Intertex IX66 AirSIP Review

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During March 2002, we reviewed the Intertex IX66-EDFLC ADSL router featuring an inbuilt firewall, Ethernet & USB support, and a well designed user interface. Since this date, Intertex have added a new wireless model to the IX66 range called the AirSIP. Although all models within the IX66 range run the same firmware, and are configured in the same way, they are differentiated by their hardware support. The AirSIP features a single Ethernet port (for connection to your local area network), a USB virtual Ethernet port for connection to a single PC and an optional wireless Compact Flash (CF) slot & card for 802.11b wireless networking.

This review focuses upon features specific to the AirSIP (namely wireless) and some of the more advanced areas including supported by the entire IX66 range of routers including Voice over IP (VoIP) using Session Initiation Protocol (SIP). For installation and basic setup instructions, please see the original review. Firmware version 2.04 was used throughout the review process.

Wireless Configuration & Support


The AirSIP may be purchased with or without a wireless card (depending upon your requirements). The great thing about this product is that it has wireless capabilities, but you don't have to pay extra unless they are required. Unlike many wireless routers which use PCMCIA cards, the AirSIP uses a Compact Flash card which is connected into a slot in the side of the unit.

Step 1 - locate the wireless flap at the side of the router

Step 2 - push the flap backwards

Step 3 - insert the wireless CF card until inserted as shown above

It is necessary to connect the wireless CF card before powering up the router, although the card may be removed and reconnected once booted up. A small green light on the CF card in addition to the "AIR" LED on the front panel illuminate when the wireless card is correctly connected and operational.

IX66 AirSIP - Printed Circuit Board with Wireless CF card attached


A new AIR box within the networking section of the web configuration pages is visible when the wireless card is connected as shown below.

The following modes of operation are supported by the USB, ET2 and AIR interfaces:

  • Inside - protected by the inbuilt firewall and Network Address Translation (NAT)

  • Outside - unprotected and exposed to the rest of the world. Used in combination with multiple IP addresses assigned by your ISP. It is strongly recommended that a firewall is installed on each individual computer system

  • DMZ - all inbound traffic is routed to this interface. Useful when running web servers or publically accessible services

  • Bridged with {ET2, AIR, USB} - when specified the IX66 operates in the same way as a switch between the two interfaces. Each interface may be bridged with one of the other two respectively.

  • Blocked - interface disabled.

In this example, the wireless interface has been set to bridge with ET2 (Ethernet port) which means that the wireless and wired portions of the network are effectively the same (i.e. a computer may use the same IP address via either interface). In turn, the ET2 interface is set to inside mode, meaning it acts as a gateway on IP address and hence the ET2 and AIR interfaces are protected by the inbuilt firewall.

The best aspect of the IX66 is that all interfaces (no matter which technology they use) are all treated in exactly the same way. Some rather advanced network structures can be employed featuring multiple segments, and an operational environment where one interface is used for externally connected computers and the others are internally protected with NAT. Unfortunately, the IX66 doesn't support multi-NAT modes of operation on the same interface. In other words, it's not possible to run a combination of external and internal computers on the same interface.

64 and 128-bit WEP encryption is supported and absolutely essential if you want your network to be secure. We always recommend using the highest available security level.

Our key has been blanked out. The "Closed System" check box should really be called "Hidden SSID" because it appears to contradict the "Network authentication" option above. Either way, checking this option enables the enhanced security features of 802.11b where the SSID is not advertised to any hosts. This really adds a little bit of extra protection because a malicious user would have to determine both the network name and encryption key before gaining entry. Not all wireless adapters support hidden SSID's so you may or may not experience difficulties with this option checked.

Access Control

A third level of security may be defined within the "Access Control" section of the web based wireless configuration pages. Connected clients may be added to the list of "Clients to be allowed" (it's possible to manually type in MAC addresses also). When access control is enabled (check box in the the top left corner), only those computers which MAC addresses listed may access the wireless network.

Range & Performance

The small CF card and lack of antenna resulted in reduced wireless coverage. We found that signal strength & quality was only 'average' and speeds were down over distances of 10 or 15 metres through one/two brick walls. In comparison to other wireless routers we've reviewed, where distances of 50m and 3 or 4 brick walls did not pose a significant problem, the IX66 is slightly lacking in terms of coverage area.

Users wishing to merely cover a single (albeit fairly large) office room, or those living in a flat may find the reduced range more of a benefit than a hindrance for security reasons. Otherwise, purchasing a non-wireless IX66 router in combination with a dedicated wireless access point may be the only way to enhance the range.

