Internet DRAFT - draft-song-mptcp-owl
draft-song-mptcp-owl
MPTCP F. Song
Internet Draft H. Zhang
Intended status: Informational Beijing Jiaotong University
Expires: Dec 18, 2019 H. Chan
A. Wei
Huawei Technologies
June 19, 2019
One Way Latency Considerations for MPTCP
draft-song-mptcp-owl-06
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 http://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 Dec 18, 2019.
Copyright Notice
Copyright (c) 2017 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.
Song, et al. Expires Dec 18, 2019 [Page 1]
Internet-Draft OWL Considerations for MPTCP June 2019
Abstract
This document discusses the use of One Way Latency (OWL) for
enhancing multipath TCP (MPTCP). Several usages of OWL, such as
retransmission policy and crucial data scheduling are analyzed. Two
kinds of OWL measurement approaches are also provided and compared.
More explorations related with OWL will be contribute to the
performance of MPTCP.
Table of Contents
1. Introduction ................................................ 2
2. Conventions and Terminology.................................. 3
3. Potential Usages of OWL in MPTCP............................. 3
3.1. Crucial Data Scheduling................................. 4
3.2. Congestion control...................................... 5
3.3. Packet Retransmission................................... 6
3.4. Bandwidth Estimation.................................... 6
3.5. Shared Bottleneck Detection............................. 7
4. OWL Measurements in TCP...................................... 7
5. Security Considerations...................................... 8
6. IANA Considerations ......................................... 8
7. References .................................................. 8
7.1. Normative References.................................... 8
7.2. Informative Reference................................... 8
Authors' Addresses ............................................. 9
1. Introduction
The terminal hosts and the intermediate devices in the Internet both
have been equipped with more and more physical networkinterfaces
basically. The efficiency of interfaces, which had been widely
used in packet forwarding at the terminal hosts, had been confirmed
and utilized [RFC6419]. In addition,in order to aggregate more
bandwidths,reduce packet delays, and provide better service, the
increased capacity provided by multiple paths created by multiple
interfaces is used. Unlike traditional TCP [RFC0793],
many transport layer protocols, such as MPTCP [RFC6182] [RFC6824]
enable the terminal hosts to concurrently transfer data on top of
multiple paths to greatly increase the overall throughput.
Round-trip time (RTT) is commonly used in congestion control and
loss recovery mechanism for data transmission. However,the key issue
with data transmission is simply the delay in data transmission along
the path that does not include the return. The uplink and downlink
delays between two peers can be very different. RTT can be
Song, et al. Expires Dec 18, 2019 [Page 2]
Internet-Draft OWL Considerations for MPTCP June 2019
easily influenced by the latency in the oppsite direction along a
path, which does not accurately reflect the delay in data
transmission along the path. Therefore, it is recommended to use
One Way Latency (OWL) to describe the exact latency from sending data
to receiving time data.
It is explained in this document that the full use of One Way Latency
(OWL) in the transmission process can further improve the performance
of the current practice of MPTCP. It may be asymmetric
of the OWL components in the forward and reverse direction of a RTT
so that it can provide a better measure to the user such as for
congestion control even with the regular TCP. It will be more
benefits when there are multiple paths to choose.
The necessary considerations of OWL in MPTCP has been discussed in
this document. The structure of this document is as follows: First,
the use cases of several OWLs in MPTCP are analyzed. Second, two
OWL measurements are listed and compared. Finally, the precautions
related to security and IANA are given.
The application programmers whose products may benefit from MPTCP
will be potential target audiences for this document significantly.
This document also demonstrates the necessary information
for MPTCP developers to implement the new version of the API in the
TCP/IP network stack.
2. Conventions and Terminology
The key words "MUST", "MUST NOT", "GLUIRED", "SHALL","SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
One Way Latency (OWL): the propagation delay between a sender and a
receiver from the time a signal is sent to the time the signal is
received.
3. Potential Usages of OWL in MPTCP
There are many OWL use cases when the sender and receiver enable
MPTCP. Although, only 5 use cases are illustrated in
this document, more explorations are still needed.
Song, et al. Expires Dec 18, 2019 [Page 3]
Internet-Draft OWL Considerations for MPTCP June 2019
3.1. Crucial Data Scheduling
During the transfer process, it is usually necessary to send some
basic data to the destination immediately. Examples of such data
include multimedia key frames and high priority appearance
communication blocks. No one can guarantee the order of arrival
by using an RTT with multiple paths alone.
The data rate in any given link can be asymmetric. In addition,
the delay in a given direction can vary depending on the number
of packet queues. Therefore, the same as the opposite direction
illustrated in Figure 1, the positive delay in the path is not
important.
