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4. Recommendation I.431
PRIMARY RATE USER-NETWORK INTERFACE - LAYER 1 SPECIFICATION
1. Introduction
This Recommendation is concerned with the layer 1 electrical, format and channel usage characteristics
of the primary rate user-network interface at the S and T reference points. In this Recommendation, the term
"NT" is used to indicate network terminating layer 1 aspects of NT1 and NT2 functional groups, and the term
"TE" is used to indicate terminal terminating layer 1 aspects of TE1, TA and NT2 functional groups, unless
otherwise indicated. The terminology used in this Recommendation is very specific and not contained in the
relevant terminology Recommendations. Therefore, AnnexE to RecommendationI.430 provides terms and
definitions used in this Recommendation. Interfaces for the 1544kbit/s primary rate and for the 2048 kbit/s
primary rate are described.
It has been an objective that differences between the interface specifications for the two rates be kept to a
minimum.
1.1 Scope and field of application
This specification is applicable to user-network interfaces at 1544kbit/s and 2048kbit/s primary rates for
ISDN channel arrangements as defined in RecommendationI.412.
2. Type of configuration
The type of configuration applies only to the layer 1 characteristics of the interface and does not imply
any constraints on modes of operation at higher layers.
2.1 Point-to-point
The primary rate access will support only the point-to-point configuration.
Point-to-point configuration at layer 1 implies that for each direction only one source (transmitter) and one
sink (receiver) are connected to the interface. The maximum reach of the interface in the point-to-point con-
figuration is limited by the specification for the electrical characteristics of transmitted and received pulses
and the type of interconnecting cable. Some of these characteristics are defined in Recommendation G.703.
2.2 Location of interfaces
The electrical characteristics for both the 1544kbit/s case (_4.1) and the 2048kbit/s case (_5.1) apply at
the interfaces Ia and Ib defined in Figure1/I.431.
Note - Ia and Ib are located at the input/output port of the TE/NT.
FIGURE 1/I.431
Location of interfaces
Examples of functional groups corresponding to TE and NT as used here are given in Recommendation
I.411, item 4.3.
3. Functional characteristics
3.1 Summary of functions (Layer 1)
Note - This power-feeding-function is optional and, if implemented, uses a separate pair of wires in the inter-
face cable.
FIGURE 2/I.431
Functional characteristics
B Channel
This function provides for the bidirectional transmission of independent B Channel signals each having a
bit rate of 64kbit/s as defined in RecommendationI.412.
H0 Channel
This function provides for the bidirectional transmission of independent H0 Channel signals each having
a bit rate of 384kbit/s as defined in RecommendationI.412.
H1 Channels
This function provides for the bidirectional transmission of an
H1 Channel signal having a bit rate of 1536(H11) or 1920(H12)bit/s as defined in RecommendationI.412.
D Channel
This function provides for the bidirectional transmission of one D Channel signal at a bit rate of 64kbit/s
as defined in RecommendationI.412.
Bit timing
This function provides bit (signal element) timing to enable the TE or NT to recover information from the
aggregate bit stream.
Octet timing
This function provides 8kHz timing towards TE or NT for the purpose of enabling an octet structure for
voice coders and for other timing purposes as required.
Frame alignment
This function provides information to enable the TE or NT to recover the time-division multiplexed chan-
nels.
Power feeding
This function provides for the capability to transfer power across the interface towards the NT1.
Maintenance
This function provides information concerning operational or failure conditions of the interface. The net-
work reference configuration activities on primary rate subscriber access is given in RecommendationI.604.
CRC procedure
This function provides for the protection against false framing and may provide for error performance
monitoring of the interface.
3.2 Interchange circuits
Two interchange circuits, one for each direction, are used for the transmission of digital signals. All the
functions listed above, with the possible exception of maintenance, are combined into two composite digital
signals, one for each direction of transmission.
If power feeding via the interface is provided, an additional interchange circuit is used for power feeding.
The two wires of the pairs carrying the digital signal may be reversed if symmetrical wiring is provided.
3.3 Activation/deactivation
The interfaces for the primary rate user-network interface will be active at all times. No activation/deacti-
vation procedures will be applied at the interface. However, to indicate the layer 1 transport capability to
layer2, the same primitive set is used as defined in RecommendationI.430. This provides for a unique appli-
cation of the layer1/layer2 interface as defined in RecommendationsI.420 and I.421 (see _3.4.5). The primi-
tives PH-AR, ▒PH-DR, MPH-DI and MPH-II are not required for this application and, therefore, they are not
used in this Recommendation.
3.4 Operational functions
In this paragraph the term network is used to indicate either:
- NT1, LT and ET functional groups in case of interface at Treference point;
or
- relevant parts of NT2 functional group in case of interface at Sreference point.
The term user side is used to indicate terminal terminating layer1 aspects of TE1, TA and NT2 functional
groups.
3.4.1 Definition of signals at the interface
Signals exchanged between the network and user sides under normal and fault conditions are listed in
Table1/I.431. Further information on these signals is given in _4.7.3 and _5.9.1
TABLE 1/I.431
Signals between the network and user sides
under normal and fault conditions
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| Name | List of the signals |
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| Normal | Operational frame with: |
| operational | - active associated CRC |
| frame | - CRC error information (see RecommendationG.704) |
| | - no defect indication |
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| | Operational frame with: |
| | - active associated CRC |
| R A I | - CRC error information (Note) |
| | - with defect indication (see RecommendationG.704)|
| | (2048 kbit/s systems only) |
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| LOS | No received incoming signal (Loss of signal) |
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| AIS | Continuous stream of ONEs (RecommendationG.803) |
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| CRC error | E bit according to RecommendationG.704, |
| information | Table 4b, set to "ZERO" if CRC block received |
| | with error (2048 kbit/s systems only) |
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Note - The 1544kbit/s systems RAI and CRC-derived error performance information cannot be sent simulta-
neously. Failure conditions may be sectionalized across the interface by obtaining additional information by
means that are for further study.
