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Packet Transmission Networks Analysis

It is the trend that Transmission network is from MSTP to PTN .under this background as network to all-IP evolution in the terminal, such as mobile phones, PC can achieve a variety of IP-based service access, business users have full use of routers, switches and gateways, servers, firewalls, under operational control of the various networks have gradually and it has turned to IP-based transmission network in order to achieve top business efficiently carried evolution from MSTP to PTN is the trend. That is Why PTN transmission become mainstream network is an inevitable trend


Transfer Multiprotocol Label Switching (MPLS-TP) technology transfer Multiprotocol Label Switching (MPLS-TP) technology from Internet Protocol/ Multi-Protocol Label Switching (IP/ MPLS) development to transport multi-protocol label switching (MPLS-TP) technology. The technology abandoned the hop by hop IP address-based mechanism, and does not depend on the control plane to establish the transmission path;it retain the ability for the end label forwarding Multiprotocol Label Switching (MPLS) connection-oriented; it has no connection and removed non-end properties, i.e., it does not use the last hop pop (PHP), label switched path merge multiple equivalent paths, and also a defined end to end transfer path.therefore, it could enhance the transport network to meet the demand and have a transport network style network protection mechanisms and OAM capabilities.


The Transmission Multiprotocol Label Switching (MPLS-TP) Technology 

Transport multi-protocol label switching (MPLS-TP) technology is developed from Internet Protocol / Multiprotocol Label Switching (IP / MPLS) development. The technology abandoned the hop by hop IP address-based mechanism, and does not depend on the control plane to establish the transmission path;it retain the ability for the end label forwarding Multiprotocol Label Switching (MPLS) connection-oriented; it has no connection and removed non-end properties, i.e., it does not use the last hop pop (PHP), label switched path merge multiple equivalent paths, and also a defined end to end transfer path.therefore, it could enhance the transport network to meet the demand and have a transport network style network protection mechanisms and OAM capabilities.


Connection-oriented Ethernet Transport Technology

Ethernet transmission technology is evolved from an Ethernet connection-oriented, such as IEEE 802.1Qay Provider Backbone Bridging specifications - Traffic Engineering (PBB-TE). The technology is proved in IEEE 802.1ah Provider Backbone Bridge (PBB, namely MAC in MAC) and canceled MAC (MAC) address learning, spanning tree and flooding and other non-Ethernet connectivity features, and adds traffic Engineering (TE) to enhance QoS capabilities. Currently PBB-TE primary support service transport and linear protection for point and multipoint connection-oriented, does not support multi-service transport and ring-multipoint connection-oriented between protection


PTN Support for L3 Functions and Services 

Currently PTN mainly is targeted at providing Layer (L2) of services, including E1 / ATM emulation services, E-Line / E- LAN / E-Tree Ethernet business. The main scenarios PTN is backhaul mobile network, including the current 3G network, and future Long Term Evolution (LTE). PTN can satisfy the needs of carrying backhaul of existing 3G networks, but LTE is able to meet the needs of people who also have doubts. 


L3 features include IP routing and forwarding, and L3 MPLS VPN also with L3 multicast. Due to uncertainty for the presence of IP traffic and multicast traffic bandwidth and routing , it is difficult to provide strict QoS support capabilities. If the PTN is introduced in two operations in order to avoid traffic on the existing L2, these two operations can be set to the minimum level of service. And L3 MPLS Virtual Private Network (VPN) is based on the MPLS implementation, so you can use the quality of service-based traffic engineering and MPLS DiffServ mechanism to protect the business. Also it can support multicast L3 MPLS VPN and  you can guarantee the same quality of service


Data Plane Loopback

Existing PTN equipment only supports the OAM loopback (LB). You can verify the source through OAM LB, maintain two-way connectivity between the endpoints to detect nodes and internal fault between nodes, but can not accurately locate the fault. As shown in Figure 1, if the link between PE2-PE3 fails, and can not be determined by OAM LBthat they are PE3 or link failure between PE2-PE3 fails. And if similar SDH device supports data plane loop, namely service loopback, you can point different loopback,achieve accurate positionfor failure


