Packet Transport Network (PTN) is a packet-switched, connection-oriented multi-service unified transmission technology, which not only can better carry carrier-grade Ethernet services, but also meets service standardization, high reliability, flexible scalability, strict quality of service (QoS) and Five basic attributes including perfect operation management and maintenance (OAM), and taking into account the support of traditional time division multiplexing (TDM) and asynchronous transmission mode (ATM) services, inheriting the graphical interface of the synchronous digital system (SDH) network management, end-to-end Configuration and other management functions. At present, PTN is applied in the area of ​​metropolitan area networks and carries QoS-required services such as mobile backhaul, enterprise private lines / private networks, and realizes the gradual evolution from TDM to packetization of China-operated mall domain transport networks. PTN has the following two specific implementation technologies: One type is the Transport Multiprotocol Label Switching (MPLS-TP) technology developed from Internet Protocol / Multiprotocol Label Switching (IP / MPLS). This technology abandons the hop-by-hop forwarding mechanism based on IP addresses and does not rely on the control plane to establish the transmission path; it retains the multi-protocol label switching (MPLS) connection-oriented end-to-end label forwarding capability; it removes its connectionless and Non-end-to-end features, that is, it does not use last-hop pop-up (PHP), label switching path merge, equal-cost multipath, etc. Therefore, it has a definite end-to-end transmission path and is enhanced to meet the needs of the transmission network; Style network protection mechanism and OAM capabilities. The other type is the connection-oriented Ethernet transport technology developed from Ethernet, such as the operator's backbone bridge-traffic engineering (PBB-TE) specified in IEEE 802.1Qay. This technology has been improved on the basis of IEEE 802.1ah operator backbone bridging (PBB, or MAC in MAC), and has eliminated Ethernet connectionless features such as media access control (MAC) address learning, spanning tree, and flooding, and added Traffic Engineering (TE) to enhance QoS capabilities. At present, PBB-TE mainly supports point-to-point and point-to-multipoint connection-oriented service transmission and linear protection, and temporarily does not support connection-oriented multipoint-to-multipoint service transmission and ring network protection. The two types of PTN implementation technologies have certain differences in data forwarding, multi-service bearing, network protection and OAM mechanisms [1-2]. From the perspective of industry chain, standardization, equipment vendors' products and operator applications, the development trend of MPLS-TP technology is better than PBB-TE. Therefore, MPLS-TP is the mainstream implementation technology of PTN that is currently concerned and applied in the industry. 1 Main content of "PTN General Technical Requirements" The "PTN General Technical Requirements" mainly regulates the PTN network functional architecture, multi-service bearing and data forwarding functions, network protection functions and performance, OAM capabilities, QoS, packet synchronization, network interface, network performance, network management functions and control plane functions. . The first four aspects are the characteristics of PTN technology, which are briefly introduced below. 1.1 PTN network function architecture PTN has the following technical characteristics: Using connection-oriented packet switching (CO-PS) technology, based on the packet switching core, it supports multi-service bearing. Strictly connected. The connection should be able to exist for a long time and can be manually configured by the NMS. Provide a reliable network protection mechanism, and can be applied to each network layer of PTN and various network topologies. Provide differentiated service quality guarantee for multiple businesses. With perfect OAM fault management and performance management functions. Packet forwarding based on label. The encapsulation, transmission and processing of OAM messages do not depend on IP encapsulation and IP processing. The protection mechanism also does not depend on IP packets. Support bidirectional point-to-point transmission path, and support unidirectional point-to-multipoint transmission path; support point-to-point (P2P) and point-to-multipoint (P2MP) transmission path traffic engineering control capabilities. The packet transport network includes three PTN layer networks, as shown in Figure 1 [3]. They are PTN virtual channel (VC) layer network, PTN virtual channel (VP) layer network and PTN virtual segment (VS) layer network. The bottom layer of the PTN is a physical media layer network, which can use IEEE 802.3 Ethernet technology or SDH, Optical Transport Network (OTN) and other connection-oriented circuit switching (CO-CS) technologies. For MPLS-TP technology, the VC layer of PTN is the pseudowire (PW) layer, and the VP layer is the label switched path (LSP) layer. 