Network Support for Multimedia Applications in Mobile Networks

1. Network Support for Multimedia Applications in Mobile Networks Major Area Exam Kimaya Sanzgiri MOMENT Lab Computer Science Dept., UCSB

2. Motivation • Growing popularity of multimedia applications • Streaming music/videos • Internet telephony • Media-rich messaging • Growing popularity of mobile wireless networks • Infrastructured • Multi-hop (ad hoc) • Increasing support for multimedia content on wireless devices

3. Characteristics of Real-time Multimedia Applications • Sensitive to end-to-end delay and jitter • Many applications can tolerate some packet loss • Different needs from other types of applications, such as bulk data transfers

4. Network Support • Due to diverse needs, packets belonging to different types of applications need to be handled differently by the network • Network needs to offer different qualities of service • Availability of sufficient resources must be ensured in order to meet application requirements

5. Characteristics of Wireless Networks • Shared nature of medium • Resource availability influenced by activities of neighboring nodes • Mobility and dynamic topology • Resource constrained devices • Higher error rates • No defined network boundary • Lack of central authority

6. Supporting Multimedia Applications • Solutions have been proposed for both wired and wireless networks that operate at different levels of the network stack • In this talk, we focus on network layer solutions • At the end, we will mention some proposed solutions at other layers

7. QoS support at the Network layer • QoS-aware routing • Admission control • Resource reservation • Packet classification and QoS-sensitive packet forwarding • Monitoring/Policing

8. Wired Network Solutions • Often not directly applicable to wireless networks due to the inherent difference in characteristics • Provide insight into the problem • Are a good starting point to address the problem in the wireless environment

9. Prominent Network-layer QoS Solutions for Wired Networks • IP Precedence and TOS • Integrated Services (IntServ) • Differentiated Services (DiffServ)

10. IP Precedence and Type of Service (TOS) • Field in the IPv4 header • Indicates that the need for QoS support was recognized since the early days of the Internet • The TOS field can be used to specify a precedence value (0-7) or a TOS (delay/throughput/reliability/cost) for each IP packet • Interpretation of this field was left ambiguous • Field remained largely unused

11. Integrated Services • Attempt to modify Internet service model to support diverse application requirements • Any data flow that desires better than best-effort delivery requests and reserves resources at routers along the path • RSVP is the recommended reservation protocol • If insufficient resources are available, the flow is denied admission into the network

12. Integrated Services (cont.) • Each router • Maintains reservation state for each flow • Classifies every packet and decides forwarding behavior • Monitors the flow to ensure that it does not consume more than the reserved resources • Advantages • Enables fine-grained QoS and resource guarantees • Disadvantages • Not scalable, harder to administer

13. Differentiated Services • Moves admission control and flow monitoring to the edge of the network • Edge nodes classify and mark packets to receive a particular type of service • Diff Serv Code Point (DSCP) • Finite set of DSCPs defined • Interior nodes determine the type of service for forwarded packets based on their DSCP values

14. Differentiated Services (cont.) • Advantages • More scalable • No per-flow state • Easier to administer • Disadvantages • Cannot provide the same per-flow guarantees as IntServ

15. QoS support at the Network layer • QoS-aware routing • Admission control • Resource reservation • Packet classification and QoS-sensitive packet forwarding • Monitoring/Policing

16. Applicability of Wired Approaches to Wireless Networks • Some ideas may be applicable directly, while some need modification and others may be inapplicable • Additional challenges in wireless networks that are not encountered in wired networks have to be addressed

17. Applicability of Wired Approaches to Wireless Networks • IntServ • Effectiveness of reservations in highly dynamic environment questionable • Per-flow state and monitoring may be resource exhaustive (depends on traffic) • DiffServ • DSCP idea may be useful • With dynamic topology and no defined network boundary, some admission control/monitoring may be necessary at each node

18. Admission Control in Wireless Networks • Determining available bandwidth at a wireless node is a complex task due to the nature of the wireless medium • Wireless medium is shared among multiple nodes • Bandwidth is affected by transmissions of nodes that are not within transmission range • Each node potentially has a different view of the medium

19. Bandwidth is affected by nodes that are not within transmission range Interference/ Carrier-Sensing Range B Transmission Range A C’s transmissions affect bandwidth at A C

20. Different views of the wireless medium at different nodes Carrier-Sensing Range of X Carrier-Sensing Range of Q Y R X Q Z P S

21. Making an Admission Control Decision Total bandwidth = 1 Mbps T Y 400 kbps R ? X Q Z 400 kbps If X admits a 400 kbps flow to Z, the medium will get congested at Q P S

22. Contention-Aware Admission Control Protocol (CACP) [Yang 2003] • Each node senses the medium to determine the fraction of time that the medium is idle • Local bandwidth availability is determined from the idle fraction • Further, each node queries all nodes within its carrier sensing range for their local bandwidths. The minimum of these is the neighborhood available bandwidth • Admission control decisions are based on the neighborhood available bandwidth

