Internet DRAFT - draft-welzl-taps-transports
draft-welzl-taps-transports
TAPS M. Welzl
Internet-Draft University of Oslo
Intended status: Informational M. Tuexen
Expires: March 24, 2016 Muenster Univ. of Appl. Sciences
N. Khademi
University of Oslo
September 21, 2015
An Approach to Identify Services Provided by IETF Transport Protocols
and Congestion Control Mechanisms
draft-welzl-taps-transports-00
Abstract
This document describes a method to identify services in transport
protocols and congestion control mechanisms. It shows the approach
using TCP and SCTP (base protocol) as examples.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 24, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. General Considerations . . . . . . . . . . . . . . . . . . . . 3
3. Pass 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Services Provided by TCP . . . . . . . . . . . . . . . . . 4
3.1.1. Excluded Services . . . . . . . . . . . . . . . . . . 7
3.2. Services Provided by SCTP . . . . . . . . . . . . . . . . 7
3.2.1. Excluded Services . . . . . . . . . . . . . . . . . . 10
4. Pass 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. CONNECTION Related Services . . . . . . . . . . . . . . . 11
4.2. DATA Transfer Related Services . . . . . . . . . . . . . . 15
5. Pass 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.1. CONNECTION Related Services . . . . . . . . . . . . . . . 17
5.2. DATA Transfer Related Services . . . . . . . . . . . . . . 20
5.2.1. Sending Data . . . . . . . . . . . . . . . . . . . . . 20
5.2.2. Receiving Data . . . . . . . . . . . . . . . . . . . . 21
5.2.3. Errors . . . . . . . . . . . . . . . . . . . . . . . . 21
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
8. Security Considerations . . . . . . . . . . . . . . . . . . . 22
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
9.1. Normative References . . . . . . . . . . . . . . . . . . . 22
9.2. Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
This document considers every form of defined interaction between a
transport protocol and its user ("upper layer protocol" or
"application") as a "service". Here, the term "service" is NOT the
same as the term used to specify the entire "above transport"
protocol that maps to a port number or service name (which is another
common meaning of the term "service" in the context of transport
protocols).
The list of services in this document is strictly based on the parts
of relevant protocol specifications that relate to what the protocol
provides to an application using it and how the application interacts
with it. It is based on text that describes what a protocol provides
to the upper layer and how it is used (abstract API descriptions),
given for the base protocols in [RFC0793], [RFC1122] and [RFC4960].
It does not cover API instances, for example the one given for SCTP
in [RFC6458]. It also does not cover parts of the protocol that are
explicitly stated as optional to implement.
The document presents a three-pass process to arrive at a list of
transport protocol services. In the first pass, the relevant RFC
text is discussed per protocol. In the second pass, this discussion
is used to derive a list of services that are uniformly categorized
across protocols. Here, an attempt is made to present services in a
slightly generalized form to highlight similarities. This is, for
example, achieved by renaming "commands" (or "transport primitives")
of protocols or by avoiding a strict 1:1-mapping between these
commands and services in the list. Finally, the third pass presents
all services from pass 2, identifying which protocol implements them.
In the list resulting from the second pass, some services are missing
because they are implicit in some protocols, and they only become
explicit when we consider the superset of all services offered by all
protocols. For example, TCP's reliability includes integrity via a
checksum, but we have to include a protocol like UDP-Lite as
specified in [RFC3828] (which has a configurable checksum) in the
list to consider an always-on checksum as a service (it would not be
a service if no protocol would allow to disable / configure the
checksum). Similar arguments apply to other protocol functions (e.g.
congestion control). The complete list of services across all
protocols is therefore only available after pass 3.
2. General Considerations
This document discusses unicast [AUTHOR'S NOTE: for simplicity, for
now. Hopefully forever, for simplicity.] transport protocols.
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[AUTHOR'S NOTE: we skip "congestion control mechanisms" for now.
This simplifies the discussion; the congestion control mechanisms
part is about LEDBAT, which is easy to add later.] Transport
protocols provide communication between processes that operate on
network endpoints, which means that they allow for multiplexing of
such communication between the same IP addresses, and normally such
multiplexing is achieved using port numbers. Port multiplexing is
therefore assumed to be always provided and not discussed as a
service.
Some protocols are connection-oriented. Connection-orientation, to
the user of an application, means that there is state shared between
the endpoints that persists across messages. Connection-oriented
protocols often use an initial call to "open" a connection before
communication can progress, and require communication to be
explicitly terminated by issuing a "close" call. Moreover, a
"connection" is the common state that some transport primitives refer
to, e.g. to adjust general configuration settings. Connections
establishment, maintenance and termination are therefore used to
categorize certain services of connection-oriented transport
protocols in pass 2 and 3.
