



TCPM                                                           M. Scharf
Internet-Draft                                      Hochschule Esslingen
Intended status: Standards Track                         M. Jethanandani
Expires: 15 March 2023                                    Kloud Services
                                                               V. Murgai
                                                                 Samsung
                                                       11 September 2022


 A YANG Model for Transmission Control Protocol (TCP) Configuration and
                                 State
                      draft-ietf-tcpm-yang-tcp-09

Abstract

   This document specifies a minimal YANG model for TCP on devices that
   are configured and managed by network management protocols.  The YANG
   model defines a container for all TCP connections, and groupings of
   authentication parameters that can be imported and used in TCP
   implementations or by other models that need to configure TCP
   parameters.  The model also includes basic TCP statistics.  The model
   is compliant with Network Management Datastore Architecture (NMDA)
   (RFC 8342).

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 15 March 2023.

Copyright Notice

   Copyright (c) 2022 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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Note to RFC Editor  . . . . . . . . . . . . . . . . . . .   4
   3.  YANG Module Overview  . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Model Design  . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   6
   4.  TCP YANG Model  . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
     5.1.  The IETF XML Registry . . . . . . . . . . . . . . . . . .  19
     5.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  20
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  21
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  23
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  25
   Appendix B.  Examples . . . . . . . . . . . . . . . . . . . . . .  25
     B.1.  Keepalive Configuration . . . . . . . . . . . . . . . . .  26
     B.2.  TCP-AO Configuration  . . . . . . . . . . . . . . . . . .  26
   Appendix C.  Complete Tree Diagram  . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   The Transmission Control Protocol (TCP) [RFC9293] is used by many
   applications in the Internet, including control and management
   protocols.  As such, TCP is implemented on network elements that can
   be configured and managed via network management protocols such as
   NETCONF [RFC6241] or RESTCONF [RFC8040].

   This document specifies a minimal YANG 1.1 [RFC7950] model for
   configuring and managing TCP on network elements that support YANG, a
   TCP connection table, a TCP listener table containing information
   about a particular TCP listener, and an augmentation of the YANG Data
   Model for Key Chains [RFC8177] to support authentication.  The YANG
   module specified in this document is compliant with Network
   Management Datastore Architecture (NMDA) [RFC8342].



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   The YANG module has a narrow scope and focuses on a subset of
   fundamental TCP functions and basic statistics.  It defines a
   container for a list of TCP connections that includes definitions
   from YANG Groupings for TCP Clients and TCP Servers
   [I-D.ietf-netconf-tcp-client-server].  The model adheres to the
   recommendation in BGP/MPLS IP Virtual Private Networks [RFC4364].
   Therefore it allows enabling of TCP-AO [RFC5925], and accommodates
   the installed base that makes use of MD5.  The module can be
   augmented or updated to address more advanced or implementation-
   specific TCP features in the future.

   This specification does not deprecate the Management Information Base
   (MIB) for the Transmission Control Protocol (TCP) [RFC4022].  The
   basic statistics defined in this document follow the model of the TCP
   MIB.  An TCP Extended Statistics MIB [RFC4898] is also available, but
   this document does not cover such extended statistics.  The YANG
   module also omits some selected parameters included in TCP MIB, most
   notably Retransmission Timeout (RTO) configuration and a maximum
   connection limit.  This is a conscious decision as these parameters
   hardly matter in a state-of-the-art TCP implementation.  It would
   also be possible to translate a MIB into a YANG module, for instance
   using Translation of Structure of Management Information Version 2
   (SMIv2) MIB Modules to YANG Modules [RFC6643].  However, this
   approach is not used in this document, because a translated model
   would not be up-to-date.

   There are other existing TCP-related YANG models, which are
   orthogonal to this specification.  Examples are:

   *  TCP header attributes are modeled in other security-related
      models, such as YANG Data Model for Network Access Control Lists
      (ACLs) [RFC8519], Distributed Denial-of-Service Open Thread
      Signaling (DOTS) Data Channel Specification [RFC8783], I2NSF
      Capability YANG Data Model [I-D.ietf-i2nsf-capability-data-model],
      or I2NSF Network Security Function-Facing Interface YANG Data
      Model [I-D.ietf-i2nsf-nsf-facing-interface-dm].

   *  TCP-related configuration of a NAT (e.g., NAT44, NAT64,
      Destination NAT) is defined in A YANG Module for Network Address
      Translation (NAT) and Network Prefix Translation (NPT) [RFC8512]
      and A YANG Data Model for Dual-Stack Lite (DS-Lite) [RFC8513].

   *  TCP-AO and TCP MD5 configuration for Layer 3 VPNs is modeled in A
      Layer 3 VPN Network YANG Model [RFC9182].  This model assumes that
      TCP-AO specific parameters are preconfigured in addition to the
      keychain parameters.





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2.  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.

2.1.  Note to RFC Editor

   This document uses several placeholder values throughout the
   document.  Please replace them as follows and remove this note before
   publication.

   RFC XXXX, where XXXX is the number assigned to this document at the
   time of publication.

