1、BRITISH STANDARD Methods of measurement for equipment used in digital microwave radio transmission systems Part 2. Measurements on terrestrial radio-relay systems Section 2.6 Protection switching The European Standard EN 60835-2-6 : 1995 has the status of a British Standard ICs 33.060.30 NO COPYING
2、WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN BS 7573 : Section 2.6 : 1996 1995 60835-2-6 : 1996 IEC 835-2-6 : CENELEC ENrb835-2- b 95 3404583 OLb7034 757 Amd. No. Date BS EN 60835-2-6 1996 Text affected Committees responsible for this British Standard The preparation of this Bri
3、tish Standard was entrusted to Technical Committee EPU12, Radio communication, upon which the following bodies were represented: British Broadcasting Corporation British Radio and Electronic Equipment Manufacturers Association British Telecommunications plc ERA Technology Ltd. Institution of Electri
4、cal Engineers Radio, Electrical and Television Retailers Association Radiocommunications Agency , This British Standard, having , been prepared under the direction of the Electrotechnicai Sector Board, was published under the authority of the Standards Board and comes into effect on 15 February 1996
5、 O BSI 1996 The following BSI references relate to the work on this standard Committee reference EPU12 Draft for comment 95/210407 DC ISBN O 680 26166 7 - CENELEC EN*b0835-2- b 95 m 3404583 OLb7035 b93 m BS EN 60835-2-6 : 1996 Contents Committees responsible National foreword page Inside front cover
6、 ii Foreword Text of EN 608352-6 2 3 O BSI 1996 i CENELEC EN*b0835-2- 6 95 = 3404583 0367036 52T BS EN 60835-2-6 : 1996 National foreword This British Standard has been prepared by Technical Committee EPLI12 and is the English language version of EN 60835-2-6 : 1995 Methods of measurementfor equipme
7、nt used in digital microwave dio transmission systems Part 2 : Measurements on terrescrial radio-relay systems Section 6 : Protection switching, published by the European Committee for Electrotechnical Standardization (CENELEC). It is identical with IEC 835-2-6 : 1995, published by the International
8、 Electrotechnical Commission (IEC) and is part of a series. BS EN 60835 is published in three Parts. The other Parts are: Part 1: Measuremmts common to terrestrial radio-relay systems and satell.ite earth stations Part 3: Measurements on satellite earth stations This Section of BS EN 60835-2 covers
9、measurement of terminal-to-terminal protection switchmg equipment associated with digital radio-relay systems. The methods described are for an N+l switching configuration but are also applicable to N+2 switching arrangements and to 1+1, twin-path and hot standby arrangements. The channel priority s
10、tatus tests described in clause 5 are applicable only to the N+l and N+2 switching arrangements. In configurations where the protection switching equipment is physically separable from the radio terminal equipment (see figure 1,) the interfaces at the input and output ports of the switching equipmen
11、t shall be measured in accordance with BS EN 6083352-5. It is expected that other Sections of IEC Publication 835 wi be published as identical British Standards, subject to their harmonization by CENELEC. Some Sections of this British Standard have already been published as Sections of BS 7573. Cros
12、s-references International standard Corresponding British Standard BS EN 60835 Methods of measurement for equipment used in digital microwave radio transmission systems Part 1: Meclsurements conanwn to terrestrial mdio-relay systmm and satellite earth stations Section 1.3 : 1995 Transmissiun chracte
13、msticsl) Part 2: Measurements on terrestrial radio-relay systems Section 2.5 : 1995 Digital signal processing sub-system EN 6083813 : 1995 EN 60835-2-5 : 1995 (IEC 835-2-5 : 1993) Compliance with a British Standard does not of itself confer immunity from legal obligations. (IEC 8351-3 : 1992) 1 in p
14、reparation. ii O BSI 1996 CENELEC EN*bO35-2- b 95 W 3401.1583 03b7037 4bb = EUROPEAN STANDARD NORME EUROPENNE EUROP in this case, the occasional traffic has no priority, and will be.removed as soon as any operating channel needs the standby channel. The principal criteria for initiating a switchover
15、 between any one of the main channels and the standby channel are as follows: a) loss of signal, .e. data missing or loss of synchronization; b) degradation of the operating channel, resulting in a BER in excess of a pre- determined value (within a range of to for example); c) restoration of a previ
16、ously failed main channel, .e. an improvement of the BER to better than a predetermined value (typically one-to-two orders of magnitude better than in item b). CCIR Recommendation 753: Preferred methods and characteristics for the supervision and profection of digital radio-relay systems. (Geneva, 1
