home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Internet Standards
/
CD2.mdf
/
ccitt
/
1992
/
g
/
g961.asc
< prev
next >
Wrap
Text File
|
1993-08-15
|
40KB
|
2,722 lines
13.2 Recommendation G.961
DIGITAL TRANSMISSION SYSTEM ON METALLIC LOCAL
LINES FOR ISDN BASIC RATE ACCESS
1. General
1.1 Scope
This Recommendation covers the characteristics and parameters of a dig-
ital transmission system at the network side of the NT1 to form part of
the digital section for the ISDN basic rate access.
The system will support the
- full duplex;
- bit sequence independent.
transmission of two B-channels and one D-channel as defined in Recom-
mendation I.412 and the supplementary functions of the digital section
defined in Recommendation I.603 for operation and maintenance.
The terminology used in this Recommendation is very specific and not
contained in the relevant terminology Recommendations. Therefore
Annex B to Recommendation G.960 provides a number of terms and def-
initions used in this Recommendation.
1.2 Definition
Figure 1/G.961 shows the boundaries of the digital transmission system
in relation to the digital section.
Note - In this Recommendation digital transmission system refers to a
line system using metallic lines. The use of one intermediate regenerator
may be required.
FIGURE 1/G.961
Digital section and transmission system boundaries
The concept of the digital section is used in order to allow a functional
and procedural description and a definition of the network requirements.
Note that the reference points T and V1 are not identical and therefore the
digital section is not symmetric.
The concept of a digital transmission system is used in order to describe
the characteristics of an implementation, using a specific medium, in sup-
port of the digital section.
1.3 Objectives
Considering that the digital section between the local exchange and the
customer is one key element of the successful introduction of ISDN into
the network the following requirements for the specification have been
taken into account.
- to meet the error performance specified in Recommendation G.960;
- to operate on existing 2-wire unloaded lines, open wires being
excluded;
- the objective is to achieve 100% cable fill for ISDN basic access
without pair selection, cable rearrangements or removal of
bridged taps (BT) which exist in many networks;
- the objective to be able to extend ISDN basic access provided ser-
vices to the majority of customers without the use of regenera-
tors. 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 transmission;
- various national regulations concerning EMI should be taken into
account;
- power feeding from the network under normal or restricted condi-
tions via the basic access shall be provided where the adminis-
tration provides this facility;
- the capability to support maintenance functions shall be provided.
1.4 Abbreviations
A number of abbreviations are used in this Recommendation. Some of
them are commonly used in the ISDN reference configuration while oth-
ers are created only for this Recommendation. The last one is given in the
following:
BER Bit Error Ratio
BT Bridged Tap
CISPR ComitΘ International SpΘcial de Perturbation RadioΘlectrique
(now part of IEC)
CL Control Channel of the line system
ECH Echo Cancellation
EMI Electro-Magnetic Interference
DLL Digital Local Line
DTS Digital Transmission System
NEXT Near-End Crosstalk
PSL Power Sum Loss
TCM Time Compression Multiplex
UI Unit Interval
2. Functions
Figure 2/G.961 shows the functions of the digital transmission system on
metallic local lines.
Note 1 - The optional use of one regenerator must be foreseen.
Note 2 - This function is optional.
FIGURE 2/G.961
Functions of the digital transmission system
2.1 B-channel
This function provides, for each direction of transmission, two indepen-
dent64 kbit/s channels for use as B-channels (as defined in Recommen-
dation I.412).
2.2 D-channel
This function provides, for each direction of transmission, one
D-channel at a bit rate of 16 kbit/s, (as defined in Recommendation
I.412).
2.3 Bit timing
This function provides bit (signal element) timing to enable the receiving
equipment to 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.
2.4 Octet timing
This function provides 8 kHz octet timing for the B-channels. It shall be
derived from frame alignment.
2.5 Frame alignment
This function enables the NT1 and the LT to recover the time division
multiplexed channels.
2.6 Activation from LT or NT1
This function restores the Digital Transmission system (DTS) between
the LT and NT1 to its normal operational status. Procedures required to
implement this function are described in section 6 of this Recommenda-
tion.
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 con-
nected, the DTS can still be activated.