   2022-09-11 with the actual date of the publication of this document.

3.  YANG Module Overview

3.1.  Scope

   TCP is implemented on different system architectures.  As a result,
   there are many different and often implementation-specific ways to
   configure parameters of the TCP engine.  In addition, in many TCP/IP
   stacks configuration exists for different scopes:

   *  System-wide configuration: Many TCP implementations have
      configuration parameters that affect all TCP connections from or
      to this TCP stack.  Typical examples include enabling or disabling
      optional protocol features.  For instance, many implementations
      can turn on or off use of window scaling Transmission Control
      Protocol (TCP) Specification [RFC9293] for all TCP connections.

   *  Interface configuration: It can be useful to use different TCP
      parameters on different interfaces, e.g., different device ports
      or IP interfaces.  In that case, TCP parameters can be part of the
      interface configuration.  Typical examples are the Maximum Segment
      Size (MSS) or configuration related to hardware offloading.

   *  Connection parameters: Many implementations have means to
      influence the behavior of each TCP connection, e.g., on the
      programming interface used by applications.  Typical examples are
      socket options in the socket API, such as disabling the Nagle
      algorithm Transmission Control Protocol (TCP) Specification
      [RFC9293] by TCP_NODELAY.  If an application uses such an
      interface, it is possible that the configuration of the



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      application or application protocol includes TCP-related
      parameters.  An example is the BGP YANG Model for Service Provider
      Networks [I-D.ietf-idr-bgp-model].

   *  Application preferences: Setting of TCP parameters can also be
      part of application preferences, templates, or profiles.  An
      example would be the preferences defined in An Abstract
      Application Layer Interface to Transport Services
      [I-D.ietf-taps-interface].

   As a result, there is no ground truth for setting certain TCP
   parameters, and traditionally different TCP implementations have used
   different modeling approaches.  For instance, one implementation may
   define a given configuration parameter globally, while another one
   uses per-interface settings, and both approaches work well for the
   corresponding use cases.  Also, different systems may use different
   default values.  In addition, TCP can be implemented in different
   ways and design choices by the protocol engine often affect
   configuration options.

   Nonetheless, a number of TCP stack parameters require configuration
   by YANG models.  This document therefore defines a minimal YANG model
   with fundamental parameters.  An important use case is the TCP
   configuration on network elements such as routers, which often use
   YANG data models.  The model therefore specifies TCP parameters that
   are important on such TCP stacks.

   This in particular applies to the support of TCP-AO [RFC5925] and the
   corresponding cryptographic algorithms [RFC5926].  TCP Authentication
   Option (TCP-AO) is used on routers to secure routing protocols such
   as BGP.  In that case, a YANG model for TCP-AO configuration is
   required.  The model defined in this document includes the required
   parameters for TCP-AO configuration, such as the values of SendID and
   RecvID.  The keychain for TCP-AO can be modeled by the YANG Data
   Model for Key Chains [RFC8177].  The groupings defined in this
   document can be imported and used as part of such a preconfiguration.

   Given an installed base, the model also allows enabling of the legacy
   TCP MD5 [RFC2385] signature option.  The TCP MD5 signature option was
   obsoleted by TCP-AO in 2010.  If current implementations require TCP
   authentication, it is RECOMMENDED to use TCP-AO [RFC5925].

   Similar to the TCP MIB [RFC4022], this document also specifies basic
   statistics, a TCP connection list, and a TCP listener list.

   *  Statistics: Counters for the number of active/passive opens, sent
      and received TCP segments, errors, and possibly other detailed
      debugging information



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   *  TCP connection list: Access to status information for all TCP
      connections.  Note, the connection table is modeled as a list that
      is read-writeable, even though a connection cannot be created by
      adding entries to the table.  Similarly, deletion of connections
      from this list is implementation-specific.

   *  TCP listener list: A list containing information about TCP
      listeners, i.e., applications willing to accept connections.

   This allows implementations of TCP MIB [RFC4022] to migrate to the
   YANG model defined in this memo.  Note that the TCP MIB does not
   include means to reset statistics, which are defined in this
   document.  This is not a major addition, as a reset can simply be
   implemented by storing offset values for the counters.

   This version of the module does not model details of Multipath TCP
   [RFC8684].  This could be addressed in a later version of this
   document.

3.2.  Model Design

   The YANG model defined in this document includes definitions from the
   YANG Groupings for TCP Clients and TCP Servers
   [I-D.ietf-netconf-tcp-client-server].  Similar to that model, this
   specification defines YANG groupings.  This allows reuse of these
   groupings in different YANG data models.  It is intended that these
   groupings will be used either standalone or for TCP-based protocols
   as part of a stack of protocol-specific configuration models.  An
   example could be the BGP YANG Model for Service Provider Networks
   [I-D.ietf-idr-bgp-model].

3.3.  Tree Diagram

   This section provides an abridged tree diagram for the YANG module
   defined in this document.  Annotations used in the diagram are
   defined in YANG Tree Diagrams [RFC8340].  A complete tree diagram can
   be found in the Appendix.














