NEMO (NEtwork MOdeling) Language
draft-xia-sdnrg-nemo-language-00

Abstract

The North-Bound Interface (NBI), located between the network 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 anther NBI fashion. Concept, model and syntax are introduced in the document.

Status of This Memo

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Related work
• 4. The NEMO Language overview
• 4.1. Network Model of the NEMO Language
• 4.2. Primitives
• 5. The NEMO Language Examples
• 6. Security Considerations
• 7. IANA Considerations
• 8. Acknowledgements
• 9. Informative References
• Authors' Addresses

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.

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.

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 think from the user perspective and abstract the network from the top down. [I-D.sdnrg-service-description-language] describe the requirements for a service description language and the design considerations.

A top-down NBI design contains following features:

• 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.
• Platform independent
  
  With the NBI, the application or user can describe 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.
• 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.
• 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 proposed NEtwork MOdeling (NEMO) language works on the user's view so the users can create topologies based on the resources the network-operators allow them to have.
• Declarative style
  
  As described above, NEMO language is designed to help defining service requirement to network, detailed configurations and instructions performed by network devices are opaque to network operators. So NEMO language should be declarative rather than imperative.

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".

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;

Network user

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

3. Related work

YANG is a data modeling language used to model configuration and state data manipulated by the Network Configuration Protocol (NETCONF), NETCONF remote procedure calls, and NETCONF notifications [RFC6020]. Although it is extensible for more data modeling in addition to NETCONF, YANG is not capable of describing high level network requirements, such as SLA (Service Level Agreement). YANG is designed for north-bound interfaces of the device, which is also the south-bound of the controller. It is not proper to model the north-bound interface of the controller, aka the NBI. Moreover, the YANG is not capable of describing the service processing logic, which typically includes transition of conditions and states.

UML (Unified Modeling Language) is a powerful modeling language, which is domain agnostic. It is hard to describe the network demand, and cannot be embedded in network applications. 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.

4. The NEMO Language overview

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. With limited number of key words and expressions, NEMO language defines the entity and capability models for users with different view of network abstraction, and enables network users/applications to describe their demands for network resources, services and logical operations in an intuitive expression. And finally the NEMO language description can be explained and executed by a language engine.

4.1. Network Model of the NEMO Language

Behind the NEMO language, there is a set of meta-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, link and flow. Each entity contains property and statistic information. With a globally unique identifier, the network entity is the basic object for operation.

• Node model: describes the entity with the capability of packet processing. According to the functionality, there are three types of node
  • The forwarding node (FN) only deals with L2/3 forwarding. It forwards packets according to the forwarding table and modifies packet heads.
  • The processing node (PN) provides L4-7 network services, and will modify the body of packets.
  • The logical node (LN) describes a set of network elements and their links, 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.
• Link model: describes the connectivity between node entities. According to the forwarding capability, links are usually divided into layer 2 and layer 3 types
• 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.

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

• Policy: control the behavior of specific entities by APP, such as flow policy, node policy. All the policies follow the same pattern "with <condition>, to execute <action>", and can be applied to any entity

4.2. Primitives

The primitives of NEMO language are derived from the network model, and fall into four categories.

Node/UnNode  entity_id  Type {FN|PN|LN} 
                        Owner node_id 
                        Properties  key1 ,value1

Node/UnNode:   create/delete a node
Entity id:     system allocated URI for the node entity 
Type:          Node type of FN (forwarding node), PN (processing node) 
               or LN (logical node) 
Owner:         since the node can be nested, this primitive figures 
               out which node the new one belongs to
Properties:    other properties to describe the node in the form of 
               (key, value).


Link/UnLink  entity_id   Endnodes (node1_id,node2_id) 
                         SLA key,value 
                         Properties  key1 ,value1 

Link/UnLink:   create/delete a link.
Entity id:     system allocated URI for the link entity
Endnodes:      two end-node IDs of the link
SLA:           SLA description for the link
Properties:    other properties to describe the link in the form of 
               (key, value).


Flow/UnFlow  entity_id  Match/UnMatch key1, value1|
                        Range(value, value) |
                        Mask(value, value) 
                        Properties  key1 ,value1 

Flow/UnFlow:   create/delete a flow.
Match/UnMatch: create/delete match items for the flow
Range:         describe the range of the value
Mask:          use mask to describe a range of the value
Properties:    other properties to describe the flow in the form of 
               (key, value).

Query   key  Value {value}
             From entity_id

Query:         generate a synchronously query
key:           the parameter name to be queried 
Value:         the return value for the query
From:          the entity to be queried (define entity_id). 


Policy/UnPolicy  policy_id  Appliesto  entity_id  
                            Condition {expression}       
                            Action {"forwardto"|"drop"|"gothrough"|
                            "bypass"|"guaranteeSLA"|"Set"|
                            "Packetout"|Node|UnNode|Link|Unlink}

Policy/UnPolicy: create/delete a policy
Appliesto:     apply the policy to an entity  
Condition:     condition to execute the policy
Action:        actions to be executed when conditions are met


Notification/UnNotification    entity_id   On  key  
                                           Every  period  
                                           RegisterListener
                                              callbackfunc 

Notification/UnNotification: create/delete a notification for an 
               entity
On:            the notification will monitor the state change of a 
               parameter identified by the "key"
Every:         time period at which to report the state 
RegisterListener: the callback function that is used to process the 
               notification.

Connect   conn_id     Address  ip_address  
                      Port port_num
Disconnect  conn_id 

Connect:       set up a connection to the controller
Address:       IP address of the controller to connect to
Port:          port of the controller to connect to
Disconnect:    disconnect to the controller.

Transaction
Commit

Transaction:   indicate the beginning of a transaction
Commit:        commit to execute the transaction

1. Resource access primitives
2. Behavior primitives
3. Connection management primitives
4. Transaction primitives

5. The NEMO Language Examples

A tenant needs two connections to carry different service flows between two datacenters.

{
   Link Link1_id 
      Endnodes (DC1_node_id, DC2_node_id) 
      Property "NAME","DC1_DC2_link_one","Bandwith",40G,"Delay",400ms 
   Link Link2_id 
      Endnodes (DC1_node_id, DC2_node_id) 
      Property "NAME","DC1_DC2_link_two","Bandwith",100M,"Delay",50ms 
}

one connection of the tenant is 40G bandwidth with less than 400ms delay, another connection is 100M bandwidth with less than 50ms delay.

{
   Flow flow1_id
      Match "srcip","10.0.1.1/24","dstip","20.0.1.1/24","Port","55555" 
      Property "NAME","CDN sync flow","Bidirection","true"
   Flow flow2_id
      Match "srcip","10.0.1.1/24","dstip","20.0.1.1/24","Port","56663" 
      Property "NAME","online Game","Bidirection","true"
   Policy  policy1_id  
      Appliesto flow1_id 
      Action "forwardto",link1_id
   Policy  policy2_id  
      Appliesto flow2_id 
      Action "gothrough",link2_id
}

{
   Policy  policy3_id  
      Appliesto flow2_id 
      Condition {Time>18:00 or Time< 2:00} 
      Action "gothrough",{woc_node_id ,link2_id}
}

6. 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.

7. IANA Considerations

This memo includes no request to IANA.

8. Acknowledgements

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

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

9. Informative References

Authors' Addresses