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Versions: (draft-zheng-netconf-udp-pub-channel) 00 01 02 03

NETCONF                                                         G. Zheng
Internet-Draft                                                   T. Zhou
Intended status: Standards Track                                A. Clemm
Expires: January 1, 2019                                          Huawei
                                                           June 30, 2018


         UDP based Publication Channel for Streaming Telemetry
                 draft-ietf-netconf-udp-pub-channel-03

Abstract

   This document describes a UDP-based publication channel for streaming
   telemetry use to collect data from devices.  A new shim header is
   proposed to facilitate the distributed data collection mechanism
   which directly pushes data from line cards to the collector.  Because
   of the lightweight UDP encapsulation, higher frequency and better
   transit performance can be achieved.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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 January 1, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Transport Mechanisms  . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Dynamic Subscription  . . . . . . . . . . . . . . . . . .   5
     4.2.  Configured Subscription . . . . . . . . . . . . . . . . .   7
   5.  UDP Transport for Publication Channel . . . . . . . . . . . .   8
     5.1.  Design Overview . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Data Format of the UPC Message Header . . . . . . . . . .   8
     5.3.  Options . . . . . . . . . . . . . . . . . . . . . . . . .  10
       5.3.1.  Reliability Option  . . . . . . . . . . . . . . . . .  10
       5.3.2.  Fragmentation Option  . . . . . . . . . . . . . . . .  11
     5.4.  Data Encoding . . . . . . . . . . . . . . . . . . . . . .  12
   6.  Using DTLS to Secure UPC  . . . . . . . . . . . . . . . . . .  12
     6.1.  Transport . . . . . . . . . . . . . . . . . . . . . . . .  12
     6.2.  Port Assignment . . . . . . . . . . . . . . . . . . . . .  13
     6.3.  DTLS Session Initiation . . . . . . . . . . . . . . . . .  13
     6.4.  Sending Data  . . . . . . . . . . . . . . . . . . . . . .  14
     6.5.  Closure . . . . . . . . . . . . . . . . . . . . . . . . .  14
   7.  Congestion Control  . . . . . . . . . . . . . . . . . . . . .  15
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  16
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     11.2.  Informative References . . . . . . . . . . . . . . . . .  17
     11.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   Streaming telemetry refers to sending a continuous stream of
   operational data from a device to a remote receiver.  This provides
   an ability to monitor a network from remote and to provide network
   analytics.  Devices generate telemetry data and push that data to a



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   collector for further analysis.  By streaming the data, much better
   performance, finer-grained sampling, monitoring accuracy, and
   bandwidth utilization can be achieved than with polling-based
   alternatives.

   Sub-Notif [I-D.ietf-netconf-subscribed-notifications] defines a
   mechanism that allows a collector to subscribe to updates of YANG-
   defined data that is maintained in a YANG [RFC7950] datastore.  The
   mechanism separates the management and control of subscriptions from
   the transport that is used to actually stream and deliver the data.
   Two transports, NETCONF transport
   [I-D.ietf-netconf-netconf-event-notifications] and HTTP transport
   [I-D.ietf-netconf-restconf-notif], have been defined so far for the
   notification messages.

   While powerful in its features and general in its architecture, in
   its current form the mechanism needs to be extended to stream
   telemetry data at high velocity from devices that feature a
   distributed architecture.  The transports that have been defined so
   far, NETCONF and HTTP, are ultimately based on TCP and lack the
   efficiency needed to stream data continuously at high velocity.  A
   lighter-weight, more efficient transport, e.g. a transport based on
   UDP is needed.

   o  Firstly, data collector will suffer a lot of TCP connections from,
      for example, many line cards equipped on different devices.

   o  Secondly, as no connection state needs to be maintained, UDP
      encapsulation can be easily implemented by hardware which will
      further improve the performance.

   o  Thirdly, because of the lightweight UDP encapsulation, higher
      frequency and better transit performance can be achieved, which is
      important for streaming telemetry.

