GB/T 11820-1989 Requirements for access to urban optical cable communication systems
Some standard content:
National Standard of the People's Republic of China
GB/T11820—1989
The requirements for urban optical fiber cable systems joined to national public telecommunication network
Published on October 25, 1989
State Administration of Technical Supervision
Implementation on July 1, 1990
National Standard of the People's Republic of China
The requirements for urban optical fiber cable systems joined to national public telecommunication network
network
1 Subject content and scope of application
GB/T11820—1989
This standard specifies the requirements for the entry of the urban optical cable communication system into the national public telecommunications network (hereinafter referred to as the network entry requirements), including the composition and main transmission characteristics of the urban optical cable communication system, the main transmission characteristics and requirements of the digital optical cable line system, the requirements of the optical cable communication system for machine and line equipment, and the reliability requirements and maintenance and use requirements of the system. This standard applies to the optical cable communication system (excluding the user optical cable communication system) of the inter-office relay (including the long-city relay) of the urban telecommunications network. It meets the requirements of open telephone services and non-telephone services such as telegrams, data, fax, and images. The inter-office (station) relay optical cable communication system used in the dedicated telecommunications network can also refer to this standard. 2 Reference standards
GB4110 Pulse code modulation communication system series GB687920 48kbit/s 30-channel pulse code modulation multiplexing equipment technical requirements GB72548 448kbit/s positive code rate adjustment sub-group digital multiplexing equipment technical requirements GB7611 Pulse code modulation communication system network digital interface parameters GB9405.134368kbit/s positive code rate adjustment tertiary group digital multiplexing equipment technical requirements 3 Composition and main transmission characteristics of optical cable communication system 3.1 Assumed reference digital link (channel)
The length of the assumed reference digital link of this system is set to 100km, consisting of two 50km assumed reference digital segments. 3.2 System sub-group digital series
The digital signal bit rate level in this system complies with the provisions of GB4110. 3.3 Wavelength selection
Mainly uses the 1300nm wavelength region.
3.4 Fiber Selection
Select single-mode or multi-mode (gradient) fiber.
3.5 General System Structure and Interface Location
The urban optical cable communication system consists of PCM and digital multiplexing equipment and digital optical cable line system. Taking the third-group optical cable communication system as an example, the system structure block diagram in one transmission direction is shown in Figure 1. The system adopts a single-cable bidirectional dual-fiber transmission system. The location of each interface point is shown in Figure 1. Interface 3(3) indicates the interface between the tertiary optical terminal and the tertiary digital multiplexing equipment; Interface 2(2) indicates the interface between the branch of the tertiary digital multiplexing equipment and the secondary digital multiplexing equipment: Interface 1(1) indicates the interface between the branch of the secondary digital multiplexing equipment and the program-controlled digital switch or the primary PCM multiplexing equipment; Interface 0(O) indicates the interface between the audio voice circuit of the primary PCM multiplexing equipment and the local (or long-distance) 2/4-wire analog switch or 64kbt/s interface; Interface 0(0) mainly corresponds to the audio distribution frame, and its interface characteristics shall comply with the national standards for electrical transmission of trunk lines between long-distance and intra-city telephone exchanges. Interfaces 1(1'), 2(2), and 3(3) correspond to the primary, secondary, and tertiary digital distribution frames, respectively, and their interface characteristics are shown in Section 3.7. Heriu
M and digital multiplexing
digital optical cable system
interface
Note: For the 4th group intra-city optical cable communication system, the TX and RX of the optical terminal are connected to the 4th group digital multiplexing equipment M (using four 3rd group digital multiplexing, positive code rate adjustment), and its interface position is interface 4 (4). The branch interface of M4 is interface 3 (3). The rest is exactly the same as Figure 1. Figure 1 Schematic diagram of the urban optical cable communication system
M1-1--a primary group PCM multiplexing device working at 2048kbit/s, M2-2--a secondary group digital multiplexing device working at 8448kbit/s and using positive code rate adjustment; Ms--a tertiary group digital machine working at 34368kbit/s and using positive code rate adjustment RX--optical receiver, REG--optical repeater multiplexing device, TX--optical transmitter
The digital optical cable line system consists of an optical terminal (optical transmitter TX and optical receiver RX), an optical cable and an optical repeater REG. 3.6 Main audio transmission characteristics
There is only one set of primary group PCM multiplexing equipment throughout the whole process, and its main audio transmission characteristics should comply with the provisions of GB6879. 3.7 System branches and interface parameters
The interface points of each digital segment are all branch transfer points of each secondary group of digital signals. The pulse waveform characteristics, code type, bit rate and its tolerance, input and output port regulations, impedance, and connection cable attenuation of the corresponding digital group at the interface during branch switching must comply with the provisions of GB7611.
