Draft: draft-ietf-quic-applicability

Commentary: These changes should be largely editorial ; I 'm happy to pull out anything controversial into a separate PR if desired . 
 A few additional suggestions , but these changes LG .
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QUIC QUIC is a new transport protocol providing a number of advanced
features.  While initially designed for the HTTP use case, it
provides capabilities that can be used with a much wider variety of
applications.  QUIC is encapsulated in UDP.  QUIC version 1 integrate
TLS 1.3 TLS13 to encrypt all payload data and most control
information.  HTTP operating over QUIC is known as HTTP/3.
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This document provides guidance for application developers that want
to use the QUIC protocol without implementing it on their own.  This
includes general guidance for applications operating over HTTP/3 or
directly over QUIC.  For specific guidance on how to integrate HTTP/3
with QUIC, see QUIC-HTTP.
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QUIC QUIC is a new transport protocol providing a number of advanced
features.  While initially designed for the HTTP use case, it
provides capabilities that can be used with a much wider variety of
applications.  QUIC is encapsulated in UDP.  QUIC version 1
integrates TLS 1.3 TLS13 to encrypt all payload data and most control
information.  The version of HTTP that uses QUIC is known as HTTP/3
QUIC-HTTP.
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This document provides guidance for application developers that want
to use the QUIC protocol without implementing it on their own.  This
includes general guidance for applications operating over HTTP/3 or
directly over QUIC.
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QUIC uses UDP as a substrate.  This enables both userspace
implementation traversal of middleboxes and NAT without requiring
updates.
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While recent measurements have shown no evidence of widespread,
systematic disadvantage of UDP traffic compared to TCP in the
Internet Edeline16, somewhere between three Trammell16 and five
Swett16 percent of networks simply block UDP traffic.  All
applications running on top of QUIC must therefore either be prepared
to accept connectivity failure on such networks, or be engineered to
fall back to some other transport protocol.  In the case of HTTP,
this fallback is TLS over TCP.
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QUIC uses UDP as a substrate.  This enables userspace implementation
and permits traversal of network middleboxes (including NAT) without
requiring updates to existing network infrastructure.
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While recent measurements have shown no evidence of a widespread,
systematic disadvantage of UDP traffic compared to TCP in the
Internet Edeline16, somewhere between three Trammell16 and five
Swett16 percent of networks block all UDP traffic.  All applications
running on top of QUIC must therefore either be prepared to accept
connectivity failure on such networks or be engineered to fall back
to some other transport protocol.  In the case of HTTP, this fallback
is TLS over TCP.
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Because QUIC is encapsulated in UDP, applications using QUIC must
deal with short network idle timeouts.  Deployed stateful middleboxes
will generally establish state for UDP flows on the first packet
state, and keep state for much shorter idle periods than for TCP.
RFC5382 suggests a TCP idle period of at least 124 minutes, though
there is not evidence of widespread implementation of this guideline
in the literature.  Short network timeout for UDP, however, is well-
documented.  According to a 2010 study (Hatonen10), UDP applications
can assume that any NAT binding or other state entry can expire after
just thirty seconds of inactivity.  Section 3.5 of RFC8085 further
discusses keep-alive intervals for UDP: it requires a minimum value
of 15 seconds, but recommends larger values, or omitting keepalive
entirely.
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Because QUIC is encapsulated in UDP, applications using QUIC must
deal with short network idle timeouts.  Deployed stateful middleboxes
will generally establish state for UDP flows on the first packet
sent, and keep state for much shorter idle periods than for TCP.
RFC5382 suggests a TCP idle period of at least 124 minutes, though
there is not evidence of widespread implementation of this guideline
in the literature.  Short network timeout for UDP, however, is well-
documented.  According to a 2010 study (Hatonen10), UDP applications
can assume that any NAT binding or other state entry can expire after
just thirty seconds of inactivity.  Section 3.5 of RFC8085 further
discusses keep-alive intervals for UDP: it requires a minimum value
of 15 seconds, but recommends larger values, or omitting keep-alive
entirely.
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of 15 seconds, but recommends larger values, or omitting keepalive
entirely.
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of 15 seconds, but recommends larger values, or omitting keep-alive
entirely.
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Ignore it, if the application-layer protocol consists only of
interactions with no or very short idle periods, or the protocol's
resistance to NAT rebinding is sufficient.
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Ignore the issue, if the application-layer protocol consists only
of interactions with no or very short idle periods, or the
protocol's resistance to NAT rebinding is sufficient.
