HTTP/2 Multiplexing vs HTTP/1.1 Connection Limits

Protocol

Page load

Requests on page 24

Max parallel connections (HTTP/1.1) 6

Link bandwidth 600 KB/s

Handshake / RTT 120 ms

Live readouts

Elapsed

0.00 s

Completed

0 / 24

Avg completion

— ms

Link utilization

Queued (waiting)

Page load time

— s

How it works

Every asset on a page (HTML, CSS, JS, images) is one HTTP request of size S_i that must be fully downloaded. At any instant the shared link of capacity C is split equally across whatever is actively transferring:

B_i(t) = C / N_active(t)
request i finishes when  ∫ B_i(t) dt = S_i

HTTP/1.1 opens at most K TCP connections per origin (browsers cap K at 6). Each connection carries exactly one request at a time — a 7th request cannot start until one of the K connections frees up, no matter how small it is. Every newly-opened connection also pays a one-off handshake delay H before its first byte:

N_active(t) = min(requests ready, K)
new connection cost = H  (TCP + TLS setup, ~1 RTT-2 RTT)

HTTP/2 multiplexes all requests as independent streams over a single TCP connection, so N_active(t) can rise to the full request count at once — nothing sits queued behind an unrelated connection slot, and only one handshake is ever paid. Small critical assets (CSS, small JS) finish almost immediately instead of waiting behind a large image on a busy connection — this is exactly the "head-of-line blocking by connection limit" that HTTP/2 multiplexing removes.

Requests on page — how many assets the page needs (mobile pages: 15–40 is typical).
Max parallel connections — the K cap; only applies in HTTP/1.1 mode.
Link bandwidth — total capacity C of the mobile connection (3G ≈ 150–300 KB/s, 4G ≈ 500–1500 KB/s, 5G ≈ 2000+ KB/s).
Handshake / RTT — per-connection setup latency; on high-latency mobile links this cost multiplies with every new HTTP/1.1 connection.

Watch the "Queued (waiting)" readout — under HTTP/1.1 it stays high until early connections vacate; under HTTP/2 it drops to zero almost immediately because every request starts transferring in parallel.

Queued request Transferring Completed

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