Difference Between Latency and Round Trip Time

Latency is the amount of time it takes a packet of data to leave your computer and receive a response back from the end point. That is why this is measure in time. This is key for time sensitive applications like VoIP and video conferencing.

Bandwidth/data rate is the amount of data (bits) you can upload or download in a given time (seconds). This is key for downloads and uploads (i.e. video streaming for Hulu, Netflix, etc). It is also important in video conferencing as you're sending/receiving a lot of video (bandwidth) and the audio portion needs to be in near real time (latency).

Ping is sending packets using ICMP and measuring the time it takes until you receive an echo-reply from the end point. It is not sending a lot of data and would not give any accurate information regarding bandwidth.

Something like iperf may be used to measure bandwidth by sending a lot of data to the end point which also would be running perf.

You can have high latency (slow round trip time for packets) but still have a lot of bandwidth. Satellite service is one example.

According to RFC 6928, the SRTT is only calculated with the formula

SRTT <- (1 - alpha) * SRTT + alpha * R'

after two RTT measurements have been made. After the first measurement, SRTT is initilized to the value of this first measurement, ie. SRTT <- R'.

You were close, according to the RFC alpha SHOULD be 1/8 (= 0.125).

Note, in RFC's, SHOULD means "there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course." (RFC 2119)