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QoS Protocols & Architectures

QoS Protocols & Architectures. by Harizakis Costas. Presentation Flow. QoS defined QoS protocols : RSVP, DiffServ, MPLS, SBM QoS architectures QoS and multicast environments Protocol comparison … … conclusions !. IP-based Networks - Internet Today. Internet today

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QoS Protocols & Architectures

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  1. QoS Protocols & Architectures by Harizakis Costas

  2. Presentation Flow • QoS defined • QoS protocols : • RSVP, DiffServ, MPLS, SBM • QoS architectures • QoS and multicast environments • Protocol comparison … • … conclusions !

  3. IP-based Networks - Internet Today • Internet today • Provides “best effort” data delivery • Complexity stays in the end-hosts • Network core remains simple • As demands exceeds capacity, service degrades gracefully (increased jitter etc.) Delivery delays cause problems to real-time applications

  4. QoS Defined • The goal : Provide some level of predictability and control beyond the current IP “best-effort” service • Fundamental principle Leave complexity at the “edges” and keep network “core” simple

  5. QoS Metrics • Performance attributes • Service availability • Delay • Delay variation (jitter) • Throughput • Packet loss rate Vary according to Service Level Agreement (SLA)

  6. Service Level Agreements (SLA)

  7. QoS Protocol Classification • QoS can be achieved by : • Resource reservation (integrated services) • Prioritization (differentiated services) • QoS can be applied : • Per flow (individual, uni-directional streams) • Per aggregate (two or more flows having something in common)

  8. QoS Protocols • ReSerVation Protocol (RSVP) • Differentiated Services (DiffServ) • Multi Protocol Labeling Switching (MPLS) • Subnet Bandwidth Management (SBM)

  9. RSVP - Resource Reservation • Attributes • The most complex of all QoS technologies • Closest thing to circuit emulation on IP networks • The biggest departure from “best-effort” IP service • Provides the highest level of QoS in terms of : • Service guarantees • Granularity of resource allocation • Detail of feedback to QoS-enabled applications

  10. RSVP - Integrated Services • Enables integrated services (IntServ) • IntServ types • Guaranteed : as close as possible to a dedicated virtual circuit • Controlled Load : equivalent to best-effort service under unloaded conditions

  11. RSVP - Implementation

  12. RSVP - Implementation • Sender • PATH message containing • traffic specification (bitrate, peak rate etc.) • Receiver • RECV message containing • the reservation specification (guaranteed or controlled) • the filter specification (type of packets that the reservation is made for)

  13. RSVP - Queuing • IntServ uses a token-bucket model to characterize I/O queuing • Token bucket attributes • Token rate • Token bucket depth • Peak rate • Minimum policed size • Maximum packet size

  14. RSVP - Conclusions • Reservations are “soft” • Periodic refresh is necessary • It is a network (control) protocol • Works in parallel to TCP and UDP • APIs are required to specify flow requirements • Reservations are receiver-based • Has to maintain a state for each flow • Multicast reservations • Merged at replication points, difficult to understood algorithms have to be used though

  15. DiffServ- Prioritization • Description • Applied on flow aggregates • Services requirements are classified • Classification is performed at network ingress points • A predefined per-hop behavior (PHB) is applied to every service class • Traffic is smoothed according to PHB applied

  16. DiffServ- Traffic Classes Two traffic classes are available : • Expeditied Forwarding (EF) - 1 codepoint • Minimizes delay and jitter • Provides the highest QoS • Traffic that exceeds the traffic profile is discarded • Assured Forwarding (AF) - 12 codepoints • 4 classes, 3 drop-precedences within each class • Traffic that exceeds the traffic profile is not delivered with such high probability

  17. DiffServ- Implementation

  18. DiffServ- Implementation • DiffServ codepoints (DSCPs) redefine the Type-of-Service (ToS) IPv4 field • Precedence bits are preserved • Type-of-Service bits are NOT

  19. DiffServ- Conclusions • Traffic classes are equivalent to IP precedence service descriptors • DiffServ unaware routers pass-through DiffServ traffic • Easy to be implemented / integrated even into the network core. • Proper classification can lead to efficient resource allocation and though improved QoS

  20. MPLS - Label Switching • Used to establish fixed bandwidth routes (similar to ATM virtual circuits) • Resides only on routers and is protocol independent • Traffic is marked at ingress and unmarked at egress boundaries • Markings are used to determine next router hop (not priority) The aim is to simplify the routing process …

  21. MPLS - Implementation • The 1st hop router, using the header information (destination address etc.) attaches a label and forwards the packet • Every MPLS-enabled router uses the label as an index to a table defining the next hop and label

  22. MPLS - Conclusions • Labels can be “stacked” • This allows MPLS “routes within routes” • Label Distribution Protocol (LDP) • Distributes labels across MPLS-enabled routers • Ensures they agree on the meaning of labels • Usually transparent to network managers • Implication : • Define a policy management that distributes labels

  23. SBM - Subnet Bandwidth Management • A top-to-bottom QoS approach • Applies to the Data Link Layer (OSI layer 2) • Makes LAN topologies (e.g. Ethernet) QoS-enabled • Fundamental requirement • All traffic must pass through at least one SBM-enabled switch

  24. SBM - Implementation • SBM Modules • Bandwidth Allocator (BA) • Hosted on switches • Performs admission control • Requestor Module (RM) • Resides in every end-station • Maps Layer 2 priority levels and the higher-layer QoS protocol parameters

  25. SBM - Conclusions • Much like the RSVP protocol • Makes the traditional Ethernet, QoS aware • Introduces an additional indirection in the routing mechanism • 8-level priority value

  26. QoS Architectures

  27. Protocol Comparison

  28. Multicast Environments • RSVP • Heterogeneous receivership makes reservation merging a difficult task • DiffServ • Its relative simplicity makes it a better fit for multicast support • MPLS • Work is underway, no standards have emerged yet • SBM • Explicit support for multicast

  29. Conclusions • Complexity at the edges – simple network core • Limit RSVP’s use on the backbone • Instead use the DiffServ • DiffServ is a perfect complement for RSVP • ToDo : • Performance attributes for each class still missing • Interworking solution for mapping IP CoS to ATM QoS

  30. References • http://www.nortelnetworks.com/solutions/collateral/qos_wp.pdf • http://www.qosforum.com/white-papers/qosprot_v3.pdf • http://www.qosforum.com/white-papers/Need_for_QoS-v4.pdf

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