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Versions: 00 01                                                         
Network                                                     Shaofu. Peng
Internet-Draft                                                  Bin. Tan
Intended status: Standards Track                         ZTE Corporation
Expires: July 14, 2022                                  January 10, 2022


                Deadline Based Deterministic Forwarding
             draft-peng-detnet-deadline-based-forwarding-00

Abstract

   This document describes a deterministic forwarding mechanism based on
   deadline.  The mechanism enhances strict priority scheduling
   algorithm with dynamically adjusting the priority of the queue
   according to its deadline attribute.

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 July 14, 2022.

Copyright Notice

   Copyright (c) 2022 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Deadline Queue  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Get Deadline Information of Packets . . . . . . . . . . . . .   6
     3.1.  Get Planned Deadline  . . . . . . . . . . . . . . . . . .   6
     3.2.  Get Existing Cumulative Planned Deadline  . . . . . . . .   7
     3.3.  Get Existing Accumulated Actual Dwell Time  . . . . . . .   7
     3.4.  Get Existing Accumulated Deadline Deviation . . . . . . .   8
   4.  Put Packets into the Deadline Queues  . . . . . . . . . . . .   8
   5.  Traffic Regulation and Shaping  . . . . . . . . . . . . . . .  11
   6.  Benefits  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   [RFC8655] describes the architecture of deterministic network and
   defines the QoS goals of deterministic forwarding: Minimum and
   maximum end-to-end latency from source to destination, timely
   delivery, and bounded jitter (packet delay variation); packet loss
   ratio under various assumptions as to the operational states of the
   nodes and links; an upper bound on out-of-order packet delivery.  In
   order to achieve these goals, deterministic networks use resource
   reservation, explicit routing, service protection and other means.
   Resource reservation refers to the occupation of resources by service
   traffic, exclusive or shared in a certain proportion, such as
   dedicated physical link, link bandwidth, queue resources, etc;
   Explicit routing means that the transmission path of traffic flow in
   the network needs to be selected in advance to ensure the stability
   of the route and does not change with the real-time change of network
   topology, and based on this, the upper bound of end-to-end delay and
   delay jitter can be accurately calculated; Service protection refers
   to sending multiple service flows along multiple disjoint paths at
   the same time to reduce the packet loss rate.  In general, a
   deterministic path is a strictly explicit path calculated by a
   centralized controller, and resources are reserved on the nodes along
   the path to meet the SLA requirements of deterministic services.

   [I-D.stein-srtsn] describes that the controller calculates the local
   deadline time of each node for the traffic to be transmitted in
   advance, which is a absolute system time, forms a stack of these
   local deadline time, and then carries them in the forwarded data
   packets.  Each node forwards the packets according to its own local



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   deadline.  [I-D.stein-srtsn] suggests that FIFO queue can not be used
   to realize this function, because the packets stored in the queue are
   always first in first out, so a special data structure is recommoned.
   The packets in this data structure will be automatically sorted with
   the order from emergency to non emergency according to the deadline
   of the packets.  However, it may be difficult to implement this
   structure in hardware, and especially for a large network it may be
   challenge to synchronize time.

   Considering that the link transmission delay is generally a fixed
   value, and we focus on the dwell time of the packets inside the node,
   an alternate approach is to make the deadline eliminate the
   interference of link delay and avoids relying on time synchronization
   between nodes.

   This document desrbies an alternate packets scheduling scheme.  It
   suggests to only use a single deadline time to control the packets
   scheduling of all nodes along the path.  The single deadline time is
   an offset time, which is based on the time when the packet enters the
   node and represents the maximum time allowed for the packet to stay
   inside the node.  However, if each node has obvious differences in
   the capability of packets forwarding and scheduling, more offset-time
   may be needed.

