draft-ietf-lwig-tcp-constrained-node-networks-00.txt   draft-ietf-lwig-tcp-constrained-node-networks-01.txt 
LWIG Working Group C. Gomez LWIG Working Group C. Gomez
Internet-Draft UPC/i2CAT Internet-Draft UPC/i2CAT
Intended status: Informational J. Crowcroft Intended status: Informational J. Crowcroft
Expires: March 2, 2018 University of Cambridge Expires: April 17, 2018 University of Cambridge
M. Scharf M. Scharf
Nokia Nokia
August 29, 2017 October 14, 2017
TCP over Constrained-Node Networks TCP Usage Guidance in the Internet of Things (IoT)
draft-ietf-lwig-tcp-constrained-node-networks-00 draft-ietf-lwig-tcp-constrained-node-networks-01
Abstract Abstract
This document provides a profile for the Transmission Control This document provides guidance on how to implement and use the
Protocol (TCP) over Constrained-Node Networks (CNNs). The Transmission Control Protocol (TCP) in Constrained-Node Networks
overarching goal is to offer simple measures to allow for lightweight (CNNs), which are a characterstic of the Internet of Things (IoT).
TCP implementation and suitable operation in such environments. Such environments require a lightweight TCP implementation and may
not make use of optional functionality. This document explains a
number of known and deployed techniques to simplify a TCP stack as
well as corresponding tradeoffs. The objective is to help embedded
developers with decisions on which TCP features to use.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 2, 2018. This Internet-Draft will expire on April 17, 2018.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . 4
2. Characteristics of CNNs relevant for TCP . . . . . . . . . . 3 3. Characteristics of CNNs relevant for TCP . . . . . . . . . . 4
3. Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Network and link properties . . . . . . . . . . . . . . . 4
4. TCP over CNNs . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. Usage scenarios . . . . . . . . . . . . . . . . . . . . . 4
4.1. TCP connection initiation . . . . . . . . . . . . . . . . 4 3.3. Communication and traffic patterns . . . . . . . . . . . 5
4.2. Maximum Segment Size (MSS) . . . . . . . . . . . . . . . 5 4. TCP over CNNs . . . . . . . . . . . . . . . . . . . . . . . . 6
4.3. Window Size . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. TCP connection initiation . . . . . . . . . . . . . . . . 6
4.4. RTO estimation . . . . . . . . . . . . . . . . . . . . . 6 4.2. Maximum Segment Size (MSS) . . . . . . . . . . . . . . . 6
4.5. TCP connection lifetime . . . . . . . . . . . . . . . . . 7 4.3. Window Size . . . . . . . . . . . . . . . . . . . . . . . 7
4.5.1. Long TCP connection lifetime . . . . . . . . . . . . 7 4.4. RTO estimation . . . . . . . . . . . . . . . . . . . . . 8
4.5.2. Short TCP connection lifetime . . . . . . . . . . . . 7 4.5. TCP connection lifetime . . . . . . . . . . . . . . . . . 8
4.6. Explicit congestion notification . . . . . . . . . . . . 8 4.5.1. Long TCP connection lifetime . . . . . . . . . . . . 8
4.7. TCP options . . . . . . . . . . . . . . . . . . . . . . . 8 4.5.2. Short TCP connection lifetime . . . . . . . . . . . . 9
4.8. Delayed Acknowledgments . . . . . . . . . . . . . . . . . 9 4.6. Explicit congestion notification . . . . . . . . . . . . 9
4.9. Explicit loss notifications . . . . . . . . . . . . . . . 10 4.7. TCP options . . . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 4.8. Delayed Acknowledgments . . . . . . . . . . . . . . . . . 11
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 4.9. Explicit loss notifications . . . . . . . . . . . . . . . 11
7. Annex. TCP implementations for constrained devices . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7.1. uIP . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
7.2. lwIP . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7. Annex. TCP implementations for constrained devices . . . . . 12
7.3. RIOT . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.1. uIP . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.4. OpenWSN . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.2. lwIP . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.5. TinyOS . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.3. RIOT . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.4. OpenWSN . . . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.5. TinyOS . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . 13 7.6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . 15 8. Annex. Changes compared to previous versions . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 8.1. Changes compared to -00 . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction 1. Introduction
The Internet Protocol suite is being used for connecting Constrained- The Internet Protocol suite is being used for connecting Constrained-
Node Networks (CNNs) to the Internet, enabling the so-called Internet Node Networks (CNNs) to the Internet, enabling the so-called Internet
of Things (IoT) [RFC7228]. In order to meet the requirements that of Things (IoT) [RFC7228]. In order to meet the requirements that
stem from CNNs, the IETF has produced a suite of protocols stem from CNNs, the IETF has produced a suite of new protocols
specifically designed for such environments specifically designed for such environments (see e.g.
[I-D.ietf-lwig-energy-efficient]. [I-D.ietf-lwig-energy-efficient]).
At the application layer, the Constrained Application Protocol (CoAP) At the application layer, the Constrained Application Protocol (CoAP)
was developed over UDP [RFC7252]. However, the integration of some was developed over UDP [RFC7252]. However, the integration of some
CoAP deployments with existing infrastructure is being challenged by CoAP deployments with existing infrastructure is being challenged by
middleboxes such as firewalls, which may limit and even block UDP- middleboxes such as firewalls, which may limit and even block UDP-
based communications. This the main reason why a CoAP over TCP based communications. This the main reason why a CoAP over TCP
specification is being developed [I-D.tschofenig-core-coap-tcp-tls]. specification is being developed [I-D.ietf-core-coap-tcp-tls].
On the other hand, other application layer protocols not specifically Other application layer protocols not specifically designed for CNNs
designed for CNNs are also being considered for the IoT space. Some are also being considered for the IoT space. Some examples include
examples include HTTP/2 and even HTTP/1.1, both of which run over TCP HTTP/2 and even HTTP/1.1, both of which run over TCP by default
by default [RFC7540][RFC2616], and the Extensible Messaging and [RFC7540] [RFC2616], and the Extensible Messaging and Presence
Presence Protocol (XMPP) [RFC 6120]. TCP is also used by non-IETF Protocol (XMPP) [RFC6120]. TCP is also used by non-IETF application-
application-layer protocols in the IoT space such as MQTT and its layer protocols in the IoT space such as the Message Queue Telemetry
lightweight variants [MQTTS]. Transport (MQTT) and its lightweight variants.
This document provides a profile for TCP over CNNs. The overarching TCP is a sophisticated transport protocol that includes many optional
goal is to offer simple measures to allow for lightweight TCP functionality and TCP options that improve performance. Many
implementation and suitable operation in such environments. optional TCP extensions require complex logic inside the TCP stack
and increase the codesize and the RAM requirements. However, many
TCP extensions are not required for interoperability with other
standard-compliant TCP endpoints. Given the limited resources on
constrained devices, careful "tuning" of the TCP implementation can
make an implementation more lightweight.
