Differentiated Services 2007

1. Differentiated Services 2007

2. Two Approaches for Providing QoS on the Internet • “Freeway model” -- integrated services Internet (intserv) • Build a dedicated highway or “circuit” between communicating points (VIP) • “Doctor’s model” -- differentiated services (diffserv) • Mark a doctor’s vehicle (e. g.,ambulance) or “packet” to get priority the road and limit the percentage of such high- priority vehicles in the total traffic mix (fire-engine, policeman)

3. Difficulties with Intserv and RSVP • Intsev • A connection-oriented solution • QoS on a per-flow basis • Depends on resource reservation (RSVP) - signaling • Scalability • Keeping a state (and using it!) for each flow overloads the routers • Periodic messages to refresh the states create more traffic • Router complexity increases • How to satisfy heterogeneous QoS requirements for different receivers • Ambitious signaling is not practical

4. Differentiated Services (Diff-Serv) • Motivations • Don’t want end-to-end signaling and per-flow state, for scalability, complexity and quick-to-deploy reasons • Connectionless mode • QoS for aggregates of traffic, such as premium, assured and best- effort • Avoid strong assumptions about traffic types • Keep the forwarding path simple • Push complexity to network edge -> Differentiated Services Domain (DS Domain) • Per-Hop-Behavior (PHB) • Define behavior of individual routers rather than end-to-end services • forwarding behavior

5. 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 Differentiated Service (DS) Field • Diff-Serv Approach: Use the TOS field to sort packets into classes and routers treat them differently • e.g., delay requirement, drop precedence etc. • DS filed reuse the first 6 bits from the TOS byte • Diff- Service Code Point (DSCP) • The other two bits are proposed to be used by ECN

6. Differentiated Services (Diffserv) • Build around the concept of domain • Domain – a contiguous region of network under the same administrative ownership • Differentiate between edge and core routers • Edge routers • Perform per aggregate shaping or policing • Mark packets with a small number of bits; each bit encoding represents a class (subclass) • Core routers • Process packets based on packet marking • Far more scalable than Intserv, but provides weaker services

7. Diffserv Architecture • Ingress routers • Police/shape traffic • Set Diff- Service Code Point (DSCP) in Diffserv (DS) field • 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

8. Differentiated Services • Two types of QoS service • Two PHBs defined so far • Premium service • EF - Expedited forwarding (type P) • Assured service • AF - Assured forwarding (type A) • 4 classes, each guaranteed a minimum amount of bandwidth and buffering • each with three drop preference partitions • Plus, best-effort service

9. Premium Service • EF - Expedited Forwarding • Provides guaranteed peak bandwidth service with negligible delay / jitter • Provides the abstraction of a virtual pipe between an ingress and an egress router • Network: guarantees that premium packets are not dropped and they experience low delay with requested profile • User: sends within profile. User does not send more than the size of the pipe • If it sends more, excess traffic is delayed, and dropped when buffer overflows • Rate limiting of EF packets at edges only, using token bucket to shape transmission

10. Assured Service (1) • AF -- Assured Forwarding • Provides an expected level of bandwidth with delay • Permits flows to use any additional available bandwidth • Network: provides 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

11. Assured Service (2) • User and network agree to some traffic profile (how much traffic is a user allowed to send) • Edges mark packets up to allowed rate as “in-profile” or low drop precedence • Other packets are marked with higher drop precedence • A congested DS node tries to protect packets with a lower drop precedence value from being lost by preferably discarding packets with a higher drop precedence value • Implemented using buffer management, e. g., RIO -- RED (random early detection) with In and Out

12. Traffic profile Ingress Assured Service (3) • Large spatial granularity service • Theoretically, user profile is defined irrespective of destination • All other services we learnt are end-to-end, i.e., we know destination(s) apriority • This makes service very useful, but hard to provision (why ?)