23. CACP Admission Control Total bandwidth = 1 Mbps T Y 400 kbps R ? X Q Z 400 kbps Neighborhood available bandwidth at X is 200 kbps, so X will not admit the 400 kbps flow P S

24. Issues with CACP approach • How does a node communicate with its carrier-sensing neighbors? • High power transmissions • May increase collisions • Local multi-hop flood • May reach nodes that are outside CS range • May not reach some nodes in CS range • Considering neighborhood bandwidth as defined by CACP may sometimes be overly conservative and prevent spatial reuse

25. Preventing Spatial Reuse Total bandwidth = 1 Mbps T Y 700 kbps R ? X Q Z Neighborhood available bandwidth at X is 700 kbps, so X will not admit the 400 kbps flow, although it could be admitted P S

26. Bandwidth Availability Determination • Other approaches have been proposed • Different trade-offs between accuracy and efficiency • Perceptive Admission Control (PAC) [Chakeres 2004] reduces overhead and improves spatial reuse compared to CACP • However, even PAC could be overly conservative in some situations • Open Question: How can bandwidth availability be determined more accurately with low overhead?

27. Multi-hop Admission Control In a multi-hop route, there could be interference between multiple hops A U B P T C Q X Y R D S E F CS Range of X CS Range of Y

28. Multi-hop Admission Control • Due to the interference between multiple hops, the bandwidth required at a node is some multiple of that requested by the application • The exact value depends on the Contention Count at the node • Contention Count at a node is the number of other nodes on the route that are contending with this node for medium access

29. Multi-hop Admission Control Contention Count at a node is determined by the number of nodes on the route that are within the nodes carrier-sensing range V A U B P T C Q X Y R D S E F Contention Count at X = 5 Contention Count at Y = 7

30. Determining Contention Count • Node must know the identities of its carrier-sensing neighbors • CACP does either high power periodic broadcasts or multi-hop broadcasts - Collision, overhead and inaccuracy problems • Node must know the identities of all other nodes on any route • Requires source routing or path accumulation in routing packets – overhead • Open Questions: Is there a better way? Can approximations be made that could reduce overhead?

31. QoS Routing • Several QoS routing protocol have been proposed. Each exhibits one or more of the following features • Extend a corresponding best-effort routing protocol (AODV/DSR/DSDV) • Find one or more QoS-satisfactory paths between source and destination • Admission control may be integrated with route discovery • Resource reservations may be established along the route

32. QoS-sensitive extensions of AODV • QoS information is added to • the RREQ packet • Intermediate nodes forward the • RREQ only if they have • sufficient resources to meet • the QoS requirement • Resource information is • updated in the RREQ by • intermediate nodes • Destination sends resource • information back to source in • the RREP message D S RREQ RREP

33. Other Challenges for QoS Routing and Admission Control Simultaneous Intersecting Requests X Simultaneous Parallel Requests P Q R S

34. QoS Monitoring • Resource availability may change over time due to mobility and changing topology • There is a need for monitoring and renegotiation of QoS parameters • Monitoring can be performed in various ways

35. QoS Monitoring Approaches • INSIGNIA [Lee 2000] uses in-band signalling • QoS parameters added to every data packet using IP options in the IP header • Intermediate nodes appropriately set the values for the parameters based on their current resource availability • Destination gathers the information from the data packets and gives feedback to the source

36. QoS Monitoring Approaches • SWAN [Ahn 2002] does monitoring at intermediate nodes and uses Explicit Congestion Notification (ECN) to regulate flow • AQOR [Xue 2003] does no monitoring at intermediate nodes. Destination does the monitoring based on the received data characteristics and gives feedback to the source • Open Questions: Can these approaches be used in combination for an effective solution? Is there a better new approach?

37. Hybrid Network Gateway Internet Mobile Network

38. Hybrid networks • A hybrid network is formed when the mobile network extends the wired Internet • To run multimedia applications in hybrid networks, QoS needs to be ensured in both the wired and wireless parts of the network • QoS mechanisms in wired and wireless networks can be very different • Open Question:How can this be addressed? • Network layer QoS gateways? • Needs exploration

39. Solutions at other layers • MAC layer • Priority-based medium access • Transport layer • QoS monitoring, rate control • Application layer • Adaptive streaming, layering techniques • Open Question:How do mechanisms at different layers interact?

40. Other Open Questions • Most of the proposed QoS solutions have been validated through simulations or analytical models. Do the observations and results hold true in real deployments? • Can special characteristics of wireless networks, such as mobility, be leveraged in any way to improve QoS?

41. Conclusions • Multimedia applications require QoS support from the network • This is particularly difficult in wireless networks owing to their special characteristics • Several solutions have been proposed at the network layer for admission control, QoS routing and monitoring in wireless networks • Many open questions still remain and there is significant scope for further research

42. Thank you! Questions/Comments?