1.1. Conventions used in this document This document provides guidance on how to implement and use TCP in
CNNs. The overarching goal is to offer simple measures to allow for
lightweight TCP implementation and suitable operation in such
environments. A TCP implementation following the guidance in this
document is intended to be compatible with a TCP endpoint that is
compliant to the TCP standards, albeit possibly with a lower
performance. This implies that such a TCP client would always be
able to connect with a standard-compliant TCP server, and a
corresponding TCP server would always be able to connect with a
standard-compliant TCP client.
This document assumes that the reader is familiar with TCP. A
comprehensive survey of the TCP standards can be found in [RFC7414].
Similar guidance regarding the use of TCP in special environments has
been published before, e.g., for cellular wireless networks
[RFC3481].
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL","SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL","SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] document are to be interpreted as described in [RFC2119].
2. Characteristics of CNNs relevant for TCP 3. Characteristics of CNNs relevant for TCP
3.1. Network and link properties
CNNs are defined in [RFC7228] as networks whose characteristics are CNNs are defined in [RFC7228] as networks whose characteristics are
influenced by being composed of a significant portion of constrained influenced by being composed of a significant portion of constrained
nodes. The latter are characterized by significant limitations on nodes. The latter are characterized by significant limitations on
processing, memory, and energy resources, among others [RFC7228]. processing, memory, and energy resources, among others [RFC7228].
The first two dimensions pose constraints on the complexity and on The first two dimensions pose constraints on the complexity and on
the memory footprint of the protocols that constrained nodes can the memory footprint of the protocols that constrained nodes can
support. The latter requires techniques to save energy, such as support. The latter requires techniques to save energy, such as
radio duty-cycling in wireless devices radio duty-cycling in wireless devices
[I-D.ietf-lwig-energy-efficient], as well as minimization of the [I-D.ietf-lwig-energy-efficient], as well as minimization of the
number of messages transmitted/received (and their size). number of messages transmitted/received (and their size).
Constrained nodes often use physical/link layer technologies that [RFC7228] lists typical network constraints in CNN, including low
have been characterized as 'lossy'. Many such technologies are achievable bitrate/throughput, high packet loss and high variability
wireless, therefore exhibiting a relatively high bit error rate. of packet loss, highly asymmetric link characteristics, severe
However, some wired technologies used in the CNN space are also lossy penalties for using larger packets, limits on reachability over time,
(e.g. Power Line Communication). Transmission rates of CNN radio or etc. CNN may use wireless or wired technologies (e.g., Power Line
wired interfaces are typically low (e.g. below 1 Mbps). Communication), and the transmission rates are typically low (e.g.
below 1 Mbps).
Some CNNs follow the star topology, whereby one or several hosts are For use of TCP, one challenge is that not all technologies in CNN may
be aligned with typical Internet subnetwork design principles
[RFC3819]. For instance, constrained nodes often use physical/link
layer technologies that have been characterized as 'lossy', i.e.,
exhibit a relatively high bit error rate. Dealing with corruption
loss is one of the open issues in the Internet [RFC6077].
3.2. Usage scenarios
There are different deployment and usage scenarios for CNNs. Some
CNNs follow the star topology, whereby one or several hosts are
linked to a central device that acts as a router connecting the CNN linked to a central device that acts as a router connecting the CNN
to the Internet. CNNs may also follow the multihop topology to the Internet. CNNs may also follow the multihop topology
[RFC6606]. [RFC6606]. One key use case for the use of TCP is a model where
constrained devices connect to unconstrained servers in the Internet.
But it is also possible that both TCP endpoints run on constrained
devices.
3. Scenario In constrained environments, there can be different types of devices
[RFC7228]. For example, there can be devices with single combined
send/receive buffer, devices with a separate send and receive buffer,
or devices with a pool of multiple send/receive buffers. In the
latter case, it is possible that buffers also be shared for other
protocols.
The main scenario for use of TCP over CNNs comprises a constrained When a CNN comprising one or more constrained devices and an
device and an unconstrained device that communicate over the Internet unconstrained device communicate over the Internet using TCP, the
using TCP, possibly traversing a middlebox (e.g. a firewall, NAT, communication possibly has to traverse a middlebox (e.g. a firewall,
etc.). Figure 1 illustrates such scenario. Note that the scenario NAT, etc.). Figure 1 illustrates such scenario. Note that the
is asymmetric, as the unconstrained device will typically not suffer scenario is asymmetric, as the unconstrained device will typically
the severe constraints of the constrained device. The unconstrained not suffer the severe constraints of the constrained device. The
device is expected to be mains-powered, to have high amount of memory unconstrained device is expected to be mains-powered, to have high
and processing power, and to be connected to a resource-rich network. amount of memory and processing power, and to be connected to a
resource-rich network.
Assuming that a majority of constrained devices will correspond to Assuming that a majority of constrained devices will correspond to
sensor nodes, the amount of data traffic sent by constrained devices sensor nodes, the amount of data traffic sent by constrained devices
(e.g. sensor node measurements) is expected to be higher than the (e.g. sensor node measurements) is expected to be higher than the
amount of data traffic in the opposite direction. Nevertheless, amount of data traffic in the opposite direction. Nevertheless,
constrained devices may receive requests (to which they may respond), constrained devices may receive requests (to which they may respond),
commands (for configuration purposes and for constrained devices commands (for configuration purposes and for constrained devices
including actuators) and relatively infrequent firmware/software including actuators) and relatively infrequent firmware/software
updates. updates.
+---------------+ +---------------+
o o <--------- TCP communication ------> | | o o <-------- TCP communication -----> | |
o o | | o o | |
o o | Unconstrained | o o | Unconstrained |
o o +-----------+ | device | o o +-----------+ | device |
o o o ------ | Middlebox | ------- | | o o o ------ | Middlebox | ------- | |
o o +-----------+ | (e.g. cloud) | o o +-----------+ | (e.g. cloud) |
o o o | | o o o | |
+---------------+ +---------------+
constrained devices constrained devices
Figure 1: TCP communication between a constrained device and an Figure 1: TCP communication between a constrained device and an
unconstrained device, traversing a middlebox. unconstrained device, traversing a middlebox.
3.3. Communication and traffic patterns
IoT applications are characterized by a number of different
communication patterns. The following non-comprehensive list
explains some typical examples:
o Unidirectional transfers: An IoT device (e.g. a sensor) can send
(repeatedly) updates to the other endpoint. Not in every case
there is a need for an application response back to the IoT
device.
o Request-response patterns: An IoT device receiving a request from
the other endpoint, which triggers a response from the IoT device.
o Bulk data transfers: A typical example for a long file transfer
would be an IoT device firmware update.
A typical communication pattern is that a constrained device
communicates with an unconstrained device (cf. Figure 1). But it is
also possible that constrained devices communicate amongst
themselves.
