Internet DRAFT - draft-joseph-quic-comparison-quic-sctp
draft-joseph-quic-comparison-quic-sctp
QUIC working group A. Joseph
Internet-Draft T. Li
Intended status: Informational UCLA
Expires: September 6, 2018 Z. He
Y. Cui
Tsinghua University
L. Zhang
UCLA
March 5, 2018
A Comparison between SCTP and QUIC
draft-joseph-quic-comparison-quic-sctp-00
Abstract
To cumulate design lessons from our protocol development efforts,
this document provides a preliminary comparison between two transport
protocol designs, Stream Control Transport Protocol (SCTP) and Quick
UDP Internet Connections (QUIC). We identify their commonalities and
differences, summarize the characteristics of QUIC which we believe
represent progresses in transport protocol designs. We hope this
draft useful in helping others to gain further understanding of both
SCTP and QUIC, and in future protocol design efforts.
Status of This Memo
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This Internet-Draft will expire on September 6, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. A High Level Overview of the Two Protocols . . . . . . . . . 4
3.1. SCTP . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. QUIC . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. A Comparative Examination of Specific Protocol Mechanisms . . 5
4.1. Packet Structure . . . . . . . . . . . . . . . . . . . . 5
4.1.1. SCTP . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1.2. QUIC . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Connection Setup . . . . . . . . . . . . . . . . . . . . 8
4.2.1. SCTP . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2.2. QUIC . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. Substreams . . . . . . . . . . . . . . . . . . . . . . . 11
4.3.1. SCTP . . . . . . . . . . . . . . . . . . . . . . . . 12
4.3.2. QUIC . . . . . . . . . . . . . . . . . . . . . . . . 12
4.4. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 13
4.4.1. SCTP . . . . . . . . . . . . . . . . . . . . . . . . 14
4.4.2. QUIC . . . . . . . . . . . . . . . . . . . . . . . . 14
4.5. Reliability and Congestion Control . . . . . . . . . . . 14
4.5.1. SCTP . . . . . . . . . . . . . . . . . . . . . . . . 15
4.5.2. QUIC . . . . . . . . . . . . . . . . . . . . . . . . 16
4.6. Flow Control . . . . . . . . . . . . . . . . . . . . . . 17
4.6.1. SCTP . . . . . . . . . . . . . . . . . . . . . . . . 18
4.6.2. QUIC . . . . . . . . . . . . . . . . . . . . . . . . 18
4.7. Connection Teardown . . . . . . . . . . . . . . . . . . . 19
4.7.1. SCTP . . . . . . . . . . . . . . . . . . . . . . . . 19
4.7.2. QUIC . . . . . . . . . . . . . . . . . . . . . . . . 19
4.8. Other Differences between QUIC and SCTP . . . . . . . . . 19
5. Current Situations of SCTP and QUIC . . . . . . . . . . . . . 20
6. Conclusions from the comparison . . . . . . . . . . . . . . . 20
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 22
8. Informative References . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
Quick UDP Internet Connections (QUIC) builds upon the design lessons
learned from many existing protocols. The purpose of this draft is
to draw parallels and display differences between the two transport
protocols, Stream Control Transport Protocol (SCTP) and Quick UDP
Internet Connections (QUIC), with a hope to gain deeper insight from
the comparison, extract general lessons, and trends.
As such, this draft is not intended to be a deep dive into the inner
working details of the protocols, but rather a high level view of
similar core functionality and mechanisms of the protocols. These
two protocols were developed years apart and for very different
purposes, however as transport protocols they share a number of
similarities. However it should be noted that at the time of this
writing, the QUIC specification is still under active development.
This means that parts of the specifications are still incomplete or
missing at this time. This draft focuses on what has been documented
so far; the reader should keep in mind that the QUIC protocol might
have changed after the time of this draft's publication.
2. Background
The SCTP protocol was originally developed in year 2000 to transport
Public Switched Telephone Network (PTSN) signaling messages over IP;
it was later adapted to be a general purpose transport protocol
[RFC4960]. The motivation of developing a new transport protocol
came from perceived drawbacks of using TCP for transmitting PTSN
messages: HOL-Blocking, lack of host multi-homing support, mismatch
between TCP's byte-stream data model and PTSN applications's message-
oriented communication, and TCP's vulnerability to SYN attacks. SCTP
uses multiple substreams to mitigate HOL blocking, enables each
transport connection to utilize multiple interfaces, and reliably
delivers application messages instead of byte streams.
The development of the QUIC protocol was started by Jim Roskind's
team at Google in 2012, aiming to remove identified performance
bottlenecks in transport protocols. As Internet bandwidths continue
to increase due to technology advances and infrastructure buildout,
the Round Trip Time (RTT) became a physical upper bound of the speed
of light. The existing transport protocols take multiple RTTs to
deliver a web page's contents [QUIC-DESIGN]. Using multiple TCP
connections to improve performance has its own limitations: it forces
client applications to bind to many different sockets to send out
multiple separate requests, resulting in redundant connection setup
and bandwidth wastage as well as inefficient allocation of computer
resources. QUIC developed an innovative design for connection setup
that integrates transport protocol and TLS functions to minimize RTT.
