1、232b414 0006033 O I TL05-03 Page 1 E Recommendation T/L 05-03 (Edinburgh 1988) DIGITAL TRANSMISSION SYSTEM ON METALLIC LOCAL LINES FOR ISDN BASIC RATE ACCESS Recommendation proposed by Working Group T/WG 12 “Transmission and multiplexing” (TM) Text of Recomrnen - to operate on existing 2-wire unload
2、ed local lines, open wires being excluded; m Edition of January 30, 1989 - 2326414 0006034 2 E TIL 05-03 E Page 2 - the objective is to achieve 100% cable fill for ISDN basic access without pair selection, cable rearrange- ments or removal of bridged taps (BTs) which exist in many networks; - the ob
3、jective to be able to extend ISDN basic access provided services to the majority of customers without the use of regenerators. In the remaining few cases special arrangements may be required; - coexistence in the same cable unit with most of the existing services like telephony and voice-band data t
4、ransmission; - various national regulations concerning EM1 should be taken into account; - power feeding from the network under normal or restricted conditions via the basic access shall be - the capability to support maintenance functions shall be provided. provided where the Administration provide
5、s this facility; 1.4. Abbreviations A number of abbreviations are used in this Recommendation. Some of them are commonly used in the ISDN reference configuration while others are created only for this Recommendation. The last one are given in the following: BER: Bit Error Ratio BT: Bridged Tap CISPR
6、: Comit International Spcial de Perturbation Radiolectrique (now part of IEC) CL: DLL: Digital Local Line DTS: Digital Transmission System ECH : Echo Cancellation EMI: Electro-Magnetic Interference NEXT: Near-End Crosstalk PSL: Power Sum Loss TCM: Time Compression Multiplex UI: Unit Interval Control
7、 Channel of the line system 2. FUNCTIONS Figure 2 (T/L 05-03) shows the functions of the digital transmission system on metallic local lines. NTI LT D channel Octet timing Activation I Deactivation I I Power feeding I L I - r 4 - Operations and maintenance Note I. The optional use 01 one i.egciici.n
8、toi. must be foreseen . I %- Figure 2 (T/L 05-03). Functions of the digital transmission system. Edition of January 30, 1989-, 1 IC, I 2326434 O006035 4 E! TIL 05-03 E Page 3 B channel This function provides, for each direction of transmission, two independent 64 kbit/s channels for use as B channel
9、s (as defined in CCITT Recommendation 1.412). D channel This function provides, for each direction of transmission, one D channel at a bit rate of 16 kbit/s (as defined in CCITT Recommendation 1.412). Bit Timing This function provides bit (signal element) timing to enable the receiving equipment to
10、recover information from the aggregate bit stream. Bit timing for the direction NT1 to LT shall be derived from the clock received by the NT1 from the LT. Octet Timing This function provides 8 kHz octet timing for the B channels. It shall be derived from frame alignment, Frame Alignment This functio
11、n enables the NT and the LT to recover the time division multiplexed channels. Activation om LT or NTl (Note 3 below) This function restores the Digital Transmission System (DTS) between the LT and NT to its normal operational status. Procedures required to implement this function are described in S
12、ection 6. of this Recommendation. Activation from the LT could apply to the DTS only or to the DTS plus the customer equipment. In case the customer equipment is not connected, the DTS can still be activated. Deactivation (Note 3 below) This is specified in order to permit the NT and the regenerator
