Bandwidth, saturation and egress
Convert bytes to link demand, budget propagation and transfer time, and predict how compression and edge caching change origin traffic and egress.
24 min8 steps
By the end you can
- Calculate serialization time with consistent bit and byte units
- Estimate aggregate bandwidth and a stated egress charge
- Choose compression, caching or capacity for a saturated link
A byte is eight bits
Links are sold in bits, responses are measured in bytes. Divide by 8. Here 1 MB = 1,000,000 bytes (a MiB is 1,048,576).
Link
100 Mbit/s
÷ 8 bits per byte
12.5 MB/s
before overhead
Separate serialization from propagation
Serialization = bytes × 8 ÷ link rate. Propagation, queueing and server work add on top.
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Aggregate traffic saturates a shared link
Demand = rate × size. Workers only enqueue bytes faster; they cannot widen the link.
- 1,000 resp/s × 50 kB400 Mbit/s
- Outbound link100 Mbit/s
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Bandwidth contention becomes latency
Ten 10 MB responses on a 10 MB/s FIFO link: the last waits 10 s with CPU idle. Bound queued bytes, not just request counts.
1 s
Response 1 done
5 s
Response 5 done
10 s
Response 10 done
Compression trades CPU for fewer bytes
Compression trades CPU for bytes. Text and JSON shrink well; images and video often do not. Cache public, versioned assets at the edge. Private responses need explicit cache policy.
Compress
- Fewer bytes sent
- Costs CPU
- Skip compressed media
Edge cache
- Fewer origin fetches
- Version the URL
- Key by representation
Never
- Path-only key on private data
- Leaks one user's data
A cache hit changes who sends the bytes
Cost = billable GB × price per GB. Edge delivery is still billed, so a 90% origin hit rate does not cut 90% of the bill.
Origin egress
10,000 GB
Cost
$800
supplied price, not a quote
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Choose a complete bandwidth intervention
Each fix has a cost; predict the new byte rate first, then watch queues and errors.
Origin shield
- Fewer repeated misses
- One more hop
Compression
- Fewer bytes
- More CPU
Bigger link
- More capacity
- Still needs overload handling
Check your mastery, then saturate a link
Score 80% or more. Keep bits and bytes explicit.
Mastery check
5 questions on fresh variants. One attempt each, no time limit. Score 80% or more to master the lesson.
Open the sandbox, constrain the response link, raise traffic until waiting grows, then shrink the response. The model shows serialization and contention, not TCP congestion control.
Answer this step to continue.