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<rfc category="std" docName="draft-xiong-rtgwg-precise-tn-problem-statement-01"
     ipr="trust200902">
  <!-- ***** FRONT MATTER ***** -->
  <front>
    <title abbrev="The Problem Statement for Precise Transport Networking">The Problem Statement for Precise Transport Networking</title>

	<author fullname="Quan Xiong" initials="Q" surname="Xiong">
      <organization>ZTE Corporation</organization>

      <address>
        <postal>
          <street>No.6 Huashi Park Rd</street>
          
          <city>Wuhan</city>
          
          <region>Hubei</region>
  
          <code>430223</code>

          <country>China</country>
        </postal>

        <phone></phone>

        <email>xiong.quan@zte.com.cn</email>
      </address>
    </author>
	
    <author fullname="Peng Liu" initials="P" surname="Liu">
      <organization>China Mobile</organization>

      <address>
        <postal>
          <street></street>
          
          <city>Beijing</city>
          
          <region></region>
  
          <code>100053</code>

          <country>China</country>
        </postal>

        <phone></phone>

        <email>liupengyjy@chinamobile.com</email>
      </address>
    </author>
	
    
   <date month="November" year="2020"/>	
    <area>Routing</area>
    <workgroup>RTGWG</workgroup>
    <keyword></keyword>
    <abstract>
	<t>As described in <xref target="I-D.xiong-rtgwg-precise-tn-requirements"></xref>, the deterministic 
	networks not only need to offer the Service Level Agreements (SLA) guarantees such 
	as low latency and jitter, low packet loss and high reliability, but also need to 
	support the precise services such as flexible resource allocation and service 
	isolation so as to the Precise Transport Networking. However, under the existing IP network 
	architecture with statistical multiplexing characteristics, the existing deterministic 
	technologies are facing long-distance transmission, queue scheduling, dynamic flows 
	and per-flow state maintenance and other controversial issues especially in Wide 
	Area Network (WAN) applications.</t>
	
    <t>This document analyses the problems in existing deterministic technologies 
	to provide precise services in various industries such as 5G networks.</t>
    </abstract>
  </front>

  <!-- ***** MIDDLE MATTER ***** -->

  <middle>
  
    <section title="Introduction">
	
	<section title="Overview">
	
	<t>5G network is oriented to the internet of everything. In addition to the 
	Enhanced Mobile Broadband (eMBB) and Massive Machine Type Communications(mMTC) 
	services, it also supports the Ultra-reliable Low Latency Communications (uRLLC) 
	services. The uRLLC services cover the industries such as intelligent electrical 
	network, intelligent factory, internet of vehicles, industry automation and other
	industrial internet scenarios, which is the key demand of digital transformation 
	of vertical domains. These uRLLC services demand SLA guarantees such as low 
	latency and high reliability and other deterministic and precise properties.</t>
	
	<t>For the intelligent electrical network, there are deterministic requirements 
	for communication delay, jitter and packet loss rate. For example, in the 
	electrical current difference model, a delay of 3~10ms and a jitter variation 
	is no more than 100us are required. The isolation requirement is also important.
	For example, the automatic operation, control of a process, isochronous data 
	and low priority service need to meet the requirements of hard isolation. In
	addition to the requirements of delay and jitter, the differential protection 
	(DP) service needs to be isolated from other services.</t>
	
	<t>The industrial internet is the key infrastructure that coordinate various 
	units of work over various system components, e.g. people, machines and things 
	in the industrial environment including big data, cloud computing, Internet of 
	Things (IOT), Augment Reality (AR), industrial robots, Artificial Intelligence 
	(AI) and other basic technologies.  For example, automation control is one of 
	the basic application and the the core is closed-loop control system. The 
	control process cycle is as low as millisecond level, so the system communication
	delay needs to reach millisecond level or even lower to ensure the realization 
	of precise control. There are three levels of real-time requirements for 
	industrial interconnection: factory level is about 1s, and process level 
	is 10~100ms, and the highest real-time requirement is motion control, 
	which requires less than 1ms.</t>
	