4. TCP over CNNs 4. TCP over CNNs
4.1. TCP connection initiation 4.1. TCP connection initiation
In the constrained device to unconstrained device scenario In the constrained device to unconstrained device scenario
illustrated above, a TCP connection is typically initiated by the illustrated above, a TCP connection is typically initiated by the
constrained device, in order for this device to support possible constrained device, in order for this device to support possible
sleep periods to save energy. sleep periods to save energy.
4.2. Maximum Segment Size (MSS) 4.2. Maximum Segment Size (MSS)
Some link layer technologies in the CNN space are characterized by a Some link layer technologies in the CNN space are characterized by a
short data unit payload size, e.g. up to a few tens or hundreds of short data unit payload size, e.g. up to a few tens or hundreds of
bytes. For example, the maximum frame size in IEEE 802.15.4 is 127 bytes. For example, the maximum frame size in IEEE 802.15.4 is 127
bytes. bytes. 6LoWPAN defined an adaptation layer to support IPv6 over IEEE
6LoWPAN defined an adaptation layer to support IPv6 over IEEE
802.15.4 networks. The adaptation layer includes a fragmentation 802.15.4 networks. The adaptation layer includes a fragmentation
mechanism, since IPv6 requires the layer below to support an MTU of mechanism, since IPv6 requires the layer below to support an MTU of
1280 bytes [RFC2460], while IEEE 802.15.4 lacked fragmentation 1280 bytes [RFC2460], while IEEE 802.15.4 lacked fragmentation
mechanisms. 6LoWPAN defines an IEEE 802.15.4 link MTU of 1280 bytes mechanisms. 6LoWPAN defines an IEEE 802.15.4 link MTU of 1280 bytes
[RFC4944]. Other technologies, such as Bluetooth LE [RFC7668], ITU-T [RFC4944]. Other technologies, such as Bluetooth LE [RFC7668], ITU-T
G.9959 [RFC7428] or DECT-ULE [RFC8105], also use 6LoWPAN-based G.9959 [RFC7428] or DECT-ULE [RFC8105], also use 6LoWPAN-based
adaptation layers in order to enable IPv6 support. These adaptation layers in order to enable IPv6 support. These
technologies do support link layer fragmentation. By exploiting this technologies do support link layer fragmentation. By exploiting this
functionality, the adaptation layers that enable IPv6 over such functionality, the adaptation layers that enable IPv6 over such
technologies also define an MTU of 1280 bytes. technologies also define an MTU of 1280 bytes.
For devices using technologies with a link MTU of 1280 bytes (e.g.
defined by a 6LoWPAN-based adaptation layer), in order to avoid IP
layer fragmentation, the TCP MSS must not be set to a value greater
than 1220 bytes in CNNs, and it must not be set to a value leading to
an IPv6 datagram size exceeding 1280 bytes. (Note: IP version 6 is
assumed.)
On the other hand, there exist technologies also used in the CNN On the other hand, there exist technologies also used in the CNN
space, such as Master Slave / Token Passing (TP) [RFC8163], space, such as Master Slave / Token Passing (TP) [RFC8163],
Narrowband IoT (NB-IoT) [I-D.ietf-lpwan-overview] or IEEE 802.11ah Narrowband IoT (NB-IoT) [I-D.ietf-lpwan-overview] or IEEE 802.11ah
[I-D.delcarpio-6lo-wlanah], that do not suffer the same degree of [I-D.delcarpio-6lo-wlanah], that do not suffer the same degree of
frame size limitations as the technologies mentioned above. The MTU frame size limitations as the technologies mentioned above. The MTU
for MS/TP is recommended to be 1500 bytes [RFC8163], the MTU in NB- for MS/TP is recommended to be 1500 bytes [RFC8163], the MTU in NB-
IoT is 1600 bytes, and the maximum frame payload size for IEEE IoT is 1600 bytes, and the maximum frame payload size for IEEE
802.11ah is 7991 bytes. Over such technologies, the TCP MSS may be 802.11ah is 7991 bytes.
set to a value greater than 1220 bytes, as long as IPv6 datagram size
does not exceed the MTU for each technology. One consideration in For the sake of lightweight implementation and operation, unless
this regard is that, when a node supports an MTU greater than 1280 applications require handling large data units (i.e. leading to an
bytes, it 'SHOULD' then support Path MTU (PMTU) discovery [RFC1981]. IPv6 datagram size greater than 1280 bytes), it may be desirable to
(Note that, as explained in RFC 1981, a minimal IPv6 implementation limit the MTU to 1280 bytes in order to avoid the need to support
may 'choose to omit implementation of Path MTU Discovery'). For the Path MTU Discovery [RFC1981].
sake of lightweight implementation and operation, unless applications
require handling large data units (i.e. leading to an IPv6 datagram An IPv6 datagram size exceeding 1280 bytes can be avoided by setting
size greater than 1280 bytes), it may be desirable to limit the MTU the TCP MSS not larger than 1220 bytes. (Note: IP version 6 is
to 1280 bytes. assumed.)
4.3. Window Size 4.3. Window Size
A TCP stack can reduce the implementation complexity by advertising a A TCP stack can reduce the RAM requirements by advertising a TCP
TCP window size of one MSS, and also transmit at most one MSS of window size of one MSS, and also transmit at most one MSS of
unacknowledged data, at the cost of decreased performance. This size unacknowledged data. In that case, both congestion and flow control
for receive and send window is appropriate for simple message implementation is quite simple. Such a small receive and send window
exchanges in the CNN space, reduces implementation complexity and may be sufficient for simple message exchanges in the CNN space.
memory requirements, and reduces overhead (see section 4.7). However, only using a window of one MSS can significantly affect
performance. A stop-and-wait operation results in low throughput for
transfers that exceed the lengths of one MSS, e.g., a firmware
download. In addition, there can be interactions with the delayed
acknowledgements (see Section 4.8).
A TCP window size of one MSS follows the same rationale as the Devices that have enough memory to allow larger TCP window size can
default setting for NSTART in [RFC7252], leading to equivalent leverage a more efficient error recovery using Fast Retransmit and
operation when CoAP is used over TCP. Fast Recovery [RFC5681]. These algorithms work efficiently for
window sizes of at least 5 MSS: If in a given TCP transmission of
segments 1,2,3,4,5, and 6 the segment 2 gets lost, the sender should
get an acknowledgement for segment 1 when 3 arrives and duplicate
acknowledgements when 4, 5, and 6 arrive. It will retransmit segment
2 when the third duplicate ack arrives. In order to have segment 2,
3, 4, 5, and 6 sent, the window has to be at least five. With an MSS
of 1220 byte, a buffer of the size of 5 MSS would require 6100 byte.
For devices that can afford greater TCP window size, it may be useful For bulk data transfers further TCP improvements may also be useful,
to allow window sizes of at least five MSSs, in order to allow Fast such as limited transmit [RFC3402].
Retransmit and Fast Recovery [RFC5681].
