1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU SERIES I: INTEGRATED SERVICES DIGITAL NETWORK Maintenance principles 1.620 (1 0196) Frame relay operation and maintenance principles and functions ITU-T Recommendation I .620 (Previously CCITT Recommendation)
2、 STDsITU-T RECMN I-bZU-ENGL 177b 48b2571 Ob32821 708 ITU-T I-SERIES RECOMMENDATIONS INTEGRATED SERVICES DIGITAL NETWORK ;ENERAL STRUCTURE Terminology Description of ISDNs General modelling methods Telecommunication network and service attributes General description of asynchronous transfer mode Scop
3、e General aspects of services in ISDN Common aspects of services in the ISDN Bearer services supported by an ISDN Teleservices supported by an ISDN Supplementary services in ISDN Network functional principles Reference models Numbering, addressing and routing Connection types Performance objectives
4、Protocol layer requirements General network requirements and functions Application of I-series Recommendations to ISDN user-network interfaces Layer 1 Recommendations Layer 2 Recommendations Layer 3 Recommendations Multiplexing, rate adaption and support of existing interfaces Aspects of ISDN affect
5、ing terminal requirements SERVICE CAPABILITIES 3VERALL NETWORK ASPECTS AND FUNCTIONS ISDN USER-NETWORK INTERFACES INTERNETWORK INTERFACES MAINTENANCE PRINCIPLE B-ISDN EQUIPMENT ASPECTS ATM equipment Management of ATM equipment 1.1 00-1.199 1.110-1.119 I. 120-1.129 I. 130-1.139 I. 1 40-1.1 49 I. 150-
6、1.199 I .200-1.299 I .200-1.209 I ,210-1.219 1.220-1.229 1.230-1.239 1.240-1.249 1.250-1.299 1.300-1.399 1.310-1.319 1.320-1.329 1.330-1.339 1.340-1.349 I .35O-l.359 I. 3604.369 1.370-1.399 1.400-1.499 I .420-1.429 1.430-1.439 1.440-1.449 1.450-1.459 1.460-1.469 1.470-1.499 1:500-1.599 1.600-1.699 1
7、.700-1.799 1.730-1.749 I .750-1.799 For further details, please refer to ITU-T List of Recommendations. STD-ITU-T RECMN I-b20-ENGL L77b m 48b2571 b32822 844 ITU-T RECOMMENDATION 1.620 FRAME RELAY OPERATION AND MAINTENANCE PRINCIPLES AND FUNCTIONS Summary This Recommendation provides the operation an
8、d maintenance principles and procedures for frame relay services at the user-to-network interface and network-to-network interface. The OAh4 functions described in support of frame relaying are based on OAM specific frames and the associated procedures. Source ITU-T Recommendation 1.620 was prepared
9、 by ITU-T Study Group 13 (1993-1996) and was approved by the WTSC (Geneva, 9-18 October 1996). STD-ITU-T RECMN I*bZU-ENGL L99b 48b257L Ob32823 780 FOREWORD ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunicati
10、on Standardization Sector (ITU-T) is a permanent organ of the IT. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conf
11、erence (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1. In some a
12、reas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized o
13、perating agency. INTELLECTUAL PROPERTY RIGHTS The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or applicability of claimed In
14、tellectual Proper e.g. a customer may initiate an end-to-end loopback. This does not preclude the reporting of loopback results to the OSF. 7.1.1.1.3 Loopback applications The loopback mechanism provides the following OAM capabilities: 1) Continuity check; 2) Fault localization. The following additi
15、onal capabilities may be provided by the use of the optional fields: 3) 4) OAM information transfer; 5) Node fault condition detection. Round Trip Delay (RTD) and delay variation measurements; 7.1.2 FR performance management functions Performance management functions are for further study. 3 Recomme
16、ndation 1.620 (10196) STD-ITU-T RECMN I-b20-ENGL L99b D 48b2571 Ob32828 2b2 W Coding O000 O001 8 The frame relay layer OAM frames contain fields common to all types of OAM frames (see Table 1) as well as specific fields for each type of OAM fiame. A received OM4 frame with a reserved code point shal
17、l be passed transparently by a frame relay node. Frame relay layer OAM frame format Table 1n.620 - Common OAM header code points Function Loopback 1111 1111 All other values User specific (Note) Reserved NOTE - User-specific functions are not to be standardized by the IT-T. 8.1 Common OAM frame fiel
18、ds All fiame relay layer OAM fiames will have the following common fields (see Figure 1): 4.922 address field format Common Function specific fields I CRC-16 1 1 with DL-CORE control=O and D/C=I 1 OAMheader 1 4 4.922 header (4 octets) !-. I octet Variable .i- 2 octets (integer number of octets) T130
19、8130-96 Figure 1A.620 - Common OAM frame format 1) 2) 3) 4) Frame header - This field consists of the address field as defined in Annex NQ.922. Identification of OAM frames is described in 8.1.1. Common OAM header (8 bits) - This field indicates the type of OAM function performed by this frame. Codi
