BESS Working Group S. Gringeri
Internet-Draft J. Whittaker
Intended status: Standards Track Verizon
Expires: January 13, 2021 C. Schmutzer, Ed.
P. Brissette
Cisco Systems, Inc.
July 12, 2020

Private Line Emulation VPWS Signalling


This document specifies the mechanisms to signal Virtual Private Wire Services (VPWS) carrying bit-stream signals over Packet Switched Networks (PSN).

Status of This Memo

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Table of Contents

1. Introduction

Virtual Private Wire Service (VPWS) is a widely deployed technology for providing point-to-point (P2P) services for various layer 2 and also layer 1 technologies. Initially VPWS were define in the Pseudowire Emulation Edge-to-Edge (PWE3) architecture [RFC3985] for Frame Relay, ATM, HDLC, PPP, Ethernet, TDM and SONET/SDH.

Later on the adoption of BGP [RFC4271] as a protocol for delivering ethernet layer 2 services led to Ethernet VPNs [RFC7432] and EVPN-VPWS [RFC8214] respectively.

This document focuses on bit stream VPWS instance types which already got introduced in [RFC3985] and describes mechanisms that can be used to discover and establish such VPWS instances by a means of a dynamic protocol rather than manual configuration on both endpoints.

Possible bit stream VPWS instance types are:

A generic VPWS reference model similar to the one defined in [RFC3985] and [PLE] is shown in Figure 1. Data received from a CEs is encapsulated by PEs into the respective VPWS established between the attachment circuits of the local and remote PE and transmitted across the Packet Switched Network (PSN) using a PSN tunnel.


    CE1 & CE2 physical                       CE3 & CE4 physical
       interfaces                                interfaces
            |      <------- PSN tunnels ----->      |
            |    +-----------------------------+    |
            |    |                             |    |
     +---+  v  +---+                         +---+  v  +---+
     |CE1|-----|   |.......... VPWS1 ........|PE2|-----|CE3|
     +---+     |   |                         +---+     +---+
               |PE1| packet switched network   |
     +----     |   |                         +---+     +---+
     |CE2|-----|   |.......... VPWS2 ........|PE3|-----|CE4|
     +---+     +---+                         +---+     +---+
               ^ |                             | ^
               | +-----------------------------+ |
               |                                 |
           attachment                       attachment
            circuits                         circuits
               |                                 |
               |<------ emulated services ------>|


Figure 1: VPWS Reference Model

In the example shown in Figure 1 there are two CE nodes (CE1 and CE2) connected to the same PE node (PE1). CE3 is connected to PE2 and CE4 is connected to PE3. There are two VPWS instances established. VPWS1 between CE1 and CE3 and VPWS2 between CE2 and CE4. For traffic to be carried across the network PSN tunnels between PE1 and PE2 and between PE1 and PE3 are needed.

In order for a bit stream VPWS instance to come up, the attachment circuit parameters must be identical on both endpoints. The control plane mechanisms described in this document are leveraged to meet this requirement. Mechanisms for misconnection detection and protection switch coordination are also described.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

1.2. Terminology

2. Solution Requirements

The scope of this document is to specify signalling mechanisms for PLE bit-stream services as defined in [PLE].

For legacy bit-stream services that have been defined for TDM [RFC4553] and [RFC5086] as well as SONET/SDH [RFC4842], additional signalling mechanisms are described to complement the mechanisms defined in [RFC5287].

To avoid redefining PW types for [RFC8214] the notion of "PW type" from [RFC8077] is maintained and only a new PW type for [PLE] has been assigned by IANA.

The concept of "CEP type" from [RFC5287] to distinguish different connection types that use the same PW type is adopted. In this document it is referred to as "PLE/CEP type". Two new connection types are defined (see Section 4.2.3).

To unambiguously identify the rate of an attachment circuit, also the concept of "CEP/TDM bit-rate" from [RFC5287] is adopted and called "PLE bit-rate" herein.

The VPWS signalling requirements are as follows:

3. Service Types

The following sections list all possible service types that are supported by the proposed signalling mechanisms.

