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... (cwnd) based on perceived congestion. Each TCP connection starts
with a pre-configured initial congestion window (ICW ...
... network for available bandwidth using the
slow-start procedure ([Jac88], [RFC2581]), doubling cwnd during each
...
... bandwidth or long delays. It may take a number
of RTTs in slow-start before the TCP connection begins to fully use
the available bandwidth ...
... congestion window of 4 segments. This time in
slow-start is not a problem for large file transfers, where the
slow-start ...
... slow-start is not a problem for large file transfers, where the
slow-start stage is only a fraction of the total transfer time.
However, in the case of moderate-sized transfers, the connection
...
... However, in the case of moderate-sized transfers, the connection
might carry out its entire transfer in the slow-start phase, taking
many round-trip times, where one or two RTTs ...
... RFC3390], in the absence of other information about the path.
In using Quick-Start, a TCP host (say, host ...
... desired sending rate in bytes per second, using a Quick-Start Option
in the IP header of a TCP ...
... router along the path could,
in turn, either approve the requested rate, reduce the requested
rate, or indicate that the Quick-Start Request is not approved. (We
note that the `routers' referred to in this document also include the
...
... routers' referred to in this document also include the
IP-layer processing of the Quick-Start Request at the sender.) In
approving a Quick-Start Request ...
... Quick-Start Request at the sender.) In
approving a Quick-Start Request, a router does not give preferential
treatment to subsequent packets from that connection ...
... sender's
requested rate. The Quick-Start mechanism can determine if there are
routers along the path that do not understand the Quick-Start Option ...
... Quick-Start mechanism can determine if there are
routers along the path that do not understand the Quick-Start Option,
or have not agreed to the Quick-Start rate request. TCP ...
... routers along the path that do not understand the Quick-Start Option,
or have not agreed to the Quick-Start rate request. TCP host B
...
... TCP packet.
If the Quick-Start Request is approved by all routers along the path,
then the TCP ...
... congestion control mechanisms of that connection. If the Quick-Start
Request is not approved, then the sender would use the default
congestion control ...
... congestion control mechanisms.
Quick-Start would not be the first mechanism for explicit
communication from routers to transport protocols ...
... [RFC3168]. In contrast, routers would not use Quick-Start to give
congestion information, but instead would use Quick-Start ...
... Quick-Start to give
congestion information, but instead would use Quick-Start as an
optional mechanism to give permission to transport protocols to use
...
... significantly underutilized.
Section 2 gives an overview of Quick-Start. The formal
specifications for Quick-Start are contained in Sections 3, 4, 6.1.1,
...
... Section 2 gives an overview of Quick-Start. The formal
specifications for Quick-Start are contained in Sections 3, 4, 6.1.1,
and 6.3. In particular, Quick-Start is specified for IPv4 ...
... specifications for Quick-Start are contained in Sections 3, 4, 6.1.1,
and 6.3. In particular, Quick-Start is specified for IPv4 and for
IPv6 ...
... non-normative discussion of interactions of
Quick-Start with IP tunnels and MPLS; however, Section 6.1.1 and 6.3
...
... MPLS; however, Section 6.1.1 and 6.3
specify behavior for IP tunnels that are aware of Quick-Start.
The rest of the document is non-normative ...
... The rest of the document is non-normative, as follows. Section 5
shows that Quick-Start is compatible with IPsec AH (Authentication
Header). Section 7 gives a non-normative ...
... Authentication
Header). Section 7 gives a non-normative set of guidelines for
specifying Quick-Start in other transport protocols, and Section 8
discusses using Quick-Start ...
... Quick-Start in other transport protocols, and Section 8
discusses using Quick-Start in transport end-nodes and routers ...
... routers.
Section 9 gives an evaluation of the costs and benefits of Quick-
Start, and Section 10 discusses implementation and deployment issues.
The appendices discuss related work, Quick-Start ...
... Start, and Section 10 discusses implementation and deployment issues.
The appendices discuss related work, Quick-Start design decisions,
and possible router algorithms ...
...
This section describes the assumptions and general principles behind
the design of the Quick-Start mechanism.
Assumptions:
...
... * The path between the two endpoints is relatively stable, such that
the path used by the Quick-Start Request is generally the same path
used by the Quick-Start packets one round-trip time ...
