High Speed Internet Via Satellite Satellite connections are used to provide the local loop between national ISPs and their commercial and private customers. Three technologies are available for this:
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IP over DVB Transmission For IP applications it is becoming common practice to use an IP encapsulator to convert raw IP data into a DVB/MPEG-2 transport stream which is then transmitted by satellite. IP Encapsulation MPEG-2 is a video standard which defines the compression of the video data both spatially (within each image frame) and temporally (from frame to frame). It also provides for the compression of stereo audio and the multiplexing of this with the video data stream. Finally it provides for an integrated transport mechanism for the multiplexing of the video, audio and data. The DVB standard for satellite delivery is an extension of MPEG 2 and specifies additional implementation functions including modulation, forward error correction and service information specification. Each MPEG 2 packet is 188 bytes long, consisting of 4 bytes of header and 184 bytes of payload. The payload can have several formats, including:
Terminals Internet trunks carrying traffic between European ISPs and the US backbone generally use large or medium sized earth stations rather than small terminals. These earth stations generally consist of:
Local Loop Connectivity - Internet Broadcast Taking advantage of the fact that local loop Internet data flow is highly asymmetric (the data received by an Internet subscriber is generally one hundred or more times higher than that sent), current systems use a conventional modem link via the PSTN to send data requests to the ISP. The requested pages are then transmitted by broadcasting them over the satellite connection. This can be taken a step further, caching commonly requested pages at the hub or cache all pages which are linked to pages being downloaded to increase the access speed perceived by the subscriber. Signal Types and Characteristics Internet broadcast networks generally use a single IP over DVB carrier which can have a data rate anywhere from 500 kb/s to 55 Mb/s depending on the equipment manufacturer and the traffic requirements. Hub Station The hub station consists of:
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Solutions. High speed trunks are used to provide high data rate direct connections between gateways on the US Internet backbone and European ISPs. Intra-regional trunks between major European Internet gateways are also being established, though much of this traffic is being carried by fiber. |
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The gateway equipment for an earth station typically costs of the order of 10 kEuro. Costs for the antenna, RFT and civil works are additional to this. Remote Terminals The remote terminal consists of an antenna with an LNB mounted on the feed and a card which is mounted inside a PC. The typical cost for the remote equipment is less than 500 Euro. Local Loop Connectivity - Internet VSATs A few manufacturers now also supply interactive hubbed VSATs configured for carrying Internet type traffic. These VSATs are the same as interactive hubbed VSATs with the following main differences:
Other than these differences, the networks are very similar and the technology will not be discussed further here. Local Loop Connectivity - Interactive TV A later development, sees the traffic from ISP to users carried by satellite on channels which are shared by television broadcasters. Many broadcasters see the WWW as a natural extension to their normal activities which has the advantage that there are very few regulatory constraints. Interactive TV is seen as a way to integrate the WWW with conventional TV broadcasting. To ease this transition a number of broadcasters have recently become ISPs in their own right. Broadcasters provide a terrestrial return link by modem over the PSTN using a similar network configuration to Internet Broadcast as described above or have the return link also carried by satellite. Each subscriber will have a personal interactive VSAT terminal capable of receiving downloaded data at high speed, but will transmit at lower rates. Both reception and transmission will be at Ku or Ka band. |