1.1.  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.  Deadline Queue

   For nodes in the network, some queues with deadline time (also termed
   as TTL) are introduced and maintained for each outgoing port.  These
   queues are called deadline queue.  Deadline queue has the following
   characteristics:

      The TTL of each deadline queue will decrease with the passage of
      time.  When it decreases to 0, the scheduling priority of the
      queue will be set to the highest, and the scheduling opportunity
      will be obtained immediately (note that there may be interference
      delay caused by a large packet being sent by a low priority
      queue).  It will prohibit receiving new packets, in which the
      buffered packets will be sent to the outgoing port immediately,
      and the maximum duration allowed to send packets is the
      authorization time.  In principle, all packets buffered in the



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      queue shall be sent within this authorization time.  If the queue
      is sent and the authorization time is still free, other queues
      with lower priority can be scheduled during this authorization
      time.

      The scheduling engine can initiate a cycle timer to decrement the
      TTL of all deadline queues, that is, whenever the timer expires,
      the deadline values of all queues will be subtracted from the
      timer interval.  Note that the time interval of the timer must be
      greater than or equal to the authorization time of the deadline
      queue.  For simplicity, they are same.

      For a deadline queue whose TTL has been reduced to 0, after a new
      round of timer timeout, the TTL will return to the maximum initial
      value, allow receiving new packets, and continue to enter the next
      round of operation that decreases with the passage of time.

      For a deadline queue whose TTL is not reduced to 0, it can receive
      packets.  In detailed, when a node receives a packet to be
      forwarded from a specific outgoing port, it first obtains the
      expected deadline of the packet, and then put the packet to the
      deadline queue with the relevant TTL value of the outgoing port
      for transmission.

      For a deadline queue whose TTL is not reduced to 0, its scheduling
      priority cannot be set to the highest value.  A local policy may
      be used to control the transmission of buffered packets.  There
      are two options: the first option, allowing to be involved in
      scheduling, also termed as early sending policy; the second
      option, not allowing, also termed as punctual sending policy.
      Early sending policy is applicable to the service requirements of
      low delay, and punctual sending policy is applicable to low delay
      jitter.

      At the beginning, all deadline queues have different TTL values,
      i.e., staggered from each other, so that the TTL of only one
      deadline queue will decrease to 0 at any time.

   The above authorization time, timer interval and maximum initial TTL
   value shall be specified according to the actual capacity of the
   node.  In fact, each node in the network can independently use
   different timer interval for different outgoing ports.  The general
   principle is that if an outgoing port has a large bandwidth (such as
   100G bps), the timer interval (and the authorization time of the
   deadline queue) can be small (such as 1us), because the link with
   large bandwidth can send the required bits amount even within a small
   time interval; If an outgoing port has a small bandwidth (e.g. 1G
   bps), the timer interval (and the authorization time of the deadline



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   queue) should be larger (e.g. 10us), because the link with small
   bandwidth needs to send the required bit amount within a larger time
   interval.

   A specific example of the deadline queue is depicted in Figure 1.

   +------------------------------+   +------------------------------+
   | Deadline Queue Group:        |   | Deadline Queue Group:        |
   |    queue-1(TTL=60us) ######  |   |    queue-1(TTL=50us) ######  |
   |    queue-2(TTL=50us) ######  |   |    queue-2(TTL=40us) ######  |
   |    queue-3(TTL=40us) ######  |   |    queue-3(TTL=30us) ######  |
   |    queue-4(TTL=30us) ######  |   |    queue-4(TTL=20us) ######  |
   |    queue-5(TTL=20us) ######  |   |    queue-5(TTL=10us) ######  |
   |    queue-6(TTL=10us) ######  |   |    queue-6(TTL=0us)  ######  |
   |    queue-7(TTL=0us)  ######  |   |    queue-7(TTL=60us) ######  |
   +------------------------------+   +------------------------------+

   +------------------------------+   +------------------------------+
   | Non-deadline Queue Group:    |   | Non-deadline Queue Group:    |
   |    queue-8  ############     |   |    queue-8  ############     |
   |    queue-9  ############     |   |    queue-9  ############     |
   |    queue-10 ############     |   |    queue-10 ############     |
   |    ... ...                   |   |    ... ...                   |
   +------------------------------+   +------------------------------+

