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

2. QoS in Wireless Systems2 Contents p QoS in wired systems u technologies - ATM, IP/MPLS u mechanisms - scheduling, routing, admission control…. u architecture – DiffServ p QoS in wireless u Wireless ATM u GPRS u MANETS p Perspective

3. QoS in Wireless Systems3 Case for QoS u “QoS is a means to convergence but a goal in itself from network point of view.” u Over provisioning of resources is not enough… u Different applications have different QoS requirements. u Particularly important from the point of how TCP reacts to packet losses and delays.

4. QoS in Wireless Systems4 QoS in Wired Networks p What is QoS? - “Better than best effort” p Associated metrics include u Guarantees on bandwidth u Bounds on delay (queuing, multiplexing) u Bounds on delay variation (jitter) u Bounds on loss probability u Minimize cost p Ideally we would like to have “end-to- end QoS” and associated pricing

5. QoS in Wireless Systems5 QoS Mechanisms p support for real-time flows in the n/w u marking such flows - precedence (ToS) u admission control u assign to different queues u priority scheduling u buffer management u constrained routing u mechanisms for signaling - within n/w as well as between users and n/w

6. QoS in Wireless Systems6 Performance measures p QoS services (depending on the level) generally involve putting all or at least a few of these mechanisms into place u Fairness - access to excess capacity u Isolation - protection from excess traffic from other users u Efficiency - number of flows accommodated per service level u complexity - implementation, control overhead

7. QoS in Wireless Systems7 IP QoS Approaches p Two broad families: u Per-flow service ä Integrated Services and RSVP ä Since per-flow information needs to be maintained, too complex and not scalable u Aggregated service ä Differentiated services ä Only class-based information required, hence more scalable, and easier to implement

8. QoS in Wireless Systems8 Differentiated Services(DiffServ) p Goals and motivations ä Data path scalability F Coarse granularity service classes (no per-flow state) F Minimum impact on packet forwarding performance l Realizable through simple mechanisms

9. QoS in Wireless Systems9 DiffServ… - continued ä Rapid deployment F Standardize service codepoints in IP header and associated expected local behaviour (Per Hop Behaviour - PHB) l Wide range of possible implementations l Avoid chicken and egg problem of signalling deployment and application/user support

10. QoS in Wireless Systems10 How it works - p IP TOS field in IPV4 or Traffic Class field in IPV6 used to mark packets p Pre-configured set of service classes (behaviours) p Expedited Forwarding (local behaviour only) u Virtual leased line type of service p Assured Forwarding (local behaviour only) u Several service classes with drop precedence within each class

11. QoS in Wireless Systems11 DiffServ Components p Edge functions u Flow classification and packet marking u Traffic conditioning p Core functions u Enforcement of Per Hop Behaviours p Boundary functions u Conformance enforcement

12. QoS in Wireless Systems12 DiffServ Components… continued p Components u Classifiers ä Select packets and assigns DS code point u Traffic conditioners ä Enforces rate limitations u Per Hop Behaviours ä Differentiated packet treatments

13. QoS in Wireless Systems13 QoS in Wireless Systems13 Multi-Protocol Label Switching (MPLS) p An attempt to exploit benefits of ATM label-switching and flexibility of IP routing. p Has roots in IP tag-switching. p MPLS works between L2 and L3. p Designed to work over different link-layer technologies- Ethernet, Frame-relay, etc. p Different network protocols supported.

14. QoS in Wireless Systems14 MPLS Features p Packets are forwarded based on a 20-bit fixed-length label in packet-header instead of destination IP address p A path (LSP - Label Switched path) is first established using a signalling protocol u Label Distribution Protocol u extensions to RSVP

15. QoS in Wireless Systems15 MPLS Architecture

16. QoS in Wireless Systems16 MPLS Architecture- contd.. p LSR- routers supporting MPLS are called Label Switching Routers p Ingress LSR - LSR where packets in a flow enter the MPLS domain p Egress LSR - LSR where packets in a flow leave the MPLS domain p FEC - packets to be forwarded in same manner are assigned to same Forwarding Equivalence Class (FEC)