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Similar to STCP, QUIC developed support for multiple substreams
instead of using multiple transport connections[QUIC-DESIGN]. QUIC's
predecessor was another transport protocol from Google called SPDY,
which ran over a single TCP connection and routinely with SSL
[QUIC-DESIGN]. The lessons learned from SPDY drove many of the
design decisions for QUIC, including the decision to run over UDP
instead of TCP to avoid TCP's HOL-Blocking, an innovative congestion
control scheme, and considerations for mobile devices in connection
teardown [QUIC-DESIGN].
3. A High Level Overview of the Two Protocols
3.1. SCTP
A SCTP connection is comprised of an association between two
endpoints, each is defined by a set of IP addresses and a port
number. A SCTP connection is referred to as an association so the
rest of this draft will use this term. While a primary IP address is
used for each endpoint, each end may inform the other end a set of
addresses it may use to transmit packets. Moving away from TCP's
approach of one-header-fitting-all, STCP designed multiple separate
data structures called "chunks" to carry association control
information and applications data messages. SCTP communicates with
an Upper Layer Protocol (ULP) through the use of message primitives
ASSOCIATE and SHUTDOWN. These primitives are how applications are
able to communicate with SCTP to setup and teardown association.
SCTP supports multiple message substreams by letting each of the two
endpoints negotiate with the other on the number of substreams they
can support at the association setup time, and ensures in-order
delivery of messages in substream to the ULP through the use of a
substream sequence number. To provide reliable message delivery for
all substreams, SCTP assigns each data chunk a unique Transmission
Sequence Number (TSN). Note that the TSN is on per association
basis, not per substream. It works in an identical way to TCP
sequence number in ensuring reliable delivery, except that the former
names a data chunk while the latter a data byte. A data may contain
either a data message, or a segment of a data message. SCTP uses the
same congestion avoidance and control mechanisms as TCP, and similar
selectively acknowledgement scheme, except that it designed a
dedicated SACK chunk, as opposed to TCP's use of its option field for
SACK.
3.2. QUIC
A QUIC connection is comprised of an association between two
endpoints defined by a pair of IP address and port number (at the
time of this writing, QUIC's multihoming/multipath support is still
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under development). The IP addresses and ports can change in the
middle of a connection. A fundamental difference between QUIC and
TCP or SCTP is that QUIC is a user space transport protocol, which
allows rapid protocol revision without having to wait for system
upgrades. To support rapid protocol revision, QUIC's connection
setup goes through a negotiation process that involves determining
the lowest common version supported between the two endpoints and a
cryptographic handshake which incorporates TLS to provide a secure
connection.
Within a QUIC connection, substreams can be started at any time,
excluding tear down phase. Either endpoint can start a substream,
which can be either bidirectional or unidirectional. QUIC inherits
TCP's byte stream data model. Dedicated control structures called
"frames" are used to communicate with and carry byte data to
endpoints.
Similar to SCTP, QUIC has a dedicated SACK frame to carry selective
acknowledgement, although the semantics of QUIC SACK differs from
that of SCTP in important ways. SACK informs which packets are
delivered to the other end; un-ACKed packets are considered lost. No
QUIC packet is ever retransmitted, packet numbers always increases
monotonically. From each received SACK frame, a QUIC endpoint can
infer which byte frames have been received by the other end. To
ensure reliable in-order data delivery of each byte stream to the
application, the sender will retransmit the byte frames that are not
acknowledged. The new frames may repackage the missing byte offsets.
As another difference from SCTP, QUIC practices flow control both on
a connection basis and on per substream basis, by advertising the max
amount of data allowed on a connection, as well as per stream. If an
endpoint transmits more than advertised, the entire connection is
torn down.
4. A Comparative Examination of Specific Protocol Mechanisms
4.1. Packet Structure
The packet structures of both SCTP and QUIC break away from TCP's
one-header-fits-all design. Instead, they used dedicated control
chunks for connections setup, teardown and SACK.
4.1.1. SCTP
The SCTP [RFC4960] packet structure contains a common header
(Figure 1) with attached DATA chunks (Figure 2) which is analogous to
QUIC's Short Header (Figure 3) and STREAM frames (Figure 4). The
common header contains fields for the set of source and destination
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IP addresses and ports, verification tag, and a checksum of the
packet. The DATA chunk has a type and reserved fields of 0. The U
bit set to 1 indicates that the data is unordered and the value in
the Stream Sequence Number (SSN) can be ignored. The SSN indicates
what number message the chunk contains for the related Stream, and
also determines the order the messages will be delivered to the ULP
(unless it is meant to be unordered). SSN always starts from 0 and
increments up to 65535 with wrap around. The Transmission Sequence
Number (TSN) enumerates the Chunks attached to the common header and
increment sequentially with wrap around over the lifetime of an
association. TSNs range from 0 to 4294967295, and can start at a
random value in the range. TSNs are repeated during retransmission
of packets to ensure reliable delivery. The Length field indicates
the length of the DATA Chunk including the 16 bytes of the fields
starting from the Type field. The Stream identifier is the number
identifying the stream the chunk belongs to. The Payload Protocol
Identifier is not relevant for the purposes of this paper and is not
used by the SCTP protocol itself, but is intended for use by
middleboxes. The User Data field contains user data which is padded
at the end to a 4 byte boundary of all-zero bytes.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Chunk #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Chunk #n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SCTP Packet Structure
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0 | Reserved|U|B|E| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Identifier S | Stream Sequence Number n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Protocol Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| User Data (seq n of Stream S) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SCTP DATA Chunk
4.1.2. QUIC
The QUIC packet structure consists of a common header called a short
header (Figure 3) and attached Frames in the protected payload
(Figure 4). A user data payload bearing packet sent after connection
is set up is called a STREAM frames (Figure 4), analogous to SCTP's
DATA Chunks (Figure 2), and is the primary frame used for data
transfer [QUIC-TRANSPORT]. The Type field indicates the type of
Frame it is: the range 0x10-0x17 indicates a STREAM Frame. The lower
three bites of the Type field also encode whether certain fields are
in the frame. 0x04 is the OFF bit, if set to 1, there is an offset
field, if set to 0, the frame starts from byte offset of 0 or there
is no data. 0x02 is the Length bit, if set to 1, there is a length
field, if set to 0, the length of the data extends to the end of the
packet. Finally the 0x01 is the FIN bit, if set to 1, it is the
final frame in a stream [QUIC-TRANSPORT]. The Stream ID identifies
the stream the frame belongs to, as well as if the stream is
bidirectional or unidirectional and if the server or the client
created the stream. If the second least significant bit is 1, the
stream is unidirectional, if it is 0, the stream is bidirectional.