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   module: ietf-tcp
     +--rw tcp!
        +--rw connections
        |     ...
        +--ro tcp-listeners* [type address port]
        |     ...
        +--ro statistics {statistics}?
              ...

     augment /key-chain:key-chains/key-chain:key-chain/key-chain:key:
       +--rw authentication {authentication}?
          +--rw keychain?    key-chain:key-chain-ref
          +--rw (authentication)?
                ...

4.  TCP YANG Model

   This YANG module references The TCP Authentication Option [RFC5925],
   Protection of BGP Sessions via the TCP MD5 Signature [RFC2385],
   Transmission Control Protocol (TCP) Specification [RFC9293], and
   imports Common YANG Data Types [RFC6991], The NETCONF Access Control
   Model [RFC8341], and YANG Groupings for TCP Clients and TCP Servers
   [I-D.ietf-netconf-tcp-client-server].

   <CODE BEGINS> file "ietf-tcp@2022-09-11.yang"
   module ietf-tcp {
     yang-version "1.1";
     namespace "urn:ietf:params:xml:ns:yang:ietf-tcp";
     prefix "tcp";

     import ietf-yang-types {
       prefix "yang";
       reference
         "RFC 6991: Common YANG Data Types.";
     }
     import ietf-tcp-common {
       prefix "tcpcmn";
       reference
         "I-D.ietf-netconf-tcp-client-server: YANG Groupings for TCP
          Clients and TCP Servers.";
     }
     import ietf-inet-types {
       prefix "inet";
       reference
         "RFC 6991: Common YANG Data Types.";
     }
     import ietf-netconf-acm {
       prefix nacm;



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       reference
         "RFC 8341: Network Configuration Access Control Model";
     }
     import ietf-key-chain {
       prefix key-chain;
       reference
         "RFC 8177: YANG Key Chain.";
     }

     organization
       "IETF TCPM Working Group";

     contact
       "WG Web:   <https://datatracker.ietf.org/wg/tcpm/about>
        WG List:  <tcpm@ietf.org>

        Authors: Michael Scharf (michael.scharf at hs-esslingen dot de)
                 Mahesh Jethanandani (mjethanandani at gmail dot com)
                 Vishal Murgai (vmurgai at gmail dot com)";

     description
       "This module focuses on fundamental TCP functions and basic
        statistics. The model can be augmented to address more advanced
        or implementation specific TCP features.

        Copyright (c) 2022 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject to
        the license terms contained in, the Simplified BSD License set
        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (https://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX
        (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
        for full legal notices.

        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 (RFC 2119) (RFC 8174) when, and only when,
        they appear in all capitals, as shown here.";

     revision "2022-09-11" {
       description
         "Initial Version";



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       reference
         "RFC XXXX, A YANG Model for Transmission Control Protocol (TCP)
                    Configuration and State.";
     }

     // Typedefs
     typedef mss {
       type uint16;
       description
         "Type definition for Maximum Segment Size.";
     }

     // Features
     feature statistics {
       description
         "This implementation supports statistics reporting.";
     }

     feature authentication {
       description
         "This implementation supports authentication.";
     }

     // Identities
     identity aes-128 {
       base key-chain:crypto-algorithm;
       description
         "AES128 authentication algorithm used by TCP-AO.";
       reference
          "RFC 5926: Cryptographic Algorithms for the TCP
           Authentication Option (TCP-AO).";
     }

     // TCP-AO Groupings

     grouping ao {
       leaf send-id {
         type uint8 {
           range "0..max";
         }
         description
           "The SendID is inserted as the KeyID of the TCP-AO option
            of outgoing segments. In a consistent configuration, the
            SendID matches the RecvID at the other endpoint.";
         reference
           "RFC 5925: The TCP Authentication Option, Section 3.1.";
       }




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       leaf recv-id {
         type uint8 {
           range "0..max";
         }
         description
           "The RecvID is matched against the TCP-AO KeyID of incoming
            segments. In a consistent configuration, the RecvID matches
            the SendID at the other endpoint.";
         reference
           "RFC 5925: The TCP Authentication Option, Section 3.1.";
       }

       leaf include-tcp-options {
         type boolean;
         default true;
         description
           "When set to true, TCP options are included in MAC
            calculation.";
         reference
           "RFC 5925: The TCP Authentication Option, Section 3.1.";
       }

       leaf accept-key-mismatch {
         type boolean;
         description
           "Accept, when set to true, TCP segments with a Master Key
            Tuple (MKT) that is not configured.";
         reference
           "RFC 5925: The TCP Authentication Option, Section 7.3.";
       }

       leaf r-next-key-id {
         type uint8;
         config false;
         description
           "A field indicating the Master Key Tuple (MKT) that is ready
            at the sender to be used to authenticate received segments,
            i.e., the desired 'receive next' key ID.";
         reference
           "RFC 5925: The TCP Authentication Option.";
       }

       description
         "Authentication Option (AO) for TCP.";
       reference
         "RFC 5925: The TCP Authentication Option.";
     }