17. QoS in Wireless Systems17 QoS and Traffic Engineering in MPLS p MPLS and DiffServ similar in the way packets are looked up and classified at the Ingress p LSPs can be set up for Different Service classes, or bits in MPLS header can be used to mark flows for QoS p LSPs can be explicitly set up based on QoS and Traffic-Engg objectives (CR-LSPs) p Many extensions to MPLS for QoS and TE proposed

18. QoS in Wireless Systems18 ATM Reference Model p Complete protocol stack, alternative to TCP/IP - fully QoS capable!! p 4 layer (upper, adaptation, ATM and physical), 3 dimensional model p Different from both OSI and TCP/IP p User Plane (data transport, flow, error control) and Control Plane (connection management) p Plane and Layer Management (RM and interlayer coordination)

19. QoS in Wireless Systems19 Service Differentiation p Two major components u Data path: identifies packets eligible for services and enforces them ä Packet classifiers ä scheduling and Buffer management u Control path: determines if and how guarantees can be provided ä signaling ä admission control ä QoS routing

20. QoS in Wireless Systems20 ATM - Connection Oriented Cell Switching p Call setup: synchronization before data transfer input 3 3 conn Id 1 2 output 2 2 conn Id 1 2 Switch S1 Switch S2 Switch S4 Switch S3 input 1 1 conn Id 1 2 output 4 3 conn Id 1 1 input 1 1 conn Id 1 2 output 4 3 conn Id 1 2 2 3 1312 2 4 2 1 input 1 conn Id 2 output 2 conn Id 1 Host A Host C Host B

21. QoS in Wireless Systems21 ATM Logical Connections Transmission Path Virtual Path Virtual Channels

22. QoS in Wireless Systems22 ATM Connection Terminology p Virtual Channel Connection (VCC), also called VC p identified by one VPI/VCI at an interface u Virtual Channel Link u Virtual Channel Identifier p no global identifier p Two types u Switched - SVCs (need connection setup) u Permanent - PVCs (service provider)

23. QoS in Wireless Systems23 More Connection Terminology p Virtual Path Connection, also called VP p identified by one VPI at one interface u Virtual Path Link u Virtual Path Identifier p no global identifier p Virtual paths make it possible for CPN to have closed user groups, with a network of VPs

24. QoS in Wireless Systems24 ATM Cells - NNI VPI VCI PT HEC 48 bytes VPI PT CLP HEC Virtual Path Identifier Virtual Channel Identifier Payload Type Cell Loss Priority Payload Header Error Control

25. QoS in Wireless Systems25 Service Categories p CBR - Constant Bit Rate (T1/E1 circuit) p VBR - Variable Bit Rate u rt VBR - real-time Video conferencing u nrt VBR - multimedia E-mail p ABR - Available Bit Rate (Browsing the web) p UBR - Unspecified Bit rate (Background file transfer). Useful for sending IP packets

26. QoS in Wireless Systems26 ATM Perspective p Standardization took too much time p no native ATM applications were written p meanwhile, runaway success of the Web and of MBone meant that killer applications were all running IP p this meant LANs would remain Ethernet p and WANs would run IP over ATM p But... ATM Hardware is selling as much as IP switches and routers today!!

27. QoS in Wireless Systems27 Wireless ATM p User (data) plane largely unchanged p Control plane u MATM adapter (handsets): UNI + Mobility u WATM & AP: support control of Radio Access (signal strength etc.) u Switches: Signaling to support mobility p QoS u Wireless QoS: reservation adds to delay u Handover QoS: blocking, re-negotiation

28. QoS in Wireless Systems28 QoS in Wireless Networks p What’s different in Wireless ? u A premium on efficiency (due to limitations in spectrum resource) u Low reliability in the worst case u Traffic limited by interference ä Similar to congestion, but more easily controllable u “Cost” of one stream related not only to rate parameters, but also to reliability(energy per bit) and acceptable delay u Best error- control coding techniques are at the physical and media- access layers

29. QoS in Wireless Systems29 Wireless Systems – GPRS p Varying Conditions of Radio interface p QoS profile consists of parameters like u precedence: u delay: includes radio access delay (uplink) or radio scheduling delay (downlink), radio transit delay, GPRS-network transit delay u reliability: error rates much higher u throughput: specified by maximum bit rate and mean bit rate

