1. Key Technologies of PTN - PWE3
V1.1

2. Contents
Introduction to PWE3 Technology
PWE3 Service Bearing

3. What is PWE3?
PWE3 (Pseudo Wire Edge to Edge Emulation), also called as VLL (Virtual Leased Line), is a service emulation mechanism. It specifies the standards for providing the emulation service on specific PSN of IETF, including the standards of encapsulation, transmission, control, management, interconnection and security.
PWE3 is used to emulate the basic features of telecom network services on the packet switching network. It can traverse the PSN with minimum impact on the performance, but it doesn't replay the emulated service perfectly.
In plain terms, PWE3 is used to build a "channel" on the PSN to implement the emulation and transmission of services.
PWE3作为一种端到端的二层业务承载技术，为各种业务（FR, ATM, Ethernet, TDM SONET/SDH）通过包交换网络（PSN）传递，在PSN网络边界提供了端到端的虚链路仿真。通过此技术可以将传统的网络与分组交换网络互连起来，从而实现资源的共用和网络的拓展。

4. Why we need PWE3? Demand from the Operators:
The telecom Operators need a unified network service platform to support unified planning/construction/operation/management and maintenance.
Trend of network development: converged and optimized PSN, with the capabilities of traffic engineering/service classification/QoS.
The telecom operators need to construct and maintain network services with high ROI: Currently, the ROI of FR/TDM leased service is still higher than that of the Internet accessing service, but the fundamental network structure is in PSN type.
The network services are interconnected and backward compatible. The Operators have constructed a lot of TDM service facilities, they want to protect their investment and get the maximum benefits of the facilities.
So we need a technology to smoothly deliver the FR/TDM service on the PSN network and continue to get the benefits of the FR/TDM service. The PWE3 technology is just invented for this purpose.

5. Functions of PWE3
Encapsulate the bit-streams of the cell, PDU or specific service at the input port
Transmit the bit-streams via the IP or MPLS network;
Create the PW at the ends of the tunnel, switch and assign the PW IDs;
Manage the service-related information at the PW border, such as signaling, timing and sequence;
Manage the alarms and status of the service.

6. Emulation Principle of PWE3
Tunnel provides edge to edge connection (between NNI ports of PE)，PW is created at the ends of the tunnel to encapsulate and deliver the services. The user's packets are encapsulated to be PW PD and transmitted via the tunnel. From the perspective of the customer equipment, the PW is a link or circuit that is exclusively occupied by specific service. Different services are carried by different PWs. This emulated circuit is called as Service Emulation.
PW is invisible inside PTN. The network element at one end doesn't need to worry whether the element at the other end is the same type of network. The PE is responsible to conduct the encapsulation/de-capsulation of the service, manage the signaling, timing, sequence information of the PW border, manage the alarms and status of the service, and maintain the attributes and features of the service. The CE cannot feel the core network and will process the services as local services.
PWE3
module
PE1
PE2
CE1
CE2
Tunnel PW
PTN network
Pseudo Wire
NNI
PW emulation service

7. PWE3 Intelligent Service Perception
BTS
BSC P PE PE
NodeB
TDM E1 PWE3
RNC EF
ATM PWE3
AF1~AF4
Ethernet PWE3 BE
Service sensing is useful for adopting suitable scheduling mode according to
the priority level of the service.
For ATM service, service sensing is based on the cell, the VPI/VCI ID mapped to different PW for processing, the priority (including the priority of dropping) can be mapped to the EXP field of the PW.
For Ethernet service, service sensing is based on outer VLAN ID or IP DSCP.
For TDM real-time service that is more sensitive to delay, the service is quickly forwarded by fixed rate.

8. PWE3 Protocol Stack Model
Emulation service, such as TDM, ATM
Payload encapsulation
PW multiplexing
PSN tunnel
PSN
Physical layer
Emulation service PW
仿真业务，如 TDM、ATM: Emulation services, such as TDM and ATM
净荷封装：Payload encapsulation
PW复用：PW Multiplexing
PSN隧道： PSN tunnel
PSN物理层： PSN physical layer
仿真业务： Emulation service
PW provides an emulated physical or virtual link for the remote peer layer.
The local service PDUs are encapsulated by the sending end PE and transmitted via the PSN. The receiving end PE peels off the encapsulation and releases the PDUs to the original format. Then the PDUs are sent to the destination CE.

