Voice over IP gateways

As their branch office and teleworker networks grow, companies are increasingly looking to connect remote users to their central phone systems using Voice over IP (VoIP) technology. One way of doing this is to throw out the existing PBX (Private Branch eXchange) hardware and replace it with a new IP-based alternative. But another, far simpler and much cheaper, approach is to use a VoIP gateway.

What’s involved?
Costing just a few hundred pounds, VoIP gateways attach to the existing analogue or digital PBX in place of one or more local extensions using so-called FXO (Foreign eXchange Office) ports. Calls to and from these extensions can then be converted into VoIP data streams and forwarded over the LAN/Internet to a receiving device -- either another gateway with phones attached to FXS (Foreign eXchange Subscriber) ports, a specialised IP phone or adapter, or even a PC running a softphone application.

Also referred to as 'long-line extensions', the remote phones can be used just like those attached to ordinary local handsets. Moreover you can expect voice quality to be the same if not better and for phone bills to be slashed because calls can be routed over a broadband Internet link rather than the PSTN (Public Switched Telephone Network).

What we found
The simplest of all VoIP applications, long-line extension gateways can fall foul of firewalls and NAT routers, so fixed IP addresses are recommended. Ideally, you should also have a VPN connection to avoid NAT problems. You should also choose your gateway with care, preferably using the same hardware at both central and remote locations.

We tested five products aimed at small to medium-sized enterprises. All delivered good results, but there were considerable differences in complexity when it came to setup and management.

Where only a single extension is required, the Sipura SPA-3000 is a good choice and very affordable; the only drawback is its somewhat complex management interface. Higher up the food chain, the Vega 50 from VegaStream is a good choice if you're connecting multiple offices and teleworkers, with the bonus of UK development and support.

Between these, the Multi-Tech and Quintum gateways both performed well, offering a variety of configurations beyond the 2-port products we tested. In the end, our Editors' Choice award went to the Quintum Tenor ASM200. This was due primarily to its simple port mapping facility -- which makes for fast, easy deployment -- and transparent operation once in place. These are the features that really make the Quintum Tenor stand out from the crowd.

VoIP gateways compared
	Multi-Tech MultiVOIP MVP210	Quintum Tenor ASM200	Sipura SPA-3000	Solwise VOIP-EL404	VegaStream Vega 50
Editors' Rating	7.8	8.5	7.0	6.0	7.5
General
LAN ports	1 x 10/100	1 x 10/100	1 x 10/100	1 x 10/100	1 x 10/100
FXO (PBX/PSTN line) ports	2*	2	1	4	10
FXS (analogue phone) ports	2*	2	1	0**	0**
Other ports	2 x E&M	-	-	-	-
PSTN breakout	yes	yes	yes	no	yes
PSTN failover	yes	yes	yes	no	yes
Signalling protocols
H.323	yes	yes	yes	no	yes
SIP	yes	yes	yes	download	yes
Other	SPP	-	-	-	-
Codecs supported
G.711	yes	yes	yes	yes	yes
G.723	yes	yes	yes	yes	yes
G.726	yes	no	yes	no	no
G.729	yes	yes	yes	yes	yes
Silence suppression	yes	yes	yes	yes	yes
Adaptive jitter removal	yes	yes	yes	n/s	yes
T.38 Fax over IP support	yes	yes	yes	yes	yes
QoS	yes	yes	yes	yes	yes
Price (ex. VAT)
	£570	£340	£82	£221	£1,114

* set in software
** FXS gateways available