NDN Live Video Broadcasting over Wireless LAN Menghan Li, Dan Pei, Xiaoping Zhang, Ke Xu Tsinghua University Beichuan Zhang University of Arizona
IP: Delivering packets to endpoints 0 4 8 16 19 31 TOS Length Version HLen Ident Flags Offset TTL Protocol Checksum SourceAddr Source Address Destination Address DestinationAddr Pad Options (variable) (variable) Data 1
Named Data Networking (NDN) Retrieving Named Data from the network Content Name Content Name 2
IP’s Node Model Accept ✓ ✗ ✓ IP Packets FIB Self? Forward ✗ Drop ✗ lookup miss ✓ lookup hit One-way traffic, stateless, no storage. 3
NDN’s node model ✗ ✗ ✓ Content Pending Interest Interest FIB Store Table (PIT) forward ✓ ✓ ✗ Data Add Incoming Face Drop or NACK Downstream Upstream ✓ forward Pending Interest Data Table (PIT) cache ✗ Content Discard Store ✗ lookup miss ✓ lookup hit Two-way traffic, stateful, explicit storage. 4
Content Distribution Example 36.7M Views ISP ISP IP needs large infrastructure and complicated technical solutions. 5
Content Distribution Example 36.7M Views ISP2 ISP4 ISP1 ISP3 NDN’s multicast and caching are native and built-in. 6
The problem at the last hop Video Server AP AP Internet AP AP Increasingly over wireless broadcast medium, ie, WiFi. But current NDN implementation treats it as multiple unicast tunnels between clients and access point (AP). 7
Design Goals Efficient and Scalable NDN-based live video broadcasting over WiFi • Support a good number of clients watching the same live video streaming via the same WiFi AP at the same time. No modification to the MAC layer • WiFi doesn’t support broadcast or multicast very well. • Built our system based on NDN/UDP. 8
Design Overview Regulate Interests so that ideally only one Interest is sent to retrieve one video packet regardless of the number of clients. • One Interest unicast to the AP, which will forward it to the video server. • One video data packet comes back to the AP, which broadcasts the packet to all clients. How to regulate the generation of Interests? How to regulate the transmission of Interests? 9
Regulating Interest Generation Video Server AP Client NDN Testbed Maintain an Interest sending window (W) at the client. • For pipelining multiple Interests to retrieve multiple data. • It needs to match data production at the server. Client periodically asks for the latest data name to infer the rate of data production, and use that to set W. W = RTT *( S 2 − S 1 ) / ( T 2 − T 1 ) 10
Regulating Interest Transmission Goal: suppress the transmission of duplicate Interests from different clients. • Ideally only one Interest is sent (from the Leader) to retrieve one video packet. The AP chooses one client (e.g., the first one) to be the Leader, and others are Followers. • The Leader transmits Interests without delay. • The Followers delay the transmission of their Interests. • The AP periodically broadcasts a heartbeat packet to all clients, stating who the Leader is, the current number of Followers, and the current progress of video data retrieval. 11
Interest suppression at Followers Outgoing Interests are delayed and stored in Delayed Interest Table (DIT). • Consumed when corresponding data is received. • Transmitted by certain probability when timeout or packet loss is inferred. Inferring packet loss from data name or AP’s heartbeat message. • Significant out-of-order packets The probability to transmit P f = 1/ ( N − R ) • N is the number of clients, and R is the number of times that the application has been asking. 12
Keep track of clients AP maintains who’s the Leader and the number of Followers. Every client periodically sends an Interest to learn the latest available data name. • This Interest is not delayed. • AP uses this Interest to keep track of the clients. If a Follower leaves, AP just updates the count. If the Leader leaves, AP will assign the next client as Leader. • In absence of Leader sending Interests, clients will timeout and send Interests on their own, based on a probability. 13
Evaluation Compare with two alternatives Unicast: The clients and AP transmit all NDN packets over UDP unicast tunnels. Broadcast: All clients send all Interests over UDP unicast, and the AP broadcasts the returned Data to all the clients. 14
Performance metrics Buffering Rate: the number of buffering events per second. Buffering Ratio: the percentage of time spend in buffering. Interest Redundancy: the number of Interests sent vs. the number Data received. Data Redundancy: Data sent by AP vs. received by clients. 15
Experiment setups AP: commodity home router • 5GHz WiFi, 6Mbps broadcast bandwidth, 720MHz CPU 20 Clients • Ubuntu VM running a single client app with a dedicated WiFi card. Software: •NDNVideo: 1Mbps H.264/AVC video 16
Scalability to the number of clients 0.06 50 NLB NLB Ucast Ucast 0.041 40 Buffer Rate(#/s) Buffer Ratio(%) Bcast Bcast 0.04 30 14.03 20 0.026 0.02 0.01 10 1.99 4.02 0 0 1 5 10 15 20 1 5 10 15 20 #client #client NLB supported 20 clients at ease, while unicast and broadcast schemes showed clear limit. 17
Packet redundancy 1000 1000 Interest Redundancy(%,log scale) Data Redundancy(%,log scale) NLB NLB Ucast Ucast Bcast Bcast 500 500 Ideal Ucast Ideal Ucast 200 200 122.96 118.75 100 100 1 5 10 15 20 1 5 10 15 20 #client #client NLB is able to suppress the majority of redundant packets, Interest and Data. 18
AP’s CPU usage 100 NLB Ucast 80 CPU Usage(%) Bcast 60 40 20 0 1 5 10 15 20 #client UCast: may be limited by CPU cycles Bcast: limited by 6Mbps broadcast bandwidth NLB: the total number of packets transmitted over WLAN grows very slowly 19
Summary NLB is a scalable and efficient receiver-driven broadcasting mechanism in wireless medium. It complements NDN’s multicast and caching capability in the wired Internet. It runs on commodity access points and mobile devices without any change to the MAC layer 20
For More Information about NDN http://www.named-data.net/ 21
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