3.4.2 Definitions of state tables at network and user sides
The user side and network side of the interface have to inform each other on the layer1 states in relation
to the different defects that could be detected.
For that purpose, two state tables are defined, the first one at the user side and the second one at the
network side. States at the user side (Fstates) are defined in _3.4.3 and states at the network side (Gstates)
are defined in _3.4.4. The state tables are defined in _3.4.6.
Defect conditions FC1-FC4 that could occur at the network side or between the network side and user
side are defined in Figure3/I.431. These defect conditions directly affect the F and G states. Information on
these defect conditions are exchanged between the user and network sides in the form of signals defined in
Table1/I.431.
Note 1 - Only stable states needed for operation and maintenance of user and network side of the interface
(system reactions, user and network responsible information) are defined. The transient states relative to the
detections of the CRC error information are not taken into account.
Note 2 - The user does not need to know where a failure is located in the network. The user must be
informed on the availability and the continuity of the layer 1 service.
Note 3 - The user has all information relative to the CRC associated with each direction of its adjacent CRC-
section. The supervision of the quality of this section is the user's responsibility.
FIGURE 3/I.431
Location of fault conditions (FC) relative to interface
3.4.3 Layer 1 states on the user side of the interface
F0 STATE: Loss of power on the user side:
In general, the TE can neither transmit nor receive signals.
F1 STATE: Operational state:
- the network clock and layer 1 service is available;
- the user side transmits and receives operational frames with associated CRC and with temporary
CRC error information (Note1);
- the user side checks the received frames and the associated CRC, and generates towards the
network operational frames containing the CRC error information, if a CRC error is detected.
F2 STATE: Fault condition No. 1:
- this fault state corresponds to the fault condition FC1;
- the network clock is available at the user side;
- the user side receives operational frames with associated CRC and with temporary CRC error
information (Note1);
- the received frames contain RAI;
- the user side transmits operational frames with associated CRC;
- the user side checks the received frames and the associated CRC and transmits to the network
side operational frames containing the CRC error information, if a CRC error is detected.
F3 STATE: Fault condition No. 2:
- this fault state corresponds to the fault condition FC2;
- the network clock is not available at the user side;
- the user side detects loss of incoming signal (this will involve loss of frame alignment);
- the user side transmits operational frames with associated CRC and RAI (Note3).
F4 STATE: Fault condition No.3:
- this fault state corresponds to fault condition FC3;
- the network clock is not available at the user side;
- the user side detects AIS;
- the user side transmits towards the network operational frames with associated CRC and RAI
(Note3).
F5 STATE: Fault condition No.4:
- this fault state corresponds to the fault condition FC4;
- the network clock is available at the user side;
- the user side receives operational frames with continuous CRC error information (optional) (Note
2);
- the received frames contain RAI;
- the user side transmits operational frames with associated CRC;
- the user side checks the received frames and the associated CRC which may generate to the net-
work side operational frames containing the CRC error information if a CRC error is detected.
F6 STATE: Power on state:
This is a transient state and the user side may change the state after detection of the signal received.
Note 1 - The interpretation of the CRC error information depends on the option used in the network (see
_5.9.2 and RecommendationI.604).
Note 2 - Only in options2 and 3, as defined in RecommendationI.604, for CRC error information.
Note 3 - The 1544kbit/s systems RAI and CRC - derived error performance information cannot be sent simul-
taneously. Failure conditions may be sectionalized across the interface by obtaining additional information by
means that are for further study.
3.4.4 Layer 1 states at the network side of the interface
GO STATE: Loss of power in the NT1:
In general, the NT1 can neither transmit nor receive any signal.
G1 STATE: Operational state:
- the network clock and layer 1 service is available;
- the network side transmits and receives operational frames with associated CRC and temporary
CRC error information;
- the network side checks the received frames and the associated CRC and generates towards the
user side the CRC error information if a CRC error is detected.
G2 STATE: Fault condition No.1:
- this fault state corresponds to the fault condition FC1;
- the network clock is provided to the user side;
- the network side receives operational frames with associated CRC;
- the network side transmits operational frames with associated CRC and RAI. The operational
frames may contain CRC error information (Note1).
G3 STATE: Fault condition No.2:
- this fault state corresponds to the fault condition FC2;
- the network clock is not provided to the user side;
- the network side transmits operational frames with associated CRC;
- the network side receives operational frames with associated CRC and RAI (Note3).
G4 STATE: Fault condition No.3:
- this fault state corresponds to the fault condition FC3;
- the network clock is not provided to the user side;
- the network side transmits AIS;
- the network side receives operational frames with associated CRC and RAI (Note3).
G5 STATE: Fault condition No.4:
- this fault states corresponds to the fault condition FC4;
- the network clock is provided to the user side;
- the network side detects loss of incoming signal or loss of frame alignment;
- the network side transmits operational frames with associated CRC and RAI and continuous CRC
error information (Notes2 and 3).