If the least significant bit is 1, the server initiated the stream,
if it is 0, the client initiated the stream. The offset field
indicates the byte offset that the STREAM Frame is carrying, and the
length field indicates the length of the stream data. There can be
multiple STREAM Frames per QUIC packet/header. [QUIC-TRANSPORT]
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
|0|C|K| Type (5)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ [Connection ID (64)] +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet Number (8/16/32) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protected Payload (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Short Header
0 1 2 3
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Type (8) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream ID (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Offset (i)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Length (i)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Data (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: STREAM Frame
4.2. Connection Setup
For connection setup, SCTP adopts the 4-way handshake with digitally
signed state cookie for preventing denial-of-service attacks (SYN-
flooding). The state cookie is sent by the server in response to the
client's INIT message, and contains all of the state that the server
needs to ensure that the association is valid, including Message
Authentication Code (MAC) [RF2104], a timestamp, and the cookie
lifespan. The cookie contains all the information needed for SCTP
association setup, so the server's SCTP stack does not need to keep
information about the associating client.
For connection setup, QUIC directly incorporates TLS key negotiation
process with the transport handshake, establishing secure connection
using 1-RTT with successful version negotiation, and 0-RTT for
connection resumptions. During initial connection setup, the server
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gives the client a cryptographic cookie known as Source Address Token
(client IP and timestamp) for source address validation. It also
sends the Server Config containing the server's long-term Diffie-
Hellman public value and server preference. These information can be
used for subsequent connections. This provides a secure and
efficient way for establishing connections, yet unlike traditional
syn-cookies for preventing syn-flood attack which are designed for
single use, QUIC's longterm cookies might bring potentials for new
types of attacks (e.g. replay attack). QUIC server also adopts
stateless address validation, the cookie stores all state necessary
to continue the connection.
4.2.1. SCTP
While SCTP is similar to TCP where a connection is defined by a pair
IP addresses and port numbers, SCTP is slightly different by defining
a set of possible IP addresses and port numbers in its common header.
This is to facilitate SCTP's multihoming features, since messages can
be sent or received at any of these addresses, even though there is a
primary address specified. A normal SCTP association begins when an
endpoint "A" sends an INIT chunk to the other endpoint. The INIT
chunk (Figure 5) will contain a Verification Tag value which is a
random number between the range of 1 and 4294967295. The
Verification Tag can be used as the initial TSN as well. The other
endpoint "Z" will respond with an INIT ACK chunk containing its own
Verification Tag as well as as generating and sending a State Cookie
back. Endpoint "A" will then respond with a COOKIE ECHO chunk which
might contain DATA chunks as well. Endpoint "Z" will acknowledged
the COOKIE ECHO with a COOKIE ACK chunk, which can also be bundled
with other DATA chunks. The ULP of each of the endpoints will then
be notified that a successful association has been established.
Within the INIT and INIT ACK chunks that were sent by each endpoint,
the number of outbound and inbound streams accepted by each endpoint
were communicated. The endpoints will take the minimum of each of
their preferred outbound streams and the minimum inbound stream of
the other endpoint, minus 1: min(local outbound stream, remote
minimum inbound streamC) - 1. All SCTP substreams are
unidirectional. The State Cookie that is sent out during connection
setup contains a Message Authentication Code (MAC) [RF2104], a
timestamp and the lifespan for the cookie. The entire SCTP
association setup results in a 4-way handshake in order to avoid a
SYN-flood situation. Once a connection is set up, it is possible
that SCTP will fragment its chunks in order to avoid IP
fragmentation. Fragmentation is done by a source host only and the
peer endpoint will reassemble once it is received.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 | Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initiate Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertised Receiver Window Credit (a_rwnd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Outbound Streams | Number of Inbound Streams |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initial TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ Optional/Variable-Length Parameters /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: SCTP INIT Chunk
4.2.2. QUIC
A normal QUIC connection begins with version negotiation between two
endpoints. An Initial packet with a long header is sent out by a
client to determine if both endpoints support the same version of
QUIC. The Version Negotiation packet (Figure 6) is sent by the
server if the client that sent out the initial packet is attempting
to create a new connection and the client's version is not accepted
by the server. If the Initial packet's version is supported by the
server or the client responds to the server's Version Negotiation
packet with a supported version, the handshake process continues.
