Private VPNs typically employ some combination of encryption, digital Networks certificates, strong user authentication and access control to provide (VPNs) security to the traffic they carry. They usually provide connectivity to many devices behind a VPN concentrator. The network can be broken into two portions, protected and unprotected: 1. The area behind the VPN server is referred to as
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White Paper 6.0 NetLink Wireless Telephones and Subnets Subnets are used to create a boundary between network segments. Although these boundaries are logical, they become somewhat of a physical boundary for mobile network devices moving throughout the enterprise. When a device with an established IP data stream (such as with an active phone call) attempts to roam across a subnet boundary, it needs to obtain a valid IP address within the new subnet. During this process the data strea
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White Paper NetLink Wireless Telephones, NetLink Telephony Gateways, NetLink 6.1 Subnets and SVP Server(s), and the wireless APs must reside on the same subnet. NetLink One reason for this requirement is that the NetLink Wireless Telephones Telephony use IP multicast messages to initialize the Wireless Telephone Gateway registration on the NetLink Telephony Gateways. Most routers deployed in multi-subnet Ethernet environments are configured to filter out Interfaces multicast and b