... the path used by the Quick-Start Request is generally the same path
used by the Quick-Start packets one round-trip time later.
[ZDPS01 ...
... Internet semantics. We
note that, while Quick-Start is incrementally deployable in this
sense, a Quick-Start Request cannot be approved for a particular
...
... note that, while Quick-Start is incrementally deployable in this
sense, a Quick-Start Request cannot be approved for a particular
connection unless both end-nodes ...
... nodes and all the routers along the path
have been configured to support Quick-Start.
General Principles:
...
...
* A router should only approve a Quick-Start Request if the output
link is underutilized. Any other approach will result in either
...
... router from storing per-flow state for making Quick-Start decisions
or for checking for misbehaving nodes.
...
... Overview of Quick-Start ...
...
In this section, we give an overview of the use of Quick-Start with
TCP to request a higher congestion window ...
... congestion window. The description in this
section is non-normative; the normative description of Quick-Start
with IP and TCP ...
... with IP and TCP follows in Sections 3 and 4. Quick-Start could be
used in the middle of a connection, e.g., after an idle or
...
... underutilized period, as well as for the initial sending rate; these
uses of Quick-Start are discussed later in the document.
Quick-Start ...
... Quick-Start are discussed later in the document.
Quick-Start requires end-points and routers to work together, with
...
... IP, and routers along the path approving, modifying,
discarding, or ignoring (and therefore disallowing) the Quick-Start
Request. The receiver uses reliable, transport-level mechanisms to
...
... transport-level mechanisms to
inform the sender of the status of the Quick-Start Request. For
example, when TCP is used, the TCP ...
... receiver sends feedback to the
sender using a Quick-Start Response option in the TCP header. In
addition, Quick-Start ...
... Quick-Start Response option in the TCP header. In
addition, Quick-Start assumes a unicast, congestion-controlled
...
... congestion-controlled
transport protocol; we do not consider the use of Quick-Start for
multicast traffic.
...
... multicast traffic.
When sent as a request, the Quick-Start Option includes a request for
a sending rate in bits per second ...
... a sending rate in bits per second, and a Quick-Start Time to Live (QS
TTL) to be decremented by every router ...
... QS
TTL) to be decremented by every router along the path that
understands the option and approves the request. The Quick-Start TTL
is initialized by the sender ...
... receiver returns the rate, information about the TTL, and the Quick-
Start Nonce to the sender using transport-level ...
... TCP,
the receiver sends this information in the Quick-Start Response in
the TCP header. In particular, the receiver ...
... TCP header. In particular, the receiver computes the difference
between the Quick-Start TTL and the IP TTL (the TTL ...
... TTL in the IP header)
of the Quick-Start Request packet, and returns this in the Quick-
Start Response. The sender ...
... of the Quick-Start Request packet, and returns this in the Quick-
Start Response. The sender uses the TTL difference to determine if
...
... TTL difference to determine if
all the routers along the path decremented the Quick-Start TTL,
approving the Quick-Start Request ...
... Quick-Start TTL,
approving the Quick-Start Request.
If the request is approved by all the routers ...
... ACK packet is received.
Figure 1 shows a successful use of Quick-Start, with the sender's IP
layer and both routers ...
... sender's IP
layer and both routers along the path approving the Quick-Start
Request, and the TCP receiver using the Quick-Start ...
... Quick-Start
Request, and the TCP receiver using the Quick-Start Response to
return information to the TCP sender ...
... return information to the TCP sender. In this example, Quick-Start
is used by TCP to establish the initial congestion window ...
... | <TTL Diff: 28>
| Quick-Start approved,
| translate to cwnd.
| Report Approved Rate.
...
... RTT. -->
Figure 1: A Successful Quick-Start Request.
Figure 2 shows an unsuccessful use of Quick-Start ...
... Quick-Start Request.
Figure 2 shows an unsuccessful use of Quick-Start, with one of the
routers along the path not approving the Quick-Start Request ...
... Quick-Start, with one of the
routers along the path not approving the Quick-Start Request. If the
Quick-Start Request is not approved, then the sender ...
... routers along the path not approving the Quick-Start Request. If the
Quick-Start Request is not approved, then the sender uses the default
congestion control ...
... | Forward packet
| without modifying
| Quick-Start Option. -->
|
| <IP TTL ...
... | <TTL Diff: 29>
| Quick-Start not approved.
| Report approved rate.