3. Pass 1
In this first iteration, the relevant text parts of the RFCs
describing the protocols are summarized, focusing on what a protocol
provides to the upper layer and how it is used (abstract API
descriptions). The resulting text is somewhat heterogeneous in
terminology - e.g. the user of the protocol is called "Application"
in TCP and "Upper-Layer Protocol (ULP)" in SCTP, and TCP's "user
commands" are called "ULP primitives" in SCTP.
3.1. Services Provided by TCP
[RFC0793] states: "TCP is a connection-oriented, end-to-end reliable
protocol (..)". Section 3.8 in [RFC0793] further specifies the
interaction with the application by listing several user commands.
It is also assumed that the Operating System provides a means for TCP
to asynchronously signal the user program. Here, we describe the
relevant user commands and notifications to the application.
open: this is either active or passive, to initiate a connection or
listen for incoming connections. All other commands are
associated with a specific connection, which is assumed to first
have been opened. An active open call contains a fully specified
foreign socket (IP address + port number). A passive open call
with a fully specified foreign socket waits for a particular
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connection; alternatively, a passive open call can leave the
foreign socket unspecified to accept any incoming connection. A
fully specified passive call can later be made active by executing
'send'. Optionally, a timeout can be specified, after which TCP
will abort the connection if data is not successfully delivered to
the destination (else a default timeout value is used). [RFC1122]
describes a procedure for aborting the connection that must be
used to avoid excessive retransmissions, and states that an
application must be able to control the threshold used to
determine the condition for aborting -- and that this threshold
may be measured in time units or as a count of retransmission.
This indicates that the timeout could also be specified as a count
of retransmission.
Also optional, for multihomed hosts, the local IP address can be
provided [RFC1122]. If it is not provided, a default choice will
be made in case of active open calls. A passive open call will
await incoming connection requests to all local addresses and then
maintain usage of the local IP address where the incoming
connection request has arrived. Finally, the 'options' parameter
is explained in [RFC1122] to let the application specify IP
options such as source route, record route, or timestamp. (It is
not stated on which segments of a connection these options should
be applied, but probably all segments, as this is also stated in a
specification given for the usage of source route (section 4.2.3.8
of [RFC1122]). As the only non-optional IP option in this
parameter, an application can specify a source route when it
actively opens a TCP connection.
send: this command hands over a provided number of bytes that TCP
should reliably send to the other side of the connection. The
PUSH flag, if set, requires data to be promptly transmitted to the
receiver without delaying it. Conversely, not using PUSH can
reduce the number of unnecessary wakeup calls to the receiving
application process. [RFC1122] states that "Generally, an
interactive application protocol must set the PUSH flag at least
in the last SEND call in each command or response sequence. A
bulk transfer protocol like FTP should set the PUSH flag on the
last segment of a file or when necessary to prevent buffer
deadlock." An optional timeout parameter can be provided that
updates the connection's timeout (see "open").
receive: This command allocates a receiving buffer for a provided
number of bytes. It returns the number of received bytes provided
in the buffer when these bytes have been received and written into
the buffer by TCP.
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close: This command closes one side of a connection. It is
semantically equivalent to "I have no more data to send" but does
not mean "I will not receive any more", as the other side may
still have data to send. This call reliably delivers any data
that has already been handed over to TCP (and if that fails,
'close' becomes 'abort'). Close also implies push function.
abort: This command causes all pending SENDs and RECEIVES to be
aborted, the TCB to be removed, and a special RESET message to be
sent to the TCP on the other side of the connection. See
[RFC0793].
close event: TCP will signal a user, even if no RECEIVEs are
outstanding, that the other side has closed, so the user can
terminate his/her side gracefully. See [RFC0793], Section 3.5.
abort event: When TCP aborts a connection upon receiving a "Reset"
from the peer, it "advises the user and goes to the CLOSED state."
See [RFC0793], Section 3.4.
USER TIMEOUT event: This event, described in Section 3.9 of
[RFC0793], is executed when the user timeout expires (see 'open').
All queues are flushed and the user is signaled "error: connection
aborted due to user timeout".
ERROR_REPORT event: This event, described in Section 4.2.4.1 of
[RFC1122], informs the application of "soft errors" that can be
safely ignored, including the arrival of an ICMP error message or
excessive retransmissions (reaching a threshold below the
threshold where the connection is aborted).
Type-of-Service: Section 4.2.4.2 of [RFC1122] states that the
application layer MUST be able to specify the Type-of-Service
(TOS) for segments that are sent on a connection. The application
should be able to change the TOS during the connection lifetime,
and the TOS value should be passed to the IP layer unchanged.
