Comtech EF Data turboIP-G2 - Manual (Page 31)

turboIP-G2 Performance Enhancement Proxy Revision 2
Introduction CD-TURBOIP-G2
1–9
1.2.4 Acceleration and WAN Optimization
WAN Optimization is available with units manufactured from November 2010
forward.
All turboIP Performance Enhancement Proxies combat the inherent challenges of transmitting
Transmission Control Protocol (TCP) over satellite links. The units provide transparent
acceleration of TCP sessions, increasing throughput over satellite links while requiring minimal
topology changes. They provide reliable connection-oriented, end-to-end data transfer for user
applications.
Powered by the industry-leading SCPS implementation, SkipWare, the turboIP-G2 overcomes
performance loss associated with conditions common in tactical networking, including weather
effects, blockage, latency and interference.
The turboIP-G2 complies with DOD requirements for volatile memory data storage by providing
RAM-based web caching. The turboIP-G2 also provides support for both IPv4 and IPv6,
allowing DOD programs to satisfy IPv6 conformance mandates.
1.2.4.1 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.