Initial checkin. This file will describe SOL in ipmitool at a high level.

ipmitool/src/plugins/lanplus/README.sol

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+This document was last updated for release 1.8.8.
+
+This document explains how Serial Over Lan is implemented on in the
+impitool IPMI client.  Obviously, the code itself is authoritative, but
+this document should serve as a good starting point.
+
+Serial Over Lan (SOL) is defined in the IPMI v2 specification published by
+Intel and available at http://www.intel.com/design/servers/ipmi/.  SOL
+functionality is built on top of the RMCP+ protocol as an additional
+payload type (type 1).
+
+The high end SOL logic is implemented in src/ipmitool/lib/ipmi_sol.c.  SOL
+sessions are begun in ipmitool using the "sol activate" command.  This
+command maps directly to the IPMI Activate Payload command.  It first
+verifies that an RMCP+ session (lanplus interface) is being used to
+establish the session.  Although the spec allows for a SOL connection to be
+established on a port different than the RMCP+ port that the "activate
+payload" command issued, impitool does not support this.
+
+Once a session has been established (the activate payload command
+succeeds), impitool simply loops over a select() on user input and data
+returned from the BMC.  All user input is first filtered so that special
+escape sequences can suspend or deactivate the SOL session and so that data
+can be broken into chunks no greater than N bytes.  This maximum is
+specified by the BMC in the response to the Activate Payload command.
+
+User input to the BMC is handled in ipmitool/src/plugins/lanplus/lanplus.c.
+Every SOL packet (with one exception) traveling in either direction causes
+the recipient to return an acknowledgement packet, though acks themself are
+not acknowledged.  The transport layer in lanplus.c handles the logic
+regarding acks, partial acks, sequence numbers.  SOL acknowledgements
+packets be acks, partial acks (the remote destination processed only some
+of the data), and nacks (requests to stop sending packets).  Nacks are not
+honored by ipmitool.
+
+Note that one way that SOL communication differs from standard IPMI
+commands, is that it is not simply a request response protocol.  Packets
+may be returned asyncrhonously from the BMC.  When establishing a SOL
+session, impitool registers a callback for asynchonously received data.
+This call back simply prints text returned from the BMC.
+
+Once a user has chosen to exit the SOL session (with ~.) ipmitool sends the
+IPMI SOL Deactivate command to the BMC.
+
+The standard code path for SOL logic follows:
+    ipmi_sol_main (ipmi_sol.c):
+
+    ipmi_sol_activate (ipmi_sol.c):
+        Argument validation
+        Creation and dispatch of IPMI Activate Payload command
+
+    ipmi_sol_red_pill (ipmi_sol.c):
+        Loop on select() for user input and data returned from the BMC
+        Periodic dispatch of "keep alive" packet to the BMC.
+        Send user input to the BMC and BMC data to the console.
+        
+        processSolUserInput (ipmi_sol.c):
+            Process possible escape sequences (~., ~B, etc.)
+            Send (with retries) user data to the BMC
+            Partial creation of packet payload
+
+                ipmi_lanplus_send_sol (lanplus.c):
+                    Completion of packet payload
+                    Send (with retries) of SOL packet
+
+                     ipmi_lanplus_send_payload (lanplus.c):
+                         Creation of RMCP+ packet
+                         Details general to all V2 packet processing, as
+                         well as a some logic to handle ack reception.
+
+                     is_sol_partial_ack (lanplus.c):
+                         Determine whether a data needs to be resent
+
+        ipmi_lanplus_recv_sol (lanplus.c):
+            Handle data received by the BMC.  Ack as appropriate.
+