Since then, parts of the TOS field have been assigned to ECN
[RFC3168] and the six most significant bits have been assigned to
DiffServ by the name of DSField [RFC3260]. Staying with the
intention behind the application's ability to specify the "Type of
Service", this should probably be interpreted to mean the value in
the DSField, which is the Differentiated Services Codepoint
(DSCP). [AUTHOR's NOTE: text trying to "read between the lines"
of RFCs here... this perhaps calls for an update to [RFC1122]?]
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Nagle: An application can disable the Nagle algorithm on an
individual connection. This algorithm delays sending data for
some time to increase the likelihood of sending a full-sized
segment.
3.1.1. Excluded Services
The 'send' and 'receive' commands include usage of an "URGENT"
mechanism, which SHOULD NOT be implemented according to [RFC6093] and
is therefore not described here. This also concerns the notification
"Urgent pointer advance" in the ERROR_REPORT described in Section
4.2.4.1 of [RFC1122].
The 'open' command specified in [RFC0793] can be handed optional
Precedence or security/compartment information according to
[RFC0793], but this was not incuded here because it is mostly
irrelevant today, as explained in [RFC7414]. The 'open' command also
includes a parameter "options" that is explained in [RFC1122] to let
the application specify IP options such as source route, record
route, or timestamp. This parameter was not included here because it
is not clear which segments of a connection (all?) these options
would then be applied to.
The 'status' command was not included because [RFC0793] calls this
command "implementation dependent" and states that it "could be
excluded without adverse effect". Moreover, while a data block
containing specific information is described, it is also stated that
not all of this information may always be available. The 'receive'
command can (under some conditions) yield the status of the PUSH flag
according to [RFC0793], but this TCP functionality is made optional
in [RFC1122] and hence not considered here. Generally, section
4.2.2.2 of [RFC1122] says that PUSH on send calls MAY be implemented,
which could be a reason not to consider it here. However, the text
then explains that "an interactive application protocol must set the
PUSH flag at least in the last SEND call in each command or response
sequence", and most implementations provide some option to cause a
behavior that is in some way similar to PUSH. Therefore PUSH is
described as a part of SEND here. [RFC1122] also introduces keep-
alives to TCP, but these are optional and hence not considered here.
[RFC1122] describes that "some TCP implementations have included a
FLUSH call", indicating that this call is optional to implement. It
is therefore not considered here.
3.2. Services Provided by SCTP
Section 1.1 of [RFC4960] lists limitations of TCP that SCTP removes.
Three of the four mentioned limitations directly translate into a
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service that is visible to an application using SCTP: 1) it allows
for preservation of message delineations; 2) these messages, while
reliably transferred, do not require to be in order unless the
application wants it; 3) multi-homing is supported. In SCTP,
connections are called "association" and they can be between not only
two (as in TCP) but multiple transport addresses at each end point.
For SCTP running over IP, [RFC4960] defines a "transport address" as
"the combination of an IP address and an SCTP port number (where SCTP
is the transport protocol)".
Section 10 of [RFC4960] further specifies the interaction with the
application (which RFC [RFC4960] calls the "Upper Layer Protocol"
(ULP)). It is assumed that the Operating System provides a means for
SCTP to asynchronously signal the user program. Here, we describe
the relevant ULP primitives and notifications to the ULP process:
Initialize: Initialize creates a local SCTP instance which it binds
to a set of local addresses (and, if provided, port number).
Initialize needs to be called only once per set of local
addresses.
Associate: This creates an association (the SCTP equivalent of a
connection) between the local SCTP instance and a remote SCTP
instance. Most primitives are associated with a specific
association, which is assumed to first have been created.
Associate can return a list of destination transport addresses so
that multiple paths can later be used. One of the transport
addresses from the returned destination addresses will be selected
by the local endpoint as default primary path for sending SCTP
packets to this peer, but this choice can be changed by the ULP
using the list of destination addresses. Associate is also given
the number of outgoing streams to request and optionally returns
the number of outgoing streams negotiated.
Send: This sends a message of a certain length in bytes over an
association. A number can be provided to later refer to the
correct message when reporting an error and a stream id is
provided to specify the stream to be used inside an association
(we consider this as a mandatory parameter here for simplicity: if
not provided, the stream id defaults to 0). An optional maximum
life time can specify the time after which the message should be
discarded rather than sent. A choice (advisory, i.e. not
guaranteed) of the preferred path can be made by providing a
destination transport address, and the message can be delivered
out-of-order if the unordered flag is set. Another advisory flag
indicates the ULP's preference to avoid bundling user data with
other outbound DATA chunks (i.e., in the same packet). The
handling of this no-bundle flags is similar to the sender side
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handling of the TCP PUSH flag. A payload protocol-id can be
provided to pass a value that indicates the type of payload
protocol data to the peer.