G6 STATE: Power on state:
This is a transient state and the network side may change the state after detection of the signal received.
Note 1 - The interpretation of the CRC error information depends on the option used in the network (see
_5.9.2 and RecommendationI.604).
Note 2 - Only in options2 and 3, as defined in RecommendationI.604 for CRC error information.
Note 3 - In 1544kbit/s systems RAI and CRC - derived error performance information cannot be sent simulta-
neously. Failure conditions may be sectionalized across the interface by obtaining additional information by
means that are for further study.
3.4.5 Definition of primitive
The following primitives should be used between layers 1 and 2 (PH) or between layer 1 and the man-
agement entity (MPH).
PH AI - PH Activate indication
PH DI - PH Deactivate Indication
MPH AI - MPH Activate Indication (is used as error recovery and initialization information)
MPH EIn - MPH Error Indication with Parameter
n - Parameter which defines the failure condition
relevant to the reported error
3.4.6 State tables
Operational functions are defined in Table 2/I.431 for the layer 1 states at the user side of the interface
and in Table 3/I.431 for the network side. The exact reaction in case of double faults may depend on the type
of double fault condition and the sequence in which they occur.
TABLE 2/I.431
Primary rate layer 1 state matrix at
user side of the interface
PA-AI = PH Activate Indication
PH-DI = PH Deactivate Indication
MPH-EIn = MPH error Indication with parameter n (n = 0 to 4)
Note 1 - These events cover different network options. The network options2 and 3 (see Recommenda-
tionI.604) of the 2048kbit/s system (which include CRC processing in the digital transmission link) provide
CRC-error information which allows the user side equipment to localize a fault indicated by means of RAI to
either:
i) network side (FC1), if frames without continuous CRC-error reports are received; or
ii) the user side (FC4), if frames with continuous CRC-error reports are received.
If network options other than 2 and 3 of the 2048kbit/s system apply, the faults FC1 and FC4 are indi-
cated identically at the interface, therefore, the signal "RAI with continuous CRC error report" does not occur.
Note 2 - These states cover two user options:
i) If a TE adopting the option to distinguish between F2 and F5 (given by options2 and 3 of 2048kbit/
s interfaces only) is used, but the network does not provide the distinction (see Note1), then signal "RAI
with continuous CRC error report" will not occur and the TE always enters state F2 on receipt of RAI;
ii) The user option not processing CRC-error information when accompanied with RAI, even if pro-
vided, merges statesF2 and F5.
TABLE 3/I.431
Primary rate layer 1 state matrix at network side of the interface
PH-AI = PH Activate Indication
PH-DI = PH Deactivate Indication
MPH-EIn = MPH Error Indication with parameter n (n = Q to 4)
Note 1 - In the case of no CRC processing in the digital link, the stateG5 is identical to stateG2.
Note 2 - In options 2 and 3 of the 2048 kbit/s systems, the RAI signal must contain CRC error information of
the section between TE and NT which can be used by the user to localize faults FC1 and FC4. In option 1
the faults FC1 and FC4 are indicated identical at the interface (see _5.9).
*The issue of this primitive depends on the capability of the digital transmission system and the option used
in the network.
4. Interface at 1544 kbit/s
4.1 Electrical characteristics
4.1.1 Bit rate
The signal shall have a bit rate of 1544kbit/s ▒ 50 parts per million(ppm).
4.1.2 Interchange circuit medium
One symmetric metallic pair shall be used for each direction of transmission.
4.1.3 Code
The B8ZS code is recommended (see Note1 under Table4/I.431 for definition of B8ZS code).
4.1.4 Specifications at the output ports
4.1.4.1 Test load
Test load impedance shall be 100 ohms, resistive.
4.1.4.2 Pulse mask
An isolated pulse measured at interfaces Ia or Ib defined in Figure1/I.431 shall have an amplitude
between 2.4 and 3.6Volts measured at the centre of the pulse.
A possible normalized pulse mask is shown in FigureI.1/I.431 (Appendix1). This pulse mask is for further
study.
An isolated pulse shall satisfy the requirements set out in Table4/I.431.
TABLE 4/I.431
Digital interface at 1544 kbit/s
Note 1 - B8ZS is a modified AMI code in which eight consecutive zeros are replaced with 000 + - 0 - + if the
preceding pulse was positive (+) : 000 - + 0 + - if the preceding pulse was negative (-).
Note 2 - The signal level is the power level measured in a 3kHz bandwidth at the output port for an all 1s pat-
tern transmitted.
4.1.4.3 Voltage of zero
The voltage within a time slot containing a zero (space) shall be no greater than either the value pro-
duced in that time slot by other pulses (marks) within the mask of Figure I-1/I.431 or ▒ 5% of the zero-to-
peak pulse (mark) amplitude, whichever is greater in magnitude.
4.1.5 Specifications at the input ports
The digital signal presented at the input port shall be as defined above but modified by the characteristic
of the interconnecting pair. The attenuation of this pair shall be assumed to follow a ╨f law and the loss at a
frequency of 772kHz shall be in the range 0 to 6dB.
4.2 Frame structure
4.2.1 The frame structure is based on Recommendation G.704, __3.1.1 and 3.1.2 and is shown in Figure4/
I.431.
FIGURE 4/I.431
Frame structure of 1544 kbit/s interface
4.2.2 Each frame is 193bits long and consists of an F-bit followed by 24 consecutive time slots, numbered 1
to 24.