  -o----------------------------------o-------------------------------->
   T0                                 T0+10us                       time

           Figure 1: Example of Deadline Queue for outgoing Port

   In this example, the timer interval for deadline queue group is
   configured to 10us.  Queue-1 ~ queue-7 are deadline queues, and other
   queues are traditional non-deadline queues.  Each deadline queue has
   its TTL attribute.  The maximum initial TTL is 60us.  At the initial
   time (T0), the TTL of all deadline queues are staggered from each
   other.  For example, the TTL of queue-1 is 60us, the TTL of queue-2
   is 50uS, the TTL of queue-3 is 40us, and so on.  At this time, only
   the TTL of queue-7 is 0, which has the highest scheduling priority.

   Suppose the scheduling engine initiates a cycle timer with a time
   interval of 10us.  After each timer timeout, the timer interval will
   be subtracted from the TTL of all deadline queues.  As shown in the
   figure, at T0 + 10us, the timer timeout, the TTL of queue-1 becomes
   50uS, the TTL of queue-2 becomes 40us, the TTL of queue-3 becomes
   30us, etc.  At this time, the TTL of queue-7 returns to the maximum
   initial TTL of 60us and is no longer set to the highest scheduling
   priority; The TTL of queue-6 becomes 0, which has the highest
   scheduling priority.



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   For simplicity, set the authorization time of the deadline queue to
   be consistent with the time interval of the cycle timer, which is
   also 10us.  When the TTL of a deadline queue becomes 0, it has a time
   limit of 10us to send packets in the queue.  During this period, it
   will be prohibited to receive new packets (in fact, there can be no
   new packets with a deadline of 0).  After the 10us time elapses, the
   cycle timer will timeout again, The TTL of another deadline queue
   will change to 0.  It is also feasible to set the authorization time
   to be less than the cycle timer interval.

   If the deadline queue with the highest priority is still free after
   sending packets within the authorized time, the scheduling engine
   will visit other queues with the second highest priority during the
   rest of the authorized time.

3.  Get Deadline Information of Packets

3.1.  Get Planned Deadline

   The planned deadline of the packet is an offset time, which is based
   on the time when the packet enters the node and represents the
   maximum time allowed for the packet to stay inside the node.  There
   are many ways to obtain the planned deadline of the packet.

      Carried in the packet.  The ingress PE node, when encapsulating
      the deterministic service flow, can explicitly insert the planned
      deadline into the packet according to SLA.  The intermediate node,
      after receiving the packet, can directly obtain the planned
      deadline from the packet.  Generally, only a single planned
      deadline needs to be carried in the packet, which is applicable to
      all nodes along the path; Or insert a stack composed of multiple
      deadlines, one for each node.  How to carry planned deadline in
      the packets will be defined in other documents.

      Included in the FIB entry.  Each node in the network can maintain
      the deterministic FIB entry.  After the packet hits the
      deterministic FIB entry, the planned deadline is obtained from the
      forwarding information contained in the FIB entry.

      Included in the policy entry.  Configure local policies on each
      node in the network, and then set the corresponding planned
      deadline according to the matched specific characteristics of the
      packet, such as 5-tuple.

   For a deterministic delay path based on deadline queue scheduling,
   the path it passes through has deterministic end-to-end delay
   requirements.  It includes two parts, one is the cumulative node
   delay and the other is the cumulative link transmission delay.  The



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   end-to-end delay requirement is subtracted from the cumulative link
   transmission delay to obtain the cumulative node delay.  A simple
   method is that the accumulated node delay is shared equally by each
   intermediate node along the path to obtain the planning deadline of
   each node.

3.2.  Get Existing Cumulative Planned Deadline

   The existing cumulative planned deadline of the packet refers to the
   sum of the planned deadline of all upstream nodes before the packet
   is transmitted to this node.  This information needs to be carried in
   the packet.  Every time the packet passes through a node, the node
   accumulates its corresponding planned deadline to the existing
   cumulative planned deadline field in the packet.  How to carry
   existing cumulative planned deadline in the packets will be defined
   in other documents.