If CoAP is used over TCP with the default setting for NSTART in
[RFC7252], a CoAP endpoint is not allowed to send a new message to a
destination until a response for the previous message sent to that
destination has been received. This is equivalent to an application-
layer window size of 1. For this use of CoAP, a maximum TCP window
of one MSS will be sufficient.
4.4. RTO estimation 4.4. RTO estimation
If a TCP sender uses very small window size and cannot use Fast The Retransmission Timeout (RTO) estimation is one of the fundamental
Retransmit/Fast Recovery or SACK, the RTO algorithm has a larger TCP algorithms. There is a fundamental trade-off: A short,
impact on performance than for a more powerful TCP stack. In that aggressive RTO behavior reduces wait time before retransmissions, but
case, RTO algorithm tuning may be considered, although careful it also increases the probability of spurious timeouts. The latter
assessment of possible drawbacks is recommended. A fundamental lead to unnecessary waste of potentially scarce resources in CNNs
trade-off exists between responsiveness and correctness of RTOs such as energy and bandwidth. In contrast, a conservative timeout
[I-D.ietf-tcpm-rto-consider]. A more aggressive RTO behavior reduces can result in long error recovery times and thus needlessly delay
wait time before retransmissions, but it also increases the data delivery.
probability of incurring spurious timeouts. The latter lead to
unnecessary waste of potentially scarce resources in CNNs such as
energy and bandwidth.
On a related note, there has been recent activity in the area of [RFC6298] describes the standard TCP RTO algorithm. If a TCP sender
defining an adaptive RTO algorithm for CoAP (over UDP). As shown in uses very small window size and cannot use Fast Retransmit/Fast
experimental studies, the RTO estimator for CoAP defined in Recovery or SACK, the Retransmission Timeout (RTO) algorithm has a
[I-D.ietf-core-cocoa] (hereinafter, CoCoA RTO) outperforms state-of- larger impact on performance than for a more powerful TCP stack. In
art algorithms designed as improvements to RFC 6298 [RFC6298] for that case, RTO algorithm tuning may be considered, although careful
TCP, in terms of packet delivery ratio, settling time after a burst assessment of possible drawbacks is recommended.
of messages, and fairness (the latter is specially relevant in
multihop networks connected to the Internet through a single device, As an example, an adaptive RTO algorithm for CoAP over UDP has been
such as a 6LoWPAN Border Router (6LBR) configured as a RPL root) defined [I-D.ietf-core-cocoa] that has been found to perform well in
[Commag]. In fact, CoCoA RTO has been designed specifically CNN scenarios [Commag].
considering the challenges of CNNs, in contrast with the RFC 6298
RTO.
4.5. TCP connection lifetime 4.5. TCP connection lifetime
[[Note: future revisions will better separate what a TCP stack should [[Note: future revisions will better separate what a TCP stack should
support, or not, and how the TCP stack should be used by support, or not, and how the TCP stack should be used by
applications, e.g., whether to close connections or not.]] applications, e.g., whether to close connections or not.]]
4.5.1. Long TCP connection lifetime 4.5.1. Long TCP connection lifetime
In CNNs, in order to minimize message overhead, a TCP connection In CNNs, in order to minimize message overhead, a TCP connection
skipping to change at page 8, line 43 skipping to change at page 10, line 17
ECN is particularly appropriate in CNNs, since in these environments ECN is particularly appropriate in CNNs, since in these environments
transactional type interactions are a dominant traffic pattern. As transactional type interactions are a dominant traffic pattern. As
transactional data size decreases, the probability of detecting transactional data size decreases, the probability of detecting
congestion by the presence of three duplicate ACKs decreases. In congestion by the presence of three duplicate ACKs decreases. In
contrast, ECN can still activate congestion control measures without contrast, ECN can still activate congestion control measures without
requiring three duplicate ACKs. requiring three duplicate ACKs.
4.7. TCP options 4.7. TCP options
A TCP implementation needs to support options 0, 1 and 2 [RFC793]. A A TCP implementation needs to support options 0, 1 and 2 [RFC0793].
TCP implementation for a constrained device that uses a single-MSS These options are sufficient for interoperability with a standard-
compliant TCP endpoint, albeit many TCP stacks support additional
options and can negotiate their use.
A TCP implementation for a constrained device that uses a single-MSS
TCP receive or transmit window size may not benefit from supporting TCP receive or transmit window size may not benefit from supporting
the following TCP options: Window scale [RFC1323], TCP Timestamps the following TCP options: Window scale [RFC1323], TCP Timestamps
[RFC1323], Selective Acknowledgements (SACK) and SACK-Permitted [RFC1323], Selective Acknowledgements (SACK) and SACK-Permitted
[RFC2018]. Other TCP options should not be used, in keeping with the [RFC2018]. Also other TCP options may not be required on a
principle of lightweight operation. constrained device with a very lightweight implementation.
Other TCP options should not be supported by a constrained device, in
keeping with the principle of lightweight implementation and
operation.
If a device, with less severe memory and processing constraints, can
afford advertising a TCP window size of several MSSs, it may support
the SACK option to improve performance. SACK allows a data receiver
to inform the data sender of non-contiguous data blocks received,
thus a sender (having previously sent the SACK-Permitted option) can
avoid performing unnecessary retransmissions, saving energy and
bandwidth, as well as reducing latency. The receiver supporting SACK
will need to manage the reception of possible out-of-order received
segments, requiring sufficient buffer space.
SACK adds 8*n+2 bytes to the TCP header, where n denotes the number If a device with less severe memory and processing constraints can
of data blocks received, up to 4 blocks. For a low number of out-of- afford advertising a TCP window size of several MSSs, it makes sense
order segments, the header overhead penalty of SACK is compensated by to support the SACK option to improve performance. SACK allows a
data receiver to inform the data sender of non-contiguous data blocks
received, thus a sender (having previously sent the SACK-Permitted
option) can avoid performing unnecessary retransmissions, saving
energy and bandwidth, as well as reducing latency. SACK is
particularly useful for bulk data transfers. The receiver supporting
SACK will need to manage the reception of possible out-of-order
received segments, requiring sufficient buffer space. SACK adds
8*n+2 bytes to the TCP header, where n denotes the number of data
blocks received, up to 4 blocks. For a low number of out-of- order
segments, the header overhead penalty of SACK is compensated by
avoiding unnecessary retransmissions. avoiding unnecessary retransmissions.
Another potentially relevant TCP option in the context of CNNs is Another potentially relevant TCP option in the context of CNNs is
(TFO) [RFC7413]. As described in section 4.5.2, TFO can be used to (TFO) [RFC7413]. As described in Section 4.5.2, TFO can be used to
address the problem of traversing middleboxes that perform early address the problem of traversing middleboxes that perform early
filter state record deletion. filter state record deletion.