13. Components of Diff-Serv (1) Edge node algorithms • Classification, policing, shaping, metering, marking, etc. (2) Router algorithms • Packet discard algorithms: RED-like methods for in-profile and out-of-profile traffic • Priority, low-latency queueing

14. Ingress Traffic conditioner Class 1 Marked traffic Traffic conditioner Class 2 Data traffic Classifier Scheduler Best-effort Per aggregate Classification (e.g., user) Ingress Edge Router

15. Drop on overflow Packet output Wait for token Set EF bit Packet input No token token Packet output Packet input Test if token Set AF “in” bit Traffic Conditioning • Traffic conditioner (TC) implement • Metering • Marking • Shaping

16. Scheduler • Employed by both edge and core routers • For premium service – use strict priority, or weighted fair queuing (WFQ) • For assured service – use RIO (RED with In and Out) • Has two classes, “In” and “Out” (of profile) • Always drop OUT packets first • For OUT measure entire queue • For IN measure only in-profile queue

17. RIO (RED with In and Out) Drop Probability P(drop) 1.0 MaxP A vgLen Min Min Max Max out in out in

18. yes high priority P-bit set? no yes low priority A-bit set? RIO no Scheduler Example • Premium traffic sent at high priority • Assured and best-effort traffic pass through RIO and then sent at low priority

19. EF What DSCP? High-priority Q Packets out AF If “in” set incr in_cnt Low-priority Q If “in” set decr in_cnt RIO queue management Core Router Output Processing

21. Control Path • 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

22. 3 2 BB BB BB 7 5 1 profile profile 6 4 profile 8 receiver sender 9 Example • Achieve end-to-end bandwidth guarantee

23. Best-Efforts Diffserv Intserv Service • Connectivity • No isolation • No guarantees • Per aggregation isolation • Per aggregation guarantee • Per flow isolation • Per flow guarantee Service Scope • End-to-end • Domain • End-to-end 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) Comparison

24. Summary • Diffserv more scalable than Intserv • Edge routers maintain per aggregate state • Core routers maintain state only for a few traffic classes • But, provides weaker services than Intserv • Per aggregate bandwidth guarantee (premium service) vs. per flow bandwidth and delay guarantee • BB is not an entirely solved problem • Single point of failure • Handle only long term reservations (hours, days)

25. Intserv over Diffserv-- Integrated Services Operation over Diffserv Networks • Intserv enables per-flow end-to-end QoS • enables hosts to request per-flow, quantifiable resources, along end-to-end data paths and to obtain feedback regarding admissibility of these requests • Diffserv enables scalability across large networks • => Intserv over Diffserv • Integrated Services Operation over Diffserv Networks

26. Network Configuration _______ ___________ ______ / \ / \ / \ / \ / \ / \ |----| | |-----| |-----| |------| |-----| | |-----| |Tx |-| |ER1|---|BR1| |BR2|---|ER2| |-|Rx | |----| | |-----| |-----| |------| |-----| | |-----| \ / \ / \ / \________/ \____________/ \_______/ Non-Diffserv region Diffserv region Non-Diffserv region • ER -- edge routers which are adjacent to the Diffserv region • BR -- border routers within the Diffserv region

27. QoS over Next Generation Networks • Concluding Remark by H. T. Kung 1998: • In 1993 ATM was in, but it was out of favor in 1997 • In 1995 IP switching was in, but it was out of favor in 1997 • In 1996 RSVP was in, but it is out of favor in 1998 • In 1998 Diff-Serv and MPLS are in, but will they also be out of favor soon? • IWQoS2000 panel discussion: • ATM is on its way out. • Intserv is dead. • Diffserv is dying. • MPLS is in misguiding. • Growing use of Multi-Protocol Label Switching now

28. Topics • Integrated and Differentiated Services • Active Buffer Management techniques, ex. RED. • Multiprotocol Label Switching • QoS in 3G wireless multimedia networks • QoS based routing • QoS management in multi-bearer IP networks including PSTN • Impact of media compression in QoS networks • QoS over Mobile IP • QoS enabled MAC design