1、Recommendation T/CAC 4 (Stockholm 1989 (CAC), revised in Nicosia 1990 (CAC) and Vienna (CAT) Page 1 MONITORING OF NETWORK PERFORMANCE ASPECTS OF QUALITY OF INTERNATIONAL PACKET-SWITCHED SERVICE USING EXTERNALLY DERIVED INDICATORS Recommendation proposed by the project team X.25 Text of the Recommend
2、ation adopted by the “Telecommiinications” Commission: “The European Conference of Posts and Telecommunications Administrations, consideritig that Recommendation T/CAC 2 E on the measurement of packet network performance and quality of service identifies in particular the need to monitor four indica
3、tors, Transmitted throughput WP), Received throughput (RTP), Round-trip delay (RTD) and call set-up delay (CSD), derived from information collected by equipment external to the network, recommends that the procedures to be used by Administrations for monitoring these indicators should be as defined
4、below.” O 1. 1.1. Definitions TRANSMITTED THROUGHPUT (TTP) AND RECEIVED THROUGHPUT (RTP) The Transmitted throughput indicator (TTP) is defined as the average rate of transfer of user data across the calling X.25 interface to the called X.25 interface, expressed in bit/s, under the conditions describ
5、ed below. The Received throughput indicator (RTP) is defined as the average rate of transfer of user data across the calling X.25 interface from the called X.25 interface, expressed in bitfs, under the conditions described below. 1.2. Requirements DTEs are connected at the X.25 interfaces which can
6、be used to generate and receive user data and conform to Annex A (DTE performance, measurement precision, etc.). BothX.25 DTE s should be connected via a standard line interface as used for customer service. They should be located on a switching unit whose characteristics and situation in the networ
7、k in relation to international interfaces are typical of units connecting actual X.25 users on that network. The X.25 DTEs should be connected at 9.6 kbit/s and use the following port configuration parameters: - frame level window of 7; - default packet level window size of 2; - default maximum data
8、 packet size of 128 octets; - default throughput class corresponding to 9.6 kbit/s. There should be no inclusion of any user facility in a call request packet. There should be no other traffic on either X.25 interface. All transmitted data packets are full (i.e. contain 128 octets of user data). 1.3
9、. Procedures 1.3.1. Single measurement To make a single measurement of transmitted throughput from an X.25 interface, the DTE makes a call to a drop function in the DTE at the other X.25 interface. To make a single measurement of received throughput from an X.25 interface, the DTE makes a call to a
10、generator function in the DTE at the other X.25 interface. Edition of August 15, 1990 CEPT T/CAC*Y*E B 2326414 0002912 B W TJCAC 4 E Page 2 1.3.2. 1.3.3. 1.3.4. 1.4. 2. 2.1. 2.2. Each measurement should conform to the following : - the measured interval is between 55 and 65 seconds; - the measured i
11、nterval begins not less than 10 seconds after the start of transmission, or successful receipt, - the entire period between the call set-up and end of the measurement interval has no premature clear The transmitted throughput is calculated as the number of data packets sent during the measurement in
12、terval, multiplied by 1024 bits per packet and divided by the measurement interval length in seconds. The received throughput is calculated as the number of data packets received during the measurement interval, multiplied by 1024 bits per packet and divided by the measurement interval length in sec
13、onds. Evaluating a daily value To evaluate either the transmitted throughput or the received throughput for a particular day, a series of appropriate individual measurements is made : - one measurement is made during each complete hour of the day; - if a measurement is invalidated by apremature clea
14、r or reset, it should be re-attempted as soon as - if there is any complete hour without a successful measurement, the evaluation for that day is abandoned. The value applicable to the day is calculated as the average of the three worst values of the 24 obtained. Evaluating a monthly value To evalua
15、te either the transmitted throughput or the received throughput for a particular month, a set of five appropriate daily values must be obtained during the month. These five values must each apply to a different day of the week, including only those which are normal working days in the countries of b
16、oth of the X.25 interfaces. The value applicable to the month is calculated as the average of the five daily values obtained. Schedule of evaluation Every year each operator of a public X.25 network should evaluate the transmitted throughput to each other public X.25 network for the month of October
17、. Similarly, the received throughput should be evaluated every year for the month of March. Additional evaluations of both transmitted throughput and received throughput for a month, day or other convenient period may be made at the discretion of the network operator. Preference should be given to l
