Online backup services work much like traditional backup software. With an online backup service, however, your important data is transmitted over the Internet and securely stored on a server in a professional data center instead of being stored on your own CDs, DVDs, or backup tapes. First off, online data backup is just as the name implies. Data is backed up over a networked connection (most likely using the TCP/IP standard protocol of the internet) to a remote location (ideally).

Typical features

1) Encryption
Data should be encrypted before it is sent across the internet, and it should be stored in its encrypted state. Encryption should be at least 256 bits, and the user should have the option of using his own encryption key, which should never be sent to the server.

2) Network backup
A backup service supporting network backup can back up multiple computers , servers or Network Attached Storage appliances on a local area network from a single computer or device.

3) Continuous backup – Continuous Data Protection CDP
Allows the service to back up continuously or on a predefined schedule. Both methods have advantages and disadvantages. Most backup services are schedule-based and perform backups at a predetermined time. Some services provide continuous data backups which are used by large financial institutions and large online retailers. However, there is typically a trade-off with performance and system resources.

4) File-by-File Restore
The ability for users to restore files themselves, without the assistance of a Service Provider by allowing the user select files by name and/or folder. Some services allow users to select files by searching for filenames and folder names, by dates, by file type, by backup set, and by tags.

5) Online access to files
Some services allow you to access backed-up files via a normal web browser. Many services do not provide this type of functionality.

6) Data compression
Data will typically be compressed with a lossless compression algorithm to minimize the amount of bandwidth used.

7) Differential data compression
A way to further minimize network traffic is to transfer only the binary data that has changed from one day to the next, similar to the open source file transfer service Rsync. More advanced online backup server support services use this method rather than transfer entire files.

8) Bandwidth usage
User-selectable option to use more or less bandwidth; it may be possible to set this to change at various times of day.