Innovative File Transfer and Management

White Papers on RELIA™ and TCP



 By Bill Gibson, Chief Technical Officer, Niwot Networks, Inc. April 12, 2000 revised January 2006



This chart compares performance of RELIA extensions vs TCP over T1 (1536kbps)Internet connections in the presence of the typical 4 per cent packet loss overping times(distance) of 80ms(National), 300ms(International) and 600ms(Satellite).
 
Introduction
 
TCP is the basic transport for Internet applications such as email, web browsing, and file transfer. When used on high speed networks with long delay (ping time) and congestion (packet loss), TCP becomes slow and less reliable. When a TCP packet is lost, the sender must retransmit the packet, and the time it waits before retransmission grows as the ping time grows.
 
The new RELIA™ technology (Patent Nos US 6,445,717 and 6,895,019) overcomes long ping times and packet loss to provide high performance reliable communication over the international and satellite Internet.
 
Background
 
Historically, the Internet was made possible by the evolution of algorithms for making an unreliable data transport act reliably. The first of these was the Ethernet standard, where hardware retransmitted lost(collision) packets without software intervention. The second was TCP, where software detects corrupted or missing packets and takes responsibility for retransmission. RELIA technology is the logical next step for environments which suffer from the combination of packet loss and longer delay, eliminating the need for the sender to retransmit in most cases.
 
Overcoming Internet Congestion with Redundant Packets
 
We know that on the Internet "congestion" means lost packets. You see the effects of congestion whenever "the Internet is crowded", and you notice that Internet performance is much better during the hours when nobody else is using it. When an information packet is lost with TCP (the protocol below FTP and HTTP), the sending side times out, then retransmits and resumes your transfer. The amount of time the sending side waits before retransmitting is determined by the ping time. While this may be only a few milliseconds on a local connection, the ping time is 300 milliseconds on the international Internet and 600 milliseconds over satellites. Not only are information packets more likely to be lost, but the time wasted before retransmitting the lost information increases as well.
 
RELIA sends a little extra data to allow the receiver to recover the lost information. This eliminates the wait time and the retransmission associated with lost information. With RELIA your data moves efficiently even when information is being lost over international or satellite links.
 
Lost information packets(congestion) are a fact of life on the Internet. By sending redundant information along with the information being transported the receiving side can recreate the lost information. RELIA offers four levels of redundancy:
 
•  RED1 can recover from 1 packet being lost at a time
 
•  RED2 can recover from a pair of packets being lost
 
•  RED4 can recover from a block of 4 packets being lost
 
•  RED8 can recover from a blocks of 8 being lost
 
The number of extra packets sent goes up as the redundancy level increases. The percentage of extra packets sent is the redundancy overhead, and it ranges from 9 per cent to 43 per cent in the initial version of RELIA.
 
It is not always possible to regenerate the lost information packets. When this occurs, RELIA will fall back and retransmit.
 
Overcoming Internet Delay with a Large Window Size
 
RELIA combines a large window size with information recovery to allow efficient use of long-delay Internet connections. These long-delay connections are found on international and satellite communications. On the international Internet, it typically takes 300 milliseconds for data to reach its Internet destination and the response to be returned (ping time). Over satellite links, this "ping time" is 600 milliseconds. The amount of data a system can send before it waits to receive an acknowledgement is called the "window size." If the window size is too small, the system spends time waiting for acknowledgements instead of sending data.
 
RFC 1323 is the Internet standard to improve TCP performance on high bandwidth, long delay links. The algorithms documented in this standard are included along with the packet recovery techniques in the RELIA implementation.
 
RELIA™ SOLUTION BENEFITS
 
RELIA extended connections have higher throughput than naked TCP in International and Satellite conditions.
 
In the standard international Internet environment of 4 per cent packet loss and 300 millisecond ping time, RELIA's RED1 technology throughput is 884% of TCP's throughput. Similar advantages are available at other combinations of packet loss and delay.
 
RELIA extended connections are more robust than naked TCP.
 
In testing against groups of 8 packets being lost out of every 200, with a ping time of 600 milliseconds, the RELIA technology lost its connection only 1/9 (11 per cent) as often as the TCP connection was lost. This difference will grow even more in RELIA's favor as the technology evolves.
 
RELIA™ EXTENSIONS PERFORMANCE MEASURED vs. NAKED TCP
 
Performance on the international Internet and satellite Internet at 4 per cent packet loss
This chart shows the superior performance of the various RELIA extension technologies as compared to naked TCP when subjected to the Internationalaverage 4 per cent packet loss over Local(10ms), National(80ms), International(300ms), and Satellite(600ms) ping times.
 
Performance on the international Internet and satellite Internet at 0 per cent packet loss
 
Performance on the international Internet and satellite Internet at 1 per cent packet loss
 
Performance on the international Internet and satellite Internet at 2 per cent packet loss
 
Performance on the international Internet and satellite Internet at 8.5 per cent packet loss
 
Performance on the international Internet and satellite Internet at 4 per cent packet loss, when 4 packets in a group out of 100 are lost
 
Performance on the international Internet and satellite Internet at 8 per cent packet loss, when 8 packets in a group out of 100 are lost
 
The Relia technology sends redundant packets, enabling the receiving side to reconstruct the missing packets and eliminate TCP's "time out and retransmission" (the sender waits some multiple of the ping time before retransmitting if it hasn't heard an acknowledgment). The Relia patent covers a variety of techniques to accomplish recovery without retransmission.
 
The RelSock demonstration implementation allows the user to easily select redundancy levels RED1(good for recovering single packet losses), RED2(good for recovering pairs of lost packets), RED4(good for recovering groups of up to 4 lost packets), or RED8(good for recovering groups of up to 8 lost packets).
 
As would be expected, the different redundancy levels offer advantages as the packets are lost in groups instead of one-at-a time. The default selection in the current demo is RED2.
 
CONCLUSION: In all cases of international and satellite Internet connections, RELIA technology significantly out-performs Naked TCP!
 
RELIA™ SOLUTION ROBUSTNESS MEASURED vs NAKED TCP
 
In our testing (NT to NT) losing a group of 8 packets out of 200 with 600 milliseconds ping time, sending a suite of 10 files, each slightly larger than a megabyte:
 
NAKED TCP: TCP connection was lost before all 10 files were transferred in 72 out of 113 trials (63 per cent of the time)
 
RED1, RED2, RED4, RED8: These connections use a conventional TCP connection to establish the RELIA connection, and it appears this process is still vulnerable to connection loss, this vulnerability will be reduced in future versions of the technology. With today's demonstration version the RELIA connection was lost before all 10 files were transferred in 8 out of 120 trials (7 per cent of the time)
 
CONCLUSION: When 8 packets in a row are lost at an overall packet loss rate of 4 per cent and a satellite delay, The RELIA connections are 9 times more robust than NAKED TCP.
 
RELIA™ technology offers the software application developer dramatically higher performance and reliability extensions to TCP when compared in the harsh international and satellite Internet environment.

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