4.2.3 Each time slot consists of eight consecutive bits, numbered 1 to 8.
4.2.4 The frame repetition rate is 8000 frames/s.
4.2.5 The multi-frame structure is shown in Table5/I.431. Each multi-frame is 24 frames long and is defined
by the multi-frame alignment signal (FAS) which is formed by every fourth F-bit and has the binary pattern
(....001011...)
4.2.6 The bits e1 to e6 in Table 5/I.431 are used for error checking, as described in _2.1.3.1.2 of Recommen-
dation G.704. A valid error check by the receiver is an indication of transmission quality and of the absence
of false frame alignment (see _4.6.3 of this Recommendation).
TABLE 5/I.431
Multi-frame structure
Note 1 - With the exception of _4.7.3 the use of the m bit/s is for further study (for example, for maintenance
and operational information).
4.3 Timing considerations
This paragraph describes the hierarchical synchronization method selected for synchronizing ISDNs. It is
based upon consideration of satisfactory customer service, ease of maintenance, administration and mini-
mizing cost.
The NT derives its timing from the network clock. The TE synchronizes its timing (bit, octet, framing) from
the signal received from the NT and synchronizes accordingly its transmitted signal.
4.4 Time slot assignment
4.4.1 D Channel
Time slot24 is assigned to the D Channel when this channel is present.
4.4.2 B channel and H channels
A channel occupies an integer number of time slots and the same time slot positions in every frame. A
BChannel may be assigned any time slot in the frame, an H0Channel may be assigned any six slots in the
frame, in numerical order (not necessarily consecutive), and an H11Channel may be assigned slots1 to 24 in
a frame. The assignment may vary on a call by call basis (see Note). Mechanisms for the assignment of
these slots for a call are specified in RecommendationI.451.
Note - For an interim period, a fixed time slot allocation to form channels may be required. An example of a
fixed assignment of slots for the case where only H0 channels are present at the interface is given in
AnnexA.
4.5 Jitter
4.5.1 Timing jitter
Timing jitter is specified as follows.
4.5.1.1 Tolerable jitter at TE input
A TE shall tolerate a sinusoidal input jitter according to the amplitude-frequency characteristic of Figure5/
I.431 without producing biterrors or losing frame alignment.
A1 : 5.0UI
A2 : 0.1UI
f1 : 120Hz
f2 : 6kHz
UI : Unit interval (648ns)
FIGURE 5/I.431
Tolerable TE input jitter characteristic
4.5.1.2 TE output jitter
With no jitter on the TE input signal that provides timing, jitter at the TE output shall not exceed the follow-
ing two limitations simultaneously:
i) Band1 (10Hz - 40kHz) : 0.5 UI (Unit Interval) peak-to-peak
ii) Band2 (8kHz - 40kHz) : 0.07 UI peak-to-peak
4.5.2 Wander
Wander is specified for frequencies below 10Hz.
4.5.2.1 Signal from the network side
Wander shall not exceed 5 UI peak-to-peak in any 15 minute interval and shall not exceed 28 UI peak-to-
peak within a period of 24 hours.
4.5.2.2 Signal from the user side
Wander shall not exceed 5 UI peak-to-peak in any 15 minute interval and shall not exceed 28 UI peak-to-
peak within a period of 24 hours.
4.6 Interface procedures
4.6.1 Codes for idle channels and idle slots
The pattern including at least three binary ONEs in an octet must be transmitted on every time slot that is
not assigned to a channel (e.g. time slots awaiting channel assignment on a per-call basis, residual slots on
an interface that is not fully provisioned, etc.), and on every time slot of a channel that is not allocated to a
call in both directions.
4.6.2 Interframe (layer 2) timefill
Contiguous HDLC flags shall be transmitted on the D Channel when its layer 2 has no frames to send.
4.6.3 Frame alignment and CRC-6 procedure
The frame alignment and CRC-6 procedures shall be in accordance with RecommendationG.706 _2.
4.7 Maintenance
4.7.1 General introduction
RecommendationI.604 specifies an overall approach to be employed in maintaining ISDN primary rate
access. However, since the required maintenance functions may influence the design of terminating pieces
of equipment, a brief description of primary rate access maintenance is presented in this Recommendation.
4.7.2. Maintenance functions
The interface divides maintenance responsibility between network and user sides.
Specified maintenance functions are as follows:
a) Supervision of layer1 capability and reporting across the interface, which includes, on the user
side, reporting loss of incoming signal or loss of frame alignment from the network side.
On the network side, reporting loss of layer1 capability and the incoming signal or frame alignment
from the user side, are included.
b) CRC performance monitoring and reporting across the interface. (This function is specified in
_4.7.4.)
c) Other maintenance functions are for further study.
4.7.3 Definition of maintenance signals at the interface
The RAI (Remote Alarm Indication) signal indicates loss of layer1 capability at the user-network interface.
RAI propagates towards the network if layer1 capability is lost in the direction of the user, and RAI propa-
gates toward the user if layer1 capability is lost in the direction of the network. RAI is coded as continuously
repeated 16-bit sequences of eightbinary ONEs and eightbinary ZEROs (1111111100000000) in the mbit.
(Note - HDLC flag patterns (01111110) are transmitted in the mbits when no information signal is to be sent.)
The AIS (Alarm Indication Signal) is used to indicate loss of layer1 capability in the ET-to-TE direction on
the network side of the user-network interface. A characteristic of AIS is that its presence indicates that the
clock provided to the TE may not be the network clock. AIS is coded as a binary all ONEs, 1544kbit/s bit
stream.
