What is Latency?
Latency is the delay between sending a request and receiving the first byte back, measured as round-trip time in milliseconds. Through a proxy it spans the client's hop out, the proxy's hop to the target and the return leg. A mobile exit adds more delay than a datacenter one, since radio scheduling and carrier NAT sit in the path.
Be precise about what you measure. An ICMP ping reports round-trip time to a host that may deprioritise or rate-limit those packets, so the number can be flattering or meaningless. Time to first byte over the real protocol includes the proxy's own handling, name resolution and the target's processing. Those are different quantities. Measure with the same client, protocol and endpoint you use for production work, take a distribution rather than a single sample, and record the median alongside the slow tail.
The milliseconds come from several places. Distance sets a hard floor, since light in fibre covers roughly two hundred kilometres per millisecond and real paths are longer than the great-circle line, so a transatlantic round trip cannot drop below the tens of milliseconds. Cellular adds radio scheduling, and a modem that has dropped to an idle radio state pays a wake-up penalty on the first packet after a pause. Handshakes multiply everything: a TCP connection costs one round trip, a TLS 1.3 handshake one more, older TLS two. Reusing connections removes that cost entirely.
Latency and throughput are separate problems. A high round-trip time does not limit how much data you can move; it limits how many sequential exchanges you can complete per second. A crawler doing four round trips per page at 200 ms will finish a little over one page per second per worker, no matter how much capacity the link has. The fix is concurrency and keep-alive connections rather than hunting for a lower ping, and HTTP/2 multiplexing helps on targets that support it.
Variance breaks automation more often than the average does. Tower congestion, a rotation event or a carrier middlebox produces occasional multi-second responses inside an otherwise steady stream, and a timeout set near the median converts those into failures and retry storms. Set timeouts from the 95th or 99th percentile you observe on your own traffic, back off on retry, and treat a rising tail as a signal to check the exit rather than to raise concurrency.
Where you meet it
Latency turns into a real decision when you size timeouts for a crawler or compare two providers whose sales pages both quote a ping figure. Run your own measurement through the client that does the work, watch the slow tail over an hour rather than a minute, and remember that a lower median buys nothing if a sequential pipeline is the thing holding you back.
Common questions
What is a good latency for a mobile proxy?
Judge it against the same route without a proxy rather than against a figure on a sales page. An exit in your own country will beat one on another continent, since distance sets a floor you cannot argue with. Consistency is worth more than a low median, because a steady response time beats a lower average punctuated by multi-second spikes.
Why is a mobile proxy slower than a datacenter proxy?
Cellular traffic waits for radio scheduling, shares cell capacity with real subscribers, and passes through carrier NAT before reaching the internet. That overhead buys the thing datacenter addresses cannot provide, which is an exit that looks like an ordinary phone on a carrier network.
Does lower latency mean faster scraping?
Only for work that runs one request after another. Once you add concurrent workers and reuse connections, total throughput depends on how many requests are in flight and how the target responds, not on the round-trip time of any single one.
Related terms
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