3.1. Ethernet Service Types

Service Type Encapsulation Standard PW Type PLE/CEP Type PLE/CEP/TDM Bit-rate
1000BASE-X [PLE] TBD1 0x3 1,250,000
10GBASE-R [PLE] TBD1 0x3 10,312,500
25GBASE-R [PLE] TBD1 0x3 25,791,300
40GBASE-R [PLE] TBD1 0x3 41,250,000
100GBASE-R [PLE] TBD1 0x3 103,125,000

3.2. Fibre Channel Service Types

Service Type Encapsulation Standard PW Type PLE/CEP Type PLE/CEP/TDM Bit-rate
1GFC [PLE] TBD1 0x3 1,062,500
2GFC [PLE] TBD1 0x3 2,125,000
4GFC [PLE] TBD1 0x3 4,250,000
8GFC [PLE] TBD1 0x3 8,500,000
10GFC [PLE] TBD1 0x3 19,518,750
16GFC [PLE] TBD1 0x3 14,025,000
32GFC [PLE] TBD1 0x3 28,050,000
128GFC [PLE] TBD1 0x3 112,200,000

3.3. OTN Service Types

Service Type Encapsulation Standard PW Type PLE/CEP Type PLE/CEP/TDM Bit-rate
ODU0 [PLE] TBD1 0x4 1,244,160
ODU1 [PLE] TBD1 0x4 2,498,775
ODU2 [PLE] TBD1 0x4 10,037,273
ODU2e [PLE] TBD1 0x4 10,399,525
ODU3 [PLE] TBD1 0x4 40,319,218
ODU4 [PLE] TBD1 0x4 104,794,445

3.4. TDM Service Types

Service Type Encapsulation Standard PW Type PLE/CEP Type PLE/CEP/TDM Bit-rate
CESoPSN basic mode [RFC5086] 0x0015 N/A N
CESoPSN with CAS [RFC5086] 0x0017 N/A N
E1 [RFC4553] 0x0011 N/A 32
DS1 [RFC4553] 0x0012 N/A 24
DS1 octet-aligned [RFC4553] 0x0012 N/A 25
E3 [RFC4553] 0x0013 N/A 535
T3 [RFC4553] 0x0014 N/A 699

N is the number of DS0 channels in the attachment circuit

3.5. SONET/SDH Service Types

Service Type Encapsulation Standard PW Type PLE/CEP Type PLE/CEP/TDM Bit-rate
VT1.5/VC-11 [RFC4842] 0x0010 0x1 26
VT2/VC-12 [RFC4842] 0x0010 0x1 35
VT3 [RFC4842] 0x0010 0x1 53
VT6/VC-2 [RFC4842] 0x0010 0x1 107
STS-Nc [RFC4842] 0x0010 0x0 783*N
VC-4-Mc [RFC4842] 0x0010 0x0 783*3*M
Fract. STS1/VC-3 [RFC4842] 0x0010 0x2 783
Fract. VC-4 [RFC4842] 0x0010 0x2 783*4
Async STS1/VC-3 [RFC4842] 0x0010 0x2 783
OC3/STM1 [PLE] TBD1 0x3 155,520
OC12/STM4 [PLE] TBD1 0x3 622,080
OC48/STM16 [PLE] TBD1 0x3 2,488,320
OC192/STM64 [PLE] TBD1 0x3 9,953,280
OC768/STM256 [PLE] TBD1 0x3 39,813,120

N=1,3,12,48,192,768 and M=1,4,16,64,256

4. EVPN-VPWS signalling

4.1. Reuse of existing BGP EVPN-VPWS capabilities

A PLE VPWS instance is identified by a pair of per-EVI ethernet A-D routes advertised by two PE nodes establishing the VPWS in accordance to [RFC8214].

The EVPN layer 2 attribute extended community defined in [RFC8214] MUST be supported and added to the per-EVI ethernet A-D route.

4.2. BGP PLE Attribute

To exchange and validate bit-stream specific attachment circuit parameters during the VPWS setup, a new BGP path attribute called "BGP PLE attribute" is defined.

The BGP PLE attribute defined in this document can be attached to EVPN VPWS routes [RFC8214]. The usage for other Address Family Identifier (AFI) / Subsequent Address Family Identifier (SAFI) combinations is not defined herein but may be specified in future specifications.

The BGP PLE attribute is an optional and transitive BGP path attribute. The attribute type code TBD2 has been assigned by IANA (see section Section 6)

The format is defined as a set of Type/Length/Value (TLV) triplets, described in the following sections and listed in Table 1. This attribute SHOULD only be included with EVPN Network Layer Reachability Information (NLRI).

BGP PLE attribute TLVs
TLV Type Name Length Mandatory
1 PW Type TLV 3 Y
2 PLE/CEP/TDM Bit-rate TLV 5 Y
3 PLE/CEP Options TLV 3 Y 1*
4 TDM Options TLV 13 Y 2*
5 PLE/CEP/TDM Payload Bytes TLV 3 N
6 Endpoint-ID TLV 0..80 N

1* PLE/CEP only, 2* TDM only

For a particular PSN it is expected that the network operator will choose a common set of parameters per VPWS type, hence efficient BGP update packing as discussed in section 12 of [RFC4277] is expected to happen.

4.2.1. PW Type TLV

The PW Type TLV MUST be present in the BGP PLE attribute to signal what type of VPWS instance has to be established. Valid PW types for the mechanisms described in this document can be found in Section 3.

