1: Multiplexed

LIKE CRAMMING MULTIPLE BITS OF PAPER INTO A SINGLE ENVELOPE - The verge

HTTP/1.x:

Ordered and blocking. only one request can be outstanding on a connection at a time.

HTTP/2:

Multiple request and response messages to be in flight at the same time

Benefits

With HTTP/1, browsers would open up to 30 connections per website
( 4 - 6 per origin * multiple origins)

Could cause overflow by bypassing TCP congestion control and "stole" network resources from other applications.

Speed and reliability

2: Server Push

Benefits

"Server Push allows the server to avoid this round trip of delay by “pushing” the responses it thinks the client will need"

Speed!

3: Header Compression

The http header define the operating parameters of an HTTP transaction.

HTTP2 will compress the headers significantly 

"If you assume that a page has about 80 assets, and each request has 1400 bytes of headers, it takes at least 7-8 round trips to get the headers sent”

This is because of "TCP slow start", which is a mechanism for detecting the max transfer speed, but also limiting the size of the first round trips.

Mobile clients, which typically see round-trip latency of several hundred milliseconds, even under good conditions.

round trips?

From high performance browser networking

Benefits

Again.. speed!