Sky x technology

Sky X Technology
Dept. of ECE, RIT, Hassan Page 1
CHAPTER 1
INTRODUCTION
Satellites are attractive option for carrying internet and other IP traffic to many
locations across the globe where terrestrial options are limited. The orbiting satellite
transmits (and receives) its information to a location on Earth called the Network
Operations Center or NOC as shown in the Fig 1.1. This simple figure shows how data
moves through a satellite network. The NOC itself is connected to the Internet (or private
network), so all communication made from a satellite dish to the orbiting satellite will
flow through the NOC before it reached the Internet. In this way satellite is used for
carrying internet. But data networking on satellite is faced with overcoming the large
latency and high bit error rates typical of satellite communications as well as the
asymmetric bandwidth design of most satellite network. Mentat, the leading supplies of
TCP/IP to the computer industry have overcome their limitations with the development of
the Sky X product family. The Sky X system replaces TCP over satellite link with a
protocol optimized for the long latency, high loss and asymmetric bandwidth conditions
of the typical satellite communication.
The Sky X family consists of Sky X Gateway, Sky X Client/Server and Sky X
OEM(Original Equipment Manufacturer) products. Sky X products increase the
performance of IP over satellite by transparency replacing. The Sky X Gateway is a
hardware solution designed for easy installation into any satellite network and provides
performance enhancement for all devices on the network. 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. The Sky X Client /Server product operates in a similar
manner except that the Sky X client software is installed on each end users PC. The Sky
X Client/Server provides performance enhancement to individual PC’s. Connection from
applications running on the PC is intercepted and sends over the satellite using the Sky X
protocol.
The Sky X Client and the Sky X Server enhance the performance of data
transmissions over satellites directly to end user PC’s, thereby increasing Web
performance by 3 times or more and file transfer speeds by 10 to 100 times. The Sky X
solution is entirely transparent to end users, works with all TCP applications and does not
require any modifications to end client and servers

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Sky X products are the leading implementation of a class of products known
variously as protocol gateway TCP Performance Enhancing Proxy (TCP/PEP), or satellite
spoofer. The Sky X gateways are available as ready to install hardware solutions which
can be added to any satellite network.
Fig 1.1: Satellite Internet Access

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CHAPTER 2
PERFORMANCE OF TCP OVER SATELLITE
On today's Internet, TCP is the protocol used by the vast majority of applications.
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
having a round trip time of approximately 540 ms, an order of magnitude larger than
terrestrial networks. The journey through the atmosphere can also introduce bit errors into
the data stream. These factors, combined with backchannel bandwidth typically much
smaller than that available on the forward channel, reduce the effectiveness of TCP which
is optimized for short hops over low-loss cables or fiber even though the TCP is very
effective in the local network connected by using cables or optical fibers by using its
many features such as Internet protocol version6 (IPV6), Internet Protocol security
(IPsec) and other leading-edge functionality. TCP is designed for efficiency, high
performance and optimized for maximum throughput and the highest transaction speeds
in local networks. But the satellite conditions adversely interact with a number of
elements of the TCP architecture, including its window sizing, congestion avoidance
algorithms, and data acknowledgment mechanisms, which contribute to severely constrict
the data throughput that can be achieved over satellite links.
In this section the adverse effects and performance issues of the features in TCP
over satellite link are discussed.
2.1 Window Size
TCP utilizes a sliding window mechanism to limit the amount of data in flight.
When the window becomes full, the sender stops transmitting until it receives new
acknowledgement. This is shown in the Fig 2.1
Over satellite networks, where acknowledgements are slow to return, the TCP
window size gradually sets a hard limit on the maximum throughput rate. The minimum
window size needed to fully utilize an error-free link known as the “bandwidth-delay
product” which is 100 KB for a T1 satellite link(The T1 carrier is the most commonly
used digital transmission service in the United States, Canada, and Japan) and 675 KB for
a 10 Mbps link. However many implementations of TCP are limited to maximum window