The PW Type TLV format is shown in Figure 2.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |      Type     |             Length            |    Reserved   |
   |R|           PW Type           |

Figure 2: PW type TLV

Type : 1

Length : 3

Reserved / R :

PW Type :

4.2.2. PLE/CEP/TDM Bit-rate TLV

The PLE/CEP/TDM Bit-rate TLV is MANDATORY but MAY be omitted if the attachment circuit type can be unambiguously derived from the PW Type carried in the PW Type TLV. The PLE/CEP/TDM Bit-rate TLV format is shown in Figure 3.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |      Type     |             Length            |    Reserved   |
   |                     PLE/CEP/TDM Bit-rate                      |

Figure 3: PLE/CEP/TDM Bit-rate TLV

Type : 2

Length : 5

Reserved :

PLE/CEP/TDM Bit-rate :

4.2.3. PLE/CEP Options TLV

The PLE/CEP Options TLV MUST be present when signalling CEP and PLE VPWS instances. The PLE/CPE Options TLV format is shown in Figure 4.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |      Type     |             Length            |    Reserved   |
   |        PLE/CEP Options        |

Figure 4: PLE/CEP Options TLV

Type : 3

Length : 3

Reserved :

    0                                       1
    0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
  |AIS|UNE|RTP|EBM|      Reserved [0:6]       |  PLE/CEP  | Async |
  |   |   |   |   |                           |    Type   |T3 |E3 |

Figure 5: PLE/CEP Options

PLE/CEP Options :

4.2.4. TDM options TLV

Whether when signalling TDM VPWS the TDM Options TLV MUST be present or MAY be omitted when signalling TDM VPWS instances is defined in [RFC5287]. The TDM Options TLV format is shown in Figure 6.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |      Type     |             Length            |    Reserved   |
   |                                                               |
   +                                                               +
   |                         TDM Options                           |
   +                                                               +
   |                                                               |

Figure 6: TDM Options TLV

Type : 4

Length : 13

Reserved :

TDM Options :

4.2.5. PLE/CEP/TDM Payload Bytes TLV

The PLE/CEP/TDM Payload Bytes TLV MAY be included if a non-default payload size is to be used. If this TLV is omitted then the default payload sizes defined in [RFC4553], [RFC5086], [RFC4842] and [PLE] MUST be assumed. The format of the PLE/CEP/TDM Payload Bytes TLV is shown in Figure 7.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |      Type     |             Length            |    Reserved   |
   |   PLE/CEP/TDM Payload Bytes   |

Figure 7: PLE/CEP/TDM Payload Bytes TLV

Type : 5

Length : 3

Reserved :

PLE/CEP/TDM Payload Bytes :

4.2.6. Endpoint-ID TLV

The Endpoint-ID TLV MAY be included to allow for misconnection detection. The Endpoint-ID TLV format is shown in Figure 8.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |      Type     |             Length            |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +
   //                Endpoint Identifier (variable)               //

Figure 8: Endpoint-ID TLV

Type : 6

Length : 0-80

Endpoint Identifier :

4.3. Control Plane Operations

The deployment model shown in figure 3 of [RFC8214] does equally apply to the operations defined in this document.

4.3.1. VPWS Setup and Teardown

After an attachment circuit has been configured to be part of a VPWS instance and has not declared any local defect, the PE node announces his endpoint using a per-EVI ethernet A-D route to other PEs in the PSN via BGP. The Ethernet Tag ID is set to the VPWS instance identifier and the BGP PLE attribute is included to carry mandatory and optional bit-stream specific attachment circuit parameters.

Both endpoints receiving the EVPN per-EVI A-D route, validate the end to end connectivity by comparing BGP PLE attributes. Upon successful validation, the VPWS instance comes up and traffic can flow through the PSN. In the scenario where the validation phase fails, the remote PE reachability information is simply ignored and totally dismiss as a destination candidate. The VPWS instance validation is performed as follow:

PLE is structure agnostic for SONET/SDH service types and hence can not validate whether a mix of SONET and SDH attachment circuits are connected (by incident) via VPWS. The detection of such misconfiguration is the responsibility of the operator managing the CE nodes.

In case of multi-homed CEs the mechanisms defined in [RFC8214] apply but are limited to the single-active and port-active scenarios.

Whenever the VPWS instance configuration is removed, the PE node MUST widthdraw its associated per-EVI ethernet A-D route.

4.3.2. Failure Scenarios Single-homed CEs

Whenever a attachment circuit does declare a local fault the following operations MUST happen:

Whenever the CE-bound IWF does enter packet loss state the operations defined in [RFC4553], [RFC5086], [RFC4842] and [PLE] MUST happen. Multi-homed CEs

Figure 9 demonstrates a multi-homing scenario. CE1 is connected to PE1 and PE2 where PE1 is the designated forwarder while PE2 is the non designated forwarder.

