NEMO (NEtwork MOdeling) Language
draft-xia-sdnrg-nemo-language-02

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Document Type Active Internet-Draft (individual)
Authors Yinben Xia  , Sheng Jiang  , Tianran Zhou  , Susan Hares 
Last updated 2015-05-04
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SDNRG                                                        Y. Xia, Ed.
Internet-Draft                                             S. Jiang, Ed.
Intended status: Standards Track                            T. Zhou, Ed.
Expires: November 5, 2015                                       S. Hares
                                            Huawei Technologies Co., Ltd
                                                             May 4, 2015

                    NEMO (NEtwork MOdeling) Language
                    draft-xia-sdnrg-nemo-language-02

Abstract

   The North-Bound Interface (NBI), located between the control plane
   and the applications, is essential to enable the application
   innovations and nourish the eco-system of SDN.

   While most of the NBIs are provided in the form of API, this document
   proposes the NEtwork MOdeling (NEMO) language which is intent based
   interface with novel language fashion.  Concept, model and syntax are
   introduced in the document.

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
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   This Internet-Draft will expire on November 5, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

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   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 . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Requirements for the Intent Based NBI Language  . . . . . . .   4
   4.  Related work  . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  The NEMO Language Specifications  . . . . . . . . . . . . . .   6
     5.1.  Network Model of the NEMO Language  . . . . . . . . . . .   6
     5.2.  Notation  . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.3.  NEMO Language Overview  . . . . . . . . . . . . . . . . .   8
     5.4.  Model Definition  . . . . . . . . . . . . . . . . . . . .   9
       5.4.1.  Data Types  . . . . . . . . . . . . . . . . . . . . .   9
       5.4.2.  Model Definition and Description Statement  . . . . .  10
     5.5.  Resource Access Statements  . . . . . . . . . . . . . . .  11
       5.5.1.  Node Operations . . . . . . . . . . . . . . . . . . .  12
       5.5.2.  Connection Operations . . . . . . . . . . . . . . . .  12
       5.5.3.  Flow Operations . . . . . . . . . . . . . . . . . . .  13
     5.6.  Behavior Statements . . . . . . . . . . . . . . . . . . .  14
       5.6.1.  Query Behavior  . . . . . . . . . . . . . . . . . . .  14
       5.6.2.  Policy Behavior . . . . . . . . . . . . . . . . . . .  14
       5.6.3.  Notification Behavior . . . . . . . . . . . . . . . .  17
     5.7.  Connection Management Statements  . . . . . . . . . . . .  17
     5.8.  Transaction Statements  . . . . . . . . . . . . . . . . .  18
   6.  The NEMO Language Examples  . . . . . . . . . . . . . . . . .  18
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   10. Informative References  . . . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   While SDN (Software Defined Network) is becoming one of the most
   important directions of network evolution, the essence of SDN is to
   make the network more flexible and easy to use.  The North-Bound
   Interface (NBI), located between the control plane and the
   applications, is essential to enable the application innovations and
   nourish the eco-system of SDN by abstracting the network
   capabilities/information and opening the abstract/logic network to
   applications.

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   The NBI is usually provided in the form of API (Application
   Programming Interface).  Different vendors provide self-defined API
   sets.  Each API set, such as OnePK from Cisco and OPS from Huawei,
   often contains hundreds of specific APIs.  Diverse APIs without
   consistent style are hard to remember and use, and nearly impossible
   to be standardized.

   In addition, most of those APIs are designed by network domain
   experts, who are used to thinking from the network system
   perspective.  The interface designer does not know how the users will
   use the device and exposes information details as much as possible.
   It enables better control of devices, but leaves huge burden of
   selecting useful information to users without well training.  Since
   the NBI is used by network users, a more appropriate design is to
   express user intent and abstract the network from the top down.