9. PWE3 Protocol Stack Model
PWE3 only provides 3 layers of functions of the protocol layer model, including the encapsulation layer, the PW duplex layer and the PSN convergence layer.
The encapsulation layer mainly includes the frame sequence control, timing and segmented transmission. The segmented transmission is closely related with the frame sequence control. As an optional function of PWE3, the encapsulation can be omitted.
After the service PDU is attached with the PW encapsulation and the PSN header information, if the packet length is larger than that of the MTU (Maximum Transmission Unit) supported by the PSN, the PW payload must be transmitted in segment at the entrance PE and be reorganized at the exit PE.
The PSN convergence layer provides the needed enhancement function to guarantee the service and provides unified interfaces for the PW layer to make the PW be independent from the PSN. If the PSN layer can satisfy the needs of the service by itself, this layer can be empty.

10. Reference Model of PWE3 Emulated Service Pseudo Wire PSN Tunnel TunnelAC AC
PE1
PE2
CE1
CE2
Customer Edge 1
Provider Edge 1
Provider Edge 2
Customer Edge 2
Native Service
Native Service

11. Basic Network Components of PWE3
Access Circuit
Pseudo Wire
Forwarders
Tunnels
Encapsulation
PW signaling protocol
Quality of Service
转发器：
CE可能通过接入网附着到VPLS-PE内部的桥接模块；桥接模块通过“仿真接口”连接到仿真以太网。
仅当两个CE设备是同一个VPLS实例（如相同的VPN）的成员时才能连接到相同的虚拟骨干网络。
对于每一个VPLS，在VPLS-PE内部都存在一个与之对应的仿真LAN实例。
仿真LAN实例由伪线互连的VPLS转发模块组成，伪线使用路由骨干的PSN隧道承载。
桥接模块必须能够以标准的方式学习MAC地址，并根据地址审查结果确定如何转发。
为了支持生成树协议的运行，桥接模块可能需要支持IEEE全桥功能。
每一个转发器表现为一个“虚拟转发实例（VSI）”，维护着一张将MAC地址映射到PW的转发表。VSI的构建过程与标准的桥接器构建转发表相同。 VPLS转发器的VSI和标准的桥接转发功能也存在着某些差别，如下：
— VPLS转发器决不学习从AC上接收帧的MAC SA，仅学习从PW接收的、来自于其它VPLS转发器帧的MAC SA。
   — 特定仿真LAN的VPLS转发器并不参与彼此之间的生成树协议，一种“水平分割”技术用于禁止环路。
— 概念上，PE桥接模块转发表与VPLS转发器VSI是不同的两个实体，但具体实现时可能共用同一个MAC地址表。

12. Basic Network Components of PWE3
AC (Access Circuit)
The access circuit is the connection circuit or virtual circuit between the CE and PE. Generally, all the user packets on the AC, including the layer 2 and layer 3 protocol packets should be completely forwarded to the peer end.
PW (Pseudo Wire)
In simple words, the virtual connection is the combination of the virtual circuit and the tunnels. The tunnel can be LSP, L2TPV3 or TE.
The virtual connection is directional. In order to create the virtual connection in PWE3, you need to transmit the VC information via the LDP or RSVP signaling, and combine the VC information with the tunnel management to form a PV.
For the PWE3 system, the PW is like a direct connection channel between the local AC and the peer end AC, and it completes the transparent delivery of the layer-2 data of the user. In simple words, one PW represents one service.

13. Basic Network Components of PWE3
Forwarders
After the PE receives the data frames from the AC, the forwarder will select the PW for forwarding the packets, i.e. the forwarder will assign the PW labels. Actually, the forwarder is the forwarding table of PWE3.
Tunnels
The tunnel is used to bear the PW. One tunnel can bear multiple PWs. Generally, the tunnels in PWE3 are MPLS tunnels.
The tunnel is a direct connection channel between the local PE and the peer end PE. It is used to complete the transparent delivery of data between the PEs.

