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Versions: 00 01 02 03                                                   
Internet Engineering Task Force                              S. Gringeri
Internet-Draft                                              J. Whittaker
Intended status: Standards Track                                 Verizon
Expires: August 26, 2021                                      N. Leymann
                                                        Deutsche Telekom
                                                       C. Schmutzer, Ed.
                                                         L. Della Chiesa
                                                          N. Nainar, Ed.
                                                            C. Pignataro
                                                     Cisco Systems, Inc.
                                                          G. Smallegange
                                                                C. Brown
                                                       Ciena Corporation
                                                                 F. Dada
                                                       February 22, 2021

          Private Line Emulation over Packet Switched Networks


   This document describes a method for encapsulating high-speed bit-
   streams as virtual private wire services (VPWS) over packet switched
   networks (PSN) providing complete signal transport transparency.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 26, 2021.

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Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction and Motivations  . . . . . . . . . . . . . . . .   3
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology and Reference Model . . . . . . . . . . . . . . .   3
     3.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Reference Models  . . . . . . . . . . . . . . . . . . . .   5
   4.  PLE Encapsulation Layer . . . . . . . . . . . . . . . . . . .   6
     4.1.  PSN and VPWS Demultiplexing Headers . . . . . . . . . . .   7
     4.2.  PLE Header  . . . . . . . . . . . . . . . . . . . . . . .   7
       4.2.1.  PLE Control Word  . . . . . . . . . . . . . . . . . .   7
       4.2.2.  RTP Header  . . . . . . . . . . . . . . . . . . . . .   9
   5.  PLE Payload Layer . . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  Constant Bit Rate Payload . . . . . . . . . . . . . . . .  10
     5.2.  Byte aligned Payload  . . . . . . . . . . . . . . . . . .  11
   6.  PLE Operation . . . . . . . . . . . . . . . . . . . . . . . .  11
     6.1.  Common Considerations . . . . . . . . . . . . . . . . . .  11
     6.2.  PLE IWF Operation . . . . . . . . . . . . . . . . . . . .  12
       6.2.1.  PSN-bound Encapsulation Behavior  . . . . . . . . . .  12
       6.2.2.  CE-bound Decapsulation Behavior . . . . . . . . . . .  12
     6.3.  PLE Performance Monitoring  . . . . . . . . . . . . . . .  14
     6.4.  QoS and Congestion Control  . . . . . . . . . . . . . . .  15
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     10.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

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1.  Introduction and Motivations

   This document describes a method for encapsulating high-speed bit-
   streams as VPWS over packet switched networks (PSN).  This emulation
   suits applications where complete signal transparency is required and
   data interpretation of the PE would be counter productive.

   One example is two ethernet connected CEs and the need for
   synchronous ethernet operation between then without the intermediate
   PEs interfering.  Another example is addressing common ethernet
   control protocol transparency concerns for carrier ethernet services,
   beyond the behavior definitions of MEF specifications.

   The mechanisms described in this document follow principals similar
   to [RFC4553] but expanding the applicability beyond TDM and allow the
   transport of signals from many technologies such as ethernet, fibre
   channel, SONET/SDH [GR253]/[G.707] and OTN [G.709] at gigabit speeds
   by treating them as bit-stream payload defined in Section 3.3.3 of

2.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

3.  Terminology and Reference Model

3.1.  Terminology

   o  ACH - Associated Channel Header

   o  AIS - Alarm Indication Signal

   o  CBR - Constant Bit Rate

   o  CE - Customer Edge

   o  CSRC - Contributing SouRCe

   o  ES - Errored Second

   o  FEC - Forward Error Correction

   o  IWF - InterWorking Function

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   o  LDP - Label Distribution Protocol

   o  LF - Local Fault

   o  MPLS - Multi Protocol Label Switching

   o  NSP - Native Service Processor

   o  ODUk - Optical Data Unit k

   o  OTN - Optical Transport Network

   o  OTUk - Optical Transport Unit k

   o  PCS - Physical Coding Sublayer

   o  PE - Provider Edge

   o  PLE - Private Line Emulation

   o  PLOS - Packet Loss Of Signal

   o  PSN - Packet Switched Network

   o  P2P - Point-to-Point

   o  QOS - Quality Of Service

   o  RSVP-TE - Resource Reservation Protocol Traffic Engineering

   o  RTCP - RTP Control Protocol

   o  RTP - Realtime Transport Protocol

   o  SES - Severely Errored Seconds

   o  SDH - Synchronous Digital Hierarchy

   o  SRTP - Secure Realtime Transport Protocol

   o  SRv6 - Segment Routing over IPv6 Dataplane

   o  SSRC - Synchronization SouRCe

   o  SONET - Synchronous Optical Network

   o  TCP - Transmission Control Protocol

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   o  UAS - Unavailable Seconds

