E1 Specifications » History » Revision 7
Revision 6 (laforge, 05/11/2018 07:19 PM) → Revision 7/8 (laforge, 05/11/2018 08:42 PM)
h1. E1 Specifications The following is an overview of relevant specifications for E1 interfaces. Wikipedia provides a good overview at https://en.wikipedia.org/wiki/E-carrier h2. G.702 "Digital Hierarchy Bit Rates" https://www.itu.int/rec/T-REC-G.702/en * describes the hierarchy of 64k/2048k/8448k/34368k/139264k and their T1 counterparts h2. G.703 "Physical/electrical characteristics of hierarchical digital interface" https://www.itu.int/rec/T-REC-G.703/en 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" https://www.itu.int/rec/T-REC-G.704/en 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] h2. G.706 "FRAME ALIGNMENT AND CYCLIC REDUNDANCY CHECK (CRC) PROCEDURES RELATING TO BASIC FRAME STRUCTURES DEFINED IN RECOMMENDATION G.704" https://www.itu.int/rec/T-REC-G.706/en Section 4 specifies the Frame alignment and CRC procedures at 2048 kbit/s interface * frame alignment is assumed lost when three consecutive incorrect frame alignment signals (FAS) are received * frame alignment is assumed lost when bit 2 in TS0 in frmaes not containing the FAS has been received with an error on three consecutive occasions The following procedure is recommended: _When a valid frame alignment signal is detected in frame n, a check should be made to ensure that a frame alignment signal does not exist in frame n + 1, and also that a frame alignment signal exists in frame n + 2. Failure to meet one or both of these requirements should cause a new search to be initiated in frame n + 2._ h2. G.711 "PULSE CODE MODULATION (PCM) OF VOICE FREQUENCIES" Specifies the aLaw and uLaw encoding of classic ISDN B-channels. h3. Bit Ordering When character signals are transmitted serially, i.e. consecutively on one physical medium, bit No. 1 (polarity bit) is transmitted first and No. 8 (the least significant bit) last. h2. I.412 "ISDN USER-NETWORK INTERFACE STRUCTURES AND ACCESS CAPABILITIES" * B-Channels carry G.711 (voice), X.1 (data) or G.722 (wideband voice) * D-Channels use layered protocol according to I.440, I.441, I.450 and I.451 (I couldn't find any of these) h2. I.431 "PRIMARY RATE USER-NETWORK INTERFACE - LAYER 1 SPECIFICATION" Sort-of an umbrella specification referring to G.703 / G.704 and specifying details which options to use * CRC4 shall be used * D-Channels shall have 64kBps and according to I.412 (default on TS16) * B-Channels shall have 64kBps and according to I.412 * Remote Alarm Indication (RAI) and LOS, referring to G.706 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