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size of 64 KB and most operating systems use a default window size of only 8 KB,
imposing a maximum throughput rate over a satellite link of only 128 Kbps per
connection , regardless of the bandwidth available. So the high bandwidth available in the
network is no longer effective, thus the data availability in a client is restricted to a small
fraction of the available bandwidth. Thus the window sizing mechanism of the TCP limits
the rate of flow of data through satellite link.
Fig 2.1: Sliding Window Mechanism in TCP
The simple data acknowledgment scheme used by TCP does not adapt well to
long latency or highly asymmetric bandwidth conditions. To provide reliable data
transmission, the TCP receiver constantly sends acknowledgments back to the sender.
The sender does not assume that any data is lost or corrupted until a multiple of the
round-trip time has passed without receiving an acknowledgment. This algorithm does
not respond well over satellite networks where the round-trip time is long and error rates
can be high. Further, this constant stream of acknowledgments wastes precious back
channel bandwidth and if the back channel is small, the return of the acknowledgments to
the sender can become the system bottleneck. The acknowledgements and error messages
will always dominate the data transfer and the rate of flow reduces very much.

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2.2 Congestion Avoidance
In order to avoid the possibility of congestive network meltdown, TCP usually
assumes that all data loss is caused by congestion and responds to this by reducing the
transmission rate. However, over satellite links, TCP misinterprets the long round-trip
time and bit errors as congestion and responds inappropriately. Similarly, the TCP “Slow
Start” algorithm is part of the congestion control strategy used by TCP shown in Fig 2.2,
the data transmission protocol used by many Internet applications. Slow-start is used in
conjunction with other algorithms to avoid sending more data than the network is capable
of transmitting, that is, to avoid causing network congestion. Slow-start begins initially
limiting the data and the value of the Congestion Window will be increased by one with
each acknowledgement (ACK) received, effectively doubling the window size each
round-trip time. While these congestion avoidance mechanisms are vital in routed
environments, they are ill-suited to single-path satellite links.
So the congestion avoidance mechanisms used by TCP is also not suited for the
satellite link since it reduces the data flow through the network and thus reduces the
overall rate of data transfer.
Fig 2.2: Slow-start Algorithm

Sky X Technology
CHAPTER 3
XPRESS TRANSPORT PROTOCOL
Xpress Transport Protocol (XTP) is a transport layer protocol for high-speed
networks promoted by the XTP Forum developed to replace TCP. XTP provides protocol
options for error control, flow control, and rate control. XTP is a new standard which
meets the data transfer requirements of many real-time systems. XTP's flexible transfer
capabilities, in conjunction with an underlying high-performance network technology
such as FDDI or Fiber channel, provide good support for the implementation of event-
type, real-time distributed systems, in both LAN and internetwork topologies, while
retaining guaranteed response service.
3.1 Principle of operation
In a single protocol XTP provides all the classic functionality of UDP, TCP, and
TP4, transport layer priorities, plus new services such as transport multicast, multicast
group management, rate and burst control, traffic descriptions for quality-of service
negotiation, and selectable error and flow control mechanisms.
Due to its efficient control and error handling algorithms, combined with its
ability to operate over IP, XTP is able to provide performance gains even when acting as
a transparent replacement for TCP, UDP and other existing networking protocols.
Especially in congested networks and over high-speed networks XTP provides
significantly higher throughput than TCP while maintaining lower bandwidth and CPU
utilization.
Fig 3.1: XTP in the OSI Protocol Stack

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3.1.1 Multi-Packet Handshaking
In XTP, multi-packet exchange sequences provide user applications with both a
transport-level virtual circuit capability and a transport-level datagram service. For
example, in XTP a connection may consist of an exchange of three packets, as shown in
Fig 3.2
Fig 3.2: 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. In this scenario, the source initially transmits packet (A). At the destination the
header is examined and it is determined that the source wishes to establish a send
connection. If the destination wishes to comply, a context is established. The packet's data
are then queued for transfer to the waiting destination user process .After successfully
transferring the received data to the host, the destination complies by sending control
packet (B). This packet acknowledges the receipt of the data, and indicates that the
destination is also ready to close the connection. On receiving packet (B), the sender
emits control packet (C), and closes its side of the connection thus completing the three
way handshake. Any buffers still associated with the connection are freed, and the sender
will no longer respond to control packets arriving for the context. When packet (C) is
received by the destination, the connection is closed.

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3.2 XTP Features

 Multicast:
Data can be sent from one transmitter to any number of receivers with a single
transmission. An application may form, or may join, any number of multicast
groups.
 Operates over Any Network Layer:
Xpress Transport Protocol is a pure transport protocol and as such operates over
any network layer, including IP and CLNP, or even none at all. If the network
layer is null then it can run directly on the Logical Link Control or Medium
Access Control for networks such as Ethernet, token ring, and FDDI, or directly
on top of the adaptation layer of an ATM network.
 Flow control:
Allows the receiver to inform the sender about the current state of its receiving
buffers. In XTP, the receiver's flow control parameters are included in control
packets sent from the receiver to the sender.
 Large Sequence Space:
In anticipation of gigabit (and even terabit) networks, XTP can track up to 264
bytes of outstanding data on each connection.
 Selective Retransmission:
This protocol only resends the requested packets and any received successfully
since need not be transmitted.
 Selective Acknowledgement:
A receiver could describe a gap using a pair of sequence numbers that bound
the gap. Instead, XTP describes the groups of bytes (called spans) which were
received. This process is known as Selective Acknowledgement.
 Traffic descriptor:
When a connection is requested by an application, it indicates the type of service
required, traffic of data flow from both the directions and quality of service
requested in each direction.
 Rate Control:
XTP uses rate control to restrict the size and time spacing of bursts of data from
the sender so that within any small time period, the number of bytes that the
sender transmits must not exceed the ability of the receiver

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3.3 Advantages of XTP
 XTP provides all the functionality of TCP and UDP.
 XTP supports a reliable transport multicast capability.
 The underlying priority system guarantees high performance and latency control
for real-time embedded systems.
 XTP's design scales from LANs to MANs to WANs without alteration

Sky X Technology
CHAPTER 4
SKY X SYSTEM
4.1 Sky X Technology Overcomes TCP Performance
Limitations
Sky X products increase the performance of IP over satellite through a
combination of protocol connection-splitting, data compression, and Web pre-fetching,
while remaining entirely transparent to end users. The Sky X gateway works by
transparently replacing TCP connections from the client and converting the data to Xpress
Transport protocol (XTP) for the hop over the satellite link which is the protocol
optimized for satellite conditions.
4.2 Sky X Gateway Operation
The SKY-x products or network have a SKY-x Gateway installed into the system.
This gateway provided by the SKY-x helps to make the network transparent to the user, it
transparently intercepts the TCP protocol transmitted by the user and convert it into the
XTP (Xpress Transport Protocol) which is optimized for the Satellite transmission. Then
on the other side it converts back the XTP protocol into the TCP protocol for the Server.
So the client and the Server side in the Network remain unaware to all this translation. It
requires no special change to be made on the part of the client or the Server in the
Network, so all the applications & the Program which were used previously keeps
functioning on this network also.
This architecture offers vastly improved performance while remaining entirely
transparent to the end user and fully compactable with the internet infrastructure. No
changes are required to the client or server and all applications continue to function
without modification. The two Sky-x Gateway pass the data between each other as if
there doesn't exists any intermediate link between client and the server. This architecture
is also referred to as TCP Performance Enhancing Proxy (TCP-PEP).

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Fig 4.1: The Sky X Gateway
The Sky X gateway splits the single TCP connection into three separate
components.
1. A TCP connection on the remote side between the client and Sky X gateway.
2. An XTP connection involving Sky X protocol over the satellite between the two
Sky X gateways.
3. A TCP connection between the opposite Sky X gateway and server.
Fig 4.2: Sky X Gateway Network Integration

