Half-Duplex And Msn Messenger

By zillah ยท 17 replies
Apr 9, 2005
  1. Dear All

    Half duplex, mean; we can not transmit and receive at the same time. It should either send or receive, it can not be both at the same time.

    Now with MSN messenger or Yahoo, why cann't we talk at the same time ? Is it because of half duplex technique? or something elase?


    I have got two type of connections (Dialup and ADSL)
  2. RealBlackStuff

    RealBlackStuff TS Rookie Posts: 6,503

    Half duplex is either send or receive.
    Set your (ADSL) NIC to full-duplex or auto, and your problem should be solved.
    Dialup is too slow to react that quick.
  3. zillah

    zillah TS Rookie Topic Starter Posts: 47

    I am using USB wireless NIC (Netgear) with ADSL router, and I could not find the feature for full-duplex mode. Any advice
  4. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    You are mixing up things here. Full or half duplex on the wire level has absolutely nothing to do with duplex on the application level.

    An application doesn't know or care what sort of a network you have. TCP/IP is always full duplex no matter what - you could be using dialup, cable or carrier pigeons - it is still full duplex.

    I don't quite get what do you mean by not being able to talk at the same time on MSN and Yahoo! Do you mean voice chat? In any case your problems are with either TCP/IP or the application setup. Leave the wires alone.
  5. zillah

    zillah TS Rookie Topic Starter Posts: 47

    As you know that modem is WAN device, and it is physical layer.

    1- Now if you physical layer is half-duplex, do you thing that your application layer (layer 7) or TCP/IP still can operate in full-duplex mode?

    2- If we are talking about old day when the infrastructure of you Telecomminication is half-duplex,,,can we run application with full-duplex mode ?
  6. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    Yes, even if your physical layer is half duplex you can build full duplex network layers on top of it.

    Even if you cannot send an electrical signal both ways at the same time you can put a buffer in front of your wire that will accept packets and send them when the half-duplex line becomes free. In modern networking and TCP/IP stacks that "buffer" is a complex set of software and hardware of course.

    In case of your dialup modem no piece of software above the driver level knows or cares about the half-duplexness of your connection.

    If I were to write an application that uses TCP/IP to communicate then all I have to do to exchange data is to say that "send this over that connection" or "read data from that connection". I do not know or care about whether the physical communication channel is occupied by something or not.

    And a simple example for you. If you are downloading something big with your dialup connection then does it become impossible for you to do anything else online? Do you have to cancel your download in order to check your e-mail?
  7. zillah

    zillah TS Rookie Topic Starter Posts: 47

    Does that mean; the problem of the physical half-duplex layer will affect the application layer unless we use buffer in front of the wire,
    or it won't have any affect ?

    Does it mean, if the line is not free, the packets should wait ? As you know full-duplex transmission (sending and receiving) happend simultaneously.

    Why do not we consider this transmission type of FDM or TDM.

    I'm really sorry about this.. I edited your post instead of replying..
  8. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    Yes, you need some sort of "buffering" and this is exactly what the network layers and encapsulation do.

    Yes, on the physical level the channel (wire) is half duplex. On some higher level (TCP) on the other hand the transmission channel (IP) is full duplex and the stations (programs using a TCP connection) can send data to each other independently and simultaneously.

    Yes, this is some sort of a TDM. The point is that it is completely hidden from programs.

    You cannot talk about transmision types and applications at the same time. Applications are completely oblivious of all the murky details about duplexness and multiplexing. Your web browser application and the web server software send data to each other asynchronously not thinking about how the wires work. The network layers take care of all the fragmentation and multiplexing and it works transparently. A program will never know what kind of physical medium is being used.
  9. zillah

    zillah TS Rookie Topic Starter Posts: 47

    Now, If the application layer (full-duplex) passes the information to the physical layer (via transport and network and data), and if my ethernet card is running in hal-duplex mode (not full-duplex mode).As you know this option is available with ethernet card.

    Does that affect the way of the transmitting (one way (half-duplex), or two way (full-duplex) ) data (that has been passed from full-duplex area "application layer") ??
  10. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    Yes, the ethernet controller and the driver have to take the half-duplexness into account and the signalling on the netwok cable is done differently than would be in the case of full duplex ethernet. This is completely transparent and will have absolutely no effect on the ethernet frames themselves or the data that is inside.
  11. zillah

    zillah TS Rookie Topic Starter Posts: 47

    My understanding to what you said, they have not effect on the data; that mean it won't modify or alter our data,,,,Am I right?

    If so, yes this is what I agree with you. Because it is only affecting the way of dilevring the frame itself.
    Is it two way lane, that mean we can carry data simultanously.
    Or one way lane, that mean we can carry data in one direction at time.

    Correct me if I am wrong
  12. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    You are absolutely right.
    But the thing is what do you mean by "we".

    If you are driving a car through a tunnel where only one direction is allowed at a time then certainly you have to acknowledge this fact. You have wait for the green light etc. The amount of lanes is important to you.

    If you are a passenger in the car then you couldn't care less. You get to your destination no matter the type of the tunnels. Futhermore, all the passengers coming in the other direction don't care either and they all get to where they are going. And if we look at the big picture then the traffic on both highways before and after the tunnel is in two directions.

    The one-directional part of the road imposes a certain delay, but it doesn't matter to the people travelling since the drivers take care of that nasty tunnel for them.

    If you sit on a bus at one end of the highway and your friend at the other and you start off at the same time then you don't collide and die in the middle of the tunnel. One of you will be waiting at the red light until the other bus comes through. Yes, there is only one of you in the tunnel at any moment, but both of you were travelling on the bus the whole time.

    Even though you know there is a one-way tunnel on your way from city A to city B you don't have to call ahead and make sure there are no buses coming from city B. You just sit on a bus and you will get to city B (eventually) no matter what traffic is coming the other way. Of course things will get complicated if the traffic is heavy both ways :p
  13. zillah

    zillah TS Rookie Topic Starter Posts: 47

    Sorry, I meant the data can be carried
    Recall my early (first) post.

    I meant, when we are talking (chatting) using MAS meesenger or Yahoo messenger, why cann't we talk simultanously, (i.e I have to wait remote party to finish his/her conversation, then I can start my conversation!!!) ?

    Is this because my dialup modem, or his/her dialup modem in half-duplex mode ? As you know when we talk the data (voice) will be travel from the upper layer (application layer 7) to buttom layer.

    This is what I meant by:
  14. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    Your problem is most likely not the duplexness of your internet connection. Especially in case of DSL which is full duplex by nature.

    Are the sound cards of both sides full duplex? Old and cheap sound cards can only process either input or output at one time.
  15. zillah

    zillah TS Rookie Topic Starter Posts: 47

    1- How can we verify the sound card is half-duplex or full-duplex ?

    2- Is normal dialup modem full-duplex or half-duplex ?
  16. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    You have to look up the specifications for the sound cards/chips.

    All dialup modems that are not museum grade support full duplex operation. It could be turned off of course. I think I have seen some settings and DIP switches for that.
  17. zillah

    zillah TS Rookie Topic Starter Posts: 47

    With the NIC you can verify the full 0r half-duplex mode from the properties, I could not find same feature with sound card. That mean I have to go to specification.

    What does that mean?

    How can we verify, is there any setting for that ?
  18. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    Read the manuals..
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