Forward Erasure Correction in VS .NET

Generator QR-Code in VS .NET Forward Erasure Correction
13.3 Forward Erasure Correction
Decode QR Code In .NET Framework
Using Barcode Control SDK for VS .NET Control to generate, create, read, scan barcode image in VS .NET applications.
In the FEC protocol, all N S data blocks in a parity group are transmitted to the clients at all time, irrespective of server failure. This protocol is simple to implement as the server schedules are xed irrespective of individual server failures. The system does not even need to detect server failures or to recon gure the system for degraded-mode operation. The client simply
QR-Code Creation In VS .NET
Using Barcode generator for VS .NET Control to generate, create QR Code JIS X 0510 image in Visual Studio .NET applications.
FEC versus PRT
QR Decoder In .NET Framework
Using Barcode reader for VS .NET Control to read, scan read, scan image in Visual Studio .NET applications.
performs erasure correction computation to recover the data blocks whenever N S K video blocks of a parity group are received.
Generating Barcode In .NET
Using Barcode printer for Visual Studio .NET Control to generate, create bar code image in VS .NET applications.
13.3.1 System Reliability
Barcode Decoder In VS .NET
Using Barcode recognizer for Visual Studio .NET Control to read, scan read, scan image in .NET framework applications.
To quantify the amount of redundancy needed to achieve a given target system MTTF, we can model the system using a continuous-time Markov chain. We assume server failures are independent and exponentially distributed with a MTTF of 1/ . Failed servers are repaired immediately and independently with a mean-time-to-repair (MTTR) of 1/ . Thus, the system forms a Markov chain with state h representing the state with h failed servers (see Figure 13.2, for an example). Assume the system is con gured with K redundant blocks per parity group, then the system fails when more than K servers fail, i.e., when the Markov chain enters the absorbing state h = K + 1. Otherwise, servers in the system in state h will have an aggregate failure rate h , given by h = (N S h) and an aggregate repair rate h , given by h = h . (13.2) (13.1)
QR Code JIS X 0510 Drawer In Visual C#.NET
Using Barcode maker for .NET framework Control to generate, create QR Code 2d barcode image in .NET framework applications.
Thus, the MTTF of the system is equivalent to the rst passage time for the system to reach state h = K + 1 from the initial state h = 0. It can be shown that the MTTF for a system with N S servers and K redundancies using FEC is given by j 1 i l K i l =0 (13.3) MTTFFEC = . j =0 j i =0 i l
Encoding QR Code In .NET
Using Barcode creation for ASP.NET Control to generate, create QR Code image in ASP.NET applications.
l =0
QR-Code Encoder In Visual Basic .NET
Using Barcode generation for .NET Control to generate, create QR Code ISO/IEC18004 image in Visual Studio .NET applications.
Therefore, using equation (13.3) we can determine the amount of redundancy needed for a given target system MTTF.
Print EAN / UCC - 14 In .NET
Using Barcode drawer for VS .NET Control to generate, create UCC.EAN - 128 image in Visual Studio .NET applications.
0,3 1,3
Encoding Bar Code In .NET Framework
Using Barcode encoder for .NET Control to generate, create bar code image in .NET applications.
: state with h servers failed and k level of redundancy : aggregate server failure rate with h server failed : aggregate repair rate with h server failed
GS1 - 12 Drawer In VS .NET
Using Barcode creator for .NET framework Control to generate, create UPC-A image in Visual Studio .NET applications.
Figure 13.2 A Markov chain mode for FEC with K = 3
USPS POSTal Numeric Encoding Technique Barcode Maker In VS .NET
Using Barcode generation for VS .NET Control to generate, create Postnet image in Visual Studio .NET applications.
h h
Generating Barcode In VB.NET
Using Barcode generator for .NET Control to generate, create bar code image in .NET framework applications.
Scalable Continuous Media Streaming Systems
Paint DataMatrix In C#.NET
Using Barcode generation for .NET Control to generate, create ECC200 image in VS .NET applications.
13.3.2 Bandwidth Overhead
Create Data Matrix In Visual Basic .NET
Using Barcode drawer for VS .NET Control to generate, create Data Matrix image in .NET framework applications.
The price to pay for the low-complexity FEC protocol is transmission overheads. In particular, with N S servers and a redundancy level of K , the bandwidth overhead incurred de ned as the ratio of extra bandwidth needed over the media bit-rate, is given by HFEC = K NS K (13.4)
Printing European Article Number 13 In Java
Using Barcode generation for Java Control to generate, create EAN13 image in Java applications.
For a small-scale system (i.e., N S small) with a high level of redundancy (i.e., K large), this overhead could become substantial. For example, with N S = 6 and K = 2, the bandwidth overhead becomes 50%. Considering that most systems are expected to operate in normal mode most of the time with no server failure, this bandwidth overhead is clearly signi cant.
Code 128 Code Set B Generation In VS .NET
Using Barcode generation for ASP.NET Control to generate, create Code 128B image in ASP.NET applications.
13.4 Progressive Redundancy Transmission
Barcode Creator In .NET Framework
Using Barcode maker for ASP.NET Control to generate, create bar code image in ASP.NET applications.
Generally speaking, media servers are usually high-end PCs with good host-level reliability (e.g., equipped with ECC memory, redundant power supply, RAID disk storage, etc.). Thus, typical server MTTF is likely to be in the range of tens of thousands of hours. Therefore, although over a long time span the system may run into multiple server failures, it is highly unlikely that more than one server will fail simultaneously within a short time interval (e.g., tens of seconds) unless catastrophic failure occurs (e.g., re, earthquake, etc.). Therefore, instead of sending all K redundancies at all times as in FEC, the system can initially transmit only k (k K ) of the K redundancies, thus reducing the bandwidth overhead to k/(N S K ) Progressive Redundancy Transmission (PRT). Clearly, in this case the client can only recover from up to k simultaneous server failures. However, in PRT the system will activate transmission of more redundant data as server failures are detected. Thus, after, say, w server failures, the number of redundant data transmission will be increased from k to (k + w). The key is to complete the recon guration quickly so that additional redundant data transmissions are activated before too many server fail. On the other hand, whenever a server is repaired and becomes operational again, the system will deactivate an existing redundant data transmission, until the number of excess redundancies (i.e., number of transmitted redundant data minus number of failed servers) transmitted reduces back to k. To implement PRT we need to address two issues. First, the system must be able to detect server failure so that it can recon gure the system to activate transmissions of additional redundant data. The detection can be done using a number of existing protocols such as heartbeat protocol [1], or by monitoring the streaming traf c in the network (cf. Section 11.3.1). Once a failure is detected, the system can be recon gured through some control protocols. For simplicity, we lump together the system recon guration time and the failure detection time and henceforth refer to the latter term only. Intuitively, the detection time should be short so as to reduce the risk of encountering additional server failures before recon guration is completed, but not too short to prevent generating too many false alarms. In particular, if more than k servers fail before recon guration is completed, then the system will still fail, even if the number of redundancies available is larger (K > k). This leads to the second problem: quantifying the impact of detection delay to
Barcode Decoder In .NET Framework
Using Barcode scanner for Visual Studio .NET Control to read, scan read, scan image in VS .NET applications.
Drawing UCC.EAN - 128 In .NET Framework
Using Barcode creation for ASP.NET Control to generate, create EAN 128 image in ASP.NET applications.