Quality of Service Frameworks

1. Quality of ServiceFrameworks Hamed Khanmirza Principles of Network University of Tehran

2. What is QoS? • The capability to control traffic handling mechanisms in the network such that the network meets the service needs of certain applications and users subject to network policies. • Applications • Elastic (delay-tolerant) • Tolerate delays and losses • Can adapt to congestion • Non-elastic (Real-Time) • Needs some kind of guarantee from network • QoS Parameters • Bandwidth • Latency • Jitter • Loss

3. Utility Curve Shapes U U Elastic Hard real-time BW BW Delay-adaptive U BW

4. Integrated Services

5. Service characteristic • Enhancing IP Service Model • Add QoS service classes • Explicit resource management at IP level • Per flow state maintained at routers which is • used for admission control and scheduling • set up by signaling protocol, users explicitly request their needs. • This is done with RSVP protocol

6. Integrated Services Example • Achieve per-flow bandwidth and delay guarantees • Example: guarantee 1MBps and < 100 ms delay to a flow Receiver Path RSVP Message Sender

7. Integrated Services Example • Allocate resources - perform per-flow admission control Receiver RESV RSVP Message Sender

8. Integrated Services Example • Install per-flow state Receiver Sender

9. Integrated Services Example • Install per flow state Receiver RESV RSVP Message Sender

10. Integrated Services Example: Data Path • Per-flow classification Receiver Sender

11. Integrated Services Example: Data Path • Per-flow buffer management Receiver Sender

12. Integrated Services Example • Per-flow scheduling Receiver Sender

13. Service Types • Multiple service classes • Service can be viewed as a contract between network and communication client • end-to-end service • other service scopes possible • Three defined services • Best-Effort for (best-effort or elastic) • Guaranteed Service for hard real-time (“Real-Time applications”) • Controlled Load for soft real-time (“tolerant” applications)

14. Differentiated Services

15. What is the Problem? • Goal: providing support for wide variety of applications: • Interactive TV, IP telephony, on-line gamming (distributed simulations), VPNs, etc • Problem: • Best-effort cannot do it • Intserv can support all these applications, but • Too complex • Not scalable • Queuing & scheduling • Classification speed • Hardware Restriction • DiffServ aims at providing QoS with simple mechanisms so that it scales and can be deployed. • push the complexity to the “edges” of the network. • Provide weaker guarantee

16. DiffServ Architecture • Ingress routers (Edge Routers) • Perform per aggregate shaping or policing (Behavior Aggregate) • Mark packets with Code Points, each CP represent a Class of Service (DSCP DiffServ Code Point) • Core routers • Implement Per Hop Behavior (PHB) for each DSCP • Process packets based on DSCP DS-2 DS-1 Egress Ingress Egress Ingress Edge router Core router

17. Differentiated Service (DS) Field • DS filed reuse the first 6 bits from the former Type of Service (TOS) byte • The other two bits are proposed to be used by ECN 0 5 6 7 DS Filed 0 4 8 16 19 31 Version HLen TOS Length Identification Flags Fragment offset IP header TTL Protocol Header checksum Source address Destination address Data

18. Per Hop Behavior (PHB) • Define behavior of individual routers rather than end-to-end services • Two PHBs • Assured Forwarding (AF, A type) • Expedited Forwarding (EF, P type) • Plus, best-effort service!

19. EF PHB (Premium) • Provides the abstraction of a “virtual pipe” between an ingress and an egress router • Network: • No loss • low delay & jitter • User: • Send traffic based on SLA • Excess traffic is delayed, and dropped when buffer overflows • Signaling, admission control may get more elaborate in future (DiffServ/RSVP)

20. Assured Forwarding PHB • Possible service: • strong assurance for traffic within profile • Out-of-profile traffic will be marked as lower class (i.e. BE) • Network: • lower loss rate than best-effort • In case of congestion best-effort packets are dropped first • User: sends no more assured traffic than its profile • If it sends more, the excess traffic is converted to best-effort • IETF defines AF as (RFC 2477) • 4 classes • Each with 3 drop precedence • Order of packets must be preserved

21. Provisioning & Configuration • To provide network QoS, some configuration and provisioning is required • Provisioning: • Static and long-term management tasks • Enhancing network equipment • Interface definition • Link speed and BW • Configuration: • Dynamic and short-term tasks • Direct manipulation of traffic handling mechanisms

22. Service Level Agreement & Policy • Agreements/service provided within a domain • Service Level Agreement (SLA) with ISP • Policy • A high level description of the quality and efficiency objectives to be met by the network • Policy is set by SLA

23. Example of an SLA Traffic submitted by customer c1 and marked with DSCP = EF and destination address in subnet 2.x.x.x and conforming to profile p1 Will be delivered to egress point B with latency not exceeding 100ms and a drop-probability less than 0.1% Traffic submitted by customer c1 and marked with DSCP = EF and destination address in subnet 2.x.x.x and not conforming to profile p1 Will be discarded

