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Thread: Somewhat OT: Serial over LAN

  1. #1

    Lightbulb Somewhat OT: Serial over LAN

    I wasn't quite sure where to post this so here it is:

    Anyone have experience with RS232 to LAN adapters? Specifically how they work?

    I have a computer which has a serial console output. Normally I can connect to it via a serial cable. I'd like to untether myself from it if I can.

    If I understand it correctly the RS232 to LAN adapter is device/OS independent. I connect my computer to the adapter. The adapter takes all I/O from the serial port and passes it over the LAN. So how does it do this? And more importantly what interface would I use to connect to it? I.E. is there a telnet server and/or HTTP server on the adapter which I can connect to?

    I don't need the gory details but the basic "here is how we get from point A to point B" would be appreciated to see if it would work for me. Also anyone using anything like this with their vintage gear? Any recommendation on HW or will the Chinese brands on eBay do? It would be nice to be able to use my Win7 laptop and connect to a system using telnet or SSH. Thanks.
    Current Wish List: 1. IBM 7531 Industrial Series PC 2. NEC MultiSync XL (JC-2001) Monitor 3. MicroSolutions MatchPoint AND/OR UniDOS card 4. Compaq 14" VGA CRT Monitor (the one that came with the SystemPro). 5. Stacker HW CoProcessor Board MCA BUS. If you have any of the above for sale please PM me. Thank you!

  2. #2
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    I have a couple of devices I use. One is a Digi PortServer 16, the other is an Equinox/Avocent ESP-4. They both have remote serial port drivers you can install on Windows systems to make them work as though the remote network attached serial ports are local as far as any applications are concerned. They may also have serial port drivers for other OS flavors. They also have telnet servers built in so you can just telnet from any system that has a telnet client to access the network attached serial ports.

    I have never bother installing the serial port drivers. I just use a telnet client to connect to them. Usually I use Kermit 95 as the telnet client. Works great for connecting to a PDP-11 or VAX console down in the basement when I'm upstairs.

    The units I have are wired 10Mb or 10Mb/100Mb, no WiFi. There are other units that are both wired and/or WiFi. I don't have Ethernet wired down in my basement so I just have the terminal server plugged into a WiFi access point down there.

    At the time I bought the Equinox/Avocent ESP-4 units on eBay I got several of them in one lot for something like $6-$7 each in brand new condition. That was a decent deal. There are lots of different brands and models of these. If you are patient you can usually find some for pretty low cost on eBay.
    Last edited by gslick; December 16th, 2014 at 03:56 PM.

  3. #3

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    Quote Originally Posted by gslick View Post
    Equinox/Avocent ESP-4
    Is this a four port unit? If so can you connect four devices to it and access each one separately or do you have to access one device at a time?

    Quote Originally Posted by gslick View Post
    They also have telnet servers built in so you can just telnet from any system that has a telnet client to access the network attached serial ports.
    Thanks for the info. This is exactly what I wanted to hear.

    Quote Originally Posted by gslick View Post
    The units I have are wired 10Mb or 10Mb/100Mb, no WiFi. There are other units that are both wired and/or WiFi. I don't have Ethernet wired down in my basement so I just have the terminal server plugged into a WiFi access point down there.
    That's fine. I have no problem (and actually prefer) running a wire to the unit. The only wifi use would be at my laptop to the router so I can access the system from any where in the house.

    Quote Originally Posted by gslick View Post
    At the time I bought the Equinox/Avocent ESP-4 units on eBay I got several of them in one lot for something like $6-$7 each in brand new condition. That was a decent deal. There are lots of different brands and models of these. If you are patient you can usually find some for pretty low cost on eBay.
    A decent deal that sounds like a phenomenal deal. I did a quick look around and they are selling for 10x the price right now in NIB condition. I don't suppose you have an extra NIB one taking up too much room in your storage ?

