Quality-of-Service Architectures for the Internet

1. Quality-of-Service Architectures for the Internet

2. Quality of Service What is Quality-of-Service? • QoS refers to traffic control mechanisms that seek to either differentiate performance based on application or network-operator requirements, or provide predictable or guaranteed performance to applications, sessions, or traffic aggregates. Why is this an issue? • The default service in many packet networks is to give all applications the same service, and not consider any service requirements to the networkThis is called a best-effort service.

3. Quality of Service Who needs Quality-of-Service? • Video and audio conferencing bounded delay and loss rate • Video and audio streaming bounded packet loss rate • Time-critical applications (real-time control)  bounded delays • “valuable applications” better service than less valuable applications How are Quality-of-Service requirements specified? • QoS requirements can be specified as • Delay • Delay Variation (Jitter) • Throughput • Error Rate

4. Components of a QoS Network • At routers: Packet Classification, Packet Scheduling • At network entrance: Traffic conditioning • At routers or somewhere in the network: Admission Control • Between hosts and routers: Signaling Admission control Sender Routers Receiver Traffic conditioning

5. Classification and Scheduling Routers need to be able to • classify arriving packets according to QoS requirements  Packet Classification • Transmit packets in order to meet QoS  Packet Scheduling

6. Traffic Conditioning • Traffic conditioning mechanisms at the network boundary need to enforce that traffic from a flow does not exceed specification • Policing Drop traffic that violates specification • Shaping Buffer traffic that violates specification • Marking Mark packets with a lower priority or as best effort, if the traffic specification is violated

7. Traffic Conditioning • The most popular traffic conditioning algorithm is the leaky bucket r token/sec are added (no tokens are added if there are b tokens) A shaper buffers packets until a token becomes available A policer drops a packet if no token is available Token pool (Bucket) has depth b Network Each packet removes a token from the pool.If pool is empty, packet cannot enter

8. I need100 ms delay for 1 Mbps traffic Reserve capacity Admit Admission Control • Admission Control is a function that decides if the network has enough resources • Admit new flow if enough resources are available • Reject the flow otherwise Admission control Sender Routers Receiver Traffic conditioning

9. Distributed Admission Control • Example: End-to-end delay must be less than a delay bound D • Calculate smallest possible delay bound at each node: d*1,d*2 ,d*3 and reserve resources • At receiver: • If D < d*1+d*2+d*3 , reject flow, send reject message to sender and release resources • If D > d*1+d*2+d*3 , accept flow, commit resource reservation and notify sender D,d1,d2,d3 R D,d1 D,d1,d2 3 D 1 2 S Reject D < d1+d2+d3 Reject Accept D > d1+d2+d3 Accept

10. Signaling • Signaling Protocol is used to reserve and release resources and to do admission control Reserve 1 Mbps Reserve 1 Mbps Reserve 1 Mbps R Reserve 1 Mbps 3 1 2 S

11. Granularityof QoS • Per-flow guarantees • Require per-flow reservations in the network • Require per-flow classification at routers

12. 1 1 1 2 1 1 2 1 2 1 2 2 2 1 2 2 1 2 1 2 Granularity of QoS 1 2 1 2 • Per-class guarantees • Bundle traffic flows with similar service requirements into “classes” • No per-flow reservations • Per-class guarantees do not immediately translate into per-flow guarantees

13. QoS Service Architectures for the Internet • Two QoS architectures have been defined for Internet. • Integrated Services (IntServ) • Proposed in 1994 • Per-flow Quality of Service • Resource reservation/admission control • Can support delay guarantees • Differentiated Services (DiffServ) • Proposed in 1998 • Class-based QoS • Resource reservation not always needed

14. Integrated Services IntServ specifies two types of services: Guaranteed Service • Guaranteed bandwidth • End-to-end delay bounds • No loss due to buffer overflows Controlled Load Service • Provides a service that is equivalent to a best effort service in a lightly loaded network • Low loss • Low delay • No absolute guarantees

15. At network entrance: Policing and Shaping Somewhere in the network: Admission Control At switches: Classification, Scheduling Between hosts and routers: Signaling FlowSpec (TSpec,RSpec) Distributed Weighted Fair Queuing or other rate-based algorithm RSVP Integrated Services in IntServ

16. Resource ReSerVation Protocol (RSVP) • RSVP is a signaling protocol that enables senders, receivers, and routers of unicast or multicast sessions to communicate with each other for setting up state to support a service • Receiver-driven • Resource reservation is initiated by receivers • Unicast and multicast sessions • Soft-state: state information of RSVP must be periodically refreshed • Separate mechanisms required for authorization, authentication, and charging

17. RSVPD Routing Process Application Policy Control Policy Control Admissions Control Admissions Control Packet Classifier Packet Scheduler Packet Classifier Packet Scheduler RSVP Functional Diagram Host Router RSVPD D A T A DATA DATA Source: Gordon Chaffee, UC Berkeley

18. Resource Reservation • Senders advertise using PATH message • Receivers reserve using RESV message • Flowspec + filterspec + policy data • Travels upstream in reverse direction of Path message • Merging of reservations • Sender/receiver notified of changes Source: Gordon Chaffee, UC Berkeley

19. 2 PATH PATH 1 3 PATH PATH 1. An application on Host A creates a session, 128.32.32.69/4078, by communicating with the RSVP daemon on Host A. 3. The PATH message follows the next hop path through R5 and R4 until it gets to Host B. Each router on the path creates soft session state with the reservation parameters. 2. The Host A RSVP daemon generates a PATH message that is sent to the next hop RSVP router, R1, in the direction of the session address, 128.32.32.69. RSVP UDP Reservation (1) R2 R3 R4 R1 Host B 128.32.32.69 Host A 24.1.70.210 R5 Source: Gordon Chaffee, UC Berkeley

