1. 2001/10/25Sheng-Feng Ho1 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

2. 2001/10/25Sheng-Feng Ho2 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

3. 2001/10/25Sheng-Feng Ho3 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

4. 2001/10/25Sheng-Feng Ho4 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)

5. 2001/10/25Sheng-Feng Ho5 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 L i (i ≦ 1 ≦ n), and it is encoded with a UEP code C of N symbols, then any L i symbols of its codeword are sufficient to retrieve the i-th symbol in the original message m.

6. 2001/10/25Sheng-Feng Ho6 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

7. 2001/10/25Sheng-Feng Ho7 UEP Codes Example (2) Apply the (6,2) B-Code on a to get a codeword of a ： A=A1..A6 (A i 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

8. 2001/10/25Sheng-Feng Ho8 UEP Codes Example (3) Apply a modified (6,3) RS-Code on b to get a codeword of b ： B=B1..B6 (B i 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 C i = c i for i = 1 to 6, thus each C i is 1/6 size of c.

9. 2001/10/25Sheng-Feng Ho9 UEP Codes Example (4) Construct a UEP codeword of the original message m ： U = U1..U6, where U i = A i B i C i for i = 1 to 6. The protection degrees of the original data symbols a, b and c are L a =2, L b =3 and L c =6 respectively. 1/L a +1/L b +1/L c =1

10. 2001/10/25Sheng-Feng Ho10 UEP Codes Example (5) Original Message m=abc UEP Codeword U=U1U2U3 U1=A1B1C1,U2=.. Server MulticastClient Receive Network Transmit UEP Codeword U=U1U2U3 a=a1..a6,b=b1.. Original Message m=abc

11. 2001/10/25Sheng-Feng Ho11 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 L i (i ≦ 1 ≦ n), then

12. 2001/10/25Sheng-Feng Ho12 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 L i, the user retrieves the i-th symbol of the original data stream and plays it out.

13. 2001/10/25Sheng-Feng Ho13 The Scheme (2) B ： normal playout unicast network bandwidth d ： the initial playout number of original data symbols The peak network bandwidth needed ： r peak B, where r peak = max(L i /(i+d)) The average network bandwidth is r ave B, where r ave B = L n /(n+d)

14. 2001/10/25Sheng-Feng Ho14 The Scheme (3) d013060 R12.8598.875.4844.796 C36.788%36.790%36.941%37.095% 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

15. 2001/10/25Sheng-Feng Ho15 Resource Consumption (1) The peak network bandwidth needed ： r peak B, where r peak = max(L i /(i+d)) Minimize r peak, set L i /(i+d) = R for all i’s R=H n+d -H d ≒ αlog 2 (1+n/d), where ½ ≦ α ≦ 1 R ≒ αlog 2 (1+n/d), where ½ ≦ α ≦ 1

16. 2001/10/25Sheng-Feng Ho16 Resource Consumption (2) Let S i 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 ：

17. 2001/10/25Sheng-Feng Ho17 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

18. 2001/10/25Sheng-Feng Ho18 Additional Initial Playout Delay d ： additional initial playout delay ： normalized backbone network bandwidth W ： client’s normalized incoming network badnwidth

19. 2001/10/25Sheng-Feng Ho19 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