Sky X Technology
XTP is a reliable, transport-layer protocol specifically designed to operate
efficiently over high-speed networks and offers a level of performance not possible with
TCP on long latency, high loss satellite links. XTP is an open standard developed by the
XTP Forum, a non-profit organization composed of networking protocol researchers,
implementers, and user organizations.
By splitting the end-to-end TCP connection, the segment over the satellite can
take advantage of the performance of XTP. TCP congestion avoidance mechanisms
remain in place over the terrestrial connections to protect the stability of the routed
network. The two Sky X gateways pass control data between each other, allowing the Sky
X gateway on the opposite side of the satellite to appear to be the original source or
destination device. This architecture maintains full TCP reliability and end-to-end flow
control.
4.3 Sky X Protocol Design
At the heart of the Sky X system is the Sky X protocol, optimized to
provide maximum throughput for satellite networks. The Sky X protocol is designed
to respond efficiently to typical satellite latency, bit errors and asymmetric bandwidth
conditions and to take advantage of optimizations possible on a single-path link with
known bandwidth. The Sky X gateway combines protocol, application and system
level enhancements to provide maximum throughput for satellite networks.
4.3.1 Efficient Acknowledgment Algorithm
The Sky X Protocol utilizes a highly efficient selective retransmission algorithm
for the acknowledgment of data. Because there is only a single path over the satellite with
no intermediate routing, any gaps in the packet sequence can be assumed to be data loss
due to corruption rather than network congestion. Because the Sky X Protocol does not
use acknowledgments as the primary means of identifying lost data, it requires only
infrequent acknowledgments to confirm data arrival and clear buffers. In contrast, TCP
sends a constant stream of acknowledgments over the reverse channel. The sky X
Protocol reduces back channel usage by 75% for Web traffic and up to 99% for file
transfers, thereby dramatically increasing the performance of networks where limited
back channel bandwidth is the system bottleneck.
4.3.2 Dynamic Window Sizing
The large Sky X Protocol window removes the dependency of the network on the
bandwidth- delay product, allowing high throughput independent of the TCP window size

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of the end nodes. The Sky X Protocol dynamically adjusts the window size based on the
link bandwidth, delay, and number of simultaneous connections to optimize utilization of
the bandwidth.
4.3.3 Rate Control
TCP uses Slow Start and Congestion Avoidance algorithms to determine a safe
transmission rate based on how quickly acknowledgments return. This wastes available
bandwidth when it transmits at too low a rate, and causes unnecessary retransmissions
when it transmits at a rate higher than the bandwidth of the link. Instead, the Sky X
gateway uses a rate control mechanism to explicitly set the transmission rate to exactly
the bandwidth of the link, thereby providing the maximum throughput possible at all
times.
4.3.4 WebPre-fetch
The Web Pre-fetch is used to fetch all the embedded objects in a web page
whenever a client sends a request for even a simple html page. Then these embedded
objects are made visible to the client as and when it is requested by the client thus
avoiding the fetch time required for fetching it from the satellite. The Sky X Protocol
dynamically adjusts the window size based on the link bandwidth, delay, and number of
simultaneous connections to optimize utilization of the bandwidth. The Sky X system
delivers the web objects to the client side of the satellite link where they can be served
locally when requested by the browser, thereby avoiding satellite delay. Thus the XTP
protocol not only provides the security & stability on the satellite network but it also
considerably increases the speed of data transfer by using the Web Pre-fetch.
4.3.5 FastStartWeb Acceleration
In addition to TCP performance enhancement, Sky X products include HTTP
specific optimizations to further accelerate web downloads. Fast Start saves one full
round trip time for each new web connection by reducing the handshaking required to
establish each new HTTP connection.
4.3.6 Data Compression
Integrated on-the-fly data compression functionality, offering lossless
compression ratios of up to 5:1, increases the amount of data that can be sent over the
link.

Sky X Technology
4.4 Sky X Client/Server
The Sky X Client/Server increases the throughput and efficiency of network
access over satellites by transparently replacing TCP with the XTP for the satellite
segment of the connection. Combined with data compression and Web-specific
enhancements, the Sky X system provides maximum performance under the long latency,
high loss, and asymmetric bandwidth conditions typical of satellite communications. The
sky X client/server system enhances the performance of the internet and private network
access over satellite links. The Sky X client/server is shown in Fig 4.3
Fig 4.3: Sky X Client/Server
The sky X client software installed on the PC’s of the end user, works in
conjunction with a sky X server hardware unit located at the network hub. Through the
use of a unique connection splitting and protocol –translation system, the sky X
client/server system overcomes the deficiencies of TCP/IP in satellite –based networks
while remaining entirely transparent to end-user applications. The sky X client is ideal for
use with any satellite receiver card or set –top box.
The Sky X Client, installed on Microsoft Windows-based computers,
transparently intercepts TCP connections from applications running on the PC and
transmits the data over the satellite link using XTP. The Sky X Server, installed at the hub
of the satellite network, establishes a new TCP connection for communication with any
device on the local network or over the Internet. Through this unique, patented
architecture, the Sky X Client / Server system requires no proxy settings while providing

