VOIP over wireless

[Evert]

First let me apologise for posting in English but my German is not good enough to make up a sensible posting...

I have been asked to proide a client with a wireless network for their new offices, so far no problem, done it lots of times before.

But now they have asked me to look into VOIP over this wireless network.
It has to be able to do the following;

1) Make calls from handset to handset (obviuosly).
2) Make calls from a handset on the internal network to an outside number on the regular telephone network.
3) Receive calls from the regular phone network.
4) Able to route calls to the correct extension.
5) call queing etc.

Basically they are looking at a 15K bill (minimum) to get a similar setup as what they have in their current offices and want to explore some alternatives.

I've been pointed to this forum by a few people and was wondering if anyone here can give me some pointers. One of the things I have been recommended to look into is the Asterisk servers..

Regards, Evert.

 

[Robinson]

Asterisk could be one way, an other and maybe easier is e.g. the Zyxel P2000W - just config and play. But, for in-company communications as whished by your client I think you will need Asterisk.
The problem is, that adapters like the one of Sipura or Grandstream are based on wired Ethernet, so you allways need an interface to change from WLAN to wired LAN to the adapter. If you really want to use WLAN only with all features of a communication networks, you need probably both, asterisk and the Zycel.

But I work only privat, maybe there are other forum members with better, smaller or easier ideas.

Welcome in the world of VoIP and good luck!

 

[Evert]

Thanks for the quick reply!
I was already thinking of using the Zyxel handsets.
My problem is not so much the LAN (internal) side of things but more how to route outgoing calls onto the "normal" telephone network and how to route incomming calls from the "normal" telephone network to the correct extension on the VOIP-wifi network..
If there is anyone here working for a company who can implement these things I would love to hear from them too!

Regards, Evert.

 

[otaku42]

A Linux box that runs Asterisk would be the best choice here IMO. Combined with the needed hardware (multiport cards from Digium, as I think this company won't be satisfied with only one or two lines to the POTS) this would make up a very flexible PBX. In turn that will take some time to get familiar with the Asterisk configuration, but it's worth the time.

One thing you should take care of: the current WLAN standards don't provide any Quality of Service. In case the WLAN handsets will use the same cells as "data clients" (i.e. Notebooks with WLAN functionality), it might lead to noticeable delay due to the limited bandwidth. Depending on the size of the company, the size of the building where the installation is going to be deployed and the amount of money that the company can spend for this project, I suggest to install a second WLAN infrastructure on independant frequencies. But mileage may vary, depending on the usage of the WLAN for data transfers.

Bye, Mike

 

[Evert]

One thing you should take care of: the current WLAN standards don't provide any Quality of Service. In case the WLAN handsets will use the same cells as "data clients" (i.e. Notebooks with WLAN functionality), it might lead to noticeable delay due to the limited bandwidth. Depending on the size of the company, the size of the building where the installation is going to be deployed and the amount of money that the company can spend for this project, I suggest to install a second WLAN infrastructure on independant frequencies. But mileage may vary, depending on the usage of the WLAN for data transfers.

Bye, Mike

This is one option but what is the typical bandwidth useage of a VOIP phone?

Regards, Evert.

 

[otaku42]

The bandwidth heavily depends on the used codec and ranges from something around 20kBit/s to over 80kBit/s per active voice channel.

Bandwidth isn't the only problem here, another one is the delay. It is desireable to have the least possible delay for VoIP data, since you'll notice any delay in the quality of the phone call. Since WLAN Access Points currently can't/don't distinct VoIP data from "bulk data" (file transfers for example) they won't handle VoIP with increased priority. Even if the bandwidth isn't fully used by the currently active clients, you might notice increasing delays while other clients are transfering data. This also might become true for two or more VoIP calls that are made in the same WLAN cell at the same time.

Bye, Mike

 

[Blackvel]

This depends much on the codec = audio voice quality.
There are several codecs:
G711 (PCMU/A or also called ulaw/alaw): 80kbit/s per channel including overhead
G729A: 8kbit/s per channel, additional overhead
iLBC: 15kbit/s per channel, additional overhead
GSM (not sure about the exact bw) 10-15kbit/s per channel, additional overhead

These are the most used codecs.
G711 is best which means same quality as PSTN.

