E1 Specifications » History » Version 6
laforge, 05/11/2018 07:19 PM
1 | 1 | laforge | h1. E1 Specifications |
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3 | 4 | laforge | The following is an overview of relevant specifications for E1 interfaces. |
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5 | 5 | laforge | Wikipedia provides a good overview at https://en.wikipedia.org/wiki/E-carrier |
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7 | 1 | laforge | h2. G.702 "Digital Hierarchy Bit Rates" |
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9 | 4 | laforge | https://www.itu.int/rec/T-REC-G.702/en |
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11 | 1 | laforge | * describes the hierarchy of 64k/2048k/8448k/34368k/139264k and their T1 counterparts |
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13 | h2. G.703 "Physical/electrical characteristics of hierarchical digital interface" |
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15 | 4 | laforge | https://www.itu.int/rec/T-REC-G.703/en |
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17 | 1 | laforge | Section 11 describes the "E12" interface at 2048 kbit/s |
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19 | * Nominal bit rate: 2048 kbit/s |
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20 | * Bit rate accuracy: +/-50 ppm (+/-102.4 bit/s) |
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21 | * Code: High density bipolar of order 3 (HDB3) (a description of this code can be found in Annex A) |
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22 | * Overvoltage protection requirements: refer to [ITU-T K.20] |
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24 | 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 |
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26 | h2. G.704 "Synchronous frame structures used at 1544, 6312, 2048, 8448 and 44 736 kbit/s hierarchical levels" |
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28 | 4 | laforge | https://www.itu.int/rec/T-REC-G.704/en |
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30 | 1 | laforge | Section 2.3 specifies the basic frame structure at 2048 kbit/s |
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32 | * the basic frame consists of 256 bits, numbered 1 to 256 |
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33 | * the frame repetition rate is 8000 Hz |
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34 | * bits 1..8 of the frame have special significance, they contain the frame alignment signal (FAS) and the S-bits |
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35 | * an optional CRC-4 mechanism can be used in bit 1 of the frame, using so-called CRC-4 multiframes composed of 16 frames |
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37 | Section 5.1 specifies the interface at 2048 kbit/s carrying 64 kbit/s channels |
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39 | 2 | laforge | * each of the 64 kbit/s channels occupise 8 bits per timeslot, numbered 1..8 |
40 | * 32 timeslots of each 8 bits form the basic frame (256bits) described above |
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41 | * timeslot 0 (TS0) is used for frame alignment and signaling, as described above |
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42 | * timeslot 1..31 are free for user data. 16 is typically used for signaling [not custom in GSM A-bis, but in general ISDN] |
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43 | * timeslot 16 can be used for channel-associated signaling (CAS) [not used in context of GSM A-bis] |
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44 | 1 | laforge | |
45 | 3 | laforge | h2. G.706 "FRAME ALIGNMENT AND CYCLIC REDUNDANCY CHECK (CRC) PROCEDURES RELATING TO BASIC FRAME STRUCTURES DEFINED IN RECOMMENDATION G.704" |
46 | 4 | laforge | |
47 | https://www.itu.int/rec/T-REC-G.706/en |
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48 | 3 | laforge | |
49 | Section 4 specifies the Frame alignment and CRC procedures at 2048 kbit/s interface |
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51 | * frame alignment is assumed lost when three consecutive incorrect frame alignment signals (FAS) are received |
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52 | * 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 |
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54 | The following procedure is recommended: |
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56 | _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._ |
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58 | 6 | laforge | h2. G.711 "PULSE CODE MODULATION (PCM) OF VOICE FREQUENCIES" |
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60 | Specifies the aLaw and uLaw encoding of classic ISDN B-channels. |
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62 | h3. Bit Ordering |
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64 | When character signals are transmitted serially, i.e. consecutively on one physical medium, bit No. 1 (polarity |
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65 | bit) is transmitted first and No. 8 (the least significant bit) last. |
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66 | 3 | laforge | |
67 | 1 | laforge | h2. HDLC |
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69 | 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. |
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71 | ISO/IEC 13239 specifies HDLC. |
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73 | * "ISO/IEC 13239 in Online Browsing Platform of IEC":https://www.iso.org/obp/ui/#iso:std:iso-iec:13239:en |
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74 | * "Official Homepage of ISO/IEC 13239":https://www.iso.org/standard/37010.html |