doc/menu_tcp_udp: Clarify TCP Client/Server

  - Remove "PVT" because the point is that this mechanism sends
    whatever data is configured, which is generic across
    serial/USB/Bluetooth.  It could be RTCM3 emitted by a base.
  - Clarify that this works in base mode; the previous PVT wording
    implied that it might not.
  - Be clearer about what client and server mean; with one's phone and
    a SparkFun device the point of view is confusing.
  - Hoist generic content to be above the TCP/UDP sections
  - Clarify that data flow is both ways in TCP, and by omission imply
    it isn't in UDP.

(Thanks to forum users ahsrabrifat and sparky.)

Author: gdt

docs/menu_tcp_udp.md

@@ -2,13 +2,16 @@
 
 Surveyor: ![Feature Supported](img/Icons/GreenDot.png) / Express: ![Feature Supported](img/Icons/GreenDot.png) / Express Plus: ![Feature Supported](img/Icons/GreenDot.png) / Facet: ![Feature Supported](img/Icons/GreenDot.png) / Facet L-Band: ![Feature Supported](img/Icons/GreenDot.png) / Reference Station: ![Feature Supported](img/Icons/GreenDot.png)
 
-![PVT Client and Server settings](<img/Terminal/SparkFun RTK Network Menu.png>)
+![Client and Server settings](<img/Terminal/SparkFun RTK Network Menu.png>)
 
-*PVT Client and Server settings*
+*Client and Server settings*
 
-## PVT Client and Server
+As an alternative to serial ports, serial over USB, or Bluetooth, the RTK device can send and receive GNSS data over TCP, and can send data over UDP.   These mechanisms sit on top of the network layer (WiFi or Ethernet).  The data could be NMEA, UBX, RTCM, and is the same data that would be sent and received over Bluetooth.  The mechanism can be used in Rover or Base mode.  There are three mechanisms, two TCP and one UDP, described below.
 
-The RTK device supports connection over TCP (aka PVT Client and Server). The TCP Client sits on top of the network layer (WiFi or Ethernet) and sends position data to one or more computers or cell phones for display. Some Data Collector software (such as [Vespucci](gis_software.md#vespucci)) requires that the SparkFun RTK device connect as a TCP Client. Other software (such as [QGIS](gis_software.md#qgis)) requires that the SparkFun RTK device acts as a TCP Server. Both are supported.
+## TCP Client and Server
+
+Configuring a TCP Client will cause the RTK device to open a TCP connection to a given address and port, and then send and receive data.  Configuring a TCP Server will cause the RTK device to listen on the given port for an incoming connection.  In either case, when a connection is established the device will send and receive data.
+Some Data Collector software (such as [Vespucci](gis_software.md#vespucci)) requires that the SparkFun RTK device connect as a TCP Client. Other software (such as [QGIS](gis_software.md#qgis)) requires that the SparkFun RTK device acts as a TCP Server. Both are supported.
 
 **Note:** Currently for WiFi: TCP is only supported while connected to local WiFi, not AP mode. This means the device will need to be connected to a WiFi network, such as a mobile hotspot, before TCP connections can occur.
 
@@ -22,4 +25,4 @@ The above animation was generated using [TCP_Server.py](https://github.com/spark
 
 ## UDP Server
 
-NMEA messages can also be broadcast via UDP on Ethernet and WiFi, rather than TCP. If enabled, the UDP Server will begin broadcasting NMEA data over the specific port (default 10110).
+Data can also be broadcast via UDP on Ethernet and WiFi, rather than TCP. If enabled, the UDP Server will begin broadcasting NMEA data over the specific port (default 10110).