    Thanks again for the info!
    Current Wish List: 1. IBM 7531 Industrial Series PC 2. NEC MultiSync XL (JC-2001) Monitor 3. MicroSolutions MatchPoint AND/OR UniDOS card 4. Compaq 14" VGA CRT Monitor (the one that came with the SystemPro). 5. Stacker HW CoProcessor Board MCA BUS. If you have any of the above for sale please PM me. Thank you!

  4. #4
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    Usually the way these work is that you telnet to the TCP/IP address of the server at one TCP/IP port number to access the configuration management interface, and telnet to other port numbers to connect to the serial ports, where each serial port is assigned a separate TCP/IP port number. So on the 4 port unit you could have 4 simultaneous telnet client connections to the 4 serial ports.

    I'll have to check on how many of the ESP-4 I have and what I actually paid for them shipped. I probably have more than really need.

    -Glen

  5. #5

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    Quote Originally Posted by gslick View Post
    So on the 4 port unit you could have 4 simultaneous telnet client connections to the 4 serial ports.
    Okay, that is what I wanted to hear. Thanks!

    Quote Originally Posted by gslick View Post
    I'll have to check on how many of the ESP-4 I have and what I actually paid for them shipped. I probably have more than really need.
    I'd appreciate it. Thanks.
    Current Wish List: 1. IBM 7531 Industrial Series PC 2. NEC MultiSync XL (JC-2001) Monitor 3. MicroSolutions MatchPoint AND/OR UniDOS card 4. Compaq 14" VGA CRT Monitor (the one that came with the SystemPro). 5. Stacker HW CoProcessor Board MCA BUS. If you have any of the above for sale please PM me. Thank you!

  6. #6
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    For reference, the manual for the Equinox / Avocent ESP-4 and the most recent driver versions are available here:
    http://pcs.mktg.avocent.com/@@conten...590524501a.pdf
    http://www.avocent.com/Legacy_Firmwa..._Products.aspx

    One limitation of the ESP-4 compared to more traditional terminal servers is that it only provides a telnet server, not a telnet client. This is sometimes referred to as reverse-telnet. You can telnet from remote hosts to the ESP-4 to connect to the configuration interface and to each of the 4 serial ports, but you cannot initiate an outgoing telnet connection to a remote host from any of the ports locally. You would typically only want to do that if you had a dumb terminal connected to one of the ports and you wanted to initiate a telnet connection to a remote host from that dumb terminal.

    I just went through all of the ESP-4 units I purchased in the single lot and checked them for basic functionality and updated them all to the lasted firmware version I could find. That was tedious but I've been meaning to do it for a while anyway.

    There is hardware button you can press to re-initialize the unit to factory defaults. If you do that then you can connect to port 1 at 19200 baud and set the admin password and network parameters to suit your local network. After than you can connect to the unit via the built-in web server interface, or by the telnet admin interface.

    Here is someone selling these for $49 each including shipping, and open to offers:
    http://www.ebay.com/itm/141052842867

    As a one time vintage-computer special I suppose I could sell you one of the units I have for $10, plus actual shipping and paid via a fee-less payment. That would include the ESP-4 unit and power supply, but no original box since the units I have came in a two unit package. Contact me through a private message to work out transaction details if you're interested.

    -Glen

    Code:
    ESP-4 Administration
    
    There is NO administration password configured.
    The password must be configured before any functions can be performed.
    
         The administration password must contain between 5 and 32 characters.
         You will be asked to enter the new password twice.
    
    enter new password:
    re-enter new password:
    
         The administration password has been updated.
    Press any key to continue ...
    
    ESP-4 Administration - Top Menu
    
        0 -> Server configuration
        1 -> Serial port attributes
        2 -> Serial port connection methods
        3 -> Port interface
        4 -> Send break
        5 -> Status
        6 -> Debug
        7 -> Change password
       99 -> Exit
    
    enter command: 0
    
    ESP-4 Administration - Server Configuration Menu
    
        0 -> Return to Top Menu
        1 -> Network configuration
        2 -> Flash status and update
        3 -> Configurable features
        4 -> Configuration File Download
        5 -> Hardware information
        6 -> Reboot
        7 -> Re-initialize (factory defaults)
       99 -> Exit
    
    enter command: 2
    
    Current flash configuration:
         bootloader : version:     0.82 size: 8e13
    
         kernel 1   : version:     0.82 size: ef08a status: Primary
         kernel 2   : version:     0.82 size: ef08a status: Backup
         app 1      : version:     3.13 size: 66000 status: Primary
         app 2      : version:     3.13 size: 66000 status: Backup
    