	
	</section>
	
    <section title="Motivation">
	
	<t>The applications in 5G networks demand much more deterministic and precise
	properties. But traditional Ethernet, IP and MPLS networks which is based on
	statistical multiplexing provides best-effort packet service and offers no
	delivery and SLA guarantee. The deterministic forwarding can only apply to 
	flows with such well-defined characteristics as periodicity and burstiness.</t> 

    <t>Technologies to provide deterministic service has been proposed to provide
	bounded latency and jitter based on a best-effort packet network. IEEE 802.1 
	Time-Sensitive Networking (TSN) has been proposed to provide bounded latency 
	and jitter in L2 LAN networks. According to <xref target="RFC8655"></xref>, Deterministic Networking 
	(DetNet) operates at the IP layer and delivers service which provides extremely
	low data loss rates and bounded latency within a network domain. However, the
	existing mechanisms are not sufficient for precise performance such as precise
	latency, jitter variation, packet loss and more other precise and deterministic
	properties. </t>

    <t>As described in [xiong-rtgwg-precise-networking-requirements], the deterministic
	networks not only need to offer the Service Level Agreements (SLA) guarantees such
	as low latency and jitter, low packet loss and high reliability, but also need to 
	support the precise services such as flexible resource allocation and service 
	isolation so as to the Precise Transport Networking. However, under the existing IP network
	architecture with statistical multiplexing characteristics, the existing  
	deterministic technologies are facing long-distance transmission, traffic 
	scheduling, dynamic flows, per-flow state maintenance and other controversial
	issues especially in Wide Area Network (WAN) applications.</t>

    <t>This document analyses the problems in existing deterministic technologies
	to provide precise services in various industries such as 5G networks.</t>
	
	
	</section>
	
  
   </section>

    <section title="Conventions used in this document">	 	
    <section title="Terminology">
	<t>The terminology is defined as <xref target="RFC8655"></xref> and 
	[xiong-rtgwg-precise-networking-requirements].</t>
	
   </section>
   
   <section title="Requirements Language">
    <t>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 <xref target="RFC2119"></xref> <xref target="RFC8174"></xref> when,
    and only when, they appear in all capitals, as shown here.</t>
    </section>
	
   </section>

   <section title="Problem Statement">

   <section title="Problem with Traffic Scheduling Mechanisms">
     
	<t>As described in <xref target="RFC8655"></xref>, the primary means by which DetNet achieves 
	its QoS assurances in IP networks is to eliminate the latency and packet
	loss by the provision of sufficient resource at each node. But only the 
	resource itself is not sufficient, the traffic scheduling mechanisms 
	such as queuing, shaping, and scheduling functions must be applied in 
	L3 networks.</t>

    <t>The congestion control, queue scheduling and other traffic mechanisms
	which have been proposed in IEEE 802.1 TSN.  But most of them are based 
	on the time synchronization and time cycle, such as IEEE802.1Qbv, 
	IEEE802.1Qch and so on.  It will be difficult to achieve precise time 
	synchronization with all network nodes due to deployment and cost reasons. 
	And the shaping and queuing methods which are not based on time 
	synchronization such as IEEE802.1Qav and IEEE802.1Qcr might not be 
	suitable or available for some L3 networks such as WAN application 
	where multiple dynamic traffic flows may be existed.</t>

    <t>Moreover, the requirements of the all nodes in WAN networks to apply
	the time synchronization and traffic scheduling mechanisms will also 
	lead to the difficulty of network scalability and deployment.</t>
   
   
   </section>
   
   <section title="Problem with Long-distance Transmission Delay and Jitter">
   
    <t>In WAN application, long-distance transmission will lead to uncertainties,
	such as increasing transmission delay, jitter and loss. The link delay of 
	transmission is variable and can not be ignored, and it must be considered
	in the end-to-end deterministic forwarding mechanisms which are based on 
	time synchronous.  So the following problems should be considered.</t>
    
