What is QoS?
- Quality of life insurance
- The ability to dictate traffic treatment
- 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)
| || Audio Requirements|| Video Requirements
|Jitter||< 30ms||< 30ms
|Delay||< 150ms||< 150ms
|Loss ||< 1%||< 1%
|QoS:||DSCP EF||DSCP AF41
Integrated Services ( IntServ ).
- A private courier for packets.
- Best with guaranteed bandwith ( VoIP | Video ).
- Tool of the trade: Resource Reservation Protocol ( RSVP ).
- 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 ).
- Can be done with access-list to capture certain traffic.
- Deep packet inspection (If an aplication uses a well known port 80).
- Looks beyond the portnumber.
- 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
- 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?
- Classify (class-map)
- Policy ( policy-map)