Note - The functions required for operations and maintenance of the NT1
and one regenerator (if required) and for some activation/deactivation
procedures are combined in one transport capability to be transmitted
along with the
2B + D-channels. This transport capability is named the CL-channel.
2.7 Deactivation
This function is specified in order to permit the NT1 and the regenerator
(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). See note in
2.6.
2.8 Power feeding
This optional function provides for remote power feeding of one regener-
ator (if required) and NT1. The provision of wetting current is recom-
mended.
Note - The provision of line feed power to the user-network interface,
normal or restricted power feeding as defined in Recommendation I.430
is required by some administrations.
2.9 Operations and Maintenance
This function provides the recommended actions and information
described inRecommendation I.603.
The following categories of functions have been identified:
- maintenance command (e.g., loopback control in the regenerator or
the NT1);
- maintenance information (e.g., line errors);
- indication of fault conditions;
- information regarding power feeding in NT1.
See note in 2.6.
3. Transmission medium
3.1 Description
The transmission medium over which the digital transmission system is
expected to operate, is the local line distribution network.
A local line distribution network employs cables of pairs to provide ser-
vices 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 transmission providing ISDN Basic Access between
LT and NT1.
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 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.
3.2 Minimum ISDN requirements
a) No loading coils;
b) No open wires;
c) When BTs are present, some restrictions may apply. Typical allow-
able
BT configurations are discussed in section 4.2.1.
3.3 DLL physical characteristics
In addition to satisfying the minimum ISDN requirements, a DLL is typi-
cally constructed of one or more twisted-pair segments that are
spliced together. In a typical local line distribution network, these
twisted-pair segments occur in different types of cables as described in
Figure 3/G.961.
FIGURE 3/G.961
DLL Physical model
3.4 DLL electrical characteristics
3.4.1 Insertion loss
The DLL will have non-linear 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 versus fre-
quency is depicted in Figure 4/G.961.
FIGURE 4/G.961
Typical insertion loss characteristic without presence of BTs
Note - The maximum value of X ranges from 37 dB to 50 dB at 80 kHz.
The minimum value could be close to zero.
3.4.2 Group delay
Typical ranges of values of DLL group delay as a function of frequency
are shown in Figure 5/G.961.
FIGURE 5/G.961
Typical group delay characteristic
Note - The maximum value of one way group delay (T) ranges from 30 to
60 microseconds at 80 kHz.
3.4.3 Characteristic impedance
Typical ranges of values of the real and imaginary parts of the character-
istic impedance of twisted pairs in different types of cables are shown in
Figure 6/G.961.
FIGURE 6/G.961
Typical ranges of values of real and imaginary
parts of characteristic impedance
3.4.4 Near-end crosstalk (NEXT)
The DLL will have finite crosstalk coupling loss to other pairs sharing
the same cable. Worst-case NEXT Power Sum Loss (PSL) varies from 44
to 57 dB at 80 kHz (refer to section 4.2.2).
The DLL loss and PSL ranges have been independently specified. How-
ever, it is not required that all points in both ranges be satisfied simulta-
neously.
A combined DLL loss/PSL representation is shown in Figure 7/G.961 to
define thecombined range of operation.
FIGURE 7/G.961
Combined representation of DLL loss/PSL range of operation
3.4.5 Unbalance about earth
The DLL will have finite balance about Earth. Unbalance about Earth is
described in terms of longitudinal conversion loss. Worst-case values are
shown in Figure 8/G.961.
FIGURE 8/G.961
Worst-case longitudinal conversion loss versus frequency
3.4.6 Impulse Noise
The DLL will have impulse noise resulting from other systems sharing
the same cable as well as from other sources.
4. System performance
4.1 Performance requirements
Performance limits for the digital section are specified in º 4 of Recom-
mendation G.960. The digital 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.
4.2 Performance measurements
Laboratory performance measurement of a particular digital transmission
system requires the following preparations:
a) definition of a number of DLL models to represent physical and
electrical characteristics encountered in local line distribution
networks;
b) simulation of the electrical environment caused by finite crosstalk
coupling loss to other pairs in the same cable;
c) simulation of the electrical environment caused by impulse noise;
d) specification of laboratory performance tests to verify that the per-
formance limits referred to in section 4.1 will be met.
