Quality of Service I ( QoS, Models, Methods )

What is QoS?

• http://docwiki.cisco.com/wiki/Quality_of_Service_Networking
• Quality of life insurance
• The ability to dictate traffic treatment
  
  • Prioritization.
    • Only happens with congestion.
  • Shaping / Policing.
    • Shaping: Mold the traffic down to a specific speed.
    • Policing: ‘evil’ traffic types ( p2p / video ).
  • Advanced Strategies ( WRED – Weighted random early detection)
    • Drop selective TCP streams so it won’t hit max.
• Strategies to fight the enemy
  • Delay ( how long it takes for a Packet A to get to the other side).
    
  • Jitter ( Delay variation, Times between Packets A,Packet B,and Packet C taking to get to the other side)
    
  • Packetloss
    

	Audio Requirements	Video Requirements
Jitter	< 30ms	< 30ms
Delay	< 150ms	< 150ms
Loss	< 1%	< 1%
QoS:	DSCP EF	DSCP AF41
Bandwith	Low	High

• https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus1000/sw/4_0/qos/configuration/guide/nexus1000v_qos/qos_6dscp_val.pdf

QoS Models

Best Effort

Integrated Services ( IntServ ).

• A private courier for packets.
• Best with guaranteed bandwith ( VoIP | Video ).
• Tool of the trade: Resource Reservation Protocol ( RSVP ).
  • https://www.cisco.com/c/dam/en_us/solutions/industries/docs/gov/SecuringQOSwp_072508.pdf
• It doesnt scale because it takes chunks from your bandwidth.

Differentiated Services ( DiffServ ).

• A lot more scaleable in comparison to IntServ.
• Prioritized delivery service for packets.
• Tool of the trade: Per Hop Behavior ( PHB ).
  • https://en.wikipedia.org/wiki/Per-hop_behaviour

QoS Methods

Classification

• Can be done with access-list to capture certain traffic.
•  NBAR.
  • Deep packet inspection (If an aplication uses a well known port 80).
  • Looks beyond the portnumber.

Marking

• Labels the traffic
• Layer 2 : Class of Service ( CoS ) bits
• Later 3 : Type of Service ( ToS )
  • differentiated services code point ( DSCP ) bits

Queueing ( Congestion Management )

• Weighted Fair Queuing ( WFQ )
  • Low traffic senders get priority over high traffic senders
• Class Based WFQ 
  • Devides Bandwidth among classes that you define
• Low Latency Queuing ( LLQ )
  • Combo of CB-WFQ, but adds a strict priority element.
  • Used to be called Priority Queuing PQ-CBWFQ

Congestion Avoidance

• https://www.cisco.com/c/en/us/td/docs/ios/12_2/qos/configuration/guide/fqos_c/qcfconav.pdf
• https://en.wikipedia.org/wiki/TCP_congestion_control

Link Efficiency

• Techniques used on low bandwidth connections
• Payload Compression ( Squishing the data ).
  • Trades CPU processing power for bandwidth.
  • Your CPU compresses the data and decompresses the data on the other end.
• Header Compression ( Squishing the header ( key for RTP ).
  • Very little data but a big header.
  • When enabled on both ends it strips off the redundant header information.
• Link Fragmentation and Interleaving – Blow up the big packets.
  • Always used on low bandwidth.
  • Hardware Queue, it takes 214ms to put 1500 byte on a 56kbps line.
    • 1500 byte gets fragmented into smaller packets
    • Leaves openings for other packets like VoIP.

Where can you apply QoS methods?

MQC:

1. Classify (class-map)
2. Policy ( policy-map)
3. Apply