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     // TCP configuration

     container tcp {
       presence "The container for TCP configuration.";

       description
         "TCP container.";

       container connections {
         list connection {
           key "local-address remote-address local-port remote-port";

           leaf local-address {
             type inet:ip-address;
             description
               "Identifies the address that is used by the local
                endpoint for the connection, and is one of the four
                elements that form the connection identifier.";
           }

           leaf remote-address {
             type inet:ip-address;
             description
               "Identifies the address that is used by the remote
                endpoint for the connection, and is one of the four
                elements that form the connection identifier.";
           }

           leaf local-port {
             type inet:port-number;
             description
               "Identifies the local TCP port used for the connection,
                and is one of the four elements that form the
                connection identifier.";
           }

           leaf remote-port {
             type inet:port-number;
             description
               "Identifies the remote TCP port used for the connection,
                and is one of the four elements that form the
                connection identifier.";
           }

           leaf mss {
             type mss;
             description
               "Maximum Segment Size (MSS) desired on this connection.



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                Note, the 'effective send MSS' can be smaller than
                what is configured here.";
             reference
               "RFC 9293: Transmission Control Protocol (TCP)
                          Specification.";
           }

           leaf pmtud {
             type boolean;
             default false;
             description
               "Turns Path Maximum Transmission Unit Discovery (PMTUD)
                on (true) or off (false).";
             reference
               "RFC 9293: Transmission Control Protocol (TCP)
                          Specification.";
           }

           uses tcpcmn:tcp-common-grouping;

           leaf state {
             type enumeration {
               enum closed {
                 value 1;
                 description
                   "Connection is closed. Connections in this state
                    may not appear in this list.";
               }
               enum listen {
                 value 2;
                 description
                   "Represents waiting for a connection request from any
                    remote TCP peer and port.";
               }
               enum syn-sent {
                 value 3;
                 description
                   "Represents waiting for a matching connection request
                    after having sent a connection request.";
               }
               enum syn-received {
                 value 4;
                 description
                   "Represents waiting for a confirming connection
                    request acknowledgment after having both received
                    and sent a connection request.";
               }
               enum established {



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                 value 5;
                 description
                   "Represents an open connection, data received can be
                    delivered to the user. The normal state for the data
                    transfer phase of the connection.";
               }
               enum fin-wait-1 {
                 value 6;
                 description
                   "Represents waiting for a connection termination
                    request from the remote TCP peer, or an
                    acknowledgment of the connection termination request
                    previously sent.";
               }
               enum fin-wait-2 {
                 value 7;
                 description
                   "Represents waiting for a connection termination
                    request from the remote TCP peer.";
               }
               enum close-wait {
                 value 8;
                 description
                   "Represents waiting for a connection termination
                    request from the local user.";
               }
               enum last-ack {
                 value 9;
                 description
                   "Represents waiting for an acknowledgment of the
                    connection termination request previously sent to
                    the remote TCP peer (this termination request sent
                    to the remote TCP peer already included an
                    acknowledgment of the termination request sent from
                    the remote TCP peer)";
               }
               enum closing {
                 value 10;
                 description
                   "Represents waiting for a connection termination
                    request acknowledgment from the remote TCP peer.";
               }
               enum time-wait {
                 value 11;
                 description
                   "Represents waiting for enough time to pass to be
                    sure the remote TCP peer received the acknowledgment
                    of its connection termination request, and to avoid



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                    new connections being impacted by delayed segments
                    from previous connections.";
               }
             }
             config false;
             description
               "The state of this TCP connection.";
           }
           description
             "List of TCP connections with their parameters.

              The list is modeled as writeable even though only some of
              the nodes are writeable, e.g. keepalive. Connections
              that are created and match this list SHOULD apply the
              writeable parameters. At the same time, implementations
              may not allow creation of new TCP connections simply by
              adding entries to the list. Furthermore, the behavior
              upon removal is implementation-specific. Implementations
              may not support closing or resetting a TCP connection
              upon an operation that removes the entry from the list.

              The operational state of this list SHOULD reflect
              connections that have configured, but not created, and
              connections that have been created. Connections in
              CLOSED state are not reflected on this list.";
         }
         description
           "A container of all TCP connections.";
       }

       list tcp-listeners {
         key "type address port";
         config false;

         description
           "A table containing information about a particular
            TCP listener.";

         leaf type {
           type inet:ip-version;
           description
             "The address type of address.  The value
              should be unspecified (0) if connection initiations
              to all local IP addresses are accepted.";
         }

         leaf address {
           type union {



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             type inet:ip-address;
             type string {
               length 0;
             }
           }
           description
             "The local IP address for this TCP connection.

              The value of this node can be represented in three
              possible ways, depending on the characteristics of the
              listening application:

              1. For an application willing to accept both IPv4 and
                 IPv6 datagrams, the value of this node must be
                 ''h (a zero-length octet-string), with the value
                 of the corresponding 'type' object being
                 unspecified (0).

              2. For an application willing to accept only IPv4 or
                 IPv6 datagrams, the value of this node must be
                 '0.0.0.0' or '::' respectively, with
                 'type' representing the appropriate address type.

              3. For an application which is listening for data
                 destined only to a specific IP address, the value
                 of this node is the specific local address, with
                 'type' representing the appropriate address type.";
         }

         leaf port {
           type inet:port-number;
           description
             "The local port number for this TCP connection.";
         }
       }

       container statistics {
         if-feature statistics;
         config false;

         leaf active-opens {
           type yang:counter64;
           description
             "The number of times that TCP connections have made a
              direct transition to the SYN-SENT state from the CLOSED
              state.";
           reference
             "RFC 9293: Transmission Control Protocol (TCP)



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                        Specification.";
         }

         leaf passive-opens {
           type yang:counter64;
           description
             "The number of times TCP connections have made a direct
              transition to the SYN-RCVD state from the LISTEN state.";
           reference
             "RFC 9293: Transmission Control Protocol (TCP)
                        Specification.";
         }

         leaf attempt-fails {
           type yang:counter64;
           description
             "The number of times that TCP connections have made a
              direct transition to the CLOSED state from either the
              SYN-SENT state or the SYN-RCVD state, plus the number of
              times that TCP connections have made a direct transition
              to the LISTEN state from the SYN-RCVD state.";
           reference
             "RFC 9293: Transmission Control Protocol (TCP)
                        Specification.";
         }

         leaf establish-resets {
           type yang:counter64;
           description
             "The number of times that TCP connections have made a
              direct transition to the CLOSED state from either the
              ESTABLISHED state or the CLOSE-WAIT state.";
           reference
             "RFC 9293: Transmission Control Protocol (TCP)
                        Specification.";
         }

         leaf currently-established {
           type yang:gauge32;
           description
             "The number of TCP connections for which the current state
              is either ESTABLISHED or CLOSE-WAIT.";
           reference
             "RFC 9293: Transmission Control Protocol (TCP)
                        Specification.";
         }

         leaf in-segments {



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           type yang:counter64;
           description
             "The total number of TCP segments received, including those
              received in error. This count includes TCP segments
              received on currently established connections.";
           reference
             "RFC 9293: Transmission Control Protocol (TCP)
                        Specification.";
         }

         leaf out-segments {
           type yang:counter64;
           description
             "The total number of TCP segments sent, including those on
              current connections but excluding those containing only
              retransmitted octets.";
           reference
             "RFC 9293: Transmission Control Protocol (TCP)
                        Specification.";
         }

         leaf retransmitted-segments {
           type yang:counter64;
           description
             "The total number of TCP segments retransmitted; that is,
              the number of TCP segments transmitted containing one or
              more previously transmitted octets.";
           reference
             "RFC 9293: Transmission Control Protocol (TCP)
                        Specification.";
         }

         leaf in-errors {
           type yang:counter64;
           description
             "The total number of TCP segments received in error
              (e.g., bad TCP checksums).";
           reference
             "RFC 9293: Transmission Control Protocol (TCP)
                        Specification.";
         }

         leaf out-resets {
           type yang:counter64;
           description
             "The number of TCP segments sent containing the RST flag.";
           reference
             "RFC 9293: Transmission Control Protocol (TCP)



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                        Specification.";
         }

         leaf auth-failures {
           if-feature authentication;
           type yang:counter64;
           description
             "The number of times that authentication has failed either
              with TCP-AO or MD5.";
         }

         action reset {
           nacm:default-deny-all;
           description
             "Reset statistics action command.";
           input {
             leaf reset-at {
               type yang:date-and-time;
               description
                 "Time when the reset action needs to be
                  executed.";
             }
           }
           output {
             leaf reset-finished-at {
               type yang:date-and-time;
               description
                 "Time when the reset action command completed.";
             }
           }
         }
         description
           "Statistics across all connections.";
       }
     }

     augment "/key-chain:key-chains/key-chain:key-chain/key-chain:key" {
       description
         "Augmentation of the key-chain model to add TCP-AO and TCP-MD5
          authentication.";

       container authentication {
         if-feature authentication;
         leaf keychain {
           type key-chain:key-chain-ref;
           description
             "Reference to the key chain that will be used by
              this model. Applicable for TCP-AO and TCP-MD5



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              only";
           reference
             "RFC 8177: YANG Key Chain.";
         }

         choice authentication {
           container ao {
             presence "Presence container for all TCP-AO related" +
                      " configuration";
             uses ao;
             description
               "Use TCP-AO to secure the connection.";
           }

           container md5 {
             presence "Presence container for all MD5 related" +
                      " configuration";
             description
               "Use TCP-MD5 to secure the connection. As the TCP MD5
                signature option is obsoleted by TCP-AO, it is
                RECOMMENDED to use TCP-AO instead.";
             reference
               "RFC 2385: Protection of BGP Sessions via the TCP MD5
                          Signature.";
           }
           description
             "Choice of TCP authentication.";
         }
         description
           "Authentication definitions for TCP configuration.
            This includes parameters such as how to secure the
            connection, that can be part of either the client
            or server.";
       }
     }
   }
   <CODE ENDS>

5.  IANA Considerations

5.1.  The IETF XML Registry

   This document registers an URI in the "ns" subregistry of the IETF
   XML Registry [RFC3688].  Following the format in IETF XML Registry
   [RFC3688], the following registration is requested:






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      URI: urn:ietf:params:xml:ns:yang:ietf-tcp
      Registrant Contact: The IESG.
      XML: N/A, the requested URI is an XML namespace.

5.2.  The YANG Module Names Registry

   The following entry is requested to be added to the "YANG Module
   Names" registry created by YANG - A Data Modeling Language for the
   Network Configuration Protocol (NETCONF) [RFC6020]:

      name:         ietf-tcp
      namespace:    urn:ietf:params:xml:ns:yang:ietf-tcp
      prefix:       tcp
      reference:    RFC XXXX (this document)

   The registration is not maintained by IANA.

6.  Security Considerations

   The YANG module specified in this document defines a schema for data
   that is designed to be accessed via network management protocols such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
   is the secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) described in Using the NETCONF
   protocol over SSH [RFC6242].  The lowest RESTCONF layer is HTTPS, and
   the mandatory-to-implement secure transport is TLS [RFC8446].

   The Network Configuration Access Control Model (NACM) [RFC8341]
   provides the means to restrict access for particular NETCONF or
   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content.

   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., "config true", which is the
   default).  These data nodes may be considered sensitive or vulnerable
   in some network environments.  Write operations (e.g., edit-config)
   to these data nodes without proper protection can have a negative
   effect on network operations.  These are the subtrees and data nodes
   and their sensitivity/vulnerability:

   *  Common configuration included from NETCONF Client and Server
      Models [I-D.ietf-netconf-tcp-client-server].  Unrestricted access
      to all the nodes, e.g., keepalive idle-timer, can cause
      connections to fail or to timeout prematurely.







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   *  Authentication configuration.  Unrestricted access to the nodes
      under authentication configuration can prevent the use of
      authenticated communication and cause connection setups to fail.
      This can result in massive security vulnerabilities and service
      disruption for the traffic requiring authentication.

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get, get-config, or
   notification) to these data nodes.  These are the subtrees and data
   nodes and their sensitivity/vulnerability:

   *  Unrestricted access to connection information of the client or
      server can be used by a malicious user to launch an attack.

   *  Similarly, unrestricted access to statistics of the client or
      server can be used by a malicious user to exploit any
      vulnerabilities of the system.

   Some of the RPC operations in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control access to these operations.  These are the
   operations and their sensitivity/vulnerability:

   *  The YANG module allows for the statistics to be cleared by
      executing the reset action.  This action should be restricted to
      users with the right permission.

   The module specified in this document supports MD5 to basically
   accommodate the installed BGP base.  MD5 suffers from the security
   weaknesses discussed in Section 2 of RFC 6151 [RFC6151] or
   Section 2.1 of RFC 6952 [RFC6952].

7.  References

7.1.  Normative References

   [I-D.ietf-netconf-tcp-client-server]
              Watsen, K. and M. Scharf, "YANG Groupings for TCP Clients
              and TCP Servers", Work in Progress, Internet-Draft, draft-
              ietf-netconf-tcp-client-server-13, 24 May 2022,
              <https://www.ietf.org/archive/id/draft-ietf-netconf-tcp-
              client-server-13.txt>.

   [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>.



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   [RFC2385]  Heffernan, A., "Protection of BGP Sessions via the TCP MD5
              Signature Option", RFC 2385, DOI 10.17487/RFC2385, August
              1998, <https://www.rfc-editor.org/info/rfc2385>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC5926]  Lebovitz, G. and E. Rescorla, "Cryptographic Algorithms
              for the TCP Authentication Option (TCP-AO)", RFC 5926,
              DOI 10.17487/RFC5926, June 2010,
              <https://www.rfc-editor.org/info/rfc5926>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [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>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.

   [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>.

   [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>.





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   [RFC8177]  Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J.
              Zhang, "YANG Data Model for Key Chains", RFC 8177,
              DOI 10.17487/RFC8177, June 2017,
              <https://www.rfc-editor.org/info/rfc8177>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC9293]  Eddy, W., Ed., "Transmission Control Protocol (TCP)",
              STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
              <https://www.rfc-editor.org/info/rfc9293>.

7.2.  Informative References

   [I-D.ietf-i2nsf-capability-data-model]
              Hares, S., Jeong, J. P., Kim, J. T., Moskowitz, R., and Q.
              Lin, "I2NSF Capability YANG Data Model", Work in Progress,
              Internet-Draft, draft-ietf-i2nsf-capability-data-model-32,
              23 May 2022, <https://www.ietf.org/archive/id/draft-ietf-
              i2nsf-capability-data-model-32.txt>.