13、 (if it exists) to be placed in a low power consumption mode or to reduce intrasystem crosstalk to other systems. The procedures and exchange of information are described in Section 6. of this Recommendation. This deactivation should be initiated only by the exchange (ET). Power Feeding This functio
14、n provides for remote power feeding of one regenerator (if required) and NTI. The provision of wetting current is recommended. Note I. The provision of line feed power to the user-network interface, normal or restricted power feeding as defined in Recommendation T/L 03-07 E is required by some Admin
15、istrations. Note 2. The general power feeding strategy, given in paragraph 8., may not be applicable for extremely long local lines. In those cases specic power feeding methods (e.g. use of batteries in the NTl or local power feeding of the NT1) may be applied. Those specific methods are outside the
16、 scope of this Recommendation. Operations and Maintenance (Note 3 below) This function provides the recommended actions and information described in CCIT Recommenda- tion 1.603. The following categories of functions have been identified: - maintenance command (e.g. loopback control in the regenerato
17、r or the NT1) - maintenance information (e.g. line errors) - indication of fault conditions - information regarding power feeding in NT1 Note 3. The functions required for operations and maintenance of the NT1 and one regenerator (if required) and for some activation/deactivation procedures are comb
18、ined in one transport capability to be transmitted along with the 2 B + D channels. This transport capability is named the CL channel. 3. TRANSMISSION MEDIUM 3.1. Description The transmission medium over which the digital transmission system is expected to operate is the local line distribution netw
19、ork. A local line distribution network employs cables of pairs to provide services to customers. In a local line distribution network, customers are connected to the local exchange via local lines. A metallic local line is expected to be able to simultaneously carry bi-directional digital transmissi
20、on providing ISDN basic access between LT and NTl. Edition of January 30, 1989 - W 2326414 0006036 b i Installation Distribution Main Exchange cable cable cable cable NTI LT - J SDP CCP MDF TIL 05-03 E 0.3 - 0.32 - 0.4 - 0.5 - 0.6 0.63 - 0.8 - 0.9 - 1.0 - 1.4 SQ or TP; L or B Page 4 3.2. 3.3. 3.3,1,
21、 3.3.2. 0.4 - 0.5 - 0.6 - 0.8 SQ or TP or UP To simplify the provision of ISDN basic access, a digital transmission system must be capable of satisfactory operation over the majority of metallic local lines without requirement of any special conditioning. Maximum penetration of metallic local lines
22、is obtained by keeping ISDN requirements at a minimum. In the following, the term Digital Local Line (DLL) is used to describe a metallic local line that meets minimum ISDN requirements. Minimum ISDN Requirements a) No loading coils b) No open wires c) When bridged taps (BTs) are present, the follow
23、ing rules apply: - maximum number of BTs: 2 (Note) - total length: for further study Note. One Administration supports the presence of 3 BTs. Wire insulation PVC Cable Characteristics Exchange cable Wire diameter (mm) 0.5 - 0.6 Structure TP; L or B I Max. number of pairs I 1200 Installation I I I Ca
24、pacitance 80 . 120 (nF/km at 800 Hz) Main 1 Distribution 1 Customer cable cable cable 2400 (0.4 mm) 600 (0.4 mm) 2 (aerial) 4800 (0.3 mm) 600 (in house) Underground Underground Aerial (drop) in ducts or aerial in ducts (in house) 25 . 36 I80 . 120 I pvc Paper, pulp Paper, PE, cell. PE PE, cell. PE P
25、olyethylene Polyvinylchloride Pulp of paper L: Layer Cell. PE: Cellular Polyethylene (foam) B: Bundles (units) Note. The information in this table is provisional. Table 1 (T/L 05-03). Cable characteristics. Edition of January 98L I 2326434 O006037 8 1 T/L 05-03 E Page 5 3.4. DLL Electrical Character