Similar to SDH, PTN currently proposed data plane loop includes remote loopback (loop back entrance), local loop (exit loop) and fiber loopback (customer loopback) in three ways. In addition to the fault location, fiber optic loop can also be single-end service performance tests, such as two-way delay, packet loss and throughput tests to facilitate network test now


PTN Network Plan 

IETF RFC5654 PTN MPLS-TP network will be divided into transmission business layer, transport layer and channel section layer. Wherein the transport service layer can be PW or business LSP, similar to the synchronous digital hierarchy (SDH) network VC- 12. PW is used to provide time-division multiplexing (TDM), Ethernet and Asynchronous Transfer Mode (ATM) and other emulation services; business LSP provides IP and MPLS network layer service. It refers to the transfer channel layer LSP layer, similar to SDH network VC-4. Section layer is used between two adjacent MPLS-TP transport service node aggregation layer or layers of information transfer channels. Section layer may use MPLS-TP technology or other techniques to achieve, such as synchronous digital hierarchy / Ethernet / optical transport network (SDH / ETH / OTN). PTN by using multi-layer network architecture can be achieved with the synchronous digital hierarchy/ OTN similar scalability.


in addition to Layer 3 MPLS-TP network concerned, PTN equipment also need to support the business layer and layer technology segment related functions . Such as service layer Ethernet OAM (belonging IEEE802.1ag and Y.1731), Ethernet link layer OAM (belonging IEEE 802.3ah), SDH overhead processing operations and links and protection functions


PTN network layers positioned

 PTN inherits SDH / MSTP good networking, protection and operation maintenance capabilities;with the use of IP-based kernel ,it provides a perfect elastic bandwidth allocation, statistical multiplexing and differentiated services capabilities, also it provides rich client-side interface for Ethernet, TDM and ATM servicesis,whichi very suitable for high-grade, small particles of flexible service access, aggregation and statistical multiplexing convergence. The maximum rate of PTN network side interface can provide only 10GE (Gigabit Ethernet) interface, with its established network backbone layer above clearly,it could not be unable to meet the bandwidth needs of today's explosive growth of the business. Therefore, PTN located in the metro aggregation network access layer, in the future,the layer with the core backbone network consists of the metro DWDM/ OTN equipment,then set up with a large bandwidth of the transmission capacity and the PON equipment to focus on intensive common user access Full Service Access Network , then together constitute the main metro transport network


The Relationship Between PTN and Other Network

 in metro aggregation access layer, China Mobile has built or is building SDH / MSTP network, IP MAN and three full-service access network network, whether PTN network construction will produce the existing network of overlapping or substitute it? From each network for carrying business type point of view, in the short term it is not generated. SDH / MSTP network for carrying TDM services and a small amount of high-grade data services, IP MAN and Full Service Access Network bearer ordinary data traffic when there is a large cost advantage, while PTN is suitable for carrying a high level of data traffic and a small amount TDM traffic, due to the TDM business and service level differentiation of demand for data services  which will not die in a short time, companies also have to further tap the potential of the current network,and it need to protect investment and therefore PTN will be long-term coexistence with the existing network, and they should work together for the user provide business and other aspects of the type ,as well as level of security services more in line with user requirements


PTN Networking Mode

1. Use a connection-oriented packet-switched (CO-PS) technology, based on packet switching core, which supports multi-service bearer

2. Strict connection-oriented. The connection should be able to exist for a long manual configuration by the NMS

3. Provide reliable network protection mechanism can be applied to various network hierarchy PTN and various network topologies

3. Provide differentiated service quality assurance

4. For a variety of businesses. It has a complete OAM fault management and performance management functions

5. Tag-based packet forwarding. OAM packet encapsulation, transmission and processing does not depend on IP encapsulation and IP processing. Protection mechanism does not rely on IP packet