   o  VPWS - Virtual Private Wire Service

   Similarly to [RFC4553] and [RFC5086] the term Interworking Function
   (IWF) is used to describe the functional block that encapsulates bit
   streams into PLE packets and in the reverse direction decapsulates
   PLE packets and reconstructs bit streams.

3.2.  Reference Models

   The generic models defined in [RFC4664] are applicable to PLE.

   PLE embraces the minimum intervention principle outlined in section
   3.3.5 of [RFC3985] whereas the data is flowing through the PLE
   encapsulation layer as received without modifications.

   For some applications the NSP function is responsible for performing
   operations on the native data received from the CE.  Examples are
   terminating FEC in case of 100GE or terminating the OTUk layer for
   OTN.  After the NSP the IWF is generating the payload of the VPWS
   which carried via a PSN tunnel.

                   |<--- p2p L2VPN service -->|
                   |                          |
                   |     |<-PSN tunnel->|     |
                   v     v              v     v
               +---------+              +---------+
               |   PE1   |==============|   PE2   |
               +---+-----+              +-----+---+
   +-----+     | N |     |              |     | N |     +-----+
   | CE1 |-----| S | IWF |.....VPWS.....| IWF | S |-----| CE2 |
   +-----+  ^  | P |     |              |     | P |  ^  +-----+
            |  +---+-----+              +-----+---+  |
     CE1 physical  ^                          ^  CE2 physical
      interface    |                          |   interface
                   |<--- emulated service --->|
                   |                          |
               attachment                 attachment
                circuit                    circuit

                       Figure 1: PLE Reference Model

   To allow the clock of the transported signal to be carried across the
   PLE domain in a transparent way the network synchronization reference

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   model and deployment scenario outlined in section 4.3.2 of [RFC4197]
   is applicable.

                       |                                         G
                       v                                         |
                       +-----+                 +-----+           v
      +-----+          |- - -|=================|- - -|          +-----+
      |     |<---------|.............................|<---------|     |
      | CE1 |          | PE1 |       VPWS      | PE2 |          | CE2 |
      |     |--------->|.............................|--------->|     |
      +-----+          |- - -|=================|- - -|          +-----+
           ^           +-----+<-------+------->+-----+
           |                          |              ^
           A                         +-+             |
                                     |I|             E

                Figure 2: Relative Network Scenario Timing

   The attachment circuit clock E is generated by PE2 via a differantial
   clock recovery method in reference to a common clock I.  For this to
   work the difference between clock I and clock A MUST be explicitly
   transferred between the PE1 and PE2 using the timestamp inside the
   RTP header.

   For the reverse direction PE1 does generate the clock J in reference
   to clock I and the clock difference between I and G.

   The way the common clock I is implemented is out of scope of this
   document.  Well established concepts for achieving frequency
   synchronization in a PSN have already been defined in [G.8261] and
   can be applied here as well.

4.  PLE Encapsulation Layer

   The basic packet format used by PLE is shown in the below figure.

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           +-------------------------------+  -+
           |     PSN and VPWS Demux        |    \
           |          (MPLS/SRv6)          |     > PSN and VPWS
           |                               |    /  Demux Headers
           +-------------------------------+  -+
           |        PLE Control Word       |    \
           +-------------------------------+     > PLE Header
           |           RTP Header          |    /
           +-------------------------------+ --+
           |          Bit Stream           |    \
           |           Payload             |     > Payload
           |                               |    /
           +-------------------------------+ --+

                     Figure 3: PLE Encapsulation Layer

4.1.  PSN and VPWS Demultiplexing Headers

   This document does not imply any specific technology to be used for
   implementing the VPWS demultiplexing and PSN layers.