V Use default initial cwnd. -->
...
... V Use default initial cwnd. -->
Figure 2: An Unsuccessful Quick-Start Request.
...
... The Quick-Start Option in IP ...
... The Quick-Start Option for IPv4 ...
...
The Quick-Start Request for IPv4 is defined as follows:
...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The Quick-Start Option for IPv4.
A Quick-Start Request ...
... Quick-Start Option for IPv4.
A Quick-Start Request.
The first byte contains the option field, which includes the one-bit ...
... The third byte includes a four-bit Function field. If the Function
field is set to "0000", then the Quick-Start Option is a Rate
Request. In this case, the second half of the third byte is a four-
bit Rate ...
... bit Rate Request field.
For a Rate Request, the fourth byte contains the Quick-Start TTL (QS
TTL) field. The sender ...
... random value.
Routers that approve the Quick-Start Request decrement the QS TTL
(mod 256) by the same amount that they decrement the IP TTL ...
... elsewhere in this document, we use the term `router' imprecisely to
also include the Quick-Start functionality at the IP layer at the
sender ...
... sender to detect if all the
routers along the path understood and approved the Quick-Start
option.
For a Rate Request, the transport ...
...
Routers can approve the Quick-Start Request for a lower rate by
decreasing the Rate Request in the Quick-Start Request. Section 4.2
...
... Routers can approve the Quick-Start Request for a lower rate by
decreasing the Rate Request in the Quick-Start Request. Section 4.2
discusses the Quick-Start Response from the TCP ...
... decreasing the Rate Request in the Quick-Start Request. Section 4.2
discusses the Quick-Start Response from the TCP receiver to the TCP ...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: The Quick-Start Option for IPv4.
Report of Approved Rate.
...
... Report of Approved Rate.
If the Function field in the third byte of the Quick-Start Option is
set to "1000", then the Quick-Start Option is a Report of Approved
...
... If the Function field in the third byte of the Quick-Start Option is
set to "1000", then the Quick-Start Option is a Report of Approved
Rate. In this case, the second four bits in the third byte are the
...
... Rate Report field, formatted exactly as in the Rate Request field in
a Rate Request. For a Report of Approved Rate, the fourth byte of
the Quick-Start Option is not used. Bytes 5-8 contain a 30-bit QS
Nonce and a 2-bit ...
... After an approved Rate Request, the sender MUST report the Approved
Rate, using a Quick-Start Option configured as a Report of Approved
Rate with the Rate Report field set to the approved rate, and the QS
Nonce set to the QS Nonce ...
... Rate with the Rate Report field set to the approved rate, and the QS
Nonce set to the QS Nonce sent in the Quick-Start Request. The
packet containing the Report of Approved Rate MUST be either a
control packet sent before the first Quick-Start ...
... Quick-Start Request. The
packet containing the Report of Approved Rate MUST be either a
control packet sent before the first Quick-Start data packet, or a
Quick-Start Option ...
... Quick-Start data packet, or a
Quick-Start Option in the first data packet itself. The Report of
Approved Rate does not have to be sent reliably; for example, if the
...
... does not necessarily know if the control packet has been dropped in
the network. If the packet containing the Quick-Start Request is
acknowledged, but the acknowledgement packet does not contain a
Quick-Start ...
... Quick-Start Request is
acknowledged, but the acknowledgement packet does not contain a
Quick-Start Response, then the sender MUST assume that the Quick-
Start ...
... Quick-Start Response, then the sender MUST assume that the Quick-
Start Request was denied, and set a Report of Approved Rate with a
rate of zero. Routers may choose to ignore the Report of Approved
...
... set to zero.
We note that, unlike a Quick-Start Request sent at the beginning of a
connection, when a Quick-Start Request ...
... Quick-Start Request sent at the beginning of a
connection, when a Quick-Start Request is sent in the middle of a
connection, the connection ...
... transport
protocol.
The use of the Quick-Start Option does not require the additional use
of the Router Alert Option [RFC2113 ...
... The Quick-Start Option for IPv6 ...
... transport receiver compares the
Quick-Start TTL with the IPv6 Hop Limit field to calculate the TTL
Diff ...
... header does not
have a checksum field, and modifying the Quick-Start Request in the
IPv6 Hop-by-Hop ...