6.Support bidirectional point to point transmission path, and support one-way multipoint transmission path; traffic engineering support point to point (P2P) and point to multipoint (P2MP) transmission path control




PTN network protection requirements

   (1) protection within PTN: Linear protection within PTN including unidirectional / bi-directional 1 + 1 path protection, bidirectional 1︰1 or 1︰N (N> 1) path protection, one-way / two-way 1 + 1 SNC / S protection and bidirectional 1︰1 SNC / S protection, should support at least bi 1︰1 protection mechanisms

   Ring protection within PTN including Wrapping and STeering two mechanisms should support at least one ring protection mechanisms

   (2) convey packet access link protection network and other networks

    1. 1 + 1 or 1︰N protection TDM / ATM access links

    2. Protection of Ethernet GE / 10GE access links that link aggregation group (LAG)

   (3) Dual-homing protection: PTN internal network protection and access link protection matched to achieve the access link or PTN access node fail-end service protection cases. Specific implementation mechanism will be studied 


The internal network protection PTN should meet the following general functional requirements

(1) PTN protection switching should support the link, network node failure and trigger external commands, and should support the various switching request priority handling. The type of fault trigger support physical links, VP / VC signal fail (SF) and the intermediate node failures, support signal degradation (SD). External command triggers support locking to work, forced switching, manual switching and network management commands to clear command

(2) protection switching modes include to support for single-ended switching and dual-ended switching type, and support configured to return or not to return to operating mode, also WTR ( Start WTR) function and WTR time setting

(3) protection switching time. In case the delay time is set to 0, the protection switching business damage caused by time should not be greater than 50 ms (except for switching SD trigger protection) 

(4) to set the delay time. In the PTN bottom network (WDM and OTN) is configured with protection case, PTN network protection should support the delay time set,and can be set to 50 ms or 100 ms. 1.4 PTN OAM network architecture and functionality requirements of PTN OAM includes the OAM mechanism within PTN, PTN network service layer OAM mechanisms and OAM mechanisms for access link layer, and so on. OAM PTN network is devided into alarm correlation of OAM, performance and other AM three categories related. Among them, the initiative OAM refers to OAM operating periodic continuous implementation. The initiative to report the results of fault detection and error performance. Demand OAM refers to a limited number of OAM operation initiated manually, usually used for fault diagnosis and localization


PTN technology trends 

PTN technology is undoubtedly a peak current transmission technology development, which is the second ATM after the failure of attempts to dominate the online world, and it seems most likely to achieve unified network technology.for Unified network, the recent application aims to triple play; from the depths of the technical point of view, through the technical evolution of the network itself,it could making the service delivery itself as a service, easier people, man and machine, and machine-machine communication use, rather than having to focus on the transfer itself;


In the future it will have to achieve self-organizing networks, self-management PTN technology in five years and will be large-scale deployment, become mainstream transport network equipment, equipment form of PTN It may be more diverse. Such as integration and access technology, integration with OTN, ROADM technology. 


But as one transmission PTN provide basic business communication network, how convenient, efficient, safe, reliable, multi-service ,and it can still continue to pursue the goal of providing current PTN mainly homogeneous type of transmission and interconnection networks; in principle speaking, you can achieve interoperability of heterogeneous networks  Or large-scale deployment possibilities and reliability of the current PTN network major consideration. Business Data-level interoperability has been well documented, for control plane UNI, ENNI interoperability interfaces transport network requires further research 


Since the 1980s generation SDH, its core technology like this has never occurred so much change. PTN technology is so amazing, it has completely changed the TDM as a central location, instead packet switching and QoS support. It can fully accept all the major networks have appeared, it is to maintain the integrity of the transmission network technology core spirit, no doubt, PTN SDH transmission network as the successor to play a cornerstone role in the network infrastructure services.