by Ilya Naumov
05/24/2006 | 04:56 PM
The past few years have marked the advent of all manner of wireless technologies, the landmarks being the beginning of commercial use of 3G mobile networks in some countries, the ratification of the WiMAX (IEEE 802.16e) standard at the end of 2005, high popularity of Bluetooth-supporting devices, RFID solutions, etc. Yet the most important event of all is the explosion-like development of Wi-Fi networks. Viewed as a rather expensive and exotic corporate solution just a few years ago, Wi-Fi technology has matured (under Intel’s aegis) so that almost each notebook is now equipped with a wireless interface and there are public Wi-Fi access points everywhere – in caf?s, restaurants, airports, even at car service centers. Wi-Fi has been getting as it has been getting more popular.
Today, any person or small business can afford deploying a wireless network and this review is about the TEW-611BRP router from TRENDnet which will help you build your own office or home Wi-Fi infrastructure for modest money.
The TEW-611BRP is an integrated solution that combines a 4-port Ethernet switch, IP router and Wi-Fi access point with support of hot technologies Super G and MIMO for higher wireless bandwidth and a wider signal range.
Before describing the functionality of the TEW-611BRP, I would first like to dwell upon the mentioned technologies for a while. What is their point and do they offer any advantages compared with the existing official standards?
Today, there are two popular high-speed protocols in the Wi-Fi family (or, officially speaking, IEEE 802.11): 802.11g and 802.11a. They provide a maximum bandwidth of 54Mbps at 2.4GHz and 5GHz frequencies, respectively. However, the effective data-transfer speed is only about 25Mbps due to hardware overhead and is also reduced proportionally to the number of network adapters which are simultaneously using the same access point. This speed is still quite sufficient for a majority of applications, including delivery of video.
But there’s no stopping to progress, especially when the laws of marketing dictate their magic of numbers – it’s no secret that an electronic device is selling better when there’s a more impressive number on its box. So even before the official 802.11g specs were approved, all the leading developers of Wi-Fi chipsets (Airgo, Agere, Atheros, Broadcom, Conexant, Texas Instruments) had started to work on their proprietary extensions to the standard intended to increase the data-transfer rate. Each company acted independently, but the solutions eventually turned to have quite a lot in common. They will be covered in the next section.
One method that almost all the developers have utilized is to reduce the overhead described by the standard protocols. For example, the standard provides an obligatory pause (Distributed Inter-Frame Space – DIFS) after transmission of each Wi-Fi frame: the transmitting station is listening to the air and begins to transmit the next frame only if other stations haven’t contended for the channel within this period of time. So, the inter-frame space is necessary to separate the data-transfer medium.
It’s clear that you can achieve a considerable performance growth if you’re transmitting several frames in a row without DIFS pauses, even though the medium has to be monopolized for the whole period of transmission. Referred to as frame bursting, this technique has got widely popular in proprietary technologies intended to increase the performance of wireless networks. In fact, frame bursting is part of the recently ratified standard extension IEEE 801.11e (Quality of Service, QoS), but it’s hard to tell what degree of compatibility there is between the existing solutions and this extension.
Besides frame bursting, a considerable performance boost (about 30%) can be achieved by merging two (Atheros) or more (Texas Instruments) frames due to a reduction of the frame transmission overhead (this method is referred to as “fast frames”, “frame concatenation”, etc.)
Some exclusive solutions also use compression of Wi-Fi frames with the Ziv-Lempel algorithm, but this compression isn’t generally very effective when applied to small-size frames.
Yet another method to get more performance is implemented by Atheros. Its point is in combining two physical radio channels into one logical high-speed channel between the receiver and transmitter (his can be viewed as analogous to Cisco Fast EtherChannel or Link Aggregation Control Protocol (IEEE802.3ad) for Ethernet networks and to the multilink PPP protocol). This Super G Turbo technology helps double the bandwidth of the channel to achieve a theoretical data throughput rate of 108Mbps. There is one hitch, however, Atheros is much criticized for. I won’t delve into details, but equipment on the Atheros chipset goes beyond the standard use of the 802.11g frequency spectrum when in Super G Turbo mode and may interfere with operation of other networks. Realizing this, Atheros provided two Super G Turbo sub-modes: dynamic and static. In dynamic mode, the utilization of the entire 802.11g range is constantly being analyzed and the bandwidth is doubled only when there are free channels available. The dynamic mode is backwards compatible with any 802.11b/g equipment which does not support Super G Turbo. The static mode is asocial in the meaning that it can interfere with neighboring networks and is only compatible with itself. Instead, it provides the maximum data-transfer speed.
There are other approaches to doubling the radio interface bandwidth. For example, Airgo solved this problem in an elegant way by improving the spectrum efficiency instead of doubling the frequency band as Atheros did.
The MIMO abbreviation stands for Multiple Input Multiple Output. What does it mean? The MIMO concept implies that Wi-Fi devices may have several independent antennas for transmitting and receiving. The outgoing stream of data is distributed among the transmitting antennas and is put on the air at the same frequency, on the standard 20MHz radio channel. The MIMO method is based on the fact that the radio signal doesn’t spread out uniformly indoors but is reflected a number of times from walls, ceilings and various objects. Using a special modulation and sophisticated algorithms of processing the sent and received signals, it is possible to establish multiple data streams at the same frequency (the so-called spatial multiplexing) with reliable reconstruction of the original stream out of the mess of signals and reflections. Thus, the Wi-Fi channel bandwidth grows up in a linear manner depending on the number of send/receive pairs on the channel’s ends. Besides that, the physical principles of MIMO help improve coverage and reliability of Wi-Fi networks indoors because signal reflections do not hinder, but even facilitate the operation of the wireless connection.
MIMO looks a very promising technology and is expected to bring great improvements into performance, reliability, spectrum efficiency and coverage of future Wi-Fi networks. Not surprisingly it is one of the key features of the new 802.11n standard currently under development. Although there’s still a long way to ratification (there’s only a draft version of 802.11n available), Wi-Fi solutions developers are actively promoting MIMO products, different and usually incompatible with each other. Moreover, some manufacturers put a different meaning into the word MIMO that has nothing to do with the technology described above. For example, Atheros uses the send/receive couples not to do spatial multiplexing (i.e. to expand the channel bandwidth), but to increase the distance the signal can travel by focusing the transmitter energy in the direction of the receivers using the so-called Intelligent Antenna technology.
You should be aware that the abbreviation MIMO in a device description may mean anything (at least until an official ratification of the 802.11n standard). You can only be sure that the device has more than one transceiver. When purchasing a MIMO-supporting product, you may want to ask the seller what the manufacturer means in this particular case.
Summarizing this section I would like to stress the fact that most of technologies for improving Wi-Fi performance are proprietary and are not officially specified. For you to enjoy the advantages of such a technology, it must be supported by both the access point and the Wi-Fi adapter (this is usually only possible when the access point and adapter are based on chipsets from the same manufacturer).
It’s time to take a closer look at the hero of this review, the TEW-611BRP router.
The wireless section of this device is based on the AR5005VL (VLocity) chipset from Atheros which supports the exclusive Super G Turbo technology for higher bandwidth. These are the key points of this technology:
So, the doubling of the bandwidth (in comparison with 802.11g) is achieved mainly by joining channels rather than by means of MIMO technology which is implemented here to improve the coverage in the first place. The maximum theoretical speed of wireless data transmission is 108Mbps; the real bandwidth, considering the overhead, is 50-70Mbps.
This link leads to the product specs page on the manufacturer’s website.
Besides the TEW-611BRP, the box contains a switching power supply, a patch cord, a quick installation manual, and a CD with a detailed user manual in PDF format. The manual is of little practical value, though, because all its texts are duplicated in the router’s web interface.
The case of the TEW-611BRP isn’t elegant like cases of some products from Belkin or Linksys, for example. It is a plain square box with two external antennas. The device can be wall-mounted. The LEDs on the device’s front panel indicate activity of the interfaces. On the back panel there are five RJ-45 ports (one for WAN interface and four for LAN), a power connector and a Reset button (to reboot the router in case of failure or to roll back to the factory settings). There’s also a wireless interface switch on the back panel, but it doesn’t physically turns the interface off. The switch just tells the router’s firmware if the WLAN interface is to be initialized at boot-up or not. Changing the position of the switch always provokes a reboot of the router which lasts for about 10 seconds and terminates all the established connections (including wired ones).
The router is set up via a web interface; no alternatives (e.g. via ssh, telnet or SNMP protocols) are provided. This fact makes the TEW-611BRP less suitable for large complex networks in which it might be necessary to run automatic scenarios depending on the device status (for example, its reboot in case of certain problems). On the other hand, this doesn’t matter much for home and small office networks this router is mainly targeted at.
By default the web interface is only available from the local network (that is, it responds to connections to the router’s LAN interfaces), but can also be invoked on the external WAN interface, too.
Appropriately for a SOHO device, the web interface of the TEW-611BRP is simple, easy-to-use, and logical so that even users with just the basic knowledge of network technologies could set up the router. The most important parameters like the security mode of the WLAN interface and the method of assigning an IP address to the WAN interface can be chosen in the menu system or with the help of two step-by-step wizards. After you’ve passed through each step of these wizards and rebooted the router, the device is in fact ready to work. At least the default values of other parameters allow that. Thus, it is only going to take you 5-10 minutes to get the router up and running.
The setup procedure isn’t without drawbacks, though. It takes some 5-6 seconds to save the changes. You also need to reboot the device (and this takes some time, too) to apply most of the settings. This would be understandable with respect to the parameters of the radio interface, but packet filtering settings, for example, might be applied “on the fly”. On the other hand, such devices are usually set up once and for all, so you will hardly have to change the router’s parameters too often.
The router’s menu consists of four basic elements: Basic, Advanced, Tools, and Status. There are submenus under each element.
Let’s browse through the web interface together to get an idea of the device’s capabilities.
The Basic Settings menu includes four submenus (besides the above-mentioned initial setup wizards) with settings of the WAN, LAN and WLAN interfaces and of the DHCP server.
Setting up the WAN int erface is about choosing the method of connecting to the Internet. That is, you must specify the way a connection to the provider is to be established, the way the IP address is assigned, the IP addresses of DNS servers and the default gateway.
The following protocols of configuring and maintaining a connection are supported: Dynamic Host Configuration Protocol (DHCP), Point to Point Protocol over Ethernet (PPPoE), Point to Point Tunneling Protocol (PPTP), Layer 2 Tunneling Protocol (L2TP). The connection parameters may be static.
The option of assigning a MAC address to the router’s WAN interface (also by “cloning” the MAC address of one of the network adapters connected to the router’s ports) may be helpful when you’re connecting to a network in which IP-addresses provided via DHCP are linked to the computers’ MAC addresses. Suppose your computer has been connected to this network with a certain static IP-address. To assign the same address to the newly bought router, you only have to assign the MAC address of the old computer to the router’s WAN interface and no one’s going to see the change.
The LAN submenu is where you specify the router’s IP-address on the local network and, if necessary, enable the RIP routing protocol and the DNS requests translation mode (DNS Relay). In this mode the router forwards DNS requests from the local hosts to the provider’s DNS server and saves the responses in cache memory. When a local host puts a DNS request whose result has already been stored in the router’s cache, the router immediately produces the response without accessing the provider’s DNS server which would require some time. Thus, the processing of DNS requests is a little accelerated. However, I noticed one annoying thing when I tested this feature: even if DNS Relay mode is enabled, the router persists in assigning (by DHCP) the clients the IP-address of the provider’s DNS server rather than of the router’s own (at least I couldn’t make the router behave otherwise). So, in order to use the retranslation of DNS requests, you have to manually write a static DNS address, the same as the router’s IP-address, in all the clients. This is not convenient and I hope this problem will be solved in firmware updates.
The WLAN interface settings include such options as the device’s ID in the wireless network (SSID), radio channel it works on, data-transfer speed, compatibility mode (it dictates the protocol network adapters can connect to the WLAN interface by: either 802.11g or 802.11b, or both). You should be aware that support of both the protocols simultaneously leads to a certain reduction of data-transfer speed as by the 802.11g protocol.
An important parameter is the Super G mode in which the exclusive extensions to the standard 802.11g protocol are enabled. If the Super G extensions are disabled, the wireless interface of the TEW-611BRP behaves like a regular 802.11g access point. In the Super G without Turbo mode frame bursting, aggregation and compression are enabled; joining of radio channels is additionally done in the Super G with Dynamic Turbo and Super G with Static Turbo modes. The difference between the dynamic and static Turbo modes has been explained in the Faster and Higher section. I’d like to note once again that all Super G extensions except for Super G with Static Turbo are backwards compatible with the 802.11g standard. You should be aware of this when you’re configuring the wireless interface.
Also on the WLAN Interface setup page, you choose the user authentication and data encryption protocol. The TEW-611BRP supports all the standard protocols, beginning from the rather insecure WEP (Wired Equivalent Protocol) and the more advanced WPA (Wi-Fi Protected Access) with the TKIP data encryption (Temporal Key Integrity Protocol) to the new and most perfect for today WPA2 (802.11i) protocol which uses the stronger AES algorithm (Advanced Encryption Standard). User authentication on the router’s side (the so-called personal mode in which all clients connected to the access point use the same password) as well as on an external RADIUS server (enterprise mode) is supported for WPA and WPA2 protocols.
The DHCP server settings are very simple and only allow specifying the range of addresses assigned to the clients and to bind statically certain IP-addresses to the MAC addresses of the network adapters.
Settings in this menu mostly refer to the operation mode of the firewall the router is equipped with. I can’t say the settings are very advanced, but you can solve some typical tasks an administrator of a small network has to.
One such typical task is opening access from the Internet to a web, SMTP, FTP or any other server that resides on the local network. This is accomplished in the Virtual Server submenu where you can open a certain port in the router’s external interface and all the packets coming in from the Internet to this port will be forwarded to the administrator-specified port of a certain computer on the local network (this mechanism is referred to as Port Address Translation – PAT).
In a likewise manner, support for network games is configured in the Gaming menu. The difference is that not one port but a range of ports can be opened to the outside for each game, and all the packets coming in to these ports of the external interface will be directed to the same ports of a certain computer on the network. The router developer has provided presets for quite a large list of popular network games, so in many cases the administrator just has to choose the necessary game from the list and specify the IP-address of the computer the game will be run on.
The Firewall submenu allows setting up a so-called demilitarized zone (DMZ), i.e. specify one host in the local network to which all the packets received at the external interfaces will be directed to. This host will be isolated from the other hosts of the LAN, so a malicious hacker won’t be able to access LAN resources even if he has managed to compromise a service in the demilitarized zone.
Also in this submenu, you can turn on dynamic packet filtering also referred to as Stateful Packet Inspection – SPI. The point of SPI is this, in a nutshell: the router analyzes packets it receives at its external interface and if a packet is a response to a request previously initiated from the LAN, the packet is passed through the firewall. Otherwise, the packet is discarded. This helps make the LAN more secure and protect it against IP spoofing, SYN attacks, etc.
For additional protection against intrusion from the Internet, the TEW-611BRP router offers a simple (which is another way of saying primitive) packet filter which is set up in the Inbound Filter submenu. It allows opening (or closing) the external interface of the router for certain IP addresses or address ranges. As far as I understand, the rules apply to all the ports open on the WAN interface at once. In other words, the administrator cannot close a certain port (for example, SMTP) for a certain host or an IP network which is of course inconvenient. Besides, the filter only supports a maximum of 8 rules.
Besides protection against attacks from the outside, the TEW-611BRP also offers you options to limit the local computers’ access to Internet resources; these options can be found in Access Control, Web Filter, and MAC Address Filter submenus.
From the Access Control menu the administrator can prohibit some or all of the local hosts to access certain IP-addresses and/or ports in the Internet (address and port ranges are supported; independent filtering for TCP and UDP is supported, too). In other words, this network filter sticks to an “allow everything which is not prohibited” policy. The usual way is to prohibit everything which is not explicitly allowed, but this is just a matter of habit. This doesn’t affect the functionality of this packet filter.
The Web Filter submenu allows creating a list of websites the users of the local network are allowed to access. This is a rather odd feature and, to my mind, quite a useless one. If you’re limiting users’ access to certain sites, it’s easier and more logical to set up a list of prohibited resources. On the other hand, if the administrator has to do this at all, he’d better solve this problem by using a dedicated transparent proxy rather than on the router level.
The MAC Address Filter submenu is very simple and allows the administrator to specify a list of MAC addresses which are permitted or denied connection to the router’s ports.
In the Traffic Shaping submenu you can divide (prioritize) the external interface bandwidth on the level of the local hosts and/or the protocols they use. The prioritization rules can be applied to all external connections as well as to certain external IP-addresses and ports, or ranges thereof.
In the Routing submenu you can view the routing table and enter static entries into it (this is a kind of web interface for the route utility available in most operating systems).
Many rules you create in the Advanced Settings menu can be scheduled to be in effect only some period of time or on an occurrence of a certain event. This is specified in the Schedules submenu; a maximum of 20 events can be created.
The remaining items of this menu are self-explanatory and do not require my comments.
The Tools menu contains mostly system options that affect the operation of the device itself. Here you can set up the administrator password, system time (and configure its synchronization by an external NTP server), delivery of router’s logs to a syslog server or a certain e-mail address. This menu also contains an option of forced reboot of the router and of rolling its settings back to the factory ones.
For some unclear reason, this system-related menu also contains an option of setting up the dynamic DNS service although it would be more appropriate among the Advanced settings, I guess. Anyway, this setting needs some comment. Suppose you have a domain and you’d want to put a web-server, physically located in your local network, on that domain. The problem is that providers (particularly, ADSL providers) usually issue a new IP-address to your client on each new connection. So, each time your address changes, you have to update the entries about your domain on the DNS servers that support it. In order to make this process automatic, there are special services (like DynDNS.org, regfish.com, tzo.com and others) that host domains for clients with a dynamically assigned, i.e. variable, IP-address. You only have to inform this service about your new IP-address, and the domain-related entries will be automatically changed. The TEW-611BRP supports as many as 9 most popular resources that provide this service. Each time the router’s external interface is assigned a new IP-address, the router connects to the appropriate service and tells it the new parameters. So, this is a rather exotic feature, but you will find it useful if you’re using one of such hosting services.
The Tools menu also contains a Firmware submenu in which you can update the router’s firmware. The latest version is 1.0.4 dated December 2005.
The Status menu is intended for viewing the router’s current operation parameters, particularly, WAN, LAN and WLAN interface settings, traffic statistics for each of the interfaces, routing table, detailed logs (the level of detail is specified here, too), and statistics for active IP connections (a cut-down analog of the Unix-based netstat utility).
Now that we know what this router can do, let’s check it under real conditions and see if the efficiency of Atheros Super G technology is as high as promised.
I benchmarked the performance of the wireless interface in all four operation modes it supports: Super G with Static Turbo, Super G with Dynamic Turbo, Super G without Turbo, and full compatibility with the 802.11g standard (Super G disabled).
The wireless interface bandwidth was measured by the iperf utility with its default settings (TCP, 8KB window size). Each test was run for 2 minutes. An AVI file was used as the source of test data (that is, the LZW compression employed in Super G mode didn’t affect the results).
To test the TEW611BRP router I took a notebook with two network interfaces (wired and wireless) between which the data was being transferred via the router. The notebook’s wired interface (SiS 900, 100Mbps, full duplex) was connected to one of the router’s LAN ports. The wireless interface was provided by a D-Link DWL-G650M adapter based on the same chipset as the TEW-611BRP and thus supporting all the exclusive technologies from Atheros. I used the latest version of the adapter driver available at the time of the test.
Here are the test results:
I guess the diagram doesn’t need my comments. Super G technology really works and it works very effectively. Even using Super G without the channels combining feature results in a 40% increase in data-transfer speed over the wireless interface (in comparison with the standard 802.11g mode). When the doubling of channels is turned on, the performance is about 2.8 times the standard speed.
Yes, this impressive result was achieved under ideal conditions: there were no devices in the test network other than the router and the wireless adapter that would affect the data-transfer speed (this is why the results of the Static and Dynamic modes almost coincide). Besides, the router and the notebook’s wireless adapter were very near each other and this helped reach a maximum performance due to lack of radio interference. In a real network, the overhead associated with providing compatibility with Super G incompatible devices, with error correction and even with sharing one access point among several adapters may prove quite big. And still, this test shows that you can achieve a considerable increase in the performance of your office wireless network by using a TEW-611BRP router with Super G compatible adapters (as for a typical home WLAN – it doesn’t differ much from our test network).
I am overall pleased with the TEW-611BRP router. The device was stable for three weeks of ordinary use through the tests and never hung up. So I recommend you the TEW-611BRP for its high stability in all operation modes and its excellent performance. It will suit well for use in a home or office network.