QoS – 642-642 Training: Introduction to Quality Of Service

QoS – 642-642 Training: Introduction to Quality Of Service

1992 – Best Effort

1994 – Integrated Services

1996 – Differentiated Services

1998 – MPLS VPN + QoS

2002 – Auto QoS (Template)

2004 – QoS For Security  (*NBAR = QoS at application level not just ports)

Understanding QoS Requirements

  • Data
  • Voice – Smooth traffic, constant stream, benign. Drop/delay sensitive
  • Video – Bursty and greedy. Drop/delay sensitive. (Not as important as voice)

Citrix application is delay sensitive and similar to voice traffic/treatment on the network.

FTP is an example of data traffic that is not sensitive at all and uses TCP.

Four Evil Villians of Voice and Video

  • Lack of bandwidth – QoS will not help you!!
  • Packet Loss
  • Delay – ITU best practice less than 150ms from point A to B. (ONE WAY only, not round trip time. PSTN quality voice…)
  • Jitter – Variation of delay. 10ms and 50ms = 40ms jitter value (Dejitter buffer in place, which can have capacity issues causing jitter)

Methods of Deploying QoS

  • CLI – Legacy
  • Modular QoS CLI (MQC) – Groupings of QoS methods.
  • AutoQoS – Great, but requires tuning.
  • QoS Policy Manager – Works with Cisco Works – Legacy?

QoS Toolbelt: Classification + Marking

  • Classification involves identifying and grouping different traffic types
  • Marking tags or colors the packet, so it is can be quickly recognized elsewhere in the network.

QoS Toolbelt: Policing and Shaping

  • Policing – Drops or marks packet when limit is reached
  • Shaping – Queues packet when limit is reached. (Kinder than policing!)

QoS Toolbelt: Congestion Avoidance

  • First In First Out – (FIFO) + Taildrop – Doors closing when buffer is full
  • Random Early Detection – (RED) – Random packets dropped to stopped buffer overflow. Not supported by Cisco!
  • Weighted Random Early Detection – (WRED) – Random packet with specific marking can be dropped. If all markings are the same, then WRED acts the same as RED.

QoS Toolbelt: Congestion Management

Queuing Methods.. more to follow.

QoS Toolbelt: Link Efficiency Tools

  • Compression
  • Link Fragmentation + Interleaving (LFI) Chop up huge packets and make them smaller! (Fragmentation) – High level explanation more to follow..

This video was fairly vague as only really an introduction to QoS. More to follow..