Network Working Group G. Montenegro
Internet-Draft Microsoft
Intended status: Informational S. Cespedes
Expires: January 9, 2017 Universidad de Chile
S. Loreto
Ericsson
R. Simpson
General Electric
July 8, 2016
H2oT: HTTP/2 for the Internet of Things
draft-montenegro-httpbis-h2ot-00
Abstract
This document makes the case for HTTP/2 for IoT.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Application Transport Alternatives and their Strengths . . . 4
2.1. HTTP/1.1 . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. MQTT . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. CoAP . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4. Protocols Comparison . . . . . . . . . . . . . . . . . . 8
3. Importance of Protocol Reuse . . . . . . . . . . . . . . . . 8
4. HTTP/2 in IoT . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Profile of HTTP/2 for IoT . . . . . . . . . . . . . . . . . . 11
6. Negotiation of HTTP/2 for IoT . . . . . . . . . . . . . . . . 12
7. Gateway and Proxying Issues . . . . . . . . . . . . . . . . . 12
8. Implementation Considerations . . . . . . . . . . . . . . . . 13
9. Experimentation and Performance . . . . . . . . . . . . . . . 13
9.1. GET Example . . . . . . . . . . . . . . . . . . . . . . . 14
9.1.1. HTTP/1.1 . . . . . . . . . . . . . . . . . . . . . . 14
9.1.2. HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . 15
9.1.3. Comparison . . . . . . . . . . . . . . . . . . . . . 16
10. HTTP/2 over UDP - QUIC . . . . . . . . . . . . . . . . . . . 16
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
12. Security Considerations . . . . . . . . . . . . . . . . . . . 17
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
14.1. Normative References . . . . . . . . . . . . . . . . . . 18
14.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
When the IETF started work on the Internet-of-Things ("IoT") with the
6lowpan WG, it was clear that in addition to the lower-layer
adaptation work for IPv6, much work elsewhere in the stack was
necessary. (In this document, the "things" in "IoT" are nodes that
are constrained in some manner--e.g., cpu, memory, power--such that
direct use of unmodified mainstream protocols is challenging.) Once
the IPv6 adaptation was understood, the next question was what
protocols to use above IP(v6) for different functions and at
different layers to have a complete stack. That question may not
have a single answer that is always best for all scenarios and use
cases. There are many such use cases, in accordance with the fact
that IoT means too many things.
Accordingly, the IoT landscape includes a proliferation of options
for any particular functionality (transport, encoding, security
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suites, authentication/authorization, etc). Different vendors and
standards organizations (or fora) offer IoT solutions by grouping
these different components into separate stacks. Even if the
components have the same name or originate in the same original
standard (or even in the same code base), each organization adapts it
ever so slightly to their own goals, often rendering the resultant
components non-interoperable. Many of these components are being
created expressly for IoT (within the IETF and elsewhere) under the
assumption that the mainstream options could not possibly be usable
for IoT scenarios. This results in multiple disparate networking and
software stacks. Given the incipient state of IoT, for the
foreseeable future multiple competing stacks will continue to exist
at least in gateways and cloud elements. The additional complexity
to IoT amplifies the attack surface. Nevertheless, properly
configured and implemented, mainstream options may not just be
workable, but may even be the best option at least in some scenarios.
The appearance of one-off stacks (as opposed to a properly configured
and adapted mainstream stack) is reminiscent of WAP 1.x, a complete
vertical stack offered for phones as they were starting to access the
Internet (albeit from within a walled garden) in the late 90's. At
that time the IETF and the W3C started efforts to develop the
mainstream alternatives. As a result, today no phone uses WAP.
Instead, phone stacks are mainstream TCP/IP protocols (properly
configured and adapted, of course). In contrast, today in IoT we see
not just one non-mainstream stack, but several (as if we had not just
WAP, but WAP1, WAP2, WAP3, etc.). And we may have to live with them
for some time, but it is essential to ponder what the mainstream
stack might look like if we are to eventually reap the benefits of a
true Internet of Things instead of a not-quite-but-kinda-close-to-
Internet-non-interoperable-hodge-podge-of-Things.
HTTP/2 [RFC7540][RFC7541] is now widely available as a transport
option. Moreover, the ongoing effort to layer HTTP/2 over UDP (i.e.,
over QUIC) adds a useful capability for IoT scenarios. We show the
current suitability of HTTP/2 for IoT scenarios and examine possible
improvements.