18、arger trafic streams, and evaluations should in particular be made after any physical or logical network configuration change affecting a trafic stream (for example, the introduction of an extra X.75 link, or the replacement of a transit route by a direct route). Processing Before the end of Novembe
19、r every year, each operator of a public X.25 network will send its results of the transmitted throughput evaluations for October to a body designated by CEPT. Similarly, the results of the received throughput evaluations for March will be sent to the designated body before the end of April. The desi
20、gnated body will compile each complete set of evaluation results it receives to produce a matrix of throughput values. This will show the values obtained for each identifiable traffic stream and will be made freely available for publication. Each network operator should, as soon as possible, inform
21、its appropriate partner operators of the results of any additional evaluations which it has made. of the first data packet of the call; or reset. convenient up to five times; ROUND-TRIP DELAY (RTD) Definition The Round-trip delay indicator (RTD) is defined as the average time interval between the st
22、art of trans- mission of a data packet at a calling X.25 interface and the end of reception of its echo from the called X.25 interface, expressed in milliseconds, under the conditions described below. The Round-trip delay indicator reflects the delay encountered by a user between sending a single da
23、ta packet to a fast host and receiving the first packet in response. Requirements DTEs are connected at the X.25 interfaces which can be used to generate and receive user data and conform to Annex B (DTE performance, measurement precision, etc.). Both X.25 DTEs should be connected via a standard lin
24、e interface as used for customer service. They should be located on a switching unit whose characteristics and situation in the network in relation to international interfaces are typical of units connecting actual X.25 users on that network. O Edition of August 15, 1990 2.3. 2.3.1. 2.3.2. 2.3.3. 2.
25、3.4. 2.4. TICAC 4 E Page 3 The X.25 DTEs should be connected at 9.6 kbit/s and use the following port configuration parameters: - frame level window of 7; - default packet level window size of 2; - default maximum data packet size of 128 octets; - default throughput class corresponding to 9.6 kbit/s
26、. Other port parameters are configured as normally used for customer service. There should be no inclusion of any user facility in a call request packet. There should be no other traffic on either X.25 interface. All transmitted data packets are full (Le. contain 128 octets of user data) and contain
27、 an M bit value of O. Procedures Single measurement To make a single measurement of round-trip delay from an X.25 interface, the DTE makes a call to an echo flinction in the DTE at the other X.25 interface. Each measurement should conform to the following: - ten transactions are performed in sequenc
28、e within the call; - each transaction consists of the transmission (as soon as flow control permits) of a data packet and - each echoed data packet is received within 30 seconds of the start of the transaction; - each transaction interval begins at the start of transmission of the data packet and en
29、ds at the end of - the time between transactions does not exceed 30 seconds: - the entire period between the call set-up and end of the tenth transaction interval has no unexpected The round-trip delay is calculated as the sum of the ten transaction intervals divided by ten. Evaluating a daily value
30、 To evaluate the round-trip delay for a particular day, a series of appropriate individual measurements is made: - one measurement is made during each complete hour of the day; - if a measurement is invalidated either by an unexpected packet level protocol event or by non-receipt of an expected echo
31、ed data packet within 30 seconds, it should be re-attempted as soon as convenient up to five times; - if there is any complete hour without a successful measurement, the evaluation for that day is abandoned. The value applicable to the day is calculated as the average of the three worst values of th
32、e 24 obtained. Evaliiatiiig CI monthly value To evaluate the round-trip delay for a particular month, a set of five appropriate daily values must be obtained during the month. These five values must each apply to a different day of the week, including only those which are normal working days in the
33、countries of both of the X.25 interfaces. The value applicable to the month is calculated as the average of the five daily values obtained. Schedule of evaliintion Every year each operator of a public X.25 network should evaluate the round-trip delay to each other public X.25 network for the month o