4 Main transmission characteristics and requirements of digital optical cable line system 4.1 Line system composition
The digital optical cable line system consists of the part between TT in Figure 2, as shown in Figure 2a when there is no repeater, and as shown in Figure 2b when there is a repeater. The number of repeaters is determined by the system design. 2
GB/T11820—1989
ToOloly RR Toi
Figure 2 Schematic diagram of digital optical cable line system
T, T/-interfaces between optical terminal and PCM multiplexing or digital multiplexing, S-optical fiber point close to the rear of optical connector C of TX or REG R-optical fiber point close to the front of optical connector C of RX or REG 4.2 System error characteristics
According to the error performance indicators and allocation principles of 27500km64kbit/s full-length digital connection, for the 50km digital section of the optical cable line system, the error performance of 64kbit/s should be:
Degraded score (BERm>10-)
Error second ES
Severe error second SES (BER,>10-3)
<0.16%;
≤0.002%.
The error characteristic of the high bit rate system is tentatively set as: BER<1X10-8 (continuous test time is not less than 24h). 4.3 System jitter characteristics
The digital optical cable line system should meet the jitter requirements at the interfaces at points T and T in Figure 2. That is, the jitter requirements for each subgroup input port are shown in Table 1. The jitter requirements for each subgroup output port throughout the entire process are shown in Table 2, and for each digital segment, the jitter of each subgroup output port is in accordance with the tolerance requirements in brackets in Table 2. The maximum gain of the jitter transfer characteristic of each 50km digital segment should not exceed 1dB. The lowest frequency of the jitter test should be as low as possible, but considering the limitations of the test instrument, it can be measured to about 10Hz. Table 1
kbit/s
139264
UIp-p (peak-to-peak value)
1.2×10-5
1.2×10-5
Frequency of sinusoidal signal of modulated digital signal
f2/kHz
fa/kHz
fa/kHz
Pseudo-random test
Test signal sequence
215—1
223— 1
kbit/s
139264
4.4 System optical power allocation
GB/T11820—1989
Maximum jitter tolerance value at the output port
1.5(0.75)
1.5(0.75)
1.5(0.75)
0.15(0.15)
0.075（0.075）
Measurement of bandpass filter bandwidth: low cutoff frequency is f1 or fs, high cutoff frequency is f4
fs/kHz
fa/kHz
The system optical power distribution is considered according to Figure 3, which is determined by many factors such as the light source C laser (LD) or light emitting tube (LED), the light detector [avalanche photodiode (APD) or photodiode (PIN)>, the attenuation of the optical cable, the attenuation of the optical fiber joint and the optical connector, and the reserved optical cable redundancy and equipment redundancy.
Generally, the total attenuation and total bandwidth or maximum dispersion between points S and R of the multimode or single-mode optical fiber system should not be less than the values listed in Table 3 under the condition that the bit error rate is not worse than 1X10-1°. H country tO-@H
Note: The optical distribution frame (or box) should be between points S and R, and the attenuation of the additional optical connector should be considered uniformly in the optical link. Figure 3
Digital rate
kbit/s
Nominal wavelength
Light source type
Schematic diagram of an optical link with a relay segment
Transmission characteristics between points S and R of a multimode system, BER≤1X10-10
3dB optical bandwidth
Transmission characteristics between points S and R of a single-mode system
BER≤1X10-10
Maximum dispersion
Not required|| tt||Digital rate
kbit/s
139264
Nominal wavelength
Type of optical source
GB/T11820—1989
Continued Table 3
Transmission characteristics between points S and R of multimode system
characteristics, BER≤1X10-10
3dB optical bandwidth
Note: The values listed in the table are the minimum requirements under the condition of maximum relay segment length, which can be relaxed for short-distance systems. 4.5 System redundancy
Transmission characteristics between points S and R of single-mode system
BER≤1X10-10
Maximum dispersion
Not required
The redundancy of each relay segment of the system without relay in Figure 2a and the system with relay in Figure 2b is determined by the cable redundancy M. and equipment redundancy M. (as shown in Figure 3).
Optical cable redundancy M. includes:
a. Maintenance changes of optical cables in future maintenance (such as adding joints, increasing the length of optical cables, etc.): b: Changes in optical cable performance caused by environmental factors c. Deterioration of the characteristics of any optical connector C between points S and R Equipment redundancy M.
