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E1 Specifications » History » Revision 2

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laforge, 05/04/2018 07:52 PM
add notes on section 5.1


E1 Specifications

G.702 "Digital Hierarchy Bit Rates"

  • describes the hierarchy of 64k/2048k/8448k/34368k/139264k and their T1 counterparts

G.703 "Physical/electrical characteristics of hierarchical digital interface"

Section 11 describes the "E12" interface at 2048 kbit/s

  • Nominal bit rate: 2048 kbit/s
  • Bit rate accuracy: /-50 ppm (/-102.4 bit/s)
  • Code: High density bipolar of order 3 (HDB3) (a description of this code can be found in Annex A)
  • Overvoltage protection requirements: refer to [ITU-T K.20]

The RJ45 / twisted pair interface uses 120 ohms differential/symmetric signaling with a nominal peak voltage of 3V and a nominal space voltage of 0V

G.704 "Synchronous frame structures used at 1544, 6312, 2048, 8448 and 44 736 kbit/s hierarchical levels"

Section 2.3 specifies the basic frame structure at 2048 kbit/s

  • the basic frame consists of 256 bits, numbered 1 to 256
  • the frame repetition rate is 8000 Hz
  • bits 1..8 of the frame have special significance, they contain the frame alignment signal (FAS) and the S-bits
  • an optional CRC-4 mechanism can be used in bit 1 of the frame, using so-called CRC-4 multiframes composed of 16 frames

Section 5.1 specifies the interface at 2048 kbit/s carrying 64 kbit/s channels

  • each of the 64 kbit/s channels occupise 8 bits per timeslot, numbered 1..8
  • 32 timeslots of each 8 bits form the basic frame (256bits) described above
  • timeslot 0 (TS0) is used for frame alignment and signaling, as described above
  • timeslot 1..31 are free for user data. 16 is typically used for signaling [not custom in GSM A-bis, but in general ISDN]
  • timeslot 16 can be used for channel-associated signaling (CAS) [not used in context of GSM A-bis]

HDLC

In the signaling timeslots (typically 64k slots, sometimes 16k sub-slots), HDLC is used for framing. It delimits the start and end of the octet and frame boundaries within the bitstream of the (sub)slot. See wikipedia for a general introduction into HDLC.

ISO/IEC 13239 specifies HDLC.

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Updated by laforge almost 6 years ago · 2 revisions

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