• fps - Frames per Second
• ping - Network Latency
• loss - % of incoming lost data packets
• choke - % of outgoing lost data packets

With now understanding the meaning behind fps, ping, loss and choke, one can now start looking at real time data to determine where performance issues may exist.  The Source engine offers a couple of tools to check your client connection speed and quality. The most popular one is the net graph, which can be enabled with net_graph 2 (or +graph). Incoming packets are represented by small lines moving from right to left. The height of each line reflects size of a packet. If a gap appears between lines, a packet was lost or arrived out of order. The lines are color-coded depending on what kind of data they contain.

Under the net graph, the first line shows your current rendered frames per second, your average latency, and the current value of cl_updaterate. The second line shows the size in bytes of the last incoming packet (snapshots), the average incoming bandwidth, and received packets per second. The third line shows the same data just for outgoing packets (user commands).

How to enable, control and disable Net_Graph:

To turn on the netgraph, type net_graph 1 (2 and 3 have additional data)
on the console. To turn it off, type net_graph 0 at the console.

The netgraph may be positioned on the left, middle or right of the screen
by setting net_graphpos to 0, 1, or 2 as needed.

You can adjust the size of the netgraph by setting the net_graphwidth CVAR.