Let's look at some application communication patterns to establish
some common language (see also section 2 of [RFC7452] for a related
discussion):
node to node: A constrained node engages in direct communication
with another constrained node.
node to gateway: A constrained node and a gateway node engage in
direct communication. A gateway node is directly on both a
constrained network (e.g., a lowpan) and on a non-constrained
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network (a normal network using mainstream stack implementations,
typically connected to the Internet).
gateway to cloud: A gateway node (see above) engages in
communication with unconstrained networks, typically a cloud
service on the Internet.
node to cloud: A node on a constrained network engages in direct
communcation with unconstrained networks, typically a cloud
service on the Internet.
In the above, a "node" may, in fact, be multiple nodes when engaging
in group communication. Group communications (e.g., via multicast)
are commonly used for discovery or routing (see also Section 2.3).
We can further categorize the above communication patterns into two
basic types of networking exchanges:
Constrained network scenario: A constrained network scenario
includes node to node and node to gateway exchanges. Group
communications are another typical aspect of these constrained
networks.
Internet scenario: An Internet scenario includes gateway to cloud
and node to cloud exchanges.
This document makes the case for HTTP/2 as the most general protocol
of choice for Internet of Things applications. HTTP/2 is most at
home in Internet scenarios and is also suitable for at least some
Constrained network scenarios.
2. Application Transport Alternatives and their Strengths
A recent survey by the Eclipse IoT working group queried IoT
developers about the protocols and technologies they are using and
planning to use [Eclipse_survey]. Some of the currently used
application transport protocols (above the link layer) for IoT
applications are as follows:
o HTTP/1.1 (61% of developers)
o MQTT (52% of developers)
o CoAP (21% of developers)
o HTTP/2 (19% of developers)
o Others: In-house, AMQP and XMPP (43% of developers)
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It is interesting to note that in the same survey done in 2015,
HTTP/2 was not even present, whereas it is now at 19% (the other
protocols are mostly unchanged). No doubt it is being used in
scenarios where there are no major constraints (precisely where
HTTP/1.x is also being used). Optimizing it for IoT can further
promote its use. The sections below provide some more details on
top-of-the-list protocols other than HTTP/2.
2.1. HTTP/1.1
HTTP/1.1 is a text-based protocol, and is widely successful as it is
the basis not just for the web, but for much non-web traffic in the
internet today. Most (but not all) of the instances of HTTP today
implement version 1.1 as specified in RFC2616 [RFC2616]. Since its
publication back in 1999 it has evolved organically, producing
countless variations and exceptions to its rules. Modern browser and
server implementations have very complex and convoluted code to deal
with parsing and handling the many nuances of the protocol. Because
of all this confusion, the HTTPbis working group set out to clarify
the existing specifications, and after a multi-year effort to clarify
its many sources of confusion, it has published a cleaner
specification in RFCs 7230-7235 [RFC7230] [RFC7231] [RFC7232]
[RFC7233] [RFC7234] [RFC7235]. In spite of this, the protocol still
has a plethora of legacy issues and remains too verbose.
HTTP/1.1 is very clearly a mismatch for the constrained devices and
networks that characterize IoT. Despite its shortcomings, it is the
most popular protocol for IoT applications (61% per the
aforementioned survey, although the survey does not clarify if this
is for Internet or constrained network scenarios). Why would such an
ill-suited protocol be clearly the most popular for IoT applications?
It is by far the most commonly known protocol. It has many
implementations (many in open source), with massive support in all
platforms, tools and APIs. It is easy to find know-how and support.
In short, it has the power and convenience that comes with being a
mainstream protocol.
Another major advantage is that it is the protocol that has the best
chance of traversing firewalls and middle boxes in the internet due
to its use of port 80 when in the clear, and, especially, its use of
port 443 when over TLS. This is a primary concern in Internet
scenarios.
2.2. MQTT
MQ Telemetry Transport (MQTT) is a publish/subscribe messaging
protocol that runs on top of TCP. It was created by IBM. Version
3.1.1 is available as an OASIS standard [mqtt_oasis] and as an ISO
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publication [mqtt_iso]. It is popular in the Internet scenario (node
to cloud, gateway to cloud) and it aims to connect embedded devices
and networks with applications and middleware. It is a compact,
binary protocol, and is very popular in certain application domains.
It has been known as a protocol suitable to be used in resource
constrained devices and unreliable networks.
It is the second most popular protocol in the survey (behind
HTTP/1.1) with 52% of developers using it. In the internet scenario,
however, TLS is probably required. This additional TLS overhead
renders all protocols slightly larger, so, e.g., MQTT loses some
relative size advantage.