In leased line circuit applications with no DChannel, some channel- associated layer maintenance mes-
sages may need to be transferred across the interface. These maintenance messages would be transported
in the mbit. Further characteristics of these messages are for further study.
4.7.4 CRC-6 in-service performance monitoring and reporting
Messages in the mbit that exercise CRC-6 performance monitoring capabilities can be used to sectional-
ize troubles in the primary rate access. This sectionalization could be accomplished from either the NT or the
TE. Characteristics of these maintenance messages are for further study.
5. Interface at 2048 kbit/s
5.1 Electrical characteristics
This interface should conform to RecommendationG.703, _6, which recommends the basic electrical
characteristics.
Note - The use of the unbalanced 75ohm (coaxial) interface is required by some administrations in the short
term. However, the balanced 120ohm (symmetric pair) interface is preferred for the ISDN primary rate appli-
cation.
5.2 Frame structure
5.2.1 Number of bits per time slot
Eight, numbered from 1 to 8.
5.2.2 Number of time slots per frame
Thirty-two, numbered from 0 to 31. The number of bits per frame is 256 and the frame repetition rate is
8000frames/s.
5.2.3 Assignment of bits in time slot 0
The bits of time slot0 are in accordance with RecommendationG.704, _2.3.2. The Ebits are assigned to
the CRC error information procedures.
Sa bits with bit position 4 and 8 are reserved for international standardization and shall be ignored by the
TE for the time being. Sa bits with position5,6,7: are reserved for national use. The terminals not making use
of these bits shall ignore any received pattern.
5.2.4 Time slot assignment
5.2.4.1 Frame alignment signal
Time slot0 provides for frame alignment in accordance with _5.2.3.
5.2.4.2 DChannel
Time slot16 is assigned to the DChannel when this channel is present. The assignment of time slot16
when not used for a DChannel is for further study.
5.2.4.3 BChannel and HChannels
A channel occupies an integer number of time slots and the same time slot positions in every frame.
A BChannel may be assigned any time slot in the frame and an H0Channel may be assigned any six
slots, in numerical order, not necessarily consecutive (Note1).
The assignment may vary on a call by call basis (Note 2). Mechanisms for the assignment of these slots
for a call are specified in RecommendationI.451.
An H12Channel shall be assigned time slots 1 to 15 and 17 to 31 in a frame and an H11Channel may be
assigned time slots as in the example given in AnnexB.
Note 1 - In any case time slot16 should be kept free for DChannel utilization.
Note 2 - For an interim period, a fixed time slot allocation to form channels may be required. Examples of a
fixed assignment of slots for the case where only H0Channels are present at the interface are given in
AnnexA.
5.2.4.4 Bit sequence independent
Time slots1 to 31 provide bit sequence independent transmission.
5.3 Timing considerations
The NT derives its timing clock from the network clock. The TE synchronizes its timing (bit, octet, framing)
from the signal received from the NT and synchronizes accordingly the transmitted signal.
In an unsynchronized condition (e.g. when the access that normally provides network timing is unavail-
able) the frequency deviation of the free- running clock shall not exceed ▒50ppm.
5.4 Jitter
5.4.1 General considerations
The jitter specifications take into account subscriber configurations with only one access and configura-
tions with multiple accesses.
In the case of one access only, this may be to a network with transmission systems of either highQ or
lowQ clock recovery circuits.
In the case of multiple accesses, all access transmission systems may be of the same kind (either lowQ
or highQ clock recovery circuits) or they may be of different kinds (some with highQ and some with lowQ
clock recovery circuits).
Examples of single and multiple accesses are given in Figure6/I.431.
The reference signal for the jitter measurement is derived from the network clock. The nominal value for
1UI is 488ns.
FIGURE 6/I.431
Examples of single and multiple accesses
5.4.2 Minimum tolerance to jitter and wander at TE inputs
The 2048kbit/s inputs of a TE shall tolerate sinusoidal input jitter/wander in accordance with Figure7/I.431
without producing bit errors or losing frame alignment.
+ûûûûûûûûû+ûûûûûûûû+ûûûûûûûû+ûûûûûûûûûû+ûûûûûûû+ûûûûûûû+ûûûûûûû+ûûûûûûûû+
| A0 | A1 | A2 | f0 | f1 | f2 | f3 | f4 |
+ûûûûûûûûû+ûûûûûûûû+ûûûûûûûû+ûûûûûûûûûû+ûûûûûûû+ûûûûûûû+ûûûûûûû+ûûûûûûûû|
| Note 1 | Note 2 | | | | | | |
| 20.5 UI | 1.0 UI | 0.2 UI |12x10-6 Hz| 20 Hz |3.6 kHz|18 kHz |100 kHz |
+ûûûûûûûûû+ûûûûûûûû+ûûûûûûûû+ûûûûûûûûûû+ûûûûûûû+ûûûûûûû+ûûûûûûû+ûûûûûûûû+
Note 1 - Jitter/wander (MRTIE - Maximum Relative Time Interval Error) as defined in Recommenda-
tionG.812.
Note 2 - TEs for multipurpose application (i.e., also to private circuit run by public telecommunications opera-
tor) a jitter tolerance of 1.5 (with corresponding f2 at 2.4kHz) may be required.