   This document specifies a higher-performance transport option for
   Sub-Notif that leverages UDP.  Specifically, it facilitates the
   distributed data collection mechanism described in
   [I-D.zhou-netconf-multi-stream-originators].  In the case of data
   originating from multiple line cards, the centralized design requires
   data to be internally forwarded from those line cards to the push
   server, presumably on a main board, which then combines the
   individual data items into a single consolidated stream.  The
   centralized data collection mechanism can result in a performance
   bottleneck, especially when large amounts of data are involved.  What
   is needed instead is the support for a distributed mechanism that
   allows to directly push multiple individual substreams, e.g. one from
   each line card, without needing to first pass them through an



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   additional processing stage for internal consolidation, but still
   allowing those substreams to be managed and controlled via a single
   subscription.  The proposed UDP based Publication Channel (UPC)
   natively supports the distributed data collection mechanism.

   The transport described in this document can be used for transmitting
   notification messages over both IPv4 and IPv6 [RFC8200].

   While this document will focus on the data publication channel, the
   subscription can be used in conjunction with the mechanism proposed
   in [I-D.ietf-netconf-subscribed-notifications] with extensions
   [I-D.zhou-netconf-multi-stream-originators].

2.  Terminology

   Streaming Telemetry: refers to sending a continuous stream of
   operational data from a device to a remote receiver.  This provides
   an ability to monitor a network from remote and to provide network
   analytics.

   Component Subscription: A subscription that defines the data from
   each individual telemetry source which is managed and controlled by a
   single Subscription Server.

   Component Subscription Server: An agent that streams telemetry data
   per the terms of a component subscription.

3.  Solution Overview

   The typical distributed data collection solution is shown in Fig. 1.
   Both the Collector and the Publisher can be distributed.  The
   Collector includes the Subscriber and a set of Receivers.  And the
   Publisher includes a Subscription Server and a set of Component
   Subscription Servers.  The Subscriber cannot see the Component
   Subscription Servers directly, so it will send the Global
   Subscription information to the Subscription Server (e.g., main
   board) via the Subscription Channel.  When receiving a Global
   Subscription, the Subscription Server decomposes the subscription
   request into multiple Component Subscriptions, each involving data
   from a separate internal telemetry source, for example a line card.
   The Component Subscriptions are distributed to the Component
   Subscription Server.  Subsequently, each data originator generates
   its own stream of telemetry data, collecting and encapsulating the
   packets per the Component Subscription and streaming them to the
   designated Receivers.  This distributed data collection mechanism may
   form multiple Publication Channels to the Receivers.  The Receiver is
   able to assemble many pieces of data associated with one Global
   Subscription.



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   The Publication Channel supports the reliable data streaming, for
   example for some alarm events.  The Collector has the option of
   deducing the packet loss and the disorder based on the information
   carried by the notification data.  And the Collector may decide the
   behavior to request retransmission.

   The rest of the draft describes the UDP based Publication Channel
   (UPC).

                    +-------------------------------------+
                    |            Collector                |
                    |                                     |
                    |  +------------+  +-----------+      |
                    |  | Subscriber |  | Receivers |      |
                    |  +----+-------+  +--^----^---+      |
                    |       |             |    |          |
                    +-------------------------------------+
                            |             |    |
               Subscription |             |    | Publication
               Channel      |             |    | Channel
                            |   +---------+    |
                            |   |              |
                    +-------------------------------------+
                    |       |   |              |          |
                    |  +----v---+-----+ +------+-------+  |
                    |  | Subscription | | Component    |  |
                    |  | Server       | | Subscription |  |
                    |  |              | | Servers      |  |
                    |  +--------------+ +--------------+  |
                    |                                     |
                    |              Publisher              |
                    +-------------------------------------+

                    Fig. 1 Distributed Data Collection

4.  Transport Mechanisms

   For a complete pub-sub mechanism, this section will describe how the
   UPC is used to interact with the Subscription Channel relying on
   NETCONF or RESTCONF.

4.1.  Dynamic Subscription

   Dynamic subscriptions for Sub-Notif are configured and managed via
   signaling messages transported over NETCONF [RFC6241] or RESTCONF
   [RFC8040].  The Sub-Notif defined RPCs which are sent and responded
   via the Subscription Channel (a), between the Subscriber and the
   Subscription Server of the Publisher.  In this case, only one



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   Receiver is associated with the Subscriber.  In the Publisher, there
   may be multiple data originators.  Notification messages are pushed
   on separate channels (b), from different data originators to the
   Receiver.