   To implement such an NBI design, we can learn from the successful
   case of SQL (Structured Query Language), which simplified the
   complicated data operation to a unified and intuitive way in the form
   of language.  Applications do not care about the way of data storage
   and data operation, but to describe the demand for the data storage
   and operation and then get the result.  As a data domain DSL, SQL is
   simple and intuitive, and can be embedded in applications.  So what
   we need for the network NBI is a set of "network domain SQL".
   [I-D.xia-sdnrg-service-description-language] describe the
   requirements for a service description language and the design
   considerations.

   This document will introduce an intent based NBI with novel language
   fashion.

2.  Terminology

   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
   [RFC2119] when they appear in ALL CAPS.  When these words are not in
   ALL CAPS (such as "should" or "Should"), they have their usual
   English meanings, and are not to be interpreted as [RFC2119] key
   words.

   Network service  also "service" for short, is the service logic that
        contains network operation requirements;

   Network APP  also "APP" for short, is the application to implement
        the network service;

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   Network user  also "user" for short, is the network administrator or
        operator.

3.  Requirements for the Intent Based NBI Language

   An intent based NBI language design contains following features:

   o  Express user intent

      To simplify the operation, applications or users can use the NBI
      directly to describe their requirements for the network without
      taking care of the implementation.  All the parameters without
      user concern will be concealed by the NBI.

   o  Platform independent

      With the NBI, the application or user can description of network
      demand in a generic way, so that any platform or system can get
      the identical knowledge and consequently execute to the same
      result.  Any low-level and device/vendor specific configurations
      and dependencies should be avoided.

   o  Intuitive Domain Specific Language (DSL) for network

      The expression of the DSL should be human-friendly and be easily
      understood by network operators.  DSL should be directly used by
      the system.

   o  Privilege control

      Every application or user is authorized within a specific network
      domain, which can be physical or virtual.  While different network
      domains are isolated without impact, the application or user may
      have access to all the resource and capabilities within its
      domain.  The user perception of the network does not have to be
      the same as the network operators.  The NBI language works on the
      user's view so the users can create topologies based on the
      resources the network-operators allow them to have.

   o  Declarative style

      As described above, the NBI language is designed to help defining
      service requirement to network, detailed configurations and
      instructions performed by network devices are opaque to network
      operators.  So the NBI language should be declarative rather than
      imperative.

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4.  Related work

   YANG [RFC6020] is a data modeling language used to model
   configuration and state data manipulated by the Network Configuration
   Protocol (NETCONF) [RFC6241], NETCONF remote procedure calls, and
   NETCONF notifications.

   UML (Unified Modeling Language) is a powerful modeling language,
   which is domain agnostic.  YANG and UML all focus on syntax
   specification which formulate grammatical structure of NBI language,
   however, they do not have the ability to express users' real
   semantics.  NBI language should facilitate users to express their own
   intent explicitly, instead of general complying with grammar syntax.
   So YANG and UML is appropriate to describe the model behind the NBI
   language not the NBI itself.

   With the emergence of the SDN concept, it is a consensus to simplify
   the network operation, which leads to many cutting-edge explorations
   in the academic area.

   Nick McKeown from Stanford University proposed the SFNet [TSFNet],
   which translated the high level network demand to the underlying
   controller interfaces.  By concealing the low level network details,
   the controller simplified the operation of resource, flow, and
   information for applications.  The SFNet is used for the SDN
   architecture design, and does not go into the NBI design.

   Jennifer from Princeton University designed the Frenetic [Frenetic]
   based on the OpenFlow protocol.  It is an advanced language for flow
   programming, and systematically defines the operating model and mode
   for the flow.  However, the network requirement from the service is
   not only the flow operations, but also includes operations of
   resource, service conditions, and service logic.

   In the book [PBNM], John Strassner defined the policy concept and
   proposed the formal description for network operations by using the
   policy.  The method for querying network information is absent in the
   book.  Virtual tenant network and operations to the tenant network
   are not considered.

   All these investigations direct to the future SDN that use simple and
   intuitive interfaces to describe the network demands without complex
   programming.