Sky X Technology
performance enhancement for all TCP applications. The Sky X Server is available in two
models namely the SS10 and SS45. The SS10 provides Sky X enhancement for links of
up to 10 Mbps while the SS45 provides Sky X enhancement for links of up to 45 Mbps.
4.4.1 Sky X multicast fan-out
Computer networking traditionally relies on unicast data transfers which establish
point-to-point connections between devices. In situations where the same data is
transferred to multiple users, the server must send a copy of the file to each recipient
independently. This process is both time consuming and wastes much of the bandwidth
resources.
In contrast, multicast technology makes it possible for multiple recipients to
receive a single data stream. This can be an especially powerful tool for satellite networks
or similar architectures where the multicast transfer can take advantage of an underlying
link layer broadcast media. Unfortunately, the only multicast capability built into the
Internet Protocol is a UDP-based, unreliable, best-effort service that is only appropriate
for real-time streaming applications such as event broadcasting. Because UDP-based IP
multicast does not include any mechanisms for detection and retransmission of lost or
corrupted data and does not re-sequence any packets that arrive out of order, IP multicast
is not suitable for file downloads and other data transfer applications. Sky X Multicast
Fan-Out offers a simple and convenient solution for reliable multicast over wide area
networks. By taking advantage of reliable multicast functionality built directly into XTP,
the open-standard transport-layer protocol used by the Sky X Gateway to transfer data
over the WAN link, the Sky X Gateway provides fast, efficient, fully reliable multicast
file transfers. Any data that is lost or corrupted is retransmitted, providing transfer
reliability and rendering special FEC software unnecessary.
The Sky X multicast fan-out, an integral component of the Sky X gateway,
transparently converts TCP unicast connections into reliable multicast transfers. Through
the use of common TCP based applications such as FTP, the Sky X gateway can deliver a
file to every remote location across a wide area network with only a single multicast
transfer. Sky X multicast fan-out is built on the industry leading Sky X gateway IP over
satellite performance enhancement system. Because the Sky X multicast fan-out process

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is transparent to the end devices , any machine can originate or receive the multicast
transfer regardless of operating system and without requiring the installation of any
specialized multicast software.
By combining this reliable multicast transmission technology with a transparent
fan-out functionality which allows any TCP connection to be converted into a multicast
transfer, the Sky X gateway marries the power of multicasting with the convenience of
using FTP or any other TCP-based application. In addition to the multicast benefits
themselves, the Sky X gateway includes on-the-fly data compression which further
increases transfer speeds for compressible data by up to 5 times. Sky X multicast fan-out
functionality is ideal for file transfers, cache replication, video file distribution, content
delivery networks, database replication, and any other distribution of data or files to
multiple users over a satellite link or other wide area network.

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CHAPTER 5
SKY X PERFORMANCE
The performance benefits of the sky X gateway depend on many factors including
the bandwidth, delay, asymmetry and bit error rate of the link, the number of
simultaneous connections, the compressibility of the data and the behavior of the
application itself. Each graph shows Sky X enhancement for three cases: no compression,
highly compressible text, and Corpus benchmark compressibility.
5.1 Window Size and Link Speed vs. Throughput
Without performance enhancement, a default window size of 8 KB limits TCP
throughput to less than 100 Kbps over satellite. The graph in the Fig 5.1 illustrates, even
on server operating systems using a 32 KB window, TCP is only able to reach a through-
put of 440 Kbps. Sky X gateway overcomes this limitation, taking full advantage of the
available bandwidth regardless of the window size of the client or server. For
compressible data, Sky X can provide throughput rates far greater than the link
bandwidth.
Fig 5.1: Effect of Link Speed & TCP window size on Throughput
5.2 Round-Trip Delay vs. Throughput
The Sky X gateway system removes the dependency of TCP on the round-trip
time of the link. Fig 5.2 shows the measured throughput on an error-free, 10 Mbps link.