17、992) CENELEC EN*bO35-2- b 95 3404583 0367040 T50 Page 4 EN 60835-2-6 : 1995 I When protection is required at the receive terminal and when the protection channel is in normal condition and not occupied, the transmit terminal is instructed, via an associated control signal, to apply the traffic of th
18、e appropriate channel to the standby channel input. Traffic continues to be applied in parallel to the original channel so that both channels are carrying nominally identical traffic. At the receive terminal, the signal of the standby channel (and in some implementations, the operating channel also)
19、 passes via a variable delay element. As the digital signal is present both at the output of the main channel and the standby channel, they are compared bit by bit, and the delay difference is systematically removed until an acceptable correlation is measured between the two inputs to the comparator
20、. When this is achieved, the standby channel is switch-selected at the receive terminal in place of the main channel. The change-over is thus arranged to give only an acceptable number of errors. The change-over is also called slipless if bit coincidence is achieved immediately prior to switching. I
21、f loss of signal in a main channel occurs, no comparison can take place. In such cases, the receive terminal will automatically force a change-over after a given delay has occurred. Confirmation of successful change-over is exchanged via the supervisory control signal. Once the performance of the ma
22、in channel is deemed to be satisfactory, receive-end slipless switch-back from the standby channel to the appropriate main channel follows. In the case of N+1 or N+2 protection systems, confirmation of successful change-over is then passed, via the supervisory control signal, to the transmit termina
23、l where switching is also restored to free the standby channel, and thus make it available for the protection of other channels. In some protection switching systems, two BER switching criteria are applied in the range of to In this case, if the standby channel is occupied by the channel in which on
24、ly the lower BER is exceeded, and another main channel with a BER exceeding the higher criterion or in the “loss-of-signal“ condition needs protection, the former channel is switched back to its original position and the standby channel will be occupied by the latter channel. In comparison with the
25、above slipless protection switching system, non-slipless protection switching systems are simpler in concept. Upon request from the receive terminal to imple- ment a change-over, the transmit terminal switches the traffic to the standby channel (Le. parallel transmission over main and standby channe
26、ls takes place). The receive terminal then switches to the standby channel once satisfactory transmission is confirmed. No attempt is made to remove the transmission delay difference between the main and standby channel. This may result in a brief interruption or even a slip in fhe operating path. ,
27、 -) In addition to automatic protection switching facilities, most equipment offers the facility for switching under manual control. This control may be carried out directly at the terminals, and in some cases also by means of an associated supervisory and control channel. Page 5 EN 60835-2-6 : 1995
28、 METHODS OF MEASUREMENT FOR EQUIPMENT USED IN DIGITAL MICROWAVE RADIO TRANSMISSION SYSTEMS - Part 2: Measurements on terrestrial radio-relay systems - Section 6: Protection switching 1 General 1.1 Scope This section of IEC 835-2 deals with the measurement of terminal-to-terminal protection switching
29、 equipment associated with digital radio-relay systems. The measurement methods described in this section of IEC 835-2 for an N+l switching configuration but are also applicable to N+2 switching arrangements. The same measurement methods are applicable to 1 +1, twin-path and hot standby arrangements
30、. The channel priority status tests described in clause 5 are only applicable to the N+l and N+2 switching arrangements. In configurations where the protection switching equipment is physically separable from the radio terminal equipment (see figure l), the interfaces at the input and output ports o
31、f the switching equipment shall be measured in accordance with IEC 835-2-5. 1.2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this section of IEC 835-2. At the time of publication, the edi- tions indicated we
32、re valid. All normative documents are subject to revision, and parties to agreements based on this section of IEC 835-2 are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. Members of IEC and IS0 maintain registers of currentl
33、y valid International Standards. IEC 835-1 -3: 1992, Methods of measurement for equipment used in digital microwave radio transmission systems - Part 7 : Measurements common to terrestrial radio-relay sys- tems and satellite earth stations - Section 3: Transmission characteristics IEC 835-2-5: 1993,
34、 Methods of measurement for equipment used in digital microwave radio transmission systems - Pari 2: Measurements on terrestrial radio-relay systems - Section 5: Digital signai processing sub-system 2 Switching 2.1 Switching configurations 2.1.1 Configurations where one dedicated standby channel is
35、used to provide protection for a number (N) of operating channels are referred to as N+l protection switching arrange- ments. in order to coordinate the change-over from main to standby, these arrangements #+ 1 and N+2 switching CENELEC EN*60835-2- 6 95 3404583 0367042 823 Page 6 EN 60835-2-6 : 1995
36、 I require the transmission of a supervisory and control signal between the terminals of the radio-relay system. A typical N+l protection switching arrangement is shown in figure 1. Configurations where two dedicated standby channels are used to provide protection for a number of operating channels
37、are referred to as N+2 protection switching arrangements and are similar to the N+l arrangement. When the system is equipped with two standby channels, a main channel can be switched to either standby A or B if they are both free. When both standby channels are occupied by main channels with differe
38、nt priorities, the lower priority channel gives way to the higher priority one. 2.1.2 7+7 switching and twin path Configurations where one dedicated standby channel is used to protect a single operating channel are referred to as 1 +1 protection switching arrangements. “Twin-path systems“ are specia
39、l cases of 1+1 configurations in which a single traffic signal is parallel-fed continuously over two radio channels. The degradation of both channels is monitored as indicated in the Introduction, and a switch, located at the receive terminal, is used to select a channel having a BER below a specifi
40、ed threshold. Twin-path systems do not perform switching at the transmit terminal, and consequently do not require a return supervisory and control signal. A typical twin-path arrangement is shown in figure 2. 2.1.3 Hot standby Protection arrangements in which a complete standby channel is not provi
41、ded but parts of the radio equipment are duplicated are known as hot standby arrangements. Hot standby systems provide protection against equipment failure but generally not against path degra- dations. In general, hot standby arrangements provide non-slipless switching. 2.2 Pre-setting facilities I
42、n some cases, manual pre-setting for maintenance and service purposes may be available as follows: - a traffic-free main channel can be locked in service regardless of its BER performance ; - any main channel can be locked on the standby channel regardless of its BER performance. In some cases, thes
43、e pre-settings can also be controlled remotely. CENELEC EN*b0835-2- b 75 3404583 0167043 7bT Page 7 EN 60835-2-6 : 1995 3 Non slipiess protection switching 3.1 Switch operation - manual mode Verify that the traffic signal of each main channel can be manually switched to the standby channel. Verify t
44、hat no switch-over to the standby takes place if the performance of the standby channel is degraded below specified limits, or if the standby channel has been manually disabled. 3.1.1 Method of measurement The equipment shall be arranged as shown in figure 3. Intermediate repeaters may be in- cluded
45、 in the test arrangement, if applicable. The measurement includes the following steps. a) With all channels in operation and each transmitting an independent pseudo ran- dom binary sequence (PRBS), actuate manual change-over from channel 1 to standby, first at the transmit side and then at the recei
46、ve side. Confirm that correct change-over is achieved, .e. after a reasonable time following the switch-over process, acceptable transmission via the standby channel takes place as measured on the BER meter. Similarly, confirm manual restoration from the standby channel to channel 1 in the re- verse
47、 order, as described above. b) Repeat as above to confirm manual switching for all remaining main channels 2 through N. c) Repeat a) and b) but now with a simulated fail condition on the standby channel, e.g. loss of signal or BER in excess of a specified limit. 1) For protection systems employing l
48、ogic controlled manual switching, verify that change-over to the protection channel no longer takes place. Likewise verify that change-over is inhibited if the standby channel has been manually disabled (locked out). 2) For protection systems with a manual switch “overriding“ the switching logic, ve
49、rify that switch-over to the standby channel takes place. 3.1.2 Presentation of results Results shall be presented as a simple pass/fail test record for each operation of the switch. 3.1.3 Detail to be specified None. 3.2 Switch operation - automatic mode Verify automatic change-over from each operating channel to the standby channel under each of the following conditions: a) loss of signal at the receive terminal; b) BER in excess of a specified threshold. CENELEC EN*bO835-2- b 95 m 3404583 01167044 bTb m Page 8 EN 60835-2-6 : 1995 Verify that such a change
