QoS in wireless systems

1. QoS in wireless systems Preetam Patil Leena Chandran-Wadia

2. Contents • QoS in wired systems • technologies - ATM, IP/MPLS • mechanisms - scheduling, routing, admission control…. • architecture – DiffServ • QoS in wireless • Wireless ATM • GPRS • MANETS • Perspective QoS in Wireless Systems

3. Case for QoS • “QoS is a means to convergence but a goal in itself from network point of view.” • Over provisioning of resources is not enough… • Different applications have different QoS requirements. • Particularly important from the point of how TCP reacts to packet losses and delays. QoS in Wireless Systems

4. QoS in Wired Networks • What is QoS? - “Better than best effort” • Associated metrics include • Guarantees on bandwidth • Bounds on delay (queuing, multiplexing) • Bounds on delay variation (jitter) • Bounds on loss probability • Minimize cost • Ideally we would like to have “end-to-end QoS” and associated pricing QoS in Wireless Systems

5. QoS Mechanisms • support for real-time flows in the n/w • marking such flows - precedence (ToS) • admission control • assign to different queues • priority scheduling • buffer management • constrained routing • mechanisms for signaling - within n/w as well as between users and n/w QoS in Wireless Systems

6. Performance measures • QoS services (depending on the level) generally involve putting all or at least a few of these mechanisms into place • Fairness - access to excess capacity • Isolation - protection from excess traffic from other users • Efficiency - number of flows accommodated per service level • complexity - implementation, control overhead QoS in Wireless Systems

7. IP QoS Approaches • Two broad families: • Per-flow service • Integrated Services and RSVP • Since per-flow information needs to be maintained, too complex and not scalable • Aggregated service • Differentiated services • Only class-based information required, hence more scalable, and easier to implement QoS in Wireless Systems

8. Differentiated Services(DiffServ) • Goals and motivations • Data path scalability • Coarse granularity service classes (no per-flow state) • Minimum impact on packet forwarding performance • Realizable through simple mechanisms QoS in Wireless Systems

9. DiffServ… - continued • Rapid deployment • Standardize service codepoints in IP header and associated expected local behaviour (Per Hop Behaviour - PHB) • Wide range of possible implementations • Avoid chicken and egg problem of signalling deployment and application/user support QoS in Wireless Systems

10. How it works - • IP TOS field in IPV4 or Traffic Class field in IPV6 used to mark packets • Pre-configured set of service classes (behaviours) • Expedited Forwarding (local behaviour only) • Virtual leased line type of service • Assured Forwarding (local behaviour only) • Several service classes with drop precedence within each class QoS in Wireless Systems

11. DiffServ Components • Edge functions • Flow classification and packet marking • Traffic conditioning • Core functions • Enforcement of Per Hop Behaviours • Boundary functions • Conformance enforcement QoS in Wireless Systems

12. DiffServ Components… continued • Components • Classifiers • Select packets and assigns DS code point • Traffic conditioners • Enforces rate limitations • Per Hop Behaviours • Differentiated packet treatments QoS in Wireless Systems

13. Multi-Protocol Label Switching (MPLS) • An attempt to exploit benefits of ATM label-switching and flexibility of IP routing. • Has roots in IP tag-switching. • MPLS works between L2 and L3. • Designed to work over different link-layer technologies- Ethernet, Frame-relay, etc. • Different network protocols supported. QoS in Wireless Systems QoS in Wireless Systems 13

14. MPLS Features • Packets are forwarded based on a 20-bit fixed-length label in packet-header instead of destination IP address • A path (LSP - Label Switched path) is first established using a signalling protocol • Label Distribution Protocol • extensions to RSVP QoS in Wireless Systems

15. MPLS Architecture QoS in Wireless Systems

16. MPLS Architecture- contd.. • LSR- routers supporting MPLS are called Label Switching Routers • Ingress LSR - LSR where packets in a flow enter the MPLS domain • Egress LSR - LSR where packets in a flow leave the MPLS domain • FEC - packets to be forwarded in same manner are assigned to same Forwarding Equivalence Class (FEC) QoS in Wireless Systems