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These results illustrate that TCP throughput drops rapidly as the round-trip time increases.
In contrast, Sky X is able to maintain full usage of the link regardless of the round-trip
time. For compressible text, Sky X consistently delivers throughput rates greater than the
actual bandwidth.
Fig 5.2: Effect of delay on Throughput
5.3 Bit Error Rate vs. Throughput
The Sky X system overcomes the high sensitivity of TCP to the bit error rate of
the link. The graph in the Fig 5.3 shows the throughput as a function of the bit error rate
for a 10 Mbps satellite link using a 1 MB TCP window. Even at low error rates, TCP is
able to deliver only 1.5 Mbps, while at an error rate of 1x10-5, TCP's throughput drops to
less than 0.03 Mbps. Sky X fully saturates the link at low error rates and even at an error
rate of 1x10-5, achieves 5.1 Mbps without compression and up to 15.8 Mbps for
compressible data.
Fig 5.3: Effect of Bit Error Rate on Throughput

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5.4 CPU, MEMORY UTILIZATION AND DATA TRANSFER
The Sky X software includes an HTTP server that supports the downloading of a
Java applet. The Java applet provides a graphical interface that is updated in real time
based on data sampled from the Sky X device. The data displayed by the Performance
Monitor give an accurate graphical display of the current state of the Sky X device.
Fig 5.4: Sky X Gateway Performance Monitor
5.4.1 CPU Utilization
The graph located in the upper left-hand corner of the Performance Monitor
window displays the percentage of the Sky X device’s CPU that is in use. The data field
under the graph displays the results numerically.
5.4.2 Memory Utilization
The graph located in the upper right-hand corner of the Sky X Performance
Monitor window displays the percentage of free memory on the Sky X device. A value
near zero means the Sky X device is operating near its capacity.

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The three data fields beneath the graph display the following:
• The total amount of memory available in the system.
• The amount of memory that is currently free.
• The least amount of memory that has been available for allocation during the current
monitoring session.
5.4.3 Active Connections
The graph located in the lower left-hand corner of the Performance Monitor
displays, in real time, the number of currently active XTP connections. The Sky X device
has no hard limits on the number of connections. The maximum sustainable connection
rate depends on available memory, the nature of the data flows, and the link
characteristics.
The three data fields beneath the active connection graph display the following:
• The total number of XTP connections serviced during the current monitoring session.
• The number of currently active XTP connections.
• The maximum number of simultaneous connections serviced during the current
monitoring session.
5.4.4 Throughput
The graph located in the lower right-hand corner of the Performance Monitor
displays the current throughput of Sky processed traffic in Kbytes/second. The throughput
of non-Sky X traffic, such as UDP, is not displayed. When tuning your Sky X devices for
optimal performance, the goal is to obtain the largest value possible on this graph. The
three data fields beneath the throughput graph display the following:
• The total data transferred during the current monitoring session in kilobytes.
• The current throughput in Kbytes/second.
• The maximum recorded throughput during the current monitoring session.
5.4.5 Control Buttons
In the left bottom corner of the Performance Monitor is a display of the IP address
of the Sky device being monitored and the sampling interval. Additionally, there is a box
labeled Sample Interval that allows a new sampling interval to be entered.
In the right bottom corner of the Performance Monitor window, there are three
buttons labeled Start, Reset, and Update.
 The function of the Start button is to start a performance monitoring session.

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 The Reset button stops the monitoring session, clears the graphs and clears all
numeric data beneath the graphs.
 The Update button is used in conjunction with the Sample Interval box to change
the sampling interval while a monitoring session is in progress.
 Alternatively, if you do not wish to preserve the graphical and numeric data from
the current session, you can simply click on the Reset button, enter the new
sampling interval in the Sample Interval box, and then click on the Start button to
start a new monitoring session using the new interval.