   +--------------+                         +--------------+
   |  Collector   |                         |  Publisher   |
   |              |                         |              |
   |  (a)   (b)   |                         |  (a)    (b)  |
   +--+------+----+                         +--+-------+---+
      |      |                                 |       |
      |      |     RPC:establish-subscription  |       |
      +---------------------------------------->       |
      |      |     RPC Reply: OK               |       |
      <----------------------------------------+       |
      |      |     UPC:notifications           |       |
      |      <-----------------------------------------+
      |      |                                 |       |
      |      |     RPC:modify-subscription     |       |
      +---------------------------------------->       |
      |      |     RPC Reply: OK               |       |
      <----------------------------------------+       |
      |      |     UPC:notifications           |       |
      |      <-----------------------------------------+
      |      |                                 |       |
      |      |     RPC:delete-subscription     |       |
      +---------------------------------------->       |
      |      |     RPC Reply: OK               |       |
      <----------------------------------------+       |
      |      |                                 |       |
      |      |                                 |       |
      +      +                                 +       +

                 Fig. 2 Call Flow For Dynamic Subscription

   In the case of dynamic subscription, the Receiver and the Subscriber
   SHOULD be colocated.  So UPC can use the source IP address of the
   Subscription Channel as it's destination IP address.  The Receiver
   MUST support listening messages at the IANA-assigned PORT-X or PORT-
   Y, but MAY be configured to listen at a different port.

   The Publication Channels MUST share fate with the subscription
   session.  In other words, when the delete-subscription is received or
   the subscription session is broken, all the associated Publication
   Channels MUST be closed.






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4.2.  Configured Subscription

   For a Configured Subscription, there is no guarantee that the
   Subscriber is currently in place with the associated Receiver(s).  As
   defined in Sub-Notif, the subscription configuration contains the
   location information of all the receivers, including the IP address
   and the port number.  So that the data originator can actively send
   generated messages to the corresponding Receivers via the UPC.

   The first message MUST be a separate subscription-started
   notification to indicate the Receiver that the pushing is started.
   Then, the notifications can be sent immediately without any wait.

   All the subscription state notifications, as defined in
   [I-D.ietf-netconf-subscribed-notifications], MUST be encapsulated to
   be separated notification messages.

   +--------------+                         +--------------+
   |  Collector   |                         |  Publisher   |
   |              |                         |              |
   |  (a)   (b)   |                         |  (a)    (b)  |
   +--+------+----+                         +--+-------+---+
      |      |                                 |       |
      |      |     Capability Exchange         |       |
      <---------------------------------------->       |
      |      |                                 |       |
      |      |     Edit config(create)         |       |
      +---------------------------------------->       |
      |      |     RPC Reply: OK               |       |
      <----------------------------------------+       |
      |      |     UPC:subscription started    |       |
      |      <-----------------------------------------+
      |      |     UPC:notifications           |       |
      |      <-----------------------------------------+
      |      |                                 |       |
      |      |     Edit config(delete)         |       |
      +---------------------------------------->       |
      |      |     RPC Reply: OK               |       |
      <----------------------------------------+       |
      |      |     UPC:subscription terminated |       |
      |      <-----------------------------------------+
      |      |                                 |       |
      |      |                                 |       |
      +      +                                 +       +

               Fig. 3 Call Flow For Configured Subscription





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5.  UDP Transport for Publication Channel

5.1.  Design Overview

   As specified in Sub-Notif, the telemetry data is encapsulated in the
   NETCONF/RESTCONF notification message, which is then encapsulated and
   carried in the transport protocols, e.g.  TLS, HTTP2.  The following
   figure shows the overview of the typical UPC message structure.

   o  The Message Header contains information that can facilitate the
      message transmission before de-serializing the notification
      message.

   o  Notification Message is the encoded content that the publication
      channel transports.  The common encoding method includes GPB [1],
      CBOR [RFC7049], JSON, and XML.
      [I-D.ietf-netconf-notification-messages] describes the structure
      of the Notification Message for both single notification and
      multiple bundled notifications.