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Either the server or the client in a QUIC application can send PING
frames as keep-alives, to prevent the connection and any on-path
state from timing out.  Recommendations for the use of keep-alives
are application specific, mainly depending on the latency
requirements and message frequency of the application.  In this case,
the application mapping must specify whether the client or server is
responsible for keeping the application alive.  While Hatonen10
suggests that 30 seconds might be a suitable value for the public
Internet when a NAT is on path, larger values are preferable if the
deployment can consistently survive NAT rebinding, or is known to be
in a controlled environments like e.g.  data centres in order to
lower network and computational load.
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Sending PING frames more frequently than every 30 seconds over long
idle periods may result in excessive unproductive traffic in some
situations, and to unacceptable power usage for power-constrained
(mobile) devices.  Additionally, time-outs shorter than 30 seconds
can make it harder to handle transient network interruptions, such as
VM migration or coverage loss during mobilty.  See RFC8085,
especially Section 3.5.
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Either the server or the client in a QUIC application can send PING
frames as keep-alives, to prevent the connection and any on-path
state from timing out.  Recommendations for the use of keep-alives
are application-specific, mainly depending on the latency
requirements and message frequency of the application.  In this case,
the application mapping must specify whether the client or server is
responsible for keeping the application alive.  While Hatonen10
suggests that 30 seconds might be a suitable value for the public
Internet when a NAT is on path, larger values are preferable if the
deployment can consistently survive NAT rebinding or is known to be
in a controlled environment (e.g.  data centres) in order to lower
network and computational load.
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Sending PING frames more frequently than every 30 seconds over long
idle periods may result in excessive unproductive traffic in some
situations, and to unacceptable power usage for power-constrained
(mobile) devices.  Additionally, timeouts shorter than 30 seconds can
make it harder to handle transient network interruptions, such as VM
migration or coverage loss during mobilty.  See RFC8085, especially
Section 3.5.
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Alternatively, the client (but not the server) can use session
resumption instead of sending keepalive traffic.  In this case, a
client that wants to send data to a server over a connection idle
longer than the server's idle timeout (available from the
idle_timeout transport parameter) can simply reconnect.  When
possible, this reconnection can use 0-RTT session resumption,
reducing the latency involved with restarting the connection.  This
approach is only valid in cases in which 0-RTT data is safe, when the
client is the restarting peer, and when the data to be sent is
idempotent.  It is also not applicable when the application binds
external state to the connection, as this state cannot reliably be
transferred to a resumed connection.
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The tradeoffs between resumption and keepalive need to be evaluated
on a per-application basis.  However, in general applications should
use keepalives only in circumstances where continued communication is
highly likely; QUIC-HTTP, for instance, recommends using PING frames
for keepalive only when a request is outstanding.
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Streams and connections can each carry a maximum of 2^62-1 bytes in
each direction, due to encoding limitations on stream offsets and
connection flow control limits.  In the presently unlikely event that
this limit is reached by an application, a new connection would need
to be established.
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Streams can be independently opened and closed, gracefully or by
error.  An application can gracefully close the egress direction of a
stream by instructing QUIC to send a FIN bit in a STREAM frame.  It
cannot gracefully close the ingress direction without a peer-
generated FIN, much like in TCP.  However, an endpoint can abruptly
close the egress direction or request that its peer abruptly close
the ingress direction; these actions are fully independent of each
other.
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Alternatively, the client (but not the server) can use session
resumption instead of sending keepalive traffic.  In this case, a
client that wants to send data to a server over a connection idle
longer than the server's idle timeout (available from the
idle_timeout transport parameter) can simply reconnect.  When
possible, this reconnection can use 0-RTT session resumption,
reducing the latency involved with restarting the connection.  Of
course, this approach is only valid in cases in which 0-RTT data is
safe, when the client is the restarting peer, and when the data to be
sent is idempotent.  It is also not applicable when the application
binds external state to the connection, as this state cannot reliably
be transferred to a resumed connection.
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The tradeoffs between resumption and keep-alives need to be evaluated
on a per-application basis.  In general, applications should use
keep-alives only in circumstances where continued communication is
highly likely; QUIC-HTTP, for instance, recommends using keep-alives
only when a request is outstanding.
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Streams can be independently opened and closed, gracefully or
abruptly.  An application can gracefully close the egress direction
of a stream by instructing QUIC to send a FIN bit in a STREAM frame.