17. QoS and Traffic Engineering in MPLS • MPLS and DiffServ similar in the way packets are looked up and classified at the Ingress • LSPs can be set up for Different Service classes, or bits in MPLS header can be used to mark flows for QoS • LSPs can be explicitly set up based on QoS and Traffic-Engg objectives (CR-LSPs) • Many extensions to MPLS for QoS and TE proposed QoS in Wireless Systems

18. ATM Reference Model • Complete protocol stack, alternative to TCP/IP - fully QoS capable!! • 4 layer (upper, adaptation, ATM and physical), 3 dimensional model • Different from both OSI and TCP/IP • User Plane (data transport, flow, error control) and Control Plane (connection management) • Plane and Layer Management (RM and interlayer coordination) QoS in Wireless Systems

19. Service Differentiation • Two major components • Data path: identifies packets eligible for services and enforces them • Packet classifiers • scheduling and Buffer management • Control path: determines if and how guarantees can be provided • signaling • admission control • QoS routing QoS in Wireless Systems

20. ATM - Connection Oriented Cell Switching • Call setup: synchronization before data transfer input 33 conn Id 12 output 22 conn Id 12 input 1 1 conn Id 1 2 output 4 3 conn Id 1 1 input 11 conn Id 12 output 43 conn Id 12 input 1 conn Id 2 output 2 conn Id 1 2 1 3 1 2 3 Switch S1 Switch S2 Switch S4 Host C 4 2 Host A Switch S3 2 1 Host B QoS in Wireless Systems

21. ATM Logical Connections Virtual Channels Transmission Path Virtual Path QoS in Wireless Systems

22. ATM Connection Terminology • Virtual Channel Connection (VCC), also called VC • identified by one VPI/VCI at an interface • Virtual Channel Link • Virtual Channel Identifier • no global identifier • Two types • Switched - SVCs (need connection setup) • Permanent - PVCs (service provider) QoS in Wireless Systems

23. More Connection Terminology • Virtual Path Connection, also called VP • identified by one VPI at one interface • Virtual Path Link • Virtual Path Identifier • no global identifier • Virtual paths make it possible for CPN to have closed user groups, with a network of VPs QoS in Wireless Systems

24. ATM Cells - NNI VPI VPI VCI VCI Virtual Path Identifier VPI VCI PT HEC Virtual Channel Identifier 48 bytes Payload Type PT Cell Loss Priority CLP Header Error Control HEC Payload QoS in Wireless Systems

25. Service Categories • CBR - Constant Bit Rate (T1/E1 circuit) • VBR - Variable Bit Rate • rt VBR - real-time Video conferencing • nrt VBR - multimedia E-mail • ABR - Available Bit Rate (Browsing the web) • UBR - Unspecified Bit rate (Background file transfer). Useful for sending IP packets QoS in Wireless Systems

26. ATM Perspective • Standardization took too much time • no native ATM applications were written • meanwhile, runaway success of the Web and of MBone meant that killer applications were all running IP • this meant LANs would remain Ethernet • and WANs would run IP over ATM • But... ATM Hardware is selling as much as IP switches and routers today!! QoS in Wireless Systems

27. Wireless ATM • User (data) plane largely unchanged • Control plane • MATM adapter (handsets): UNI + Mobility • WATM & AP: support control of Radio Access (signal strength etc.) • Switches: Signaling to support mobility • QoS • Wireless QoS: reservation adds to delay • Handover QoS: blocking, re-negotiation QoS in Wireless Systems

28. QoS in Wireless Networks • What’s different in Wireless ? • A premium on efficiency (due to limitations in spectrum resource) • Low reliability in the worst case • Traffic limited by interference • Similar to congestion, but more easily controllable • “Cost” of one stream related not only to rate parameters, but also to reliability(energy per bit) and acceptable delay • Best error- control coding techniques are at the physical and media- access layers QoS in Wireless Systems

29. Wireless Systems – GPRS • Varying Conditions of Radio interface • QoS profile consists of parameters like • precedence: • delay: includes radio access delay (uplink) or radio scheduling delay (downlink), radio transit delay, GPRS-network transit delay • reliability: error rates much higher • throughput: specified by maximum bit rate and mean bit rate QoS in Wireless Systems