FIGURE 7/I.431
Minimum Tolerable jitter and wander at TE input
5.4.3 TE and NT2 output jitter
Two cases must be considered:
5.4.3.1 TE and NT2 with only one user-network interface
a) With no jitter at the input supplying timing or in the running mode, the TE output jitter shall be in
accordance with the table below:
+ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûû+
| Measurement Filter bandwidth: | Output jitter: |
+ûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûû+ |
| Lower Cutoff | Upper Cutoff | UI Peak-to-peak |
+ûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûû+
| 20 Hz | 100 kHz | ≡ 0.125 UI |
| 700 Hz | 100 kHz | ≡ 0.02 UI |
+ûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûû+
b) With jitter present at the input supplying timing, the output jitter is the sum of the intrinsic jitter of
the TE plus the input jitter multiplied with the jitter transfer characteristics.
The jitter transfer characteristics shall conform to Figure8/I.431:
+ûûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+
| y | x | fa | fb | fc | fd |
+ûûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+
|-19.5 dB | 0.5 dB | 10 Hz | 40 Hz | 400 Hz | 100 kHz |
+ûûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûû+
FIGURE 8/I.431
Jitter transfer characteristics
5.4.3.2 TE with more than one user-network interface to the same network.
a) With no jitter at the input (or inputs) supplying timing or in the free running mode see _5.4.3.1 a).
b) In the multi-access case the output jitter depends on:
- the input jitter of each access;
- the transfer characteristic;
- the timing extraction and distribution concept;
- the future growth of the TE. Since the timing extraction and distribution concept of the TE is
out of the scope of this Recommendation the output jitter at each individual access can be
controlled only by the definition of the appropriate jitter transfer characteristic in the TE.
In order to restrict the output jitter to tolerable values and to simplify testing, the jitter transfer
characteristic between any receiver and its associated transmitter shall be tested to the transfer
characteristic given in Figure8/I.431 and the following parameters:
+ûûûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûûûûûû+ûûûûûûûûû+ûûûûûûû+ûûûûûûûûû+
| y | x | fa | fb | fc | fd |
+ûûûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûûûûûû+ûûûûûûûûû+ûûûûûûû+ûûûûûûûûû+
| -19.8dB | 0.2dB | not to be | 0.1Hz | 1Hz | 100kHz |
| | | defined | | | |
| | | | | | |
+ûûûûûûûûûûû+ûûûûûûûûû+ûûûûûûûûûûûûû+ûûûûûûûûû+ûûûûûûû+ûûûûûûûûû+
5.5 Tolerable longitudinal voltage
Minimum tolerance to longitudinal voltage at input ports.
The receiver shall operate without errors with any valid input signal in the presence of a longitu-
dinal voltage VL.
VL = 2 Vrms over frequency range 10Hz to 30MHz.
The test configuration is given in Figure9/I.431.
Note - The inherent longitudinal conversion loss of the T-balancing network should be 20dB better
than required at the interface under test (see Recommendation0.121).
FIGURE 9/I.431
Test of tolerance to longitudinal voltage
5.6 Output signal balance
Output signal balance, which is measured in accordance with Recommendation0.121, _2.7,
shall meet the following requirements:
a) f = 1MHz : è 40dB
b) 1MHz < f ≡ 30MHz: minimum value decreasing from 40dB at 20dB/decade.
5.7 Impedance towards ground
The impedance towards ground of both the receiver input and the transmitter output shall meet
the following requirements:
10Hz < f ≡ 1MHz: > 1000Ohm
This requirement is met if the test according to Figure10/I.431 results in a voltage Vtest ≡
20mVrms.
FIGURE10/I.431
Test of minimum impedance towards ground
5.8 Interface procedures
5.8.1 Codes for idle channels and idle slots
The pattern including at least three binary ONEs in an octet must be transmitted on every time
slot that is not assigned to a channel (e.g. time slots awaiting channel assignment on a per-call
basis, residual slots on an interface that is not fully provisioned, etc.), and on every time slot of a
channel that is not allocated to a call in both directions.
5.8.2 Interframe (layer 2) time fill
Contiguous HDLC flags will be transmitted on the DChannel when its layer2 has no frames to
send.
5.8.3 Frame alignment and CRC-4 procedures
The frame alignment and CRC procedures shall be in accordance with RecommendationG.706, _4.
5.9 Maintenance at the interface
The network reference configuration for the maintenance activities on primary rate subscriber
access is given in RecommendationI.604.
The associated maintenance procedure, which is described there, needs a continuous supervision
procedure on layer 1 for the automatic fault detection, automatic failure confirmation and information.
Note - The terms anomaly, defect, fault, and failure are defined in RecommendationM.20.
5.9.1 Definitions of maintenance signals
The RAI (Remote Alarm Indication) signal indicates loss of layer1 capability at the user-network
interface. RAI propagates towards the network if layer1 capability is lost in the direction of the user, and
RAI propagates toward the user if layer 1 capability is lost in the direction of the network. RAI is coded
in bit A, i.e. bit 3 of time slot 0 of the operational frame which does not contain the frame alignment sig-
nal (see Table4b/G.704).
RAI - A-bit set to 1
No RAI - A-bit set to 0
The AIS (Alarm Indication Signal) is used to indicate loss of layer1 capability in the ET-to-TE direc-
tion on the network side of the user-network interface. A characteristic of AIS is that its presence indi-
cates that the clock provided to the TE may not be the network clock. AIS is coded as a binary all
ONEs, 2048kbit/s bit stream.