   [I-D.ietf-i2nsf-nsf-facing-interface-dm]
              Kim, J. T., Jeong, J. P., Park, J., Hares, S., and Q. Lin,
              "I2NSF Network Security Function-Facing Interface YANG
              Data Model", Work in Progress, Internet-Draft, draft-ietf-
              i2nsf-nsf-facing-interface-dm-29, 1 June 2022,
              <https://www.ietf.org/archive/id/draft-ietf-i2nsf-nsf-
              facing-interface-dm-29.txt>.








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   [I-D.ietf-idr-bgp-model]
              Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
              YANG Model for Service Provider Networks", Work in
              Progress, Internet-Draft, draft-ietf-idr-bgp-model-14, 3
              July 2022, <https://www.ietf.org/archive/id/draft-ietf-
              idr-bgp-model-14.txt>.

   [I-D.ietf-taps-interface]
              Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G.,
              Kuehlewind, M., Perkins, C., Tiesel, P. S., and T. Pauly,
              "An Abstract Application Layer Interface to Transport
              Services", Work in Progress, Internet-Draft, draft-ietf-
              taps-interface-16, 31 August 2022,
              <https://www.ietf.org/archive/id/draft-ietf-taps-
              interface-16.txt>.

   [RFC4022]  Raghunarayan, R., Ed., "Management Information Base for
              the Transmission Control Protocol (TCP)", RFC 4022,
              DOI 10.17487/RFC4022, March 2005,
              <https://www.rfc-editor.org/info/rfc4022>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC4898]  Mathis, M., Heffner, J., and R. Raghunarayan, "TCP
              Extended Statistics MIB", RFC 4898, DOI 10.17487/RFC4898,
              May 2007, <https://www.rfc-editor.org/info/rfc4898>.

   [RFC6151]  Turner, S. and L. Chen, "Updated Security Considerations
              for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
              RFC 6151, DOI 10.17487/RFC6151, March 2011,
              <https://www.rfc-editor.org/info/rfc6151>.

   [RFC6643]  Schoenwaelder, J., "Translation of Structure of Management
              Information Version 2 (SMIv2) MIB Modules to YANG
              Modules", RFC 6643, DOI 10.17487/RFC6643, July 2012,
              <https://www.rfc-editor.org/info/rfc6643>.

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
              <https://www.rfc-editor.org/info/rfc6952>.







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   [RFC8512]  Boucadair, M., Ed., Sivakumar, S., Jacquenet, C.,
              Vinapamula, S., and Q. Wu, "A YANG Module for Network
              Address Translation (NAT) and Network Prefix Translation
              (NPT)", RFC 8512, DOI 10.17487/RFC8512, January 2019,
              <https://www.rfc-editor.org/info/rfc8512>.

   [RFC8513]  Boucadair, M., Jacquenet, C., and S. Sivakumar, "A YANG
              Data Model for Dual-Stack Lite (DS-Lite)", RFC 8513,
              DOI 10.17487/RFC8513, January 2019,
              <https://www.rfc-editor.org/info/rfc8513>.

   [RFC8519]  Jethanandani, M., Agarwal, S., Huang, L., and D. Blair,
              "YANG Data Model for Network Access Control Lists (ACLs)",
              RFC 8519, DOI 10.17487/RFC8519, March 2019,
              <https://www.rfc-editor.org/info/rfc8519>.

   [RFC8684]  Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
              Paasch, "TCP Extensions for Multipath Operation with
              Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March
              2020, <https://www.rfc-editor.org/info/rfc8684>.

   [RFC8783]  Boucadair, M., Ed. and T. Reddy.K, Ed., "Distributed
              Denial-of-Service Open Threat Signaling (DOTS) Data
              Channel Specification", RFC 8783, DOI 10.17487/RFC8783,
              May 2020, <https://www.rfc-editor.org/info/rfc8783>.

   [RFC9182]  Barguil, S., Gonzalez de Dios, O., Ed., Boucadair, M.,
              Ed., Munoz, L., and A. Aguado, "A YANG Network Data Model
              for Layer 3 VPNs", RFC 9182, DOI 10.17487/RFC9182,
              February 2022, <https://www.rfc-editor.org/info/rfc9182>.

   [RFC9235]  Touch, J. and J. Kuusisaari, "TCP Authentication Option
              (TCP-AO) Test Vectors", RFC 9235, DOI 10.17487/RFC9235,
              May 2022, <https://www.rfc-editor.org/info/rfc9235>.

Appendix A.  Acknowledgements

   Michael Scharf was supported by the StandICT.eu project, which is
   funded by the European Commission under the Horizon 2020 Programme.

   The following persons have contributed to this document by reviews
   (in alphabetical order): Mohamed Boucadair, Gorry Fairhurst, Jeffrey
   Haas, and Tom Petch.

Appendix B.  Examples






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B.1.  Keepalive Configuration

   This particular example demonstrates how both a particular connection
   can be configured for keepalives.