The MQTT protocol requires an underlying transport that provides an
ordered, lossless, stream of bytes from the Client to Server and
Server to Client. It cannot be used over UDP. There is an
alternative (and not standardized) variant called MQTT-SN (previously
called MQTT-S) which can use UDP, Zigbee or other datagram
transports, but this is a substantially different protocol which has
been tailored to meet the needs of small, battery-powered sensors
connected by wireless sensor networks (WSNs), and relies upon a MQTT-
SN Gateway or forwarder for external communications.
MQTT is closely tied to PUBLISH/SUBSCRIBE operations and this is the
only mode of message transfer. This means that MQTT cannot be used
for "node to node" communications because a server is required (the
server forwards messages between publishers and subscribers, manages
subscriptions, and performs user authorization functions.) The
exclusive use of publish/subscribe operations can complicate some IoT
operations, such as request-response traffic, and transferring large
payloads (e.g. firmware updates). It is sometimes desirable to use a
different protocol (like HTTP) for transferring large payloads, even
though MQTT supports a maximum per-message payload size of 256 MiB.
The OASIS MQTT-TC is considering proposals involving changes in
handling request-response traffic and large message transfers.
MQTT is deployed over TCP (port 8833 when over TLS, port 1883 without
TLS). Even when using TLS, it has the well-known firewall traversal
issues common to any protocol not over port 443.
2.3. CoAP
CoAP is a compact, binary, UDP-based protocol based on RESTful
principles and closely patterned after HTTP. It has been designed to
be used in constrained devices and constrained networks. The
protocol specification has been published [RFC7252], although
additional functionalities such as congestion control, block-wise
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transfer, TCP and TLS transfer and HTTP mapping are still being
specified.
The protocol meets IoT requirements through the modification of some
HTTP functionalities to achieve low-power consumption and operation
over lossy links. To avoid undesirable packet fragmentation the CoAP
specification provides an upper bound to the message size, dictating
that a CoAP message, appropriately encapsulated, SHOULD fit within a
single IP datagram:
If the Path MTU is not known for a destination, an IP MTU of 1280
bytes SHOULD be assumed; if nothing is known about the size of the
headers, good upper bounds are 1152 bytes for the message size and
1024 bytes for the payload size.
CoAP interaction with HTTP must traverse a proxy, with the
concomitant issues of breaking end-to-end security (Section 7), but
at least the common REST architecture makes it easier.
CoAP works on port 5683 and offers optional reliable delivery (thru a
retransmission mechanism), support for unicast and multicast, and
asynchronous message exchange. Multicast (see Section 1 is typically
used by IoT SDO's for routing and discovery. A common use of
multicast within CoAP is for discovery, something addressed in
mainstream (and even some IoT) scenarios via mDNS [RFC6762] and DNS-
SD [RFC6763]. More general uses of multicast within CoAP (and, in
general, at the application transport, e.g., to address group
communication for IoT), introduces complexity for security, IPv6
scoping, wireless reliability, etc.
A typical CoAP message can be between 10 and 20 bytes.
It is the third most popular protocol in the survey with a 21%
preference. Nevertheless, since CoAP is UDP-based, in the Internet
scenario it also suffers from firewall traversal issues, verbosity
(as compared to TCP) to maintain state in NAT boxes and lack of
integration with existing enterprise infrastructures. There is
ongoing work to specify the use of CoAP over TCP as well as CoAP over
TLS, in an attempt to overcome issues with middleboxes and improve
its applicability to Internet scenarios.
As noted above, there is much ongoing work on CoAP, and much of it
seeks to define a transport on top of UDP. This is a very complex
task not to be underestimated. QUIC is also embarking on this task,
but it appears to be benefitting from many more resources within the
networking community at large.
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2.4. Protocols Comparison
The aformentioned protocols have been compared in both experimental
and emulated environments [IEEE_survey]. Previous reports show that
performance is highly dependent on the network conditions: in good
link conditions with low packet loss, MQTT delivers packets with
lower delay than CoAP, but CoAP outperforms when high packet losses
are present; in terms of packet sizes, if packet loss is under 25%
and messages are of a small size, CoAP demonstrates a better link
usage than MQTT. However, other experiments report a better
performance of MQTT in high traffic/high packet loss scenarios
[IoT_analysis]. CoAP has also been compared to HTTP/1.1. In terms
of power consumption and response time, naturally CoAP behaves better
than HTTP/1.1 thanks to the reduced packet sizes.
