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Differentiated Services

Differentiated Services. MPLS vs DiffServ. MPLS. Per-label service state at every hop. Scalability problems. Brokerage distributed through signaling process. BB. BB. DiffServ. Abstract/manage each cloud’s resources (BBs) Packets colored with “behavior”

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Differentiated Services

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  1. Differentiated Services

  2. MPLS vs DiffServ MPLS • Per-label service state at every hop • Scalability problems • Brokerage distributed through • signaling process BB BB DiffServ • Abstract/manage each cloud’s resources (BBs) • Packets colored with “behavior” • Focus on aggregates not flows • Policing at edge to get services

  3. QoS Techniques

  4. Integrated Services

  5. Differentiated Services

  6. Markings • Best-effort (be)—The router does not apply any special CoS handling to packets with000000 in the DiffServ field, a backward compatibility feature. There is usually a high probability that these packets will be dropped under congested network conditions. • Assured forwarding (af)—The router offers a high level of assurance that the packets are delivered aslong as the packet flow from the customer stays within a certain service profile (the service provider defines the values). The router accepts excess traffic, but applies a random early discard (RED) drop profile to decide if the excess packets should be dropped and not forwarded. Three drop probabilities (low, medium, and high) are defined for this service class.

  7. Markings • Expedited forwarding (ef)—The router delivers assured bandwidth, low loss, low delay, and low delay variation (jitter) end-to-end for packets in this service class. Routers accept excess traffic in this class, but in contrast to assured forwarding, out-of-profile expedited-forwarding packets can be forwarded out of sequence or dropped. • Conversational services (cs)—The router delivers assured (usually low) bandwidth with low delay and jitter for packets in this service class.Packets can be dropped, but never delivered out of sequence. Packetized voice is a good example of a conversational service. • Network control (nc)—The router delivers packets in this service class with a low priority (these packets are not delay-sensitive). Typically, these packets represent routing protocol hello or keepalive messages and loss of these packets jeopardizes proper network operation, so delay is preferable to discard

  8. Diffserv

  9. Comparison • Scalability • Intserv: Stat Information causes overhead • Diffserv: Much less State Information than IntServ, scales well • Deployment • Intserv: All routers must have all four components • Diffserv: Classification, marking, policing, shaping operations only needed at network boundary, ISP core routers only need to have forwarding COS differentiation. • Service • Intserv: Quality Guarantee • Diffserv: Poorer quality

  10. DiffServ Overview • Exploits edge/core distinction for scalability • Applications contract for specific QoS profiles • Policing at network periphery • A few simple, differentiated per-hop forwarding behaviors (PHBs) • Indicated in packet header • Applied to PHB traffic aggregates • PHBs + policing rules = range of services • Clouds contract for aggregate QoS traffic profiles • Policing at cloud-cloud boundary • Supports simple, bilateral business agreements

  11. DiffServ Architecture Bandwidth Brokers (perform admissions control, manage network resources, configure leaf and edge devices) Destination Source BB BB Core routers Core routers Ingress Edge Router (classify, police, mark aggregates) Egress Edge Router(shape aggregates) Leaf Router (police, mark flows)

  12. Example Service #1: Premium • Contract: leased line emulation at aspecified peak rate • PHB = “forward me first” (EF) • Policing rule = drop out-of-profile packets • On egress, clouds must shape EF aggregates to mask induced burstiness

  13. Example Service #2: Assured • Contract: network looks “lightly-loaded” for traffic within a specified rate and burst profile • PHB  “drop me last” (AF) • Policing rule = remark out-of-profile packets to have higher drop probability • AF is actually a family of PHBs: • 4 independent AF classes • 3 drop preference levels within each class • Traffic within a class shares single queue • On cloud egress, clouds may need to shape AF aggregates to mask induced burstiness

  14. Example Service #3: CoS • Contract: “better” service relative to the schmucks who pay less • PHB = “drop the lower classes first ” (AF) • Policing rule = drop or remark out-of-profile packets • “Olympic” classes of BE service: • “Gold” • “Silver” • “Bronze”

  15. DiffServ & The Three Big QoS Problems • Applications: Framework supports a broad range of services depending on PHB and configuration of policers • Scalability: Simplicity of PHBs & pushing “smarts” towards edge, lets core routers be simple, dumb, and fast, but still supports QoS! • Interoperability: • PHBs suggest but do not imply implementations • QoS through concatenations of simple bilateral SLAs • Administratability also a big win

  16. The best of both worlds • Use MPLS to perform traffic engineering and to specify routes • Use Diffserv to limit core complexity • Not much has happened since 1999

  17. For more information... • QBone home page:http://www.internet2.edu/qbone • Internet2 QoS Working Group home page:http://www.internet2.edu/qos/wg

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