14. Basic Network Components of PWE3
Encapsulation
The PW adopts standard encapsulation format and technology to transmit the packets.
You can refer to "draft-ietf-pwe3-iana-allocation-X" for the detailed definitions of different types of PWE3 packet encapsulation.
PW Signaling Protocol
As the basis of PWE3, the PW signaling protocol is used to create and maintain the PW. Currently, there are mainly two types of PW signaling protocols: LDP and RSVP (supported by 6000 V2.0).
Quality of Service
The priority information contained in the header of the layer-2 packets are mapped to the priority of QoS on the public network.
PW的LDP/RSVP:（6000 V2.0版本开始支持，9000早期版本已经支持）

15. Contents
Introduction to PWE3 Technology
PWE3 Service Bearing

16. Bi-directional Tunnel
PWE3 Features: Unified Bearing of Multiple Services
TDM E1
Abis
PWE3
IMA
ATM
AAL2/5
Iub
STM1
ETH
802.1Q IP
TDM E1
IMA E1
Ethernet
ATM STM-1
Eth PWE3
TDM PWE3
ATM PWE3
Bi-directional Tunnel
Tunnel
PHY
6100/6200
6300
PTN
BSC/RNC
NodeB
BTS
SR/BRAS
MSC/MGW
PWE3对多种业务进行较为统一的封装，都有PHY、Tunnel、PWE3几层标签。
通过PWE3实现 TDM/ATM/IMA/MLPPP 灵活的协议处理、业务感知和按需配置
TDM: 支持非结构化和结构化仿真，支持结构化的时隙压缩
ATM/IMA: 支持VPI/VCI 交换和空闲信元去除
传统的SDH设备也能接入各种业务，但是需要不同的处理单板和接口，但是这个，同一块支路板既能接入IMA E1，又能接入TDM E1信号
CAPEX－－－资本开支
OPEX－－－Operating Expense管理支出，运营成本
IMA E1：IMA（Inverse Multiplexing for ATM）技术，即ATM反向复用技术，利用这项技术，网络设计者和管理者可以根据实际需要的带宽，通过多条T1、E1连接实现ATM接入，而不需要使用昂贵的T3或E3线路。
ATM异步传输模式:ATM面向连接,它需要在通信双方向建立连接,通信结束后再由信令拆除连接。但它摈弃了电路交换中采用的同步时分复用，改用异步时分复用，收发双方的时钟可以不同，可以更有效地利用带宽
所有信元具有同样的大小-53 byte，不像帧中继及局域网系统数据分组大小不定，预计和保证应用所需要的带宽。如同轿车在繁忙交叉路口必须等待长卡车转弯一样，可变长度的数据分组容易在交换设备处引起通信延迟
VPI:虚路径标识符
VCI:虚通道标识符
上行方向IMA组转换为ATM信元，NP将单个ATM信元或多个ATM信元添加TMC封装，实现过程中可以对ATM信元做流量限制；下行方向执行相反的操作
ATM信元适配到TMC的两种模式（在PTN产品上要求支持N-to-one模式，其中N为1~8）：
one-to-one模式：一个ATM VCCs（或一个ATM VPCs）适配到一根伪线（PW）上
N-to-one模式：多个ATM VCCs（或多个ATM VPCs）适配到一根伪线（PW）上
2. TDM E1：
上行方向的接入层把E1链路添加AAL1的ATM封装处理，NP对ATM信元解封装后，将多个信元静荷重组后添加TMC标签。
N-to-one模式：多个ATM VCCs（或多个ATM VPCs）适配到一根伪线（PW）上。
3. MLPPP:
接入层实现多链路PPP报文的分片（下行）/重组（上行），支持按照N*DS0(64K)链路或N*E1链路构建的PPP组（bundles）。上行方向NP实现对PPP报文添加TMC和TMP封装；下行方向依次实现TMPLS封装、以太网封装的剥离后，再添加PPP封装
PWE3 can support multiple interfaces, including TDM E1/ IMA E1/ POS STM-n/ chSTM-n/FE/GE/10GE;
PWE3 can realize unified bearing of the TDM, ATM/IMA, Ethernet services;
PWE3 provides unified packets transmission platform to reduce the CAPEX and OPEX.

