BROADBAND MULTIMEDIA OFFERINGS• VSAT platform services

• Broadband Wireless (BBW)

• Internet platform services

VARIOUS SOLUTIONS:• 6 BBW products

• 6 VSAT products

• Internet, IP streaming, multicasting & hosting

• Virtual Private Networks (VPN)

• Video conferencing

SENTECH INTRODUCTION

SENTECH INTRODUCTION

VSAT TECHNOLOGY

VSAT TECHNOLOGY

DESCRIPTION

VSAT provides…

…broadband connectivity (including Internet access) or networkingbetween remote points enabling data transfer or…

…the connecting of local area networks into wide area networks.

A VSAT network is the delivery mechanism. The Sentech VSAT product is branded VSTAR.

VSAT TECHNOLOGY

DESCRIPTION (Continued)• VSAT = Very Small Aperture Terminal (typically smaller than 3.8m)• Other satellite devices with small dish sizes are also referred to as

VSAT’s, but not in Sentech’s context• There are two fundamental ways of setting up a VSAT network: star or

mesh topology• In a star network, all traffic is routed though a central hub• In a mesh network, sites can communicate directly with each other• Star networks are cheaper than mesh networks due to expensive

equipment required for a mesh network (CPE 10 times more expensive than with star network)

REMOTE SITE

LAN

REMOTE SITE

LAN

REMOTE SITE

LAN

CUSTOMER HQ

LAN

NETWORKOPERATION

SYSTEM

SATELLITE CAPACITY (KU-BAND)

DESCRIPTION (Star topology)

ConnectivityOptions

VSAT TECHNOLOGY

REMOTE SITE

LAN

REMOTE SITE

LAN

REMOTE SITE

LAN

CUSTOMER HQ

LAN

HUB(NETWORK

MANAGEMENTSYSTEM)

SATELLITE CAPACITY (KU-BAND)

DESCRIPTION (Mesh topology)

ConnectivityOptions

TERRESTRIAL BACKHAUL

VSAT TECHNOLOGY

VSAT TECHNOLOGY

DESCRIPTION (Terminology)

• RCST = return channel satellite terminal (also referred to as the VSAT)• Traffic outbound from the hub to the RCST in TDM (time division

multiplex)• Traffic inbound from the RCST to the hub in TDMA (time division multiple

access)• CIR = committed information rate• BBR = Burstable bit rate; the maximum information rate a RCST can

obtain by taking up unused bandwidth; never more than the total bandwidth allocated to the specific network

• IP = Internet Protocol version 4

VSAT TECHNOLOGY

DESCRIPTION (Terminology cont.)• The hub is the central point of a network and comprises transmit and

receive equipment for two-way communication with the RCST’s via satellite. The hub also houses the network management system, the modulation equipment and the main system processors and interfaces with the customer. This hub is located at STP. Sentech’s hub can accommodate up to 10 000 RCST’s.

• IDU = indoor unit• ODU = outdoor unit• On-air availability is the percentage that Sentech’s guarantees the

customer’s network to be operational according to specifications. Normally on-air availability will be in the region of 99.5%, unless altered due to certain operational issues.

VSAT TECHNOLOGY

DESCRIPTION (Terminology cont.)

• Contention = sharing a fixed bandwidth (allocated to a network or to a product set) by the RCST’s in that network.

There are three ways in which traffic in a network can be set-up:1. Static CIR: Each RCST gets a predetermined bandwidth, whether it is

used or not.2. Contended: There is a fixed bandwidth allocated to the network. The

bandwidth is split between the RCST’s as required.3. CIR with contention: The sum of all the CIR of the network is less than

the bandwidth allocated to the network. A RCST can burst into the spare bandwidth as required.

VSAT TECHNOLOGY

DESCRIPTION (LinkStar)

• The VSAT network deployed by Sentech is the LinkStar star topology system provided by ViaSat

• Provides a service in the PAS 7 footprint• In- and output is an Ethernet port on the IDU• KU-band up- and downlink• 1.2m dishes and 2W units (1.8m dishes and 4W units also)• The current configuration limits inbound traffic to 256kbps per RCST.