Coexistence among the protocols has also been tested with varied
network configurations. For the most part, interaction of CoAP with
HTTP has been studied [Web_things], demonstrating successful exchange
when there is a CoAP server running on a constrained node and the
HTTP client is requesting resources from it, or when there is a CoAP
client requesting resources from an HTTP server. In both cases a
proxy is necessary to enable translation between the protocols.
Another network configuration with a CoAP client - CoAP proxy - CoAP
server has been compared to the CoAP client - CoAP/HTTP proxy - HTTP
server configuration, in which case the response times of the only-
CoAP configuration resulted to be lower even when the number of
concurrent requests increases [CoAP_integration].
To date, no reports have been found comparing MQTT or CoAP to HTTP/2.
3. Importance of Protocol Reuse
These protocols often do not exist in a vacuum. Typically, they are
mandated as part of a given stack specified by any of several IoT
consortia (e.g., OCF, AllSeen Alliance/AllJoyn, Thread Group). We
know that these multiple IoT protocols (and stacks) provide very
useful sources of information for prying eyes (See "US intelligence
chief says we might use the IoT to spy on you" at
http://www.wired.com/2012/03/petraeus-tv-remote/). Security and
privacy issues are exacerbated because:
o IoT is the worst of all security worlds: (1) constraints push
devices into taking shortcuts and (2) there is less physical
security with such devices (after installation they are typically
reachable by unfriendly hands).
o Each of these protocols is an island with its own security
measures (or lack thereof) and very limited review.
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The previous two points can be summarized as follows:
A security and privacy environment even more challenging than usual:
This is receiving much attention from the research and
standardization communities. It is the sort of challenge that
stimulates researchers into high gear. It is a daunting problem
for sure, but at least it is on the radar of folks and consortia
working on IoT. Nevertheless, many issues will arise because of
this (e.g., discovery of serious flaws in IoT devices like locks
is a common occurrence).
Many different protocol stacks at play: This is a much more
worrisome issue if one considers that a vast majority of issues
arising with security have less to do with cryptography (the first
point above) and more to do with software engineering, and silly
bugs. Each stack added creates more attack surface. At the same
time, each one of these stacks gather less attention and scrutiny
than software used for mainstream scenarios (such as the web). We
have seen no shortage of issues on OpenSSL and similar heavily-
used software. We can expect much worse from stacks that are not
nearly as well exercised nor examined. And if we have not one,
but several of these stacks untested by millions of eyeballs, we
are inviting disaster.
A recent Harvard report on the state of surveillance and erosion of
privacy [Going_Dark] concludes among its findings that the projected
substantial growth of IoT will drastically change surveillance
(surveillance is not merely limited to government agencies of
course), and that the fragmentation of ecosystems hinders the
deployment of countermeasures (e.g., end-to-end encryption) as that
requires more coordination and standardization than currently
available. This not only gives rise to rogue surveillance sites such
as Shodan (https://www.shodan.io/), but also represents a great
opportunity for government agencies' surveillance needs [Clapper].
Furthermore, multiple stacks defeat one of the main benefits of the
"I" in IoT: interoperability. Also, reusing mainstream protocols
affords the benefits of using better-known technology, with easier
access to reference implementations (including open source), people
with the required skills and experience, training, etc. These are
basically the same arguments that were used originally to justify the
use of IP-based networking over custom-built stacks. The message was
heard loud and clear but for the most part it was applied to only a
limited set of components (e.g., IP, UDP, DTLS). Other components
are still being custom built (albeit, on top of IP).
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4. HTTP/2 in IoT
As noted above, for the foreseeable future the IoT landscape requires
several stacks. Thinking about a canonical stack based on mainstream
protocols is not an exercise in the delusion that one single stack
will be enough. Rather, it is an attempt to define an option that
can serve IoT better into the future, and one that can be recommended
whenever there is a choice (often there isn't one).
The goals in pursuing a canonical stack are the following:
o Maximize Standards-based Elements across technologies and IoT
stacks
o Reduce IoT protocol idiosyncrasies and specificity
o Reduce the number of "translators" needed in an IoT hub
To arrive at a canonical stack the mainstream standards-based stack
must be properly profiled and optimized. This requires optimizing
aspects such as:
o Authentication and Authorization framework by adapting OAUTH
instead of inventing a new system [I-D.ietf-ace-oauth-authz].
o Device Management and Object Model/Descriptions (currently being
defined).
o Discovery via mDNS [RFC6762] and DNS-SD [RFC6763] perhaps
augmented with IoT considerations, e.g.,
[I-D.aggarwal-dnssd-optimize-query]. Another option to
investigate is that of HTTP/2 over multicast. Whereas there have
been some forays into HTTP over multicast, it is not nearly as
well deployed, implemented and understood as mDNS.
o Application Transport based on HTTP/2.