17. TDM to PWE3 伪线（内层标签）：PW (inner tag) 隧道（外层标签）: Tunnel(outer tag)
E1接口(UNI): E1 interface（UNI）
隧道接口（NNI）： Tunnel interface (NNI)
E1帧: E1 frame
STM-1帧： STM-1 frame
汇聚层: Convergence layer
接入层: Access layer
语音专线: Voice leased line

18. Implementation Process of TDM to PWE3
Bi-directional Tunnel
Implementation Process of TDM to PWE3
BTS1 PWE3
BTS1 PWE3
BTS1 E1 E1
BSC E1 E1 E1 E1 P E1 E1 PE PE
NodeB2
RNC
Abis
TDM E1
TDM E1
TDM
TDM E1
Abis E1
TDM
Abis
PWE3
1 IMA E1：上行方向IMA组转换为ATM信元，NP将单个ATM信元或多个ATM信元添加TMC封装，实现过程中可以对ATM信元做流量限制；下行方向执行相反的操作
ATM信元适配到TMC的两种模式（在PTN产品上要求支持N-to-one模式，其中N为1~8）：
one-to-one模式：一个ATM VCCs（或一个ATM VPCs）适配到一根伪线（PW）上
N-to-one模式：多个ATM VCCs（或多个ATM VPCs）适配到一根伪线（PW）上
2. TDM E1：
上行方向的接入层把E1链路添加AAL1的ATM封装处理，NP对ATM信元解封装后，将多个信元静荷重组后添加TMC标签。
N-to-one模式：多个ATM VCCs（或多个ATM VPCs）适配到一根伪线（PW）上。
3. MLPPP:
接入层实现多链路PPP报文的分片（下行）/重组（上行），支持按照N*DS0(64K)链路或N*E1链路构建的PPP组（bundles）。上行方向NP实现对PPP报文添加TMC和TMP封装；下行方向依次实现TMPLS封装、以太网封装的剥离后，再添加PPP封装
Tunnel
PHY
PWE3 can support emulated transmission of traditional TDM services. TDM circuit emulation requires both ends of the PTN to support the interconnection function. At the entrance of the PTN, the TDM data are converted into a set of packets. At the exit of the PTN, the packets are restored to TDM circuit.
Provides unified packets transmission platform.
PWE3 is used to realize TDM service perception and configure the service according to the needs
TDM: Supports structured/unstructured emulation, as well as structured timeslot compression.

19. Two Intelligent Modes of TDM E1 Processing
TDM-E1/STM-N
TDM-E1
PTN
6100/6200
NodeB
6300
RNC
E1 Unframe payload
E1 unframe payload
VC ID
Tunnel ID
E1 Unframe payload 1
For non-structured TDM E1, adopt transparent transmission to keep the integrity of E1
Services Aggregating
Multiple E1 aggregated to a PW
Multiple time slots aggregated to multiple PW 2
6100/
6200
6300
NodeB
Services recovery
For structured TDM E1, provides idle timeslot compression to save the bandwidth resource

20. ATM to PWE3 IMA/ATM接口（UNI）：IMA/ATM interface(UNI)
隧道接口（NNI）：Tunnel interface (NNI)
伪线（内层标签）：PW (inner tag)
隧道（外层标签）：Tunnel (outer tag)
ATM 信元：ATM cell

