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Diffstat (limited to 'Documentation/networking/dccp.txt')
| -rw-r--r-- | Documentation/networking/dccp.txt | 39 |
1 files changed, 32 insertions, 7 deletions
diff --git a/Documentation/networking/dccp.txt b/Documentation/networking/dccp.txt index afb66f9a8aff..39131a3c78f8 100644 --- a/Documentation/networking/dccp.txt +++ b/Documentation/networking/dccp.txt @@ -14,24 +14,35 @@ Introduction ============ Datagram Congestion Control Protocol (DCCP) is an unreliable, connection -based protocol designed to solve issues present in UDP and TCP particularly -for real time and multimedia traffic. +oriented protocol designed to solve issues present in UDP and TCP, particularly +for real-time and multimedia (streaming) traffic. +It divides into a base protocol (RFC 4340) and plugable congestion control +modules called CCIDs. Like plugable TCP congestion control, at least one CCID +needs to be enabled in order for the protocol to function properly. In the Linux +implementation, this is the TCP-like CCID2 (RFC 4341). Additional CCIDs, such as +the TCP-friendly CCID3 (RFC 4342), are optional. +For a brief introduction to CCIDs and suggestions for choosing a CCID to match +given applications, see section 10 of RFC 4340. It has a base protocol and pluggable congestion control IDs (CCIDs). -It is at proposed standard RFC status and the homepage for DCCP as a protocol -is at: - http://www.read.cs.ucla.edu/dccp/ +DCCP is a Proposed Standard (RFC 2026), and the homepage for DCCP as a protocol +is at http://www.ietf.org/html.charters/dccp-charter.html Missing features ================ -The DCCP implementation does not currently have all the features that are in -the RFC. +The Linux DCCP implementation does not currently support all the features that are +specified in RFCs 4340...42. The known bugs are at: http://linux-net.osdl.org/index.php/TODO#DCCP +For more up-to-date versions of the DCCP implementation, please consider using +the experimental DCCP test tree; instructions for checking this out are on: +http://linux-net.osdl.org/index.php/DCCP_Testing#Experimental_DCCP_source_tree + + Socket options ============== @@ -46,6 +57,12 @@ 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_SERVER_TIMEWAIT enables the server (listening socket) to hold +timewait state when closing the connection (RFC 4340, 8.3). The usual case is +that the closing server sends a CloseReq, whereupon the client holds timewait +state. When this boolean socket option is on, the server sends a Close instead +and will enter TIMEWAIT. This option must be set after accept() returns. + 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 @@ -72,6 +89,8 @@ 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). +On unidirectional connections it is useful to close the unused half-connection +via shutdown (SHUT_WR or SHUT_RD): this will reduce per-packet processing costs. Sysctl variables ================ @@ -123,6 +142,12 @@ sync_ratelimit = 125 ms sequence-invalid packets on the same socket (RFC 4340, 7.5.4). The unit of this parameter is milliseconds; a value of 0 disables rate-limiting. +IOCTLS +====== +FIONREAD + Works as in udp(7): returns in the `int' argument pointer the size of + the next pending datagram in bytes, or 0 when no datagram is pending. + Notes ===== |