4.2.1 DLL physical models
For the purposes of laboratory testing of performance of a digital trans-
mission system providing ISDN Basic Access, some models representa-
tive 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 50 dB at 80 kHz to satisfy requirements of the particular
network. Similarly, the lengths of BTs are optionally set within the range
defined in Figure 9/G.961.
FIGURE 9/G.961
DLL physical models for laboratory testing
Note 1 - The value of X varies from 37 to 50 dB at 80 kHz.
Note 2 - Equivalent gauges can be used. For example 0.6mm is equiva-
lent to AWG 22. AWG stands for American Wire Gauge.
4.2.2 Intrasystem crosstalk modelling
4.2.2.1 Definition of intrasystem crosstalk
Crosstalk noise in general results due to finite coupling loss between
pairs sharing the same cable, especially those pairs that are physically
adjacent. Finite coupling loss between pairs causes a vestige of the signal
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. Intra-
system NEXT or self NEXT results when all pairs interfering with each
other in a cable carry the same digital transmission system. Intersystem
NEXT results when pairs carrying different digital transmission systems
interfere with each other. Definition of intersystem NEXT is not part of
this Recommendation.
Intrasystem NEXT noise coupled into a disturbed DLL from a number of
DLL disturbers is represented as being due to an equivalent single dis-
turber DLL with a coupling loss versus frequency characteristic known
as PSL. Worst-case PSL encountered in a local line distribution network
is defined in
Figure 10/G.961. All DLLs are assumed to have fixed resistance termina-
tions of Ro Ohms. The range of Ro is 110 to 150 Ohms.
FIGURE 10.G.961
Worst-case Power Sum Loss (PSL)
4.2.2.2 Measurement arrangement
Simulation of intrasystem NEXT noise is necessary for performance test-
ing of digital transmission systems. Intrasystem noise coupled into the
receiver of the disturbed DLL depends on:
a) Power spectrum of the transmitted digital signal. The power spec-
trum is a function of the line code and the transmit filter;
b) Spectrum shaping due to the PSL characteristic of
Figure 10/G.961.
The measurement arrangement of Figure 11/G.961 can be used for test-
ing of performance with intrasystem crosstalk noise.
FIGURE 11/G.961
Crosstalk Noise Simulation and Testing
The measurement arrangement in Figure 11/G.961 is described in the fol-
lowing:
a) box 1 represents a white noise source of constant spectral density.
Spectrum is flat from 100 Hz to 500 kHz rolling off afterwards
at a rate _ 20 dB/decade;
b) box 2 is a variable attenuator;
c) box 3 is a filter that shapes the power spectrum to correspond to a
particular line code and a particular transmit filter;
d) box 4 is a filter that shapes the power spectrum according to the PSL
characteristic of Figure 10/G.961;
e) box 5 is a noise insertion circuit which couples the simulated
crosstalk noise into the DLL without disturbing its perfor-
mance. The insertion circuit therefore must be of sufficiently
high output impedance relative to the magnitude of the charac-
teristic impedance of the DLL under test. A value _ 4.0 K_ in
the frequency range 0 to 1 000 kHz is recommended.
Boxes 3, 4 and 5 in Figure 11/G.961 are conceptual. Dependent on the
particular realization, they could possibly be combined into one circuit.
The measurement arrangement in Figure 11/G.961 is calibrated accord-
ing to the following steps:
a) by terminating the output of Box 5 with a resistor of a value of Ro/2
Ohm, and measuring the true r.m.s. (root-mean-square) volt-
age across it in a bandwidth extending from 100 Hz to over
500 kHz. The power dissipated in the Ro/2 resistor is 3 dB
higher than the power coupled into the receiver of the DLL
under test;
b) the shape of the noise spectrum measured across the Ro/2 resistor
should be within:
- +1 dB for values within 0 dB to 10 dB down from the theoret-
ical peak;
- +3 dB for values within 10 dB to 20 dB down from the theoretical peak;
for measurement purposes a resolution bandwidth of _ 10 kHz is
recommended;
c) the peak factor of the noise voltage across the Ro/2 resistor should
be _ 4. This in turn fixes the dynamic range requirements of
the circuits used in the measurement arrangement.
With the specified calibrated measurement arrangement, intraystem
crosstalk noise due to a worst-case PSL can be injected into the DLL
under test while monitoring its performance. The noise level can be
increased or decreased to determine positive or negative performance
margins.