20、ng is accordance with Table 1. Function-specific fields (variable: integer multiple of 8 bits) - These fields carry information specific to the OAM function being performed, Error detection code (16 bits) - This field carries a CRC-16 error detection code as defined in Recommendation Q.921. 8.1.1 OA
21、M frame identification The following method is used to distinguish OAM frames from user frames. The OAM frame uses the 4-octet address field format of Q.922 with D/C=1. The DL-CORE control field shall be encoded as O00000 in an OAM frame. The OAM frame has the same DLCI value as the user data frame
22、for each link of the frame relay connection. NOTE - User frames are described in Recommendation 4.922. OAM frames can Co-exist with, and are distinguishable from, ali types of user frames. 4 Recommendation 1.620 (10/96) STD-ITU-T RECMN I-bZU-ENGL 277b 48b257L b32827 IT7 Correlation L Send Node Count
23、 7 bits I 1 octet Tag(CT) B (SNC) 8.2 Loopback function Return Node Count Time Stamp (TS) Additional function-specific 1 octet (optional) field(s) (optional) TLV notation TLV notation (RW 8.2.1 FR Loopback frame format The Loopback (LB) frame format is shown in Figure 2. Source point Loopback point
24、Figure 2n.620 - Function-specific fields and format of FR-OAM loopback Correlation Tag (CT): 7 bits This field is used to correlate the transmitted LB frame with the received LB frame, in conjunction with the return node count value (see below). Loopback Indicator (LBI): 1 bit This field provides a
25、Boolean indication as to whether or not the frame has been looped back (send or return direction indication). For a send frame, the LBI is set to 1. For a return frame, the LBI is set to o. A means to confirm that loopback is performed at the frame relay layer, rather than at the physical layer, is
26、provided by requiring the loopback point to change the loopback indication field within the loopback frame payload. This principle is illustrated in Figure 3. Loopback indication = 1 T1308150-96 Loopback indication = O Figure 3fl.620 - The loopback indication function Send Node Count (SNC): 1 octet
27、This field is set by the sending node to indicate the number of FR nodes to be traversed before loopback. If the SNC is set to zero, the LB frame should be passed by every node to the connection end point for initialization purposes as described below. If the SNC is set to ail-ones, the LB frame sho
28、uld be passed by every node to the connection end point for the specific case of an end-to-end loopback. Recommendation 1.620 (10196) 5 STD.ITU-T RECMN I-bZU-ENGL L77b = Lidlb2571 b32830 711 Return Node Count (RNC): 1 octet The RNC value is incremented by 1 by each FR node traversed if the LBI is se
29、t to 1. The RNC value is decremented by 1 by each FR node traversed if the LBI is set to O. Time Stamp (TS): Optional. Variable length (integer number of octets) This field may optionally be used to encode a time stamp for Round Trip Delay (RTD) measurements. The use of TS for single direction delay
30、 measurements is for Mher study. The format and encoding of the TS field is in accordance with the ASN.1 notation for Type-Length-Value (TLV). Codepoints of type are given in Table 2. Additional Function-Specific Field(s) (AFSF): Optional. Variable length (integer number of octets) The format of thi
31、s field is in accordance with the ASN.1 notation for TLV as for TS (see Table 2). This(ese) field(s) may optionally be used for enhancement of other OM functions such as QOS monitoring, etc. and may be implementation specific. The use of this(ese) field(s) for additional OAM function is for frther s
32、tudy. An additional function-specific field with a reserved code point in a received OAM frame shall be ignored. Table 2fi.620 - Codepoints of type for time stamp and additional function-specific fields -Coding I Type of function I I O000 O001 I Time stamp I 11111 1111 I User specific (Note) I I All
33、 other values I Reserved I I NOTE - User-specific functions are not to be standardized by the ITU-T. I 8.2.2 Initialization procedure Any FR node may determine the number of nodes upstream and downstream for LB purposes by using the send and return node counts as follows. The FR node sends the LB fr
34、ame with SNC=O. LB Frames with SNC=O are used for initialization purposes only and are called Initialization Loopback (ILB) frames. Every FR node must pass this frame after incrementing the value of the RNC field by 1 if the LBI is set to 1 (send direction). The connection endpoint should copy the R