24. Example of an SLA Traffic submitted by customer c1 and marked with DSCP = EF and destination address in subnet 3.x.x.x and conforming to profile p2 Will be delivered to egress point C with latency not exceeding 100ms and a drop-probability less than 0.1% Traffic submitted by customer c1 and marked with DSCP = EF and destination address in subnet 3.x.x.x and not conforming to profile p2 Will be discarded

25. Example of an SLA Traffic submitted by customer c1 and marked with DSCP = EF and destination address not in subnet 2.x.x.x and destination address not in subnet 3.x.x.x Will be discarded Traffic submitted by customer c1 and not marked with DSCP = EF Will be delivered with best-effort service P1: Conforming traffic must not exceed 64kbps over any 5msec interval P2: Conforming traffic must not exceed 128kbps over any 2.5msec interval

26. Pushed vs. Signaled

27. Components of Policy System Functional Layers No physical

28. Distributed Data Store - Directory

29. Interior Provisioning

30. Assured Service Traffic profile Ingress • Large spatial granularity service • Theoretically, user profile is defined irrespective of destination • This makes service very useful, but hard to provision • Over provision?

31. Multicast Problems in DiffServ • Multicast • Problem • Dynamic trees • Solutions • Different DSCP • Some determined tree structure • Remarking and shaping at boundaries

32. DiffServ Implementations • Two important proposals • RIO Mechanism (1 service) • The Scalable Share Differentiation architecture (SSD) • Two-Bit architecture • RFC (2475)

33. Two-Bit Architecture • Proposes three different levels of service: • Premium Service. • Assured Service. • Best Effort Service. • Two-bit architecture: • Packets get differentiated by two bits in their header. • Premium bit (P-bit) • Assured Service bit (A-bit)

34. Leaf Router Input Functionality Marker 1 Flow 1 Marker N Flow N Arriving packet MF Packet classifier Forwarding engine Clear A&P bits Best effort classify packets based on packet header

35. Markers in Leaf Routers Drop on overflow Packet output Wait for token Set P bit Packet input No token token Packet output Packet input Test if token Set A bit RIO is applied here

36. Red with In or Out (RIO) Dropping probability 1 OUT IN Average queue length • Similar to RED • With two separate probability curves • In (of profile) • Out (of profile) • “Out” class has • lower Minthresh, so packets are dropped from this class first • Based on queue length of all packets • “In” Class • As avg queue length increases, “in” packets are also dropped • Based on queue length of only “in” packets

37. Output Forwarding • 2 queues: • High Priority: EF packets • Lower priority queue implements RED “In or Out” scheme (RIO) • Usually scheduling scheme is “Strict Priority” EF P bit set? High-priority Q Send Packet AF If A bit set incr a_cnt Low-priority Q If A bit set decr in_cnt RIO queue management

38. Intra Domain Behavior • Each domain is assigned a Bandwidth Broker (BB) • Usually, used to perform ingress-egress bandwidth allocation • BB is responsible to perform admission control in the entire domain • BB not easy to implement • Require complete knowledge about domain • Single point of failure, may be performance bottleneck • Designing BB still a research problem

39. Example 3 2 7 5 1 profile profile 6 4 profile 8 9 • Achieve end-to-end bandwidth guarantee BB BB BB receiver sender

40. RFC 2475: Overall Architecture • Classifiers: • Multifield Classifier (MF) • Behavior Aggregate Classifier (BA)

41. Traffic Conditioning • Schedulers • Work-conserving • Non-work-conserving • Traffic conditioning uses Non-work-conserving ones • Implementations • Leaky Bucket • Token Bucket • Hybrid approaches • Leaky-Token Bucket • Dual Token Bucket

42. Leaky Bucket • Smoothes traffic and generates constant rate b bits r b/s

43. Token Bucket Filter • Described by 2 parameters: • Token rate r: rate of tokens placed in the bucket • Bucket depth b: capacity of the bucket • Operation: • Tokens are placed in bucket at rate r • If bucket fills, tokens are discarded • Sending a packet of size P uses P tokens • If bucket has P tokens, packet sent at max rate, else must wait for tokens to accumulate

44. Token Bucket Operation Tokens Tokens Tokens Overflow Packet Packet Not enough tokens  wait for tokens to accumulate Enough tokens  packet goes through, tokens removed

45. Token Bucket • On the long run, rate is limited to r • On the short run, a burst of size b can be sent • Token Bucket 3 possible uses • Shaping • Delay pkts from entering net (shaping) • Policing • Drop pkts that arrive without tokens • Metering (Marking) • Let all pkts pass through, mark ones without tokens

46. Comparison Best-Effort Diffserv Intserv • Per aggregation isolation • Per aggregation guarantee • Connectivity • No isolation • No guarantees • Per flow isolation • Per flow guarantee Service • End-to-end • Domain • End-to-end Service Scope Complexity • No set-up • Long term setup • Per flow setup Scalability • Highly scalable • (nodes maintain only routing state) • Scalable (edge routers maintains per aggregate state; core routers per class state) • Not scalable (each router maintains per flow state)