Requirements for Time-Based Loss Detection
Internet Engineering Task Force M. Allman
File: draft-ietf-tcpm-rto-consider-15.txt June 8, 2020
Intended Status: Best Current Practice
Expires: December 8, 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 December 8, 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: December 8, 2020 [Page 1]
draft-ietf-tcpm-rto-consider-15.txt June 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
As a network of networks, the Internet consists of a large variety
of links and systems that combine to form "best effort" network
paths. The path that traffic takes through the network is generally
unknown a priori. Further, the path and the path properties that
traffic experiences dynamically vary over time. As two examples,
consider delay and loss. In the general case, delay across a
network path depends not only on distance, but also a number of
variable components such as the route and the level of buffering in
intermediate devices. Since our wide-area network paths are best
effort, packet loss is a regular occurrence. While there are
numerous causes of packet loss, the conservative general approach
that has historically served us well---and we use in this
document---is to treat loss as an implicit indication of network
Given that packet loss is routine in best effort networks, 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.
As we mention above, packet loss is often taken as an
implicit 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
Various mechanisms are used to detect losses in a packet stream.
Often we use continuous or periodic acknowledgments from the
Show full document text