	<t>Precise measurement of the link delay.</t>

    <t>The symmetry of bidirectional forwarding of the link delay.</t>

    <t>Time cycle alignment in flows aggregation scenario.</t>
   
   </section>
   
   <section title="Problem with SLA Guarantees of Dynamic Flows">
   
    <t>As described in <xref target="RFC8557"></xref>, deterministic forwarding can only apply to 
	flows with such well-defined characteristics as periodicity and burstiness. 
	As defined in DetNet architecture <xref target="RFC8655"></xref>, the traffic characteristics 
	of an App-flow can be CBR (constant bit rate) or VBR (variable bit rate) 
	of L1, L2 and L3 layers (VBR takes the maximum value when reserving resources). 
	But the current scenarios and technical solutions only consider CBR flow, 
	without considering the coexistence of VBR and CBR, the burst and aperiodicity
	of flows. The operations such as shaping or scheduling have not been specified.
	Even TSN mechanisms are based on a constant and forecastable traffic
    characteristics.</t>

    <t>It will be more complicated in WAN applications where much more flows 
	coexist and the traffic characteristics is more dynamic.  It is required 
	to offer reliable delivery and SLA guarantee for dynamic flows. For example,
	periodic flow and aperiodic flow (including micro burst flow, etc.), CBR 
	and VBR flow, flow with different periods or phases, etc. When the network
	needs to forward these deterministic flows at the same time, it must solve
	the problems of time window selection, queue processing and aggregation 
	of multiple flows.</t>

    <t>Moreover, the existing solutions do not consider the characteristics 
	analysis of service requirements, including the impact of dynamic 
	characteristics analysis on the network, mainly about how to ensure 
	the certainty in the case of dynamic flows.</t>
   
   </section>
   
   <section title="Problem with Service Isolation">
   
    <t>In some scenarios, such as intelligent electrical network, the 
	isolation requirements are very important. For example, the automatic 
	operation or control of a process or isochronous data and low priority
	service need to meet the requirements of hard isolation. In addition to
	the requirements of delay and jitter, the differential protection (DP) 
	service needs to be isolated from other services and hard isolated 
	tunnel is required.</t>

    <t>The resource reservation in DetNet can only ensure the statistical
	reuse of bandwidth resources, but it can not guarantee the precise 
	isolation and control of instantaneous burst and can not realize the 
	hard isolation of each flow. The existing solutions cannot achieve 
	the requirements of service isolation.</t>
   
   </section>
   
   
  <section title="Problem with Precise Resource Allocation">
   
   <t>As described in <xref target="RFC8655"></xref>, the primary means by which DetNet achieves 
   its QoS assurances is to reduce, or even completely eliminate, packet loss
   by the provision of sufficient buffer storage at each node. But it can not
   be achieved by not enough resource which can be allocated due to practical 
   and cost reason. The existing solutions can not achieve the precise resource 
   allocation. </t>
   
   </section>
   
   </section>
    
   
    
   <section title="Security Considerations">
    <t>TBA</t>
   </section>

    <section anchor="Acknowledgements" title="Acknowledgements">
    <t>TBA</t>
    </section>
	
	<section anchor="IANA" title="IANA Considerations">
	<t>TBA</t>
    </section>
	
  </middle>

  <!--  *****BACK MATTER ***** -->

  <back>
  
    <references title="Normative References">
    <?rfc include='reference.RFC.2119'?>
	<?rfc include='reference.RFC.8655'?>
    <?rfc include='reference.RFC.8557'?>
	<?rfc include='reference.RFC.8174'?>
    <?rfc include='reference.I-D.xiong-rtgwg-precise-tn-requirements'?>
    </references>
        
  </back>
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