Interfaces - 25.6 Mbit/s (ATM) interface according to the ITU-T I.432.5

Application, services, topology, data changing wires, electrical characteristics

Application:

Interface according to ITU-T I.432.5 is four-wired, whole duplex interface with transmitting abilities, with a transmission rate of 25.6 Mbit/s. Interface was developed for forwarding ATM cells. Interface consists of two transceivers and a 2 x 2 metallic wire, which connects them. In the ATM reference model it realizes sublayers TC and PMD.

Elements of the recommendation, standard, describing the interface:

• ITU-T I.432.5 physical/electrical characteristics

Interface provides the following services towards the higher layers:

• Transmission capatibilty
• Bit sycnchronization
• Generation/control of HEC (CRC)
• Cell scramblering/descramblering
• Line coding/decoding (4B/5B + NRZI)
• Cell delineation (ESC sequence)
• Cell rate decoupling (idle cell insertion)

Interface topology:

Interface realizes a point-to-point connection.

Data changing wires:

For realization of the interface it is necessary to have a symmetric UTP of 100 ohms, consisting of a 2 x 2 wire (unshadowed twisted pairs), or an STP of 120 or 150 ohms (shadowed twisted pairs), with a transmission capacity of 25.6 Mbit/s to both directions.

    Pin positions:

    RJ-45 (EIA/TIA-464-B)

         UNI          NNI
    1    Tx+          Rx+
    2    Tx-          Rx-
    3    unused      unused
    4    unused      unused
    5    unused      unused
    6    unused      unused
    7    Rx+          Tx+
    8    Rx-          Tx-

• bit RATE: 25.6 Mbit/s +/- 100 ppm
• line coding: 4B/5B / NRZI
• symbol rate: 32 MBaud

  nominal impedance	100 ohm	120 ohm	150 ohm
  pulse amplitude (peak to peak)	2.7...3.4 V	2.95...3.75 V	3.3 ... 4.2 V

• reflexion:
  • 14 dB (1 - 6 MHz)
  • 12 dB (6 - 17 MHz)
  • 8 dB (17 - 25 MHz)