It cannot gracefully close the ingress direction without a peer-
generated FIN, much like in TCP.  However, an endpoint can abruptly
close the egress direction or request that its peer abruptly close
the ingress direction; these actions are fully independent of each
other.
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If a QUIC receiver has opened the maximum allowed concurrent streams,
and the sender indicates that more streams are needed, it doesn't
automatically lead to an increase of the maximum number of streams by
the receiver.  Therefore it can be valuable to expose the maximum
number of allowed, currently open, and currently used streams to the
application to make the mapping of data to streams dependent on this
information.
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If a QUIC receiver has opened the maximum allowed concurrent streams,
and the sender indicates that more streams are needed, it does not
automatically lead to an increase of the maximum number of streams by
the receiver.  Therefore it can be valuable to expose the maximum
number of allowed, currently open, and currently used streams to the
application to make the mapping of data to streams dependent on this
information.
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The method of allocating stream identifiers to streams opened by the
application might vary between transport implementations.  Therefore,
an application should not assume a particular stream ID will be
assigned to a stream that has not yet been allocated.  For example,
HTTP/3 uses Stream IDs to refer to streams that have already been
opened, but makes no assumptions about future Stream IDs or the way
in which they are assigned.
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The method of allocating stream identifiers to streams opened by the
application might vary between transport implementations.  Therefore,
an application should not assume a particular stream ID will be
assigned to a stream that has not yet been allocated.  For example,
HTTP/3 uses Stream IDs to refer to streams that have already been
opened, but makes no assumptions about future Stream IDs or the way
in which they are assigned Section 6 of QUIC-HTTP).
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provide the respective credentials), the cost of establishing another
connection is extremely low.
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provide the necessary credentials), the cost of establishing another
connection is extremely low.
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Stream prioritization is not exposed to either the network or the
receiver.  Prioritization is managed by the sender, and the QUIC
transport should provide an interface for applications to prioritize
streams QUIC.  Further applications can implement their own
prioritization scheme on top of QUIC: an application protocol that
runs on top of QUIC can define explicit messages for signaling
priority, such as those defined for HTTP/2; it can define rules that
allow an endpoint to determine priority based on context; or it can
provide a higher level interface and leave the determination to the
application on top.
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Priority handling of retransmissions can be implemented by the sender
in the transport layer.  QUIC recommends to retransmit lost data
before new data, unless indicated differently by the application.
Currently, QUIC only provides fully reliable stream transmission,
which means that prioritization of retransmissions will be beneficial
in most cases, by filling in gaps and freeing up the flow control
window.  For partially reliable or unreliable streams, priority
scheduling of retransmissions over data of higher-priority streams
might not be desirable.  For such streams, QUIC could either provide
an explicit interface to control prioritization, or derive the
prioritization decision from the reliability level of the stream.
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Stream prioritization is not exposed to either the network or the
receiver.  Prioritization is managed by the sender, and the QUIC
transport should provide an interface for applications to prioritize
streams QUIC.  Applications can implement their own prioritization
scheme on top of QUIC: an application protocol that runs on top of
QUIC can define explicit messages for signaling priority, such as
those defined for HTTP/2; it can define rules that allow an endpoint
to determine priority based on context; or it can provide a higher
level interface and leave the determination to the application on
top.
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Priority handling of retransmissions can be implemented by the sender
in the transport layer.  QUIC recommends retransmitting lost data
before new data, unless indicated differently by the application.
Currently, QUIC only provides fully reliable stream transmission,
which means that prioritization of retransmissions will be beneficial
in most cases, by filling in gaps and freeing up the flow control
window.  For partially reliable or unreliable streams, priority
scheduling of retransmissions over data of higher-priority streams
might not be desirable.  For such streams, QUIC could either provide
an explicit interface to control prioritization, or derive the
prioritization decision from the reliability level of the stream.
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Large messages can produce deadlocking if the recipient does not
process the message incrementally.  If the message is larger than
flow control credit available and the recipient does not release
additional flow control credit until the entire message is received
and delivered, a deadlock can occur.  This is possible even where
stream flow control limits are not reached because connection flow
control limits can be consumed by other streams.
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Large messages can produce deadlocking if the recipient does not
process the message incrementally.  If the message is larger than the
flow control credit available and the recipient does not release
additional flow control credit until the entire message is received
and delivered, a deadlock can occur.  This is possible even where
stream flow control limits are not reached because connection flow
control limits can be consumed by other streams.