4.2.3 Impulse noise modelling
4.2.3.1 Definition of impulse noise
Impulse noise energy appears concentrated in random short time inter-
vals during which it attains substantial levels. For the rest of the time
impulse noise effects are negligible.
4.2.3.2 Measurement arrangement
Figure 12/AB shows a possible arrangement for impulse noise testing.
FIGURE 12/G.961
Impulse Noise Simulation and Testing
The impulse noise source in Figure 12/G.961 is for further study. Two
possible classes of impulse noise signals are described in the following:
- white noise of flat spectral density level of 5-10 ╡V/ Hz and a band-
width > 4 times the Nyquist frequency of the particular sys-
tem. The peak factor of the noise must be > 4;
- a particular waveform, as represented in Figure 13/G.961.
FIGURE 13/G.961
Possible Waveform to Simulate Impulse Noise
Note - In some local line distribution networks and as a national option,
crosstalk noise performance tests are considered sufficient to evaluate a
particular digital transmission system. In such cases proper DLL engi-
neering rules are applied to guard against impulse noise.
4.2.4 Performance tests
Five types of tests are required to describe the overall performance of a
particular digital transmission system to qualify it for operation over the
local line distribution network modelled in this Recommendation.
4.2.4.1 Dynamic range
Dynamic range performance describes the ability of a particular digital
transmission system to operate with received signals varying in level
over a wide range. DLL models 1 and 2 in Figure 9/G.961 have a loss
varying from very low (0 dB) to very high (37 - 50 dB at 80 kHz).
When testing with DLL models 1 and 2 in Figure 9/G.961, no errors
should be observed in any 15 minutes (provisional) measuring interval
when monitoring any B-channel.
Specification of data sequences to be used for this measurement are for
further study.
4.2.4.2 Immunity to echoes
The remaining DLL models in Figure 9/G.961 are used to test perfor-
mance of digital transmission systems in the presence of BTs and/or
diameter changes.
In each model, no errors should be observed in any 15 minutes (provi-
sional) measuring interval when monitoring any B-channel.
Specification of data sequences to be used for this measurement are for-
further study.
4.2.4.3 Intrasystem crosstalk
Using the crosstalk arrangement described in section 4.2.2.2 with simu-
lated crosstalk noise injected in each DLL model in Figure 9/G.961 the
observed bit error ratio (BER) should be _ 10-6 (provisional).
When BER measurements are performed in a B-channel, a measuring
interval of at least 15 minutes (provisional) is required.
In each DLL model, performance margins are determined. Definition of a
minimum positive performance margin is left for further study. This is
required to account for additional DLL loss due to splices, and environ-
mental effects (e.g. temperature change).
Specification of data sequences to be used for this measurement are for
further study.
4.2.4.4 Impulse noise
For further study.
4.2.4.5 Longitudinal Voltages Induced from Power Lines
For further study.
5. Transmission method
The transmission system provides for duplex transmission on 2-wire
metallic local lines. Duplex transmission shall be achieved through the
use of ECHO CANCELLATION (ECH) or TIME COMPRESSION
MULTIPLEX (TCM). With the
ECH method, illustrated in Figure 14/G.961, the echo canceller produces
a replica of the echo of the transmitted signal that is subtracted from the
total received signal. The echo is the result of imperfect balance of the
hybrid and impedance discontinuities in the line.
With the TCM or "burst mode" method, illustrated in Figure 15/G.961,
transmissions on the DLL are separated in time (bursts). Blocks of bits
(bursts) are sent alternatively in each direction. Bursts are passed through
buffers at each transceiver terminal such that the bit stream at the input
and output of the TCM transceiver terminal is continuous at the rate R.
The bit rate on the line is required to be greater than 2R to provide for an
idle interval between bursts which is necessary to allow for the transmis-
sion delay and transmitter/receiver turn around (switching of Sn and SR
in Figure 15/G.961.
6. Activation/deactivation
6.1 General
The functional capabilities of the activation/deactivation procedure are
specified in Recommendation G.960. The transmission system has to
meet
the requirements specified in Recommendation G.960. In particular, it
has to make provision to convey the signals defined in Recommendation
G.960 which are required for the support of the procedures.
6.2 Physical Representation of Signals
The signals used in the digital transmission system are system dependent
and can be found in Annex A and in the Appendices to this Recommen-
dation.