4.8. Delayed Acknowledgments 4.8. Delayed Acknowledgments
A device that advertises a single-MSS receive window needs to avoid TCP Delayed Acknowledgements reduce the number of transferred bytes
use of delayed ACKs in order to avoid contributing unnecessary delay within a TCP connection, but they may increase the time until a
(of up to 500 ms) to the RTT [RFC5681]. sender may receive an ACK. For certain traffic patterns Delayed
Acknowledgements may have a detrimental effect. Advanced TCP stacks
may use heuristics to determine the maximum delay for an ACK. For
CNNs, the recommendation depends on the expected communication
patterns.
When traffic over a CNN is expected to be mostly of transactional A device that advertises a single-MSS receive window should avoid use
type, with transaction size typically below one MSS, delayed ACKs are of delayed ACKs in order to avoid contributing unnecessary delay (of
not recommended. For transactional-type traffic between a up to 500 ms) to the RTT [RFC5681], which limits the throughput and
constrained device and a peer (e.g. backend infrastructure) that uses can increase the data delivery time.
delayed ACKs, the maximum ACK rate of the peer will be typically of
one ACK every 200 ms (or even lower). If in such conditions the peer
device is administered by the same entity managing the constrained
device, it is recommended to disable delayed ACKs at the peer side.
On the other hand, delayed ACKs allow to reduce the number of ACKs in A device that can send at most one MSS of data is significantly
bulk transfer type of traffic, e.g. for firmware/software updates or affected if the receiver uses delayed ACKs, e.g., if a TCP server or
for transferring larger data units containing a batch of sensor receiver is outside the CNN. One known workaround is to split the
readings. data to be sent into two segments of smaller size. A standard
compliant TCP receiver will then immediately acknowledge the second
segment, which can improve throughput. This "split hack" works if
the TCP receiver uses Delayed Acks, but the downside is the overhead
of sending two IP packets instead of one.
Also for larger windows, it may make sense to use a small timeout or
disable delayed ACKs when traffic over a CNN is expected to mostly be
small messages with a size typically below one MSS. For request-
response traffic between a constrained device and a peer (e.g.
backend infrastructure) that uses delayed ACKs, the maximum ACK rate
of the peer will be typically of one ACK every 200 ms (or even
lower). If in such conditions the peer device is administered by the
same entity managing the constrained device, it is recommended to
disable delayed ACKs at the peer side.
In contrast, delayed ACKs allow to reduce the number of ACKs in bulk
transfer type of traffic, e.g. for firmware/software updates or for
transferring larger data units containing a batch of sensor readings.
4.9. Explicit loss notifications 4.9. Explicit loss notifications
There has been a significant body of research on solutions capable of There has been a significant body of research on solutions capable of
explicitly indicating whether a TCP segment loss is due to explicitly indicating whether a TCP segment loss is due to
corruption, in order to avoid activation of congestion control corruption, in order to avoid activation of congestion control
mechanisms [ETEN] [RFC2757]. While such solutions may provide mechanisms [ETEN] [RFC2757]. While such solutions may provide
significant improvement, they have not been widely deployed and significant improvement, they have not been widely deployed and
remain as experimental work. In fact, as of today, the IETF has not remain as experimental work. In fact, as of today, the IETF has not
standardized any such solution. standardized any such solution.
5. Security Considerations 5. Security Considerations
If TFO is used, the security considerations of RFC 7413 apply. Best current practise for securing TCP and TCP-based communication
also applies to CNN. As example, use of Transport Layer Security
(TLS) is strongly recommended if it is applicable.
There exist TCP options which improve TCP security. Examples include There are also TCP options which can improve TCP security. Examples
the TCP MD5 signature option [RFC2385] and the TCP Authentication include the TCP MD5 signature option [RFC2385] and the TCP
Option (TCP-AO) [RFC5925]. However, both options add overhead and Authentication Option (TCP-AO) [RFC5925]. However, both options add
complexity. The TCP MD5 signature option adds 18 bytes to every overhead and complexity. The TCP MD5 signature option adds 18 bytes
segment of a connection. TCP-AO typically has a size of 16-20 bytes. to every segment of a connection. TCP-AO typically has a size of
16-20 bytes.
For the mechanisms discussed in this document, the corresponding
considerations apply. For instance, if TFO is used, the security
considerations of [RFC7413] apply.
6. Acknowledgments 6. Acknowledgments
Carles Gomez has been funded in part by the Spanish Government Carles Gomez has been funded in part by the Spanish Government
(Ministerio de Educacion, Cultura y Deporte) through the Jose (Ministerio de Educacion, Cultura y Deporte) through the Jose
Castillejo grant CAS15/00336 and by European Regional Development Castillejo grant CAS15/00336 and by European Regional Development
Fund (ERDF) and the Spanish Government through project Fund (ERDF) and the Spanish Government through project
TEC2016-79988-P, AEI/FEDER, UE. Part of his contribution to this TEC2016-79988-P, AEI/FEDER, UE. Part of his contribution to this
work has been carried out during his stay as a visiting scholar at work has been carried out during his stay as a visiting scholar at
the Computer Laboratory of the University of Cambridge. the Computer Laboratory of the University of Cambridge.
The authors appreciate the feedback received for this document. The The authors appreciate the feedback received for this document. The
following folks provided comments that helped improve the document: following folks provided comments that helped improve the document:
Carsten Bormann, Zhen Cao, Wei Genyu, Michael Scharf, Ari Keranen, Carsten Bormann, Zhen Cao, Wei Genyu, Ari Keranen, Abhijan
Abhijan Bhattacharyya, Andres Arcia-Moret, Yoshifumi Nishida, Joe Bhattacharyya, Andres Arcia-Moret, Yoshifumi Nishida, Joe Touch, Fred
Touch, Fred Baker, Nik Sultana, Kerry Lynn, and Erik Nordmark. Simon Baker, Nik Sultana, Kerry Lynn, Erik Nordmark, Markku Kojo, and
Brummer provided details on the RIOT TCP implementation. Xavi Hannes Tschofenig. Simon Brummer provided details on the RIOT TCP
Vilajosana provided details on the OpenWSN TCP implementation. implementation. Xavi Vilajosana provided details on the OpenWSN TCP
implementation. Rahul Jadhav provided details on the uIP TCP
implementation.
7. Annex. TCP implementations for constrained devices 7. Annex. TCP implementations for constrained devices
This section overviews the main features of TCP implementations for This section overviews the main features of TCP implementations for
constrained devices. constrained devices.
7.1. uIP 7.1. uIP
uIP is a TCP/IP stack, targetted for 8 and 16-bit microcontrollers. uIP is a TCP/IP stack, targetted for 8 and 16-bit microcontrollers.
uIP has been deployed with Contiki and the Arduino Ethernet shield. uIP has been deployed with Contiki and the Arduino Ethernet shield.
skipping to change at page 11, line 4 skipping to change at page 12, line 51
7. Annex. TCP implementations for constrained devices 7. Annex. TCP implementations for constrained devices
This section overviews the main features of TCP implementations for This section overviews the main features of TCP implementations for
constrained devices. constrained devices.