Sky X Technology
CHAPTER 6
SKY X OEM (ORIGINAL EQUIPMENT
MANUFACTURER)
6.1 Manufacturer’s description
Mentat ( U.S company) now acquired by Packeteer(IT company) licenses its Sky
X gateway technology in software source code form for OEM integration into satellite
modems, VSAT’s, routers, cache or any other satellite networking equipment. The Sky X
OEM software is available for various computer and real time operating systems.
Fig 6.1: Sky X Gateway
6.2 Sky X Accelerators
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 6.2: Packeteer SkyX 250

Sky X Technology
The SkyX 250 Accelerator is a 1U rack-mountable appliance that supports up to
20,000 concurrent sessions and accepts 45 Mbps of inbound traffic for compression. The
system supports link speeds ranging from 2 - 45 Mbps. Another high end Sky X
accelerator is the SkyX 750 Accelerator which is also a 1U rack mountable appliance
capable of supporting up to 80,000 concurrent sessions and accepts 45 Mbps of inbound
traffic for compression. Link speed options range from 10 - 155 Mbps.
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.
Fig 6.3: Sky X Accelerator
The Sky X Accelerator performs the following functions
 Accelerate file transfers, large and small.
 Speed XML and HTTP sessions, disaster recovery, database sync and backups.
 Optimize application performance over high-latency and satellite links.
 Increase link utilization on fat WAN links.
 Maximize bandwidth utilization.
 Minimize retransmission and recover more quickly from errors.
6.2.1 TCP Acceleration
Enjoy faster database connectivity, Web and remote-access applications while
maintaining full TCP reliability and end-to-end flow control. Specifically optimized for
long delay, high bit error and asymmetric bandwidth conditions. Accelerate all TCP-
based applications—including Web access, FTP file transfers, ERP and e-mail.

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6.2.2 Data CenterReplicationAcceleration
Sky X Accelerator technology overcomes latency effect on TCP over high-
bandwidth links by using bandwidth much more efficiently and improving replication
performance over high capacity data center-to-data center links. Replication sessions
complete up to 100 times faster and are not subject to the stalls and session drops
associated with packet loss.
6.2.3 XML and Web Acceleration
Response times improve dramatically with enhanced HTTP performance.
Sky X Xpress Web and Xpress XML technology speeds delivery of embedded
objects in Web-based applications. Further accelerate Web downloads by reducing
time needed to establish each new HTTP connection.

Sky X Technology
CHAPTER 7
ADVANTAGES, LIMITATIONS AND
APPLICATIONS OF SKY X
7.1 ADVANTAGES
 Increased Performance
The Sky X Gateway increases the throughput rate by 3 times or more Web
traffic and up to 10 to 100 times for file download.
 Reduced FEC Usage
The Sky X Gateway offers high levels of performance even at bit error rates that
reduce TCP performance to near zero. Improved response to bit errors reduces
the effects of rain fade and lowers the level of forward error correction encoding
required.
 Easy Installation
The Sky X gateway includes two 10/100base T Ethernet ports for easy
installation into any standard TCP/IP network.
 High Performance
The Sky X Gateway enhances the performance of Internet, intranet, extranet,
private network, or any other TCP/IP connections over satellite links.
 Web-Based Monitoring Console
Performance of the Sky X gateway can be monitored through a Web-based
console, accessible from any browser.
7.2 LIMITATIONS
 It is costly compared to the TCP protocol installation.
 It is very sensitive and thus greatly effects on its working in changing
environment.
7.3 APPLICATIONS
 Used in Satellite Communication.
 Used for Accessing Web in fastest Speed.
 Used for Data and File Transfer Efficiently.

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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.
The world is reducing to a global village by the use of satellite communication
and so the improvement in the rate of information interchange through satellite is a must
and thus sky X technology becomes unavoidable.

Sky X Technology
REFERENCES
• TCP/IP Protocol Suite, by Forouzan B.
• Computer Networks A.Tanenbaum
• A 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.
• https://en.wikipedia.org/wiki/Packeteer
• http://www.cs.virginia.edu/~acw/netx/xtp_middle.html
• http://www.xiplink.com/introscps-tp.html

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