20. 4 RESV 5 RESV RESV 6 RESV 4. An application on Host B communicates with the local RSVP daemon and asks for a reservation in session 128.32.32.69/4078. The daemon checks for and finds existing session state. 6. The RESV message continues to follow the next hop path through R5 and R1 until it gets to Host A. Each router on the path makes a resource reservation. 5. The Host B RSVP daemon generates a RESV message that is sent to the next hop RSVP router, R4, in the direction of the source address, 24.1.70.210. RSVP UDP Reservation (2) R2 R3 R4 PATH R1 PATH Host B 128.32.32.69 PATH PATH Host A 24.1.70.210 R5 Source: Gordon Chaffee, UC Berkeley

21. RSVP Flowspecs Sender TSpec, Controlled Load Flowspec . . . Token Bucket Rate [r] Token Bucket Size [b] Peak Data Rate [p] Minimum Policed Unit [m] Maximum Policed Unit [M] Guaranteed Flowspec . . . Token Bucket Rate [r] Token Bucket Size [b] Peak Data Rate [p] Minimum Policed Unit [m] Maximum Policed Unit [M] Rate [R] Slack Term [S] Source: Gordon Chaffee, UC Berkeley

22. (7) 100 Kbs Reservation Merging (3) 50Kbs R1 Reservations merge as they travel up tree. (6) 100 Kbs R3 (2) 50Kbs (5) 100 Kbs (9) 60Kbs R4 R6 R7 (1) 50Kbs (8) 60Kbs (4) 100 Kbs Receiver #1 Receiver #2 Receiver #3 Source: Gordon Chaffee, UC Berkeley

23. Summary of IntServ • Advantages: • Strong guarantees (bounded delays) • Disadvantages: • Requires that all routers implement IntServ • Scalability concerns since routers must maintain state information • Charging and authentication of reservations must be solved • Interdomain issues are difficult to resolve

24. DiffServ • Motivation: • The Integrated Services (IntServ) model is not scalable since it requires per-flow state in each node Goal: • Push complexity to the network edge and keep network core simple • Avoid per-flow state within the network as much as possible

25. Differentiated Service Mechanisms • Definitions: • Mechanisms that allow providers to allocate different levels of service to different users of the Internet • broad view: Any mechanism that treats different users differently, including signaling (RSVP), per-session scheduling, etc. • Internet context: Simple and lightweight mechanisms that do not depend entirely on per-flow reservation

26. Components of Differentiated Services (1) Service profilebetween user and network defines commitment of the network to the user (2) Aggregate traffic from each user is policed at the network entrance according to profile (3) Node behavior: network nodes implement a variety of forwarding, scheduling, buffer management techniques (4) Bits in packet header trigger action at nodes

27. Common to Most Proposed Services • Traffic marking (in-profile, out-profile) and enforcement is done only at network boundaries • Inside the network: Only differentiate a few service classes, based on marking of the packets

28. Operational Model network boundary network boundary ISP 1 ISP2 Host Meters Host Meters Source negotiates a traffic profile Nodes perform scheduling and buffer management based on marking of packets(“per-hop behavior”) Policing, shaping, or marking based on profile Policing, shaping, or marking based on profile

29. Aspects of a Differentiated Service (1) Semantics of the service: Which service is given to in-profile traffic of a user? (2) Spatial Granularity: Is the profile applied to a single destination, a subset of destinations, or all destinations? (3) Assurance Level: What is the level of certainty that an in-profile packet will be delivered?

30. DiffServ Services • Two services defined: • Assured Forwarding (AF) • customers sign service agreements with ISPs • Edge routers mark packets as being “in” or “out” of profile • core routers run RIO: RED with in/out • Distinguishes different classes: • Expedited Forwarding (EF) • Hard guarantee on the delay and delay variations

31. Assured Forwarding - 1 • User defines traffic profile (token bucket) • Profile meter at network entrance tag packets as in-profile or out-profile • Service guarantee:In-profile packets are unlikely to be dropped • Out-profile packets have higher drop preference at routers “in” Profile meter “out”

32. Assured Forwarding - 2Mechanisms • Mechanisms Needed : • Dropping Mechanisms at routers • Mechanism for tagging packets (“Meters”) • Method to classify packets ISP 1 ISP 2 Host Meters Host Meters drop

33. Assured Forwarding - 3RIO • Routers have different dropping mechanism: RIO = RED with `in’ and `out’ • Routers do not perform separate queueing • RED (Random Early Detection): When the avgerage queue size exceeds a threshold drop each packet with a certain probability (Pdrop) P(drop) P(drop) 1 1 Pmax_in Pmax_out Avg. queue Avg. queue Min_in Max_in Min_out Max_out

34. Expedited Forwarding - 1 • EF traffic must be served at a configured rate of R or faster, independent of the load • Service is equivalent to a “virtual leased line” • Routers have two priority levels (premium and best effort) • Admission Control via Bandwidth Brokers P-bit marking Spaced to peak rate R

35. Expedited Forwarding - - 2 Admission Control • “Bandwidth Brokers” perform admission control at ingress router • Only the ingress router differentiates flows ISP 1 ISP 2 Host Packet Marking Packet Marking dest Host Bandwidth broker Bandwidth broker

36. Summary of DiffServ • Advantages: • No per-flow processing in network core • Per-flow processing only at the network edge • Simpler to implement than IntServ • No signaling protocol • Disadvantages: • AF has weaker service guarantees • EF service raises same issues with charging and authentication as IntServ services

37. Leaf Router: Input(Leaf router = the router closest to the source)

38. Border Router: Input (Border router = ingress router of a network)

39. Router: Output