This document deals only with the application layer transport based
on HTTP/2.
HTTP/2 is a good match for IoT for several reasons:
o Binary and Compact (9 byte header)
o Header Compression [RFC7541]
o Traversal past firewalls/middle boxes via TLS over port 443
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o Support of RESTful model in major development frameworks
o Know-how widely available
5. Profile of HTTP/2 for IoT
HTTP/2 has many negotiable settings that can improve its performance
for IoT applications by reducing bandwidth, codespace, and RAM
requirements. Specifically, the following settings and values have
been found to be useful in IoT applications:
o SETTINGS_HEADER_TABLE_SIZE: this setting allows hosts to limit the
size of the header compression table used for decoding, reducing
required RAM, but potentially increasing bandwidth requirements.
Initial value per HTTP/2 is 4096. IoT scenarios might benefit
from changing this to a smaller value (e.g., 512), however, to
avoid increased bandwidth usage, IoT scenarios should judiciously
use HTTP headers and the dynamic header table [RFC7541].
o SETTINGS_ENABLE_PUSH: This setting allows clients to enable or
disable server push. This functionality may not be required in
some IoT applications. The initial value per HTTP/2 is 1.
o SETTINGS_MAX_CONCURRENT_STREAMS: this setting allows a sender to
limit the number of simultaneous streams that a receiver can
create for a connection. HTTP/2 recommends this value be no
smaller than 100. IoT scenarios may wish to limit this to a much
smaller number, such as 2 or 3.
o SETTINGS_INITIAL_WINDOW_SIZE: this setting allows hosts to limit
the flow control window, potentially reducing buffer requirements
at the expense of potentially underutilized bandwidth-delay
products. Per HTTP/2 the initial value is 2^16-1 (65,535) octets.
IoT scenarios may wish to limit this to smaller values in
accordance with the node's constraints (e.g., a few kilo-octets).
o SETTINGS_MAX_FRAME_SIZE: this setting allows hosts to specify the
largest frame size they are willing to receive. Per HTTP/2 the
initial value is 2^14 (16,384) octets. Somewhat
counterintuitively, IoT hosts may wish to leave this value large
and rely on flow control to avoid unnecessary framing overhead.
o SETTINGS_MAX_HEADER_LIST_SIZE: this setting allows hosts to limit
the maximum size of the header list they are willing to receive.
Per HTTP/2 the initial value of this setting is unlimited. IoT
scenarios may wish to limit this to smaller values in accordance
with the node's constraints (e.g., a few kilo-octets).
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6. Negotiation of HTTP/2 for IoT
For Constrained and Internet scenarios, it is assumed that HTTP/2
runs over TLS. Accordingly, the ALPN negotiation in section 3.3 of
[RFC7540] applies. As seen above, an IoT scenario may wish to depart
from the default SETTINGS. To do so, the usual SETTINGS negotiation
applies. In this case, the initial SETTINGS negotiation setup is
based on the first message exchange initiated by the client. This is
simpler than general HTTP/2 case: not having an in-the-clear Upgrade
path means the client is always in control of first HTTP/2 message,
including any SETTINGS changes it may wish.
Additionally, the use of "prior knowledge" per section 3.4 of
[RFC7540] is likely to also work particularly well in IoT scenarios
in which a client and its web service are likely to be closely
matched. In such scenarios, prior knowledge may allow for SETTINGS
to be set in accordance with some shared state implied by the the
prior knowledge. In such cases, SETTINGS negotiation may not be
necessary in order to depart from the defaults as defined by HTTP/2.
7. Gateway and Proxying Issues
The proliferation of application and security protocols in the IoT
has produced the deployments of islands of IoT devices, each using
one of the several protocols available. However, usually an IoT
deployment needs to communicate to another one, or at least needs to
communicate with the Web, both because they have to upload data to
the Cloud or because usually they are controlled by a Web
application.
In such cases, communication is facilitated by a cross-protocol proxy
or a gateway translating from one protocol syntax and semantic into
another one. However, the presence of Cross-Protocol or Application
gateways has at least two main drawbacks that need to be analyzed and
addressed carefully.
o while the translation may be trivial for the basic scenarios,
there are a lot of cases where the translation can lead to
information loss or an incompatibility due to the different way
different proxies make the translation.
o The presence of such devices may also become a critical point for
security.