-------- OWL(s-to-c,path1)=16ms <--------
/ \
| -----> OWL(c-to-s,path1)= 5ms ----- |
| / RTT(path1)=21ms \ |
| | | |
+------+ +------+
| |-----> OWL(c-to-s,path2)= 8ms -----| |
|Client| |Server|
| |----- OWL(s-to-c,path2)= 8ms <-----| |
+------+ RTT(path2)=16ms +------+
| | | |
| \ / |
| -----> OWL(c-to-s,path3)=10ms ----- |
\ /
-------- OWL(s-to-c,path3)= 8ms <--------
RTT(path3)=18ms
Figure 1. Example with 3 paths between the client and the server
with OWL as indicated in the figure. RTT information alone would
indicate to the client that the fastest path to the server is
path 2, followed by path 3, and then followed by path 1. Although
path 2 is the fastest, whereas OWL indicates to the client that the
fastest path to the server is path 1, followed by path 2, and then
followed by path 3.
For critical data transfers, the sender can easily select a faster
path by using OWL measurements (forward delay). In addition, the
confirmation of these critical data can be sent on the path with
minimal reverse delay. If the duplex communication mode is adopted,
the piggybacking is also useful.
Song, et al. Expires Dec 18, 2019 [Page 4]
Internet-Draft OWL Considerations for MPTCP June 2019
3.2. Congestion control
Congestion in a given direction does not necessarily imply the
congestion in the reverse direction.
-------- No congestion (path 1) <--------
/ \
| -----> Congestion (path 1) ----- |
| / \ |
| | | |
+------+ +------+
|Client| |Server|
+------+ +------+
| | | |
| \ / |
| -----> No congestion (path 2) ----- |
\ /
-------- Congestion (path 2) <--------
Figure 2. Example of a congestion situation with 2 paths between
the client and the server. There is congestion from client to
server along both path 1 and path 2. RTT information alone will
indicate congestion in both paths, whereas OWL information will
show the client that path 2 is the more lightly loaded path to get
to the server.
We can use OWL instead of RTT to better describe network congestion
in a given direction. Especially when congestion can be the case in
a one-way path, congestion in the path from the client to the server
is different from congestion in the path from the server to the
client. The delay of interest for data transmission along a path
cannot be reflected by the RTT accurately. For MPTCP, the client
needs to choose a more lightly loaded path to send packets [RFC6356].
Instead of comparing the RTT among different paths, it should use
OWL to compare among the paths.
Current version of MPTCP includes different kinds of congestion
control mechanisms [RFC6356]. The network congestion situation in a
single direction could be better described by reasonably utilizing
OWL.
Song, et al. Expires Dec 18, 2019 [Page 5]
Internet-Draft OWL Considerations for MPTCP June 2019
3.3. Packet Retransmission
Continuous Multi-Path Transport (CMT) improves throughput by
simultaneously transmitting new data from the source to the target
host through multiple paths. However, when the packet is identified
as lost by three repeated acknowledgments or timeouts, the sender
needs to select the appropriate retransmission path. Outstanding
packets on multiple paths may reach to the destination disorderly
and trigger Receive Buffer Blocking (RBB) problem (Figure 3), which
will further affect the transmission performance, due to the popular
mechanisms of sequence control in reliable transport protocols.
Packetwith octets sequence # 0- 499(lost)
---> Packetwith octets sequence #1000-1499(rcvd) ------
/ Packetwith octets sequence #2000-2499(rcvd) \
| |
+------+ +--------+
|Sender| |Receiver|
+------+ +--------+
| |
\ Packetwith octets sequence # 501- 999(lost) /
-----> Packetwith octets sequence #1501-1999(lost) -----
Packetwith octets sequence #2501-2999(lost)
Figure 3. Example of Receive Buffer Blocking: The packet containing
octets 0-499 is lost. On the other hand the packets containing
Octets 500-999, 1000-1499, 1500-1999, 2000-2499, and 2500-2999 have
all been received. The octets 500-2999 are then all buffered at the
receiver, and are blocked by the missing octets 0-499.
By using the results of the OWL measurements, the sender can quickly
determine the specific path of the positive minimum delay. Once the
receiver gets the most needed packet, the RBB can be released and
submitted to the upper layer.
3.4. Bandwidth Estimation
Understanding bandwidth conditions such as packet scheduling and
load balancing is critical. OWL can be integrated with bandwidth
estimation methods without disrupting the regular transmission of
packets.
Song, et al. Expires Dec 18, 2019 [Page 6]
Internet-Draft OWL Considerations for MPTCP June 2019
3.5. Shared Bottleneck Detection
Fairness is essential when MPTCP and normal TCP coexist in the same
network. The sender can treat the OWL measurement as a sample
process for shared bottleneck detection, and the sender adjusts the
amount of packets on multiple paths accordingly.