Receive: Messages are received from an association, and optionally a
stream within the association, with their size returned. The ULP
is notified of the availability of data via a DATA ARRIVE
notification. If the sender has included a payload protocol-id,
this value is also returned. If the received message is only a
partial delivery of a whole message, a partial flag will indicate
so, in which case the stream id and a stream sequence number are
provided to the ULP.
Shutdown: This primitive gracefully closes an association, reliably
delivering any data that has already been handed over to SCTP. A
return code informs about success or failure of this procedure.
Abort: This ungracefully closes an association, by discarding any
locally queued data and informing the peer that the association
was aborted. Optionally, an abort reason to be passed to the peer
may be provided by the ULP. A return code informs about success
or failure of this procedure.
Change Heartbeat / Request Heartbeat: This allows the ULP to enable/
disable heartbeats and optionally specify a heartbeat frequency as
well as requesting a single heartbeat to be carried out upon a
function call, with a notification about success or failure of
transmitting the HEARTBEAT chunk to the destination.
Set Protocol Parameters: This allows to set values for protocol
parameters per association; for some parameters, a setting can be
made per transport address. The set listed in [RFC4960] is:
RTO.Initial; RTO.Min; RTO.Max; Max.Burst; RTO.Alpha; RTO.Beta;
Valid.Cookie.Life; Association.Max.Retrans; Path.Max.Retrans;
Max.Init.Retransmits; HB.interval; HB.Max.Burst.
Set Primary: This allows to set a new primary default path for an
association by providing a transport address. Optionally, a
default source address to be used in IP datagrams can be provided.
Status: The 'Status' primitive returns a data block with information
about a specified association, containing: association connection
state; destination transport address list; destination transport
address reachability states; current receiver window size; current
congestion window sizes; number of unacknowledged DATA chunks;
number of DATA chunks pending receipt; primary path; most recent
SRTT on primary path; RTO on primary path; SRTT and RTO on other
destination addresses.
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COMMUNICATION UP notification: When a lost communication to an
endpoint is restored or when SCTP becomes ready to send or receive
user messages, this notification informs the ULP process about the
affected association, the type of event that has occurred, the
complete set of transport addresses of the peer, the maximum
number of allowed streams and the inbound stream count (the number
of streams the peer endpoint has requested).
DATA ARRIVE notification: When a message is ready to be retrieved
via the Receive primitive, the ULP process is informed by this
notification.
SEND FAILURE notification / Receive Unsent Message / Receive
Unacknowledged Message: When a message cannot be delivered via an
association, the sender can be informed about it and learn whether
the message has just not been acknowledged or (e.g. in case of
lifetime expiry) if it has not even been sent.
NETWORK STATUS CHANGE notification: The NETWORK STATUS CHANGE
notification informs the ULP about a transport address becoming
active/inactive.
COMMUNICATION LOST notification: When SCTP loses communication to an
endpoint (e.g. via Heartbeats or excessive retransmission) or
detects an abort, this notification informs the ULP process of the
affected association and the type of event (failure OR termination
in response to a shutdown or abort request).
SHUTDOWN COMPLETE notification: When SCTP completes the shutdown
procedures, this notification is passed to the upper layer,
informing it about the affected assocation.
3.2.1. Excluded Services
For the 'Set Primary' primitive, an optional possibility to specify
the source transport address to be used in outgoing IP datagrams is
described, but the RFC text says "some implementations may allow you
to", indicating that implementing this in SCTP is optional. This
functionality is therefore not considered here. The 'Receive'
primitive can also return certain additional information, but this is
also left up to the implementation and therefore not considered.
With a COMMUNICATION LOST notification, some more information may
optionally be passed to the ULP (e.g., identification to retrieve
unsent and unacknowledged data). SCTP "can invoke" a COMMUNICATION
ERROR notification and "may send" a RESTART notification, making
these two notifications optional to implement. The list provided
under 'Status' includes "etc", indicating that more information could
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be provided. The primitive 'Get SRTT Report' returns information
that is included in what 'Status' provides and is therefore not
discussed. Similarly, 'Set Failure Threshold' sets only one out of
various possible parameters included in 'Set Protocol Parameters'.
The 'Destroy SCTP Instance' primitive was excluded: it erases the
SCTP instance that was created by 'Initialize', but this does not
translate into a service for the ULP.
4. Pass 2
Here we categorize the services from pass 1 based on whether they
relate to a connection or to data transmission. Services are
presented following the nomenclature
"CATEGORY.[SUBCATEGORY].SERVICENAME.PROTOCOL". We present
"connection" as a general protocol-independent concept and use it to
refer to both TCP's connections (which are identifiable by a unique
socket pair, where a socket is defined as an IP address and TCP port)
and SCTP's associations (which are identifiable by multiple IP
address and port number pairs). We define the "transport address" as
"the combination of an IP address and a transport protocol's port
number". The "application" is the user of the protocol (called
"Upper-Level Protocol (ULP)" in SCTP).
