udp: squashed the wsa work and added documentation work

1 files changed, 30 insertions, 12 deletions

diff --git a/host/docs/transport.rst b/host/docs/transport.rst
index f28d1efcb..b601cd8ff 100644
--- a/host/docs/transport.rst
+++ b/host/docs/transport.rst
@@ -19,7 +19,10 @@ The transport parameters are defined below for the various transports in the UHD
 ------------------------------------------------------------------------
 UDP transport (sockets)
 ------------------------------------------------------------------------
-The UDP transport is implemented with standard user-space/Berkeley sockets.
+The UDP transport is implemented with user-space sockets:
+
+* **UNIX:** standard Berkeley sockets API using send()/recv()
+* **Windows:** Windows Sockets API (WSA) using overlapped IO
 
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 Transport parameters
@@ -31,21 +34,18 @@ The following parameters can be used to alter the transport's default behavior:
 * **send_frame_size:** The size of a single send buffer in bytes
 * **num_send_frames:** The number of send buffers to allocate
 
-**Note1:** num_recv_frames and num_send_frames do not affect performance.
+**Note1:**
+num_recv_frames does not affect performance (all platforms).
+
+**Note2:**
+num_send_frames does not affect performance (UNIX only).
 
-**Note2:** recv_frame_size and send_frame_size can be used to
+**Note3:**
+recv_frame_size and send_frame_size can be used to
 increase or decrease the maximum number of samples per packet.
 The frame sizes default to an MTU of 1472 bytes per IP/UDP packet,
 and may be increased if permitted by your network hardware.
 
-**Note3:** For lower latency at low sample rates, use smaller buffers
-
-**Note4:** For overall lower latency, look for Interrupt Coalescing settings
-for your OS and ethernet chipset.  It seems the Intel ethernet chipsets offer
-fine-grained control in Linux.  Also, consult:
-
-* http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibm.aix.prftungd/doc/prftungd/interrupt_coal.htm
-
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 Flow control parameters
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -73,6 +73,25 @@ The following parameters can be used to alter socket's buffer sizes:
 **Note:** Large send buffers tend to decrease transmit performance.
 
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Latency Optimization
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Latency is a measurement of the time it takes a sample to travel between the host and device.
+Most computer hardware and software is bandwidth optimized which may negatively affect latency.
+If your application has strict latency requirements, please consider the following notes:
+
+**Note1:**
+The time taken by the device to populate a packet is proportional to the sample rate.
+Therefore, to improve receive latency, configure the transport for a smaller frame size.
+
+**Note2:**
+For overall latency improvements,
+look for "Interrupt Coalescing" settings for your OS and ethernet chipset.
+It seems the Intel ethernet chipsets offer fine-grained control in Linux.
+Also, consult:
+
+* http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibm.aix.prftungd/doc/prftungd/interrupt_coal.htm
+
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 Linux specific notes
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 On linux, the maximum buffer sizes are capped by the sysctl values
@@ -90,7 +109,6 @@ Windows specific notes
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 On Windows, it is important to change the default UDP behavior such that
 1500 byte packets still travel through the fast path of the sockets stack.
-
 FastSendDatagramThreshold registry key to change documented here:
 
 * http://www.microsoft.com/windows/windowsmedia/howto/articles/optimize_web.aspx#appendix_e