35、NC value to the SNC field and set LBI to zero before looping back the ILB frame. In the return direction, each node decrements the RNC value by 1 as per the normal procedures described below. The origination node extracts the ILB frame on the condition RNC=O. The value in the SNC field is then the n
36、umber of nodes in the connection (for the given direction). For the specific case of end-to-end loopback (SNC=all-ones), the initialization procedure need not be used. 8.2.3 Loopback procedures Once the FR node has determined the number of participating nodes involved in the connection using the abo
37、ve procedure in each direction, LB procedures for either end-to-end or segment can proceed normally as follows. 6 Recommendation 1.620 (10196) STD.ITU-T RECMN I-b2D-ENGL L97b H 4862591 Ob32831 57 m The originating node sets the value of the SNC field to the required number of nodes to be traversed b
38、efore loopback (the LB node). The LBI is set to 1 and a valid correlation tag value (e.g. sequence number) is inserted in the CT field. The RNC is set to O. Each node traversed increments the RNC by 1 when the LBI is set to 1, The condition SNC=RNC determines the loopback point. The LB node sets the
39、 LBI to O before looping back the LB frame. The LB frame may be copied for subsequent processing of the function- specific fields by the management system. In the return direction (LBI=O), each node decrements the RNC value by 1. The condition RNC=O identifies the originating node. The originating n
40、ode extracts (or copies) the LB frame for processing by the management system. For the specific case of end-to-end loopback, the originating endpoint sets the SNC to all-ones. Other procedures are the same as in the general case. Loopback procedures can be initiated by management action on demand, o
41、r by end users as required. Loopback frames may be sent periodically if required. The period is under management control and depends on service requirements. 8.2.4 Non-participating nodes Any FR node may be configured by the management interface to be a participating or a non- participating node for
42、 the purposes of the FR-LB-OAM test. In the case that the node is considered to be non-participating in the LB test, it is required to pass transparently the LB-OAM frames. Changes in configuration will require that the ILB frame be used to determine the new number of participating nodes in the conn
43、ection. 8.2.5 LBI error condition In the event that an LB point does not set the LBI=O (e.g. as an error condition), the RNC values in the return direction will continue to be incremented, resulting in the originating point not extracting the LB frame. However, in this case, the downstream FR connec
44、tion endpoint node should discard the LB frame when it detects the condition where LBI=1 and SNC is not equal to RNC. ANNEX A Network applications of loopback The loopback capability supports the following network applications as shown in Figure A. 1. a) b) c) End-to-end loopback: An FR loopback fra
45、me is inserted by an FR endpoint, and looped back by the corresponding FR endpoint. Access line loopback: An FR loopback frame is inserted by the customer or the network, and looped back by the first frame relay node in the network or customer equipment respectively. Inter-domain loopback: An FR loo
46、pback fi-ame is inserted by one network operator, and looped back by the first frame relay node (at the FR level) in an adjacent network operator domain. Network-to-endpoint loopback: An FR frame is inserted by one network operator, and looped back by the FR endpoint in another domain. Intra-domain
47、loopback: An FR loopback frame is inserted by an FR connecting point, and looped back by another FR connecting point. d) e 7 Recommendation 1.620 (10196) 8 O n n A .n n n n n ni u :w U U u V. a STD-ITU-T RECMN I-bEU-ENGL L79b m 48b257L Ob32832 773 m O n u n n .n n n n -i W “ .w W u u. O I. n n n in
48、n n n n ni d) Network-to-endpoint loopback ci $! n n n .A n n n n ni W U u :u W U “ e) Intra-domain loopback c n n an n n n ni O n w u W u. O 7 Connection endpoint o Connecting point + T1308160-96 i Domain boundary Figure A.10.620 - Loopback applications Recommendation 1.620 (10/96) STD-ITU-T RECMN
49、I-bZU-ENGL L77b 9 48b257L Ob32833 b2T ,cries A leries B ieries C ;eries D ;eries E jeries F 3eries G Series H series I Series J Series K Series L Series M Series N Series O Series P Series Q Series R Series S Series T Series U Series V Series X Series Z ITU-T RECOMMENDATIONS SERIES Organization of the work of the ITU-T Means of expression: definitions, symbols, classification General telecommunication statistics General tariff principles Overall network operation, telephone service, service operation and human factors Non-telephone telecommunication services Transmission systems and