7.1. uIP 7.1. uIP
uIP is a TCP/IP stack, targetted for 8 and 16-bit microcontrollers. uIP is a TCP/IP stack, targetted for 8 and 16-bit microcontrollers.
uIP has been deployed with Contiki and the Arduino Ethernet shield. uIP has been deployed with Contiki and the Arduino Ethernet shield.
A code size of ~5 kB (which comprises checksumming, IP, ICMP and TCP) A code size of ~5 kB (which comprises checksumming, IP, ICMP and TCP)
has been reported for uIP [Dunk]. has been reported for uIP [Dunk].
uIP provides a global buffer for incoming packets, of single-packet uIP uses same buffer both incoming and outgoing traffic, with has a
size. A buffer for outgoing data is not provided. In case of a size of a single packet. In case of a retransmission, an application
retransmission, an application must be able to reproduce the same must be able to reproduce the same user data that had been
packet that had been transmitted. transmitted.
The MSS is announced via the MSS option on connection establishment The MSS is announced via the MSS option on connection establishment
and the receive window size (of one MSS) is not modified during a and the receive window size (of one MSS) is not modified during a
connection. Stop-and-wait operation is used for sending data. Among connection. Stop-and-wait operation is used for sending data. Among
other optimizations, this allows to avoid sliding window operations, other optimizations, this allows to avoid sliding window operations,
which use 32-bit arithmetic extensively and are expensive on 8-bit which use 32-bit arithmetic extensively and are expensive on 8-bit
CPUs. CPUs.
Contiki uses the "split hack" technique (see Section 4.8) to avoid
delayed ACKs for senders using a single MSS.
7.2. lwIP 7.2. lwIP
lwIP is a TCP/IP stack, targetted for 8- and 16-bit microcontrollers. lwIP is a TCP/IP stack, targetted for 8- and 16-bit microcontrollers.
lwIP has a total code size of ~14 kB to ~22 kB (which comprises lwIP has a total code size of ~14 kB to ~22 kB (which comprises
memory management, checksumming, network interfaces, IP, ICMP and memory management, checksumming, network interfaces, IP, ICMP and
TCP), and a TCP code size of ~9 kB to ~14 kB [Dunk]. TCP), and a TCP code size of ~9 kB to ~14 kB [Dunk].
In contrast with uIP, lwIP decouples applications from the network In contrast with uIP, lwIP decouples applications from the network
stack. lwIP supports a TCP transmission window greater than a single stack. lwIP supports a TCP transmission window greater than a single
segment, as well as buffering of incoming and outcoming data. Other segment, as well as buffering of incoming and outcoming data. Other
skipping to change at page 12, line 14 skipping to change at page 14, line 14
7.4. OpenWSN 7.4. OpenWSN
The TCP implementation in OpenWSN is mostly equivalent to the uIP TCP The TCP implementation in OpenWSN is mostly equivalent to the uIP TCP
implementation. OpenWSN TCP implementation only supports the minimum implementation. OpenWSN TCP implementation only supports the minimum
state machine functionality required. For example, it does not state machine functionality required. For example, it does not
perform retransmissions. perform retransmissions.
7.5. TinyOS 7.5. TinyOS
TBD TODO: To be verified
7.6. Summary TinyOS has an experimental TCP stack that uses a simple nonblocking
library-based implementation of TCP. The application is responsible
for buffering. The TCP library does not do any receive-side
buffering. Instead, it will immediately dispatch new, in-order data
to the application and otherwise drop the segment. A send buffer is
provided so that the TCP implementation can automatically retransmit
missing segments.
7.6. Summary
+-------+---------+---------+------+---------+--------+ +-------+---------+---------+------+---------+--------+
| uIP |lwIP orig|lwIP 2.0 | RIOT | OpenWSN | TinyOS | | uIP |lwIP orig|lwIP 2.0 | RIOT | OpenWSN | TinyOS |
+--------+----------------+-------+---------+---------+------+---------+--------+ +--------+----------------+-------+---------+---------+------+---------+--------+
| | Data size | * | * | * | * | * | * | | | Data size | * | * | * | * | * | * |
| Memory +----------------+-------+---------+---------+------+---------+--------+ | Memory +----------------+-------+---------+---------+------+---------+--------+
| | Code size (kB) | < 5 |~9 to ~14| * | * | * | * | | | Code size (kB) | < 5 |~9 to ~14| * | * | * | * |
+--------+----------------+-------+---------+---------+------+---------+--------+ +--------+----------------+-------+---------+---------+------+---------+--------+
| |Window size(MSS)| 1 | Multiple| Multiple| 1 | 1 | * | | |Window size(MSS)| 1 | Multiple| Multiple| 1 | 1 |Multiple|
| +----------------+-------+---------+---------+------+---------+--------+ | +----------------+-------+---------+---------+------+---------+--------+
| | Slow start | No | Yes | Yes | No | No | * | | | Slow start | No | Yes | Yes | No | No | Yes |
| T +----------------+-------+---------+---------+------+---------+--------+ | T +----------------+-------+---------+---------+------+---------+--------+
| C | Fast rec/retx | No | Yes | Yes | No | No | * | | C | Fast rec/retx | No | Yes | Yes | No | No | Yes |
| P +----------------+-------+---------+---------+------+---------+--------+ | P +----------------+-------+---------+---------+------+---------+--------+
| | Keep-alive | No | * | * | No | No | * | | | Keep-alive | No | * | * | No | No | No |
| +----------------+-------+---------+---------+------+---------+--------+ | +----------------+-------+---------+---------+------+---------+--------+
| f | TFO | No | No | * | No | No | * | | f | TFO | No | No | * | No | No | No |
| e +----------------+-------+---------+---------+------+---------+--------+ | e +----------------+-------+---------+---------+------+---------+--------+
| a | ECN | No | No | * | No | No | * | | a | ECN | No | No | * | No | No | No |
| t +----------------+-------+---------+---------+------+---------+--------+ | t +----------------+-------+---------+---------+------+---------+--------+
| u | Window Scale | No | No | Yes | No | No | * | | u | Window Scale | No | No | Yes | No | No | No |
| r +----------------+-------+---------+---------+------+---------+--------+ | r +----------------+-------+---------+---------+------+---------+--------+
| e | TCP timestamps | No | No | Yes | No | No | * | | e | TCP timestamps | No | No | Yes | No | No | No |
| s +----------------+-------+---------+---------+------+---------+--------+ | s +----------------+-------+---------+---------+------+---------+--------+
| | SACK | No | No | Yes | No | No | * | | | SACK | No | No | Yes | No | No | No |
| +----------------+-------+---------+---------+------+---------+--------+ | +----------------+-------+---------+---------+------+---------+--------+
| | Delayed ACKs | No | Yes | Yes | No | No | * | | | Delayed ACKs | No | Yes | Yes | No | No | No |
+--------+----------------+-------+---------+---------+------+---------+--------+ +--------+----------------+-------+---------+---------+------+---------+--------+
Figure 2: Summary of TCP features for differrent lightweight TCP Figure 2: Summary of TCP features for differrent lightweight TCP
implementations. implementations.
