16 Datagram Congestion Control Protocol (DCCP) is an unreliable, connection
17 based protocol designed to solve issues present in UDP and TCP particularly
18 for real time and multimedia traffic.
20 It has a base protocol and pluggable congestion control IDs (CCIDs).
22 It is at proposed standard RFC status and the homepage for DCCP as a protocol
24 http://www.read.cs.ucla.edu/dccp/
29 The DCCP implementation does not currently have all the features that are in
32 The known bugs are at:
33 http://linux-net.osdl.org/index.php/TODO#DCCP
38 DCCP_SOCKOPT_SERVICE sets the service. The specification mandates use of
39 service codes (RFC 4340, sec. 8.1.2); if this socket option is not set,
40 the socket will fall back to 0 (which means that no meaningful service code
41 is present). Connecting sockets set at most one service option; for
42 listening sockets, multiple service codes can be specified.
44 DCCP_SOCKOPT_GET_CUR_MPS is read-only and retrieves the current maximum packet
45 size (application payload size) in bytes, see RFC 4340, section 14.
47 DCCP_SOCKOPT_SEND_CSCOV and DCCP_SOCKOPT_RECV_CSCOV are used for setting the
48 partial checksum coverage (RFC 4340, sec. 9.2). The default is that checksums
49 always cover the entire packet and that only fully covered application data is
50 accepted by the receiver. Hence, when using this feature on the sender, it must
51 be enabled at the receiver, too with suitable choice of CsCov.
53 DCCP_SOCKOPT_SEND_CSCOV sets the sender checksum coverage. Values in the
54 range 0..15 are acceptable. The default setting is 0 (full coverage),
55 values between 1..15 indicate partial coverage.
56 DCCP_SOCKOPT_SEND_CSCOV is for the receiver and has a different meaning: it
57 sets a threshold, where again values 0..15 are acceptable. The default
58 of 0 means that all packets with a partial coverage will be discarded.
59 Values in the range 1..15 indicate that packets with minimally such a
60 coverage value are also acceptable. The higher the number, the more
61 restrictive this setting (see [RFC 4340, sec. 9.2.1]).
63 The following two options apply to CCID 3 exclusively and are getsockopt()-only.
64 In either case, a TFRC info struct (defined in <linux/tfrc.h>) is returned.
65 DCCP_SOCKOPT_CCID_RX_INFO
66 Returns a `struct tfrc_rx_info' in optval; the buffer for optval and
67 optlen must be set to at least sizeof(struct tfrc_rx_info).
68 DCCP_SOCKOPT_CCID_TX_INFO
69 Returns a `struct tfrc_tx_info' in optval; the buffer for optval and
70 optlen must be set to at least sizeof(struct tfrc_tx_info).
75 Several DCCP default parameters can be managed by the following sysctls
76 (sysctl net.dccp.default or /proc/sys/net/dccp/default):
79 The number of active connection initiation retries (the number of
80 Requests minus one) before timing out. In addition, it also governs
81 the behaviour of the other, passive side: this variable also sets
82 the number of times DCCP repeats sending a Response when the initial
83 handshake does not progress from RESPOND to OPEN (i.e. when no Ack
84 is received after the initial Request). This value should be greater
85 than 0, suggested is less than 10. Analogue of tcp_syn_retries.
88 How often a DCCP Response is retransmitted until the listening DCCP
89 side considers its connecting peer dead. Analogue of tcp_retries1.
92 The number of times a general DCCP packet is retransmitted. This has
93 importance for retransmitted acknowledgments and feature negotiation,
94 data packets are never retransmitted. Analogue of tcp_retries2.
97 Whether or not to send NDP count options (sec. 7.7.2).
100 Whether or not to send Ack Vector options (sec. 11.5).
103 The default Ack Ratio (sec. 11.3) to use.
106 Default CCID for the sender-receiver half-connection.
109 Default CCID for the receiver-sender half-connection.
112 The initial sequence window (sec. 7.5.2).
115 The size of the transmit buffer in packets. A value of 0 corresponds
116 to an unbounded transmit buffer.
118 sync_ratelimit = 125 ms
119 The timeout between subsequent DCCP-Sync packets sent in response to
120 sequence-invalid packets on the same socket (RFC 4340, 7.5.4). The unit
121 of this parameter is milliseconds; a value of 0 disables rate-limiting.
126 DCCP does not travel through NAT successfully at present on many boxes. This is
127 because the checksum covers the psuedo-header as per TCP and UDP. Linux NAT
128 support for DCCP has been added.