+DCCP_SOCKOPT_SERVICE sets the service. The specification mandates use of
+service codes (RFC 4340, sec. 8.1.2); if this socket option is not set,
+the socket will fall back to 0 (which means that no meaningful service code
+is present). On active sockets this is set before connect(); specifying more
+than one code has no effect (all subsequent service codes are ignored). The
+case is different for passive sockets, where multiple service codes (up to 32)
+can be set before calling bind().
+
+DCCP_SOCKOPT_GET_CUR_MPS is read-only and retrieves the current maximum packet
+size (application payload size) in bytes, see RFC 4340, section 14.
+
+DCCP_SOCKOPT_SEND_CSCOV and DCCP_SOCKOPT_RECV_CSCOV are used for setting the
+partial checksum coverage (RFC 4340, sec. 9.2). The default is that checksums
+always cover the entire packet and that only fully covered application data is
+accepted by the receiver. Hence, when using this feature on the sender, it must
+be enabled at the receiver, too with suitable choice of CsCov.
+
+DCCP_SOCKOPT_SEND_CSCOV sets the sender checksum coverage. Values in the
+ range 0..15 are acceptable. The default setting is 0 (full coverage),
+ values between 1..15 indicate partial coverage.
+DCCP_SOCKOPT_RECV_CSCOV is for the receiver and has a different meaning: it
+ sets a threshold, where again values 0..15 are acceptable. The default
+ of 0 means that all packets with a partial coverage will be discarded.
+ Values in the range 1..15 indicate that packets with minimally such a
+ coverage value are also acceptable. The higher the number, the more
+ restrictive this setting (see [RFC 4340, sec. 9.2.1]). Partial coverage
+ settings are inherited to the child socket after accept().
+
+The following two options apply to CCID 3 exclusively and are getsockopt()-only.
+In either case, a TFRC info struct (defined in <linux/tfrc.h>) is returned.
+DCCP_SOCKOPT_CCID_RX_INFO
+ Returns a `struct tfrc_rx_info' in optval; the buffer for optval and
+ optlen must be set to at least sizeof(struct tfrc_rx_info).
+DCCP_SOCKOPT_CCID_TX_INFO
+ Returns a `struct tfrc_tx_info' in optval; the buffer for optval and
+ optlen must be set to at least sizeof(struct tfrc_tx_info).
+
+
+Sysctl variables
+================
+Several DCCP default parameters can be managed by the following sysctls
+(sysctl net.dccp.default or /proc/sys/net/dccp/default):
+
+request_retries
+ The number of active connection initiation retries (the number of
+ Requests minus one) before timing out. In addition, it also governs
+ the behaviour of the other, passive side: this variable also sets
+ the number of times DCCP repeats sending a Response when the initial
+ handshake does not progress from RESPOND to OPEN (i.e. when no Ack
+ is received after the initial Request). This value should be greater
+ than 0, suggested is less than 10. Analogue of tcp_syn_retries.
+
+retries1
+ How often a DCCP Response is retransmitted until the listening DCCP
+ side considers its connecting peer dead. Analogue of tcp_retries1.
+
+retries2
+ The number of times a general DCCP packet is retransmitted. This has
+ importance for retransmitted acknowledgments and feature negotiation,
+ data packets are never retransmitted. Analogue of tcp_retries2.
+
+send_ndp = 1
+ Whether or not to send NDP count options (sec. 7.7.2).
+
+send_ackvec = 1
+ Whether or not to send Ack Vector options (sec. 11.5).