   When a MPLS PSN layer is used.  A VPWS label provides the
   demultiplexing mechanism as described in section 5.4.2 of [RFC3985].
   The PSN tunnel can be a simple best path Label Switched Path (LSP)
   established using LDP [RFC5036] or Segment Routing [RFC8402] or a
   traffic engineered LSP established using RSVP-TE [RFC3209] or SR-TE

   When PLE is applied to a SRv6 based PSN, the mechanisms defined in
   [RFC8402] and the End.DX2 endpoint behavior defined in [SRV6NETPROG]
   do apply.

4.2.  PLE Header

   The PLE header MUST contain the PLE control word (4 bytes) and MUST
   include a fixed size RTP header [RFC3550].  The RTP header MUST
   immediately follow the PLE control word.

4.2.1.  PLE Control Word

   The format of the PLE control word is inline with the guidance in
   [RFC4385] and as shown in the below figure:

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       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
      |0 0 0 0|L|R|RSV|FRG|   LEN     |       Sequence number         |

                        Figure 4: PLE Control Word

   The first nibble is used to differentiate if it is a control word or
   Associated Channel Header (ACH).  The first nibble MUST be set to
   0000b to indicate that this header is a control word as defined in
   section 3 of [RFC4385].

   The other fields in the control word are used as defined below:


      Set by the PE to indicate that data carried in the payload is
      invalid due to an attachment circuit fault (client signal
      failure).  The downstream PE MUST play out an appropriate
      replacement data.  The NSP MAY inject an appropriate native fault
      propagation signal.


      Set by the downstream PE to indicate that the IWF experiences
      packet loss from the PSN or a server layer backward fault
      indication is present in the NSP.  The R bit MUST be cleared by
      the PE once the packet loss state or fault indication has cleared.


      These bits are reserved for future use.  This field MUST be set to
      zero by the sender and ignored by the receiver.


      These bits MUST be set to zero by the sender and ignored by the


      In accordance to [RFC4385] section 3 the length field MUST always
      be set to zero as there is no padding added to the PLE packet.  To
      detect malformed packets the default, preconfigured or signaled
      payload size MUST be assumed.

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   Sequence Number

      The sequence number field is used to provide a common PW
      sequencing function as well as detection of lost packets.  It MUST
      be generated in accordance with the rules defined in Section 5.1
      of [RFC3550] for the RTP sequence number and MUST be incremented
      with every PLE packet being sent.

4.2.2.  RTP Header

   The RTP header MUST be included and is used for explicit transfer of
   timing information.  The RTP header is purely a formal reuse and RTP
   mechanisms, such as header extensions, contributing source (CSRC)
   list, padding, RTP Control Protocol (RTCP), RTP header compression,
   Secure Realtime Transport Protocol (SRTP), etc., are not applicable
   to PLE VPWS.

   The format of the RTP header is as shown in the below figure:

        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
       |V=2|P|X|  CC   |M|     PT      |       Sequence Number         |
       |                           Timestamp                           |
       |           Synchronization Source (SSRC) Identifier            |

                           Figure 5: RTP Header

   V: Version

      The version field MUST be set to 2.

   P: Padding

      The padding flag MUST be set to zero by the sender and ignored by
      the receiver.

   X: Header Extension

      The X bit MUST be set to zero by sender and ignored by receiver.

   CC: CSRC Count

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      The CC field MUST be set to zero by the sender and ignored by the

   M: Marker

      The M bit MUST be set to zero by sender and ignored by receiver.

   PT: Payload Type

      A PT value MUST be allocated from the range of dynamic values
      define by [RFC3551] for each direction of the VPWS.  The same PT
      value MAY be reused both for direction and between different PLE

   Sequence Number

      The packet sequence number MUST continuously cycle from 0 to
      0xFFFF.  It is generated and processed in accordance with the
      rules established in [RFC3550].  The PLE receiver MUST sequence
      packets according to the Sequence Number field of the PLE control
      word and MAY verify correct sequencing using RTP Sequence Number


      Timestamp values are used in accordance with the rules established
      in [RFC3550].  For bit-streams up to 200 Gbps the frequency of the
      clock used for generating timestamps MUST be 125 MHz based on a
      the common clock I.  For bit-streams above 200 Gbps the frequency
      MUST be 250 MHz.

   SSRC: Synchronization Source

      The SSRC field MAY be used for detection of misconnections.