7. Operation and Maintenance
7.1 Operation and Maintenance Functions
The operation and maintenance functions in the digital transmission sys-
tem using metallic local lines for the ISDN basic rate access, are defined
in Recommendation G.960.
7.2 CL Channel
7.2.1 CL-Channel Definition
This channel is conveyed by the digital transmission system in both
directions between LT and NT1. It is used to transfer information con-
cerning operation, maintenance and activation/deactivation of the digital
transmission system and of the digital section.
7.2.2 CL-Channel Requirements
For further study.
The minimum number of functions (optional or mandatory) the CL chan-
nel should support is for further study.
7.3 Transfer Mode of Operation and Maintenance Links
For further study.
8. Power Feeding
8.1 General
This section deals with power feeding of the NT1, one regenerator (if
required), and the provision of power to the user-network interface
according to Recommendation I.430 under normal and restricted condi-
tions.
When activation/deactivation procedures are applied, power down modes
at the NT1, regenerator (if required) and the LT are defined.
8.2 Power Feeding Options
Power feeding options under normal and restricted conditions are consid-
ered. For this purpose, a restricted condition is entered after failure of AC
mains power at the NT1 location.
a) Power feeding of NT1 under normal conditions will be provided
using one of the following options:
- AC mains powering;
- remote powering from the network (or via a regenerator, if
required).
In both cases the NT1 may provide power to the user-network inter-
faceaccording to Recommendation I.430. This power is
derived from AC mains or remotely from the network.
b) Power feeding of NT1 under restricted conditions, when provided,
employs one of the following optional sources:
- back-up battery;
- Remote powering from the network (or via a regenerator, if
required).
In both cases the NT1 may provide power to the user-network inter-
face according to Recommendation I.430.
Power feeding options are chosen to satisfy national regulations.
8.3 Power Feeding and Recovery Methods
Two power feeding and recovery methods are possible and are described
in Figure 16/G.961.
When no regenerator is present on the DLL connecting the LT and the
NT1, for each case in Figure 16/G.961 the power source could be either a
constant voltage source with current limiting or a constant current source
with voltage limiting.
When a regenerator is present, both methods of power feeding and recov-
ery in Figure 16/G.961 remain applicable. However, when a constant
voltage source is used at the LT, the regenerator power sink is connected
in parallel to the DLLs and when a constant current source is used at the
LT, the regenerator power sink is connected in series with the DLLs. The
resulting configurations are shown in Figure 17/G.961.
8.4 DLL Resistance
This parameter is a particular subject of the individual local network and
therefore out of the scope of this Recommendation. Its maximum value
depends on the LT output voltage, the power consumption of the NT1
and regenerator (if required) and the power feeding arrangement for the
user-network interface.
8.5 Wetting Current
The NT1 shall provide a DC termination to allow a minimum wetting
current to flow (the value has to be defined) including the power down
mode or in case of local power feeding of the NT1.
8.6 LT Aspects
A current limitation for voltage source configuration or a voltage limita-
tion for current source configuration is required. The values shall take
into account the relevant IEC Publications and national safety regula-
tions.
Short-term overload of the feeding current may be tolerated (charging
condition of the capacitor of DC/DC converter in NT1).
8.7 Power Requirements of NT1 and Regenerator
8.7.1 Power Requirements of NT1
a) active state without powering of user-network interface: to be
defined;
b) active state including restricted powering of the user-network inter-
face as defined in Recommendation I.430: to be defined;
c) active state including normal powering of user-network interface as
defined in Recommendation I.430: to be defined;
d) power down mode: to be defined.
8.7.2 Power Requirements of Regenerator
For further study.
8.8 Current Transient Limitation
The rate of change of current drawn by the NT1 or regenerator from the
network shall not exceed X mA/╡s. The value of X is to be defined.
9. Environmental Conditions
9.1 Climatic Conditions
Climatograms applicable to the operation of NT1 and LT equipment in
weather protected and non-weather protected locations can be found in
IECPublication721-3. The choice of classes is under national responsi-
bility.
9.2 Protection
9.2.1 Isolation
Isolation between various points at the NT1 can be identified:
- between line interface and T reference point;
- between line interface or T reference point and AC mains (this is
generally defined in IEC Guide 105 and IEC Publication 950
but the test requirements may be different in various coun-
tries);
- between line interface and the protective ground of AC mains.
