Comtech EF Data turboIP-45 - Manual (Page 15)

turboIP-45 Performance Enhancement Proxy Revision 0
Introduction CD/TURBOIP45.IOM
1–3
1.2 TCP/IP Performance Limitations
Due to its design, TCP/IP does not perform well over impaired links. The link impairment could be due
to delay or noise or both. A typical satellite link suffers due to high delay and high noise. The main
reasons for poor TCP/IP performance over an impaired link can be summarized as:
Slow start algorithm Slow start algorithm allows a TCP sender to increase the data transmission rate
without overwhelming the network. It achieves this goal by gradually increasing
the number of unacknowledged segments at the start of the session. The time
required for an acknowledgement over the satellite link severely limits the ramp
up in transmission rate.
TCP window size The most unacknowledged data that a TCP sender can have outstanding is
limited by the sender’s window size. This limits the transmission rate in the
steady state to Window_Size/Round_Trip_Time (e.g., for a typical receive
windows size of 64 kbytes and satellite round trip time of 540 ms, the maximum
throughput is limited to approximately 121 kbps).
Congestion avoidance
algorithms The congestion avoidance and control mechanism of TCP attributes packet loss
to network congestion, as opposed to corruption due to noise in the channel.
This leads to drastic reduction in transmission rates. Recovery from congestion
is slowed due to the high round trip time and noise in the satellite channel.
1.3 TCP/IP Performance Enhancement Proxy
Comtech EF Data’s turboIP-45 Performance Enhancement Proxy is designed to alleviate TCP/IP
bottlenecks in an impaired environment (high delay, high bit error rate, or both), while preserving
interoperability with any TCP device. It achieves this by combining TCP with a number of
enhancements that modernize IP transport.
turboIP-45 is based on SCPS-TP, the Transport Protocol of SCPS, an open standard specifically defined
for space communications. This standard is open, published, and internationally distributed. SCPS-TP is
an ISO standard (15893), a CCSDS standard (714.0-B-1), and a MIL-STD (MIL-STD-2045-44000).
turboIP-45 is fully compatible with network devices that use TCP, supporting existing Internet
standards, including network congestion and retransmission schemes. This allows turboIP-45 at one end
of the link to operate with TCP devices at the other end of the link without the need for a peer turboIP-
45 device, providing partial performance enhancement. However, it is recommended that TCP traffic
pass through a pair of turboIP TM Performance Enhancement Proxies, in order to take full advantage of
the SCPS-TP protocol.