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A common flow control implementation technique is for a receiver to
extend credit to the sender as a the data consumer reads data.  In
this setting, a length-prefixed message format makes it easier for
the data consumer to leave data unread in the receiver's buffers and
thereby withhold flow control credit.  If flow control limits prevent
the remainder of a message from being sent, a deadlock will result.
A length prefix might also enable the detection of this sort of
deadlock.  Where protocols have messages that might be processed as a
single unit, reserving flow control credit for the entire message
atomically ensures that this style of deadlock is less likely.
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A common flow control implementation technique is for a receiver to
extend credit to the sender as a the data consumer reads data.  In
this setting, a length-prefixed message format makes it easier for
the data consumer to leave data unread in the receiver's buffers and
thereby withhold flow control credit.  If flow control limits prevent
the remainder of a message from being sent, a deadlock will result.
A length prefix might also enable the detection of this sort of
deadlock.  Where protocols have messages that might be processed as a
single unit, reserving flow control credit for the entire message
atomically makes this style of deadlock less likely.
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Some deadlocking scenarios might be resolved by cancelling affected
streams with STOP_SENDING or RST_STREAM.  Cancelling some streams
results in the connection being terminated in some protocols.
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QUIC provides an interface that provides multiple streams to the
application; however, the application usually cannot control how data
transmitted over one stream is mapped into frames or how those frames
are bundled into packets.
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By default, many implementations will try to maximally pack QUIC
packets with one or more stream data frames to minimize bandwidth
consumption and computational costs (see section 13 of QUIC).  If
there is not enough data available to fill a packet, an
implementation might wait for a short time, to optimize bandwidth
efficiency instead of latency.  This delay can either be pre-
configured or dynamically adjusted based on the observed sending
pattern of the application.
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Some deadlocking scenarios might be resolved by cancelling affected
streams with STOP_SENDING or RESET_STREAM.  Cancelling some streams
results in the connection being terminated in some protocols.
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QUIC exposes an interface that provides multiple streams to the
application; however, the application usually cannot control how data
transmitted over those streams is mapped into frames or how those
frames are bundled into packets.
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By default, many implementations will try to maximally pack QUIC
packets DATA frames from one or more streams to minimize bandwidth
consumption and computational costs (see Section 13 of QUIC).  If
there is not enough data available to fill a packet, an
implementation might wait for a short time, to optimize bandwidth
efficiency instead of latency.  This delay can either be pre-
configured or dynamically adjusted based on the observed sending
pattern of the application.
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In general, port numbers serves two purposes: "first, they provide a
demultiplexing identifier to differentiate transport sessions between
the same pair of endpoints, and second, they may also identify the
application protocol and associated service to which processes
connect" RFC6335.  The assumption that an application can be
identified in the network based on the port number is less true today
due to encapsulation, mechanisms for dynamic port assignments, and
NATs.
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In general, port numbers serve two purposes: "first, they provide a
demultiplexing identifier to differentiate transport sessions between
the same pair of endpoints, and second, they may also identify the
application protocol and associated service to which processes
connect" RFC6335.  The assumption that an application can be
identified in the network based on the port number is less true today
due to encapsulation, mechanisms for dynamic port assignments, and
NATs.
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As QUIC is a general purpose transport protocol, there are no
requirements that servers use a particular UDP port for QUIC.  For
applications with a fallback to TCP that do not already have an
alternate mapping to UDP, usually the registration (if necessary) and
use of the UDP port number corresponding to the TCP port already
registered for the application is appropriate.  For example, the
default port for HTTP/3 QUIC-HTTP is UDP port 443, analogous to
HTTP/1.1 or HTTP/2 over TLS over TCP.
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As QUIC is a general-purpose transport protocol, there are no
requirements that servers use a particular UDP port for QUIC.  For
applications with a fallback to TCP that do not already have an
alternate mapping to UDP, usually the registration (if necessary) and
use of the UDP port number corresponding to the TCP port already
registered for the application is appropriate.  For example, the
default port for HTTP/3 QUIC-HTTP is UDP port 443, analogous to
HTTP/1.1 or HTTP/2 over TLS over TCP.
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Applications could define an alternate endpoint discovery mechanism
to allow the usage of ports other than the default.  For example,
HTTP/3 (QUIC-HTTP Sections 3.1.1 and 3.1.2) specifies the use of HTTP
Alternative Services for an HTTP origin to advertise the availability
of an equivalent HTTP/3 endpoint on a certain UDP port by using the
"h3" ALPN token RFC7301.  Note that HTTP/3's ALPN token ("h3")
identifies not only the version of the application protocol, but also
the binding to QUIC as well as the version of QUIC itself; this
approach allows unambiguous agreement between the endpoints on the
protocol stack in use.