Voice over IP with Session Initiation Protocol (SIP)

Voice over IP (VoIP) is all about talking to each other using the IP protocol, instead of a typical PSTN telephone network (such as the BT PSTN network). Using the IP protocol is logical because we already have a worldwide network which implements it (the Internet!). Being able to talk over an IP network has distinct advantages. Possibly the greatest benefit is cost reduction - placing a call between two computers doesn't cost anything other than a small portion of your broadband Internet connection's bandwidth, which is usually in reasonable supply.

Session Initiation Protocol (SIP) is a relatively new protocol which is really starting to develop a firm grip within the areas of Internet conferencing, telephony and instant messaging. In essence, SIP allows users to establish direct (peer to peer) connections between each other (providing each side has an SIP enabled gateway), which is an essentiality when making a telephone call over the Internet (you need to be able to connect directly). The Intertex IX66 range of ADSL routers are fully SIP enabled, one of a small number of manufactures currently supplying routers with such support.

In the context of the IX66, all inbound and outbound sessions are managed automatically. The inbuilt SIP server ensures that the necessary rules are dynamically added and removed from the firewall to allow authorised two-way communications between hosts.

SIP Compatible Software / Hardware

To take advantage of VoIP using SIP, you'll require some compatible software (often referred to as a 'soft phone'). Some of the more popular products include:-

  • Windows Messenger v4.7 or better
  • Xten VoIP Softphones (Windows, PocketPC & MAC)
  • Linphone (Linux)

During our review we used the Xten X-Lite soft phone under Windows 2000. Additionally, a number of manufactures including Cisco and Pingtel are selling hard phones with SIP support inbuilt.

IP to PSTN Gateway Service

To be able to make and receive telephone calls to/from any UK land line or mobile, we used an increasingly popular service called SIPCall. A selection of service options are available including a free account for IP to IP calls, a pre-paid account for PSTN calls to/from any UK land-line or a post-paid business account.

During our review, we used the SIPCall Standard account which includes an 0870 number for inbound PSTN to IP telephone calls. All IP to IP calls are free of charge no matter which package you choose.

The SIPCall Basic (free) account can be viewed in the same way as an email service such as Hotmail. Instead of running your own local SIP server on the IX66 (which ideally requires a static IP address and/or a domain name), all of the work is done at the remote end. All you have to do is authenticate with the remote server, and hand out your SIP address to your friends (with SIPCall, you'll get an address in the format of: The following section explains how we configured the IX66 to receive IP telephone calls directly.

Running Your Own SIP Server on the IX66

SIP uses an addressing format identical to the email system (i.e. user@domain). The domain name is used to determine where data should be routed to. Of course, if you wish to receive telephone calls to your IX66, your domain name requires an SRV DNS record which points to the IP of your internet connection. You can think of this in the same was as running your website on your broadband internet connection.

Individual users must be added on the IX66 so that it knows where to route inbound telephone calls to. Each user must authenticate with a username and password which is entered into the soft or hard phone accordingly. Once registered, the IX66 simply directs calls to the authenticated device. By default up to 5 users are licenced with a cost of £14 per additional user licence (see pricing at end of review).

The IX66 configured as a SIP server (just like a miniature PABX) with 3 users

Additionally, it's possible to allow authentication from the outside world. This is a powerful concept which means that employees can still receive telephone calls via IP even if they are on the other side of the world! Once the IX66 knows the IP address of the host used to authenticate, calls are simply routed over the Internet or Local Area Network as normal.

Example where all external users are permitted to register on the SIP server

Under the SIP Settings portion of the web based interface, entries can be added to control where users are allowed to authenticate from. In the example above, any users were allowed to authenticate from any location on the Internet (obviously they require a valid username and password). You may prefer to enter more stringent access controls.

Note: Your active firewall configuration must be configured to allow inbound SIP requests.

Quality & Latency

We were amazed and extremely excited about the quality of VoIP telephone conversations. It was clearly apparent that both VoIP software and hardware has made leaps and bounds since its conception. Certainly the advent of broadband Internet has greatly enhanced the overall experience.

Xten X-Lite Software - Active Telephone Conversation

A single telephone conversation (either IP to IP, or to/from a PSTN line) consumed 80Kbps of inbound and outbound bandwidth, which was slightly more than we expected however the sound quality was truly fantastic (equivalent to an ISDN to ISDN telephone call). Most hard and soft phones (including X-Lite) support a range of audio codecs which can cut down the amount of bandwidth consumed. It's a balancing act between quality and bandwidth.