5.  PLE Payload Layer

5.1.  Constant Bit Rate Payload

   A bit-stream is mapped into a packet with a fixed payload size
   ignoring any structure being present.  The number of bytes MUST be
   defined during VPWS setup, MUST be the same in both directions of the
   VPWS and MUST remain unchanged for the lifetime of the VPWS.

   For constant bit rate payloads the PLE packet is filled with incoming
   bits of the bit stream starting from the most significant to the
   least significant bit.

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   All PLE implementations MUST be capable of supporting the default
   payload size of 1024 bytes.

   For PCS based CE interface types supporting FEC the NSP function MUST
   terminate the FEC and pass the PCS encoded signal to the IWF

   For PCS based CE interface types supporting virtual lanes (i.e.
   100GE) a PLE payload MUST carry information from all virtual lanes in
   a bit interleaved manner after the NSP function has performed PCS
   layer de-skew and re-ordering.

   A PLE implementation MUST support the transport of all service types
   except ODUk bit-streams using the constant bit rate payload.

5.2.  Byte aligned Payload

   In case of an OTN bit-stream, the NSP function MUST present to the
   IWF an extended ODUk including a valid frame alignment overhead.  The
   IWF is performing byte-aligned mapping into PLE packets.  The egress
   NSP function will recover the ODUk by searching for the frame
   alignment overhead.

   For byte aligned payloads PLE uses the following order for

   o  The order of the payload bytes corresponds to their order on the
      attachment circuit.

   o  Consecutive bits coming from the attachment circuit fill each
      payload byte starting from most significant bit to least

   All PLE implementations MUST support the payload size of 1024 bytes.

   All PLE implementations MUST support the transport of OTN bit-streams
   using the byte aligned payload.

6.  PLE Operation

6.1.  Common Considerations

   A PLE VPWS can be established using manual configuration or
   leveraging mechanisms of a signalling protocol

   Furthermore emulation of bit-stream signals using PLE is only
   possible when the two attachment circuits of the VPWS are of the same
   type (OC192, 10GBASE-R, ODU2, etc) and are using the same PLE payload

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   type and payload size.  This can be ensured via manual configuration
   or via a signalling protocol

   Extensions to the PWE3 [RFC4447] and EVPN-VPWS [RFC8214] control
   protocols are described in a separate document [PLESIG].

6.2.  PLE IWF Operation

6.2.1.  PSN-bound Encapsulation Behavior

   After the VPWS is set up, the PSN-bound IWF does perform the
   following steps:

   o  Packetise the data received from the CE is into a fixed size PLE

   o  Add PLE control word and RTP header with sequence numbers, flags
      and timestamps properly set

   o  Add the VPWS demultiplexer and PSN headers

   o  Transmit the resulting packets over the PSN

   o  Set L bit in the PLE control word whenever attachment circuit
      detects a fault

   o  Set R bit in the PLE control word whenever the local CE-bound IWF
      is in packet loss state

6.2.2.  CE-bound Decapsulation Behavior

   The CE-bound IWF is responsible for removing the PSN and VPWS
   demultiplexing headers, PLE control word and RTP header from the
   received packet stream and play-out of the bit-stream to the local
   attachment circuit.

   A de-jitter buffer MUST be implemented where the PLE packets are
   stored upon arrival.  The size of this buffer SHOULD be locally
   configurable to allow accommodation of specific PSN packet delay
   variation expected.

   The CE-bound IWF SHOULD use the sequence number in the control word
   to detect lost and mis-ordered packets.  It MAY use the sequence
   number in the RTP header for the same purposes.

   The payload of a lost packet MUST be replaced with equivalent amount
   of replacement data.  The contents of the replacement data MAY be
   locally configurable.  All PLE implementations MUST support

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   generation of "0xAA" as replacement data.  The alternating sequence
   of 0s and 1s of the "0xAA" pattern does ensure clock synchronization
   is maintained.  While playing out the replacement data, the IWF will
   apply a holdover mechanism to maintain the clock.

   Whenever the VPWS is not operationally up, the CE-bound NSP function
   MUST inject the appropriate native downstream fault indication signal
   (for example ODUk-AIS or ethernet LF).

   Whenever a VPWS comes up, the CE-bound IWF enters the intermediate
   state, will start receiving PLE packets and will store them in the
   jitter buffer.  The CE-bound NSP function will continue to inject the
   appropriate native downstream fault indication signal until a pre-
   configured amount of payloads is stored in the jitter buffer.