... flow
label must be originated with the same hop-by-hop header contents,
which would be incompatible with Quick-Start. However, a later IPv6
flow label ...
... IPv6 and removes this restriction. Therefore, Quick-Start is
compatible with the current IPv6 specifications.
...
... Processing the Quick-Start Request at Routers ...
... sending rate is zero. Each participating router can
either terminate or approve the Quick-Start Request. A router MUST
only approve a Quick-Start Request ...
... Quick-Start Request. A router MUST
only approve a Quick-Start Request if the output link is
underutilized, and if the router ...
... senders. Otherwise, the router reduces or terminates
the Quick-Start Request.
While the paragraph above defines the *semantics ...
... While the paragraph above defines the *semantics* of approving a
Quick-Start Request, this document does not specify the specific
algorithms to be used by routers ...
... algorithms to be used by routers in processing Quick-Start Requests
or Reports. This is similar to RFC 3168prop, which specifics the
...
...
A router that wishes to terminate the Quick-Start Request SHOULD
either delete the Quick-Start Request ...
... Quick-Start Request SHOULD
either delete the Quick-Start Request from the IP header or zero the
QS TTL ...
... QS TTL, QS Nonce, and Rate Request fields. Deleting the Quick-Start
Request saves resources because downstream routers will have no
...
... routers to implement. As suggested in [B05], future
additions to Quick-Start could define error codes for routers to
...
... QS Nonce field to report back to the sender the
reason that the Quick-Start Request was denied, e.g., that the router
is denying all Quick-Start Requests ...
... Quick-Start Request was denied, e.g., that the router
is denying all Quick-Start Requests at this time, or that this
router, as a matter of policy, does not grant Quick-Start requests ...
... Quick-Start Requests at this time, or that this
router, as a matter of policy, does not grant Quick-Start requests.
A router that doesn't understand the Quick-Start Option ...
... Quick-Start requests.
A router that doesn't understand the Quick-Start Option will simply
forward the packet with the Quick-Start Request unchanged (ensuring
...
... router that doesn't understand the Quick-Start Option will simply
forward the packet with the Quick-Start Request unchanged (ensuring
that the TTL Diff will not match and Quick-Start ...
... Quick-Start Request unchanged (ensuring
that the TTL Diff will not match and Quick-Start will not be used).
If the participating router ...
...
If the participating router has decided to approve the Quick-Start
Request, it does the following:
* The router ...
... * If the router is only willing to approve a Rate Request less than
that in the Quick-Start Request, then the router replaces the Rate
Request with a smaller value. The router ...
... Request with a smaller value. The router MUST NOT increase the
Rate Request in the Quick-Start Request. If the router decreases
...
...
If the router approves the Quick-Start Request, this approval SHOULD
be taken into account in the router's decision to accept or reject
...
... be taken into account in the router's decision to accept or reject
subsequent Quick-Start Requests (e.g., using a variable that tracks
the recent aggregate of accepted Quick-Start Requests). This
...
... subsequent Quick-Start Requests (e.g., using a variable that tracks
the recent aggregate of accepted Quick-Start Requests). This
consideration of earlier approved Quick-Start Requests is necessary
...
... the recent aggregate of accepted Quick-Start Requests). This
consideration of earlier approved Quick-Start Requests is necessary
to ensure that the router only approves a Quick-Start Request ...
... Quick-Start Requests is necessary
to ensure that the router only approves a Quick-Start Request when
the router judges that the output link ...
... router judges that the output link will remain underutilized if
this and earlier Quick-Start Requests are used by the senders.
...
... senders.
In addition, the approval of a Quick-Start Request SHOULD NOT be used
by the router to affect the treatment of the data packets ...
... round-trip times. That is, the
approval by the router of a Quick-Start Request does not give
differential treatment for Quick-Start data packets ...
... router of a Quick-Start Request does not give
differential treatment for Quick-Start data packets at that router;
...
... router that the router believes that
the subsequent Quick-Start data packets from this connection will not
...
...
A non-participating router forwards the Quick-Start Request
unchanged, without decrementing the QS TTL. The non-participating
...
... RFC1812]. As a result, the sender will be
able to detect that the Quick-Start Request had not been understood
or approved by all of the routers along the path.
...
... router that uses multipath routing for packets within a single
connection MUST NOT approve a Quick-Start Request. This is discussed
in more detail in Section 9.2.
...
...