For iLBC/G729A/GSM the total bandwidth probably will be 20-35kbit/s.

 

[thorsten001]

In short: Get a real telephone switchboard supporting H.323. There are "normal" switchboards out there updateable with H.323 cards.
Use DECT wireless telefones.

 

[Evert]

In short: Get a real telephone switchboard supporting H.323. There are "normal" switchboards out there updateable with H.323 cards.
Use DECT wireless telefones.

Why?
Do you think that VOIP over a WiFi network is not a viable option?

E.

 

[koehler]

@Evert:

This 15k is your budget or your clients current phone bill ?

Asterisk could be a solution if you are a computer expert. If not, you may consider alternatives like the Cisco Callmanager or Sysmaster/Voicemaster.

If you considered Asterisk, then it is also possible to get an out of the box system. There are plenty garage shacks around the globe (check: www.voip-info.org and look for your local country representatives) which could do the asterisk job for you. But have in mind that Asterisk is open source and there are more pitfalls than features with this software. Some guys told that "Asterisk" could be the short for "astronomic risk".

VoIP at wireless only ethernet networks is a very expensive facility, an alternative is to setup some ATA's with pots DECT-Wireless Handset connected to the main ethernet switch. This would save about 50% of investment, reduce maintenance costs and increase ROI. Another benefit is that these pots DECT phones have a greater air coverage than WiFi VoIP phones (except for high radiation omni or beam radio systems, but i think you now that already)

When you settle for WiFi VoIP, the hooked bandwidth depends on the voice encode/decoder (codec) you choose for the WiFi phones. Common codecs are g.711 (alaw/ulaw), g.729 and g.723. g.711 gives the best voice quality but it also could be a traffic killer at a WiFi network. g.729 and g.723 are narrow band codecs with even good quality without static. Consider these codecs on a < 56mbit Wifi network and even with a broadband connection with less than 2mbit. (Example, for a common network of 30 phone users)

Also think about the maintenance times. In case you are using WEP encryption and MAC filters it will raise setup time unexpectedly.


Good luck,

Michael

 

[ganjamen]

i think its far from perfect runing for now ... also certain wireless lan gear is quite sensible if you use for instance 2.4GHZ wireless equipment you can have interference trouble with other 2.4ghz gear like DECT phones other wireless networks etc.

from my knowledge there are no wireless lan VOIP phones available with 5ghz 802.11a standard

i think its much better to use DECT phones only for wireless phonecalls and use some kind of switchboard/PBX with sip or H.323 support to connect them.

 

[koehler]

Just for the files, i never heard of any interference troubles with DECT and VoIP phones.

802.11a is 5ghz (ofdm phy) and mostly used in US because the 5ghz band is for free there. Not to mention that 802.11b/g are common now, even in the US.

ack, dect phones are a good solution. What do you think about a Cisco 7920 wifi/Callmanager solution with SCCP signalling ?

 

[ganjamen]

@koehler just check the d-link and netgear forums on www.dslreports.com . they are full of userreports which having troubles with 2.4ghz devices and their wlan. it seems to be a software problem of the atheros chipset ar5001X drivers in certain routerboards.

btw the 5ghz band is free europe aswell since some time.

 

[koehler]

I beware of reading these never-ending-threads Guess, you have to get your dect from radioshack instead of next-corners-el-cheapo-mart.

Also sounds like they are using dwarf-hand-crafted phones made in mexico, used in small square rooms by fools who set the wifi router to maximum throughput (for example the x22 or x200 dlink feature) which makes traffic unstable and signal bad Not wondering at all.




michael

 

[otaku42]

you can have interference trouble with other 2.4ghz gear like DECT phones

DECT does not use 2.4 GHz, but is working in the 1.9 GHz spectrum. At least those systems that are widely used. IIRC in the US there are some 2.4 GHz wireless phones (analog), but they don't conform to DECT or any 802.11 WLAN standard.

Bye, Mike

 

[ganjamen]

ok i mixed something with dect and 2.4 phones.... my mistake ...

 

[koehler]

We also get off topic