QoS | Queueing Strategy ex. fifo

I ever resume about queueing & congestion, there are
- occur at any point where there re points of speed mismatches, aggregation or confluence
- queuing manages congestion to provide bandwidth & delay guarantees

- queuing algorithms
.fifo: simplest algorithm, one queue
.pq (priority queuing): allows certain traffic to be strictly-prioritized, multiple queue, allow priority
.round robin: allows serveral traffic flows to share bandwidth, multiple queue, no prioritization
.wrr (weighted round robin): allows sharing of bw with preferential treatment, allow priority, assign a 'weight' to each queue, drawbacks not allocate bw accurately
.drr (deficit round robin): resolves problem with some wrr implementations (inaccurate bw), keeps track number of 'extra' bytes dispatched in each round, add 'deficit' in next round

- queuing components
.hardware queuing always use fifo
.software queuing can be selected: schedules packets into hardware queue
- queue mechanisms incl classification of packets
.after classification put packet into queue or drop
.drop if queue is full
.some mechanisms use intelligent dropping ex. wfq, wred
- soft queue use if hardware queue is full
- a full hardware queue indicates int congestion & soft queue is used to manage it
- a packet forward, router bypass soft queue
- hardware queue (txq) size

- logical interface like subinterface / vlan there is not have dedicated queueing but shared with main interface / physical interface

I have experience about queue, serial interface limit using time slot (controller E1) ex. 128Kbps, moment full traffic if try ping / telnet across the link still done but slow, result ping slow but sure (no time out), but ethernet interface using subinterface limit using rate-limit / policy-map ex. 128Kbps, condition full traffic if try ping / telnet across the link intermitten even time out (in ICMP) like ping. WHY ?

ok look at a little resume in there about queue management, serial default using 'weighted fair' so time-out if try ping just slow but sure, different about ethernet default using 'fifo' there is no queue, if tail drop happen packet are drop. if you want ethernet interface like serial can using command 'fair-queue' in interface configuration that mean enable fair queuing on an interface ;)

so remember default of queueing management every interface model is different.