Includes the impact of time and environmental factors on equipment performance. For example, transmission optical power, receiving sensitivity, degradation of optical connector characteristics, etc. M. for multimode optical fiber is 0.3dB/km, M. for single-mode optical fiber is 0.2dB/km, but the minimum is 3dB and the maximum is 10dB. M. is 3dB.
4.6 System transmission code type
The transmission code type of the urban digital optical cable line system is 5B6B code. 4.7 Transmitting optical power
The average transmitting optical power of the optical transmitter TX or optical repeater REG optical connector C output (point S) shall meet the requirements in Table 4. Table 4
Light source type
Test conditions
Average transmitting optical power injected into multimode fiber at point S
≥-23
Average transmitting optical power injected into single-mode fiber at point S
≥-28
50% duty cycle return to zero (RZ) pseudo-random code measurement Note: ① The long-distance system should be appropriately selected to meet the requirements between points S and R. ② The short-distance system can be appropriately relaxed, but when using LD, it should not be less than -9dBm. 4.8 Receiving sensitivity
The receiving sensitivity is the lowest receiving optical power value measured under the condition of BER=1X10-1°. The average minimum received optical power at the optical connector C input (point R) of the optical receiver RX or optical repeater REG, measured under the condition of BER<1X10-1°, shall not be inferior to the values listed in Table 5.
Transmission capacity
Secondary group
Third group
Quaternary group
GB/T11820—1989
Photodetector
Input=1300nm
PIN-FET
PIN-PET
Note: ① Long-distance system should be appropriately selected to meet the requirements between points S and R. ② Short-distance system can be appropriately relaxed.
4.9 System dynamic range
Receiving sensitivity, dBm
Element=850nm
For systems in the 850nm wavelength region, the dynamic range should not be less than 20dB; for systems in the 1300nm wavelength region, the dynamic range should not be less than 18dB.
Note: The original system designed for 15dB can continue to work. 5 Requirements for machine and line equipment in optical cable communication systems 5.1 The interface requirements between various equipment in the system are the same as those in 3.7 system branches and interface parameters.
5.2 Requirements for PCM and digital multiplexing equipment 5.2.1 Primary group PCM multiplexing equipment
Should comply with the provisions of GB6879.
5.2.2 Secondary group digital multiplexing equipment
Should comply with the provisions of GB7254.
5.2.3 Tertiary digital multiplexing equipment
Should comply with the provisions of GB9405.1.
5.2.4 Quaternary digital multiplexing equipment
Should comply with the following basic requirements:
5.2.4.1 Basic characteristics
The multiplexing method of cyclically embedding bits and positive code rate adjustment in the order of branch numbers is adopted. Table 6 gives the maximum code rate adjustment rate and nominal code rate adjustment ratio of each branch. Multiplex 4 34368kbit/s branches. Voice channel capacity 1920 channels. 6Www.bzxZ.net
Branch bit rate, kbit/s
Number of branches
Frame structure
Frame positioning signal (111110100000)
Alarm indication to the digital multiplexing equipment at the other endBits reserved for domestic use
Bits from each branch
Code rate adjustment service bits O(n=1～4)
Bits from each branch
Code rate adjustment service bits 05
Bits from each branch that can be used for code rate adjustmentBits from each branch
Number of bits per branch
Maximum code rate adjustment ratio per branch
Nominal code rate adjustment ratio
GB/T11820—1989
Note: C represents the nth code rate adjustment service bit of the jth branch. 5.2.4.2 Bit rate
The nominal value of the bit rate is 139264 kbit/s, with a tolerance of ±15×10-65.2.4.3 Timing signal
The timing signal of the equipment can be obtained from both external and internal sources. 5.2.4.4 Frame structure
The frame length is 2.928 bits, and the branch bit rate is 34368 kbit/s. The number of branches is 4. 5.2.4.5 Frame loss and frame alignment recovery
Bit number
17~488
Group I to V
2928 bits
47.560 kbit/s
When an erroneous frame alignment signal is received at its predetermined position for four consecutive frames, a frame loss shall be considered to have occurred. When the frame is out of position, if the frame positioning device detects the positioning signal for three consecutive frames, it should be judged that the positioning has been effectively restored. 5.2.4.6 Fault alarm
The equipment should detect the following fault conditions and issue audible and visual alarm indications. a.