1.2 Multi-service bearer and data forwarding function of PTN In the multi-service bearer architecture of PTN network based on MPLS-TP [4], the network client layer of MPLS-TP includes PW-based simulation services, MPLS label-based services and IP services. At this stage, the standard of the bearer architecture mainly regulates PW-based simulation services, including TDM services, Ethernet layer 2 services, and ATM services. The functional requirements for carrying IP and MPLS services using peer-to-peer models are for further study. The service bearer of PTN adopts the connection-oriented mechanism, and the implementation mechanism based on connectionlessness is not within the scope of the standard. For PW-based simulation services, PTN based on MPLS-TP should meet the following functional requirements: (1) PTN uniformly uses PWE3 encapsulation to carry simulation services. The use of PWE3 control words should comply with RFC4385. (2) PTN supports TDM service simulation and transmission. The specific requirements are as follows: Should support TDM service bearer based on unstructured simulation (SAToP) mode. The PWE3 package and control word should comply with RFC4553. SAToP mode is suitable for TDM circuit simulation of any signal structure. Optional support for TDM service bearer based on structured simulation (CESoPSN) mode. PWE3 package and control characters conform to RFC5086. CESoPSN mode is mainly used for TDM circuit simulation of N × 64kbit / s signal structure, and can save bandwidth. Optional support for TDM service bearer based on SDH emulation (CEP) mode. PWE3 package and control characters conform to RFC4842. CEP mode is mainly used for SDH circuit simulation based on VC12 or VC-4 signal structure. (3) PTN supports the simulation and transmission of Ethernet Layer 2 services. Specific requirements are as follows: Support Ethernet line service (E-Line), Ethernet private network service (E-LAN) and Ethernet root multipoint service (E-Tree), and comply with the corresponding specifications of ITU-T and MEF. It should support the binding of services and VC / VP based on port, port + VLAN. It should support the static configuration of network management to establish Ethernet services. Optional support for dynamic establishment of Ethernet services using signaling. The PWE3 package and control word should comply with RFC4448. (4) PTN can optionally support ATM service simulation and transmission. PWE3 package and control characters conform to RFC4717. PTN supports 1: 1 virtual channel connection / virtual channel connection (VCC / VPC) and N: 1 VCC / VPC encapsulation modes; supports unidirectional and bidirectional point-to-multipoint virtual channel connection (VPC) or virtual channel connection (VCC) Establishment; optional support for ATM inverse multiplexing (IMA) group processing function. PTN based on MPLS-TP should meet the following data forwarding function requirements: (1) The data forwarding mechanism of MPLS-TP is a subset of MPLS data forwarding (RFC3031), and should meet the transmission requirements specified in RFC5654. MPLS-TP does not use an IP-based hop-by-hop forwarding mechanism, and does not support Equal Cost Multipath (ECMP), Last Hop Popup (PHP), and LSP merge functions. (2) The label stacking function of MPLS-TP should comply with the specifications of RFC3032 and RFC5462. The MPLS time-to-live (TTL) processing mechanism should conform to the specifications of RFC3443 (the VC and VP two-layer TC and TTL models are consistent, and the pipeline model should be used). (3) The range of PW and LSP tags should support 1 to 1 048 575 (that is, 2 20-1), where 0 to 15 are reserved tags (used or reserved for OAM in the PTN network). Four reserved tag values ​​are defined in RFC3032. (4) The following label switching function requirements should be supported: The source node correctly adds PW and LSP labels, and supports multiplexing multiple PWs into one LSP. The sink node performs proper stripping of PW and LSP labels. It should support single-segment pseudo wire (SS-PW) and multi-segment pseudo wire (MS-PW) switching functions. The architecture of SS-PW should comply with the provisions of RFC3985. Multi-segment pseudowire exchange is to exchange PWs of different LSPs into the same LSP. 1.3 PTN network protection function requirements The protection methods supported by the PTN network are divided into the following three categories: (1) Protection method in PTN network Linear protection in PTN networks includes unidirectional / bidirectional 1 + 1 path protection, bidirectional 1: 1 or 1: N (N> 1) path protection, unidirectional / bidirectional 1 + 1 SNC / S protection and bidirectional 1: 1 SNC / S protection should support at least two-way 1: 1 protection mechanism. The ring network protection in the PTN network includes two protection mechanisms: Wrapping and Steering. At least one ring network protection mechanism should be supported. (2) Protection of access link between packet communication network and other networks 1 + 1 or 1: N protection for TDM / ATM access links. Ethernet GE / 10GE access link protection, that is, link aggregation group (LAG). (3) Dual homing protection The protection in the PTN network and the protection of the access link cooperate to achieve end-to-end service protection in the event of failure of the access link or PTN access node. The specific implementation mechanism is to be studied. The PTN network protection method should meet the following general functional requirements: (1) The protection switching of PTN shall support the triggering