   After the pre-configured amount of payload is present in the jitter
   buffer the CE-bound IWF transitions to the normal operation state and
   the content of the jitter buffer is played out to the CE in
   accordance with the required clock.  In this state the CE-bound IWF
   MUST perform egress clock recovery.

   The recovered clock MUST comply with the jitter and wander
   requirements applicable to the type of attachment circuit, specified

   o  [G.825] and [G.823] for SDH

   o  [GR253] for SONET

   o  [G.8261] for synchronous ethernet

   o  [G.8251] for OTN

   Whenever the L bit is set in the PLE control word of a received PLE
   packet the CE-bound NSP function SHOULD inject the appropriate native
   downstream fault indication signal instead of playing out the

   If the CE-bound IWF detects loss of consecutive packets for a pre-
   configured amount of time (default is 1 millisecond), it enters
   packet loss (PLOS) state and a corresponding defect is declared.

   If the CE-bound IWF detects a packet loss ratio (PLR) above a
   configurable signal-degrade (SD) threshold for a configurable amount
   of consecutive 1-second intervals, it enters the degradation (DEG)
   state and a corresponding defect is declared.  Possible values for
   the SD-PLR threshold are between 1..100% with the default being 15%.

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   Possible values for consecutive intervals are 2..10 with the default

   While either a PLOS or DEG defect is declared the CE-bound NSP
   function SHOULD inject the appropriate native downstream fault
   indication signal.  Also the PSN-bound IWF SHOULD set the R bit in
   the PLE control word of every packet transmitted.

   The CE-bound IWF does change from the PLOS to normal state after the
   pre-configured amount of payload has been received similarly to the
   transition from intermediate to normal state.

   Whenever the R bit is set in the PLE control word of a received PLE
   packet the PLE performance monitoring statistics SHOULD get updated.

6.3.  PLE Performance Monitoring

   PLE SHOULD provide the following functions to monitor the network
   performance to be inline with expectations of transport network

   The near-end performance monitors defined for PLE are as follows:

      ES-PLE : PLE Errored Seconds

      SES-PLE : PLE Severely Errored Seconds

      UAS-PLE : PLE Unavailable Seconds

   Each second with at least one packet lost or a PLOS/DEG defect SHALL
   be counted as ES-PLE.  Each second with a PLR greater than 15% or a
   PLOS/DEG defect SHALL be counted as SES-PLE.

   UAS-PLE SHALL be counted after configurable number of consecutive
   SES-PLE have been observed, and no longer counted after a
   configurable number of consecutive seconds without SES-PLE have been
   observed.  Default value for each is 10 seconds.

   Once unavailability is detected, ES and SES counts SHALL be inhibited
   up to the point where the unavailability was started.  Once
   unavailability is removed, ES and SES that occurred along the
   clearing period SHALL be added to the ES and SES counts.

   A PLE far-end performance monitor is providing insight into the CE-
   bound IWF at the far end of the PSN.  The statistics are based on the
   PLE-RDI indication carried in the PLE control word via the R bit.

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   The PLE VPWS performance monitors are derived from the definitions in
   accordance with [G.826]

6.4.  QoS and Congestion Control

   The PSN carrying PLE VPWS may be subject to congestion, but PLE VPWS
   representing constant bit-rate (CBR) flows cannot respond to
   congestion in a TCP-friendly manner as described in [RFC2913].

   Hence the PSN providing connectivity for the PLE VPWS between PE
   devices MUST be Diffserv [RFC2475] enabled and MUST provide a per
   domain behavior [RFC3086] that guarantees low jitter and low loss.

   To achieve the desired per domain behavior PLE VPWS SHOULD be carried
   over traffic-engineering paths through the PSN with bandwidth
   reservation and admission control applied.

7.  Security Considerations

   As PLE is leveraging VPWS as transport mechanism the security
   considerations described in [RFC7432] and [RFC3985] are applicable.

8.  IANA Considerations

   Applicable signalling extensions are out of the scope of this

   PLE does not introduce additional requirements from IANA.

9.  Acknowledgements

   The authors would like to thank Andreas Burk for reviewing this
   document and providing useful comments and suggestions.

