Three ADSL modems. Outside, inside, and their internal OS

    It so happened that at one time I had three ADSL modems from different companies at once. Under the cut, photos of all three devices, both outside and inside, as well as a little about the internal operating systems of modems and their firmware. The article does not have any conclusions and screenshots of the modems' Web interfaces.

    Patient # 1: ZTE 831 A II

    This modem should be familiar to many, I suppose. They connected almost all users of MGTS and Stream; even once, when connected, they “presented” this modem for free. I am not an exception, and I got this modem in this way. The modem looks simple enough, everything is “standard” - a hole for RJ-11 (telephone wire), a hole for Ethernet, lights on the front panel: There is also a USB output, which means that the modem can be connected to a computer via Ethernet or USB .

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    By the way, not many people know that you can connect two computers at once to this modem. One computer via USB, the second via Ethernet. To do this, you just need to register in the TCP / IP settings on the computer connected via USB, the IP address 192.168.100.2, for example. But I was a little distracted. Let's take a look at the modem circuit board:

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    modem is built on a chip from Broadcom BCM6338 with a frequency of 240 Mhz and MIPS architecture. It has 8 Mb of RAM, represented by the Hynix chip, and 16 megabytes (2 Mb) of flash memory. Using a BCM processor in the modem gives hope that the modem’s internal operating system will be nothing more than a stripped-down copy of Linux. Something like the one used in the famous ASUS WL-500GP router. Indeed, by telneting to 192.168.1.1 we see this picture:

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    Familiar teams, right? But something is missing, for example, you cannot view the list of files with the ls command. Here a little ingenuity (or Google) comes to the rescue - we enter the sh command, and voila. We get into the BusyBox. The set of commands is also limited, but now you can take a look at cpuinfo, for example:

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    Naturally, you can change the settings, see how much memory is used, reboot the device. Everything is done conveniently for a person who is slightly familiar with Linux. The structure of directories and configuration files is approximately similar to the WL-500GP router from ASUS, as well as other network hardware based on Broadcom chips.

    It can be added that the modem in terms of hardware completely coincides with the TP-LINK 8811 modem, so it can be safely reflashed with TP-LINK firmware. As bonuses, we get DynamicDNS and, possibly, support for some additional protocols (firmware for TP-LINK comes out much more often than firmware from ZTE).

    Patient No. 2: ZyXEL P-660RT EE

    The dimensions of the modem are about the same as that of ZTE. It also looks similar - in front of the LEDs, behind the hole. The only visual difference is that the modem does not have the ability to connect to a computer via USB, only Ethernet, and accordingly there is no possibility to connect two computers to the modem simultaneously without using a switch. Appearance: It is

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    not difficult to configure the modem using the wizard, and it has all the same functions as the ZTE, except that DynamicDNS is out of the box. However, the filling differs significantly:

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    See the huge picture

    When I wrote these lines, I discovered that this modem has an older twin brother P-660RU EE, which is carefully and thoroughly written in the article http://www.thg.ru/network/ zyxel_p-660ru_ee / print.html. They differ only in the presence of a USB output. Therefore, I will continue to narrate in a somewhat compressed format so as not to repeat what has already been written.

    The modem is built on a TRENDCHIP TC3162L-LQ128 processor, information about which is scarce. Presumably, this is a 32bit MIPS RISC processor with a frequency of 200 Mhz. The second chip is less engaged in ADSL and USB, which, if you look closely, is simply not soldered to the board. Here we see the standard for this class of 8 Mb memory modems represented by the Winboard chip. Flash memory is located on the reverse side of the printed circuit board apparently due to lack of free space and is still the same 16 megabits (2 Mb).

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    The modem’s operating system is called ZyNOS and it is an explosive mixture of Zyxel’s own experience and Cisco IOS, as it seems to me. First, the user enters the text menu, but from item 24.8 can exit to CLI command line mode. The initial menu is available to the user:

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    Here, also using the menu, you can change the settings, display various information and control the device. From the point of view of a non-Linux user, this approach is more convenient. But take a look at the command mode:

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    Zyxel uses a similar operating system in its other SOHO devices, for example, P-330W EE routers. But here, without a preliminary reading of the documentation, everything is not so intuitive. And it seems not Cisco IOS and it seems not Linux-based. On the other hand, the OS is interesting in just this - the difference from other OSs.

    A few words about the firmware: in general, the modem is flashed standardly via the web interface. But there is still a separate version from the firmware versions of the bootloaders, which are only flashed through the tftp command. On the Russian support site, apparently so as not to torment ordinary users, only firmware is available, while in English both firmware and loader are available. For example, I downloaded the latest firmware for the P-660R-T1 from the English version of the site, took only the loader (file with the .rom extension) from there, then logged in with telnet in one window, switched to CLI mode (menu item 24.8) and gave “sys stdio 0” command to prevent the console from exiting by timeout. Then in another window we write the command: “c: \ tftp -i [PrestigeIP] put [localfile.rom] rom-0”. Then you can flash the latest firmware from the Russian site via the web interface ...

    Patient # 3: TRENDnet TEW-435BRM

    This modem differs from the previous ones by the presence of a Wi-Fi module and also has five Ethernet ports. Naturally, the size of the device also grew in length:

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    The settings for Wi-Fi were added to the web interface ... Since the modem does not have control via Telnet. Let's just take a look at the circuitry technique and this is the end of this article:

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    modem based on the Infineon PSB7200 chip is built, this is the former TI TNEDT7200A. The core clock frequency is 212MHz. It has 16 Mb RAM on an EtronTech chip and 4 Mb flash memory.

    UPD: Hmm, as it turned out, it's called Level One WBR-3460A aka NetGear DG834G v3.
    It also turned out that it runs Linux kernel with OpenBox.
    Thank you all for your attention.

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