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  • Packet Vs Circuit Switch

    From Bo Simonsen@2:236/100 to Andy Ball on Friday, October 22, 2004 00:25:49
    Hello Andy!

    Monday October 18 2004 08:54, you wrote to me:

    Out-of-order packet reception springs to mind.

    Hm. Please explain, not familear with that expression.

    On a circuit-switched link (such as a dial-up call between my modem
    and yours) all the data sent from my end to your end take the same
    route and arrive in the same order that they were sent.

    Yes,

    On a
    packet-switched network (such as the Internet), it is possible for
    packets to take different routes to reach you, and for a packet to
    arrive ahead of one that was sent before it was (arriving out of
    order).

    Thinking about it though, Telnet works over TCP which almost certainly re-orders packets that it receives in the wrong order before passing
    them up to Telnet, so although it's a valid difference between circuit-switched and packet- switched networks, it's sort of
    irrelevent from Telnet's point of view. :-)

    But if we see in the OSI model, it's not really the application layers job to make scure the data is valid. Which we actually do anyhow, with fx. CRC check in Zmodem and brothers.

    Bo
    --- GoldED+/LNX 1.1.5
    * Origin: The Night Express - 45-36959335 - 1200 BPS only (2:236/100)
  • From Andy Ball@1:10/345 to Bo Simonsen on Monday, October 18, 2004 09:54:46
    Hello Bo,

    AB> Out-of-order packet reception springs to mind.

    BS> Hm. Please explain, not familear with that expression.

    On a circuit-switched link (such as a dial-up call between my modem and yours) all the data sent from my end to your end take the same route and arrive in the
    same order that they were sent. On a packet-switched network (such as the Internet), it is possible for packets to take different routes to reach you, and for a packet to arrive ahead of one that was sent before it was (arriving out of order).

    Thinking about it though, Telnet works over TCP which almost certainly re-orders packets that it receives in the wrong order before passing them up to
    Telnet, so although it's a valid difference between circuit-switched and packet- switched networks, it's sort of irrelevent from Telnet's point of view.
    :-)

    - Andy Ball

    * SLMR 2.1a *
    --- BBBS/NT v4.01 Flag-5
    # Origin: FamilyNet Sponsored by http://www.christian-wellness.net (8:8/2)
    * Origin: BBS Networks @ www.bbsnets.com 808-839-6036 (1:10/345)
  • From Andy Ball@1:10/345 to Bo Simonsen on Saturday, October 23, 2004 03:07:24
    Hello Bo,

    BS> But if we see in the OSI model, it's not really the application
    > layers job to make scure the data is valid. Which we actually do
    > anyhow, with fx. CRC check in Zmodem and brothers.

    What is "fx"? Which is older, the OSI model or XModem?

    - Andy Ball

    * SLMR 2.1a *
    --- BBBS/NT v4.01 Flag-5
    # Origin: FamilyNet Sponsored by http://www.christian-wellness.net (8:8/2)
    * Origin: BBS Networks @ www.bbsnets.com 808-839-6036 (1:10/345)
  • From Bo Simonsen@2:236/100 to Andy Ball on Tuesday, October 26, 2004 18:25:59
    Hello Andy!

    Saturday October 23 2004 02:07, you wrote to me:

    But if we see in the OSI model, it's not really the application
    layers job to make scure the data is valid. Which we actually do
    anyhow, with fx. CRC check in Zmodem and brothers.

    What is "fx"? Which is older, the OSI model or XModem?

    Example.. Not even danes use it, sometimes I think I'm the only one..

    I've not clue about the age, but something tells me Xmodem is older..

    Bo
    --- GoldED+/LNX 1.1.5
    * Origin: The Night Express - 45-36959335 - 1200 BPS only (2:236/100)
  • From Andy Ball@1:10/345 to Bo Simonsen on Friday, October 29, 2004 09:05:34
    Hello Bo,

    BS> I've not clue about the age, but something tells me
    > Xmodem is older..

    XModem was apparently developed in 1977 (I thought it was from the late 1970s, but I had to look up the actual year
    ;-) OSI was apparently developed during the 1980s, although
    it was probably influenced by an earlier 4-layer model from the U.S. Department
    of Defense.

    - Andy Ball

    * SLMR 2.1a *
    --- BBBS/NT v4.01 Flag-5
    # Origin: FamilyNet Sponsored by http://www.christian-wellness.net (8:8/2)
    * Origin: BBS Networks @ www.bbsnets.com 808-839-6036 (1:10/345)
  • From Mike Powell@1:2320/105 to Bo Simonsen on Monday, November 01, 2004 13:05:00
    I've not clue about the age, but something tells me Xmodem is older..

    I also think it is older. Older comm programs don't have support for Zmodem, but do have support for Xmodem.

    Mike
    ---
    * SLMR 2.1a * ...a host of holy horrors to direct our aimless dance...


    --- GTMail 1.26
    * Origin: Kentucky's Capitol City Online * 502/875-8938 (1:2320/105.0)
  • From Lance Lyon@3:712/313.1 to Mike Powell on Tuesday, November 02, 2004 12:36:20
    I've not clue about the age, but something tells me Xmodem is older..

    I also think it is older. Older comm programs don't have
    support for Zmodem,
    but do have support for Xmodem.

    Xmodem was developed by Ward Christensen in 1977, Ymodem somewhat later & Zmodem later still.

    cheers,

    Lance
    ---
    * Origin: Timeline BBS (3:712/313.1)