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5.  The NEMO Language Specifications

   NEMO language is a domain specific language (DSL) based on
   abstraction of network models and conclusion of operation patterns.
   It provides NBI fashion in the form of language.  Instead of tons of
   abstruse APIs, with limited number of key words and expressions, NEMO
   language enables network users/applications to describe their demands
   for network resources, services and logical operations in an
   intuitive way.  And finally the NEMO language description can be
   explained and executed by a language engine.

5.1.  Network Model of the NEMO Language

   Behind the NEMO language, there is a set of basic network models
   abstracting the network demands from the top down according to the
   service requirement.  Those demands can be divided into two types:
   the demand for network resources and the demands for network
   behaviors.

   The network resource is composed of three kinds of entities: node,
   connection and flow.  Each entity contains property and statistic
   information.  With a globally unique identifier, the network entity
   is the basic object for operation.  Users can construct their own
   topology or network traffic arbitrarily with these basic objects
   without considering about real physical topology.  In addition, NEMO
   Engine also has the ability of obtaining available resources
   automatically as operation objects when users don't define them.

   o  Node model: describes the entity with the capability of packet
      processing.  According to the functionality, there are two types
      of node

      *  The function node (FN) provides network services or forwarding
         with user concern, such as, firewall, load balance, vrouter,
         etc.

      *  The business node (BN) describes a set of network elements and
         their connections, such as subnet, autonomous system, and
         internet.  It conceals the internal topology and exposes
         properties as one entity.  It also enables iteration, i.e., a
         network entity may include other network entities.

   o  Connection model: describes the connectivity between node
      entities.  This connection is not limited at the connectivity
      between single entity and single entity, but it also can express
      the connectivity between single entity and multiply entities, or
      multiply entities and multiply entities.

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   o  Flow model: describes a sequence of packets with certain common
      characters, such as source/destination IP address, port, and
      protocol.  From the northbound perspective, flow is the special
      traffic with user concern, which may be per device or across many
      devices.  So the flow characters also include ingress/egress node,
      and so on.

   Network behavior includes the information and control operations.

   The information operation provides two methods to get the network
   information for users.

   o  Query: a synchronous mode to get the information, i.e., one can
      get the response when a request is sent out.

   o  Notification: an asynchronous mode to get the information, i.e.,
      with one request, one or multiple responses will be sent to the
      subscriber automatically whenever trigger conditions meet.

   The NEMO language uses policy to describe the control operation.

   o  Policy: control the behavior of specific entities by APP, such as
      flow policy, node policy.  All the policies follow the same
      pattern "when <condition>, to execute <action>, with
      <constraint>", and can be applied to any entity.  But some of
      policy elements can be omitted according to users' requirement.

5.2.  Notation

   The syntactic notation used in this specification is an extended
   version of BNF ("Backus Naur Form" or "Backus Normal Form").  In BNF,
   each syntactic element of the language is defined by means of a
   production rule.  This defines the element in terms of a formula
   consisting of the characters, character strings, and syntactic
   elements that can be used to form an instance of it.  The version of
   BNF used in this specification makes use of the following symbols:

      < >

   Angle brackets delimit character strings that are the names of
   syntactic elements.

      ::=

   The definition operator.  This is used in a production rule to
   separate the element defined by the rule from its definition.  The
   element being defined appears to the left of the operator and the
   formula that defines the element appears to the right.

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      [ ]

   Square brackets indicate optional elements in a formula.  The portion
   of the formula within the brackets may be explicitly specified or may
   be omitted.

      { }

   Braces group elements in a formula.  The portion of the formula
   within the braces shall be explicitly specified.

      |

   The alternative operator.  The vertical bar indicates that the
   portion of the formula following the bar is an alternative to the
   portion preceding the bar.  If the vertical bar appears at a position
   where it is not enclosed in braces or square brackets, it specifies a
   complete alternative for the element defined by the production rule.
   If the vertical bar appears in a portion of a formula enclosed in
   braces or square brackets, it specifies alternatives for the contents
   of the innermost pair of such braces or brackets.

      !!

   Introduces ordinary English text.  This is used when the definition
   of a syntactic element is not expressed in BNF.