30. GPRS (1) • Each GPRS subscription will be associated with one QoS profile (HLR) • SGSN will negotiate QoS for the flow • Based on subscribed default in HLR • The requested profile from the MN • Current availability of GPRS resources • SGSN must distribute resources fairly among flows, it may renegotiate QoS if necessary QoS in Wireless Systems

31. QoS in Wireless Systems

32. GPRS (2) QoS Classes • Four traffic classes • Conversational,streaming, interactive, background • (1) Conversational, streaming: for carrying real-time flows • difference is the extent of delay sensitivity • Forward error correction • (2) interactive, background: for traditional internet traffic • interactive class has higher response • better error recovery using retransmissions QoS in Wireless Systems

33. QoS Profile Parameters • Eight other parameters are used for defining the specific QoS-profile • MAX bit rate, Guaranteed bit rate • Delivery order, Reliability • PDU size information, Transfer delay • Traffic handling priority, Allocation priority • Values will depend on main traffic class • More complex, but will reflect different applications better • Applications must signal QoS requirements QoS in Wireless Systems

34. Conversational Class • Assumed to be relatively non-bursty • Real time, low delay - Voice • Characterized by • maximum bit rate • guaranteed bit rate • guaranteed transfer delay • rest optional, but usually specified • lower classes specify fewer parameters QoS in Wireless Systems

35. Re-negotiation of QoS • MN, BSS & SGSN have the capability to trigger a modification of the QoS profile associated with an ongoing data flow • due to congestion or shortage of radio resources • in order to map QoS parameters of the packet data network into the GPRS network QoS in Wireless Systems

36. Traffic Flow Templates Assign different QoS-profiles to different applications - Signaling done using RSVP API QoS in Wireless Systems

37. QoS in MANets • Availability of link state information and its management is difficult • QoS of wireless link is apt to change in dynamic environment • mobility of hosts • resource limitations (time varying) • DiffServ a possible solution • what are the boundary routers? • concept of SLA does not exist QoS in Wireless Systems

38. QoS in MAC protocols • MAC protocol design goals • solve medium contention • deal with hidden/exposed terminal problem • improve throughput • QoS MACs must provide resource reservation and QoS guarantees to real-time traffic • Wireless LANs – Black burst contention etc • Manets – MACA/PR QoS in Wireless Systems

39. MACA/PR • Multiple Access Collision Avoidance with Piggyback Reservations • Rapid and reliable transmission to non-real time datagrams • Guaranteed b/w support to real-time traffic • NRT traffic waits for “free” window in reservation table plus additional random time equivalent to single hop round-trip delay • proceed with RTS-CTS-PKT-ACK dialogue • Reservation table records all reserved send and receive windows of all stations in range QoS in Wireless Systems

40. MACA/PR - RT • To send first data packet of a RT connection, sender initiates RTS-CTS and then proceeds with PKT-ACK • For subsequent data packets only PKT-ACK is needed • If sender fails to receive several ACKs then restarts RTS-CTS dialogue • MACA/PR does not retransmit after collisions • To reserve b/w for real-time traffic, RT scheduling information is carried in headers of PKTS and ACKs QoS in Wireless Systems

41. MACA/PR -RT • Sender piggybacks reservation information for its next data packet transmission on the current data PKT • Receiver inserts reservation in its Reservation table and confirms it with the ACK to the sender • Neighbors of receiver R will defer their transmission on receiving the ACK • ACK also tells them next scheduled receiving time of R, so they can avoid transmission QoS in Wireless Systems

42. MACA/PR -RT • Real-time packets are protected from hidden hosts by the propagation of reservation tables among neighbors, not by RTS-CTS dialogues • Thus, through piggybacked reservation of information and the maintenance of reservation tables, bandwidth is reserved and guaranteed for real-time traffic… QoS in Wireless Systems

43. Perspective • Essentially, concept of QoS must be accepted and supported by every element in the value chain • Infrastructure and terminal developers • Mobile network operators • Application developers • End users QoS in Wireless Systems