9.2.2 Overvoltage Protection
To conform with Recommendations K.12, K.20 for LT.
To conform with Recommendations K.12, K.Y for NT1.
9.3 Electromagnetic Compatibility
9.3.1 Susceptibility, Radiated and Conducted Emission Levels for LT or
NT1 Equipment
This is outside of the scope of this Recommendation. CISPR Publ. 22 and
national regulations have to be considered.
9.3.2 Limitation of the Output Power to the Line
Due to limited longitudinal conversion loss of the line at high frequencies
and the limitation of radiation according to CISPR Publ. 22 and national
regulations, the output power shall be limited. The specific values are
outside the scope of this Recommendation.
ANNEX A
(to Recommendation G.961)
General Structure for an Appendix on Electrical Characteristics
A. Electrical Characteristics
Short general characterization of the digital transmission system.
Note - The content of this Annex is a guideline for the presentation of the
description of the digital transmission systems and is not intended to con-
strain any of the systems which will be included.
A.1 Line Code
For both directions of the transmission the line code is ....
And the coding scheme will be ...
A.2 Symbol Rate
The symbol rate is determined by the line code, the bit rate of the infor-
mation stream and the frame structure. The symbol rate is ...kBaud.
A.2.1 Clock Requirements
A.2.1.1 NT1 Free Running Clock Accuracy
The accuracy of the free running clock in the NT1 shall be ▒ ... ppm.
A.2.1.2 LT Clock Tolerance
The NT1 and LT shall accept a clock accuracy from the ET of ▒ ... ppm.
A.3 Frame Structure
The frame structure contains a frame word, N times (2B+D) and a CL
channel.
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû
ûûûûûû+
_ _ _ _
_ Frame word _ N times (2B+D) _ CL channel _
_ _ _ _
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûû
ûûûûûûûûûû+
A.3.1 Frame Length
The number N of (2B+D) slots in one frame is ...
A.3.2 Bit Allocation in Direction LT-NT1
In Figure A-1/G.931 the bit allocation is given.
Figure A-1/G.931 bit allocation in direction LT-NT1.
A.3.3 Bit Allocation in Direction NT1-LT
In Figure A-2/G.931 the bit allocation is given.
Figure A-2/G.961 bit allocation in direction NT1-LT.
A.4 Frame Word
The frame word is used to allocate bit positions to the 2B+D+CL chan-
nels. It may, however, also be used for other functions.
A.4.1 Frame Word in Direction LT-NT1
The code for the frame word will be ...
A.4.2 Frame Word in Direction NT1-LT
The code for the frame word will be ...
A.5 Frame Alignment Procedure
A.6 Multiframe
To enable bit allocation of the CL channel in more frames next to each
other a multiframe structure may be used. The start of the multiframe is
determined by the frame word. The total number of frames in a multi-
frame is ...
A.6.1 Multiframe Word in Direction NT1-LT
The multiframe will be identified by ...
A.6.2 Multiframe Word in Direction LT-NT1
The multiframe will be identified by ...
A.7 Frame Offset between LT-NT1 and NT1-LT Frames
The NT1 shall synchronize its frame on the frame received in the direc-
tion LT to NT1 and will transmit its frame with an offset.
A.8 CL Channel
A.8.1 Bit rate
A.8.2 Structure
A.8.3 Protocols and Procedures
A.9 Scrambling
Scrambling will be applied on 2B+D channels and the scrambling algo-
rithm shall be as follows:
In direction LT to NT1
In direction NT1 to LT.
A.10 Activation/Deactivation
Description of system activation/deactivation procedure including
options that are supported and options that are not supported.
See also CCITT Recommendation AA, section 5.
A.10.1 Signals used for Activation
A list and definition of the signals used for activation/deactivation
(SIGs).
- signals used for start-up (CL not available)
- bits in CL channel in an already established frame.
A.10.2 Definition of Internal Timers
A.10.3 Description of the Activation Procedure (based on arrow sequence
for the error-free case)
- activation from the network side
- activation from the user side
A.10.4 State transition table NT1 as a function of INFOs, SIGs, internal
timers
The description of loop backs and options supported is given in such a
way, that the minimum implementation may be clearly identified.
