QoS Scheduling in Cable and Broadband Wireless Networks

1. QoS Scheduling in Cable and Broadband Wireless Networks Mohammed Hawa and David W. Petr Information and TelecommunicationTechnology Center (ITTC), University of Kansas Project Funded by Sprint Corporation

2. Presentation Outline • What is QoS and QoS Management? • Difference between QoS in wired and wireless networks. • A scheduling architecture to support QoS in broadband wireless access networks. • Infrastructure MAC Protocol • Support for UGS, rtPS, nrtPS and BE Traffic • Scheduler Features and Advantages • Discussion © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

3. Quality of Service (QoS) • Packet switched networks (e.g., Internet) were designed to provide best effort service. • A QoS architecture introduces tools to treat packets differently, thus one flow receives better performance on the expense of others. • Provides guaranteed services to end users (better than best effort). • QoS guarantees can be characterized by: • Delay, delay jitter, bandwidth and error rate. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

4. QoS Management • Supporting QoS in packet switched networks requires collaboration of many components: • Admission Control: Limits number of flows admitted into the network so that each individual flow obtains its desired QoS. • Scheduling: Which packet gets transmitted first on the output link significantly impacts QoS guarantees for different flows. • Scheduling affects delay, jitter and loss rate. • Allows protection against misbehaving flows. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

5. QoS Management (Cont.) • Buffer Management: Control the buffer size and decide which packets to drop. • Controls packet loss rate. • Many packet drop strategies including weighted Random Early Detection (RED). • Congestion Control: Prevent, handle and recover from network congestion scenarios. • Challenging feedback problem because Internet traffic shows self-similar behavior. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

6. IETF QoS Architectures • IntServ: • Resource reservation per flow using RSVP. • Similar to ATM virtual connections. • Problems with scalability. • DiffServ: • Aggregation of flows into per-hop behavior groups. • Expedited forwarding and Assured forwarding. • A good wireless QoS architecture should integrate with both IETF standards. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

7. Wireless Networks • The Internet is expanding to the wireless realm, specially in recent years: • Wireless Local Area Networks (WLANs) based on the IEEE 802.11 standard, called Wi-Fi™. • WLAN Hot Spots by companies such as: Boingo, Surf and Sip, T-Mobile HotSpot and Wayport. • Broadband Wireless Access Networks (BWAs) based on IEEE 802.16, called WiMAX. • Supported by Intel, Nokia, and Fujitsu. • Need to expand QoS to the wireless side. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

8. Wireless QoS Observations • Several new technical challenges: • Quality of the wireless channel is typically different for different users, and randomly changes with time (on both slow and fast time scales). • Wireless bandwidth is usually a scarce resource that needs to be used efficiently (can not overprovision the wireless link). • Excessive amount of interference and higher error rates are typical. • Mobility complicates resource allocation. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

9. The MAC Protocol • For wireless networks it is natural to integrate the QoS architecture with the MAC protocol. • The MAC protocol coordinates communication over the shared wireless medium (and the shared HFC cable medium as well). • IEEE 802.16 is the most talked about standard for broadband wireless access (BWA) systems, and is based on DOCSIS. • DOCSIS is the de facto standard for delivering broadband services over HFC networks. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

10. DOCSIS Introduction • A Cable Modem Termination System (CMTS) controls many terminating Cable Modems (CMs). • Upstream and downstream channels are separated using FDD. • Each upstream channel is further divided into a stream of fixed-size time minislots. • DOCSIS MAC utilizes a request/grant mechanism to coordinate transmission between multiple CMs. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

11. DOCSIS Operation © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

12. QoS in DOCSIS • To support QoS, DOCSIS 1.1 introduces the concept of a service flow. • IEEE 802.16 defines identical upstream service flow types. • Upstream Service Flow Types in DOCSIS and IEEE 802.16: • Unsolicited Grant Service (UGS) • Real-Time Polling Service (rtPS) • Non Real-Time Polling Service (nrtPS) • Best Effort (BE) © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

13. Real-Time Service Flows • Unsolicited Grant Service (UGS): • Supports real-time traffic (Voice over IP). • Offers fixed size unsolicited data grants (transmission opportunities) on a periodic basis. • Real-Time Polling Service (rt-PS): • Supports real-time flows that generate variable size data packets on a periodic basis (MPEG). • Offers periodic unicast request opportunities. The CMs specify the size of the desired data grants. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

14. Non Real-Time Service Flows • Non Real-Time Polling Service (nrt-PS): • Supports flows that require variable size data grants on a regular basis (high bandwidth FTP). • Offers infrequent unicast polls plus contention and piggybacking. • Best Effort (BE): • The CM uses contention and piggybacking only. • Key service parameters for nrt-PS and BE: • Minimum Reserved Traffic Rate. • Traffic Priority. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

15. The New CMTS Scheduler © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

16. Scheduler Architecture • Requests arrive at the CMTS. • Through contention, unicast requests and piggybacking. • Requests are translated into upstream data grants. • Data grants are scheduled on a frame-by-frame basis by building a corresponding allocation MAP: • The hardware block responsible for creating the MAP is represented by a server. • Each data grant (or unicast request opportunity) is treated as a packet. Actual transmission of the corresponding data packet takes place in the next frame. • Data grants are queued in three types of buffers: Type 1, Type 2 and Type 3 buffers. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

17. Extra Features • Dynamic Contention Minislot Allocation: An appropriate number of contention request minislots is allocated in each frame period to reduce collisions and to shorten contention resolution. • A Buffer Management mechanism based on RED was also suggested. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

18. Scheduler Advantages • Easy to implement in hardware thus gaining a performance advantage over software-based alternatives. • Takes advantage of the Tolerated Jitter parameter for UGS to fit as many packets as possible in the upstream frame thus avoiding fragmentation and being more efficient. • Lends itself to easier and straightforward performance analysis via classical queuing theory techniques. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

19. Future Work • Stochastic analysis of FQ algorithms have not been given much attention due to difficulty in tracing the dynamics of fair queuing algorithms. • Validation of the analysis and comparing the architecture performance to other architectures will be done through simulation using OPNET. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

20. Summary • Introduced QoS concepts in both the wired and wireless parts of the network. • Summary of DOCSIS and IEEE 802.16 standards and their QoS features. • Introduced a new scheduling architecture to integrate QoS within the MAC layer of such protocols. • Discussed the features of the architecture and its advantages. • Suggested possible future work. © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

21. Discussion • Thank you! © Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas