Wireless Office - What am I missing?

I have a small office, 3000 sqft, with 5 POTS lines (4 for voice, 1 for fax), all in support of a dozen people.

I would like to migrate from a very old conventional phone/voicemail system to an Asterisk wireless system. That is to say wireless within the office, but tied to my existing standard phone service. I have read and read about myriad of equipment out there, but I feel like I’m missing something.

Seems to me I need a reasonably fast Linux box, a line card like one of Digium units for my telephone service, a dedicated wireless router and bunch of wireless IP phones. What am I missing?


Thanks, with all the vendors selling “bundles” of equipment I was beginning to think there was some fundamental component that I did not understand in the equation.

I understand your roaming comment, but since we have no problem with 5GHz full signal strength roaming in our office with laptops, so I am pretty confident that IP phones in the same band will work well. I have had a hard time finding good info on the bandwidth required for concurrent calls. I saw one article that says, depending on the codec, that you may require up to 80kps per call. Theoretically that sounds reasonable since POTS phone service uses about 3-4kHz of bandwidth, but then I see so many forums posts on bandwidth issues, I can’t figure out why people are having issues. Perhaps the issues I am reading relate more to users trying to combine data traffic with voip? Any words of wisdom about this? I am thinking that dedicated wireless/g setup should have plenty of room for 4 concurrent calls with lots of room for growth (with or without QOS).


Thanks Walter, I very much appreciate your help. I am lucky enough to have several staff members that second to Java programming, like to work on Linux systems and configure networks. They will be thrilled to setup an Asterisk system with some nice PTT Polycom 8030 phones. Thanks again for your feedback. Brent

I am following up this thread with information on how to get the Polycom / Sprectralink Netlink 8000 8030 phones working with Asterisk as I have spent weeks trying to get them work. The information below is not intended to be a HOWTO, I’m only identifying the those major stumbling blocks that took me a long to figure out. Most of these issues/requirement are undocumented, poorly documented and even unknown to Polycom tech support.

  • In order to run SIP on the Netlink 8000 phones the “telephony mode” must be set to 36. This is documented in several Spectralink manuals, but no one seems to know how to do it. Given a new phone, the only way to do this is by powering off the phone, then holding down the green button, next holding down the red button, after a moment the phone will chirp, then quickly release the red button and lastly release the green button. Now the phone menu is accessible and the telephony mode can be changed.
  • The Handset Admin Tool Build Date Jan 22, 2008 is needed to configure SIP parameters for the phone. Polycom/SpectraLink tech support does not have this version of the tool, nor is it available on the support FTP site. However, with this knowledge and a few phone calls to tech support they should be able to get it for you (assuming you have purchased the tool that ships with a CD, ie. a valid hand tool license). Note, if you can lay your hands on the hand set admin tool, a standard USB cable (like the type used for an cell phone) will plug into a dual charger cradle to allow it to work.
  • The handset admin tool writes TFTP config files. Set up a tftpsite. Although, with expert knowledge, one could hand create the TFTP config files and hand program a few IP addresses into the phone. Having the handset admin tool, a TFTP site and the knowledge how to get into the phone’s config menu (green button, red, chirp, release red, green) all together this info is invaluable and work together to get these phones operational.
  • Once this is done the [TYPE36] slnk_cfg.cfg file can be placed on your tftpsite with the latest firmware. This is available from the SpectraLink software updates website (after registering). This firmware was released 1/16/2008.
  • The Netlink phones will not work without some piece of SpectraLink “infrastructure” that speaks “SRP” (SpectraLink Radio Protocol). This requirement is poorly documented. The cheapest way to achieve this is to get a SVP-xxx (where xxx can be 010, 020 or 100) box. This little box runs embedded Linux and proxies Netlink phone messages. I suspect SpectaLink builds them to order because it took me a month to get mine and no one stocks the units. According to tech support, the source code for the protocol might be available. If one could track it down it would make much more sense to run this SRP proxy on your own Linux box, the same one that runs Asterisk. Asterisk Business Edition apparently “supports” the Netlink 8000 phones, I’m not sure if that means it has built in SRP support. If it does that would eliminate the need for a SVP box which would probably be cost effective. Since the Asterisk Business Edition documentation does not explicitly say this, I expect is does not.
  • Enable network multicast. The Netlink 8000 phones, even when in SIP mode, want to talk SRP. This is done using multicast (224.0.x.x) broadcasts. This may require setting up multicast on the Asterisk server NIC and/or the wireless router, depending the hardware used for the solution. Suffice to say, the Netlink phones multicast to the SRP/SVP server, if the the phone cannot reach a SRP server this will refuse to work. Using of the tcpdump (in Linux) command can be rather useful in seeing the broadcast messages when diagnosing this connectivity.

By combining a Linux Asterisk server, a wireless router, SVP-020 and a bunch of Netlink 8030 phones. A premium 20 extension office wireless phone system (with a range of about 300’ given one good router) can be had for <$10,000USD, several times less than what it would cost try to obtain such a system from a vendor. At that, I’m not even sure if anyone bundles such a system.