If the Quick-Start Option has the Function field set to "1000", then
this is a Report of Approved Rate, rather than a Rate Request. The
router ...
... router may implement some policy for cheaters. For instance, the
router MAY decide to deny future Quick-Start Requests from this
sender, including, if desired, deleting Quick-Start Requests ...
... Quick-Start Requests from this
sender, including, if desired, deleting Quick-Start Requests from
future packets from this sender. Section 9.4.1 discusses misbehaving
...
... downstream routers have approved the
Quick-Start Request for a smaller rate or denied the use of Quick-
Start, and adjust its bandwidth ...
... Quick-Start Request for a smaller rate or denied the use of Quick-
Start, and adjust its bandwidth allocations accordingly.
...
... The Quick-Start Mechanisms in TCP ...
...
This section describes how the Quick-Start mechanism would be used in
TCP. We first sketch the procedure and then tightly define it in the
...
... sending rate in bits per second,
appropriately formatted, in the Quick-Start Option in the IP header
of the TCP ...
... IP header
of the TCP packet, called the Quick-Start Request packet. (We will
be somewhat loose in our use of "packet" vs. "segment" in this
...
... be somewhat loose in our use of "packet" vs. "segment" in this
section.) When used for initial start-up, the Quick-Start Request
packet can be either the SYN ...
... segment" in this
section.) When used for initial start-up, the Quick-Start Request
packet can be either the SYN or SYN ...
... receiver (say, host B) returns the
Quick-Start Response option in the TCP header in the responding
SYN ...
... host A of the results of their request.
If the acknowledging packet does not contain a Quick-Start Response,
or contains a Quick-Start Response with the wrong value for the TTL
Diff ...
... If the acknowledging packet does not contain a Quick-Start Response,
or contains a Quick-Start Response with the wrong value for the TTL
Diff or the QS Nonce, then host ...
... TTL
Diff or the QS Nonce, then host A MUST assume that its Quick-Start
request failed. In this case, host A sends a Report of Approved Rate
with a Rate Report of zero, and uses TCP ...
... TCP's default congestion control
procedure. For initial start-up, host A uses the default initial
congestion window ...
...
If the returning packet contains a valid Quick-Start Response, then
host A uses the information in the response, along with its
...
... host A uses the information in the response, along with its
measurement of the round-trip time, to determine the Quick-Start
congestion window (QS ...
... data packets are defined as
data packets sent as the result of a successful Quick-Start request,
up to the time when the first Quick-Start packet is acknowledged.
...
... data packets sent as the result of a successful Quick-Start request,
up to the time when the first Quick-Start packet is acknowledged.
The sender also sends a Report of Approved Rate. In order to use
...
... The sender also sends a Report of Approved Rate. In order to use
Quick-Start, the TCP host MUST use rate-based pacing [VH97 ...
... host MUST use rate-based pacing [VH97] to
transmit Quick-Start packets at the rate indicated in the Quick-Start
Response, at the level of granularity possible by the sending host ...
... VH97] to
transmit Quick-Start packets at the rate indicated in the Quick-Start
Response, at the level of granularity possible by the sending host.
...
... TCP end-hosts can independently decide whether to request
Quick-Start. For example, host A could send a Quick-Start Request in
...
... Quick-Start. For example, host A could send a Quick-Start Request in
the SYN packet, and host ...
... Sending the Quick-Start Request ...
... ACK, or data packet. In this case, if the packet is acknowledged
but no Quick-Start Response is included, then the sender knows that
the Quick-Start Request ...
... Quick-Start Response is included, then the sender knows that
the Quick-Start Request has been denied, and can send a Report of
Approved Rate.
...
... Approved Rate.
In addition to the use of Quick-Start when a connection is
established, there are several additional points in a connection ...
... a transport protocol may want to issue a Rate Request. We first
reiterate the notion that Quick-Start is a coarse-grained mechanism.
That is, Quick-Start's Rate Requests are not meant to be used for
...
... reiterate the notion that Quick-Start is a coarse-grained mechanism.
That is, Quick-Start's Rate Requests are not meant to be used for
fine-grained control of the transport's sending rate ...
... sending rate.
The following are potential points where Quick-Start may be useful:
(1) At or soon after connection initiation ...
... RFC3124], or other mechanisms for sharing
congestion information may not need Quick-Start to determine an
appropriate rate.)