               +-------+  +--------------+  +--------------+
               |  UDP  |  |   Message    |  | Notification |
               |       |  |   Header     |  | Message      |
               +-------+  +--------------+  +--------------+

                  Fig. 4 UDP Publication Message Overview

5.2.  Data Format of the UPC Message Header

   The UPC Message Header contains information that can facilitate the
   message transmission before de-serializing the notification message.
   The data format is shown as follows.

      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
     +-------+---------------+-------+-------------------------------+
     | Vers. |    Flag       |  ET   |      Length                   |
     +-------+---------------+-------+-------------------------------+
     |                       Message-Generator-ID                    |
     +---------------------------------------------------------------+
     |                       Message ID                              |
     +---------------------------------------------------------------+
     ~                       Options                                 ~
     +---------------------------------------------------------------+


                     Fig. 3 UPC Message Header Format




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   The Message Header contains the following field:

   o  Vers.: represents the PDU (Protocol Data Unit) encoding version.
      The initial version value is 0.

   o  Flag: is a bitmap indicating what features this packet has and the
      corresponding options attached.  Each bit associates to one
      feature and one option data.  When the bit is set to 1, the
      associated feature is enabled and the option data is attached.
      The sequence of the presence of the options follows the bit order
      of the bitmap.  In this document, the flag is specified as
      follows:

      *  bit 0, the reliability flag;

      *  bit 1, the fragmentation flag;

      *  other bits are reserved.

   o  ET: is a 4 bits identifier to indicate the encoding type used for
      the Notification Message. 16 types of encoding can be expressed:

      *  0: GPB;

      *  1: CBOR;

      *  2: JSON;

      *  3: XML;

      *  others are reserved.

   o  Length: is the total length of the message, measured in octets,
      including message header.

   o  Message-Generator-ID: is a 32-bit identifier of the process which
      created the notification message.  This allows disambiguation of
      an information source, such as the identification of different
      line cards sending the notification messages.  The source IP
      address of the UDP datagrams SHOULD NOT be interpreted as the
      identifier for the host that originated the UPC message.  The
      entity sending the UPC message could be merely a relay.

   o  The Message ID is generated continuously by the message generator.
      Different subscribers share the same notification ID sequence.

   o  Options: is a variable-length field.  The details of the Options
      will be described in the respective sections below.



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5.3.  Options

   The order of packing the data fields in the Options field follows the
   bit order of the Flag field.

5.3.1.  Reliability Option

   The UDP based publication transport described in this document
   provides two streaming modes, the reliable mode an the unreliable
   mode, for different SLA (Service Level Agreement) and telemetry
   requirements.

   In the unreliable streaming mode, the line card pushes the
   encapsulated data to the data collector without any sequence
   information.  So the subscriber does not know whether the data is
   correctly received or not.  Hence no retransmission happens.

   The reliable streaming mode provides sequence information in the UDP
   packet, based on which the subscriber can deduce the packet loss and
   disorder.  Then the subscriber can decide whether to request the
   retransmission of the lost packets.

   In most case, the unreliable streaming mode is preferred.  Because
   the reliable streaming mode will cost more network bandwidth and
   precious device resource.  Different from the unreliable streaming
   mode, the line card cannot remove the sent reliable notifications
   immediately, but to keep them in the memory for a while.  Reliable
   notifications may be pushed multiple times, which will increase the
   traffic.  When choosing the reliable streaming mode or the unreliable
   streaming mode, the operate need to consider the reliable requirement
   together with the resource usage.

   When the reliability flag bit is set to 1 in the Flag field, the
   following option data will be attached

      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
     +---------------------------------------------------------------+
     |            Previous Message ID                                |
     +---------------------------------------------------------------+

                     Fig. 4 Reliability Option Format

   Current Message ID and Previous Message ID will be added in the
   packets.