Some minor details are omitted for the sake of generalization --
e.g., for SCTP's 'close', [RFC4960] states that success or failure is
returned, whereas this is not described in the same way for TCP in
[RFC0793], but this detail plays no significant role for the service
provided by either TCP or SCTP.
4.1. CONNECTION Related Services
ESTABLISHMENT:
Active creation of a connection from one transport address to one or
more transport addresses.
o CONNECT.TCP:
Command / event: 'open' (active) or 'open' (passive) with
destination transport address, followed by 'send'
Parameters: 1 local IP address (optional); 1 destination transport
address (for active open; else the destination transport address
and the local IP address of the succeeding incoming connection
request will be maintained); timeout (optional); options
(optional)
Comments: If the local IP address is not provided, a default
choice will automatically be made. [AUTHOR'S NOTE: [RFC1122] does
not clearly state this, but it seems to be the implication of some
text there.] The timeout can also be a retransmission count. The
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options are IP options to be used on all segments of the
connection. At least the Source Route option is mandatory for TCP
to provide.
o CONNECT.SCTP:
Command / event: 'initialize', followed by 'associate'
Parameters: list of local transport addresses (initialize); 1
destination transport address; outbound stream count
Returns: destination transport address list
Comments: 'initialize' needs to be called only once per local
transport address list. One destination transport address will
automatically be chosen; it can later be changed in MAINTENANCE.
AVAILABILITY:
Preparing to receive incoming connection requests.
o LISTEN.TCP:
Command / event: 'open' (passive)
Parameters: 1 local IP address (optional); 1 destination transport
address (optional); timeout (optional)
Comments: if the transport address and/or local IP address is
provided, this waits for incoming connections from only and/or to
only the provided address. Else this waits for incoming
connections without this / these restraint(s). ESTABLISHMENT can
later be done with 'send'.
o LISTEN.SCTP:
Command / event: 'initialize', followed by 'COMMUNICATION UP'
notification
Parameters: list of local transport addresses (initialize)
Returns: destination transport address list; outbound stream
count; inbound stream count
Comments: initialize needs to be called only once per local
transport address list. COMMUNICATION UP can also follow a
COMMUNICATION LOST notification, indicating that the lost
communication is restored.
MAINTENANCE:
Adjustments made to an open connection, or notifications about it.
These are out-of-band messages to the protocol that can be issued at
any time, at least after a connection has been established and before
it has been terminated (with one exception: CHANGE-TIMEOUT.TCP can
only be issued when new data are handed over for sending).
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o CHANGE-TIMEOUT.TCP:
Command / event: 'send'
Parameters: timeout value
Comments: when sending data, the connection's timeout value (time
after which the connection will be aborted if data cannot be
delivered) can be adjusted.
o CHANGE-TIMEOUT.SCTP:
Command / event: 'Change HeartBeat' combined with 'Set Protocol
Parameters'
Parameters: 'Change HeartBeat': heartbeat frequency; 'Set Protocol
Parameters': Association.Max.Retrans (whole association) or
Path.Max.Retrans (per transport address)
Comments: Change Heartbeat can enable / disable heartbeats in SCTP
as well as change their frequency. The parameter
Association.Max.Retrans defines after how many unsuccessful
heartbeats the connection will be terminated; thus these two
commands / parameters together can yield a similar behavior to
CHANGE-TIMEOUT.TCP.
o DISABLE-NAGLE.TCP:
Command / event: not specified
Parameters: one boolean value
Comments: the Nagle algorithm delays data transmission to increase
the chance to send a full-sized segment. An application must be
able to disable this algorithm for a connection. This is related
to the no-bundle flag in DATA.SEND.SCTP.
o REQUESTHEARTBEAT.SCTP:
Command / event: 'Request HeartBeat'
Parameters: destination transport address
Returns: success or failure
Comments: requests a heartbeat to be immediately carried out on a
path, returning success or failure.
o SETPROTOCOLPARAMETERS.SCTP:
Command / event: 'Set Protocol Parameters'
Parameters: RTO.Initial; RTO.Min; RTO.Max; Max.Burst; RTO.Alpha;
RTO.Beta; Valid.Cookie.Life; Association.Max.Retrans;
Path.Max.Retrans; Max.Init.Retransmits; HB.interval; HB.Max.Burst
o SETPRIMARY.SCTP:
Command / event: 'Set Primary'
Parameters: destination transport address
Returns: result of attempting this operation
Comments: update the current primary address to be used, based on
the set of available destination transport addresses of the
association.
