Efficient and Scalable On-Demand Data Streaming Using UEP Codes

1. Efficient and Scalable On-Demand Data Streaming Using UEP Codes Lihao Xu Washington University in St. Louis ACM Multimedia 2001 Sept. 30 – Oct. 5, 2001 Sheng-Feng Ho

2. Outline • Introduction • Unequal Error Protection Codes • UEP Codes Example • Theorem • The Scheme • Resource Consumption • Network Bandwidth • Client’s Buffer Space • Client’s Network Bandwidth • Additional Initial Playout Delay • Conclusion Sheng-Feng Ho

3. Introduction • Streaming Method • Unicast：Point-to-point • Resource consumption is proportional to the number of requests. • Multicast：Pyramid or Skyscraper • The lowest resource consumption with no initial data playout delay is proportional to logarithm of the average request arrival rate. • The reliability：Automatic-Repeat-Request、 Forward Error Correction Sheng-Feng Ho

4. Unequal Error Protection Codes • (N,K) block code encodes an original message of K symbols into a codeword of N data symbols of the same size. • A data symbol is a general data unit of certain size：a bit, a byte, a packet or a frame. • Original K data symbols can be recovered from any M data symbols of its codeword. (M≧K) Sheng-Feng Ho

5. Unequal Error Protection Codes • For a UEP code, certain data symbols of its codeword are protected against a greater number of errors than others. • For a message m with n data symbols, if the error protection degree of its i-th symbol is Li (i≦1 ≦n), and it is encoded with a UEP code C of N symbols, then any Li symbols of its codeword are sufficient to retrieve the i-th symbol in the original message m. Sheng-Feng Ho

6. UEP Codes Example (1) • Message m has 3 symbols of equal size：a, b and c. (m=abc) • Partition symbol • a into 6 sub-symbols of equal size：a=a1..a6, • b into 9 sub-symbols：b=b1..b9 • c into 6 sub-symbols：c1..c6 Sheng-Feng Ho

7. UEP Codes Example (2) • Apply the (6,2) B-Code on a to get a codeword of a：A=A1..A6 (Ai is ½ size of a) • A1 = a1, a2+a3, a4+a6, • A2 = a2, a3+a4, a5+a1, • A3 = a3, a4+a5, a6+a2, • A4 = a4, a5+a6, a1+a3, • A5 = a5, a6+a1, a2+a4, • A6 = a6, a1+a2, a3+a5, • and + is the simple bit-wise binary exclusive or (XOR) operations Sheng-Feng Ho

8. UEP Codes Example (3) • Apply a modified (6,3) RS-Code on b to get a codeword of b：B=B1..B6 (Bi is 1/3 size of b) • B1 = b1, b2, b3, • B2 = b1+b3+b4, b2+b4+b5, b2+b3+b6, • B3 = b6+b7, b4+b6+b8, b5+b9, • B4 = b3+b6+b7, b1+b4+b7+b8, b2+b5+b9 • B5 = b4+b6+b9, b4+b7,？ • B6 = b7, b8, b9 • “+” is the XOR operation • Let Ci = ci for i = 1 to 6, thus each Ci is 1/6 size of c. Sheng-Feng Ho

9. UEP Codes Example (4) • Construct a UEP codeword of the original message m：U = U1..U6, where Ui = AiBiCi for i = 1 to 6. • The protection degrees of the original data symbols a, b and c are La=2, Lb=3 and Lc=6 respectively. • 1/La+1/Lb+1/Lc=1 Sheng-Feng Ho

10. UEP Codes Example (5) Original Messagem=abc Original Messagem=abc UEP CodewordU=U1U2U3a=a1..a6,b=b1.. UEP CodewordU=U1U2U3U1=A1B1C1,U2=.. Network Transmit Server Multicast Client Receive Sheng-Feng Ho

11. Theorem • For a message m with n symbols, if there exists a UEP code such that the error protection degree of the i-th symbol in the original message m is Li (i≦1 ≦n), then Sheng-Feng Ho

12. The Scheme (1) • Encoding the original data of n symbols into a UEP codeword of N symbols. • Multicast the UEP codeword in a cyclic fashion. • Once the number of data symbols in user’s buffer space reaches Li, the user retrieves the i-th symbol of the original data stream and plays it out. Sheng-Feng Ho

13. The Scheme (2) • B：normal playout unicast network bandwidth • d：the initial playout number of original data symbols • The peak network bandwidth needed：rpeakB, where rpeak = max(Li/(i+d)) • The average network bandwidth is raveB, where raveB = Ln/(n+d) Sheng-Feng Ho

14. The Scheme (3) Resource Consumption vs. Initial Playout Delay for Multicasting a 2-hour Video. d：initial playout delay in seconds R：normalized backbone network bandwidth C：normalized client buffer space needed Sheng-Feng Ho

15. R≒αlog2(1+n/d), where ½≦α≦1 Resource Consumption (1) • The peak network bandwidth needed：rpeakB, where rpeak = max(Li/(i+d)) • Minimize rpeak, set Li/(i+d) = R for all i’s • R=Hn+d-Hd≒αlog2(1+n/d), where ½≦α≦1 Sheng-Feng Ho

16. Resource Consumption (2) • Let Si be the buffer space needed between the retrieval of the i-th and the (i+1)th original data symbols, then • Client’s Buffer Space： Sheng-Feng Ho

17. Resource Consumption (3) • The normalized network bandwidth a client needs to consume between the retrieval of the i-th and (i+1)th original data symbols is Sheng-Feng Ho

18. Additional Initial Playout Delay • d：additional initial playout delay • ：normalized backbone network bandwidth • W：client’s normalized incoming network badnwidth Sheng-Feng Ho

19. Conclusion • Our scheme utilizes nice properties of error control codes, particularly UEP codes. • The scheme also tolerates packet loss during transmission, thus further reduces multicast cost. • Problem：Fast Seek Sheng-Feng Ho