The CRC error information: Ebit in time slot0 of operational frames not containing the frame align-
ment signal.
5.9.2 Use of CRC procedure
5.9.2.1 Introduction
At the user-network interface the CRC procedure according to RecommendationsG.704 and G.706
is applied to gain security in frame alignment and detect block errors. The CRC error information uses
the Ebits as defined in Table4b of RecommendationG.704, the coding is E="0" for block with failure and
E="1" for block without failure. With respect to CRC error information to the other side of the interface
and processing of this information two different options exist, the one has CRC processing in the trans-
mission link and the other not.
The use of CRC procedure at the user-network interface involves:
i) that the user side shall generate towards the interface a 2048kbit/s frame with associated
CRC procedure;
ii) that the network side shall generate towards the interface a 2048kbit/s frame with associated
CRC procedure;
iii) that the user side shall monitor the CRC procedure associated to the received frames (CRC
codes calculation and comparison with received CRC codes);
iv) that the user side shall detect the CRC blocks received with error;
v) that the user side shall generate the CRC error information according with the CRC proce-
dure;
vi) that the network side shall monitor the CRC procedure associated to the received frames;
vii) that the network side shall detect the CRC blocks received with error;
viii) that the network side shall generate the CRC error information according with the CRC pro-
cedure;
ix) that the network side shall detect the CRC error information and to process all the received
information according with RecommendationI.604.
5.9.2.2 Localization of the CRC functions in the subscriber access from the user point of view.
5.9.2.2.1No CRC processing in the transmission link
Figure11/I.431 gives the locations of the CRC function processes in a subscriber access without
CRC processing in the transmission link.
LEGEND:
G = CRC generator L = Local "CRC error" information
M = CRC monitor R = Remote "CRC error" information
- = Mandatory .... = Optional
FIGURE11/I.431
Localization of CRC processing functions for a subscriber access
when the transmission link does not process the CRC
5.9.2.2.2 CRC processing in the digital transmission link
Figure 12/I.431 gives the locations of CRC function processes in a subscriber access with CRC pro-
cessing in the NT.
LEGEND:
G = CRC generator L = Local "CRC error" information
M = CRC monitor R = Remote "CRC error" information
- = Mandatory .... = Optional
Note - The processing of remote CRC error information provides enhanced defect localization from the
user point of view.
FIGURE 12/I.431
Localization of CRC processing function for a subscriber access
with CRC processing in the digital transmission link
5.9.3 Maintenance Functions
5.9.3.1 General requirements
The equipments located on the user side and on the network side of the interface shall:
- detect the anomalies;
- detect the defects;
- take actions for reporting the detected anomalies and defects (defect indication signals AIS,
RAI,....);
- detect the received defect indication signals.
5.9.3.2 Maintenance functions on the user side
5.9.3.2.1 Anomalies and defect detection
The user side shall detect the following defects or anomalies:
- loss of power on the user side;
- loss of incoming signal at interface (see Note);
- loss of frame alignment (see RecommendationG.706);
- CRC error.
Note - The detection of this defect is required only when it has not the effect of a loss of frame align-
ment indication.
5.9.3.2.2 Detection of defect indication signals
The following defect indications received at interface shall be detected by the user side:
- remote alarm indication (RAI) (Note);
- alarm indication signal (AIS).
Note - The RAI signal is used to indicate loss of layer1 capability. It may be used to indicate:
- loss of signal or loss of framing;
- excessive CRC errors, (optional);
- loopbacks applied in the network.
The conditions of excessive CRC errors are outside the scope of this Recommendation.
5.9.3.2.3 Consequent actions:
Table 6/I.431 gives the actions that the user side (TE function) has to take after the detection of a defect or
of a defect indication signal.
Note 1 - When the defect conditions have disappeared or when the defect indication signals are not received
any more, the defect indications AIS and RAI must disappear as soon as possible.
Note 2 - The following points are required to ensure that an equipment is not removed from service due to
short breaks in transmission:
i) The persistence of an RAI or of an AIS shall be verified for at least 100ms before action is taken;
ii) When an RAI or an AIS disappears, action shall be taken immediately.
TABLE 6/I.431
Defect conditions and indication signals of defect
detected by the user side and consequent actions
+ûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûûûûûûûûûû+
| Defect | Consequent actions |
| conditions and +ûûûûûûûûûûûûûûûûûûûûûûûûûûûûû+
| Defect | Defect indications |
| indication | at the interface |
| signals +ûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| detected by | Generation |Generation of |
| the user side | of RAI |CRC error info|
| | |(see Note 4) |
+ûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Loss of power |Not applicable|Not applicable|
| on user side | | |
+ûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Loss of signal | Yes | Yes |
| | | (see Note 1) |
+ûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Loss of frame | Yes | No |
| alignment | | (see Note2) |
+ûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Reception of RAI| No | No |
| | | |
+ûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Reception of AIS| Yes | No |
| | | (see Note 3) |
+ûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Detection by NT2| No | Yes |
| of CRC errors | | |
+ûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
Note 1 - Only when loss of frame alignment has not yet occurred.
Note 2 - The loss of frame alignment inhibits the process associated with the CRC procedure.
Note 3 - The AIS signal is detected only after the loss of frame alignment fault, so the process associated with
the CRC procedure is inhibited.
Note 4 - If CRC errors are detected in frames carrying the RAI signal then CRC error reports should be gen-
erated.