After a version is settled on by both endpoints, the transport and
cryptographic handshake begins. Stream 0, is a reserved substream
that is used for the cryptographic handshake process. The current
version of QUIC uses TLS 1.3 to encrypt the connection and
authenticate the server and optionally authenticate the client. QUIC
is able to reduce handshake delay caused by RTT by combining the
transport and cryptographic handshake together to provide a secure
connection from the start of a connection. QUIC embeds the TLS
functionality within the protocol itself, without having to run a
separate TLS handshake and session after the transport handshake.
During the cryptographic handshake, each endpoint advertises
transport parameters that define the initial parameters for the
connection. These transport parameters includes values that
determine the maximum amount of data that can be transmitted per
stream, as well as per connection data maximums. These values are
updated during the lifetime of a connection to facilitate flow
control. Once a connection is established, substreams can be created
during any point of the connection lifetime. QUIC also supports both
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unidirectional and bidirectional substreams which is determined
during sub stream setup.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
|1| Unused (7) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Connection ID (64) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version (32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Supported Version 1 (32) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Supported Version 2 (32)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Supported Version N (32)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: QUIC Version Negotiation Packet
4.3. Substreams
One of the major features of both of these protocols are multiplexed
streams. An issue with TCP is that a dropped packet can block
message delivery for all application-level streams since TCP uses a
single-byte stream abstraction. This blockage is called Head-of-Line
Blocking. SCTP and QUIC solve for this by supporting multiplex
streams within the protocol itself. If a dropped packet occurs for
either protocol, in-order messages/byte streams can still be
delivered for other streams if they are available.
SCTP intended to get rid of HOL-Blocking by substreams, but its
Transmission Sequence Number (TSN) couples together the transmission
of all data chunks. For SCTP, each packet contains different data
chunks from different streams identified by Stream ID (SID), if the
data chunk of one streams is lost, the data of other streams should
still be received by the application. However, a TSN is assigned to
every data chunk in the association. For SCTP Cumulative ACK, the
value of the Cumulative TSN ACK parameter is the last TSN received
before a break in the sequence of received TSNs. The next TSN value
following this one has not yet been received at the endpoint sending
the SACK. This parameter therefore acknowledges receipt of all TSNs
less than or equal to its value. As a result, in SCTP if a packet is
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lost, all the packets with TSN after this lost packet cannot be
received until it is retransmitted.
QUIC adopts two levels of numbering. User data is uniquely
identified by stream ID and offset, it also has a monotonically
increasing packet sequence number.The packet sequence number is used
for congestion control and loss detection and it numbers all the
packets (SCTP don't number control packets). QUIC selective ack,
acknowledges packet sequence number of the last received packet, and
QUIC retransmits the lost packet using a new sequence number. As a
result, the congestion window could open up for more packets, and the
lost packet does not affect the packets following it from being
received, thus avoiding the HOL-Blocking problem. However, as QUIC
SACK tells which packets get lost but does not retransmit the lost
packet, QUIC has to keep internal mapping of which stream frame in
which packet, to know which one needs to be retransmitted, which
introduces additional processing.
4.3.1. SCTP
SCTP substream setup requires the number of substreams as well as
their Stream IDs be declared at association setup. SCTP does not
have the functionality to start streams during a association since it
does not differentiate between client-initiated and server-initiated
streams. Additionally, streams persist through the lifetime of an
active association. SCTP's INIT Chunk declares two fields, Number of
Outbound Streams (OS) and Number of Inbound Streams (NIS), to help
negotiate the number of streams to be created during an association.
The number of streams is not negotiated in the traditional sense, but
instead the minimum of the requested streams and offered streams is
taken. For example, if a receiver advertises 6 streams in its MIS
field, and a sender advertises 12 streams in its OS field, the number
of streams to the receiver will be 6. If either of these fields is
set to 0, the association will be aborted. If a sender is limited to
less streams than was requested, it can communicate to its
application layer it failed to secure the number of streams that was
required, and the application can decide to continue the association
or abort it. SCTP substreams are only unidirectional and each
stream's sequence number must start from 0. Since streams are
created during association setup, if the number of streams needs to
be changed, the association needs to be torn down and re-setup.
4.3.2. QUIC
QUIC has the functionality to start or teardown a substream during
any point of the connection (aside from connection teardown). The
parity of the Stream ID allows QUIC to spawn new substreams on either
the client or server side without the need to undergo negotiations
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between each side to decide on an ID. Since parity is decided by the
least significant bit, a client only picks even Stream IDs, and the
server only picks odd Stream IDs. QUIC substreams support
unidirectional and bidirectional streams which is determined by
setting the second to least significant bit in the Stream ID. The
bit reservations allow for streams to be started at anytime during
the lifetime of a connection without the need for negotiation. Each
endpoint is restricted to their own non-overlapping range of IDs,
thus canceling out the need to negotiate for an ID in order to avoid
conflicts.The protocol defines several transport parameters and
frames to define and control the behavior of the streams. The
MAX_STREAM_DATA frame is advertised by the receiver to flow control
individual streams. If a peer attempts to send more data than is
advertised, the connection is terminated. MAX_STREAM_ID is a similar
frame advertised by the receiver to indicate the maximum number of
streams allowed on the connection. If a peer attempts to start a
stream with a Stream ID higher than the advertised maximum, the
connection is terminated. The sender can communicate with the
receiver that it is unable to send more data, or start a new stream
through STREAM_BLOCKED and STREAM_ID_BLOCKED frames respectively.