5.3.  NEMO Language Overview

   NEMO language provides 5 classes of commands: model definition,
   resource access, behavior, connection management, transaction to
   facilitate the user intent description.

 <NEMO_cmd> := <model_definition_cmd> | <resource_access_cmd> |
               <behavior_cmd>
 <model_definition_cmd> := <node_definition> | <connection_difinition> |
                           <action_deifinition> | <model_description>
 <resource_access_cmd> := <node_cu> | <node_del> | <connection_cu> |
                          <connection_del> | <flow_cu> | <flow_del>
 <behavior_cmd> := <query_cmd> | <policy_cu> | <policy_del> |
                   <notification_cu> | <notification_del>
 <connection_mgt_cmd> := <connect_cmd> | <disconnect_cmd>
 <transaction_cmd> := <transaction_begin> | <transaction _end>

   NEMO language provides limited number of key words to enables network
   users/applications to describe their intent.  The key words supported
   by the language are as follows:

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 <key_word> := Boolean | Integer | String | Date | UUID | EthAddr |
               IPPrefix | NodeModel | ConnectionModel | FlowModel |
               ActionModel | Description | Porperty | Node | Connection|
               Flow | No | EndNodes | Type | NW | Match | List |
               Range| Query | From | Notification | Listener |
               Policy | ApplyTo | Priority | Condition | Action |
               Connect | Disconnect | Address | Port | Transaction |
               Commit

5.4.  Model Definition

5.4.1.  Data Types

   NEMO language provides several build-in data types:

   Boolean  This data type is used for simple flags that track true/
      false conditions.  There are only two possible values: true and
      false.  The Boolean literal is represented by the token <boolean>.

   Integer  A number with an integer value, within the range from
      -(2^63) to +(2^63)-1.  The Integer literal is represented by the
      token <integer>.

   String  A sequence of characters.  The string is always in the
      quotation marks.  The String literal is represented by the token
      <string>.

   Date  A string in the format yyyy-mm-dd hh:mm:ss, or yyyy-mm-dd, or
      hh:mm:ss.  The Date literal is represented by the token <date>.

   UUID  A string in the form of Universally Unique IDentifier
      [RFC4122], e.g.  "6ba7b814-9dad-11d1-80b4-00c04fd430c8".  A
      typical usage of the UUID is to identify network entities,
      policies, actions and so on.  The UUID literal is represented by
      the token <UUID>.

   EthAddr  A string in the form of MAC address, e.g.
      "00:00:00:00:00:01".  The EthAddr literal is represented by the
      token <eth_addr>.

   IPPrefix  A string in the form of IP address, e.g.  "192.0.2.1".  The
      mask can be used in the IP address description, e.g.
      "192.0.2.0/24".  The IPPrefix literal is represented by the token
      <ip_prefix>.

   The token <data_type> can be defined as follows:

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   <data_type> := Boolean | Integer | String | Date | UUID |
                  EthAddr | IPPrefix

   And a generic <data_type> literal is represented by the token <value>

   <value> := <boolean> | <integer> | <string> | <date> | <UUID> |
              <eth_addr> | <ip_ prefix>

5.4.2.  Model Definition and Description Statement

   In addition to default build-in network models, NEMO language
   facilitates users to define new model types.

   The token <naming> is a string that MUST start with a letter and
   followed by any number of letters and digits.  More specific naming
   can be defined as follows:

   <node_type> := <naming> !!type name of the node model
   <connection_type> := <naming> !!type name of the connection model
   <flow_type> := <naming> !!type name of the flow model
   <entity_type> := <node_type> | <connection_type> | <flow_type>
   <action_type> := <naming> !!type name of the action model
   <model_type> := <entity_type> | <action_type>
   <property_name> := <naming> !!name of the property in a model

   The <node_definition> statement is used to create a node model:

   <node_definition> := NodeModel <node_type>
                     Property { <data_type> : <property_name> };

   The NodeModel specifies a new node type.

   The Property is followed by a list of "<data_type> : <property_name>"
   pairs to specify properties for the new node type.  Since belonging
   network is the intrinsic property for a node model, there is no need
   to redefine the belonging network in the property list.

