Update the session/SOL mgmt section in ipmi doc

phosphor-ipmi-net manages session(RMCP+) & SOL commands directly
and responses to those commands. As these commands can also be
requested through host (KCS) interface, phosphor-ipmi-host daemon
must also need details about session & SOL. In order to maintain
sync between phosphor-ipmi-net & phosphor-ipmi-host daemon,
session & SOL are exposed in D-Bus, which phosphor-ipmi-host
can query and respond to commands issued through host interface(KCS).

Signed-off-by: Suryakanth Sekar <suryakanth.sekar@linux.intel.com>
Change-Id: I629c35b20ee225972be6c2588514281cafa40157
diff --git a/ipmi-architecture.md b/ipmi-architecture.md
index 13960ee..d5cf749 100644
--- a/ipmi-architecture.md
+++ b/ipmi-architecture.md
@@ -16,14 +16,28 @@
 
 
 ```
-___________          ___________________
-| KCS/BT  |          |                 |
-| Channel | <------> |                 |
-----------/          | IPMI Daemon     |
------------          |   (ipmid)       |
-| RMCP+   |          |                 |
-| Channel | <------> |                 |
-----------/          ------------------/
+                                                     /------------------\
+    /----------------------------\                   |                  |
+    |      KCS/BT - Host         | <-All IPMI cmds-> |                  |
+    |                            |                   |                  |
+    \----------------------------/                   |   IPMI Daemon    |
+                                                     |    (ipmid)       |
+                                                     |                  |
+   /-----------------------------\                   |                  |
+   |            LAN - RMCP+      |                   |                  |
+   | /--------------------------\|                   |                  |
+   | |*Process the Session and  || <-All IPMI cmds-> |                  |
+   | | SOL commands.            ||  except session   |                  |
+   | |*Create Session Objs      ||  and SOL cmds     |                  |
+   | \--------------------------/|                   |                  |
+   \-----------------------------/                   \------------------/
+                :                                             ^
+                :                                             |
+                :                                             |
+     /-------------------------\                              |
+     | Active session/SOL Objs | <---------Query the session-/
+     | - Properities           |           and SOL data via Dbus
+     \-------------------------/
 ```
 
 
@@ -88,6 +102,14 @@
 completion code would prevent the command from executing and would be returned
 to the caller.
 
+The network channel bridges (netipmid), executing one process per interface,
+handle session (RMCP+) and SOL commands and responses to those commands.
+Get/Set SOL configuration, Get session info, close session commands can also be
+requested through KCS/BT interface, ipmid daemon must also need details about
+session and SOL. In order to maintain sync between ipmid and netipmid
+daemon, session and SOL are exposed in D-Bus, which ipmid can query and respond
+to commands issued through host interface (KCS/BT).
+
 The next phase is parameter unpacking and validation. This is done by
 compiler-generated code with variadic templates at handler registration time.
 The registration function is a templated function that allows any type of