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Applications could define an alternate endpoint discovery mechanism
to allow the usage of ports other than the default.  For example,
HTTP/3 (Sections 3.2 and 3.3 of QUIC-HTTP) specifies the use of HTTP
Alternative Services for an HTTP origin to advertise the availability
of an equivalent HTTP/3 endpoint on a certain UDP port by using the
"h3" ALPN token RFC7301.  Note that HTTP/3's ALPN token ("h3")
identifies not only the version of the application protocol, but also
the version of QUIC itself; this approach allows unambiguous
agreement between the endpoints on the protocol stack in use.
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Use of a non-empty connection ID for the server is strongly
recommended if any clients are behind a NAT or could be.  A non-empty
connection ID is also strongly recommended when migration is
supported.
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Use of a non-zero-length connection ID for the server is strongly
recommended if any clients are behind a NAT or could be.  A non-zero-
length connection ID is also strongly recommended when migration is
supported.
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Only the client can actively migrate.  However, servers can indicate
during the handshake that they prefer to transfer the connection to a
different address after the handshake.  For instance, this could be
used to move from an address that is shared by multiple servers to an
address that is unique to the server instance.  The server can
provide an IPv4 and an IPv6 address in a transport parameter during
the TLS handshake and the client can select between the two if both
are provided.  See also Section 9.6 of QUIC.
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Only the client can actively migrate in version 1 of QUIC.  However,
servers can indicate during the handshake that they prefer to
transfer the connection to a different address after the handshake.
For instance, this could be used to move from an address that is
shared by multiple servers to an address that is unique to the server
instance.  The server can provide an IPv4 and an IPv6 address in a
transport parameter during the TLS handshake and the client can
select between the two if both are provided.  See also Section 9.6 of
QUIC.
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An immediate close will emit an CONNECTION_CLOSE frame.  This frame
has two sets of types: one for QUIC internal problems that might lead
to connection closure, and one for closures initiated by the
application.  An application using QUIC can define application-
specific error codes (see, for example, QUIC-HTTP, Section 8.1).
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An immediate close will emit an CONNECTION_CLOSE frame.  This frame
has two sets of types: one for QUIC internal problems that might lead
to connection closure, and one for closures initiated by the
application.  An application using QUIC can define application-
specific error codes (see, for example, Section 8.1 of QUIC-HTTP).
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Alternatively, a QUIC connection can be silently closed by each
endpoint separately after an idle timeout.  If enabled as indicated
by a transport parameter in the handshake, the idle timeout is
announced for each endpoint during connection establishment and the
effective value for this connection is the minimum of the two values
advertised by client and server.  An application therefore should be
able to configure its own maximum value as well as have access to the
computed minimum value for this connection.  An application may
adjust the maximum idle timeout based on the number of open or
expected connections as shorter timeout values may free-up memory
more quickly.
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If an application desires to keep the connection open for longer than
the announced timeout, it can send keep-alive messages, or a QUIC
implementation may provide an option to defer the time-out to avoid
unnecessary load, as specified in Section 10.1.2 of QUIC.  See
resumption-v-keepalive for further guidance on keep-alives.
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QUIC exposes some information to the network in the unencrypted part
of the header, either before the encryption context is established,
because the information is intended to be used by the network.  QUIC
has a long header that is used during connection establishment and
for other control processes, and a short header that may be used for
data transmission in an established connection.  While the long
header always exposes some information (such as the version and
connection IDs), the short header exposes at most only a single
connection ID.
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Alternatively, a QUIC connection can be silently closed by each
endpoint separately after an idle timeout.  If enabled as indicated
by a transport parameter in the handshake, the idle timeout is
announced for each endpoint during connection establishment and the
effective value for this connection is the minimum of the two values
advertised by client and server.  An application therefore should be
able to configure its own maximum value as well as have access to the
computed minimum value for this connection.  An application may
adjust the maximum idle timeout for new connections based on the
number of open or expected connections, since shorter timeout values
may free-up memory more quickly.
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If an application desires to keep the connection open for longer than
the announced timeout, it can send keep-alive messages; a QUIC
implementation may provide an option to defer the time-out by sending
keep-alive messages at the transport layer to avoid unnecessary load,
as specified in Section 10.1.2 of QUIC.  See resumption-v-keepalive
for further guidance on keep-alives.
