Traffic Shaping and Prioritization

Prioritization: Letting Important Traffic Jump the Queue

Router's outgoing queue, without prioritization:
[ file chunk ][ voice packet ][ file chunk ][ voice packet ]  (first-in-first-out, no priority)

Router's outgoing queue, with prioritization:
[ voice packet ][ voice packet ][ file chunk ][ file chunk ]  (voice traffic served first)

Prioritization means high-priority traffic (like voice packets) gets processed and sent ahead of lower-priority traffic (like a background download) waiting in the same queue, even if the lower-priority traffic arrived first.

Traffic Shaping: Deliberately Smoothing Out Bursts

Traffic shaping deliberately delays certain traffic to smooth out sudden bursts into a steadier, more predictable flow, rather than letting large spikes momentarily overwhelm available capacity all at once.

Without shaping:  burst burst burst ---- quiet ---- burst burst burst (uneven, bursty)
With shaping:      steady - steady - steady - steady - steady - steady (smoothed out)

Rate Limiting: A Related, Simpler Technique

Rate limiting simply caps a specific type of traffic at a maximum allowed rate, regardless of how much bandwidth might otherwise be available - a blunter but simpler tool than full traffic shaping, often used to prevent one type of traffic from ever fully saturating a link.

Why Classifying Traffic Correctly Comes First

None of these techniques can work without first correctly identifying what type of traffic something actually is - voice, video, bulk file transfer, and so on - which is exactly the underlying purpose of the marking and classification systems covered in the next note (DiffServ and IntServ).

Why Prioritization and Shaping Are Often Used Together

Prioritization decides what order traffic gets sent in; shaping decides how evenly it's sent over time. Combined, they let a network handle a genuine mix of latency-sensitive and bulk traffic gracefully, rather than letting one type of traffic dominate at the other's expense.