Requirements for Time-Based Loss Detection
Internet Engineering Task Force M. Allman
File: draft-ietf-tcpm-rto-consider-10.txt February 4, 2020
Intended Status: Best Current Practice
Expires: August 4, 2020
Requirements for Time-Based Loss Detection
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), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
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."
The list of current Internet-Drafts can be accessed at
The list of Internet-Draft Shadow Directories can be accessed at
This Internet-Draft will expire on August 4, 2020.
Copyright (c) 2020 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
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.
Many protocols must detect packet loss for various reasons (e.g., to
ensure reliability using retransmissions or to understand the level
of congestion along a network path). While many mechanisms have
been designed to detect loss, protocols ultimately can only count on
the passage of time without delivery confirmation to declare a
packet "lost". Each implementation of a time-based loss detection
mechanism represents a balance between correctness and timeliness
and therefore no implementation suits all situations. This document
Expires: August 4, 2020 [Page 1]
draft-ietf-tcpm-rto-consider-10.txt February 2020
provides high-level requirements for time-based loss detectors
appropriate for general use in the Internet. Within the
requirements, implementations have latitude to define particulars
that best address each situation.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119
Loss detection is a crucial activity for many protocols and
applications and is generally undertaken for two major reasons:
(1) Ensuring reliable data delivery.
This requires a data sender to develop an understanding of
which transmitted packets have not arrived at the receiver.
This knowledge allows the sender to retransmit missing data.
(2) Congestion control.
Packet loss is often taken as an indication that the sender
is transmitting too fast and is overwhelming some portion of
the network path. Data senders can therefore use loss to
trigger transmission rate reductions.
Various mechanisms are used to detect losses in a packet stream.
Often we use continuous or periodic acknowledgments from the
recipient to inform the sender's notion of which pieces of data are
missing. However, despite our best intentions and most robust
mechanisms we cannot place ultimate faith in receiving such
acknowledgments, but can only truly depend on the passage of time.
Therefore, our ultimate backstop to ensuring that we detect all loss
is a timeout. That is, the sender sets some expectation for how
long to wait for confirmation of delivery for a given piece of data.
When this time period passes without delivery confirmation the
sender concludes the data was lost in transit.
The specifics of time-based loss detection schemes represent a
tradeoff between correctness and responsiveness. In other words we
wish to simultaneously:
- wait long enough to ensure the detection of loss is correct, and
- minimize the amount of delay we impose on applications (before
repairing loss) and the network (before we reduce the
Show full document text