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o ERROR.TCP:
Command / event: 'ERROR_REPORT'
Returns: reason (encoding not specified); subreason (encoding not
specified)
Comments: soft errors that can be ignored without harm by many
applications; an application should be able to disable these
notifications. The reported conditions include at least:
Excessive Retransmissions and ICMP error message arrived.
o STATUS.SCTP:
Command / event: 'Status' and 'NETWORK STATUS CHANGE' notification
Returns: data block with information about a specified
association, containing: association connection state; destination
transport address list; destination transport address reachability
states; current receiver window size; current congestion window
sizes; number of unacknowledged DATA chunks; number of DATA chunks
pending receipt; primary path; most recent SRTT on primary path;
RTO on primary path; SRTT and RTO on other destination addresses.
The NETWORK STATUS CHANGE notification informs the application
about a transport address becoming active/inactive.
o CHANGE-DSCP.TCP:
Command / event: not specified
Parameters: DSCP value
Comments: This allows an application to change the DSCP value. It
was only specified for the TOS field in [RFC1122], which is here
interpreted to refer to the DSField as per [RFC3260].
TERMINATION:
Gracefully or forcefully closing a connection, or being informed
about this event happening.
o CLOSE.TCP:
Command / event: 'close'
Comments: this terminates the sending side of a connection after
reliably delivering all remaining data. Close also implies push
function (see DATA.SEND.TCP).
o CLOSE.SCTP:
Command / event: 'Shutdown'
Comments: this terminates a connection after reliably delivering
all remaining data.
o ABORT.TCP:
Command / event: 'abort'
Comments: this terminates a connection without delivering
remaining data and sends an error message to the other side.
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o ABORT.SCTP:
Command / event: 'abort'
Parameters: abort reason to be given to the peer (optional)
Comments: this terminates a connection without delivering
remaining data and sends an error message to the other side.
o TIMEOUT.TCP:
Command / event: 'USER TIMEOUT' event
Comments: the application is informed that the connection is
aborted. This event is executed when the timeout set in
CONNECTION.ESTABLISHMENT.CONNECT.TCP (and possibly adjusted in
CONNECTION.MAINTENANCE.CHANGE-TIMEOOUT.TCP) expires.
o TIMEOUT.SCTP:
Command / event: 'COMMUNICATION LOST' event
Comments: the application is informed that the connection is
aborted. this event is executed when the timeout that should be
enabled by default (see beginning of section 8.3 in [RFC4960]) and
was possibly adjusted in CONNECTION.MAINTENANCE.CHANGE-
TIMEOOUT.SCTP expires.
o ABORT-EVENT.TCP:
Command / event: not specified
o ABORT-EVENT.SCTP:
Command / event: 'COMMUNICATION LOST' event
Returns: abort reason from the peer (if available)
Comments: the application is informed that the other side has
aborted the connection using CONNECTION.TERMINATION.ABORT.SCTP.
o CLOSE-EVENT.TCP:
Command / event: not specified
o CLOSE-EVENT.SCTP:
Command / event: 'SHUTDOWN COMPLETE' event
Comments: the application is informed that
CONNECTION.TERMINATION.CLOSE.SCTP was successfully completed.
4.2. DATA Transfer Related Services
All commands in this section refer to an existing connection, i.e. a
connection that was either established or made available for
receiving data. In addition to the listed parameters, all sending
commands contain a reference to a data block and all receiving
commands contain a reference to available buffer space for the data.
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o SEND.TCP:
Command / event: 'send'
Parameters: PUSH flag (optional); timeout (optional)
Comments: If the push flag is set, the data block should promptly
be transmitted to the receiver without waiting. The timeout can
be configured with this call whenever data are sent (see also
CONNECTION.MAINTENANCE.CHANGE-TIMEOUT.TCP).
o SEND.SCTP:
Command / event: 'Send'
Parameters: stream number; context (optional); life time
(optional); destination transport address (optional); unordered
flag (optional); no-bundle flag (optional); payload protocol-id
(optional)
Comments: the 'stream number' denotes the stream to be used. The
'context' number can later be used to refer to the correct message
when an error is reported. The 'life time' specifies a time after
which this data block will not be sent. The 'destination
transport address' can be used to state which path should be
preferred, if there are multiple paths available (see also
CONNECTION.MAINTENANCE.SETPRIMARY.SCTP). The data block can be
delivered out-of-order if the 'unordered flag' is set. The 'no-
bundle flag' can be set to indicate a preference to avoid bundling
(this is related to CONNECTION.MAINTENANCE.DISABLE-NAGLE.TCP).