10.  References

10.1.  Normative References

   [G.823]    International Telecommunication Union (ITU), "G.823: The
              control of jitter and wander within digital networks which
              are based on the 2048 kbit/s hierarchy",

   [G.825]    International Telecommunication Union (ITU), "G.825: The
              control of jitter and wander within digital networks which
              are based on the synchronous digital hierarchy (SDH)",

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   [G.8251]   International Telecommunication Union (ITU), "G.8251: The
              control of jitter and wander within the optical transport
              network (OTN)", <https://www.itu.int/rec/T-REC-G.8251>.

   [G.8261]   International Telecommunication Union (ITU), "G.8261:
              Timing and synchronization aspects in packet networks",

   [PLESIG]   IETF, "Private Line Emulation VPWS Signalling",

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,

   [RFC3086]  Nichols, K. and B. Carpenter, "Definition of
              Differentiated Services Per Domain Behaviors and Rules for
              their Specification", RFC 3086, DOI 10.17487/RFC3086,
              April 2001, <https://www.rfc-editor.org/info/rfc3086>.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <https://www.rfc-editor.org/info/rfc3550>.

   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              DOI 10.17487/RFC3551, July 2003,

   [RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", RFC 3985,
              DOI 10.17487/RFC3985, March 2005,

   [RFC4197]  Riegel, M., Ed., "Requirements for Edge-to-Edge Emulation
              of Time Division Multiplexed (TDM) Circuits over Packet
              Switching Networks", RFC 4197, DOI 10.17487/RFC4197,
              October 2005, <https://www.rfc-editor.org/info/rfc4197>.

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   [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,
              "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
              Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385,
              February 2006, <https://www.rfc-editor.org/info/rfc4385>.

   [RFC4447]  Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
              G. Heron, "Pseudowire Setup and Maintenance Using the
              Label Distribution Protocol (LDP)", RFC 4447,
              DOI 10.17487/RFC4447, April 2006,

   [RFC4664]  Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
              2 Virtual Private Networks (L2VPNs)", RFC 4664,
              DOI 10.17487/RFC4664, September 2006,

   [RFC7432]  Sajassi, A., Ed., 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, <https://www.rfc-editor.org/info/rfc7432>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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,

10.2.  Informative References

   [G.707]    ITU-T, "Network node interface for the synchronous digital
              hierarchy (SDH)", <https://www.itu.int/rec/T-REC-G.707>.

   [G.709]    International Telecommunication Union (ITU), "G.709:
              Interfaces for the optical transport network",

   [G.826]    ITU-T, "End-to-end error performance parameters and
              objectives for international, constant bit-rate digital
              paths and connections",

   [GR253]    Telcordia, "SONET Transport Systems : Common Generic
              Criteria", <https://telecom-info.telcordia.com>.

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   [RFC2913]  Klyne, G., "MIME Content Types in Media Feature
              Expressions", RFC 2913, DOI 10.17487/RFC2913, September
              2000, <https://www.rfc-editor.org/info/rfc2913>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,

   [RFC4553]  Vainshtein, A., Ed. and YJ. Stein, Ed., "Structure-
              Agnostic Time Division Multiplexing (TDM) over Packet
              (SAToP)", RFC 4553, DOI 10.17487/RFC4553, June 2006,

   [RFC5036]  Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
              "LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
              October 2007, <https://www.rfc-editor.org/info/rfc5036>.

   [RFC5086]  Vainshtein, A., Ed., 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,

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

              IETF, "Segment Routing Policy Architecture",

              IETF, "SRv6 Network Programming",

Authors' Addresses

   Steven Gringeri

   Email: steven.gringeri@verizon.com

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   Jeremy Whittaker

   Email: jeremy.whittaker@verizon.com

   Nicolai Leymann
   Deutsche Telekom

   Email: N.Leymann@telekom.de

   Christian Schmutzer (editor)
   Cisco Systems, Inc.

   Email: cschmutz@cisco.com

   Luca Della Chiesa
   Cisco Systems, Inc.

   Email: ldellach@cisco.com

   Nagendra Kumar Nainar (editor)
   Cisco Systems, Inc.

   Email: naikumar@cisco.com

   Carlos Pignataro
   Cisco Systems, Inc.

   Email: cpignata@cisco.com

   Gerald Smallegange
   Ciena Corporation

   Email: gsmalleg@ciena.com

   Chris Brown
   Ciena Corporation

   Email: cbrown@ciena.com

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   Faisal Dada

   Email: faisald@xilinx.com

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