   Example:

   NodeModel "DPI" Property String : "name", Boolean : "is_enable"; The
   statement generates a new node model named DPI with two properties,
   "name" and "is_enable".

   The <connection_definition> statement is used to create a connection
   model:

   <connection_definition> := ConnectionModel <connection_type>
                    Property { <data_type> : <property_name> };

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   The ConnectionModel specifies a new connection type.

   The Property is followed by a list of "<data_type> : <property_name>"
   pairs to specify properties for the new connection type.  Since end
   nodes are intrinsic properties for a connection model, there is no
   need to redefine the end nodes in the property list.

   The <flow_definition> statement is used to create a flow model:

   <flow_definition> := FlowModel <flow_type>
                    Property { <data_type> : <property_name> };

   The FlowModel specifies a new flow type.

   The Property is followed by a list of "<data_type> : <property_name>"
   pairs to specify fields for the new flow type.  The
   <action_definition> statement is used to create an action model:

   <action_definition> := ActionModel <action_type>
                      Property  { <data_type> : <property_name> };

   The ActionModel specifies a new action type.

   The Property is followed by a list of "<data_type> : <property_name>"
   pairs to specify properties for the new action.

   NEMO language also supports querying the description of a defined
   model by using the <model_description> statement:

   <model_description> := Description <model_type>;

   The keyword Description is follow by a model type name.  The
   description of the queried model will return from the language
   engine.

5.5.  Resource Access Statements

   In NEMO language, each resource entity instance is identified by a
   <UUID>.  We use the following token to indicate the identifier given
   to the resource entity instance.

 <node_id> := <naming> !! name to identify the node instance
 <connection_id> := <naming> !! name to identify the connection instance
 <flow_id> := <naming> !! name to identify the flow instance
 <entity_id> := <node_id>|<connection_id>|<flow_id>

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5.5.1.  Node Operations

   The <node_cu> statement is used to create or update a node instance:

   <node_cu> := Node <node_id> Type  <node_type>
                               NW <node_id>
                               [Property {<property_name>: <value>}];

   The Node is followed by a user specified <node_id>.  If the <node_id>
   is new in the system, a new node will be created automatically.
   Otherwise, the corresponding node identified by <node_id> will be
   updated with the following information.

   The Type specifies the type of the node to operate.

   The NW specifies the dependence where the node is located.

   The Property is an optional keyword followed by a list of
   "<property_name>: <value>" pairs.  Multiple "<property_name>:
   <value>" pairs are separated by commas.  The <property_name> MUST be
   selected from the property definition of the corresponding node
   definition.

   Node "Headquater"
        Type      "logicnw"
        NW        "LN-1"
        Property  "location" : "Beijing";

   The statement creates a switch type node that is located in the
   logical network "LN-1".

   The <node_del> statement is used to delete a node instance:

   <node_del> := No Node <node_id>;

   The No Node is to delete a node in user's network.

5.5.2.  Connection Operations

   The <connection_cu> statement is used to create or update a
   connection:

   <connection_cu> := Connection <connection_id>
                EndNodes <node_id>, <node_id>
                [Property {<property_name>: <value>}];

   The Connection is followed by a user specified <connection_id>.  If
   the <connection_id> is new in the system, a new connection will be

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   created automatically.  Otherwise, the corresponding connection
   identified by the <connection_id> will be updated with the following
   information.

   The EndNodes specifies the two end nodes, identified by "<node_type>
   : <node_id>", of a connection.  The Property is an optional keyword
   followed by a list of "<property_name>: <value>" pairs.  Multiple
   "<property_name>: <value>" pairs are separated by commas.  The
   <property_name> MUST be selected from the property definition of the
   corresponding connection definition.

   Example:

   Connection "connection-1"
        EndNodes "S1", "S2"
        Property "bandwidth" : 1000, "delay" : 40;

   The statement creates a connection between two nodes, and sets the
   connection property.

   The <connection_del> statement is used to delete a node instance:

   <connection_del> := No Connection <connection_id>;

   The No Connection is to delete a connection in user's network.

5.5.3.  Flow Operations

   The <flow_cu> statement is used to create or update a flow:

   <flow_cu> := Flow <flow_id> Match {<property_name>: <value>
                                      | Range (<value>, <value>)
                                      | List({<value>})}

   The Flow is followed by a user defined <flow_id>.  If the <flow_id>
   is new in the system, a new flow will be created automatically.
   Otherwise, the corresponding flow identified by the <flow_id> will be
   updated with the following information.

   The Match specifies a flow by indicate match fields.  NEMO language
   also provides two keywords to assist the expression of values:

   o  The List is used to store a collection of data with the same data
      type.

   o  The Range is used to express a range of values.

   Example:

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   Flow "flow-1"
         Match "src_ip" : Range ("192.0.2.1", "192.0.2.243");

   The statement describes a flow with the source IP address ranging
   from 192.0.2.1 to 192.0.2.243.

   The <flow_del> statement is used to delete a flow instance:

   <flow_del> := No Flow <flow_id>;

   The No Flow is to delete a flow in user's network.

5.6.  Behavior Statements

5.6.1.  Query Behavior

   The query statement is to retrieve selected data from specified model
   object.

   The <query_statement> generate a query:

   <query_cmd> := Query {<property_name>}
                  From {<entity_id>|<policy_id>}

   The Query is followed by one or more <property_name>s which are
   defined properties of the object to be queried.

   The From is followed by the one or more queried objects.  NENO
   language support query operation to network entities and the policy.

5.6.2.  Policy Behavior

   In NEMO language, each policy instance is identified by a <naming>

   <policy_id> := <naming> !! name to identify the policy instance

   Create and update a policy

   <policy_cu> := Policy <policy_id> ApplyTo <entity_id>
                  Priority <integer>
                  [Condition {<expression>}]
                  Action {<action_type> : {<value>}}
                  [Constraint {<expression>}];

   The Policy is followed by a user defined <policy_id>.  If the
   <policy_id> is new in the system, a new policy will be created
   automatically.  Otherwise, the corresponding notification identified
   by the <policy_id> will be updated with the following information.

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   The ApplyTo specifies the entity to which the policy will apply.

   The Priority specifies the globe priority of the policy in the tenant
   name space.  The <value> with lower number has a higher priority,
   i.e. priority 0 holds the highest priority.

   The Condition is an optional keyword follow by an expression.  It
   tells your program to execute the following actions only if a
   particular test described by the expression evaluates to true.  And
   users also can define which objects won't need to execute these
   actions with Constraint.

   A NEMO language expression is a construct made up of variables,
   operators, and method invocations, which are constructed according to
   the syntax of the language and evaluates to a single value.  NEMO
   language supports many operators to facilitate the construction of
   expressions.  Assume variable A holds 10 and variable B holds 0,
   then:

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   +----------+----------------------------------------------+---------+
   | Operator |                                  Description | Example |
   +----------+----------------------------------------------+---------+
   | &&       |     Called Logical AND operator. If both the | (A &&   |
   |          |    operands are non-zero, then the condition | B) is   |
   |          |                                becomes true. | false.  |
   | ||       |    Called Logical OR Operator. If any of the | (A ||   |
   |          |          two operands are non-zero, then the | B) is   |
   |          |                      condition becomes true. | true.   |
   | !        | Called Logical NOT Operator. Use to reverses | !(A &&  |
   |          |       the logical state of its operand. If a | B) is   |
   |          |  condition is true then Logical NOT operator | true.   |
   |          |                             will make false. |         |
   | ==       |     Checks if the values of two operands are | (A ==   |
   |          |  equal or not, if yes then condition becomes | B) is   |
   |          |                                        true. | not     |
   |          |                                              | true.   |
   | !=       |     Checks if the values of two operands are | (A !=   |
   |          |   equal or not, if values are not equal then | B) is   |
   |          |                      condition becomes true. | true.   |
   | >        |       Checks if the value of left operand is | (A > B) |
   |          |  greater than the value of right operand, if | is not  |
   |          |             yes then condition becomes true. | true.   |
   | >=       |       Checks if the value of left operand is | (A >=   |
   |          |  greater than or equal to the value of right | B) is   |
   |          | operand, if yes then condition becomes true. | not     |
   |          |                                              | true.   |
   | <        |  Checks if the value of left operand is less | (A < B) |
   |          | than the value of right operand, if yes then | is      |
   |          |                      condition becomes true. | true.   |
   | <=       |  Checks if the value of left operand is less | (A <=   |
   |          | than or equal to the value of right operand, | B) is   |
   |          |          if yes then condition becomes true. | true.   |
   +----------+----------------------------------------------+---------+

