PC network

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The IBM PC Network (IBM PC Network) was a simple solution offered by IBM from 1984 for the local networking of PCs with a data rate of 2 Mbit / s. The NetBIOS programming interface was introduced with the PC network . Direct access to the network medium (and thus support for other network protocols ) was not intended.

Format of the frames

A frame of the PC network consists of the following fields:

  • Start delimiter - start delimiter (SD) - 1 byte
  • LAN head
    • Destination address - 6 bytes
    • Source address - 6 bytes
    • Zeros - 2 bytes
    • Optional routing field - up to 18 bytes
  • Optional DLC header field - 3 to 4 bytes
    • DSAP - 1 byte
    • SSAP - 1 byte
    • Control - 1 to 2 bytes
  • Optional information
  • Frame check sequence (FCS) - 4 bytes
  • Frame status - Frame status (FS) - 1 byte
  • Fill character

The LAN head of the PC network differs from that of the Token Ring network, but the compatibility for application programs is not impaired. In those cases in which the application program needs access control and frame control bytes, the protocol drivers simply leave the bytes out of the transmitted frame and insert 2 bytes with zeros after the original address. To be on the safe side, the protocol driver checks whether the frame control byte specifies an LLC frame and not a MAC frame. The formats of the routing information, the DLC header data and the information fields are identical in both networks.

hardware

The network adapters for the PC network were available in baseband and broadband versions.

In the baseband version , the computers were connected using twisted pair cables with RJ-45 plugs. The network adapters have two sockets for connecting the left and right neighboring nodes, unused sockets at the end of the network segment are equipped with a terminal resistor .

The rarely used, more expensive broadband version allowed the installation of spatially more extensive and more complex networks. It used different frequency ranges for sending and receiving data via coaxial cable (RG-11, 75 Ohm). A frequency converter at the end of the cable ensured that the transmitted data was forwarded to the receiving frequency range.

In this case, the term broadband network refers to the bandwidth occupied by the signal on the carrier medium , i.e. H. the data is modulated onto a high-frequency signal . (This technology is no longer used for wired data networks; today we speak of broadband for networks with high speeds.)

software

The PC operating system PC-DOS from version 3.10 supported network functions via NetBIOS.

A computer (PC, XT , AT or PS / 2 ) equipped with the IBM PC network program could function as a redirector, receiver, messenger or server .

The successor version 1.10 was renamed in 1986 in IBM PC Local Network Program, which also supported the standardized LAN systems Token-Ring and (later) Ethernet .

literature

  • IBM PC Network Technical Reference ( part number 6322505 )
  • S68X-2268 - IBM PC Network Broadband Guide
  • S68X-2269 - IBM PC Network Baseband Planning Guide
  • SC30-3520 - IBM PC Network Adapters Technical Reference
  • SC30-3587-01 - LAN Technical Reference: 802.2 and NetBIOS APIs

Web links

IBM announcement letter