         DF  +---+    |         |   +---+   +---+
    +---+/   +---+    |   VPWS1/|   +---+   +---+
    |CE1|             |       / |
    +---+\   +---+    |      /  |
          +--|PE2|----|-----+   |
        NDF  +---+    |         |


Figure 9: EVPN-VPWS multi-homing redundancy

In Figure 9 PE1 and PE2 are configured for single-active load-balancing mode. Both PEs are advertising a per-ES ethernet A-D route with the same non-zero Ethernet Segment (ES) value and the single-active bit set. This non-zero ES value is called Ethernet Segment Identifier (ESI).

In this example PE1 is elected as Designated Forwarder (DF) for the shared ESI where as PE2 is the Non-Designated Forwarder (NDF) for that segment. The signalling of primary / backup follows exactly the procedure defined in [RFC8214] where P and B bits of the layer 2 attribute extended community are used to settle proper connectivity.

Upon link failure between CE1 and PE1, PE1 and PE2 follows EVPN Ethernet Segment DF Election procedures described in [RFC8214] and [pref_df] for EVPN-VPWS. PE1 leverage mass-withdraw mechanism to tell PE3 to steer traffic over backup connectivity. The per-EVI ethernet A-D route advertisement remains intact. The main purpose is to keep reachability information available for fast convergence purpose. Therefore, the per-EVI ethernet A-D route MAY be withdrawn only under local fault and MUST be withdraw when the circuit is un-configured.

Port-active operation happens in the same way as single-active load-balancing mode described before but at the port level instead of being at the sub-interface level.

5. VPWS signalling using LDP

This section is already under construction and will be soon be publicly announced

6. IANA Considerations

This document defines a new BGP path attribute known as the BGP PLE attribute. IANA is requested to assign attribute code type TBD2 to the BGP PLE attribute from the "BGP Path Attributes" registry.

This document defines a new PW Type for PLE VPWS. IANA is requested to assign a PW type value TBD1 from the "MPLS Pseudowire Types" registry.

7. Security Considerations

The same Security Considerations described in [RFC8214] and [RFC5287] are valid for this document.

8. Acknowledgements

9. References

9.1. Normative References

[PLE] Schmutzer, C., "draft-cisco-bess-mpls-ple-00", 2020.
[pref_df] IETF, "Preference-based EVPN DF Election"
[RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3)", BCP 116, RFC 4446, DOI 10.17487/RFC4446, April 2006.
[RFC4553] Vainshtein, A. and YJ. Stein, "Structure-Agnostic Time Division Multiplexing (TDM) over Packet (SAToP)", RFC 4553, DOI 10.17487/RFC4553, June 2006.
[RFC4842] Malis, A., Pate, P., Cohen, R. and D. Zelig, "Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) Circuit Emulation over Packet (CEP)", RFC 4842, DOI 10.17487/RFC4842, April 2007.
[RFC5086] Vainshtein, A., Sasson, I., Metz, E., Frost, T. and P. Pate, "Structure-Aware Time Division Multiplexed (TDM) Circuit Emulation Service over Packet Switched Network (CESoPSN)", RFC 5086, DOI 10.17487/RFC5086, December 2007.
[RFC5287] Vainshtein, A. and Y(J). Stein, "Control Protocol Extensions for the Setup of Time-Division Multiplexing (TDM) Pseudowires in MPLS Networks", RFC 5287, DOI 10.17487/RFC5287, August 2008.
[RFC8077] Martini, L. and G. Heron, "Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)", STD 84, RFC 8077, DOI 10.17487/RFC8077, February 2017.
[RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J. and J. Rabadan, "Virtual Private Wire Service Support in Ethernet VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017.
[srv6_netprog] IETF, "SRv6 Network Programming"
[srv6_overlay] IETF, "SRv6 BGP based Overlay services"

9.2. Informative References

[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", RFC 3985, DOI 10.17487/RFC3985, March 2005.
[RFC4271] Rekhter, Y., Li, T. and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006.
[RFC4277] McPherson, D. and K. Patel, "Experience with the BGP-4 Protocol", RFC 4277, DOI 10.17487/RFC4277, January 2006.
[RFC7432] Sajassi, A., Aggarwal, R., Bitar, N., Isaac, A., Uttaro, J., Drake, J. and W. Henderickx, "BGP MPLS-Based Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February 2015.

Authors' Addresses

Steven Gringeri Verizon EMail:
Jeremy Whittaker Verizon EMail:
Christian Schmutzer (editor) Cisco Systems, Inc. Vienna, Austria EMail:
Patrice Brissette Cisco Systems, Inc. Ottawa, ON Canada EMail: