DetNet D. Huang
Internet-Draft ZTE
Intended status: Standards Track Dec 07, 2018
Expires: June 10, 2019
Single-path PREF
draft-huang-detnet-single-path-pref-02
Abstract
This document specifies PREF on the single path for low-rate traffic,
and illustrates in details the implementation solutions as well as
the impacts on the data plane specified in [I-D.ietf-detnet-dp-alt].
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Huang Expires June 10, 2019 [Page 1]
Internet-Draft Single-path PREF Dec 2018
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Convention used in this document . . . . . . . . . . . . . . 3
3. Terminology and definitions . . . . . . . . . . . . . . . . . 3
4. Encapsulation impacts . . . . . . . . . . . . . . . . . . . . 3
4.1. Flow ID/Label . . . . . . . . . . . . . . . . . . . . . . 3
4.2. Control word . . . . . . . . . . . . . . . . . . . . . . 4
5. Replication solutions . . . . . . . . . . . . . . . . . . . . 4
5.1. Discontinuous traffic . . . . . . . . . . . . . . . . . . 5
5.2. Continuous traffic . . . . . . . . . . . . . . . . . . . 5
6. Forwarder clarifications . . . . . . . . . . . . . . . . . . 5
6.1. Edge node clarifications . . . . . . . . . . . . . . . . 5
6.2. Relay node clarification . . . . . . . . . . . . . . . . 5
7. Traffic rate limit . . . . . . . . . . . . . . . . . . . . . 6
8. Normative References . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
PREF is designed to protect the Detnet traffic against path or node
failures in [I-D.ietf-detnet-architecture] by directing multiple
copies of the traffic into multiple paths. Lost packets would be
recovered at the converging node (or terminating node) from the
undamaged traffic in other path. Nevertheless, path and node failure
always result in disastrous consequences for the ongoing service,
large blocks of data loss or even total service breakdown, while PREF
with multiple paths protection would also provide good cross-check
for the minor packet loss which guarantees the data integrity as well
as latency benefits (retransmission reduced significantly). When it
comes to the latter scenario, PREF on the single path will do the
better job particularly for the low-rate traffic.
Packet replication is executed in edge node, what's significantly
different from the multi-path PREF is the copies would be arranged in
the same traffic flow rather than delivering along different paths,
either transport or forwarding nodes do not have to execute PREF
which should only be done at the terminating node. The rationale is
that if packet loss occurs at any intermediary nodes, the multiple
packet copies could execute cross-checking and rebuild the damaged
data flow, and make the usual retransmission unnecessary to a large
degree. Two major benefits follow, intermediary network nodes do not
need support PREF, and if the node is a PREF node, it does not
execute PREF. Secondly, no or reduced buffer reservation should be
required in the nodes along the routing path.
Multiple copies in the same data traffic put bandwidth pressure upon
the network without appropriate constraints. Low-rate traffic
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