Power failure;
The 34368kbit/s input signal at the branch input end disappears; The input signal at the 139264kbit/s port disappears; Sequential loss;
GB/T11820—1989
e. Receive an alarm signal from the multiplexing device at the opposite end at the 139264kbit/s port; f. Receive an alarm indication signal (AIS) at the 139264kbit/s port. 5.2.4.7 Interface
The 34368kbit/s and 139264kbit/s digital interfaces should comply with the requirements of Article 3.7 above. 5.2.4.8 Jitter
a.Jitter transfer characteristics:
-When a 34368kbit/s signal modulated by sinusoidal jitter is added to the input of the equipment, the jitter gain of the equipment (multiplexer) output should be below the frame shown in Figure 4. The equivalent binary content of the test signal should be 1000. d
Figure 4 Jitter transfer characteristics frame diagram
b. Branch output jitter:
When measured at a frequency point below 800kHz, the peak-to-peak jitter of the branch output without input jitter should not exceed 0.3U1. c. Multiplexed signal output jitter:
When the transmission timing signal is obtained by the internal generator, when tested in the range of f1=200Hz to f3500kHz, the peak-to-peak jitter of the 139264kbit/s output terminal shall not exceed 0.05U1. 5.3 Requirements for optical terminals
The basic requirements are as follows:
5.3.1 The series
shall comply with the 2048kbit/s series.
5.3.2 The electrical interface
shall comply with the provisions of GB7611.
5.3.3 Optical transmitter
5.3.3.1 Light source wavelength
The nominal wavelengths of the light source are 850nm and 1300nm, which represent any wavelength in the range of 820~910nm and 1270~1330nm respectively. For a 4×140Mbit/s single-mode system, the nominal wavelength of 1300nm represents any wavelength in the range of 1285~1330nm. 5.3.3.2 Code type
The transmission code type is 5B6B code.
5.3.3.3 Average transmitted optical power
Depending on whether the light source is LD or LED, the average transmitted optical power is required to comply with Table 4 of Article 4.7. 5.3.4 Optical receiver
5.3.4.1 Receiving sensitivity
GB/T11820—1989
The average minimum received optical power input to the optical detector is measured under the condition of BER<1X10-1°. Depending on whether the optical detector is APD or PIN, PIN-FET, the wavelength and transmission capacity are different, it should comply with Table 5. 5.3.4.2 Dynamic range
The dynamic range of the receiver should meet the requirements of Article 4.9. 5.3.5 Fault alarm function
The optical terminal should detect the following fault conditions and issue audible and optical alarm signals. a.
Power failure;
No optical signal is sent;
No optical signal is received;
Input electrical signal disappears;
Out-of-step alarm
BER reaches 10-,
Business communication failure;
For 8448kbit/s and 2048kbit/s systems, BER reaches 10-5, for 34368kbit/s and above systems, BER reaches 10-6, only delayed maintenance alarm indication is issued; light source LD performance deteriorates, only delayed maintenance alarm indication is issued. j.
5.4 Requirements for optical repeaters
Should meet the requirements of 5.3.3 and 5.3.4.
5.5 Requirements for optical fiber and optical cable
5.5.1 Optical fiber in optical cable
The characteristics of multimode graded-index optical fiber and single-mode optical fiber shall meet the following basic requirements: 5.5.1.1 Size
Multimode optical fiber: core diameter 50±3um, cladding diameter 125±3um. Single-mode optical fiber: mode field diameter nominal value 9~10um, deviation less than 10%, cladding diameter 125±3um. 5.5.1.2 The nominal value of the maximum theoretical numerical aperture NAtma multimode optical fiber NAtmx is 0.20, and the deviation between the actual value and the nominal value is ±0.025.5.1.3 Attenuation constant
The attenuation constant of multimode optical fiber should be less than 4dB/km in the 850nm region. It should be less than 2dB/km in the 1300nm region. The attenuation constant of single-mode fiber should be less than 0.9dB/km in the 1300nm region. 5.5.1.4 Bandwidth or total dispersion
The bandwidth of multimode fiber should be greater than 200MHz·km in both the 850nm and 1300nm regions. The total dispersion of single-mode fiber should be no more than 3.5ps/nm·km in the 1285~1330nm region and no more than 6ps/nm·km in the 1270~1340nm region.
5.5.1.5 Cut-off wavelength
The effective cut-off wavelength of the LPU mode of 1300nm single-mode fiber should be within the range of 11001280nm when measured on a 2m long fiber sample. Or it should be less than 1270nm when measured on a 22m long optical cable sample. 5.5.2 Cable manufacturing length
The nominal manufacturing length of the optical cable is 1km and 2km. 5.5.3 Mechanical and protective properties of optical cables
Optical cables should have corresponding mechanical properties according to the conditions of use, and should also have moisture-proof and waterproof properties. Petroleum-filled optical cables or gas-filled optical cables can be used according to local conditions. In addition, they should also have protective properties such as anti-termite, rat, insect bites, and anti-corrosion according to the conditions of use and the needs of the installation environment.