The receiver can advertise new data and stream limits any time during
a connection and is bound to honor these limits, e.g. a receiver
cannot advertise a higher limit and refuse it once a sender starts
sending. An important implementation note is that if a QUIC packet
is dropped, every stream that was in that packet is blocked. It is
up to the QUIC implementation to determine the number of streams to
be sent per packet to limit the occurrences of HOL-Blocking. QUIC
needs to balance sending data for all its dream with the chance of
stream blockage when a dropped packet occurs. Once an endpoint of a
stream has finished transmitting its data, it will set the FIN bit on
its last STREAM frame or the frame after the last STREAM frame to
indicate the stream is closed in the direction of the endpoint,
resulting in a half closed stream. Once both endpoints have sent
STREAM frames with the FIN bit set, the stream is fully closed.
4.4. Fragmentation
For data model, SCTP uses application-defined messages. However,
QUIC adopts the bidirectional byte stream model of TCP, the reasoning
of which is probably the desire of close coupling with HTTP/2 that
was originally designed to run over TCP. Consequently, not only does
it facilitate the movement of applications from TCP to QUIC, but also
liberates QUIC from message fragmentation that SCTP has to take care
of.
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4.4.1. SCTP
In order to avoid IP fragmentation, SCTP fragments its own chunks, so
that its packets can fit under the Path MTU [QUIC]. Since SCTP
relies on messages as its unit of data, it needs to determine how to
fragment and reassemble its payload to keep the rest of the protocol
functioning, meaning it needs to keep its headers unfragmented and
handle reassembly of the data once it is received. SCTP achieves
this by utilizing bit flags in the DATA Chunk header and numeric
values in its TSN and SSN fields. The B bit set to 1 indicates that
the chunk is the first fragment of a user message. The E bit set to
1 indicates that the chunk is the last fragment of a user message.
If both B and E are set to 1, then the message is not fragmented. If
both B and E are set to 0, then the chunk is a middle fragment of the
user message. The TSN field indicates the Transmission Sequence
Number of the DATA Chunk which is used to identify and acknowledge
successfully received Chunks. Each DATA Chunk in a packet shares a
different sequential TSN and SSN, whereas each fragmented DATA Chunk
must also shares a different sequential TSN, but the same SSN among
the fragmented DATA Chunks containing the same message. A receiver
will then be able to acknowledge all the Chunks it received with its
corresponding TSN, and rebuild the underlying messages by matching
DATA Chunks with payloads sharing the same SSN.
4.4.2. QUIC
A QUIC packet must contain whole frames, and not have frames split up
between packets. A QUIC packet must fit under the Path MTU
[QUIC-TRANSPORT]. QUIC can resize packets without the need of
complex mechanisms to track fragments of messages like in SCTP since
every QUIC data payload is just a byte stream and is easily
adjustable through changing byte offset field in the STREAM Frame.
There is no message to fragment since the data is already at its most
granular form. The actual size of a QUIC packet is determined by
implementation of the protocol and how the application using it
behaves. The current draft does not go into much detail on how to
pack QUIC packets with frames aside from recommending to pack as many
frames as possible to minimize per-packet bandwidth and computational
cost [QUIC-TRANSPORT]. However a balance needs to occur. If there
are too many frames in a packet, and the packet is lost, all those
streams are blocked, if there are too little frames, there is
increased per-packet bandwidth and computational cost.
4.5. Reliability and Congestion Control
Reliable delivery in transport protocols is defined as providing the
abstraction of guaranteeing delivery of every message on an active
connection . Congestion control is defined to be how an endpoint
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limits the number of messages it sends out on a network in order to
prevent the network from becoming clogged and dropping packets. QUIC
and SCTP both provide reliable delivery as well as forms of
congestion control. SCTP borrows most of its congestion control
concepts from TCP and QUIC utilizes TCP's and its own mechanisms.
The ACK blocks indicate ranges of packet numbers that were received
below the Largest Acknowledged, with GAP blocks indicating gaps in
the packet number series. This is unlike SCTP's Cumulative TSN ACK
which tracks the lowest contiguous acknowledged TSN.
