Satellite: A New Opportunity For Broadband Applications
This chapter is a look at the way in which satellite providers have evolved to serve the residential market, with an eye toward those who are outside the areas in which connection via cable is feasible.
Satellite Delivery Systems
There are three classifications of system:
- A one-way system, in which data is sent to a receiving station and no data can be transmitted back the other way
- A hybrid system in which data is sent to a receiving station and data transmitted from the remote station is sent back via another channel (generally telephone)
- A two-way system in which information can be sent from base station to remote, or back from remote to base station, via the satellite
The main advantage of a hybrid system is that there is a lower cost to provision it (the base station does not need to be configured to accept inbound traffic via satellite, not does the remote station have to have broadcast power via that channel) - though its obvious weakness is the reliance on a surface network for upstream communication.
Attributes & Characteristics
Generally, a satellite has asynchronous data communications, with massive downstream capacity but limited upstream capacity, even when the communication is two-way.
Satellites currently have a very large footprint: a single satellite can reach an entire continent, or an entire hemisphere, and communication can be beamed from one satellite to another (rather than rely on terrestrial lines) to completely cover the globe.
The cost of providing access is distance-independent: whether a receiving station is five feet or a thousand miles from the base station, the costs of setting up a satellite uplink are the same.
Applications
Currently, satellites are used for broadcast (a single packet is intended for all users), multicast (a single packet is intended for a group of users), and uncast (a single packet is intended for a single user).
Specifically, the following applications are currently being used:
- Broadcast and multicast: Digital TV and radio, business TV, video streaming, news tickers, content delivery, software updates, caching,
- Web browsing, FTP, e-mail, voice, gaming, video-on-demand
Any packet transmitted is available to all users, though it may be intended only for some (or one). Receiving equipment is tuned only to receive only those packets that are applicable, and encryption technology attempts to prevent unauthorized access.
Security Design Considerations
On the topic of unauthorized access, security is a concern with satellite transmission. On terrestrial networks, access is controlled by physical connection to the network, and each hub on a network sorts out traffic and directs it to its intended users, so it requires physical access to the network to intercept traffic.
Satellite is essentially like radio - everyone receives the signal - including both signals transmitted from base to receivers as well as from each receiver back to the base.
Encryption is the primary form of access restriction - while any remote station can receive a packet, only those who can decrypt it can access the real information it contains.
Firewalls are also important to protect one's own received station from unauthorized transmissions, such that while packets from all sources are received, any that come from unknown or un-trusted sources are discarded rather than interpreted.
As with wired networks, these two basic security measures can be rigged to provide virtual private networks, secure point-to-point connections, and the like.