A.10.5 State transition table LT as a function of FEs, SIGs, internal timers
The description of loop backs and options supported is given in such a
way, that the minimum implementation may be clearly identified.
A.10.6 Activation times
See CCITT Recommendation AA, ºº 5.5.1 and 5.5.2.
A.11 Jitter
Jitter tolerances are intended to ensure that the limits of CCITT Recom-
mendation I.430 are supported by the jitter limits of the transmission sys-
tem on local lines. The jitter limits given below must be satisfied
regardless of the length of the local line and the inclusion of one regener-
ator, provided that they are covered by the transmission media character-
istics (see section 3). The limits must be met regardless of the bit patterns
in the B, D and CL channels.
A.11.1 NT1 Input Signal Jitter Tolerance
The NT1 shall meet the performance objectives with wander/jitter at the
maximum magnitudes (J1, J2) indicated in Figure A.3/G.961, for single
jitter frequencies in the range of F1 Hz to F3 kHz (F3 = 1/4 F6, F6 = sym-
bol rate frequency), superimposed on the test signal source. The NT1
shall also meet the performance objectives with wander per day of up to
...UI peak-to-peak where the maximum rate of change of phase is ...UI/
hour.
A.11.2 NT1 Output Jitter Limitations
With the wander/jitter as specified in A.11.1 superimposed on the NT1
input signal, the jitter on the transmitted signal on the NT1 towards the
network shall conform to the following:
a) The jitter shall be equal to or less than .... UI peak-to-peak and less
than ...UI r.m.s. when measured with a high-pass filter have a
20 dB/decade roll-off below M.F2 Hz (M _ 1).
b) The jitter in the phase of the output signal relative to the phase of the
input signal (from the network) shall not exceed ....UI peak-to-
peak or ....UI r.m.s. when measured with a band-pass filter
have a 20 dB/decade roll-off above N.F2 Hz (N_2) and a
20dB/decade roll-off below K.Fk (Fk << 1). This requirement
applies with superimposed jitter in the phase of the input sig-
nal as specified in A.11.1 for single frequencies up to F2 Hz.
A.11.3 Test Conditions for Jitter Measurements
Due to bidirectional transmission on the 2-wire and due to severe
intersymbol interference no well defined signal transitions are available
at the NT1 2-wire point.
Note- Two possible solutions are proposed:
a) A test point in the NT1 is provided to measure jitter with an undis-
turbed signal.
b) A standard LT transceiver including an artificial local line is defined
as a test instrument.
A.12 Transmitter Output Characteristics of NT1 and LT
The following specifications apply with a load impedance of ....
A.12.1 Pulse Amplitude
The zero to peak nominal amplitude of the largest pulse shall be ....V and
the tolerance shall be ▒ ....%.
A.12.2 Pulse Shape
The pulse shape shall meet the pulse mask of Figure ....
A.12.3 Signal Power
The average signal power shall be between ....dBm and ....dBm.
A.12.4 Power Spectrum
The upper bound of the power spectral density shall be within the tem-
plate in Figure ....
A.12.5 Transmitter Signal Nonlinearity
This is a measure of the deviations from ideal pulse heights and the indi-
vidual pulse nonlinearity.
The measurement method is for further study.
A.13 Transmitter/Receiver Termination
A.13.1 Impedance
The nominal input/output impedance looking toward the NT1 or LT
respectively shall be ....
A.13.2 Return Loss
The return loss of the impedance shall be greater than shown in the tem-
plate Figure ....
A.13.3 Longitudinal Conversion Loss
The minimum longitudinal conversion loss shall be as follows:
....kHz ....dB
....kHz ....dB
Appendices I to IV
(to Recommendation G.961)
The text of these Appendices has not been included in the final report,
but will be printed in the Blue Book at the appropriate place.
A.14 New Supplements Nos. 35 and 36
Supplement No. 35 - Guidelines concerning the measurement of wander
(Contribution from United States of America, referred to in Recommen-
dations G.812 and G.824.)
Supplement No. 36 - Jitter and wander accumulation in digital networks
(Referred to in Recommendation G.824.)
The text of these supplements has not been included in the final report,
but will be printed in the Blue Book at the appropriate place.
ûûûûûûûûûû