4. OWL Measurements in TCP
The timestamp option in TCP [RFC7323] may be invoked to estimate
latency. The time (TSval) of sending the data is provided in the
option when sending data. The receiver acknowledges the receipt of
this data by echoing this time (TSecr). And also the time (TSval) of
sending this acknowledgment is provided. Although there are two
problems, these differences in time when validating data from the
sender can help estimate the OWL from the sender to the receiver.
First, there may be a delay from the time the recipient of the data
is received until the time the acknowledgment is sent. Then, the
above value can be the upper limit of the OWL.
Second, the clock between the sender and the receiver may not be
synchronized. OWL can only be displayed in different paths by the
above measures when the clock is synchronized. The comparison of
OWL between different paths is limited to showing the OWL
difference between them without clock synchronization.
Two kinds of OWL measurement approaches are available: absolute
value measurement and relative value measurement.
In order to obtain the absolute value of OWL, the primary condition
of measurement is clock synchronization. End hosts can calibrate the
local clock with the remote NTP server by using network time
protocol (NTP) [RFC5905]. The additional information or optional
capabilities can even be added via extension fields in the standard
NTP header [RFC7822]. The calibration accuracy can reach to the
millisecond level in less congested situations. The obvious burden
here is to persuade the end hosts to initialize the NTP option.
In some cases it is more than enough to get the relative value of
OWL to build an application on it. For example, the sender may only
care which path has the minimum forwarding delay when retransmission
is required. When estimating bandwidth, the difference in forward
latency in all available paths is required, ie incremental latency.
Song, et al. Expires Dec 18, 2019 [Page 7]
Internet-Draft OWL Considerations for MPTCP June 2019
Both sides could obtain therelative value of OWL by exchanging
with correspondent end host the local timestamps of receiving and
sending the packets.
Overhead is an additional protocol requirement and synchronization
accuracy, while OWL's absolute value measurement is more convenient
for the application. Instead, relative values are not needed to
worry about accuracy, and overhead is to add timestamps to the
original protocol stack.
5. Security Considerations
This document does not contain any safety precautions. However, the
future application of OWL in MPTCP definitely needs to establish
related mechanisms to improve security.
6. IANA Considerations
This document presents no IANA considerations.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI
10.17487/RFC2119, March 1997, <http://www.rfc-
editor.org/info/rfc2119>.
7.2. Informative Reference
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<http://www.rfc-editor.org/info/rfc5905>.
[RFC6182] Ford, A., Raiciu, C., Handley, M., Barre, S., and J.
Iyengar, "Architectural Guidelines for Multipath TCP
Development", RFC 6182, DOI 10.17487/RFC6182, March 2011,
<http://www.rfc-editor.org/info/rfc6182>.
Song, et al. Expires Dec 18, 2019 [Page 8]
Internet-Draft OWL Considerations for MPTCP June 2019
[RFC6356] Raiciu, C., Handley, M., and D. Wischik, "Coupled
Congestion Control for Multipath Transport Protocols", RFC
6356, DOI 10.17487/RFC6356, October 2011, <http://www.rfc-
editor.org/info/rfc6356>.
[RFC6419] Wasserman, M. and P. Seite, "Current Practices for
Multiple-Interface Hosts", RFC 6419, DOI 10.17487/RFC6419,
November 2011, <http://www.rfc-editor.org/info/rfc6419>.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
<http://www.rfc-editor.org/info/rfc6824>.
[RFC7323] Borman, D., Braden, B., Jacobson, V., and R. Scheffenegger,
Ed., "TCP Extensions for High Performance", RFC 7323, DOI
10.17487/RFC7323, September 2014, <http://www.rfc-
editor.org/info/rfc7323>.
[RFC7822] Mizrahi, T. and D. Mayer, "Network Time Protocol Version 4
(NTPv4) Extension Fields", RFC 7822, DOI 10.17487/RFC7822,
March 2016, <http://www.rfc-editor.org/info/rfc7822>.
Authors' Addresses
Fei Song
Beijing Jiaotong University
Beijing, 100044
P.R. China
Email: fsong@bjtu.edu.cn
Hongke Zhang
Beijing Jiaotong University
Beijing, 100044
P.R. China
Email: hkzhang@bjtu.edu.cn
Song, et al. Expires Dec 18, 2019 [Page 9]
Internet-Draft OWL Considerations for MPTCP June 2019
H Anthony Chan
Huawei Technologies
5340 Legacy Dr. Building 3
Plano, TX 75024
USA
Email: h.a.chan@ieee.org
Anni Wei
Huawei Technologies
Xin-Xi Rd. No. 3, Haidian District
Beijing, 100095
P.R. China
Email: weiannig@huawei.com
Song, et al. Expires Dec 18, 2019 [Page 10]