By using large antennas (1.8m) and more powerful amplifiers (4W), this can be boosted to 2Mbps. Outbound traffic is limited to a maximum of 10Mbps per terminal and 36Mbps overall for a customer’s network

• In future a wide Africa coverage will also be possible from the existing hub (PAS 10 or similar satellite)

DESCRIPTION (LinkStar IDU)VSAT TECHNOLOGY

VSAT TECHNOLOGY

DESCRIPTION (LinkStar IDU)

VSAT TECHNOLOGY

DESCRIPTION (LinkStar IDU)

DESCRIPTION (LinkStar IDU)VSAT TECHNOLOGY

• 1.2m or 1.8m

DESCRIPTION (LinkStar ODU)

VSAT TECHNOLOGY

• BUC (block-up converter)• LNB (low noise block down converter)

DESCRIPTION (LinkStar ODU)VSAT TECHNOLOGY

FEATURES AND FACTS (UDP/IP)Sentech’s VSAT network carries IP (Internet Protocol) traffic, but can carry most other forms of digital data (including voice, video and TDM) by encapsulating them in IP.

IP has two major data transmission formats, TCP and UDP. UDP (user datagram protocol) sends individual data packets, with no guarantees relating to delivery. Packets may arrive out of sequence, in duplicate or not at all. UDP is used as the underlying transport mechanism for many protocols that then add their own error checking and recovery mechanisms.

VSAT TECHNOLOGY

FEATURES AND FACTS (TCP/IP)TCP (transmission control protocol) creates an error-free end-to-end data stream. Data is still sent as a sequence of packets, which the receiver re-sequences and checks for errors. Missing or error packets are retransmitted. TCP will only send a certain number of packets before waiting for an acknowledgement. The high latency of satellite transmission (or multi-hop terrestrial links) limits the effective throughput, regardless of the actual bandwidth available.

Sentech’s TCP acceleration (spoofing) generates acknowledgements at the sender’s end of the satellite data path, eliminating the latency issue. The accelerator has its own error-free protocol across the satellite channel, which is optimised for satellite characteristics. The receiving satellite station converts back to normal TCP for final delivery.

VSAT TECHNOLOGY

VSAT TECHNOLOGYFEATURES AND FACTS (The IP chain at STP)

TCP/IP ACCELERATOR

ENCAPSULATOR

DVB-IP

MUX

MODULATOR (QPSK)

UP CONVERTER (KU-BAND)

AMPLIFIER

RF

HUB (POLICY ROUTER)

TRANSMIT

CUSTOMER (ETHERNET)

FEATURES AND FACTS (The RCST IP chain)VSAT TECHNOLOGY

DVB-MPE

DEMODULATOR (QPSK)

TCP/IP (ETHERNET)

RECEIVE

LAN

MODULATOR (QPSK)

TDMA TRANSMIT

VSAT TECHNOLOGY

FEATURES AND FACTS (Internet)Sentech offers Internet access with the LinkStar RCST. The Internet access is provisioned on the WAN connectivity provided by the VSAT network. The contention ratio of this Internet access could be 1:1 or 2.5. Sentech lands its own Internet access from the European backbone via STP and provisions it at the hub.

VSAT TECHNOLOGY

FEATURES AND FACTS (QoS)The Sentech VSAT network supports end-to-end quality of service (QoS). This allows predictable, guaranteed network performance. QoS can give certain types of traffic preference, for example slowing downloads to boost interactive on-line terminal performance.

This can be further enhanced with the Allot traffic shaping device, which has extremely flexible traffic prioritisation policies.

VSAT TECHNOLOGY

FEATURES AND FACTS (Turbocoding)The Viasat equipment used for Sentech’s VSAT network makes use of Turbocoding FEC (forward error correction). FEC provides redundant information so that errors can be repaired, rather than retransmitted. Turbocoding feeds error rate information back to the sender, so that the FEC rate can be adjusted.

Under high error conditions, the FEC rate is increased to cut the error rate while slightly reducing effective bandwidth. This delivers far better performance than a static FEC rate, which would lead to retransmissions.

Where the error rate drops, the FEC rate is reduced accordingly, thereby increasing effective throughput.

VSAT TECHNOLOGY

FEATURES AND FACTS (Latency)Geostationary satellites orbit the earth every 24 hours, so that they stay in one place relative to the earth. The physics of gravity and acceleration means that the satellites have to be 36,000 km above the equator. Microwaves travel at the same speed as light, giving a latency from terminal to satellite to hub of just over a quarter of a second.

While this may not seem much, a terminal-to-hub connection would have a round-trip time (terminal -> satellite -> hub -> satellite -> terminal) of 0.7 seconds. A terminal-to-terminal connection in a conventional star network would have a four satellite hops (a total of 8 earth-satellite or satellite-earth legs), for a round-trip delay of around 1.5 seconds.