of links, node failures and external commands of the network management, and shall support the priority processing of various switching requests. Fault type triggering supports physical link, VP / VC signal failure (SF) and intermediate node failure, and supports signal degradation (SD). External command triggering supports network management commands such as lock to work, forced switching, manual switching, and clear commands. (2) Protection switching methods include support for single-ended switching and dual-ended switching types, support for return or non-return operation mode, support for the start of wait recovery (WTR) function and the setting of wait recovery time. (3) Protection switching time. When the delay time is set to 0, the service damage time caused by protection switching should be no more than 50 ms (except for protection switching triggered by SD). (4) Delay time setting. In the case where PTN's underlying network (such as WDM and OTN) is configured with a protection method, the PTN network protection method should support the delay time setting, which can be set to 50 ms or 100 ms. 1.4 PAM network OAM architecture and functional requirements The OAM functions of the PTN network include the OAM mechanism in the PTN network, the OAM mechanism at the service layer of the PTN network, and the OAM mechanism at the access link layer. The OAM in the PTN network is divided into three categories: alarm-related OAM, performance-related OAM, and other OAM. The OAM functional requirements of the VC, VP, and VS layer 3 are shown in Table 1. Among them, active OAM refers to OAM operations that are periodically and continuously implemented. Actively report fault and error detection performance results. On-demand OAM refers to a limited number of OAM operations initiated manually, usually used for fault diagnosis and location. 2 Discussion on key issues in the PTN standard In the process of drafting PTN industry standards, there are some controversial key issues, involving standard technology selection, PTN network application and subsequent development. We took the lead in organizing relevant discussions, some of which have preliminary conclusions, and some still need follow-up research, here to share with you: (1) OAM implementation mechanism and encapsulation format of MPLS-TP There are currently three options for T-MPLS G.8114, G-ACh [5] + Y.1731 OAM PDU [6], IETF BFD extension [7] + new OAM tool. From the perspective of protecting the existing interests of Chinese operators and equipment vendors and facilitating future software upgrades, all units in China have unanimously agreed to adopt the G-ACh + Y.1731 OAM PDU format and hope to form a joint effort to promote the adoption of MPLS-TP international standards . However, because the IETF MPLS working group is dominated by data experts such as Cisco and Juniper, it is quite difficult to select this technology as the MPLS-TP standard option. (2) Implementation mechanism of PTN ring network protection At present, the IETF has initially approved the ring network protection requirements, but the specific implementation mechanisms include MPLS-TE FRR applied in ring network topology [8], IEEE multi-segment protection [9], ITU-T Wrapping and Steering ring network protection [10] 3 options . On the one hand, we need to deeply analyze the differences in service configuration, bandwidth sharing, OAM, and cross-ring protection from the technical perspective of the three types of mechanisms; on the other hand, we must consider the impact of operators' network operation and maintenance habits. At present, according to the product situation of Chinese equipment vendors and the application requirements of operators, two ring network protection mechanisms based on ITU-T Wrapping and Steering are selected in the line standard. mechanism. (3) PTN and MSTP mixed networking requirements and interworking function requirements Since the mission of PTN is to gradually replace MSTP based on SDH, operators must face the problem of hybrid networking and interworking between PTN and MSTP during the network deployment process. If there is a hybrid networking scenario where the PTN convergence ring directly brings the MSTP access ring, how to specify the standard in the standard has also become a controversial issue, which needs subsequent coordination and discussion. (4) PTN supports IP / MPLS Layer 3 function requirements Under the development trend of full-service operation and LTE mobile backhaul bearer, does PTN need to support some Layer 3 functions of IP / MPLS? How to coordinate with the existing router network division of labor? All these require operators to clarify specific application requirements before organizing targeted research. This will become an open question to be studied in this version of the PTN line standard. PTN technology has gradually developed in an environment of competition and integration with IP / MPLS, and it has been applied to IP-based 3G mobile backhaul networks. From the perspective of standardization and industrial application, the next two years will be a critical period for the development of PTN technology. I hope that the industrial chain of PTN technology will continue to grow and develop. DVB Antenna,DVB-T1 Antenna,DVB T2 Antenna,DVB T2 Antenna Outdoor Yetnorson Antenna Co., Ltd. , https://www.yetnorson.com