8. References TODO: Add information about RAM requirements (in addition to
codesize)
8.1. Normative References 8. Annex. Changes compared to previous versions
RFC Editor: To be removed prior to publication
8.1. Changes compared to -00
o Changed title and abstract
o Clarification that communcation with standard-compliant TCP
endpoints is required, based on feedback from Joe Touch
o Additional discussion on communication patters
o Numerous changes to address a comprehensive review from Hannes
Tschofenig
o Reworded security considerations
o Additional references and better distinction between normative and
informative entries
o Feedback from Rahul Jadhav on the uIP TCP implementation
o Basic data for the TinyOS TCP implementation added, based on
source code analysis
9. References
9.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989, <https://www.rfc- DOI 10.17487/RFC1122, October 1989,
editor.org/info/rfc1122>. <https://www.rfc-editor.org/info/rfc1122>.
[RFC1323] Jacobson, V., Braden, R., and D. Borman, "TCP Extensions [RFC1323] Jacobson, V., Braden, R., and D. Borman, "TCP Extensions
for High Performance", RFC 1323, DOI 10.17487/RFC1323, May for High Performance", RFC 1323, DOI 10.17487/RFC1323, May
1992, <https://www.rfc-editor.org/info/rfc1323>. 1992, <https://www.rfc-editor.org/info/rfc1323>.
[RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August
1996, <https://www.rfc-editor.org/info/rfc1981>.
[RFC2018] Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP [RFC2018] Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP
Selective Acknowledgment Options", RFC 2018, Selective Acknowledgment Options", RFC 2018,
DOI 10.17487/RFC2018, October 1996, <https://www.rfc- DOI 10.17487/RFC2018, October 1996,
editor.org/info/rfc2018>. <https://www.rfc-editor.org/info/rfc2018>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997,
editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option", RFC 2385, DOI 10.17487/RFC2385, August
1998, <https://www.rfc-editor.org/info/rfc2385>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>. December 1998, <https://www.rfc-editor.org/info/rfc2460>.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616,
DOI 10.17487/RFC2616, June 1999, <https://www.rfc-
editor.org/info/rfc2616>.
[RFC2757] Montenegro, G., Dawkins, S., Kojo, M., Magret, V., and N.
Vaidya, "Long Thin Networks", RFC 2757,
DOI 10.17487/RFC2757, January 2000, <https://www.rfc-
editor.org/info/rfc2757>.
[RFC2884] Hadi Salim, J. and U. Ahmed, "Performance Evaluation of
Explicit Congestion Notification (ECN) in IP Networks",
RFC 2884, DOI 10.17487/RFC2884, July 2000,
<https://www.rfc-editor.org/info/rfc2884>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP", of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001, RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>. <https://www.rfc-editor.org/info/rfc3168>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, [RFC3402] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
"Transmission of IPv6 Packets over IEEE 802.15.4 Part Two: The Algorithm", RFC 3402, DOI 10.17487/RFC3402,
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, October 2002, <https://www.rfc-editor.org/info/rfc3402>.
<https://www.rfc-editor.org/info/rfc4944>.
[RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, DOI 10.17487/RFC3819, July 2004,
<https://www.rfc-editor.org/info/rfc3819>.
[RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion [RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
Control", RFC 5681, DOI 10.17487/RFC5681, September 2009, Control", RFC 5681, DOI 10.17487/RFC5681, September 2009,
<https://www.rfc-editor.org/info/rfc5681>. <https://www.rfc-editor.org/info/rfc5681>.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925, Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <https://www.rfc-editor.org/info/rfc5925>. June 2010, <https://www.rfc-editor.org/info/rfc5925>.
[RFC6092] Woodyatt, J., Ed., "Recommended Simple Security
Capabilities in Customer Premises Equipment (CPE) for
Providing Residential IPv6 Internet Service", RFC 6092,
DOI 10.17487/RFC6092, January 2011, <https://www.rfc-
editor.org/info/rfc6092>.
[RFC6298] Paxson, V., Allman, M., Chu, J., and M. Sargent, [RFC6298] Paxson, V., Allman, M., Chu, J., and M. Sargent,
"Computing TCP's Retransmission Timer", RFC 6298, "Computing TCP's Retransmission Timer", RFC 6298,
DOI 10.17487/RFC6298, June 2011, <https://www.rfc- DOI 10.17487/RFC6298, June 2011,
editor.org/info/rfc6298>. <https://www.rfc-editor.org/info/rfc6298>.
[RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
Statement and Requirements for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Routing",
RFC 6606, DOI 10.17487/RFC6606, May 2012,
<https://www.rfc-editor.org/info/rfc6606>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228, Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014, <https://www.rfc- DOI 10.17487/RFC7228, May 2014,
editor.org/info/rfc7228>. <https://www.rfc-editor.org/info/rfc7228>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014, <https://www.rfc-
editor.org/info/rfc7252>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP [RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<https://www.rfc-editor.org/info/rfc7413>. <https://www.rfc-editor.org/info/rfc7413>.
[RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets 9.2. Informative References
over ITU-T G.9959 Networks", RFC 7428,
DOI 10.17487/RFC7428, February 2015, <https://www.rfc-
editor.org/info/rfc7428>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015, <https://www.rfc-
editor.org/info/rfc7540>.
[RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low
Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015,
<https://www.rfc-editor.org/info/rfc7668>.
[RFC8105] Mariager, P., Petersen, J., Ed., Shelby, Z., Van de Logt,
M., and D. Barthel, "Transmission of IPv6 Packets over
Digital Enhanced Cordless Telecommunications (DECT) Ultra
Low Energy (ULE)", RFC 8105, DOI 10.17487/RFC8105, May
2017, <https://www.rfc-editor.org/info/rfc8105>.
[RFC8163] Lynn, K., Ed., Martocci, J., Neilson, C., and S.
Donaldson, "Transmission of IPv6 over Master-Slave/Token-
Passing (MS/TP) Networks", RFC 8163, DOI 10.17487/RFC8163,
May 2017, <https://www.rfc-editor.org/info/rfc8163>.
8.2. Informative References
[Commag] A. Betzler, C. Gomez, I. Demirkol, J. Paradells, "CoAP [Commag] A. Betzler, C. Gomez, I. Demirkol, J. Paradells, "CoAP
Congestion Control for the Internet of Things", IEEE Congestion Control for the Internet of Things", IEEE
Communications Magazine, June 2016. Communications Magazine, June 2016.
[Dunk] A. Dunkels, "Full TCP/IP for 8-Bit Architectures", 2003. [Dunk] A. Dunkels, "Full TCP/IP for 8-Bit Architectures", 2003.
