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-rw-r--r--Documentation/networking/dccp.txt29
1 files changed, 23 insertions, 6 deletions
diff --git a/Documentation/networking/dccp.txt b/Documentation/networking/dccp.txt
index a62fdf7a6bf..271d524a4c8 100644
--- a/Documentation/networking/dccp.txt
+++ b/Documentation/networking/dccp.txt
@@ -1,18 +1,20 @@
DCCP protocol
-============
+=============
Contents
========
-
- Introduction
- Missing features
- Socket options
+- Sysctl variables
+- IOCTLs
+- Other tunables
- Notes
+
Introduction
============
-
Datagram Congestion Control Protocol (DCCP) is an unreliable, connection
oriented protocol designed to solve issues present in UDP and TCP, particularly
for real-time and multimedia (streaming) traffic.
@@ -29,9 +31,9 @@ It has a base protocol and pluggable congestion control IDs (CCIDs).
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 Linux DCCP implementation does not currently support all the features that are
specified in RFCs 4340...42.
@@ -45,7 +47,6 @@ http://linux-net.osdl.org/index.php/DCCP_Testing#Experimental_DCCP_source_tree
Socket options
==============
-
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
@@ -112,6 +113,7 @@ DCCP_SOCKOPT_CCID_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
================
Several DCCP default parameters can be managed by the following sysctls
@@ -155,15 +157,30 @@ 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.
+
+Other tunables
+==============
+Per-route rto_min support
+ CCID-2 supports the RTAX_RTO_MIN per-route setting for the minimum value
+ of the RTO timer. This setting can be modified via the 'rto_min' option
+ of iproute2; for example:
+ > ip route change 10.0.0.0/24 rto_min 250j dev wlan0
+ > ip route add 10.0.0.254/32 rto_min 800j dev wlan0
+ > ip route show dev wlan0
+ CCID-3 also supports the rto_min setting: it is used to define the lower
+ bound for the expiry of the nofeedback timer. This can be useful on LANs
+ with very low RTTs (e.g., loopback, Gbit ethernet).
+
+
Notes
=====
-
DCCP does not travel through NAT successfully at present on many boxes. This is
because the checksum covers the pseudo-header as per TCP and UDP. Linux NAT
support for DCCP has been added.