21. Implementation Process of ATM to PWE3
Bi-directional Tunnel
Implementation Process of ATM to PWE3
NB2 ATM PWE3
NB2 ATM PWE3
BTS1
ATM
ATM
ATM
BSC
ATM
ATM P
ATM
ATM
ATM PE PE
NodeB2
RNC
IMA E1
Iub
ATM STM-1
IMA E1
ATM
AAL
Iub
AAL
STM1
ATM
AAL
Iub
ATM
1 IMA E1：上行方向IMA组转换为ATM信元，NP将单个ATM信元或多个ATM信元添加TMC封装，实现过程中可以对ATM信元做流量限制；下行方向执行相反的操作
ATM信元适配到TMC的两种模式（在PTN产品上要求支持N-to-one模式，其中N为1~8）：
one-to-one模式：一个ATM VCCs（或一个ATM VPCs）适配到一根伪线（PW）上
N-to-one模式：多个ATM VCCs（或多个ATM VPCs）适配到一根伪线（PW）上
2. TDM E1：
上行方向的接入层把E1链路添加AAL1的ATM封装处理，NP对ATM信元解封装后，将多个信元静荷重组后添加TMC标签。
N-to-one模式：多个ATM VCCs（或多个ATM VPCs）适配到一根伪线（PW）上。
3. MLPPP:
接入层实现多链路PPP报文的分片（下行）/重组（上行），支持按照N*DS0(64K)链路或N*E1链路构建的PPP组（bundles）。上行方向NP实现对PPP报文添加TMC和TMP封装；下行方向依次实现TMPLS封装、以太网封装的剥离后，再添加PPP封装
PWE3
Tunnel
PHY
Provides unified packets transmission platform.
Realizes TDM service perception and configure the service according to the needs.
ATM/IMA: Supports VPI/VCI switching and idle cell removing.

22. Bi-directional Tunnel
ETH to PWE3
NB2 HSDPA PWE3
Bi-directional Tunnel
ETH B PE
ETH
ETH
ETH A PE
ETH
ETH
ETH C PE
Iub
Ethernet
Ethernet IP
1 IMA E1：上行方向IMA组转换为ATM信元，NP将单个ATM信元或多个ATM信元添加TMC封装，实现过程中可以对ATM信元做流量限制；下行方向执行相反的操作
ATM信元适配到TMC的两种模式（在PTN产品上要求支持N-to-one模式，其中N为1~8）：
one-to-one模式：一个ATM VCCs（或一个ATM VPCs）适配到一根伪线（PW）上
N-to-one模式：多个ATM VCCs（或多个ATM VPCs）适配到一根伪线（PW）上
2. TDM E1：
上行方向的接入层把E1链路添加AAL1的ATM封装处理，NP对ATM信元解封装后，将多个信元静荷重组后添加TMC标签。
N-to-one模式：多个ATM VCCs（或多个ATM VPCs）适配到一根伪线（PW）上。
3. MLPPP:
接入层实现多链路PPP报文的分片（下行）/重组（上行），支持按照N*DS0(64K)链路或N*E1链路构建的PPP组（bundles）。上行方向NP实现对PPP报文添加TMC和TMP封装；下行方向依次实现TMPLS封装、以太网封装的剥离后，再添加PPP封装
ETH
802.1Q IP
Iub
ETH
802.1Q IP
Iub
802.1Q
ETH
PWE3
Tunnel
PHY
Supports emulated transmission of ETH services.
Provides unified packets transmission platform.
Supports the E-LINE, E-LAN and E-TREE services.

23. Ethernet Service Types
E-Line service
E-LAN service
P-t-P EVC
MP-t-MP EVC
UNI
UNI
PTN CE CE
PTN
E-Tree service
Leaf
Root
Leaf
PTN
无论是MEF还是ITU-T，均没有对以太网业务的实现技术进行规定，可以使用的技术如QinQ，MAC in MAC、PBT、T-MPLS等
EVC:以太网虚连接
Leaf
Rooted P-t-MP EVC

24. Ethernet service: E-Line
E-Line service
The E-Line service is a point-to-point service. The connectivity is decided by the two points. The access point of the customer is called as UNI. According to the definition given by MEF, the E-Line service is a "Point-to-Point EVC" service.
The E-Line service falls into two types: EPL and EVPL. The major difference between the two types is that in the EPL service, the EVC is assigned only according to the UNI port, while in the EVPL service, the EVC is assigned according to both the UNI port and the CEVLAN.