   For example, there are two subscriber A and B,




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   o  Message IDs for the generator are : [1, 2, 3, 4, 5, 6, 7, 8, 9],
      in which Subscriber A subscribes [1,2,3,6,7] and Subscriber B
      subscribes [1,2,4,5,7,8,9].

   o  Subscriber A will receive [Previous Message ID, Current Message
      ID] like: [0,1][1,2][2,3][3,6][6,7].

   o  Subscriber B will receive [Previous Message ID, Current Message
      ID] like: [0,1][1,2][2,4][4,5][5,7][7,8][8,9].

5.3.2.  Fragmentation Option

   UDP palyload has a theoretical length limitation to 65535.  Other
   encapsulation headers will make the actual payload even shorter.
   Binary encodings like GPB and CBOR can make the message compact.  So
   that the message can be encapsulated within one UDP packet, hence
   fragmentation will not easily happen.  However, text encodings like
   JSON and XML can easily make the message exceed the UDP length
   limitation.

   The Fragmentation Option can help not Application layer can split the
   YANG tree into several leaves.  Or table into several rows.  But the
   leaf or the row cannot be split any further.  Now we consider a very
   long path.  Since the GPB and CBOR are so compact, it's easy to fit
   into a UDP packet.  But for JSON or XML, it is possible that even one
   leaf will exceed the UDP boundary.

    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
   +-------------------------------------------------------------+-+
   |            Fagment Number                                   |L|
   +-------------------------------------------------------------+-+

                    Fig. 5 Fragmentation Option Format

   The Fragmentation Option is available in the message header when the
   fragmentation flag is set to 1.  The option contains:

   Fragment Number: indicates the sequence number of the current
   fragment.

   L: is a flag to indicate whether the current fragment is the last
   one.  When 0 is set, current fragment is not the last one, hence more
   fragments are expected.  When 1 is set, current fragment is the last
   one.






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5.4.  Data Encoding

   Subscribed data can be encoded in GPB, CBOR, XML or JSON format.  It
   is conceivable that additional encodings may be supported as options
   in the future.  This can be accomplished by augmenting the
   subscription data model with additional identity statements used to
   refer to requested encodings.

   Implementation may support different encoding method per
   subscription.  When bundled notifications is supported between the
   publisher and the receiver, only subscribed notifications with the
   same encoding can be bundled as one message.

6.  Using DTLS to Secure UPC

   The Datagram Transport Layer Security (DTLS) protocol [RFC6347] is
   designed to meet the requirements of applications that need secure
   datagram transport.

   DTLS can be used as a secure transport to counter all the primary
   threats to UDP based Publication Channel:

   o  Confidentiality to counter disclosure of the message contents.

   o  Integrity checking to counter modifications to a message on a hop-
      by-hop basis.

   o  Server or mutual authentication to counter masquerade.

   In addition, DTLS also provides:

   o  A cookie exchange mechanism during handshake to counter Denial of
      Service attacks.

   o  A sequence number in the header to counter replay attacks.

6.1.  Transport

   As shown in Figure 6, the DTLS is layered next to the UDP transport
   is to provide reusable security and authentication functions over
   UDP.  No DTLS extension is required to enable UPC messages over DTLS.










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                            +-----------------------------+
                            |           UPC Message       |
                            +-----------------------------+
                            |            DTLS             |
                            +-----------------------------+
                            |            UDP              |
                            +-----------------------------+
                            |            IP               |
                            +-----------------------------+

                Fig. 6: Protocol Stack for DTLS secured UPC

   The application implementer will map a unique combination of the
   remote address, remote port number, local address, and local port
   number to a session.

   Each UPC message is delivered by the DTLS record protocol, which
   assigns a sequence number to each DTLS record.  Although the DTLS
   implementer may adopt a queue mechanism to resolve reordering, it may
   not assure that all the messages are delivered in order when mapping
   on the UDP transport.

   Since UDP is an unreliable transport, with DTLS, an originator or
   relay may not realize that a collector has gone down or lost its DTLS
   connection state, so messages may be lost.

   The DTLS record has its own sequence number, the encryption and
   decryption will done by DTLS layer, UPC Message layer will not
   concern this.

