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QoS Protocols & Architectures by Harizakis Costas.

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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 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 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 1 st 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

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