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* Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
#include <stddef.h>
#include <stdint.h>
#include "absl/types/optional.h"
#include "net/dcsctp/public/types.h"
namespace dcsctp {
struct DcSctpOptions {
// The largest safe SCTP packet. Starting from the minimum guaranteed MTU
// value of 1280 for IPv6 (which may not support fragmentation), take off 85
// bytes for DTLS/TURN/TCP/IP and ciphertext overhead.
// Additionally, it's possible that TURN adds an additional 4 bytes of
// overhead after a channel has been established, so an additional 4 bytes is
// subtracted
// 1280 IPV6 MTU
// -40 IPV6 header
// -8 UDP
// -24 GCM Cipher
// -13 DTLS record header
// -4 TURN ChannelData
// = 1191 bytes.
static constexpr size_t kMaxSafeMTUSize = 1191;
// The local port for which the socket is supposed to be bound to. Incoming
// packets will be verified that they are sent to this port number and all
// outgoing packets will have this port number as source port.
int local_port = 5000;
// The remote port to send packets to. All outgoing packets will have this
// port number as destination port.
int remote_port = 5000;
// The announced maximum number of incoming streams. Note that this value is
// constant and can't be currently increased in run-time as "Add Incoming
// Streams Request" in RFC6525 isn't supported.
// The socket implementation doesn't have any per-stream fixed costs, which is
// why the default value is set to be the maximum value.
uint16_t announced_maximum_incoming_streams = 65535;
// The announced maximum number of outgoing streams. Note that this value is
// constant and can't be currently increased in run-time as "Add Outgoing
// Streams Request" in RFC6525 isn't supported.
// The socket implementation doesn't have any per-stream fixed costs, which is
// why the default value is set to be the maximum value.
uint16_t announced_maximum_outgoing_streams = 65535;
// Maximum SCTP packet size. The library will limit the size of generated
// packets to be less than or equal to this number. This does not include any
// overhead of DTLS, TURN, UDP or IP headers.
size_t mtu = kMaxSafeMTUSize;
// The largest allowed message payload to be sent. Messages will be rejected
// if their payload is larger than this value. Note that this doesn't affect
// incoming messages, which may larger than this value (but smaller than
// `max_receiver_window_buffer_size`).
size_t max_message_size = 256 * 1024;
// The default stream priority, if not overridden by
// `SctpSocket::SetStreamPriority`. The default value is selected to be
// compatible with, section 4.2-4.3.
StreamPriority default_stream_priority = StreamPriority(256);
// Maximum received window buffer size. This should be a bit larger than the
// largest sized message you want to be able to receive. This essentially
// limits the memory usage on the receive side. Note that memory is allocated
// dynamically, and this represents the maximum amount of buffered data. The
// actual memory usage of the library will be smaller in normal operation, and
// will be larger than this due to other allocations and overhead if the
// buffer is fully utilized.
size_t max_receiver_window_buffer_size = 5 * 1024 * 1024;
// Maximum send buffer size. It will not be possible to queue more data than
// this before sending it.
size_t max_send_buffer_size = 2'000'000;
// A threshold that, when the amount of data in the send buffer goes below
// this value, will trigger `DcSctpCallbacks::OnTotalBufferedAmountLow`.
size_t total_buffered_amount_low_threshold = 1'800'000;
// Max allowed RTT value. When the RTT is measured and it's found to be larger
// than this value, it will be discarded and not used for e.g. any RTO
// calculation. The default value is an extreme maximum but can be adapted
// to better match the environment.
DurationMs rtt_max = DurationMs(60'000);
// Initial RTO value.
DurationMs rto_initial = DurationMs(500);
// Maximum RTO value.
DurationMs rto_max = DurationMs(60'000);
// Minimum RTO value. This must be larger than an expected peer delayed ack
// timeout.
DurationMs rto_min = DurationMs(400);
// T1-init timeout.
DurationMs t1_init_timeout = DurationMs(1000);
// T1-cookie timeout.
DurationMs t1_cookie_timeout = DurationMs(1000);
// T2-shutdown timeout.
DurationMs t2_shutdown_timeout = DurationMs(1000);
// For t1-init, t1-cookie, t2-shutdown, t3-rtx, this value - if set - will be
// the upper bound on how large the exponentially backed off timeout can
// become. The lower the duration, the faster the connection can recover on
// transient network issues. Setting this value may require changing
// `max_retransmissions` and `max_init_retransmits` to ensure that the
// connection is not closed too quickly.
absl::optional<DurationMs> max_timer_backoff_duration = absl::nullopt;
// Hearbeat interval (on idle connections only). Set to zero to disable.
DurationMs heartbeat_interval = DurationMs(30000);
// The maximum time when a SACK will be sent from the arrival of an
// unacknowledged packet. Whatever is smallest of RTO/2 and this will be used.
DurationMs delayed_ack_max_timeout = DurationMs(200);
// The minimum limit for the measured RTT variance
// Setting this below the expected delayed ack timeout (+ margin) of the peer
// might result in unnecessary retransmissions, as the maximum time it takes
// to ACK a DATA chunk is typically RTT + ATO (delayed ack timeout), and when
// the SCTP channel is quite idle, and heartbeats dominate the source of RTT
// measurement, the RTO would converge with the smoothed RTT (SRTT). The
// default ATO is 200ms in usrsctp, and a 20ms (10%) margin would include the
// processing time of received packets and the clock granularity when setting
// the delayed ack timer on the peer.
// This is described for TCP in
DurationMs min_rtt_variance = DurationMs(220);
// The initial congestion window size, in number of MTUs.
// See which defaults at ~3
// and which argues for at least ten
// segments.
size_t cwnd_mtus_initial = 10;
// The minimum congestion window size, in number of MTUs, upon detection of
// packet loss by SACK. Note that if the retransmission timer expires, the
// congestion window will be as small as one MTU. See
size_t cwnd_mtus_min = 4;
// When the congestion window is at or above this number of MTUs, the
// congestion control algorithm will avoid filling the congestion window
// fully, if that results in fragmenting large messages into quite small
// packets. When the congestion window is smaller than this option, it will
// aim to fill the congestion window as much as it can, even if it results in
// creating small fragmented packets.
size_t avoid_fragmentation_cwnd_mtus = 6;
// The number of packets that may be sent at once. This is limited to avoid
// bursts that too quickly fill the send buffer. Typically in a a socket in
// its "slow start" phase (when it sends as much as it can), it will send
// up to three packets for every SACK received, so the default limit is set
// just above that, and then mostly applicable for (but not limited to) fast
// retransmission scenarios.
int max_burst = 4;
// Maximum Data Retransmit Attempts (per DATA chunk). Set to absl::nullopt for
// no limit.
absl::optional<int> max_retransmissions = 10;
// Max.Init.Retransmits ( Set
// to absl::nullopt for no limit.
absl::optional<int> max_init_retransmits = 8;
// RFC3758 Partial Reliability Extension
bool enable_partial_reliability = true;
// RFC8260 Stream Schedulers and User Message Interleaving
bool enable_message_interleaving = false;
// If RTO should be added to heartbeat_interval
bool heartbeat_interval_include_rtt = true;
// Disables SCTP packet crc32 verification. For fuzzers only!
bool disable_checksum_verification = false;
// Controls the "zero checksum option" feature, as defined in
// To have this feature enabled, both peers must be configured to use the
// same (defined, not "none") alternate error detection method.
zero_checksum_alternate_error_detection_method =
} // namespace dcsctp