   The Action specifies the execution when conditions meet.

   Example:

   Policy "policy-1"
           ApplyTo "flow-1"
           Priority 100
           Condition ("time">"18:00") || ("time"<"21:00")
           Action  "gothrough" : "backup_connection";

   The statement creates a policy which indicates the flow to go through
   backup connection from 18:00 to 21:00.

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   Delete a policy:

   <policy_del> := No Policy <policy_id>;

   The No Policy is to delete a policy in user's network.

5.6.3.  Notification Behavior

   In NEMO language, each notification instance is identified by a
   <naming>

   <notification_id> := <naming> !! name to identify the notification
                        instance

   Create and update a notification

   <notification_cu> := Notification <notification_id>
                        [(Query {<property_name>}
                        From {<entity_id>})]
                        Condition {<expression>}
                        Listener <callbackfunc>;

   The Notification is followed by a user defined <notification_id>.  If
   the <notification_id> is new in the system, a new notificaiton will
   be created automatically.  Otherwise, the corresponding notification
   identified by the <notification_id> will be updated with the
   following information.

   The Query clause is nested in the notification statement to indicate
   the information acquisition.

   The Condition clause is the same as in policy statement, which
   triggers the notification.

   The Listener specifies the callback function that is used to process
   the notification.

   Delete a notification:

   <notification_del> := No Notification <notification_id>;

   The No Notification is to delete a notification in user's network.

5.7.  Connection Management Statements

   In NEMO language, each connection instance is identified by a
   <naming>

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   <conn_id> := <naming> !! name to identify the connection instance

   Setup a connection to the NEMO language engine:

   <connet_cmd> := Connect <conn_id> Address <ip_prefix>
                   Port <integer>

   The Connect is followed by a user defined <conn_id>.  If the
   <conn_id> is new in the system, a new connection will be created
   automatically.  Otherwise, the corresponding connection identified by
   <conn_id> will be updated with the following information.

   The Address and Prot specify the IP address and the port of the NEMO
   language engine to connect separately.

   Disconnect the connection to the NEMO language engine:

   <disconnect_cmd> := Disconnect <conn_id>

   The Disconnect is to remove the connection with an ID equals to
   <conn_id> from the NEMO language engine.

5.8.  Transaction Statements

   <transaction_begin> := Transaction
   <transaction_end> := Commit

   The keywords Transaction and Commit are used to tag begin and end of
   a transaction.  The code between the two key words will be
   interpreted as a transaction and executed by the NEMO language
   engine.

6.  The NEMO Language Examples

   An enterprise with geographically distributed headquarter and branch
   sites has the requirement to dynamically balance the backup traffic.

   In order to implement this scenario, the virtual WAN tenant creates
   two logicnw, and generates two connections with different SLA to
   carry diverse service flows.  One connection has 100M bandwidth with
   less than 50ms delay, which is used for normal traffic.  And the
   other connection has 40G bandwidth with less than 400ms delay, which
   is used for backup traffic after work (from 19:00 to 23:00).  With
   self defined flow policy, the tenant can manage the connection load
   balancing conveniently.

