Zoom X4 ADSL Router Review

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The Zoom X4 is a combined ADSL modem and router in one. The router has both Ethernet and USB connections, making it the ideal product to consider for those upgrading from a USB ADSL modem. The router should work with all BT Wholesale ADSL services. In addition it will also work with PPPoE or LLC based services, including Karoo ADSL in the Hull area, as well as a number of European providers in France, Spain and Portugal.

The router supports two main modes of operation. A simple NAT router, sharing a single IP address among many computers, or a PPP Half Bridge mode that will present the ISP assigned IP address to a single computer. Users with accounts that have a block of static IP addresses, may be able to use the router by disabling the NAT component, but this configuration is not documented with the router. The common platform (Conexant chipset) means that NON-NAT setup guides for other hardware should be easily translatable for use with the Zoom X4.

What you get for your money

The router comes with what is a fairly standard set of bits and pieces. These are a 15V (0.8A) power brick, manual, RJ-11 to RJ-11 lead, USB type A-B lead to connect router to a PC, two Zoom ADSL micro filters, RJ-45 Cat5 Ethernet patch cable, driver CD and finally the router itself. The router is perhaps one of the smallest ones on the market, measuring just 145mm (width) x 110mm (depth) x 30mm (height). The general standard of construction is pretty good, and certainly not as flimsy as some of the cheaper Conexant based routers.

The front of the router features four LED's to provide user feedback. The LAN LED, is illuminated whenever a PC is connected to the router, either via Ethernet or USB. The RXD LED lights up to indicate the router is receiving data. The LINK LED will light up as soon as an ADSL link has been detected and synchronised. The final PWR LED simply indicates that the router is switched on.

Given the small size of the unit, the back of the router is pretty tightly packed. The connections provided are: power socket, an on/off rocker switch, a USB Type B socket, recessed reset button, 10/100Mbps auto-MDI/MDIX RJ-45 Ethernet socket, an RJ-11 socket providing a filtered phone connection and finally an RJ-11 socket for the incoming ADSL signal. To reset the router back to its default configuration, simply press and hold the reset button with a paper clip (or similar pointed object) for a count of five, then once you release the button the router's Link LED should turn off and come back on, blinking about once a second. Under normal operation, the router is not totally silent and will make a small clicking noise when you switch it on, and when the ADSL signal is plugged in or disconnected. This is normal and appears to be from a line isolation device inside the router.

The addition of a phone socket is a little unusual, particularly as this is a fully filtered socket, i.e. you can plug a phone in without the need for a micro-filter. There are however two issues when using a phone in this way. Firstly, you cannot use a standard BT plug but need an RJ-11-to-BT adaptor. Secondly, there is no UK ring capacitor, so only phones with their own ability to generate a ringing signal can work without an appropriate adaptor.

Click image for a larger view

Standard NAT Configuration

The software CD that comes with the router provides a wizard that can be used to configure your PC's network card settings. Simply select the Modem Installation Wizard from the auto-play CD and then follow the instructions. Once this software finishes, reboot the PC and you will hopefully be able to access the router when the PC comes back to life. The use of this software is optional, it would appear that all it does is set your network card to use DHCP to obtain the IP address, gateway and DNS settings. It also creates a shortcut on your desktop to which is the default IP address of the router.

When you initially access the inbuilt web server, the router displays the screen shown above. To get to this stage you will have had to authenticate with the router, the default username and password are admin and zoomadsl respectively. We recommend you change these values as soon as you are happy the router is working properly to ensure unauthorised users do not gain access to the configuration. The basic setup page is the only page you need to enter data on to actually get the router connected and on-line. The fields you need to fill in are Username and Password (these are the ones supplied by your ISP, e.g. [email protected]), and we would recommend ensuring Automatic Reconnect is enabled. Leaving the Default Timeout value at 0, means the router will never timeout, in other words it should maintain a permanent connection. To store the settings in the router, you need to press the 'Save Changes' button, and then to ensure the settings are retained if the router loses power, press the Write Settings to Flash and Reboot button. The router takes about thirty seconds to reboot and after another thirty seconds it should have logged onto the ISP and a working Internet connection established. Opening a web browser and browsing a website should verify this. If that fails we suggest looking at the ADSL status page. The example below was taken from a connected and working ADSL line.

The ADSL status page updates dynamically, and displays Line Attenuation for the ADSL line. In the screen shot above, the line has downstream a line attenuation of 40.1dB. This figure compares well with 41dB for a BT 'woosh' test on the line used for the review. The loss of signal can be caused by unplugging the ADSL line, or excessive interference on the line, perhaps caused by a phone that is not plugged in via a micro-filter.

Using the USB Network Connection

A number of routers now support USB connections for PCs and this is a distinctive advantage as the vast majority of PCs come with USB ports, whilst not all yet come with network cards. The main rule with ADSL modems and USB connections is DO NOT PLUG THE USB LEAD IN UNTIL THE DRIVERS ARE INSTALLED. Failure to adhere to this rule can result in the PC misidentifying the new USB device, and if you try to install the drivers at a later date, they may not work. Always check the hardware installation guide, as one or two USB devices do not follow this rule.