    Update flash application image ? (y or n) [n]
    Update flash bootstrap image ? (y or n) [n]
    
    ESP-4 Administration - Server Configuration Menu
    
        0 -> Return to Top Menu
        1 -> Network configuration
        2 -> Flash status and update
        3 -> Configurable features
        4 -> Configuration File Download
        5 -> Hardware information
        6 -> Reboot
        7 -> Re-initialize (factory defaults)
       99 -> Exit
    
    enter command: 5
    
    Hardware Information
         Model number      : 5 (ESP-4 Mc)
         Hardware revision : 2
         Number of ports   : 4
         Prom revision     : 1
         SDRAM (MBs)       : 32
         Flash (MBs)       : 4
         EEPROM cfg (KBs)  : 4
         MAC address       : 00.80.7d.bc.23.2d
         Serial number     : WJ11555
         Part number       :
    
    Press any key to continue ...
    
    ESP-4 Administration - Server Configuration Menu
    
        0 -> Return to Top Menu
        1 -> Network configuration
        2 -> Flash status and update
        3 -> Configurable features
        4 -> Configuration File Download
        5 -> Hardware information
        6 -> Reboot
        7 -> Re-initialize (factory defaults)
       99 -> Exit
    
    enter command: 1
    
    Current network parameters:
         IP Address  : 10.0.0.150
         Subnet Mask : 255.255.255.0
         Gateway     : 0.0.0.0
         IP Addr Base: 10.0.0.150
         Interface   : auto-negotiate
    
    Modify network parameters ? (y or n) [n] y
    Specify new network parameters.
    (<Enter> to leave a parameter unchanged)
         IP Address  [10.0.0.150] : 192.168.1.70
         Subnet Mask [255.255.255.0] :
         Gateway     [0.0.0.0] : 192.168.1.1
         IP Addr Base[10.0.0.150] : 192.168.1.70
    
    ESP-4 Administration - Network Interface Selection Menu
    
        0 -> auto-negotiate
        1 -> 10 Mb/sec (half or full duplex)
        2 -> 10 Mb/sec, half duplex
        3 -> 10 Mb/sec, full duplex
        4 -> 100 Mb/sec (half or full duplex)
        5 -> 100 Mb/sec, half duplex
        6 -> 100 Mb/sec, full duplex
    
    enter command: [auto-negotiate]
    
    New network parameters:
         IP Address  : 192.168.1.70
         Subnet Mask : 255.255.255.0
         Gateway     : 192.168.1.1
         IP Addr Base: 192.168.1.70
         Interface   : auto-negotiate
    
    Commit these changes ? (y or n) [n] y
    The new network parameters will take effect on the next reboot.
    Press any key to continue ...
    
    ESP-4 Administration - Server Configuration Menu
    
        0 -> Return to Top Menu
        1 -> Network configuration
        2 -> Flash status and update
        3 -> Configurable features
        4 -> Configuration File Download
        5 -> Hardware information
        6 -> Reboot
        7 -> Re-initialize (factory defaults)
       99 -> Exit
    
    enter command: 6
    
    Rebooting, this session will be terminated...
    ESP4-Web.jpg

  7. #7

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    Well, in such a price range as these pieces of iron are now, it will be easier and more reliable to use software like https://www.serial-over-ethernet.com. Remote access to com ports will be simple and independent of hardware boxes.
    I understand that the post is old, but maybe this method is useful to someone.

  8. #8
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    Yeah, if you have almost $300 to drop...

  9. #9
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    You can probably rig something up for not a lot of money with an ESP8266 wifi module. I've done telnet with one.

  10. #10

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    What about the Wifi232 or similar devices?

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