   The setting of "existing cumulative planned deadline" in the packet
   needs to be friendly to the chip for reading and writing.  For
   example, it should be designed as a fixed position in the packet.
   The chip may support flexible configuration for that position.

3.3.  Get Existing Accumulated Actual Dwell Time

   The existing cumulative actual dwell time of the packet, refers to
   the sum of the actual dwell time of all upstream nodes before the
   packet is transmitted to this node.  This information needs to be
   carried in the packet.  Every time the packet passes through a node,
   the node accumulates its corresponding actual dwell time to the
   existing cumulative actual dwell time field in the packet.  How to
   carry existing cumulative actual dwell time in the packets will be
   defined in other documents.

   The setting of "existing cumulative actual dwell time" in the packet
   needs to be friendly to the chip for reading and writing.  For
   example, it should be designed as a fixed position in the packet.
   The chip may support flexible configuration for that position.

   Although other methods can also be, for example, carrying the
   absolute system time of receiving and sending in the packet to
   compute the actual dwell time indirectly, that has a low
   encapsulation efficiency and require strict time synchronization
   between nodes.

   A possible method to get the actual dwell time in the node is that,
   the receiving and sending time of the packet can be recorded in the
   auxiliary data structure (note that is not packet itself) of the




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   packet, and the actual dwell time of the packet in the node can be
   calculated according to these two times.

3.4.  Get Existing Accumulated Deadline Deviation

   The existing accumulated deadline deviation equals existing
   cumulative planned deadline minus existing cumulative actual dwell
   time.  This value can be positive or negative.

   If the existing cumulative planned deadline and the existing
   cumulative actual dwell time are carried in the packet, it is not
   necessary to carry the existing accumulated deadline deviation.
   Otherwise, it is necessary.  The advantage of the former is that it
   can be applied to more scenarios.

4.  Put Packets into the Deadline Queues

   The lifetime of the packet inside the node mainly includes two parts:
   the first part is to lookup the forwarding table when the packet is
   received from the incoming port (or generated by the control plane)
   and deliver the packet to the line card where the outgoing port is
   located; the second part is to store the packet in the queue of the
   outgoing port for transmission.  These two parts contribute to the
   actual dwell time of the packet in the node.  The former can be
   called forwarding delay and the latter can be called queuing delay.
   The forwarding delay is related to the chip implementation and is
   generally constant; The queuing delay is unstable.

   When a node receives a packet from an upstream node, it can first get
   the existing accumulated deadline deviation, and then add it to the
   planned deadline of the packet at this node to obtain the deadline
   adjustment value, and then on the basis of the deadline adjustment
   value, deducting the forwarding delay of the packet in the node, the
   allowable queuing delay value is obtained, and then the packet will
   be put to the deadline queue with TTL as the above allowable queuing
   delay value for sending.

   Under normal circumstances, if each hop strictly controls the
   scheduling of the packet according to its planned deadline, the
   actual dwell time of the packet will be very close to the planned
   deadline, and the absolute value of the existing accumulated deadline
   deviation will be very small.

   More generally, assume that the local node in a deterministic path is
   i, all upstream nodes are from 1 to i-1, and downstream nodes are i +
   1, the planned deadline is D, the actual dwell time is R, the
   deadline adjustment value is M, the forwarding delay inside the node
   is P, the existing accumulated deadline deviation is E, and the



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   allowable queuing delay is Q, then the allowable queuing delay (Q) of
   the packet on this node i is calculated as follows:

      E(i-1) = D(1) + D(2) + ... + D(i-1) - R(1) - R(2) - ... - R(i-1)

      M(i) = D(i) + E(i-1)

      Q(i) = M(i) - P(i)

   Consider some extreme cases.  For example, many upstream nodes adopt
   the early sending policy to send packets quickly.  Packets almostly
   need not queue in these nodes, but only depend on the forwarding
   delay.  Then the existing accumulated deadline deviation (E) may be a
   very large positive value, resulting in a large allowable queuing
   delay (Q).  If this value exceeds the maximum initial TTL of the
   deadline queue maintained by the node, the allowable queuing delay
   (Q) should be modified to the maximum initial TTL.

