2. CONTENTS
• INTRODUCTION
• PERFORMANCE OF TCP OVER SATELLITE
• XPRESS TRANSPORT PROTOCOL
• SKY X FAMILY
• PERFORMANCE OF SKY X SYSTEM
• MANUFACTURER’S DESCRIPTION
• SKY X ACCELERATORS
• ADVANTAGES AND APPLICATIONS OF SKY X SYSTEM
• CONCLUSION
• REFERENCES
1
3. INTRODUCTION
• Satellites are ideal for providing internet and private network access over long
distance and to remote locations.
Fig 1: Satellite Internet Access
• The Internet Protocols i.e TCP/IP are not optimized for satellite conditions.
2
4. • Mentat, the leading supplies of TCP/IP to the computer industry developed Sky X
product family.
• The Sky X family consists of Sky X Gateway, Sky X Client/Server and Sky X
OEM products.
• The Sky X gateway works by intercepting the TCP connection from client and
converting the data to Sky X Protocol for transmission over the satellite.
• By the use of Sky X Client and the Sky X server the web performance can be
increased by 3 times or more and file transfer speeds can be increased by 10 to 100
times.
• Sky X system works with all TCP applications and does not require any
modifications to end client and servers.
3
5. Performance of TCP over satellite
• The performance of TCP over long-delay networks will have direct impact on the performance of
Internet access using GEO satellites orbiting at an altitude of 22,300 miles.
• The adverse effects and performance issues of the features in TCP over satellite link are as follows
i) Window Size
Fig 2: Sliding window mechanism in TCP
Over satellite networks, where acknowledgements are slow to return, the TCP window size gradually
sets a hard limit on the maximum throughput rate.
4
6. ii) Congestion Avoidance
• “Slow Start” algorithm is part of the congestion control strategy used by TCP.
Fig 3: Slow-start Algorithm
• TCP misinterprets the long round-trip time and bit errors as congestion and responds
inappropriately.
5
7. Xpress Transport Protocol
• XTP is a transport layer protocol developed to replace TCP for high-speed networks.
Fig 4: XTP in the OSI protocol stack
6
8. Multi packet handshaking in XTP:
Fig 5: Three Packet Connection-mode handshake
The scenario above depicts how XTP can reliably set up a connection between
two user processes, transmit data, and close the connection with a minimum of three
packets.
7
9. XTP features:
• Multicast
• Operates over any network layer
• Flow control
• Selective retransmission
• Selective acknowledgement
• Traffic descriptor
• Rate control
Advantages of XTP:
• XTP provides all the functionality of TCP and UDP.
• XTP supports a reliable transport multicast capability.
• Guarantees high performance and latency control for real-time embedded systems.
• XTP's design scales from LANs to MANs to WANs without alteration
8
10. Sky X system
• Sky X products increases the performance of IP over satellite while remaining
entirely transparent to end users.
Fig 6: Sky X network integration
9
11. Sky X Gateway
• The Sky X gateway works by transparently replacing TCP connections from the client
and converting the data to Xpress Transport protocol which is the protocol optimized for
satellite conditions.
Fig 7: The Sky X Gateway
10
12. Sky X Protocol design
• Efficient Acknowledgement Algorithm
• Dynamic Window Sizing
• Rate Control
• Web Pre-fetch
• Fast Start Web Acceleration
• Data Compression
11
13. Sky X Client/Server
• The Sky X Client/Server enhances the performance of the internet and private
network access over satellite links.
Fig 8: Sky X Client/Server
12
14. Sky X Performance
• Window Size and Link Speed vs. Throughput
Fig 9: Effect of Link Speed & TCP window size on Throughput
13
15. • Round-Trip Delay vs. Throughput
Fig 10: Effect of delay on Throughput
• Bit Error Rate vs. Throughput
Fig 11: Effect of Bit Error Rate on Throughput
14
16. • CPU, MEMORY UTILIZATION AND DATA TRANSFER
The data displayed by the Performance Monitor give an accurate graphical display
of the current state of the Sky X device.
Fig 12: Sky X performance monitor
15
17. Manufacturer’s description
Mentat ( U.S company) now acquired by Packeteer (IT company) licenses
its Sky X gateway technology for OEM integration into satellite modems, VSAT’s,
routers, cache or any other satellite networking equipment.
Fig 13: Sky X Gateway
• The Sky X OEM software is available for various computer and real time operating
systems.
16
18. Sky XAccelerators
Packeteer which is a global leader in WAN Application Optimization introduced
New Sky X Accelerators for improved TCP-Based Application Performance. New Sky X
Accelerators Support Expanded Range of Link Speeds.
Fig 14: Packeteer SkyX 250
When TCP protocol design limitations such as high latency and lost packets
threaten application connection speed, Sky X Accelerator ramps flow, fully utilize links
and keeps data moving along.
17
19. ADVANTAGESANDAPPLICATIONS
ADVANTAGES OF SKY X SYSTEM:
• Increased Performance
• Reduced FEC Usage
• Easy Installation
• High Performance
• Web-Based Monitoring Console
APPLICATIONS OF SKY X SYSTEM:
• Satellite Communication.
• Accessing Web in fastest Speed.
• Data and File Transfer Efficiently.
18
20. CONCLUSION
The sky X gateway is the leading solution for overcoming the limitations
of TCP/IP over satellite. ISPs, corporations, governments, and military organizations
around the world rely on sky X gateway to enhance the performance of their satellite
networks. Testing by independent third parties including INTELSAT and NASA
confirms that the sky X Gateway dramatically improves performance for the internet
and private access over satellite networks.
19
21. REFERENCES
• TCP/IP Protocol Suite, Fourth Edition by Behroz A. Forouzan
• Computer Networks, 4th Ed, Andrew S. Tanenbaum
• Top Down Approach Featuring the Internet, James F. Kurose and KW. Ross
• E. T. Saulnier and R. J. Mitchell, "Impact of implementation on XTP throughput
performance," Communications,1992.Communications,1992.ICC'92,Conference
record, SUPERCOMM/ICC '92, Discovering a New World of Communications.,
IEEE International Conference on, Chicago, IL, 1992, pp. 976-980 vol.2.
20
