IP - DiffServ Overview (QoS Study Note)

IP - DiffServ Overview (QoS Study Note)

DiffServ (DS)) Summary
- A simpler approach was then designed by the IETF called, Differentiated Services (DiffServ).
- DiffServ takes a class-based (as opposed to IntSev flow-based) approach to QoS
- Diffserv is on supporting QoS for flow aggregates.
- This is known as behavior aggregate (BA) classification (RFC 2475).
- For Agreements/service provided within a domain: SLA with ISP
- These different DiffServ networks may have different Service Level Agreement (SLA).
- Needs for adequate switches/routers and adapted applications

- DSCP: Differentiated Services Code Point, DSCP - 6 Bits) in the IPv4 ToS (Type of Services) Octet or the IPv6 Traffic Class Octet - 64 possible levels
- DiffServ networks classify packets into one of a small number of aggregated flows or "classes", based on the DiffServ codepoint (DSCP) in the packet's IP header.
- DSCP value of DiffServ traffic is assigned in ingress router and a mapping between different SLAs may be needed.

- Diffserv defines an architecture and a set of forwarding behaviors.
- Traffic is classified into one of five forwarding classes at the edge of a DiffServ network
- At each DiffServ router, packets are subjected to a "per-hop behavior" (PHB), which is invoked by the DSCP (RFC 2474).
- DiffServ routers apply pre-provisioned Per-Hop Behaviors (PHBs) to packets according to the encoded forwarding class
- Forwarding classes are encoded in the Differentiated Services Codepoint (DSCP) field of each packet’s IP header

- By classifying traffic to control and assign the priority of different traffic type, it can meet the guarantee of quality of different services
- DiffServ network may connect to other peering DiffServ networks to provides end-to-end QoS.
- RSVP is used as signaling protocol in IntServ, and Common Open Policy Service (COPS) is employed in DiffServ by the BB.

Please refer to http://tw.myblog.yahoo.com/jw!HBFkhByWERmsTjQ93kTmwdsbhyg-

• Why Differentiated Services?
• Diffserv defines an architecture and a set of forwarding behaviors.
• One of the main motivations for Diffserv is Scalability.
• Differentiated Service (DS) architecture
• DiffServ Boundary Nodes are responsible for classifying and conditioning packets as they enter a given DiffServ Domain
• Differentiated Service Architecture
• DiffServ includes:
• Classifying Packets into Classes
• Policing (Dropping)/Shaping
• PHB by Queuing, Buffering and Scheduling
• PHB by Queuing and/ Dropping - Dropping can happen:
• Forwarding (via PHB)
• Resource allocation
• Per-Hop-Behavior (PHB): Two classes of QoS defined in DiffServ networks for PHB
• Per-Hop-Behavior (PHB) Groups
• Expedited Forwarding (EF): Premium service (RFC-2598)
• AFxy, Assured Forwarding / Olympic service (RFC-2597)
• Class Selector DiffServ Class
• The best of both worlds – Aggregated RSVP integrated with DiffServ