QoS | Congestion Management

In my archieve, I ever post about Queueing Strategy and Queueing Strategy part 2. it's part of Congestion Management in QoS. Congestion management use marking on each packet to determine in which queue to place packets, mechanisms queuing algorithms each interface must have a queuing mechanism to prioritize transmission of packets. Congestion management to control congestion by determining order in which packets are sent out an interface based on priorities assigned to packets. Congestion occur at any point where there re-points of speed mismatches, aggregation or confluence, queuing manages congestion to provide bandwidth and delay guarantees.

Queueing components divide two : hardware and software. Hardware queuing always use FIFO, software queuing can be selected schedules packets into hardware queue. Software queue use if hardware queue is full. What is hardware and what is software queueing ?

- Hardware Queueing is queue happen in real interface, this handle by hardware component
- Software Queueing is queue happen in software based to schedules packet into hardware queue

Softwere queue use if hardware queue is full. A full hardware queue indicates interface congestion and software queue is used to manage it. If a packet forward that mean router bypass software queue. Router determine length hard queue based on config bandwidth interface in 'tx-ring' value. In subinterface or software interface like tunnel, dialer etc. not have separate tx-ring. You can adjust length of value with 'txt-ring-limit' command IOS. So only hardware interface have a tx-ring.

Congestion management is sophisticated queuing technology, there are algorithms of queuing or congestion management QoS features :
- FIFO (first in, first out)
- PQ (priority queuing)
- CQ (custom queuing)
- WFQ (weighted fair queuing)
- CBWFQ (class-based weighted fair queuing)
- LLQ (low latency queuing) hybrid PQ and CBWFQ

We can assign only one queueing mechanism type to an interface. A variety of queueing mechanisms can be configured using multilink, for example, Multichassis Multilink PPP (MMP). However, if only PPP is used on a tunneled interface—for example, virtual private dialup network (VPND), PPP over Ethernet (PPPoE), or PPP over Frame Relay (PPPoFR)—no queueing can be configured on the virtual interface.

1 of 2 but not a half

Thank's God, thank's God, thank's God, I passed CCIE Routing Switching Written in first attempt last day in August (08/31). It's really cool, I done 75 hour's learning dedicated for written and -/+4 month studied for CCIP. for CCIE written preparation I use all CCIP guide, SND guide for securiy, cisco univercd for new IOS technology multicast IPv6, some book from ciscopress for bridge switching & troubleshooting.

Pass written not a half of journey CCIE but it just 1 of 2. I need more deep understand and try all technology in blueprint, more lab, not believe all teory but need try with my self.

in last word, congratulation for my CCIE written, 1 step for 2 step. I hope enjoy with this journey going to CCIE.

QoS | Types of Delay

- Processing delay: time it takes for a router to take the packet from an input interface, examine it & put it into the output queue of the output interface (depends cpu speed/utilization, ip switching mode, router architecture, configured feature on both in/out interface)
- Queuing delay: time a packets resides in the output queue of a router (depens on number of & size of packets already in queue, bw of int, queue mechanism)
- Serialization delay: time it takes to place the 'bit on the wire' (physical medium for transport)
- Propagation delay: time it takes to transmit a packet (depends on the type of media interface)

Ways to reduce delay: upgrade bandwidth, forward important packets first, compress payload of layer 2 frame, compress ip packet headers