   For another example, if some upstream nodes are abnormal and have a
   very large actual dwell time (R), the existing accumulated deadline
   deviation (E) may be a negative number, resulting in the allowable
   queuing delay (Q) may be less than or equal to 0, which is smaller
   than the cycle timer interval of the deadline queue maintained in the
   node, then the allowable queuing delay (Q) should be modified to the
   cycle timer interval value.

   Figure 2 depicts an example of packets buffered to the deadline
   queue.























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    packet-2        packet-1          +------------------------------+
   +--------+      +--------+         | Deadline Queue Group:        |
   | D=20us |      | D=30us |         |    queue-1(TTL=60us) ######  |
   | E=10us |      | E=-10us|   +--+  |    queue-2(TTL=50us) ######  |
   +--------+      +--------+   |\/|  |    queue-3(TTL=40us) ######  |
  ------incoming port-1------>  |/\|  |    queue-4(TTL=30us) ######  |
                                |\/|  |    queue-5(TTL=20us) ######  |
    packet-4        packet-3    |/\|  |    queue-6(TTL=10us) ######  |
   +--------+      +--------+   |\/|  |    queue-7(TTL=0us)  ######  |
   |        |      | D=30us |   |/\|  +------------------------------+
   +--------+      | E=-30us|   |\/|
                   +--------+   |/\|
  ------incoming port-2------>  |\/|  +------------------------------+
                                |/\|  | Non-deadline Queue Group:    |
    packet-6        packet-5    |\/|  |    queue-8  ############     |
   +--------+      +--------+   |/\|  |    queue-9  ############     |
   |        |      | D=40us |   |\/|  |    queue-10 ############     |
   +--------+      | E=40us |   |/\|  |    ... ...                   |
                   +--------+   +--+  +------------------------------+
  ------incoming port-2------>        ---------outgoing port---------->

  -o----------------------------------o-------------------------------->
   receiving-time base                +P                            time

        Figure 2: Time Sensitive Packets Buffered to Deadline Queue

   As shown in Figure 2, the node successively receives six packets from
   three incoming ports, among which packet 1, 2, 3 and 5 have
   corresponding deadline information, while packet 4 and 6 are
   traditional packets.  These packets need to be forwarded to the same
   outgoing port according to the forwarding table entries.  It is
   assumed that they arrive at the line card where the outgoing port is
   located at almost the same time after the forwarding delay in the
   node (P = 10us).  At this time, the queue status of the outgoing port
   is shown in the figure.  Then:

      The allowable queuing delay (Q) of packet 1 in the node is 30 - 10
      -10 = 10us, and it will be put into the deadline queue-6 (its TTL
      is 10us).

      The allowable queuing delay (Q) of packet 2 in the node is 20 + 10
      -10 = 20us, and it will be put into the deadline queue-5 (its TTL
      is 20us).

      The allowable queuing delay (Q) of packet 3 in the node is 30 - 30
      -10 = -10us, and it will be modified to the minimum positive value
      10 us then put into the deadline queue-6 (its TTL is 10us).  Note




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      that the minimum positive value is a timer interval that is a
      local parameter per port based on port's bandwidth.

      The allowable queuing delay (Q) of packet 5 in the node is 40 + 40
      -10 = 70us, and it will be modified to the maximum positive value
      60 us then put into the deadline queue-1 (its TTL is 60us).  Note
      that the maximum positive value is an empirical value that can be
      configured according to the maximum delay requirements of
      deterministic services.

      Packets 4 and 6 will be put into the non-deadline queue in the
      traditional way.