26、istics a 3.4.1. Insertion Loss The DLL will have non-iinear loss versus frequency characteristic. For any DLL of a particular gauge mix, with no BTs and with an insertion loss of X dB at 80 kHz, the typical behaviour of its insertion loss (measured between 130 Cl) versus frequency is depicted in Fig
27、ure 4 (T/L 05-03). 1.75 x 1.50 x h o) - (o 1.25 8 Li (o o) c .- - v X M 0 u3 u3 2 0.75 x -1 -1 n 0.50 x 0.25 x 1 2 5 10 20 50 100 200. 80 FREQUENCY kHz (log scale) Figure 4 (T/L 05-03). Typical Insertion Loss Characleristic without Presence of BTs. Note. The maximum value of X ranges from 37 dB to 4
28、2 dB. The minimum value could be close to zero. Edition of Janiiary 30, 1989 T- ,Y I 2326434 0006038 T W TIL 05-03 E Page 6 3.4.2. Gsoup Delay Typical ranges of values of DLL group delay as a function of frequency are shown in Figure 5 (T/L 05-03). 1.7 T 1.6 T 1.5 T 1.4T 1.3 T 1.2T 1.1 T T 0.9 T 0.8
29、 T 0.7 T 0.6 T 0.5 T 5 10 50 1 O0 500 1 O00 FREQUENCY kHz Figure 5 (T/L 05-03). Typical Group Delay Characteristic. Note. The maximum value of one way group delay (T) ranges from 30 to 60 microseconds at 80 kHz. Edition of January 30, 1989 - = 2326434 0006039 I m TIL 05-03 E Page 7 3.4.3. Charncteri
30、stic Impedance Typical ranges of values of the real and imaginary parts of the characteristic impedance of twisted pairs in different types of cables are shown in Figure 6 (T/L 05-03). 500 - 400 E 2 300 tl r L? 200 a; - 100 O : .E E v 2= -100 - m a m L m a- - 0 5 -200 a ,$ -300 2 -400 -500 C IJ .- -
31、 1 10 1 O0 400 FREQUENCY kHz1 (log scale) Figure 6 (T/L 05-03). Typical Ranges of Values of Real and Imaginary Parts of Characteristic Impedance. Edition of January 30, 1989 - - . 2326434 000b040 8 = TIL 05-03 E Page 8 3.4.4. Near-End Crosstalk (NEXT) The DLL will have finite crosstalk coupling loss
32、 to other pairs sharing the same cable. Worst-case NEXT Power Sum Loss (PSL) is 44 dB at 80 kHz (refer to Section 4.2.2.). The DLL Loss and PSL ranges have been independently specified. However, it is not required that all points in both ranges be satisfied simultaneously. A combined DLL Loss/PSL re
33、presentation is shown in Figure 7 (T/L 05-03) to define the coinbined ranpe of operation. Power Sum Loss dB at 80 kHz (linear scale) Figure 7 (T/L 05-03). Conibiiiccl Kcpi-esciiiaiioii of DLL Loss/PSL Range of Operation. O In this area, it is mandatory that systems work in. O In this area, it is des
34、irable, but not mandatory, that systems can work in order to reduce the number of regenerators. Edition of January 30, 198% - 7 ! - l i ._ I 2326414 000b041 T TIL 05-03 E Page 9 3.4.5. Unbalance About Earth The DLL will have finite balance about earth. Unbalance about earth is described in terms of
35、longitudinal conversion loss. Worst-case values are shown in Figure 8 (T/L 05-03). I I I I 1 I I 8 80 800 FREQUENCY kHz (log scale) Figure 8 (T/L 05-03). Worst-case Longitudinal Conversion Loss Versus Frequency. 3.4.6. Impidse Noise The DLL will have impulse noise resulting from other systems sharin
36、g the same cables as well as from other sources. e Edition of January 30, 1989 - E 2326434 0006042 3 E TIL 05-03 E Page 10 4. 4.1. 4.2. 4.2.1, SYSTEM PERFORMANCE Performance Requirements Performance limits for the digital section are specified in paragraph 4. of Recommendation T/L 03-13 E. The Digit
37、al Transmission System Performance must be such that these performance limits are met. For that purpose, a Digital Transmission System is required to pass specific laboratory performance tests that are defined in the next sections. Performance Measurements Laboratory performance measurement of a par
