Aspera's file transfer products are built on fasp file transport, an innovative reliable transfer protocol designed to meet the speed, bandwidth control, and security requirements of business-critical file transfer over any IP network (LAN, WAN, satellite, and wireless).

Network Independent Speed

Unlike TCP throughput, fasp throughput is perfectly independent of network delay and robust to extreme packet loss. The bar graph below shows a comparison of throughput obtained by fasp versus the maximum throughput achievable for TCP-based file transfers on an OC-3 (155 Mbps) link under various latency and packet loss conditions. fasp transfer times are as fast as possible (up to 1,000x standard FTP) and highly predictable, regardless of network conditions. The maximum transfer speed is limited only by the resources (typically disk throughput) of the endpoint computers.

Delay and Loss Independent with Near-Zero Overhead. fasp uses standard UDP and achieves reliability in the application layer through a theoretically optimal approach that retransmits precisely the real packet loss on the channel. At 10% packet loss, fasp achieves 90% of the targeted throughput with less than 1% redundant data overhead.

Single Transport Stream. Unlike brute-force parallel TCP or similar protocols that divide a single file into constituent chunks and attempt to improve overall throughput through a parallel transmission, fasp achieves ideal efficiency with a single stream. In contrast, parallel TCP techniques exhaust system resources, don't work for small files, reduce speed on packet loss, and hog bandwidth from single stream flows.

Perfect Efficiency for Large Sets of Small Files. Using a novel file streamlining technique, fasp achieves the same ideal efficiency for transfers of large numbers of small files. For example, one thousand 2 MB files can be transmitted from the US to New Zealand with an effective transfer speed of 155 Mbps, filling an entire OC-3. As a result, fasp enables replication of large data sets, regardless of file sizes, at line speed on even the longest, fastest wide area networks.

Distance Neutral, Fast, Smooth Progressive Transfer. FASP supports progressive-style transfers where incoming data is processed during the transfer, such as feeding a media player. The transfer speed is maximum (for the earliest possible start of playback), and will not change with variable network conditions, in contrast to progressive download applications using HTTP that are slow to start playback, and may be plagued by glitches and interruptions due to congestion on the link.

Automatic Adaptive Rate Control

While fasp can fill any available bandwidth, fasp also includes an intelligent adaptive rate control mechanism that allows transfer rates to throttle down for precision fairness to standard TCP traffic, but automatically ramp up to fully utilize unused bandwidth (see Figures 1 and 2).

Automatic Adaptation to the Full, Available Bandwidth and Fair. The adaptive rate control algorithm is an original equation-based approach. When TCP's rate is self-limited on an uncongested link, fasp detects the unclaimed bandwidth and ramps up to fill it (Figure 1). When congestion builds up, fasp reduces rate to the TCP rate and equally shares the link with multiple TCP flows (Figure 2). This approach has fundamental benefits over the window-based flow control algorithm used by standard TCP and even new accelerated or "high-speed" TCP's:

Configurable, Per-Flow Bandwidth Policies. The aggressiveness of any particular fasp flow relative to standard TCP or other fasp flows is configurable, and enables pre-set or user-defined bandwidth sharing policies such as equally fair and transparent background flows. For example, in Figure 2, two fasp flows configured to use a TCP-fair bandwidth policy share a 2 Mbps network with two standard TCP flows.

1) As the TCP flows enter, the fasp flows detect the congestion and precisely divide the available bandwidth equally between one another, and with TCP.
2) As the TCP flows exit, the fasp flows detect the newly available bandwidth and immediately ramp up for full utilization.

Fast, precise, automatic discovery of the available bandwidth. Through state-of-the-art diagnostic algorithms, fasp is able to accurately discover the bottleneck link capacity (minimum capacity of all links) between any source and destination pair, within only a few seconds. This feature is not only useful for network profiling, but also allows for automatic configuration of the transfer rate, and maximum and minimum caps, as a percentage of the user's bandwidth capacity.