1. Overlay Network and Data Transmission Over Wireless For EE290T Minghua Chen EECS@UC, Berkeley

2. Outline Overlay network & virtual overlay network Data transmission over wireless Improving TCP performance over wireless Improving video performance over wireless

3. Overlay Network What is overlay network? “A configuration within which a base network is used to support some second network, “layered” upon the underlying infrastructure” Another layer, logical network Virtual overlay network – the interface used to provide service are virtual Send(): reliable_send(), fast_send()… Why overlay network? Deploy/testing new protocol/service with minimal affecting the lower IP infrastructure IPv6 TestBed Multicast QoS Content Addressable Network (CAN, a hash lookup system)

4. Example – v6 Over v4 Overlay “ Backbone ” Network

5. The Challenges Assume underlying infrastructure can guarantee the bandwidth (even latency) between overlay nodes Still need trust between AS Management Combine all extended services overlay into one overlay Heterogeneous multimedia distribution overlay network Multicast overlay network

6. ON ’ s Advantages & Disadvantages Advantages Can apply RSVP, providing isolation (e.g., flow isolation Flexible security approach (IPSec, PK/SK) New service (anycast etc) Disadvantages Efficiency Latency How many nodes need to be modified? What if one day the underlying network changes to support all the functionalities?

7. Improving TCP Performance over Wireless Problem Packet may get loss on wireless due to channel error or hand-off TCP treat packet loss as hint for congestion  not necessarily decrease congestion window size  low bandwidth usage efficiency Solution: shield sender from error-based packet loss Split connection End-to-End with error loss notification (ELN) Need some point on route to set the ELN bit Link Layer based solution LL retransmission  In WLAN, After LL retransmission, packet loss rate ~ 3%* LL-SMART-TCP-AWARED (snoop+sack)  +30% improvement compare to LL retransmission *:A TRACE-BASED APPROACH FOR MODELING WIRELESS CHANNEL BEHAVIOR -- G. Nguyen et.al @1996

8. Architecture

9. Comparison

10. What Improves TCP Over Wireless Shield sender from the effect of the packet loss due to wireless channel error loss LL retransmission TCP-AWARED Prepare for hand-off Multicast the data on fly to nearby BS when the MS is in hand-off period Do this in LL? Drawbacks of LL-SMART-TCP-AWARED Need to modify the Link layer What if there is another hop between BS and MH? Can’t distinguish packet loss with wireless link congestion Has reached the end? How about ad-hoc

11. One Point of View SBS Relay R 1 11 Packet No. 1 arrived BS, but loss at Relay point due to congestion on Relay point -- When the BS notice there is a packet loss between BS—Relay, he could not distinguish this loss between congestion-based or channel-error-based LL-TCP-AWARED sits here

12. Improving Multimedia Transmission Performance over Wireless Use FEC Real-time multimedia may not afford long-time retransmission Modify UDP protocol Traditional UDP: small part error in packet  drop the entire packet – there are still some useful information in the corrupted packet UDP-lite: pass the partly corrupted packet to upper layer CUDP: Vertical Packet Coding (VPC, similar to interleaving) + improved UDP-lite (use the frame error information to help decoder to locate the error position (thus can do error concealment) But need to modify the layers to enable information exchange between the layers

13. CUDP result

14. Improving Multimedia Transmission Performance over Wireless Scheduling: Instead of sending packets only in deadline order, try to send them in app-specified order (e.g., importance or deadline order) When need scheduling: in-order delivery could not guarantee all the packets meet its deadline (e.g., when bandwidth decrease due to channel error) How to scheduling Important packet first Send lower important packet iff  Important packets would meet their deadline  Current lower important packet won’t miss the deadline

15. Scheduling Pkt No. 1234567 Importance index (I_index) Sending reference value: S(i) = F(I_index(i), D_index(i)) F – function I_index(i) – importance index D_index(i) – deadline index *Send out packet in increasing order of S(i)*

16. An Example [46] Transmit this layer 3 packet if and only if all the layer0/1/2 packets in following frames will “successful” transmit over wireless link; “successful” is in a probabilistic means.

17. So … All these works on multimedia over wireless focus on How to combat with channel error What should we do when packet loss happens But one step back @ what rate should we send multimedia data? Send @ maximum available rate, how? Over wired network: TCP-friendly Over wireless network?... Could we reduce the number of packet loss in case of hand-off, temporary out-of-range and channel error? LL retransmission – cost: out of order delivery + delay How about hand-off?

18. Summary Overlay network shows some good properties. But not sure about its future, whether it is a temporary solution or it will be a long-lived service-providing logic infrastructure Data transmission over wireless Reliable data transmission: cake has gone… Real-time data transmission: is there a cake?