VSAT TECHNOLOGY

FEATURES AND FACTS (Latency continued)This has an impact on timing-sensitive traffic, such as voice and certain client-server data applications. Such traffic may be successfully transmitted over a single hop, but fail over a multi-hop network. In such cases, the server is usually located near the hub (at a Sentech client hosting facility, for example), or linked to the hub with a terrestrial network (Sentech’s multi-media network or Telkom). Alternatively, consider a (considerably more expensive) fully-meshed network.

The technical characteristics of the TCP/IP protocol along with the high latency of the satellite link means that under normal circumstances TCP/IP traffic is limited to about 330kbps on a satellite service, regardless of how much bandwidth is actually available. Sentech’s VSAT network uses a TCP accelerator (spoofer) which removes this constraint and delivers the full bandwidth provisioned on the satellite to the client.

VSAT TECHNOLOGY

FEATURES AND FACTS (Bandwidth on demand)As satellite connectivity is dependent only on being able to see the satellite, satellite services are ideal for “bandwidth on demand”. In this context, the term covers a multitude of concepts, including fast set-up time (install a dish and you’re online), sharing bandwidth between terminals (a number of branch offices can share a space segment and “compete” for and share the available bandwidth) and the ability to turn bandwidth on and off at a moment’s notice.

Clients can also be provided with a guaranteed minimum bandwidth per terminal (CIR), but be allowed to burst into whatever bandwidth is available when additional bandwidth is needed.

VSAT TECHNOLOGY

FEATURES AND FACTS (BoD continued)This is in contrast to a conventional terrestrial network, where obtaining more bandwidth means having more cables installed, new terminating equipment, and a lead time of weeks, if not months. With VSAT, it can be done in minutes.

VSAT TECHNOLOGY

FEATURES AND FACTS (Multicast)Satellite is also a broadcast medium, and the signal from the satellite can be received by more than one terminal at the same time. When a client wants to distribute the same data to a number of recipients (eg radio or video broadcasts, software updates), they can use the multicast capabilities of the Sentech VSAT network to send the data once to be received by multiple sites at the same time.

This has major cost benefits, and where there are large amounts of data involved (hence long transmission times), this approach ensures that all the recipients have the same information at the same time (instead of some having out-dated information).

VSAT TECHNOLOGY

FEATURES AND FACTS (Geographic independency)Provided that the satellite dish can see the satellite and is within the satellite’s footprint (the area that the transponder illuminates), connectivity is independent of geographic location. This makes VSAT ideal for under-serviced areas, whether in South Africa or the rest of Africa.

VSAT TECHNOLOGY

FEATURES AND FACTS (Reliability)Communication is dependent on a clear view of the sky and electrical power. VSAT networks are not dependent on cables, which can be damaged or stolen, and have fewer points of failure (such as junction boxes and telephone exchanges) between sites.

There are two factors that are beyond our control that can affect reliability: solar flares and rain. Solar fade occurs when the sun is directly behind the satellite and swamps the satellite signal. It lasts for a few minutes, decreasing bandwidth and finally blacking out totally. It is easy to predict and of short duration (a few minutes per day, a few days per year). Heavy rainstorms can cause signal fading, with similar effects. Unfortunately, they cannot be reliably predicted, but are usually of short duration. The use of larger antennas and amplifiers will minimise the effect of rain fade in tropical or high rainfall areas.

FEATURES AND FACTS (Immediately available)• Internet Access

• Intranet Communications (secure or other)

• Intranet Database Access

• E-Mail and messaging

• Multicast / Broadcast File Distribution (data, software, video, audio)

• Client-Server Applications

• Point-to-Point File Transfers

• Bank and ATM Fund Transfers

• Reservations (eg Airline and Hotels)

• Document delivery and distribution (eg legal services)

VSAT TECHNOLOGY

VSAT TECHNOLOGY

FEATURES AND FACTS (Available in future)

• Video on Demand

• Video Conferencing

• Data backup services

• Business-to-Business Electronic Commerce (eg ASP solutions)

• Voice (?)

• Education

• Network and other IT security services

VSAT TECHNOLOGY

BENEFITS• Reliable scalable connectivity• Fast set-up time (minutes)• Shared bandwidth / bursting (sharing bandwidth with committed information

rates)• Bandwidth on demand (ad-hoc)• Any where in PAS 7 coverage• On-air availability (reliable)• Multicasting

But• Latency• Rain fade and solar activity