Comtech EF Data turboIP v4.0 - Manual (Page 15)

turboIPv4.0 Revision 6
Overview MN/TURBOIP.IOM
1.2 TCP/IP P ERFORMANCE L IMITATIONS
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 P
ERFORMANCE
E
NHANCEMENT
P
ROXY
Comtech EF Data’s turboIP™ 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™ 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™ is fully compatible with network devices that use TCP, supporting existing Internet
standards, including network congestion and retransmission schemes. This allows turboIP™ 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™ 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.
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