Latency and Bandwidth

Speed is a feature

Empircal facts. Faster sites lead to

• Better engagement
• Better retention
• Higher conversions

2 critical components govern performance of traffic

• latency time from source sending a packet to destination receiving it
• bandwidth maximum throughput

Components of Latency

What contributes to latency? Latency is the sum of

• Propagation delay- time for message to travel from sending to reciever
  • Governed by: distance / medium of the signal’s travel
• Transmission delay- time to push all of packet’s bits into link
  • Governed by: data rate of transmitting link
• Processing delay- time to process pacet header, check for bit-level errors, determine packet’s destination
• Queuing delay- time incoming packet waits in queue until processed

Speed of light and Propagation Latency

Light is fast. Very fast.

But our packets travel through a medium like wire or fiber optic cable, which slows it down.

The refractive index of a material detemines the speed of light in that material. Larger refractive index → slow light travel.

Rules of thumb:

• Seped of light in fiber- 200M meters / second. This is a refractive index of ~1.5
• 100ms delay- “laggy”
• 300ms delay- “sluggish”
• 1000ms delay- context switch

last mile latency

Infamous last-mile problem: the real latency is often introduced in the “last mile”, not traversing the oceans. Often takes as much time as traveling across a continent would.

Test it out by doing traceroute website.com

Bandwidth at the Network Edge

Fiber links can move hundreds of terabits per second, but edges of network have much much less capacity and varies based on deployed tech

Examples

• Dial up
• DSL
• Cable
• Fiber-to-the-home

User’s bandwidth- lowest capcity link between client and destination server

Delivering higher bandwidth + lower latencies

How to increase

• Bandwidth: add more fiber links and make better tech
• Latency: we’re almost to the speed of light already…

So, we need to architect + optimize protocols / networking code with awareness of limiitations of available bandwidth and the speed of light.

• Hide latency through caching
• Reduce round trips
• Move data near clients