5.  Traffic Regulation and Shaping

   On the ingress PE node, traffic regulation is performed on UNI port,
   so that the service traffic does not exceed its reserved bandwidth.
   Suppose there are N sources, and the packets they send carry the same
   deadline.  These packets may arrive at an intermediate node at the
   same time and put into the same deadline queue.  If the reserved
   bandwidth of deadline queue at N sources is M0, and the reserved
   bandwidth of deadline queue at intermediate nodes is Mx, then it
   needs to meet: N * M0 < = Mx.

   On the ingress PE node, traffic shaping is performed on NNI port.
   Multiple continuous packets of the specific service flow are stored
   in the deadline queue with corresponding remaining time according to
   the planned deadline of the service flow.  Note that these packets
   are not stored in the same queue over time.  The amount of bits that
   can be stored in one queue is equal to the reserved bandwidth *
   authorization time, however, at least one whole packet shall be
   loaded.  For example, if the allowable queuing delay is 20us, then
   within the current timer interval, the first sequence of the packets
   will be put into the current deadline queue with TTL = 20us until the
   reserved bandwidth limit is reached; Then, within the next timer
   interval, the next sequence of packets will be put into the current
   TTL = 20us queue until the reserved bandwidth limit is reached; and
   so on, until the total service bits are loaded.

   Figure 3 depicts an example of deadline based traffic shaping on the
   ingress PE node.  It is assumed that the packets loaded in each timer
   interval do not exceed the reserved bandwidth of the service.









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          1st packet
              |
              v
             +-+ +-+      +----+ +-+ +--+   +------+
             |1| |2|      | 3  | |4| |5 |   |  6   | <= packet sequence
             +-+ +-+      +----+ +-+ +--+   +------+
             |   |        |      |   |      |
                         ~+P ~+P      ~+P    ~+P ~+P    ~+P
             |   |        |      |   |      |
    UNI      v   v        v      v   v      v
ingress PE -+--------+--------+--------+--------+--------+--------+---->
    NNI     ^        ^        ^        ^        ^        ^        ^
            |        |        |        |        |        |        |
            |interval|interval|interval|interval|interval|interval|
            |        |        |        |        |        |        |
            ~+Q      ~+Q      ~+Q      ~+Q      ~+Q      ~+Q      ~+Q
            |        |        |        |        |        |        |
            +-+ +-+  +----+   +-+ +--+ +------+
            |1| |2|  | 3  |   |4| |5 | |  6   |
            +-+ +-+  +----+   +-+ +--+ +------+


                 Figure 3: Deadline Based Traffic Shaping

6.  Benefits

   The mechanism described in this document has the following benefits:

      Time synchronization is not required between network nodes.  Each
      node can flexibly set the authorization time length of the
      deadline queue according to its own outgoing port bandwidth.

      Packet multiplexing based, it is an enhancement of PQ scheduling
      algorithm, friendly to the upgrade of packet switching network.
      All nodes in the network can independently use cycle timers with
      different timeout intervals to traverse the deadline queues.

      The packet can control its expected dwell time in the node.  A
      single set of deadline queues supports multiple levels of dwell
      time.

      For early sending policy, the end-to-end delay is H*(P~D), jitter
      is H*Q; For punctual sending policy, the end-to-end delay is H*D,
      jitter is a just single authorization time.







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Internet-Draft              Deadline Routing                January 2022


7.  IANA Considerations

   There is no IANA requestion for this document.

8.  Security Considerations

   TBD

9.  Acknowledgements

   TBD

10.  Normative References

   [I-D.stein-srtsn]
              Stein, Y. (., "Segment Routed Time Sensitive Networking",
              draft-stein-srtsn-01 (work in progress), August 2021.

   [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>.

   [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>.

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,
              <https://www.rfc-editor.org/info/rfc8655>.

Authors' Addresses

   Shaofu Peng
   ZTE Corporation
   China

   Email: peng.shaofu@zte.com.cn


   Bin Tan
   ZTE Corporation
   China

   Email: tan.bin@zte.com.cn





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