We conducted a couple of rudimentary latency tests (talking into one microphone and listening at the other end) and concluded that over an ADSL line, there were no noticeable latency issues. Although there was a discernable time taken for voice to arrive at the other end, this time was never apparent during a normal telephone conversation. We estimate that typical latency was roughly 100 to 200ms (around 1 tenth to 1 fifth of a second).

Should I switch to VoIP?

So is it worth throwing away your analogue PSTN telephones and entirely switching over to IP? Unfortunately not quite. At present, IP telephony replaces only a subset of the conventional PSTN system however this will improve as time progresses and awareness to the potential of VoIP is realised. Perhaps the greatest barrier that faces a global IP telephone network is the protocol itself.

Internet Protocol (IP) was developed multiple decades ago long before the Internet existed. At the time (early 1980's and prior) nobody assumed the IP protocol would grow to such a global scale, and of course, nobody imagined the system could be exploited by individuals with a malicious intent. Many of us are becoming more and more aware about the dangers of attacks over the Internet such as Denial of Service (DoS) where malicious users with adequate knowledge can disrupt services with little or no cost to themselves.

This means your telephone call could potentially be interrupted because your ISP is suffering from an attack of some sort. Equally possible may be the impact of a power failure somewhere along the line between two callers. Given there is no regulatory framework governing the uptime and service quality over the Internet, a business cannot rely solely upon IP telephony at present.

Nonetheless, the key to improving IP telephony is to start using it between friends or distant relatives. Even small businesses can benefit from free IP to IP telephone calls to offices in other countries. If you have an IX66, or similar SIP enabled gateway, it's time to start making people aware that you can be contacted via IP telephony!

During the review, we didn't encounter any reliability problems. We made over 4 hours of IP to IP and IP to PSTN telephone calls, including a 45 minute telephone call to Intertex in Sweden.

We also tested downloading files while communicating over voice. The IX66 does a good job of prioritising voice traffic however, many simultaneous users and/or downloads could cause glitches or breaks in a conversation. Version 2.04 of the firmware supports Quality of Service (QoS). A  Differentiated Services Code Point (DSCP) value can be specified for voice traffic however, your ISP must be configured to recognise and prioritise this traffic before it will be of any use. Ideally the entire Internet needs to be configured to understand and prioritise voice traffic.

In summary, a non-exhaustive list of pro's and con's of Voice over the Internet is as follows:-

Benefits Disadvantages
  • IP to IP calls are free of charge. Ideal for talking to distant relatives, even on the other side of the world
  • International IP to PSTN calls are often much cheaper (depending upon your provider)
  • Multiple calls (possibly up to 5 or more on a typical 512k DSL line with a suitable codec selected) can be made over the same broadband internet connection
  • Superior quality (assuming normal operating conditions and audio codec) especially if a good telephone or microphone headset is used
  • The latest voice technology is a 'must have' for any enthusiast especially when impressing friends!
  • Potential reliability issues ranging from an ISP somewhere on the Internet to your own DSL connection at home or in the office
  • Often dependent upon a single company operating the IP/PSTN gateway
  • Calls to PSTN lines within the UK may not be cheaper than simply picking up the analogue telephone
  • Capacity limited by fixed DSL upstream speed. SDSL services are only available in a select few areas (Sept 2003)


Since our original IX66 review in March 2002, Intertex have dedicated their support and technical knowledge to ensure their range of routers are kept up to date and filled with many of the latest features expected of a modern broadband router. It's probably fair to say that Intertex produce more firmware updates with additional features and improvements than most other manufacturers. Rest assured, it's extremely likely your IX66 will support new protocols and technologies into the future.

The IX66 AirSIP delivers reliable 802.11b wireless access, albeit a slightly shorter range than most other wireless products on the market. The use of a Compact Flash (CF) wireless adapter card ensures the size of the AirSIP is no larger than its counterparts.

Intertex IX66 AirSIP sitting on top of IX66 EDFLC

In summary, the AirSIP is a worthy addition to the IX66 range and should be considered regardless of whether wireless requirements are present (wireless card can be purchased separately). All IX66 routers support SIP which means you can start making and receiving telephone calls straight away. Voice over IP proved to be a thoroughly exciting and impressive experience which we strongly recommend.

Prices: £174 - Intertex IX66 AirSIP
£227 - Intertex IX66 AirSIP including Wireless CF card
£14 per additional SIP user license beyond the standard 5 user limit
Prices listed above are excluding postage and VAT.
Links: Intertex Website
Where to Buy:
List of Intertex Retailers
Specs: Online Manual

Jeremy Ainsworth

The contents of this review should not be relied upon in making a purchasing decision - You should always discuss your requirements with your service provider and hardware supplier.