30. QoS in Wireless Systems30 GPRS (1) p Each GPRS subscription will be associated with one QoS profile (HLR) p SGSN will negotiate QoS for the flow u Based on subscribed default in HLR u The requested profile from the MN u Current availability of GPRS resources p SGSN must distribute resources fairly among flows, it may renegotiate QoS if necessary

31. QoS in Wireless Systems31

32. QoS in Wireless Systems32 GPRS (2) QoS Classes p Four traffic classes u Conversational,streaming, interactive, background u (1) Conversational, streaming: for carrying real-time flows ä difference is the extent of delay sensitivity ä Forward error correction u (2) interactive, background: for traditional internet traffic ä interactive class has higher response ä better error recovery using retransmissions

33. QoS in Wireless Systems33 QoS Profile Parameters p Eight other parameters are used for defining the specific QoS-profile u MAX bit rate, Guaranteed bit rate u Delivery order, Reliability u PDU size information, Transfer delay u Traffic handling priority, Allocation priority p Values will depend on main traffic class p More complex, but will reflect different applications better p Applications must signal QoS requirements

34. QoS in Wireless Systems34 Conversational Class p Assumed to be relatively non-bursty p Real time, low delay - Voice p Characterized by u maximum bit rate u guaranteed bit rate u guaranteed transfer delay p rest optional, but usually specified p lower classes specify fewer parameters

35. QoS in Wireless Systems35 Re-negotiation of QoS p MN, BSS & SGSN have the capability to trigger a modification of the QoS profile associated with an ongoing data flow u due to congestion or shortage of radio resources u in order to map QoS parameters of the packet data network into the GPRS network

36. QoS in Wireless Systems36 Traffic Flow Templates Assign different QoS-profiles to different applications - Signaling done using RSVP API

37. QoS in Wireless Systems37 QoS in MANets p Availability of link state information and its management is difficult p QoS of wireless link is apt to change in dynamic environment u mobility of hosts u resource limitations (time varying) p DiffServ a possible solution u what are the boundary routers? u concept of SLA does not exist

38. QoS in Wireless Systems38 QoS in MAC protocols p MAC protocol design goals u solve medium contention u deal with hidden/exposed terminal problem u improve throughput p QoS MACs must provide resource reservation and QoS guarantees to real- time traffic u Wireless LANs – Black burst contention etc u Manets – MACA/PR

39. QoS in Wireless Systems39 MACA/PR p Multiple Access Collision Avoidance with Piggyback Reservations u Rapid and reliable transmission to non-real time datagrams u Guaranteed b/w support to real-time traffic p NRT traffic waits for “free” window in reservation table plus additional random time equivalent to single hop round-trip delay p proceed with RTS-CTS-PKT-ACK dialogue p Reservation table records all reserved send and receive windows of all stations in range

40. QoS in Wireless Systems40 MACA/PR - RT p To send first data packet of a RT connection, sender initiates RTS-CTS and then proceeds with PKT-ACK p For subsequent data packets only PKT-ACK is needed p If sender fails to receive several ACKs then restarts RTS-CTS dialogue p MACA/PR does not retransmit after collisions p To reserve b/w for real-time traffic, RT scheduling information is carried in headers of PKTS and ACKs

41. QoS in Wireless Systems41 MACA/PR -RT p Sender piggybacks reservation information for its next data packet transmission on the current data PKT p Receiver inserts reservation in its Reservation table and confirms it with the ACK to the sender p Neighbors of receiver R will defer their transmission on receiving the ACK p ACK also tells them next scheduled receiving time of R, so they can avoid transmission

42. QoS in Wireless Systems42 MACA/PR -RT p Real-time packets are protected from hidden hosts by the propagation of reservation tables among neighbors, not by RTS-CTS dialogues p Thus, through piggybacked reservation of information and the maintenance of reservation tables, bandwidth is reserved and guaranteed for real-time traffic…

43. QoS in Wireless Systems43 Perspective p Essentially, concept of QoS must be accepted and supported by every element in the value chain u Infrastructure and terminal developers u Mobile network operators u Application developers u End users