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Key Technologies of PTN - PWE3
V1.1
Contents
Introduction to PWE3 Technology PWE3 Service Bearing
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.
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.
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.
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.
PW emulation service
PWE3module
PE1 PE2
CE1 CE2
TunnelPW
PTN network
PWE3module
Tunnel
Pseudo Wire
NNI
EF
BTS BSC
NodeB
TDM E1 PWE3
ATM PWE3
Ethernet PWE3
RNC
PE PEP
AF1~AF4
BE
PWE3 Intelligent Service Perception
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.
PWE3 Protocol Stack Model
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.
Emulation service, such as TDM, ATM
Payload encapsulation
PW multiplexing
PSN tunnel
PSN
Physical layer
Emulation service
PW
PSN tunnel
Emulation service, such as TDM, ATM
Payload encapsulation
PW multiplexing
PSN tunnel
PSN
Physical layer
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.
Reference Model of PWE3
PE1
CE1 Tunnel CE2
Emulated ServicePseudo
WirePSN
Tunnel
PE2
Native Service
Native Service
Customer Edge
1
Customer Edge 2
Provider Edge
2
Provider Edge
1
AC AC
Basic Network Components of PWE3
Access Circuit Pseudo Wire Forwarders Tunnels Encapsulation PW signaling protocol Quality of Service
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.
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.
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.
Contents
Introduction to PWE3 Technology PWE3 Service Bearing
PWE3 Features: Unified Bearing of Multiple Services
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.
TDM
E1
Abis PWE3
TDM
Abis
E1
TDM
Abis
IMA
E1
ATM
AAL2/5
Iub
PWE3
ATM
AAL2/5
Iub
STM1
ATM
AAL2/5
Iub
ETH
802.1Q
IP
Iub ETH
PWE3
802.1Q
IP
Iub
ETH
802.1Q
IP
Iub
TDM E1IMA E1 EthernetATM STM-1
TDM E1Ethernet
Eth PWE3
TDM PWE3
ATM PWE3Bi-directional TunnelTDM PWE3
ATM PWE3
Eth PWE3
Tunnel Tunnel Tunnel
PHYPHYPHY
6100/6200 6300
PTNBSC/RNCNodeB
BTS
SR/BRAS
MSC/MGW
TDM to PWE3
TDM
E1
Abis PWE3
TDM
Abis
E1
TDM
Abis
TDM E1TDM E1
BTS1 PWE3
BTS1 BSC
NodeB2
Bi-directional TunnelBTS1 PWE3
RNC
PEPE
Tunnel
PHY
E1
E1
E1E1E1PE1
E1
E1
Implementation Process of TDM to PWE3
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.
Two Intelligent Modes of TDM E1 Processing
E1 Unframe payload
TDM-E1TDM-E1/STM-N
E1 unframe payload
VC ID Tunnel ID
E1 Unframe payload
6100/6200 6300NodeB RNC
PTN
For non-structured TDM E1, adopt transparent transmission to keep the integrity of E1
1
2
Services Aggregating
Services recovery
Multiple E1 aggregated to a PW
Multiple time slots aggregated to multiple PW
6100/
6200 6300
NodeB
For structured TDM E1, provides idle timeslot compression to save the bandwidth resource
ATM to PWE3
IMA
E1
ATM
AAL
Iub
PWE3
ATM
AAL
Iub
STM1
ATM
AAL
Iub
IMA E1ATM STM-1
NB2 ATM PWE3
BTS1 BSC
NodeB2
Bi-directional TunnelNB2 ATM PWE3
RNC
PEPE
Tunnel
PHY
ATM
ATM
ATMATMATMPATM
ATMATM
Implementation Process of ATM to PWE3
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.
NB2 HSDPA PWE3Bi-directional TunnelNB2 HSDPA PWE3
PE
PE
ETH
ETH ETH
ETH ETH
ETH
Supports emulated transmission of ETH services. Provides unified packets transmission platform. Supports the E-LINE, E-LAN and E-TREE services.
ETH to PWE3
ETH
802.1Q
IP
Iub
Ethernet
ETH
PWE3
802.1Q
IP
Iub
Tunnel
PHY
ETH
802.1Q
IP
Iub
Ethernet
PE
ETH
A
B
C
PTN
CECE
UNIUNI UNIUNI
E-LAN service
MP-t-MP EVC
PTN
RootLeaf
Leaf
Leaf
Rooted P-t-MP EVC
E-Tree service
PTN
Ethernet Service Types
Servi ce Type Port-Based(Al l to one bundl i ng)
VLAN-Based(Servi ce mul ti pl exed)
E-Li ne EPL EVPL , VPWS
E-LAN EP-LAN EVP-LAN, VPLS
E-Tree EP-Tree EVP-Tree
P-t-P EVC
CECE
E-Line service
Ethernet service: E-LineE-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.
EPL Service
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.
PTNCECE
UNIUNI UNIUNI
P-t-P EVC
CECEPEPE PEPE
NNINNI NNINNI
EVPL Service
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.
PTNCECE
UNIUNIUNIUNI
P-t-P EVC
CECEPEPE PEPE
Customer1 ： VLAN1001Customer2 ： VLAN1002 Customer1 ： VLAN1001
Customer2 ： VLAN1002
NNINNI NNINNI
Ethernet Srvice: E-LANE-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.
EPLAN Service
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.
MP-t-MP EVC
PTN
EVPLAN Service
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.
MP-t-MP EVC
PTN
Customer1 ： VLAN1001Customer2 ： VLAN1002
Customer1 ： VLAN1001Customer2 ： VLAN1002
Customer2 ： VLAN1002
Customer1 ： VLAN1001
Customer2 ： VLAN1002
Customer2 EVC
Customer1 EVC
Ethernet Srvice: E-TreeE-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.
EPTREE Service
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.
Root
Leaf
Leaf
Leaf
Rooted P-t-MP EVC
PTN
EVPTREE Service
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.
RootLeaf
Leaf
Leaf
Rooted P-t-MP EVC
PTN
Customer 1 ： VLAN 1001Customer 2 ： VLAN 1002
Customer 1 ： VLAN 1001Customer 2 ： VLAN 1002
Customer 1 ： VLAN 1001Customer 2 ： VLAN 1002
Customer 1 ： VLAN 1001
Customer 2 EVC
Customer 1 EVC