...
... probe the network to see if it can send at a
higher rate. (Alternatively, traditional slow-start should be
used in this case when Quick-Start is not available.)
...
... higher rate. (Alternatively, traditional slow-start should be
used in this case when Quick-Start is not available.)
(4) After an application-limited period ...
... capacity and has no valid estimate for its fair share. In this
case, Quick-Start may be an appropriate mechanism to determine if
the sender can send at a higher rate. For instance, consider an
...
... TCP sender MAY attempt
to use Quick-Start in cases (1) and (2). It is NOT RECOMMENDED that
a TCP sender ...
... a TCP sender use Quick-Start for case (3) at the current time. Case
(3) requires external notifications not presently defined for TCP ...
... transport protocols. Finally, a TCP SHOULD NOT use Quick-
Start for case (4) at the current time. Case (4) requires further
thought and investigation with regard to how the transport protocol
...
... could determine it was in a situation that would warrant transmitting
a Quick-Start Request.
As a general guideline, a TCP ...
... round-trip time.
Section 4.7 discusses some of the issues of using Quick-Start at
connection initiation, and Section 4.8 discusses issues that arise
...
... connection initiation, and Section 4.8 discusses issues that arise
when Quick-Start is used to request a larger sending rate after an
idle period ...
... The Quick-Start Response Option in the TCP header ...
... TCP receiver responds
to the receipt of a Quick-Start Request with a Quick-Start Response,
using the Quick-Start ...
... receiver responds
to the receipt of a Quick-Start Request with a Quick-Start Response,
using the Quick-Start Response Option in the TCP header ...
... Quick-Start Request with a Quick-Start Response,
using the Quick-Start Response Option in the TCP header. TCP's
...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: The Quick-Start Response Option in the TCP Header.
...
... TCP Header.
The first byte of the Quick-Start Response option contains the option
kind, identifying the TCP option.
...
... TCP option.
The second byte of the Quick-Start Response option contains the
option length in bytes. The length field MUST be set to 8 bytes.
...
... 8 bytes.
The third byte of the Quick-Start Response option contains a four-
bit Reserved field ...
... Reserved field, and the four-bit allowed Rate Request, formatted
as in the Quick-Start Rate Request option.
The fourth byte of the TCP option ...
... IP TTL and QS TTL fields in
the received Quick-Start Request packet, as calculated in equations
(1) or (2) (depending on whether IPv4 or IPv6 ...
...
We note that, while there are limitations on the potential size of
the Quick-Start Response Option, a Quick-Start Response Option of
eight bytes should not be a problem. The TCP Options ...
... We note that, while there are limitations on the potential size of
the Quick-Start Response Option, a Quick-Start Response Option of
eight bytes should not be a problem. The TCP Options field can
...
... TCP: Sending the Quick-Start Response ...
... host B) that receives an IP packet containing a
Quick-Start Request passes the Quick-Start Request, along with the
value in the IP TTL ...
... IP packet containing a
Quick-Start Request passes the Quick-Start Request, along with the
value in the IP TTL field, to the receiving ...
... If the TCP host is willing to permit the Quick-Start Request, then a
Quick-Start Response option is included in the TCP header ...
... host is willing to permit the Quick-Start Request, then a
Quick-Start Response option is included in the TCP header of the
corresponding acknowledgement packet. The Rate Request in the
...
... TCP header of the
corresponding acknowledgement packet. The Rate Request in the
Quick-Start Response option is set to the received value of the Rate
Request in the Quick-Start Option, or to a lower value if the TCP ...
... Quick-Start Response option is set to the received value of the Rate
Request in the Quick-Start Option, or to a lower value if the TCP
...
... receiver is only willing to allow a lower Rate Request. The TTL Diff
in the Quick-Start Response is set to the difference between the IP
TTL value and the QS TTL value as given in equation (1) or (2)
...
... Response is set to the received value of the QS Nonce in the Quick-
Start Option.
If an end host ...
... If an end host receives an IP packet with a Quick-Start Request with
a rate request of zero, then that host SHOULD NOT send a Quick-Start ...
... Quick-Start Request with
a rate request of zero, then that host SHOULD NOT send a Quick-Start
Response.
...
... Response.
The Quick-Start Response MUST NOT be resent if it is lost in the
network. Packet loss ...