4.5.1. SCTP
SCTP ensures reliable in-order delivery of data through the use of
the TSN. Unlike QUIC's Packet Number, TSN is not a monotonically
increasing value. TSNs are used to identify and acknowledge chunks
by a receiver, and if a sender does not receive an acknowledgement in
a certain amount of time, it knows what chunks to retransmit because
of their associated TSN. TSNs are used to track missing chunks, and
chunks are retransmitted with the same TSN that they had when they
were originally dropped so the receiver knows it is no longer missing
a chunk. This allows SCTP to guarantee reliable delivery of DATA
Chunks. Since TSN is separate from SSN, the in-order delivery
mechanism for streams is kept separate from the reliable delivery
mechanism. SSN controls in-order delivery to the ULP, while TSN
controls reliable delivery between endpoints. TSN is also agnostic
to what stream it belongs to. SCTP keeps track of the Cumulative TSN
ACK, the last TSN an endpoint has received before a break in the
series of TSN values. Every TSN below the Cumulative TSN ACK value
is contiguously acknowledged by the receiver. If a receiver has gaps
in TSNs that were not received, it will communicate only what it has
received, leaving the sender to determine what is missing. A
receiver sends out a SACK Chunk (Figure 7) to acknowledge the receipt
of TSNs. GAP blocks are attached to the SACK Chunk to acknowledge
sequences of TSN values above the Cumulative TSN ACK. A GAP block
indicates ranges of TSNs that are acknowledged by the receiver. Gap
Ack Block Start indicates the inclusive start offset of TSNs from the
Cumulative TSN ACK. Gap Ack Block End indicates the inclusive end
offset of TSNs from the Cumulative TSN ACK. A sender determines what
TSNs are missing through repeated GAP blocks containing the same gaps
in TSN ranges, which indicate the same chunks are missing repeatedly.
The sender will then retransmit the missing chunks. Congestion
control in SCTP is governed by the same mechanisms that TCP utilizes
such as slow start, fast retransmit and retransmission timer.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 3 |Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cumulative TSN Ack |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertised Receiver Window Credit (a_rwnd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Gap Ack Blocks = N | Number of Duplicate TSNs = X |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Gap Ack Block #1 Start | Gap Ack Block #1 End |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Gap Ack Block #N Start | Gap Ack Block #N End |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Duplicate TSN 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Duplicate TSN X |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: SCTP SACK Chunk
4.5.2. QUIC
QUIC ensures reliable in-order delivery of data through the use of
the byte offset field in STREAM frames. If a packet is dropped, the
individual frames within the packet will be retransmitted, not the
packet itself. This means that a new packet with a new packet number
will be constructed, and the dropped frames will be attached and sent
with it. The packet number in a QUIC packet is always monotonically
increasing, or in other words, a duplicate packet number will never
be sent making it easy to distinguish acknowledgements of
retransmission from the original packets [QUIC-RECOVERY]. This plays
into the stream abstraction concept that is present within QUIC:
there is always a constant stream of data being sent on a connection.
It is up to the implementation to decide how many packets to use to
resend dropped frames. Additionally, since endpoints know which sent
packets of theirs is missing, they know what byte offsets are
missing, allowing them the ability to resize frames for transmission
as they see fit. At time of writing, the QUIC draft does not specify
how the frames are resized [QUIC-TRANSPORT]. The ACK Delay field
indicates the time in microseconds that the largest acknowledged
packet was received by which facilitates creating an accurate RTT
timer [QUIC-RECOVERY]. The Largest Acknowledged field in the ACK
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Frame (Figure 8) indicates the largest packet number that was
received. The reason QUIC tracks the latest packet number is due to
the packet number always being monotonically increasing allowing
transmission order to be easily tracked. SCTP tracks the lowest
contiguous TSN in its Cumulative TSN ACK field since SCTP might
retransmit TSNs which is not an issue with QUIC. Just as SCTP
utilizes the same mechanisms as TCP for congestion control, so does
QUIC, however with some important modifications. QUIC simplifies its
congestion control and loss detection by splitting out its source of
information for reliable delivery: stream id and byte offsets, from
its source of information for transmission order: monotonically
increasing packet numbers. SCTP and TCP both conflate reliable
delivery and transmission order into one source of information, the
TSNs. Another simplification that QUIC brings is that QUIC ACK's are
always honored, and never reneged upon, unlike SCTP which uses a SACK
similar to TCP and can be reneged [QUIC-RECOVERY]. TCP's congestion
control algorithms such as slow start, fast retransmit, and RTT
timers are still used in QUIC, just adapted to use its packet number
as well as some other minute differences [QUIC-RECOVERY].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Largest Acknowledged (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACK Delay (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACK Block Count (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACK Blocks (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: QUIC ACK Frame
4.6. Flow Control
Flow control is defined as the pressure or limit a receiving endpoint
advertises to a sender in order to prevent the receiver from being
overwhelmed and drop packets. Flow control is similar to congestion
control, but whereas congestion control focuses on preventing
congestion on the network or system, flow control focuses on
preventing an endpoint from being overwhelmed. A common flow control
concept is a sliding window, in which an endpoint advertises an
amount of bytes its sending counterpart can transmit. Both of these
protocols practice a form of sliding window. Unlike UIC, there is no
flow control data that is sent between sender and receiver on a per
stream basis, but rather flow control is done on a per association
basis.
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4.6.1. SCTP
Flow Control in SCTP is done only on a per association basis using
mechanisms similar to TCP as defined in TCP Congestion Control
[RFC2581]. When a receiver sends out a SACK Chunk (Figure 7), it
includes a field called Advertiser Receiver Window Credit (a_rwnd).