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8. Implementation Considerations
This section assumes HTTP/2 over TCP.
In addition to underlying stack considerations with respect to IPv4,
IPv6, TCP, and TLS, there are implementation considerations for
HTTP/2 for IoT.
A primary consideration is the number of allowed simultaneous HTTP/2
connections. As each connection has associated overhead, as well as
overhead for each stream, constrained hosts may wish to limit their
number of simultaneous connections. However, implementers should
consider that some popular browsers require more than one connection
to operate.
In addition to minimizing the number of simultaneous connections,
hosts should consider leaving connections open if there is a
possibility of further communication with the remote peer. HTTP/2
contains mechanisms such as PING to periodically check idle
connections. Leaving established connections open when there is a
possibility of future communication allows connection establishment
overhead (and potentially TLS session establishment overhead) to be
avoided.
Should TLS be used, implementers may wish to consider utilizing
hardware-based encryption to further reduce codespace and RAM
requirements.
9. Experimentation and Performance
This section presents some simple results obtained using the
Deuterium HTTP/2 library [Deuterium] and is not intended to be
complete, but rather a start for discussion. From an IoT
perspective, the reduced message sizes presented help to conserve
both bandwidth and battery life, as well as potentially saving some
memory/buffer space.
The results presented in this section make the following assumptions
and considerations:
o Overhead from TCP and TLS are ignored
o An attempt to minimize the headers used has been made while still
maintaining RFC compliance
o No entries are made into the HTTP/2 dynamic table, thus removing
some potential optimization
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o Connection establishment and teardown have been ignored, though
clearly these are important considerations for IoT application
protocols
o Only happy path transmissions are shown, thus no comparison of
failure modes or retransmissions is given
9.1. GET Example
This first example compares and contrasts a GET method to a resource
containing an XML representation of a simple switch using HTTP/1.1
and HTTP/2.
9.1.1. HTTP/1.1
1. Client sends (47 octets):
4745 5420 2f6f 6e6f 6666 2048 5454 502f 312e 310d
0a48 6f73 743a 2066 6f6f 0d0a 4163 6365 7074 3a20
2a2f 2a0d 0a0d 0a
In ASCII:
GET /onoff HTTP/1.1\r\n
Host: foo\r\n
Accept: */*\r\n
\r\n
2. Server sends (107 + 36 octets):
4854 5450 2f31 2e31 2032 3030 204f 4b0d 0a44 6174
653a 204d 6f6e 2c20 3039 204d 6172 2032 3031 3520
3036 3a32 363a 3434 2047 4d54 0d0a 436f 6e74 656e
742d 4c65 6e67 7468 3a20 3336 0d0a 436f 6e74 656e
742d 5479 7065 3a20 6170 706c 6963 6174 696f 6e2f
786d 6c0d 0a0d 0a
3c4f 6e4f 6666 3e0a 093c 7374 6174 653e 6f66 663c
2f73 7461 7465 3e0a 3c2f 4f6e 4f66 663e
In ASCII:
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HTTP/1.1 200 OK\r\n
Date: Mon, 09 Mar 2015 06:26:44 GMT\r\n
Content-Length: 36\r\n
Content-Type: application/xml\r\n
\r\n
<OnOff>\n
\t<state>off</state>\n
</OnOff>
9.1.2. HTTP/2
1. Client sends (34 octets):
0000 1901 0500 0000 01
8286 0585 60f5 1e59 7f01 8294 e70f 0489 f963 e7ef
b401 5c00 07
Representing:
:method: GET
:path: /onoff
:scheme: http
:authority: foo
accept: */*
2. Server sends (54 octets):
0000 2d01 0400 0000 01
880f 1296 d07a be94 03ea 681d 8a08 016d 4039 704e
5c69 a531 68df 0f10 8b1d 75d0 620d 263d 4c79 a68f
0f0d 8265 cf
Representing:
:status: 200
content-type: application/xml
content-length: 36
date: Mon, 09 Mar 2015 06:26:44 GMT
3. Server sends (45 octets):
0000 2400 0100 0000 01
3c4f 6e4f 6666 3e0a 093c 7374 6174 653e 6f66 663c
2f73 7461 7465 3e0a 3c2f 4f6e 4f66 663e
Representing:
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<OnOff>
\t<state>off</state>
</OnOff>
9.1.3. Comparison
In total and ignoring the payload (36 octets), the HTTP/2 flow is 37%
smaller than the HTTP/1.1 flow.
The use of additional headers, particularly common headers that are
present in the HTTP/2 static table, will result in greater savings.
