Adding networking course for level102 (#113)

* Adding networking course for level102

* Adding URL and minor fix

Co-authored-by: Arun Thiagarajan <athiagar@athiagar-ld2.linkedin.biz>
Co-authored-by: kalyan <ksomasundaram@linkedin.com>

courses/level102/networking/rtt.md

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+> *Latency plays a key role in determining the overall performance of the
+distributed service/application, where calls are made between hosts to
+serve the users.*
+
+RTT is a measure of time, it takes for a packet to reach B from A, and
+return to A. It is measured in milliseconds. This measure plays a role
+in determining the performance of the services. Its impact is seen in
+calls made between different servers/services, to serve the user, as
+well as the TCP throughput that can be achieved.
+
+It is fairly common that service makes multiple calls to servers within
+its cluster or to different services like authentication, logging,
+database, etc, to respond to each user/client request. These servers can
+be spread across different cabinets, at times even between different
+data centres in the same region. Such cases are quite possible in cloud
+solutions, where the deployment spreads across different sites within a
+region. As the RTT increases, the response time for each of the calls
+gets longer and thereby has a cascading effect on the end response being
+sent to the user.
+
+### Relation of RTT and throughput
+
+RTT is inversely proportional to the TCP throughput. As RTT increases,
+it reduces the TCP throughput, just like packet loss. Below is a formula
+to estimate the TCP throughput, based on TCP mss, RTT and packet loss.
+
+![Diagram, schematic Description automatically
+generated](./media/RTT.png)
+
+As within a data centre, these calculations are also, important for
+communication over the internet, where a client can connect to the DC
+hosted services, over different telco networks and the RTT is not very
+stable, due to the unpredictability of the Internet routing policies.