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                           Real-time Connection
                          +--------------------+
                 192.0.2.0/24                  198.51.100.0/24
                 +---------+                  +-------------+
                 | Branch  |------------------| Headquarter |
                 +---------+                  +-------------+
                          |                    |
                          +--------------------+
                           Broadband Connection

   The detailed operation and code are shown as follows.

   o  Step1: Create two virtual logicnw nodes in the WAN

   Node "Branch"
         Type  "logicnw"
         NW    "LN-1"
         Property "ipv4Prefix" : 192.0.2.0/24;

   Node "Headquarter"
         Type "logicnw"
         NW   "LN-1"
         Property "ipv4Prefix" : 198.51.100.0/24;

   o  Step2: Connect the two virtual nodes with two virtual connections
      with different SLA.

   Connection "broadband_connection"
        EndNodes "Branch", "Headquater"
        Property   "bandwidth" : 40000, "delay" : 400;

   Connection "realtime_connection"
        EndNodes "Branch", "Headquater"
        Property  "bandwidth" : 100, "delay" : 50;

   o  Step3: Indicate the flow to be operated.

   Flow "flow_all"
         Match "src_ip" : "192.0.2.0/24", "dst_ip": "198.51.100.0/24";

   Flow "flow_backup"
         Match "src_ip" : "192.0.2.0/24", "dst_ip": "198.51.100.0/24",
               "port": 55555;

   o  Step4: Apply policies to corresponding flows.

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   P1:
   Policy "policy4all"
          ApplyTo "flow_all"
          Priority 200
          Action  "forward_to": "realtime_connection";
   P2:
   Policy "policy4backup"
           ApplyTo "flow_backup"
           Priority 100
           Condition ("time">"19:00:00") || ("time"<"23:00:00")
           Action  "forward_to": "broadband_connection";

7.  Security Considerations

   Because the network customers are allowed to customize their own
   services, they may bring potentially big impacts to a running IP
   network.  A strong user authentication mechanism is needed for the
   northbound interface of the SDN controller.  User authorization
   should be carefully managed by the network administrator to avoid any
   dangerous operations and prevent any abuse of network resources.

8.  IANA Considerations

   This memo includes no request to IANA.

9.  Acknowledgements

   The authors would like to thanks the valuable comments made by Wei
   Cao, Xiaofei Xu, Fuyou Miao, Yali Zhang and Wenyang Lei.

   This document was produced using the xml2rfc tool [RFC2629].

10.  Informative References

   [Frenetic]
              Foster, N., Harrison, R., Freedman, M., Monsanto, C.,
              Rexford, J., Story, A., and D. Walker, "Frenetic: A
              Network Programming Languages, ICFP' 11".

   [I-D.xia-sdnrg-service-description-language]
              Xia, Y., Jiang, S., and S. Hares, "Requirements for a
              Service Description Language and Design Considerations",
              draft-xia-sdnrg-service-description-language-02 (work in
              progress), May 2015.

   [PBNM]     Strassner, J., "Policy-Based Network Management: Solutions
              for the Next Generation, Morgan Kaufmann Publishers Inc.
              San Francisco, CA, USA.", 2003.

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

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122, July
              2005.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)", RFC
              6241, June 2011.

   [TSFNet]   Yap, K., Huang, T., Dodson, B., Lam, M., and N. McKeown,
              "Towards Software-Friendly Networks, APSys 2010, pp:49-54,
              2010, New Delhi, India.".

Authors' Addresses

   Yinben Xia (editor)
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus, No.156 Beiqing Road
   Hai-Dian District, Beijing, 100095
   P.R. China

   Email: xiayinben@huawei.com

   Sheng Jiang (editor)
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus, No.156 Beiqing Road
   Hai-Dian District, Beijing, 100095
   P.R. China

   Email: jiangsheng@huawei.com

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   Tianran Zhou (editor)
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus, No.156 Beiqing Road
   Hai-Dian District, Beijing, 100095
   P.R. China

   Email: zhoutianran@huawei.com

   Susan Hares
   Huawei Technologies Co., Ltd
   7453 Hickory Hill
   Saline, CA  48176
   USA

   Email: shares@ndzh.com

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