38、ticular digital transmission system requires the following preparations: a) Definition of a number of DLL models to represent physical and electrical characteristics encountered b) Simulation of the electrical environment caused by finite crosstalk coupling loss to other pairs in the same c) Simulat
39、ion of the electrical environment caused by impulse noise. d) Specification of laboratory performance tests to verify that the performance limits referred to in DLL Physical Models For the purposes of laboratory testing of performance of a digital transmission system providing ISDN basic access, som
40、e models representative of DLLs to be encountered in a particular local line distribution network are required. The maximum loss in each model is optionally set between 37 and 42 dB at 80 kHz to satisfy requirements of the particular network. Similarly, the lengths of BTs are optionally set within t
41、he range defined in Figure 9 (T/L 05-03). in local line distribution networks. cable. Section 4.1. will be met. Edition of January 30, 199-, I 2326434 080b043 3 I X dB 0.4, 0.5 or 0.6 mm 2. r. 0.25 X 0.25 X 0.25 X 0.25 X dB 3. 0.4 0.5 I 0.6 0.4 mm 0.05 X 0.9 x 0.05 X dB 0.4 0.8 0.4 mm 4. :BTI BT2 BT
42、3 0.2 x 0.4 X 0.2 x dB 0.4 0.4 0.4 . mm 5. BTI = O - 0.5 km/0.4 mm BT3 = O - 0.5 km/0.4 mm BT2 = O - 0.5 km/0.4 m-m 0.03 X 0.65 X 0.25 X 0.07 X dB 0.32 0.4 0.5 0.63 mm I 6. Figure 9 (T/L 05-03). DLL Physical Models for Laboratory Testing. Note. The value of X varies from 37 to 42 dB at 80 Hz. Editio
43、n of January 30, 1989 I 2326434 0006044 5 W TIL 05-03 E Page 12 4.2.2, Intrasystem Crosstalk Modelling 4.2.2.1. Definition of Intrasystem Crosstalk Crosstalk noise in general results from finite coupling loss between pairs sharing the same cable, especially those pairs that cause a vestige of the si
44、gnal flowing on one DLL (disturber DLL) to be coupled into an adjacent DLL (disturbed DLL). This vestige is known as crosstalk noise. Near-end crosstalk (NEXT) is assumed to be the dominant type of crosstalk. Intrasystem NEXT or self NEXT results when all pairs interfering with each other in a cable
45、 carry the same digital transmission system. Intersystem NEXT results when pairs carrying different digital transmission systems interfere with each other. Definition of intersys- tem NEXT is not part of this Recommendation. Intrasystem NEXT noise coupled into a disturbed DLL from a number of DLL di
46、sturbers is represented as being due to an equivalent single disturber DLL with a coupling loss versus frequency characteristic known as Power Sum Loss. Worst-case Power Sum Loss encountered in a local line distribution network is defined in Figure 10 (T/L 05-03). All DLLs are assumed to have fixed
47、resistance terminations of Ro ohms. The range of Ro is 110 to 150 ohins. 80 FREQUENCY kHz (log scale) Figure 10 (T/L 05-03). Worst-Case power sum loss. Edition of January 30, l98. 1 232b414 OOOb045 i + NTI DLL. or 4 c LT Under test i T/L 05-03 E Page 13 LT or NTI 4.2.2.2. Measurement Arrangement . 5
48、 Noise insertion circuit White. noise Calibrated source attenuator t-fT-t-$l shaping Line code and transmit filter Figure 11 (T/L 05-03). Crosstalk noise simulation and testing. The measurement arrangement in Figure 11 (T/L 05-03) is. described in the following: a) Box 1 represents a white noise sou
49、rce of constant spectral density. Spectrum is flat from 100 Hz to 500 kHz rolling off afterwards. b) Box 2 is a vasiable attenuator. c) Box 3 is a lter that shapes the power spectrum to correspond to the line code and the transmit filter of the system under test. d) Box 4 is a filter that shapes the power spectrum according to the Power Sum Loss characteristic of Figure 10 (T/L 05-03). e) Box 5 is a noise insertion circuit which couples the simulated crosstalk noise into the DLL without disturbing its performance. The insertion circuit therefo