34、f November. Additional evaluations of round-trip delay for a month, day or other convenient period may be made at the discretion of the network operator. Preference should be given to larger traffic streams, and evaluations should in particular be made after, any physical or logical network configur
35、ation change affecting a trafic stream (for example, the introduction of an extra X.75 link, or the replacement of a transit route by a direct route). Processing Before the end of December every year, each operator of a public X.25 network will send its results of the round-trip delay evaluations fo
36、r November to a body designated by CEPT. The designated body will compile each complete set of evaluation results it receives to produce a matrix of delay values. This will show the values obtained for each identifiable traffic stream and will be made freely available for publication. Each network o
37、perator should, as soon as possible, inform its appropriate partner operators of the results of any additional evaluations which it has made. subsequent reception of the echoed data packet; reception of the echoed data packet; packet level protocol event. Edition of August 15, 1990 CEPT T/CAC*4*E 89
38、 232b414 O002914 1 T/CAC 4 E Page 4 2.5. Further analysis As quoted in Recommendation T/CAC 2 E, the round-trip delay indicator is related to the CCITT X.135 parameter Data packet transfer delay. The nature of this relation is described below. The round-trip delay indicator includes, while the X.135
39、 parameter values numerically do not, the trans- mission times of both the generated and echoed data packets over both the calling and called X.25 network access links. At 9.6 kbitls, the transmission time of a 128 octet data packet is not less than 113 ms, and the component of round-trip delay due
40、to the access links will therefore be just over 450 ms. Also included in the round-trip delay indicator, and not in the X.135 parameter, are the data packet processing times of both the generating and echoing X.25 DTEs. Each of the two X.25 DTEs involved in a round-trip delay measurement may contrib
41、ute up to 40 ms of processing delay (see Annex B), and the component due to DTE processing may therefore be up to 80 ms. Finally, the round-trip delay indicator covers a two-way data packet transfer, whereas the X. 135 parameter applies to a one-way transfer. An estimate of the value of the X.135 pa
42、rameter corresponding to a given round-trip delay indicator can be calculated by taking into account all of the factors described above and assuming that there is no difference between the two directions of data transfer. 3. CALL SET-UP DELAY (CSD) 3.1. Definition The Call set-up delay indicator (CS
43、D) is defined as the average time interval between the start of trans- mission of a call request packet at a calling X.25 interface and the end of reception of the corresponding call connected packet, expressed in milliseconds, under the conditions described below. The Call set-up delay indicator re
44、flects the delay encountered by a user between sending a call request packet to a fast host and receiving the call connected packet in response. 3.2. Requirements DTEs are connected at the X.25 interfaces which can be used to generate and receive virtual calls and conform to Annex C (DTE performance
45、, measurement precision, etc.). Both X.25 DTEs should be connected via a standard line interface as used for customer service. They should be located on a switching unit whose characteristics and situation in the network in relation to international interfaces are typical of units connecting actual
46、X.25 users on that network. The X.25 DTEs should be connected at 9.6 kbit/s and use the following port configuration parameters: - frame level window of 7; - default packet level window size of 2; - default maximum data packet size of 128 octets; - default throughput class corresponding to 9.6 kbit/
47、s. Other port parameters are configured as normally used for customer service. There should be no inclusion of any user facility in a call request packet. There should be no other trafic on either X.25 interface. 3.3. Procedures 3.3.1. Single measurement To make a single measurement of call set-up d
48、elay from an X.25 interface, the DTE makes a call to the DTE at the other X.25 interface. Each measurement should conform to the following: - it consists of the transmission (on a free logical channel) of a call request packet and subsequent reception - the call connected packet is received within 3
49、0 seconds of the call request; - the period of the call set-up has no unexpected packet level protocol event; - the call is eventually cleared. of the call connected packet; Edition of August 15, 19902, . - 3.3.2. TICAC 4 E Page 5 The call set-up delay is calculated as the time between the start of transmission of the call request packet and the end of reception of the corresponding call connected packet. Note. The specific requirements for clearing depend on whether other indicators are to be measured once the call has been established. Evalimting a daily value To evaluate the call s
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