The 'payload protocol-id' is a number that will, if it was
provided, be handed over to the receiving application.
o RECEIVE.TCP:
Command / event: 'receive'
o RECEIVE.SCTP:
Command / event: 'DATA ARRIVE' notification, followed by 'Receive'
Parameters: stream number (optional)
Returns: stream sequence number (optional), partial flag
(optional)
Comments: if the 'stream number' is provided, the call to receive
only receives data on one particular stream. If a partial message
arrives, this is indicated by the 'partial flag', and then the
'stream sequence number' must be provided such that an application
can restore the correct order of data blocks an entire message
consists of.
o SENDFAILURE-EVENT.SCTP:
Command / event: 'SEND FAILURE' notification, optionally followed
by 'Receive Unsent Message' or 'Receive Unacknowledged Message'
Returns: cause code; context; unsent or unacknowledged message
(optional)
Comments: 'cause code' indicates the reason of the failure, and
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'context' is the context number if such a number has been provided
in DATA.SEND.SCTP, for later use with 'Receive Unsent Message' or
'Receive Unacknowledged Message', respectively. These commands
can be used to retrieve the complete unsent or unacknowledged
message if desired.
5. Pass 3
Here we present the superset of all services in all protocols, based
on the list in pass 2 but also on text in pass 1 to include services
that can be configured in one protocol and are static properties in
another. Again, some minor details are omitted for the sake of
generalization -- e.g., TCP may provide various different IP options
but only supporting source route is mandatory to implement, and this
detail is no longer visible in "Specify IP Options". The detail was
removed because no other protocols provide this features. [AUTHOR'S
NOTE: and if we find another one that does, we need that detail
again.]
[AUTHOR'S NOTE: the list here looks pretty similar to the list in
pass 2 for now. This will change as more protocols are added. For
example, if we add UDP, we will find that UDP does not do congestion
control, which is relevant to the application using it. This will
have to be reflected in pass 1 and pass 2, only for UDP. In pass 3,
we can derive "congestion control" as a service of TCP and SCTP
because it probably does not make much sense to write that only UDP
provides a congestion control related service: the "service" of not
doing it -- meaning that it may require more work from the
application developer.]
5.1. CONNECTION Related Services
ESTABLISHMENT:
Active creation of a connection from one transport address to one or
more transport addresses.
o Specify IP Options
Protocols: TCP
o Request multiple streams
Protocols: SCTP
o Obtain multiple destination transport addresses
Protocols: SCTP
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AVAILABILITY:
Preparing to receive incoming connection requests.
o Listen, 1 specified local interface
Protocols: TCP, SCTP
o Listen, N specified local interfaces
Protocols: SCTP
o Listen, all local interfaces (unspecified)
Protocols: TCP, SCTP
o Obtain requested number of streams
Protocols: SCTP
MAINTENANCE:
Adjustments made to an open connection, or notifications about it.
NOTE: all services except "set primary path" in this category apply
to one out of multiple possible paths (identified via destination
transport addresses) in SCTP, whereas TCP uses only one path (one
destination transport address).
o Change timeout for aborting connection (using retransmit limit or
time value)
Protocols: TCP, SCTP
o Disable Nagle algorithm
Protocols: TCP
Comments: This is available in SCTP implementations, but not
specified in [RFC4960].
o Request an immediate heartbeat, returning success/failure
Protocols: SCTP
o Set protocol parameters
Protocols: SCTP
SCTP parameters: RTO.Initial; RTO.Min; RTO.Max; Max.Burst;
RTO.Alpha; RTO.Beta; Valid.Cookie.Life; Association.Max.Retrans;
Path.Max.Retrans; Max.Init.Retransmits; HB.interval; HB.Max.Burst
Comments: in future versions of this document, it might make sense
to split out some of these parameters -- e.g., if a different
protocol provides means to adjust the RTO calculation there could
be a common service for them called "adjust RTO calculation".
o Notification of Excessive Retransmissions (early warning below
abortion threshold)
Protocols: TCP
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o Notification of ICMP error message arrival
Protocols: TCP
o Status (query or notification)
Protocols: SCTP
SCTP parameters: association connection state; destination
transport address list; destination transport address reachability
states; current receiver window size; current congestion window
sizes; number of unacknowledged DATA chunks; number of DATA chunks
pending receipt; primary path; most recent SRTT on primary path;
RTO on primary path; SRTT and RTO on other destination addresses;
transport address becoming active / inactive
o Set primary path
Protocols: SCTP
o Change DSCP
Protocols: TCP
Comments: This is described to be changeable for SCTP too in
[RFC6458].
TERMINATION:
Gracefully or forcefully closing a connection, or being informed
about this event happening.
o Close after reliably delivering all remaining data, causing an
event informing the application on the other side
Protocols: TCP, SCTP
Comments: TCP's locally only closes the connection for sending; it
may still receive data afterwards.
o Abort without delivering remaining data, causing an event
informing the application on the other side
Protocols: TCP, SCTP
Comments: In SCTP a reason can optionally be given by the
application on the aborting side, which can then be received by
the application on the other side.
o Timeout event when data could not be delivered for too long
Protocols: TCP, SCTP
Comments: the timeout is configured with CONNECTION.MAINTENANCE
"Change timeout for aborting connection (using retransmit limit or
time value)".
