]> Simula Metropolitan Centre for Digital Engineering

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Münster University of Applied Sciences

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HAW Hamburg, Informatics Department

Berliner Tor 7 20099 Hamburg Germany +49-40-42875-8104 martin.becke@haw-hamburg.de http://www.scimbe.de/about.html

Internet-Draft This document describes an extension to the SCTP sockets API for querying information about the sender queue.

Introduction This draft describes an extension to the SCTP sockets API (see , ) which allows an application to query the sender queue utilization per stream. This information is necessary for applications to make efficient use of a mapping of streams to dissimilar paths. A detailed description including simulation results can be found in . In particular, this API extension is useful when using the CMT-SCTP, CMT/RPv1-SCTP, CMT/RPv2-SCTP and MPTCP-like extensions (see , , , , , , ) for Concurrent Multipath Transfer (CMT) with SCTP.

Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Sender Queue Info (SCTP_SQINFO) This socket option obtains the maximum sender queue size (in bytes), the current total sender queue utilization (in bytes) as well as the current utilization per stream (in bytes). The following structure is used to obtain the sender queue information:

sq_assoc_id:

This parameter is ignored for one-to-one style sockets. For one-to-many style sockets this parameter indicates which association the user is performing an action upon. It is an error to use SCTP_{CURRENT|ALL}_ASSOC in sq_assoc_id.

sq_queue_limit:

This field gives the maximum sender queue size in bytes.

sq_total_queued:

This field gives the current total sender queue utilization in bytes.

sq_number_of_streams:

This field gives the number of outgoing streams. That is, it will contain the number of valid sq_queued_on_stream entries.

sq_queued_on_stream:

This array gives the current number of bytes queued for the streams 0 to sq_number_of_streams-1.

Note, that the caller of getsockopt() MUST provide a sctp_sndqueueinfo structure which can hold at least as many sq_queued_on_stream entries as the association's number of outgoing streams. Otherwise, the getsockopt() call will fail and return an error.

Testbed Platform A large-scale and realistic Internet testbed platform with support for the multi-homing feature of the underlying SCTP protocol is NorNet. A description of NorNet is provided in , , some further information can be found on the project website .

Security Considerations Security considerations for the SCTP sockets API are described by .

IANA Considerations This document does not require IANA actions.

Acknowledgments The authors would like to thank Michael Tuexen and Irene Ruengeler for their support.

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document obsoletes RFC 2960 and RFC 3309. It describes the Stream Control Transmission Protocol (SCTP). SCTP is designed to transport Public Switched Telephone Network (PSTN) signaling messages over IP networks, but is capable of broader applications. SCTP is a reliable transport protocol operating on top of a connectionless packet network such as IP. It offers the following services to its users: -- acknowledged error-free non-duplicated transfer of user data, -- data fragmentation to conform to discovered path MTU size, -- sequenced delivery of user messages within multiple streams, with an option for order-of-arrival delivery of individual user messages, -- optional bundling of multiple user messages into a single SCTP packet, and -- network-level fault tolerance through supporting of multi-homing at either or both ends of an association. The design of SCTP includes appropriate congestion avoidance behavior and resistance to flooding and masquerade attacks. [STANDARDS-TRACK] This document describes a mapping of the Stream Control Transmission Protocol (SCTP) into a sockets API. The benefits of this mapping include compatibility for TCP applications, access to new SCTP features, and a consolidated error and event notification scheme. This document is not an Internet Standards Track specification; it is published for informational purposes. University of Delaware HAW Hamburg SimulaMet University of Delaware Franklin and Marshall College Cisco Systems Netflix Muenster Univ. of Appl. Sciences The Stream Control Transmission Protocol (SCTP) supports multi-homing for providing network fault tolerance. However, mainly one path is used for data transmission. Only timer-based retransmissions are carried over other paths as well. This document describes how multiple paths can be used simultaneously for transmitting user messages. SimulaMet HAW Hamburg University of Duisburg-Essen This document describes extensions to the SCTP sockets API for configuring the CMT-SCTP and CMT/RP-SCTP extensions. Informative References