Lecture 9, Part 2 (Feb 13, 2018)

Midterm

Covers chapters 1-3; no need to memorize all TCP connections

Router Architecture

Output Ports

Buffering required when datagrams arrive from fabric faster than the transmission rate
Scheduling discipline chooses among queued datagrams for transmission

How much buffering?

RFC 3439 rule of thumb: average buffering equal to typical RTT times link capacity C
Recent recommendation: with N flows, buffering = RTT*C/sqrt(N)

Scheduling Mechanisms

Scheduling: choose next packet to send on link
FIFO scheduling: send in order of arrival to queue
- Discard policy: if packet arrives to full queue: who to discard?
  - Tail drop: drop arriving packet
  - Priority: drop/remove on priority basis
  - Random: drop/remove randomly

Scheduling Policies: Priority

Send highest priority queued packet
Multiple classes with different priorities