... congestion on the
return path, in which case it is better not to approve the Quick-
Start Request.
...
... host (say, TCP host A) that sent a Quick-Start Request and
receives a Quick-Start Response in an acknowledgement first checks
...
... host A) that sent a Quick-Start Request and
receives a Quick-Start Response in an acknowledgement first checks
that the Quick-Start Response is valid ...
... receives a Quick-Start Response in an acknowledgement first checks
that the Quick-Start Response is valid. The Quick-Start Response is
...
... that the Quick-Start Response is valid. The Quick-Start Response is
valid if it contains the correct value for the TTL Diff ...
... TTL Diff, and an equal
or lesser value for the Rate Request than that transmitted in the
Quick-Start Request. In addition, if the received Rate Request is K,
then the rightmost 2K bits of the QS Nonce ...
... bits in
the QS Nonce sent in the Quick-Start Request. If these checks are
not successful, then the Quick-Start Request failed, and the TCP ...
... QS Nonce sent in the Quick-Start Request. If these checks are
not successful, then the Quick-Start Request failed, and the TCP host
...
... TCP congestion window that it would have used
without Quick-Start. If the rightmost 2K bits of the QS Nonce do not
...
... match those bits in the QS Nonce sent in the Quick-Start Request, for
a received Rate Request of K, then the TCP host ...
... TCP host MUST NOT send
additional Quick-Start Requests during the life of the connection.
Whether or not the Quick-Start Request ...
... Quick-Start Requests during the life of the connection.
Whether or not the Quick-Start Request was successful, the host
receiving ...
... host
receiving the Quick-Start Response MUST send a Report of Approved
Rate. Similarly, if the packet containing the Quick-Start Request is
...
... receiving the Quick-Start Response MUST send a Report of Approved
Rate. Similarly, if the packet containing the Quick-Start Request is
acknowledged, but the acknowledgement does not include a Quick-Start
...
... Rate. Similarly, if the packet containing the Quick-Start Request is
acknowledged, but the acknowledgement does not include a Quick-Start
Response, then the sender MUST send a Report of Approved Rate.
...
... and the TCP host is going to use the Quick-Start Request, it MUST
start using it within one round-trip time ...
... host is going to use the Quick-Start Request, it MUST
start using it within one round-trip time of receiving the Quick-
...
... round-trip time of receiving the Quick-
Start Response, or within three seconds, whichever is smaller. To
use the Quick-Start Request, the host ...
... Start Response, or within three seconds, whichever is smaller. To
use the Quick-Start Request, the host sets its Quick-Start congestion
window ...
... use the Quick-Start Request, the host sets its Quick-Start congestion
window (in terms of MSS-sized segments ...
... QS-cwnd is used, the TCP host sets a flag that it is in Quick-Start
mode, and while in Quick-Start mode, the TCP ...
... host sets a flag that it is in Quick-Start
mode, and while in Quick-Start mode, the TCP sender MUST use rate-
...
... TCP sender MUST use rate-
based pacing to pace out Quick-Start packets at the approved rate.
If, during Quick-Start mode, the TCP ...
... based pacing to pace out Quick-Start packets at the approved rate.
If, during Quick-Start mode, the TCP sender receives ACKs ...
... sender receives ACKs for packets
sent before this Quick-Start mode was entered, these ACKs are
processed as usual, following the default congestion control ...
... processed as usual, following the default congestion control
mechanisms. Quick-Start mode ends when the TCP host receives an ACK ...
... If the congestion window has not been fully used when the first ack
arrives ending the Quick-Start mode, then the congestion window is
decreased to the amount that has actually been used so far. This is
...
... congestion window is
decreased to the amount that has actually been used so far. This is
necessary because when the Quick-Start Response is received, the TCP
sender ...
... routers processing the
IP Quick-Start Option, or because of delays at the receiver in
responding to the Quick-Start Request ...
... Quick-Start Option, or because of delays at the receiver in
responding to the Quick-Start Request packet. In this case, an
overly large round-trip-time estimate could have caused the TCP ...
... TCP
sender to translate the approved Quick-Start sending rate in bytes
per second into a congestion window ...
... sender receiving an ACK for the first Quick- Start packet
before the entire congestion window has been used. Thus, when the
...
... TCP sender receives the first ACK for a Quick-Start packet, the
sender MUST reduce the congestion window ...
... As an example, a