5.9.3.3 Maintenance functions on the network side
5.9.3.3.1 Defect detection
All the following defect conditions shall be detected by the network side of T interface (NT1, LT, ET func-
tions)(see Note 2):
- loss of power on the network side;
- loss of incoming signal;
- loss of frame alignment (see RecommendationG.706);
- CRC error.
Note 1 - The equipment of the primary rate digital link (NT1, LT,...) have to detect loss of incoming signal and
then to generate downstream towards the interface the fault indication signal AIS.
Note 2 - Some equipment in the network may detect only part of the defects or fault conditions listed above.
5.9.3.3.2 Detection of defect indication signals
The following defect indications received at interface shall be detected by the network side:
- remote alarm indication (RAI);
- CRC error informations.
5.9.3.3.3 Consequent actions
Table7/I.431 gives the actions that the network side (NT1, ET functions) has to take after defect detection
or defect indication detection.
Note 1 - When the defect conditions have disappeared or the defect indication signals are not received any
more, the defect indication signals AIS and RAI should disappear as soon as possible.
Note 2 - The following points are required to ensure that an equipment is not removed from service due to
short breaks in transmission:
i) The persistence of an RAI or of an AIS shall be verified for at least 100ms before action is taken;
ii) When an RAI or an AIS disappears, action shall be taken immediately.
TABLE 7/I.431
Defect conditions and defect indication signals detected by
the network side of interface and consequent actions
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû+
| Defect | Consequent actions |
| conditions +ûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûûû+
| and defect | Defect indications |
| signal | at interface |
| indications +ûûûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| detected by | Generation | Generation |Generation of |
| network side | RAI | AIS |CRC error info|
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Loss of power |Not applicable| Yes |Not applicable|
| on network side | | if possible| |
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Loss of signal | Yes | No | Yes |
| | | | (Note 1) |
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Loss of frame | Yes | No | Option 1: No |
| alignment | | | Option 2: YES|
| | | | (Note 3) |
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Detection of | | | |
| defect in the | No | Yes | No |
| network-to-user | | | |
| direction | | | |
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Reception of RAI | No | No | No |
| | | | (Note 2) |
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Detection of | | | |
| defect in the | Yes | No | No |
| user-to-network | | | |
| direction up to | | | |
| ET | | | |
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Detection of | No | No | Yes |
| CRC errors | | | |
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Reception of | | | |
| CRC error | No | No | No |
| information | | | |
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
| Excessive CRC | Yes | No |Not applicable|
| error rate | (Optional) | | |
+ûûûûûûûûûûûûûûûûûû+ûûûûûûûûûûûûûû+ûûûûûûûûûûûû+ûûûûûûûûûûûûûû+
Note 1 - Only when loss of frame alignment has not yet occurred.
Note 2 - If CRC errors are detected in frames carrying the RAI signal then CRC error reports shall be gener-
ated.
Note 3 - See CCITT RecommendationI.604.
6. Connector
Interface connectors and contact assignments are the subject of ISO and IEC standards. However, per-
manent wiring connections of TEs to NTs are also permitted.
7. Interface wiring
In case of symmetrical wiring, the magnitude of the characteristic impedance of the interface cables shall
be 120ohm ▒ 20% in a frequency range 200kHz to 1MHz and 120ohm ▒ 10% at 1MHz.
For coaxial interfaces, the magnitude of the characteristic impedance of the interface cables shall be
75ohm (▒5% at 1024kHz).
8. Power feeding
8.1 Provision of power
The provision of power to the NT via user network interface using a separate pair of wires to those used
for transmission, is optional.
8.2 Power available at the NT
The power available at NT via the user-network interface, when provided, shall be at least 7Watt.
8.3 Feeding voltage
The feeding voltage for the NT shall be in the range of -32 to -57volt.
The polarity of the voltage towards ground shall be negative.
8.4 Safety requirements
In principle safety requirements are outside the scope of this Recommendation. However, in order to har-
monize power source requirements the following information is provided:
i) the voltage source and the feeding interface should be protected against short circuit or overload.
The specific requirements are for further study;
ii) the power input of NT1 shall not be damaged by an interchange of wires.
With respect to the feeding interface of the power source, which is regarded as a touchable part in the
sense of IEC Publication 950, the protection methods against electric shock specified in IEC Publication 950
may be applied.
Annex A
(to Recommendation I.431)
Time slot assignment for interfaces having only H0 Channels
The following are examples of fixed assignment of time slots when only H0 Channels are present at the
interface.
i) 1544kbit/s interface
*This fourth H0Channel is available if time slot 24 is not used for a
DChannel.
ii) 2048kbit/s interface
Example1
Example2
Note - The time slot assignment in Example2 is the one described in RecommendationG.704 for nx64kbit/s
interface with N =6 and fixed first time slot allocation. It is therefore the preferred assignment.
AnnexB
(to RecommendationI.431)
Time slot assignment for 2048 kbit/s interfaces having H11 Channel
The following is an example of fixed assignment of times slots when H11Channel is present at the inter-
face.
Note - Time slot16 is to be assigned to the DChannel, when this channel is present. Time slots26 to 31 may
be used for H0Channel or six BChannels.
Appendix I/I.431
Pulse mask for interface at 1544kbit/s
An isolated pulse, when scaled by a constant factor, shall fit the pulse mask shown in FigureI-1/I.431.
Note - UI = Unit Interval = 647.7ns
FIGURE I-1/I.431
Pulse mask for interface at 1544 kbit/s