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5.2. DATA Transfer Related Services
All services in this section refer to an existing connection, i.e. a
connection that was either established or made available for
receiving data. In addition to the listed parameters, all sending
commands contain a reference to a data block and all receiving
commands contain a reference to available buffer space for the data.
Reliable data transfer entails delay -- e.g. for the sender to wait
until it can transmit data, or due to retransmission in case of
packet loss.
5.2.1. Sending Data
All services in this section are provided by DATA.SEND from pass 2.
DATA.SEND is given a data block from the application, which we here
call a "message".
o Reliably transfer data
Protocols: TCP, SCTP
o Notifying the receiver to promptly hand over data to application
Protocols: TCP
Comments: This seems unnecessary in SCTP, where data arrival
causes an event for the application.
o Message identification
Protocols: SCTP
o Choice of stream
Protocols: SCTP
o Choice of path (destination address)
Protocols: SCTP
o Message lifetime
Protocols: SCTP
o Choice between unordered (potentially faster) or ordered delivery
Protocols: SCTP
o Request not to bundle messages
Protocols: SCTP
o Specifying a "payload protocol-id" (handed over as such by the
receiver)
Protocols: SCTP
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5.2.2. Receiving Data
All services in this section are provided by DATA.RECEIVE from pass
2. DATA.RECEIVE fills a buffer provided to the application, with
what we here call a "message".
o Receive data
Protocols: TCP, SCTP
o Choice of stream to receive on
Protocols: SCTP
o Message identification
Protocols: SCTP
Comments: In SCTP, this is optionally achieved with a "stream
sequence number". The stream sequence number is always provided
in case of partial message arrival.
o Information about partial message arrival
Protocols: SCTP
Comments: In SCTP, partial messages are combined with a stream
sequence number so that the application can restore the correct
order of data blocks an entire message consists of.
5.2.3. Errors
This section describes sending failures that are associated with a
specific call to DATA.SEND from pass 2.
o Notification of unsent messages
Protocols: SCTP
o Notification of unacknowledged messages
Protocols: SCTP
6. Acknowledgements
The authors would like to thank Joe Touch for comments on the TCP
part. This work has received funding from the European Union's
Horizon 2020 research and innovation programme under grant agreement
No. 644334 (NEAT). The views expressed are solely those of the
author(s).
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7. IANA Considerations
XX RFC ED - PLEASE REMOVE THIS SECTION XXX
This memo includes no request to IANA.
8. Security Considerations
Security will be considered in future versions of this document.
9. References
9.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, DOI 10.17487/
RFC1122, October 1989,
<http://www.rfc-editor.org/info/rfc1122>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<http://www.rfc-editor.org/info/rfc4960>.
9.2. Informative References
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<http://www.rfc-editor.org/info/rfc3168>.
[RFC3260] Grossman, D., "New Terminology and Clarifications for
Diffserv", RFC 3260, DOI 10.17487/RFC3260, April 2002,
<http://www.rfc-editor.org/info/rfc3260>.
[RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., Ed.,
and G. Fairhurst, Ed., "The Lightweight User Datagram
Protocol (UDP-Lite)", RFC 3828, DOI 10.17487/RFC3828,
July 2004, <http://www.rfc-editor.org/info/rfc3828>.
[RFC6093] Gont, F. and A. Yourtchenko, "On the Implementation of the
TCP Urgent Mechanism", RFC 6093, DOI 10.17487/RFC6093,
January 2011, <http://www.rfc-editor.org/info/rfc6093>.
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[RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
Yasevich, "Sockets API Extensions for the Stream Control
Transmission Protocol (SCTP)", RFC 6458, DOI 10.17487/
RFC6458, December 2011,
<http://www.rfc-editor.org/info/rfc6458>.
[RFC7414] Duke, M., Braden, R., Eddy, W., Blanton, E., and A.
Zimmermann, "A Roadmap for Transmission Control Protocol
(TCP) Specification Documents", RFC 7414, DOI 10.17487/
RFC7414, February 2015,
<http://www.rfc-editor.org/info/rfc7414>.
Authors' Addresses
Michael Welzl
University of Oslo
PO Box 1080 Blindern
Oslo, N-0316
Norway
Phone: +47 22 85 24 20
Email: michawe@ifi.uio.no
Michael Tuexen
Muenster University of Applied Sciences
Stegerwaldstrasse 39
Steinfurt 48565
Germany
Email: tuexen@fh-muenster.de
Naeem Khademi
University of Oslo
PO Box 1080 Blindern
Oslo, N-0316
Norway
Email: naeemk@ifi.uio.no
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