25. EPL Service PTN The UNI port cannot be multiplexed.
P-t-P EVC PE
NNI
The UNI port cannot be multiplexed.
One UNI port of the PE device can be accessed by one user only.
The users accessing the UNI ports are not distinguished via different VLANs.
The PE-PE connection is guaranteed with Qos.
When different services are transmitted between the PE devices, the bandwidths of the services are guaranteed.
The Ethernet connection between the PE devices adopts P-t-P connection.

26. EVPL Service PTN The UNI port can be multiplexed.
P-t-P EVC PE
Customer1：VLAN1001
Customer2：VLAN1002
NNI
The UNI port can be multiplexed.
One UNI port of the PE device can be accessed by multiple users.
The users are distinguished via different VLANs.
The Ethernet connection between the PE devices adopts P-t-P connection.

27. Ethernet Srvice: E-LAN
E-LAN service
The E-LAN service is a point-to-multipoint service. The connectivity is decided by the points. The access point of the customer is called as UNI. According to the definition given by MEF, E-LAN is a Multipoint-to-Multipoint EVC .
The E-LAN service falls into two types: EPLAN and EVPLAN. The major difference between the two types is that in the EPLAN service, the EVC is assigned only according to the UNI port, while in the EVPLAN service, the EVC is assigned according to both the UNI port and the CEVLAN.

28. EPLAN Service PTN The UNI port cannot be multiplexed.
MP-t-MP EVC
PTN
The UNI port cannot be multiplexed.
One UNI port of the PE device can be accessed by one user only.
The users accessing the UNI ports are not distinguished via different VLANs.
The PE-PE connection is guaranteed with Qos.
When different services are transmitted between the PE devices, the bandwidths of the
services are guaranteed.
The Ethernet connection between the PE devices adopts MP-t-MP connection.

29. EVPLAN Service PTN The UNI port can be multiplexed.
MP-t-MP EVC
PTN
Customer1：VLAN1001
Customer2：VLAN1002
Customer2 EVC
Customer1 EVC
The UNI port can be multiplexed.
One UNI port of the PE device can be accessed by multiple users.
The users are distinguished via different VLANs.
The Ethernet connection between the PE devices adopts MP-t-MP connection.

30. Ethernet Srvice: E-Tree
E-Tree service
The E-Tree service is a point-to-multipoint service. The connectivity is decided by the points. The access point of the customer is called as UNI. According to the definition given by the MEF, the E-Tree service is a "Point-to-Multipoint EVC" service. In the E-TREE service, the UNI ports are classified as Root UNI and Leaf UNI. The Root UNI can communicate with the other Root UNIs and the Leaf UNIs. The Leaf UNI can only communicate with the Root UNIs.
The E-Tree service falls into two types: EPTree and EVPTree. The major difference between the two types is that in the EPTree service, the EVC is assigned only according to the UNI port, while in the EVPTree service, the EVC is assigned according to both the UNI port and the CEVLAN.

31. EPTREE Service PTN The UNI port cannot be multiplexed.
Root
Leaf
Rooted P-t-MP EVC
PTN
The UNI port cannot be multiplexed.
One UNI port of the PE device can be accessed by one user only.
The users accessing the UNI ports are not distinguished via different VLANs.
The PE-PE connection is guaranteed with Qos.
When different services are transmitted between the PE devices, the bandwidths of the services are guaranteed.
The Ethernet connection between the PE devices adopts P-t-MP connection.

32. EVPTREE Service PTN The UNI port can be multiplexed.
Root
Leaf
Rooted P-t-MP EVC
PTN
Customer 1：VLAN 1001
Customer 2：VLAN 1002
Customer 2 EVC
Customer 1 EVC
The UNI port can be multiplexed.
One UNI port of the PE device can be accessed by multiple users.
The users are distinguished via different VLANs.
The Ethernet connection between the PE devices adopts P-t-MP connection.