To install the drivers, simply run the supplied CD and after selecting the ADSL Modem Installation Wizard select the USB ADSL modem option. This will pre-install the necessary drivers for your PC.

Once the drivers are installed it is safe to plug the USB lead into the PC and Microsoft Windows should detect a new piece of USB hardware and start the hardware wizard.

The hardware wizard will find the drivers automatically, since they have just been installed onto the computer. One cautionary note for XP users is that you may see the screen below. This indicates that the drivers for the Zoom USB connection are not Microsoft certified. Normally it is safe to ignore this warning, by simply pressing the 'Continue Anyway' button. Later versions of the CD will ship with XP certified drivers.

Once the USB driver setup has finished, the configuration process proceeds in a manner identical to the Ethernet procedure. The USB installation creates a USB network connection which is generally less processor intensive than modems like the Alcatel Speed Touch USB. The biggest difference is that all the complexity of handling the ADSL connection, and ATM to TCP/IP data conversion is all done by the router hardware rather than the PC's USB sub-system and CPU.

During the course of the review a new set of USB drivers and installation CD were released (part number: 289-00135). The original CD supplied with the review modem was part number 289-00101-A. If you want a copy of the new drivers, which are actually XP certified then you need to contact the Zoom UK Technical Support Team on 0870 720 0030 or e-mail them at [email protected].

The USB connection can be used at the same time as the single Ethernet port and hence, with the supplied leads, you can run two computers simultaneously. This effectively creates a small local network between the two computers, allowing file and printer sharing. Another set-up example would be to plug a wireless access point into the Ethernet socket, and the PC closest to the router could continue to use the USB connection. The USB network connection advertises that it requires 500mA to the Operating System. When connected to a non-powered USB hub, Windows complained. When connected direct to a USB port on a laptop, no complaints were raised. If the USB connection was left unplugged overnight, the router would refuse to provide an IP address via DHCP when plugged back in the following morning. A reboot of the X4 fixed this.

Advanced Setup

The straight forward setup process is helped by the fact that the number of features have been kept to a minimum. The main areas that most people may need to use are the Virtual Server (port forwarding), LAN settings and possibly the DMZ (default host).

The Virtual Server page is needed if you have an application that requires explicit ports to be mapped in the incoming direction through the NAPT component of the router. NAPT or Network Address Port Translation refers to the ability to map specific ports from the Internet side of a router, to a specific port and computer on the LAN side of the router. An example of an application that often needs a port mapping is running your own SMTP mail server. A lot of people will have no need for port forwarding but any half-decent ADSL NAT router will offer the option. The vast majority of software that is used over the Internet will not require any port mapping but if you are unsure, look on the software manufacturer's website for information about running the program behind a NAT router or firewall. Web pages such as http://www.practicallynetworked.com/sharing/specialapps.htm may also help answer your questions.

To configure a port mapping you need four pieces of information:

  • Public port
  • Private port
  • TCP or UDP type connection
  • IP address of the computer on your LAN that will be running the application.

Generally speaking, the public and private ports are identical. The screenshot shows the configuration required to enable an SMTP server running on the PC with the IP address

The X4 unfortunately does not support forwarding ranges of ports, and is restricted to just 20 port mappings, potentially becoming a problem if you have three or four computers and these are running a range of applications that need ports mapped. One possible solution exists for a single computer and that is to have all the ports mapped to it, i.e. the DMZ option. This does however forward all unsolicited incoming traffic to that single computer, exposing it to the outside world. If you decide to use the DMZ option, it is imperative that a software firewall or other measures are put in place to secure that computer. One final option, PPP Half Bridge exists which is detailed below. This mode works by allowing just one computer to use the full external Internet IP address, which is similar behaviour to USB or PCI ADSL modems.

In common with most ADSL routers, it's possible to alter the default LAN IP address and even change the IP range used. This is useful for people who have existing LANs and do not want to reconfigure too much. In our case we review a lot of routers, and using the same IP address for all ADSL routers allows us to swap devices in a matter of seconds. Additionally the X4 allows you to turn off the DHCP server if you want to, which may be useful if you wish to run your own DHCP server on another system. The Ethernet mode option allows you to control the speed of the single LAN port, between 10 and 100Mbps speeds as well as full/half duplex. The ability to control the LAN speed is useful if you are having problems with network cabling, as often a cable will work at 10Mbps reliably while causing intermittent problems at faster speeds.

PPP Half Bridge Mode

The PPP Half Bridge is sometimes called DHCP Spoofing. This mode sets the X4 to present the Internet side IP address to a single computer that obtains this IP address via DHCP. The mode is relatively easy to configure, with just a couple of changes required from the standard NAT setting, and takes just a couple of minutes to complete. The primary use of PPP Half Bridge mode is for applications that cannot be made to work with NAT. PPP Half Bridge mode is in fact the only way that the video and audio components of MSN Messenger will work on the X4, because of the lack of UPnP support.