This value represents the remaining available buffer space at the
receiver. Since SACKs can be received out of order, a sender will
not necessarily assume they have a_rwnd amount of buffer space to
send. At the start of a SCTP association, each endpoint will receive
the a_rwnd of its peer in the INIT (Figure 5) or INIT ACK Chunk, and
will take that to be the actual receiving window (rwnd) of the
corresponding endpoint. As the association lifetime continues, each
endpoint will subtract the size of DATA chunks that are sent or
retransmitted to a peer from the peer's rwnd. This is because the
sender assumes the peer's buffer space will be taken up by the
transmitted chunk. Each endpoint will also add the size of DATA
chunks that are marked for retransmission. With each SACK an
endpoint receives, it will update its rwnd according to a_rwnd in the
SACK, minus any outstanding bytes from missing chunks that have not
be acknowledged yet.
4.6.2. QUIC
Flow Control in QUIC is done on both a connection and substream
basis. The most important parameters for flow control in QUIC are
the transport parameters MAX_DATA and MAX_STREAM_DATA parameters.
These two parameters are communicated during connection setup, and
also have corresponding Frames which can be communicated during a
connection. Once a value is advertised for these parameters by an
endpoint, the endpoint must honor it. MAX_DATA indicates the maximum
amount of data that can be communicated on a connection.
MAX_STREAM_DATA indicates the maximum amount of data that can be
communicated on a stream basis. It is up to each endpoint to divide
up the data between all of its streams. As the connection and stream
lifetime continues, endpoints will advertise higher MAX_DATA and
MAX_STREAM_DATA to flow control its sending peer. If either of these
variables are disobeyed by a sender on any of the streams, the entire
connection is torn down. An exception is made for Stream 0, which is
reserved for the cryptographic handshake on setup. None of the byte
usage of Stream 0 is counted towards the limits of the transport
parameters [QUIC-TLS]. Since QUIC utilizes a byte stream paradigm
and byte offsets are communicated in STREAM frames, data usage is
easily calculated on both endpoints by recording largest received
byte offsets. This leads to virtually no chance of an endpoint
breaking this agreement unless there is a bug in its implementation
or it is a malicious actor.
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4.7. Connection Teardown
4.7.1. SCTP
Once it is time for a SCTP association to end, the endpoints engage
in a 3-way handshake to shutdown the association. The ULP will send
out a SHUTDOWN primitive to the lower layer where it will wait for
all its sent chunks to be acknowledged or retransmit missing ones.
The endpoint will then send out a SHUTDOWN chunk to initiate a clean
close of the association after it has confirmed its peer has received
all sent data. On receipt of the SHUTDOWN chunk, the peer endpoint
will stop accepting data from its ULP and confirm it has received all
data and then respond with a SHUTDOWN-ACK. Finally, the initiating
endpoint will send out a SHUTDOWN-Complete chunk to close the
association.
4.7.2. QUIC
Once it is time for a QUIC connection to shut down, an endpoint sends
out a closing frame, CONNECTION_CLOSE or APPLICATION_CLOSE to its
peer and enters a closing state in which it discards all internal
state except what is required to build closing frames. If there are
open substreams when the frame is received, the streams are
implicitly closed. If the initiator of the shutdown receives packets
while it is in a closing state, it replies to each of them with
either a closing frame. The receiver of the closing frame enters a
draining state in which it does not send anymore packets and discards
internal state. Before the receiver enters the draining state, it
can also send a closing frame. At most, a QUIC connection teardown
is a two-way handshake unless there are dropped packets from the
initiator. Another way the connection might close down is implicitly
through no network activity, resulting in the endpoints timing out.
4.8. Other Differences between QUIC and SCTP
SCTP supports multi-homing. Specifically, an endpoint can include
multiple IP addresses in the INIT or INIT ACK chunk, so the other
endpoint can establish a multi-path connection with the endpoint.
When one of the connections times out, a chunk can be retransmitted
through another active connection, increasing the resilience of SCTP
connection. Nonetheless, QUIC itself does not support multi-homing.
Instead, there exists an Multipath Extension for QUIC Draft working
in progress to add multipath capability into QUIC protocol
[MULTIPATH-QUIC] .
QUIC greatly resembles the combination of TCP, TLS and HTTP/2. QUIC
packets are always encrypted (except for the public header) and
authenticated (including the public header). The encryption prevents
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middle box parsing the congestion information and breaking with any
forward changes, which is currently a problem for TCP. The public
header is required either for routing or for decrypting the packet so
it is unencrypted. However, this packet is also fully authenticated,
preventing in-network tampering. Any modification of the QUIC packet
will cause the teardown of the connection. Nevertheless, SCTP
protocol itself does not include encryption or authentication, just
like TCP.
5. Current Situations of SCTP and QUIC
Temporarily, SCTP is used mostly in the telecom industry. However,
as for the IP network, the deployment of SCTP is not much widespread.
In-network devices, for example, NAT gateways, does not support SCTP
well. NAT gateways need to be upgraded to be SCTP-aware.
Nevertheless, the cruel truth is that modification of middle boxes is
very expensive, and internet service providers are supposed to seek
their own interests to update the devices. As a matter of fact, some
firewalls only allow TCP or UDP packets to pass through, which
constrains SCTP to very small living space. Considering that MPTCP
can meet such needs, there is less motivation to deploy SCTP. The
worse thing is that, unlike MPTCP, the SCTP socket APIs differ
greatly from TCP, and developers need to update their source code to
deploy SCTP, thus significantly impeding the wide deployment of SCTP.
Designed by Google, QUIC is now widely used in Chrome clients
accessing Google services. QUIC is deployed as a substitution of
SPDY, representing about 7% of the Internet traffic. QUIC works atop
of UDP, so mostly in-network devices that support UDP will support
QUIC. At least, it is more friendly to middleboxes than SCTP. Since
QUIC works in the application layer, it is supposed to be upgraded
much more frequently than TCP stack in kernel. Fortunately, QUIC
provides a new set of APIs, which are not transparent to the upper
applications. Similar to SCTP, developers also need to rewrite the
source code to allow the former applications to use QUIC. Tech
giants, like Tencent, are trying to deploy QUIC to provide better
service for users. With the support of giants and communities, the
deployment of QUIC is promising in the future.
6. Conclusions from the comparison
QUIC has adopted a number of features from long years of protocol
design efforts. QUIC and SCTP share some commonalities and
differences. We conclude some design considerations of QUIC as
following.
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o Latency: QUIC combines transport and crypto handshakes, utilizing
cryptographic cookie for connection resumption, minimizing
connection latency.
o Security: QUIC packets are always encrypted (except for the public
header) and authenticated (including the public header). QUIC
also address the security issues inherent in allowing data
exchange during the 0-rtt handshake, through the use of a security
token for address validation. However, QUIC's use longterm
cryptographic cookie and connection ID brings window for new types
of attacks. Balancing tradeoff of gains and losses is always a
part of protocol design.
o Compatibility: QUIC runs in userspace, allowing fast deployment
and experimentation. As it runs over UDP, it is compatible with
most middlebox implementations. QUIC also adopts a fall back
mechanism for normal TCP handshake incase one of the parties do
not support the protocol. QUIC also adopts congestion control
protocol to achieve fairness with existing TCP connections. The
compatibility issue is one of the reasons why SCTP was not widely
deployed.
o Parallelism: Through stream multiplexing, the missing frames of
one stream will not block the delivery of other streams payload
data, avoiding HOL-Blocking problem, but also introduces
additional processing, as QUIC has to keep internal mapping of
which stream frame in which packet, to know which one needs to be
retransmitted.
o Flexibility: QUIC has a pluggable congestion control mechanism and
has more signaling than TCP, which makes QUIC more informative for
congestion control algorithms. It also provides opportunities for
further experimentation of congestion control features.
o Fine granularity: QUIC supports the traffic control both in stream
and connection level, following HTTP/2.
o Adjustability: The QUIC connection can survive IP address changes
and NAT rebinding due to the stable connection ID during
connection migration.
o Lightness: QUIC adopts the bidirectional byte stream model of TCP,
which facilitates the movement of applications from TCP to QUIC
and liberates QUIC from message fragmentation that SCTP has to
take care of.
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Hopefully these advantages of QUIC can serve as the general
principles for future development of QUIC and the design of other
incipient protocols.
7. Contributors
Hang Shi
Tsinghua University
P.R. China
Email: shihang7422166@gmail.com
Yuming Hu
Tsinghua University
P.R. China
Email: Kumius@foxmail.com
8. Informative References
[MULTIPATH-QUIC]
Coninck, Q. and O. Bonaventure, "Multipath Extension for
QUIC, https://tools.ietf.org/html/
draft-deconinck-multipath-quic-00", draft-tsvwg-quic-
protocol-00 (work in progress), October 2017.
[QUIC] Iyengar, J. and I. Swett, "QUIC: A UDP-Based Secure and
Reliable Transport for HTTP/2,
https://tools.ietf.org/html/draft-tsvwg-quic-protocol-00",
draft-tsvwg-quic-protocol-00 (work in progress), June
2015.
[QUIC-DESIGN]
"QUIC: Design Document and Specification Rationale, Jim
Roskind, Chromium Contributor", 2012.
[QUIC-RECOVERY]
Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control", draft-ietf-quic-recovery-09 (work
in progress), January 2018.
[QUIC-TLS]
Thomson, M., Ed. and S. Turner, Ed., "Using Transport
Layer Security (TLS) to Secure QUIC", draft-ietf-quic-
tls-09 (work in progress), January 2018.
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[QUIC-TRANSPORT]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", draft-ietf-quic-
transport-09 (work in progress), January 2018.
[RFC2581] Allman, M., Paxson, V., and W. Stevens, "TCP Congestion
Control", RFC 2581, DOI 10.17487/RFC2581, April 1999,
<https://www.rfc-editor.org/info/rfc2581>.
[RFC4896] Surtees, A., West, M., and A. Roach, "Signaling
Compression (SigComp) Corrections and Clarifications",
RFC 4896, DOI 10.17487/RFC4896, June 2007,
<https://www.rfc-editor.org/info/rfc4896>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/info/rfc4960>.
Authors' Addresses
Arun Joseph
UCLA
Los Angeles
USA
Email: ajoseps@ucla.edu
Tianxiang Li
UCLA
Los Angeles
USA
Email: tianxiang@cs.ucla.edu
Zihao He
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6278-5822
Email: hezihao9512@gmail.com
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Yong Cui
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6260-3059
Email: cuiyong@tsinghua.edu.cn
Lixia Zhang
UCLA
Los Angeles
USA
Email: lixia@cs.ucla.edu
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