Project

General

Profile

E1 Specifications » History » Version 5

laforge, 05/04/2018 08:36 PM

1 1 laforge
h1. E1 Specifications
2
3 4 laforge
The following is an overview of relevant specifications for E1 interfaces.
4
5 5 laforge
Wikipedia provides a good overview at https://en.wikipedia.org/wiki/E-carrier
6
7 1 laforge
h2. G.702 "Digital Hierarchy Bit Rates"
8
9 4 laforge
https://www.itu.int/rec/T-REC-G.702/en
10
11 1 laforge
* describes the hierarchy of 64k/2048k/8448k/34368k/139264k and their T1 counterparts
12
13
h2. G.703 "Physical/electrical characteristics of hierarchical digital interface"
14
15 4 laforge
https://www.itu.int/rec/T-REC-G.703/en
16
17 1 laforge
Section 11 describes the "E12" interface at 2048 kbit/s
18
19
* Nominal bit rate: 2048 kbit/s
20
* Bit rate accuracy: +/-50 ppm (+/-102.4 bit/s)
21
* Code: High density bipolar of order 3 (HDB3) (a description of this code can be found in Annex A)
22
* Overvoltage protection requirements: refer to [ITU-T K.20]
23
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
25
26
h2. G.704 "Synchronous frame structures used at 1544, 6312, 2048, 8448 and 44 736 kbit/s hierarchical levels"
27
28 4 laforge
https://www.itu.int/rec/T-REC-G.704/en
29
30 1 laforge
Section 2.3 specifies the basic frame structure at 2048 kbit/s
31
32
* the basic frame consists of 256 bits, numbered 1 to 256
33
* the frame repetition rate is 8000 Hz
34
* bits 1..8 of the frame have special significance, they contain the frame alignment signal (FAS) and the S-bits
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
36
37
Section 5.1 specifies the interface at 2048 kbit/s carrying 64 kbit/s channels
38
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
41
* timeslot 0 (TS0) is used for frame alignment and signaling, as described above
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]
43
* timeslot 16 can be used for channel-associated signaling (CAS) [not used in context of GSM A-bis]
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
48 3 laforge
49
Section 4 specifies the Frame alignment and CRC procedures at 2048 kbit/s interface
50
51
* frame alignment is assumed lost when three consecutive incorrect frame alignment signals (FAS) are received
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
53
54
The following procedure is recommended:
55
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._
57
58
59 1 laforge
h2. HDLC
60
61
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.
62
63
ISO/IEC 13239 specifies HDLC.
64
65
* "ISO/IEC 13239 in Online Browsing Platform of IEC":https://www.iso.org/obp/ui/#iso:std:iso-iec:13239:en
66
* "Official Homepage of ISO/IEC 13239":https://www.iso.org/standard/37010.html
Add picture from clipboard (Maximum size: 48.8 MB)