Aspera’s fasp transfer technology is an innovative software that eliminates the fundamental bottlenecks of conventional file transfer technologies such as FTP, HTTP, and Windows CIFS, and dramatically speeds transfers over public and private IP networks. The approach achieves perfect throughput efficiency, independent of the latency of the path and robust to packet losses. In addition, users have extra-ordinary control over individual transfer rates and bandwidth sharing, and full visibility into bandwidth utilization. File transfer times can be guaranteed, regardless of the distance of the endpoints or the dynamic conditions of the network, including even transfers over satellite, wireless, and inherently long distance and unreliable international links. Complete security is built-in, including secure endpoint authentication, on-the-fly data encryption, and integrity verification.
fasp Transport Characteristics
- Maximum Speed
- Enables large data set transfers over any network at maximum speed, source disk to destination disk, regardless of network conditions or distance.
- Over gigabit WANs with 1 second RTT and 5% packet loss, achieves 700-800 Mbps file transfers on high-end PCs with RAID-0 and 400-500 Mbps transfers on commodity PCs.
- Even with extreme packet loss and latency (30%/1 second RTT), sustains over 100 Mbps WAN transfers, and fills a satellite transponder.
- Transfers large data sets of small files with the same efficiency as large single files.
- Very lightweight. Does not require specialized or powerful hardware to maintain high speeds.
- Extraordinary Bandwidth Control
- Provides precise rate control (pre-set and on-the-fly) forguaranteed transfer times.
- Uses an automatic adaptive rate control to fully utilize available bandwidth while remaining fair to other traffic.
- Provides fast, automatic discovery of the bandwidth capacity between the source and destination.
- Supports on-the-fly configurable bandwidth sharing policies. Users may pre-set and change individual transfer rates and finish times as needed.
- Supports perfect progressive-style transfers, e.g. for media playout. Transfer speeds do not degrade with congestion or distance, ensuring smooth, immediate processing of the incoming data.
- Complete Security
- Includes complete, built-in security using open standard cryptography for user authentication, data encryption and data integrity verification.
- Software Only
- Uses standard, unmodified IP networking and is implemented in software as an application protocol. Requires no changes to the operating system or driver installation on the file transfer endpoints, no new appliances, and no network changes.
- Robust
- Provides end-to-end transfer progress reporting and detailed performance statistics for monitoring and billing, as well as custom pre- and post-transfer processing.
- Automatically resumes partial transfers and retries failed transfers.
- Flexible Open Architecture
- Supports interoperable file and directory transfers between all major operating systems and provides a complete, modern software API to build upon. ]
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The TCP Bottleneck in File Transfer
The transmission control protocol (TCP) that provides reliable data delivery for conventional file transfer protocols has aninherent throughput bottleneck that becomes more severe with increased packet loss and latency.
The throughput has a hard theoretical limit that depends only on the network round-trip time (RTT) and the packet loss. Note that adding more bandwidth does not change the effective throughput. File transfer speeds do not improve and expensive bandwidth is underutilized.
The source of the throughput bottleneck is the mechanism TCP uses to regulate its data flow rate. The TCP sender requires an acknowledgment of every packet from the TCP receiver in order to inject more data into the network. When an acknowledgment is missed, TCP assumes that it is overdriving the network capacity and enters an aggressive congestion avoidance algorithm which severely reduces the data rate, with a slow recovery time. Even small variation in round-trip latency or bit errors due to the network media can cause TCP to enter congestion avoidance.
The consequences to file transfer are dramatic:
- In local area networks, where packet loss and latency are small but non-negligible (0.1%/10ms), the maximum TCP throughput is 50 Mbps. Typical file transfer rates are lower, 20-40 Mbps on gigabit ethernet. Because standard TCP halves its throughput in response to a single packet loss event, at high speeds, even a low loss percentage significantly lowers TCP throughput.
- The bandwidth utilisation problem compounds on wide area links where increased network latency combines with packet loss. For example, a typical FTP transfer across the United States has a maximum theoretical limit of 1.7 megabits per second (Mbps), the maximum throughput of a single TCP stream for 90ms latency and 1% loss, independent of link bandwidth. On intercontinental links the effective file transfer throughput may be as low as 0.1% to 10% of available bandwidth.
- TCP file transfers over difficult networks (with high packet loss or variable latency) are extremely slow and unreliable. TCP does not distinguish packet losses due to network congestion from normal latency variations or bit errors on some physical channels such as satellite links and wireless LANs, and severely self-throttles.
- TCP file transfer rates and times are unpredictable. TCP overdrives the network until packets are dropped by intervening routers, and in the best case, oscillates around its optimal rate, causing instabilities in the network for file transfer and other applications. Over commodity Internet links where traffic loads vary, file transfer rates may vary widely with network load.