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QUIC exposes some information to the network in the unencrypted part
of the header, either before the encryption context is established or
because the information is intended to be used by the network.  QUIC
has a long header that exposes some additional information (the
version and the source connection ID), while the short header exposes
only the destination connection ID.  In QUIC version 1, the long
header is used during connection establishment, while the short
header is used for data transmission in an established connection.
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An endpoint that selects a zero-length connection ID will receive
packets with a zero-length destination connection ID.  The endpoint
needs to use other information, such as its IP address and port
number to identify which connection is referred to.  An endpoint can
choose to use the source IP address and port on datagrams, but this
could mean that the endpoint is unable to match datagrams to
connections successfully if these values change, making migration
effectively impossible.
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An endpoint that selects a zero-length connection ID will receive
packets with a zero-length destination connection ID.  The endpoint
needs to use other information, such as the source and destination IP
address and port number to identify which connection is referred to.
This could mean that the endpoint is unable to match datagrams to
connections successfully if these values change, making the
connection effectively unable to survive NAT rebinding or migrate to
a new path.
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Server deployments with load balancers and other routing
infrastructure need to ensure that this infrastructure consistently
routes packets to the correct server instance.  This might require
coordination between servers and infrastructure.  One method of
achieving this involves encoding routing information into the
connection ID.  This ensures that there is no need to for servers and
infrastructure to coordinate routing information for each connection.
See further QUIC-LB.
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Server deployments with load balancers and other routing
infrastructure need to ensure that this infrastructure consistently
routes packets to the correct server instance.  This might require
coordination between servers and infrastructure.  One method of
achieving this involves encoding routing information into the
connection ID.  This ensures that there is no need to for servers and
infrastructure to coordinate routing information for each connection.
See QUIC-LB for more information.
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The most efficient mitigations for these attacks are through network
design and/or operational practice, by using a load balancing
architecture that loads more flows onto a single server-side address,
by coordinating the timing of migrations to attempt to increase the
number of simultaneous migrations at a given time, or through other
means.
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The most efficient mitigations for these attacks are through network
design and/or operational practice, by using a load balancing
architecture that loads more flows onto a single server-side address,
by coordinating the timing of migrations in an attempt to increase
the number of simultaneous migrations at a given time, or through
other means.
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can directly offer a Retry services as further described in QUIC-LB.
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RFC5077 Section 4 describes an example approach for constructing TLS
resumption tickets that can be also applied for validation tokens,
however, the use of more modern cryptographic algorithms is highly
recommended.
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QUIC assumes that all packets of a QUIC connection or at least with
the same 5-tuple {dest addr, source addr, protocol, dest port, source
port} will receive similar network treatment as feedback about loss
or delay of each packet is used as input to the congestion
controller.  Therefore it is not recommended to use different
DiffServ Code Points (DSCPs) RFC2475 for packets belonging to the
same connection.  If differential network treatment, e.g. by the use
of different DSCPs, is desired, multiple QUIC connections to the same
server may be used.  However, in general it is recommended to
minimize the number of QUIC connections to the same server, to avoid
increased overheads and, more importantly, competing congestion
control.
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can directly offer a Retry service as further described in QUIC-LB.
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Section 4 of RFC5077 describes an example approach for constructing
TLS resumption tickets that can be also applied for validation
tokens, however, the use of more modern cryptographic algorithms is
highly recommended.
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QUIC assumes that all packets of a QUIC connection, or at least with
the same 5-tuple {dest addr, source addr, protocol, dest port, source
port}, will receive similar network treatment since feedback about
loss or delay of each packet is used as input to the congestion
controller.  Therefore it is not recommended to use different
DiffServ Code Points (DSCPs) RFC2475 for packets belonging to the
same connection.  If differential network treatment, e.g. by the use
of different DSCPs, is desired, multiple QUIC connections to the same
server may be used.  However, in general it is recommended to
minimize the number of QUIC connections to the same server, to avoid
increased overheads and, more importantly, competing congestion
control.
Paragraph (version A):
Further QUIC-HTTP provides security considerations specific to HTTP.
However, discussions such as on cross protocol attacks, traffic
analysis and padding, or migration might be relevant for other
applications using QUIC as well.
Paragraph (version B):
Further, QUIC-HTTP provides security considerations specific to HTTP.
However, discussions such as on cross-protocol attacks, traffic
analysis and padding, or migration might be relevant for other
applications using QUIC as well.