6.2.  Port Assignment

   The Publisher is always a DTLS client, and the Receiver is always a
   DTLS server.  The Receivers MUST support accepting UPC Messages on
   the UDP port PORT-Y, but MAY be configurable to listen on a different
   port.  The Publisher MUST support sending UPC messages to the UDP
   port PORT-Y, but MAY be configurable to send messages to a different
   port.  The Publisher MAY use any source UDP port for transmitting
   messages.

6.3.  DTLS Session Initiation

   The Publisher initiates a DTLS connection by sending a DTLS Client
   Hello to the Receiver.  Implementations MUST support the denial of
   service countermeasures defined by DTLS.  When these countermeasures
   are used, the Receiver responds with a DTLS Hello Verify Request
   containing a cookie.  The Publisher responds with a DTLS Client Hello
   containing the received cookie, which initiates the DTLS handshake.



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   The Publisher MUST NOT send any UPC messages before the DTLS
   handshake has successfully completed.

   Implementations MUST support DTLS 1.0 [RFC4347] and MUST support the
   mandatory to implement cipher suite, which is
   TLS_RSA_WITH_AES_128_CBC_SHA [RFC5246] as specified in DTLS 1.0.  If
   additional cipher suites are supported, then implementations MUST NOT
   negotiate a cipher suite that employs NULL integrity or
   authentication algorithms.

   Where privacy is REQUIRED, then implementations must either negotiate
   a cipher suite that employs a non-NULL encryption algorithm or else
   achieve privacy by other means, such as a physically secured network.

6.4.  Sending Data

   All UPC messages MUST be sent as DTLS "application data".  It is
   possible that multiple UPC messages be contained in one DTLS record,
   or that a publication message be transferred in multiple DTLS
   records.  The application data is defined with the following ABNF
   [RFC5234] expression:

   APPLICATION-DATA = 1*UPC-FRAME

   UPC-FRAME = MSG-LEN SP UPC-MSG

   MSG-LEN = NONZERO-DIGIT *DIGIT

   SP = %d32

   NONZERO-DIGIT = %d49-57

   DIGIT = %d48 / NONZERO-DIGIT

   UPC-MSG is defined in section 5.2.

6.5.  Closure

   A Publisher MUST close the associated DTLS connection if the
   connection is not expected to deliver any UPC Messages later.  It
   MUST send a DTLS close_notify alert before closing the connection.  A
   Publisher (DTLS client) MAY choose to not wait for the Receiver's
   close_notify alert and simply close the DTLS connection.  Once the
   Receiver gets a close_notify from the Publisher, it MUST reply with a
   close_notify.

   When no data is received from a DTLS connection for a long time
   (where the application decides what "long" means), Receiver MAY close



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   the connection.  The Receiver (DTLS server) MUST attempt to initiate
   an exchange of close_notify alerts with the Publisher before closing
   the connection.  Receivers that are unprepared to receive any more
   data MAY close the connection after sending the close_notify alert.

   Although closure alerts are a component of TLS and so of DTLS, they,
   like all alerts, are not retransmitted by DTLS and so may be lost
   over an unreliable network.

7.  Congestion Control

   Congestion control mechanisms that respond to congestion by reducing
   traffic rates and establish a degree of fairness between flows that
   share the same path are vital to the stable operation of the Internet
   [RFC2914].  While efficient, UDP has no build-in congestion control
   mechanism.  Because streaming telemetry can generate unlimited
   amounts of data, transferring this data over UDP is generally
   problematic.  It is not recommended to use the UDP based publication
   channel over congestion-sensitive network paths.  The only
   environments where the UDP based publication channel MAY be used are
   managed networks.  The deployments require the network path has been
   explicitly provisioned for the UDP based publication channel through
   traffic engineering mechanisms, such as rate limiting or capacity
   reservations.

8.  IANA Considerations

   This RFC requests that IANA assigns three UDP port numbers in the
   "Registered Port Numbers" range with the service names "upc" and
   "upc-dtls".  These ports will be the default ports for the UDP based
   Publication Channel for NETCONF and RESTCONF.  Below is the
   registration template following the rules in [RFC6335].

