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Deploying NetLink Wireless Telephones

Best Practices

White Paper

Version 1.0

May 2004

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Summary of Contents for NetLink Series

Page 1: ...Deploying NetLink Wireless Telephones Best Practices White Paper Version 1 0 May 2004 ...

Page 2: ... most significant difference is their tolerance for network errors and delays Whereas data applications are designed to accept just about any amount of packet delays and retransmissions voice quality will suffer with just a few hundred milliseconds of delay or a very small percentage of lost packets Data applications are typically bursty in terms of bandwidth utilization while a telephone conversa...

Page 3: ...erminals Telephone users tend to walk as they talk while data users are most often stationary NetLink Wireless Telephones are usually held next to the user s head introducing additional radio signal attenuation Data terminals are usually set on a surface or held out at arms length so the user s body has little affect Because of these factors a wireless telephone may have less range than a data ter...

Page 4: ...ration that includes wireless bridges and does not recommend using wireless bridges within any wireless voice network 2 2 Channel and Power Considerations Adjacent APs need to use different radio channels to prevent interference between them The 802 11b standard utilized by NetLink Wireless Telephones provides three non interfering channels channels 1 6 and 11 for North America Access points withi...

Page 5: ...th poor coverage or interfering channels With the NetLink e340 and i640 Wireless Telephones the entire coverage area should be checked to ensure that at least one access point s reading is stronger than 70 dBm in all areas Also if the site survey mode indicates 2 APs using the same channel then at least one other AP must be indicated at 10 dBm stronger than those APs to avoid channel conflicts Aft...

Page 6: ... packet rate will determine the size of the voice packets along with any additional overhead information required for the protocol The payload information makes up a little more than half of a typical voice packet with 802 11 and IP protocol overhead filling the rest The 802 11 protocols include timing gaps for collision avoidance which means bandwidth utilization is more accurately quantified as ...

Page 7: ...endor specific characteristics associated with individual access points that make it difficult to quantify the concurrent calls per AP without thoroughly testing specific configurations As a general rule based on lab tests and experience wireless LAN designs for NetLink Wireless Telephones should consider no more than 12 simultaneous calls at 11 Mb s or no more than 7 calls at 2 Mb s using either ...

Page 8: ... number of call resources available Telephone usage is measured in units of Erlangs One Erlang is equivalent to the traffic generated by a single telephone call that lasts for one hour A typical office telephone user will generate 0 10 to 0 15 Erlangs of usage which equates to six to nine minutes on the telephone during a one hour period Heavy telephone users may generate 0 20 to 0 30 Erlangs or 1...

Page 9: ...7 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 by installing addition APs with smaller coverage areas But for most enterprise applications the number of calls supported within the coverage area of an...

Page 10: ...her static or DHCP address assignment When utilizing multiple NetLink SVP Servers with an IP telephony server the master NetLink SVP server must be assigned a static IP address When operating with an IP telephony server the NetLink SVP Server also requires a range of IP addresses that covers the total number of Wireless Telephones supported by that NetLink SVP server When a NetLink Wireless Teleph...

Page 11: ...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 12: ... minimizing random backoff and priority queuing require a packet filtering mechanism Packet filtering requires recognizing the packet s protocol identifier which for SpectraLink packets is registered protocol ID 119 for the SpectraLink Radio Protocol SRP The NetLink SVP Server also performs packet delivery timing in the link to the Wireless Telephones that is critical for ensuring seamless handoff...

Page 13: ...s Telephones by those devices MAC addresses Allocation is done by dividing the MAC address by the number of NetLink SVP Servers and assigning the device based on the remainder For example if three NetLink SVP Servers are used the first NetLink SVP Server is assigned to all APs and NetLink handsets with MAC addresses that are even multiples of three The second NetLink SVP Server is assigned to MAC ...

Page 14: ...ming FSR 802 1x based authentication protocols such as EAP TLS or Cisco s LEAP were developed to provide a higher level of security for wireless networks These advanced methods require a back end authentication server to authenticate users and generate new keys This authentication and re keying process can take up to several seconds and is required each time a user hands off from one AP to the nex...

Page 15: ...other words the Ethernet switch ports must not be configured as trunked ports 5 3 MAC Filtering and Authentication Access points can be configured to filter certain MAC addresses which can be used as a method of securing the wireless LAN This process generally works but does cause some performance issues on some APs A more robust method of using MAC addresses to secure the network utilizes authent...

Page 16: ...er 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 5458 The push to talk PTT mode of the NetLink i640 Wireless Telephone uses the multicast IP address 224 0 1 116 which is also used by the NetLink Wireless Telephones and in...

Page 17: ...itive network equipment may reside Utilizing VPNs can be an extremely effective method of securing a wireless network Many customers have been implementing VPNs to maintain the integrity of their wireless LANs by requiring wireless users who need access to the protected portion of the network to connect through a firewall Voice devices such as the NetLink Wireless Telephone do not require access t...

Page 18: ...itches and third party devices have implemented methods to facilitate device mobility While these methods are transparent to the client device they often cause enough delay and latency to manifest poor voice quality In addition many of these methods do not work well under loaded conditions such as might be experienced with a large number of highly mobile wireless voice users NetLink Wireless Telep...

Page 19: ... the timely delivery of voice packets essential Routers can introduce latency and delay between the NetLink SVP Server and the APs which manifests as poor voice quality Ethernet connectivity between the NetLink SVP Server and the IP telephony server should never exceed 100 ms of network delay and 10 ms of network jitter regardless of the physical properties of the link The ability to cross a subne...

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