E1 Specifications » History » Revision 2
Revision 1 (laforge, 05/04/2018 07:48 PM) → Revision 2/8 (laforge, 05/04/2018 07:52 PM)
h1. E1 Specifications h2. G.702 "Digital Hierarchy Bit Rates" * describes the hierarchy of 64k/2048k/8448k/34368k/139264k and their T1 counterparts h2. 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 h2. 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] FIXME h2. 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":https://en.wikipedia.org/wiki/High-Level_Data_Link_Control for a general introduction into HDLC. ISO/IEC 13239 specifies HDLC. * "ISO/IEC 13239 in Online Browsing Platform of IEC":https://www.iso.org/obp/ui/#iso:std:iso-iec:13239:en * "Official Homepage of ISO/IEC 13239":https://www.iso.org/standard/37010.html