The first setting that needs changing is to disable NAPT, which is done via the NAT configuration screen. Click 'Save Changes' once you have made the change. Remember if you want to turn off the Half Bridge mode you must select NAPT on this screen. The NAT option in the NAT field will actually only support a single computer connected to the router. Finally, you need to enable PPP Half Bridge mode in the Miscellaneous Configuration screen and again press Save Changes.

When we tried this, we found that the router had switched into a PPPoE LLC encapsulation mode (in the basic settings). This must be changed back to PPPoA VC-Mux for a BT Wholesale ADSL line, or else the router will not connect. After the changes have been saved, a reboot is required. Once the router has rebooted, you should obtain your Internet IP address assigned to the PC over DHCP.

One side effect of the PPP Half Bridge mode is that the router is no longer visible at its default IP address of To be able to access the web configuration you have to unplug the ADSL line and turn the router off and on again, so that it would re-issue a 10.0.0.x range IP address to the computer. One would think that PPP Half Bridge mode is an ideal way of connecting the X4 to a wireless router, or even a cable/DSL router that actually has support for UPnP, but alas the tricks used in the DHCP process to give the Internet IP address to a computer often do not work well with routers. The specialised Ethernet modems such as the D-Link 300G+ and ADSLNation X-modem work better for this task.


The router was given our usual batch of testing, which ranges from simple day to day use, using a network of around four computers, to specific testing to determine if Microsoft NetMeeting and MSN Messenger work.

Online gaming worked well, with Counter-Strike not exhibiting any problems during the update of the game server list. We were also able to continue using the connection for web browsing at the same time. The USB or Ethernet network connections seem to give virtually identical performance for gaming. Other applications such as online banking, PPTP VPN, connecting to a SQL database, and all the other tasks you would expect from the normal day to day user or computer enthusiast worked without any problems. Video streaming managed to play for hours on end, which says as much about the router, as it does for the advantages of broadband. In terms of raw download speeds we did not see anything to indicate that the X4 is faster or slower than any other device on the market.

Microsoft NetMeeting is where the performance testing becomes a lot more variable with different devices. To test NetMeeting, the X4 was running a basic NAT configuration, and the base requirement of forwarding TCP Port 1720 to the computer running Microsoft NetMeeting via the virtual server page was done. The other machine used in the testing was a laptop with a 56K dialup modem and web cam. We were able to initiate calls in both directions, but to get video operating on an incoming call we had to point the DMZ option at the IP address of the machine running NetMeeting. Calls originating from the X4's local network to the dialup computer worked successfully. The file send/receive components, text chat and whiteboard in NetMeeting were all checked and found to work.

The lack of Universal Plug and Play (UPnP) in the X4 meant that we were unable to test MSN Messenger beyond the basic text chat feature.

Whilst the router does allow you to enable remote access to its configuration from the Internet, we would not recommend this unless you are using a strong password, require this feature and understand the security implications of doing so. It should be noted that even if the external web configuration server is disabled the actual port used appears OPEN to the various port scanners on the Internet, though actually trying to access the web configuration from the Internet does result in a 'you are not authorized' message. The problem is that the presence of the open port may actually attract more than the average number of automated attacks. You can close this port by forwarding TCP port 80 to another IP address on the local network that does not exist, making it invisible to the Internet.


The X4 is a basic ADSL modem/router and being based around the Conexant chipset means that there are lots of other devices with similar performance levels out there, so it is competing mainly on price and the level of support from the manufacturer. The retail price of the X4 whilst not vastly expensive, is at the upper end for its capabilities at £79.99 (May 2003). The X4 is stocked by a number of retail stores so is relatively easy to source, and perhaps return if you do have problems. Hopefully the level of technical support and two year guarantee available from Zoom will help to make the price more worthwhile.

The router generally does do what it sets out to do, and doesn't make any extra-ordinary claims. If you're on the market for a small router to get one or two computers or a gaming console online, the X4 may well be for you. The bells and whistles that other hardware provides, such as stateful inspection firewalls, denial of service protection and content filtering are not present in the X4.

In terms of general reliability, the Ethernet side is pretty flawless, but using the PPP Half Bridge mode can be unstable. The router doesn't always issue the Internet IP address. A reboot of the router usually fixed that. On the down-side, the router is limited by its 20 port forwarding rules and a single Ethernet port. It would have been better to remove the phone socket and add a 2nd or 3rd Ethernet port.

For someone shopping around for their first ADSL router, the documentation should be a great help. This covers the basics steps (e.g. entering your username and password) but also, very kindly, shows how your copy of Internet Explorer or Netscape should be configured. Furthermore, the documentation covers how to set the TCP/IP settings for various Operating Systems, e.g. Windows 95, Mac OS 7.6.1 to Mac OS 9.2.2 and OS X and most uncommonly, Linux.

Prices: £68.08 Zoom X4 Model 5551 ADSL Modem/Router (£79.99 including VAT)
Prices listed above are excluding postage and VAT.
Links: http://www.zoomtel.com/ts1/adsl_5551.shtml
Where to Buy: See our DSL Hardware FAQ

Andrew Ferguson
[email protected]

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.