   Service Name: upc

   Transport Protocol(s): UDP

   Assignee: IESG <iesg@ietf.org>

   Contact: IETF Chair <chair@ietf.org>

   Description: UDP based Publication Channel

   Reference: RFC XXXX

   Port Number: PORT-X

   Service Name: upc-dtls



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   Transport Protocol(s): UDP

   Assignee: IESG <iesg@ietf.org>

   Contact: IETF Chair <chair@ietf.org>

   Description: UDP based Publication Channel (DTLS)

   Reference: RFC XXXX

   Port Number: PORT-Y

9.  Security Considerations

   TBD

10.  Acknowledgements

   The authors of this documents would like to thank Eric Voit, Tim
   Jenkins, and Huiyang Yang for the initial comments.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2914]  Floyd, S., "Congestion Control Principles", BCP 41,
              RFC 2914, DOI 10.17487/RFC2914, September 2000,
              <https://www.rfc-editor.org/info/rfc2914>.

   [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", RFC 4347, DOI 10.17487/RFC4347, April 2006,
              <https://www.rfc-editor.org/info/rfc4347>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.




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   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165,
              RFC 6335, DOI 10.17487/RFC6335, August 2011,
              <https://www.rfc-editor.org/info/rfc6335>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/info/rfc6347>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

11.2.  Informative References

   [I-D.ietf-netconf-netconf-event-notifications]
              Voit, E., Clemm, A., Prieto, A., Nilsen-Nygaard, E., and
              A. Tripathy, "NETCONF Support for Event Notifications",
              draft-ietf-netconf-netconf-event-notifications-09 (work in
              progress), May 2018.

   [I-D.ietf-netconf-notification-messages]
              Voit, E., Birkholz, H., Bierman, A., Clemm, A., and T.
              Jenkins, "Notification Message Headers and Bundles",
              draft-ietf-netconf-notification-messages-03 (work in
              progress), February 2018.





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   [I-D.ietf-netconf-restconf-notif]
              Voit, E., Rahman, R., Nilsen-Nygaard, E., Clemm, A., and
              A. Bierman, "RESTCONF and HTTP Transport for Event
              Notifications", draft-ietf-netconf-restconf-notif-06 (work
              in progress), June 2018.

   [I-D.ietf-netconf-subscribed-notifications]
              Voit, E., Clemm, A., Prieto, A., Nilsen-Nygaard, E., and
              A. Tripathy, "Customized Subscriptions to a Publisher's
              Event Streams", draft-ietf-netconf-subscribed-
              notifications-13 (work in progress), June 2018.

   [I-D.zhou-netconf-multi-stream-originators]
              Zhou, T., Zheng, G., Voit, E., Clemm, A., and A. Bierman,
              "Subscription to Multiple Stream Originators", draft-zhou-
              netconf-multi-stream-originators-02 (work in progress),
              May 2018.

11.3.  URIs

   [1] https://developers.google.com/protocol-buffers/

Appendix A.  Change Log

   (To be removed by RFC editor prior to publication)

   A.1. draft-ietf-zheng-udp-pub-channel-00 to v00

   o  Modified the message header format.

   o  Added a section on the Authentication Option.

   o  Cleaned up the text and removed unnecessary TBDs.

   A.2. v01

   o  Removed the detailed description on distributed data collection
      mechanism from this document.  Mainly focused on the description
      of a UDP based publication channel for telemetry use.

   o  Modified the message header format.

   A.2. v02

   o  Add the section on the transport mechanism.

   o  Modified the fixed message header format.




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   o  Add the fragmentation option for the message header.

   A.2. v03

   o  Clarify term through the document.

   o  Add a section on DTLS support.

Authors' Addresses

   Guangying Zheng
   Huawei
   101 Yu-Hua-Tai Software Road
   Nanjing, Jiangsu
   China

   Email: zhengguangying@huawei.com


   Tianran Zhou
   Huawei
   156 Beiqing Rd., Haidian District
   Beijing
   China

   Email: zhoutianran@huawei.com


   Alexander Clemm
   Huawei
   2330 Central Expressway
   Santa Clara, California
   USA

   Email: alexander.clemm@huawei.com
















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