6 Reliability requirements
6.1 System reliability indicators
GB/T11820—1989
The entire system of 100km can tolerate four failures per year. The corresponding indicators of the 50km digital segment and the reliability indicators of the optical cable line system, PCM and digital multiplexing equipment are shown in Table 7. Table 7
8, 34, 140Mbit/s system
50km digital section (bidirectional)
Optical cable line system (bidirectional)
PCM and digital multiplexing equipment (one end station)
The system availability is required to be 99.99%.
6.2 Light source life
The light source life should be greater than 5×10h.
6.3 Photodetector life
The photodetector life should be greater than 20×10h.
6.4 Environmental conditions
Reliability MTBF (years)
Computer room: The ambient temperature is 5~40℃, and the relative humidity is less than 85%. Pipeline optical cable: -5～40℃
Aerial optical cable: -20～60℃ south of the Yellow River -30～50℃ north of the Yellow River
For an environment below 30℃, it is recommended not to use overhead optical cables. 7 Requirements for maintenance and use
Calculate the inter-bureau relay system of the intra-city optical cable communication under the condition of 5:1 main and standby automatic switching. In addition to having the specified transmission characteristics, from the perspective of network management and monitoring of the entire network, and from the perspective of facilitating maintenance and operation, in addition to the system itself having a monitoring auxiliary system as part of the maintenance entity, it is also required that the system can send the monitoring control signal through the interface to the maintenance center. Generally, the functions that the system must have are as follows: 7.1 Monitoring function
It should at least have:
Optical path sending indication: indicates the status of optical signal sending; b.
Optical path receiving indication: indicates the status of optical signal receiving c.
Error monitoring: can monitor the error without interrupting communication and reflect the error situation; Relay station monitoring: can reflect whether each relay station is working normally at the centralized monitoring station d.
The optical terminal has a test board, disk or monitoring holes that reflect the characteristics of important interface points of the circuit and optical path, and can perform local and remote self-looping to facilitate testing, maintenance and fault inspection and judgment. 7.2 Alarm function
When an abnormal state is encountered in the above monitoring functions or other obstacles occur in the whole machine, an alarm should be given immediately (the light is on, the bell rings and a stop switch is attached). At least the following alarms should be available:
Power failure or main-backup power conversion,
Bit error rate exceeds 10-\ (only the light is on);
Bit error rate exceeds 10-3,
No optical signal at the sending and receiving ends;
GB/T11820—1989
No signal is sent to the optical terminal from the digital multiplexing device; e.
No signal is sent to the digital multiplexing device from the optical terminal: f.
Name: No signal is sent to the optical terminal from the digital multiplexing device at the opposite end (only the light is on); h. Failure of the optical relay station.
7.3 System conversion function
When the main system has an immediate alarm and the bit error rate exceeds 10-3 (or 10-6, determined by the user), it will automatically switch to the backup system and send an alarm signal at the same time. Usually, the interface point for automatic conversion is a standard digital interface point. After the main system is repaired, it should be able to automatically switch back to the main system from the backup system by manually pressing a button. The switching process should not interrupt communication, at least not interrupt calls. 7.4 Business contact function
There should be direct contact telephones between system terminals and relay stations to facilitate business contact and operation testing. 7.5 Photoelectric measurement and wiring function within the office
In order to facilitate the measurement of optical path, circuit adjustment and characteristics of important optical and electrical interface points within the office, optical distribution frames (boxes, panels) and digital distribution frames of each subgroup can be set. The connection attenuation and interchange attenuation of optical connectors on the optical distribution frame should be uniformly considered in the design of the optical system. 7.6 Power supply conditions
Use the DC power supply of the city telephone office room, and the positive pole is grounded. The nominal voltage value is -60V, with a tolerance of ±6V. Or the nominal voltage value is 48V, with a tolerance of ±4.8V. Or the nominal voltage value is -24V, with a tolerance of ±2.4V. The allowable value of the pulse voltage is not more than 5mV measured by a noise meter. When using a voltage of -24V, it should not be more than 2mV. Additional remarks:
This standard is proposed by the Ministry of Posts and Telecommunications of the People's Republic of China. This standard is under the jurisdiction of the Telecommunications Transmission Research Institute of the Ministry of Posts and Telecommunications. This standard is drafted by the Telecommunications Transmission Research Institute of the Ministry of Posts and Telecommunications. The main drafters of this standard are Bai Qizhang and Peng Chengzhu.
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