While not compared here, HTTP/2's ability to reuse connections for
multiple streams reduces connection establishment overhead, such as
TCP connection establishment and TLS session establishment.
10. HTTP/2 over UDP - QUIC
QUIC (Quick UDP Internet Connections) is a new multiplexed transport
protocol designed to run in user space above UDP, optimized for
HTTP/2 semantics. In this document, "QUIC" refers to the upcoming
IETF standard. The protocol is still in its early days and the
standardization work in IETF has just started.
QUIC provides functionality already present in TCP and HTTP/2
o connection semantics, reliability, and congestion control
equivalent to TCP.
o multiplexing and flow control equivalent to HTTP/2
Where functionality is similar to that of existing protocols, it has
been re-designed to be more efficient. For example, the native
multistream provides multiplexing without the head-of-line blocking
inherent to HTTP/2 over TCP.
QUIC will use DTLS 1.3. Accordingly, connections will commonly
benefit from 0-RTT as defined by TLS 1.3, meaning that on most QUIC
connections, data can be sent immediately without waiting for a reply
from the server. Furthermore, packets are always authenticated and
typically the payload is fully encrypted.
QUIC has been designed to provide richer information to congestion
control algorithms than TCP, moreover the actual congestion control
is plugable in QUIC.
Even if QUIC has been initially designed with HTTP/2 as the primary
application protocol to support, it is meant to become a modern
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general-purpose transport protocol. The IETF standardization effort
will also focus on describing the mapping of HTTP/2 semantics using
QUIC specifically with the goal of minimizing web latency using QUIC.
This mapping will accommodate the extension mechanisms defined in the
HTTP/2 specification.
QUIC also dictates that packets should be sized to fit within the
path's MTU to avoid IP fragmentation. However path MTU discovery is
work in progress, and the current QUIC implementation uses a
1350-byte maximum QUIC packet size for IPv6, 1370 for IPv4.
Judging from its current state, QUIC may bring some potential
benefits like the possibility to design and use a specific congestion
control algorithm suited to IoT scenarios and possibility to reduce
header overhead as compared to that of TCP plus HTTP/2. The latter
is possible since these two layers are more integrated in QUIC.
11. IANA Considerations
This document has no considerations for IANA.
12. Security Considerations
Section 1 and Section 3 above point out security issues in the
current IoT landscape, namely, the additional attack vectors from
having several bespoke stacks instead of one mainstream stack and
protocols. This document seeks to improve security of the IoT by
encouraging use of mainstream protocols which are better understood
and more thoroughly debugged (both in their specifications as well as
in their implementations).
Section 7 point out another issue with the current IoT landscape: the
proliferation of gateways and proxies. Whereas they serve useful
functions in IoT, allowing more constrained nodes to have much lower
duty cycles or filtering them from much traffic, there are inherent
security issues, not the least of which is that they break end-to-end
security. Enabling more mainstream protocols would not preclude
using a proxy or gateway whenever the tradeoff dictated it, but would
also allow for end-to-end security.
Given the security challenges in IoT scenarios, HTTP/2 is assumed to
use TLS services. In Internet scenarios, [RFC7540] has clear
guidance in this respect. In Constrained network scenarios, the
guidance for IoT is [I-D.ietf-dice-profile]. However, these are
currently at odds. For example, Section 4.2 of
[I-D.ietf-dice-profile] mandates the ciphersuite
TLS_PSK_WITH_AES_128_CCM_8 for preshared key-based authentication
(quite common in IoT deployments). On the other hand, Appendix A of
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[RFC7540] includes TLS_PSK_WITH_AES_128_CCM_8 in the HTTP/2 Black
List of disallowed cipher suites, despite it being an AEAD
ciphersuite. This is still to be resolved. The other IoT
ciphersuite mandated by [I-D.ietf-dice-profile], namely,
TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 (used for both certificate-based
and Raw Public Key-based authentication) is not on the HTTP/2 Black
List.
13. Acknowledgements
Thanks to the following individuals for helpful comments and
discussion: Brian Raymor, Dave Thaler, Ed Briggs.
This document was produced using the xml2rfc tool [RFC2629][RFC7749].
14. References
14.1. Normative References
[I-D.ietf-dice-profile]
Tschofenig, H. and T. Fossati, "TLS/DTLS Profiles for the
Internet of Things", draft-ietf-dice-profile-17 (work in
progress), October 2015.
[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>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.
[RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Conditional Requests", RFC 7232,
DOI 10.17487/RFC7232, June 2014,
<http://www.rfc-editor.org/info/rfc7232>.