  NOTE: '\' line wrapping per RFC 8792

  <?xml version="1.0" encoding="UTF-8"?>
  <!--
  This example shows how TCP keepalive, MSS and PMTU can be configured \

  for a given connection. An idle connection is dropped after
  idle-time + (max-probes * probe-interval).
  -->
  <tcp
      xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp">
    <connections>
      <connection>
        <local-address>192.0.2.1</local-address>
        <remote-address>192.0.2.2</remote-address>
        <local-port>1025</local-port>
        <remote-port>22</remote-port>
        <mss>1400</mss>
        <pmtud>true</pmtud>
        <keepalives>
          <idle-time>5</idle-time>
          <max-probes>5</max-probes>
          <probe-interval>10</probe-interval>
        </keepalives>
      </connection>
    </connections>
  </tcp>

B.2.  TCP-AO Configuration

   The following example demonstrates how to model a TCP-AO [RFC5925]
   configuration for the example in TCP-AO Test Vectors [RFC9235].  The
   IP addresses and other parameters are taken from the test vectors.













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NOTE: '\' line wrapping per RFC 8792

<?xml version="1.0" encoding="UTF-8"?>
<!--
This example sets TCP-AO configuration parameters similar to
the examples in RFC 9235.
-->

<key-chains
    xmlns="urn:ietf:params:xml:ns:yang:ietf-key-chain">
  <key-chain>
    <name>ao-config</name>
    <description>"An example for TCP-AO configuration."</description>\

    <key>
      <key-id>55</key-id>
      <lifetime>
        <send-lifetime>
          <start-date-time>2017-01-01T00:00:00Z</start-date-time>
          <end-date-time>2017-02-01T00:00:00Z</end-date-time>
        </send-lifetime>
        <accept-lifetime>
          <start-date-time>2016-12-31T23:59:55Z</start-date-time>
          <end-date-time>2017-02-01T00:00:05Z</end-date-time>
        </accept-lifetime>
      </lifetime>
      <crypto-algorithm
          xmlns:tcp=
          "urn:ietf:params:xml:ns:yang:ietf-tcp">tcp:aes-128</crypto-algorit\
hm>
      <key-string>
        <keystring>testvector</keystring>
      </key-string>
      <authentication
          xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp">
        <keychain>ao-config</keychain>
        <ao>
          <send-id>61</send-id>
          <recv-id>84</recv-id>
        </ao>
      </authentication>
    </key>
  </key-chain>
</key-chains>







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Appendix C.  Complete Tree Diagram

   Here is the complete tree diagram for the TCP YANG model.

   module: ietf-tcp
     +--rw tcp!
        +--rw connections
        |  +--rw connection*
        |          [local-address remote-address local-port remote-port]
        |     +--rw local-address     inet:ip-address
        |     +--rw remote-address    inet:ip-address
        |     +--rw local-port        inet:port-number
        |     +--rw remote-port       inet:port-number
        |     +--rw mss?              mss
        |     +--rw pmtud?            boolean
        |     +--rw keepalives! {keepalives-supported}?
        |     |  +--rw idle-time         uint16
        |     |  +--rw max-probes        uint16
        |     |  +--rw probe-interval    uint16
        |     +--ro state?            enumeration
        +--ro tcp-listeners* [type address port]
        |  +--ro type       inet:ip-version
        |  +--ro address    union
        |  +--ro port       inet:port-number
        +--ro statistics {statistics}?
           +--ro active-opens?             yang:counter64
           +--ro passive-opens?            yang:counter64
           +--ro attempt-fails?            yang:counter64
           +--ro establish-resets?         yang:counter64
           +--ro currently-established?    yang:gauge32
           +--ro in-segments?              yang:counter64
           +--ro out-segments?             yang:counter64
           +--ro retransmitted-segments?   yang:counter64
           +--ro in-errors?                yang:counter64
           +--ro out-resets?               yang:counter64
           +--ro auth-failures?            yang:counter64
           |       {authentication}?
           +---x reset
              +---w input
              |  +---w reset-at?   yang:date-and-time
              +--ro output
                 +--ro reset-finished-at?   yang:date-and-time

     augment /key-chain:key-chains/key-chain:key-chain/key-chain:key:
       +--rw authentication {authentication}?
          +--rw keychain?    key-chain:key-chain-ref
          +--rw (authentication)?
             +--:(ao)



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             |  +--rw ao!
             |     +--rw send-id?               uint8
             |     +--rw recv-id?               uint8
             |     +--rw include-tcp-options?   boolean
             |     +--rw accept-key-mismatch?   boolean
             |     +--ro r-next-key-id?         uint8
             +--:(md5)
                +--rw md5!

Authors' Addresses

   Michael Scharf
   Hochschule Esslingen - University of Applied Sciences
   Kanalstr. 33
   73728 Esslingen
   Germany
   Email: michael.scharf@hs-esslingen.de


   Mahesh Jethanandani
   Kloud Services
   Email: mjethanandani@gmail.com


   Vishal Murgai
   Samsung
   Email: vmurgai@gmail.com
























Scharf, et al.            Expires 15 March 2023                [Page 29]