[ETEN] R. Krishnan et al, "Explicit transport error notification [ETEN] R. Krishnan et al, "Explicit transport error notification
(ETEN) for error-prone wireless and satellite networks", (ETEN) for error-prone wireless and satellite networks",
Computer Networks 2004. Computer Networks 2004.
[I-D.delcarpio-6lo-wlanah] [I-D.delcarpio-6lo-wlanah]
Vega, L., Robles, I., and R. Morabito, "IPv6 over Vega, L., Robles, I., and R. Morabito, "IPv6 over
802.11ah", draft-delcarpio-6lo-wlanah-01 (work in 802.11ah", draft-delcarpio-6lo-wlanah-01 (work in
progress), October 2015. progress), October 2015.
[I-D.ietf-core-coap-tcp-tls]
Bormann, C., Lemay, S., Tschofenig, H., Hartke, K.,
Silverajan, B., and B. Raymor, "CoAP (Constrained
Application Protocol) over TCP, TLS, and WebSockets",
draft-ietf-core-coap-tcp-tls-09 (work in progress), May
2017.
[I-D.ietf-core-cocoa] [I-D.ietf-core-cocoa]
Bormann, C., Betzler, A., Gomez, C., and I. Demirkol, Bormann, C., Betzler, A., Gomez, C., and I. Demirkol,
"CoAP Simple Congestion Control/Advanced", draft-ietf- "CoAP Simple Congestion Control/Advanced", draft-ietf-
core-cocoa-01 (work in progress), March 2017. core-cocoa-01 (work in progress), March 2017.
[I-D.ietf-lpwan-overview] [I-D.ietf-lpwan-overview]
Farrell, S., "LPWAN Overview", draft-ietf-lpwan- Farrell, S., "LPWAN Overview", draft-ietf-lpwan-
overview-06 (work in progress), July 2017. overview-07 (work in progress), October 2017.
[I-D.ietf-lwig-energy-efficient] [I-D.ietf-lwig-energy-efficient]
Gomez, C., Kovatsch, M., Tian, H., and Z. Cao, "Energy- Gomez, C., Kovatsch, M., Tian, H., and Z. Cao, "Energy-
Efficient Features of Internet of Things Protocols", Efficient Features of Internet of Things Protocols",
draft-ietf-lwig-energy-efficient-07 (work in progress), draft-ietf-lwig-energy-efficient-07 (work in progress),
March 2017. March 2017.
[I-D.ietf-tcpm-rto-consider] [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
Allman, M., "Retransmission Timeout Requirements", draft- for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August
ietf-tcpm-rto-consider-05 (work in progress), March 2017. 1996, <https://www.rfc-editor.org/info/rfc1981>.
[I-D.tschofenig-core-coap-tcp-tls] [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Bormann, C., Lemay, S., Technologies, Z., and H. Signature Option", RFC 2385, DOI 10.17487/RFC2385, August
Tschofenig, "A TCP and TLS Transport for the Constrained 1998, <https://www.rfc-editor.org/info/rfc2385>.
Application Protocol (CoAP)", draft-tschofenig-core-coap-
tcp-tls-05 (work in progress), November 2015.
[MQTTS] U. Hunkeler, H.-L. Truong, A. Stanford-Clark, "MQTT-S: A [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Publish/Subscribe Protocol For Wireless Sensor Networks", Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
2008. Transfer Protocol -- HTTP/1.1", RFC 2616,
DOI 10.17487/RFC2616, June 1999,
<https://www.rfc-editor.org/info/rfc2616>.
[RFC2757] Montenegro, G., Dawkins, S., Kojo, M., Magret, V., and N.
Vaidya, "Long Thin Networks", RFC 2757,
DOI 10.17487/RFC2757, January 2000,
<https://www.rfc-editor.org/info/rfc2757>.
[RFC2884] Hadi Salim, J. and U. Ahmed, "Performance Evaluation of
Explicit Congestion Notification (ECN) in IP Networks",
RFC 2884, DOI 10.17487/RFC2884, July 2000,
<https://www.rfc-editor.org/info/rfc2884>.
[RFC3481] Inamura, H., Ed., Montenegro, G., Ed., Ludwig, R., Gurtov,
A., and F. Khafizov, "TCP over Second (2.5G) and Third
(3G) Generation Wireless Networks", BCP 71, RFC 3481,
DOI 10.17487/RFC3481, February 2003,
<https://www.rfc-editor.org/info/rfc3481>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<https://www.rfc-editor.org/info/rfc4944>.
[RFC6077] Papadimitriou, D., Ed., Welzl, M., Scharf, M., and B.
Briscoe, "Open Research Issues in Internet Congestion
Control", RFC 6077, DOI 10.17487/RFC6077, February 2011,
<https://www.rfc-editor.org/info/rfc6077>.
[RFC6092] Woodyatt, J., Ed., "Recommended Simple Security
Capabilities in Customer Premises Equipment (CPE) for
Providing Residential IPv6 Internet Service", RFC 6092,
DOI 10.17487/RFC6092, January 2011,
<https://www.rfc-editor.org/info/rfc6092>.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
March 2011, <https://www.rfc-editor.org/info/rfc6120>.
[RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
Statement and Requirements for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Routing",
RFC 6606, DOI 10.17487/RFC6606, May 2012,
<https://www.rfc-editor.org/info/rfc6606>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7414] Duke, M., Braden, R., Eddy, W., Blanton, E., and A.
Zimmermann, "A Roadmap for Transmission Control Protocol
(TCP) Specification Documents", RFC 7414,
DOI 10.17487/RFC7414, February 2015,
<https://www.rfc-editor.org/info/rfc7414>.
[RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets
over ITU-T G.9959 Networks", RFC 7428,
DOI 10.17487/RFC7428, February 2015,
<https://www.rfc-editor.org/info/rfc7428>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low
Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015,
<https://www.rfc-editor.org/info/rfc7668>.
[RFC8105] Mariager, P., Petersen, J., Ed., Shelby, Z., Van de Logt,
M., and D. Barthel, "Transmission of IPv6 Packets over
Digital Enhanced Cordless Telecommunications (DECT) Ultra
Low Energy (ULE)", RFC 8105, DOI 10.17487/RFC8105, May
2017, <https://www.rfc-editor.org/info/rfc8105>.
[RFC8163] Lynn, K., Ed., Martocci, J., Neilson, C., and S.
Donaldson, "Transmission of IPv6 over Master-Slave/Token-
Passing (MS/TP) Networks", RFC 8163, DOI 10.17487/RFC8163,
May 2017, <https://www.rfc-editor.org/info/rfc8163>.
Authors' Addresses Authors' Addresses
Carles Gomez Carles Gomez
UPC/i2CAT UPC/i2CAT
C/Esteve Terradas, 7 C/Esteve Terradas, 7
Castelldefels 08860 Castelldefels 08860
Spain Spain
Email: carlesgo@entel.upc.edu Email: carlesgo@entel.upc.edu
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