[RFC7233] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"Hypertext Transfer Protocol (HTTP/1.1): Range Requests",
RFC 7233, DOI 10.17487/RFC7233, June 2014,
<http://www.rfc-editor.org/info/rfc7233>.
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[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014,
<http://www.rfc-editor.org/info/rfc7234>.
[RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Authentication", RFC 7235,
DOI 10.17487/RFC7235, June 2014,
<http://www.rfc-editor.org/info/rfc7235>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<http://www.rfc-editor.org/info/rfc7540>.
[RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for
HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
<http://www.rfc-editor.org/info/rfc7541>.
14.2. Informative References
[Clapper] "US intelligence chief: we might use the internet of
things to spy on you", February 2016,
<http://www.theguardian.com/technology/2016/feb/09/
internet-of-things-smart-home-devices-government-
surveillance-james-clapper>.
[CoAP_integration]
Giang, N., Ha, M., and D. Kim, "SCoAP: An integration of
CoAP protocol with web-based application", Proc. IEEE
GLOBECOM , 2013.
[Deuterium]
Simpson, R., "Deuterium HTTP/2 Library", June 2016,
<http://robbysimpson.org/deuterium/>.
[Eclipse_survey]
Eclipse Foundation, "IoT Developer Survey", April 2016,
<http://iot.ieee.org/images/files/pdf/
iot-developer-survey-2016-report-final.pdf>.
[Going_Dark]
"Dont Panic: Making Progress on Going Dark Debate",
February 2016, <https://cyber.law.harvard.edu/pubrelease/
dont-panic/
Dont_Panic_Making_Progress_on_Going_Dark_Debate.pdf>.
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[I-D.aggarwal-dnssd-optimize-query]
Aggarwal, A., "Optimizing DNS-SD query using TXT records",
draft-aggarwal-dnssd-optimize-query-00 (work in progress),
July 2014.
[I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE)", draft-ietf-ace-oauth-
authz-02 (work in progress), June 2016.
[IEEE_survey]
Al-Fuqaha, A., Guizani, M., Mohammadi, M., Aledhari, M.,
and M. Ayyash, "Internet of Things: A Survey on Enabling
Technologies, Protocols, and Applications", IEEE
Communication Surveys and Tutorials , November 2015.
[IoT_analysis]
Colina, M., Bartolucci, M., Vanelli-Coralli, A., and G.
Corazza, "Internet of Things application layer protocol
analysis over error and delay prone links", Proc. ASMS/
SPSC Conference , 2014.
[mqtt_iso]
ISO, "ISO/IEC 20922:2016 Information technology -- Message
Queuing Telemetry Transport (MQTT) v3.1.1", June 2016,
<http://www.iso.org/iso/
catalogue_detail.htm?csnumber=69466>.
[mqtt_oasis]
OASIS, "MQTT Version 3.1.1 becomes an OASIS Standard",
October 2014, <https://www.oasis-
open.org/news/announcements/mqtt-version-3-1-1-becomes-an-
oasis-standard>.
[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,
<http://www.rfc-editor.org/info/rfc2616>.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
DOI 10.17487/RFC2629, June 1999,
<http://www.rfc-editor.org/info/rfc2629>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<http://www.rfc-editor.org/info/rfc6762>.
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[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<http://www.rfc-editor.org/info/rfc6763>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
[RFC7452] Tschofenig, H., Arkko, J., Thaler, D., and D. McPherson,
"Architectural Considerations in Smart Object Networking",
RFC 7452, DOI 10.17487/RFC7452, March 2015,
<http://www.rfc-editor.org/info/rfc7452>.
[RFC7749] Reschke, J., "The "xml2rfc" Version 2 Vocabulary",
RFC 7749, DOI 10.17487/RFC7749, February 2016,
<http://www.rfc-editor.org/info/rfc7749>.
[Web_things]
Lerche, C., Laum, N., Golatowski, F., Timmermann, D., and
C. Niedermier, "Connecting the web with the web of things:
lessons learned from implementing a CoAP-HTTP proxy",
Proc. IEEE MASS , 2012.
Authors' Addresses
Gabriel Montenegro
Microsoft
Email: Gabriel.Montenegro@microsoft.com
Sandra Cespedes
NIC Chile Research Labs, Universidad de Chile
Email: scespedes@ing.uchile.cl
Salvatore Loreto
Ericsson
Email: salvatore.loreto@ericsson.com
Robby Simpson
General Electric
Email: rsimpson@gmail.com
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