Satellite Broadcast Networks

In the past, satellite links have been used for international telecommunications and broadcasting. Recently, there’s been a surge in sending Internet Protocol packets over satellite networks. These packets may carry voice, video, or data information. New applications include: military, security, satellite radio, satellite phones, satellite TV, disaster recovery, branch office communications, distance learning, video conferencing, and telematics services.

The figure above illustrates a simple satellite network. The data network clouds could be a LAN or a WAN. The network of three satellites can be viewed as another WAN cloud since they will cause impairments to occur such as delay, jitter, packet loss, and bit errors. Therefore for end to end transmission between the PC’s, packets will transverse three network clouds.

These new digital satellite applications can be divided into two groups: UDP (User Datagram Protocol) and TCP (Transmission Control Protocol). UDP is a connectionless protocol with few error recovery mechanisms. Real time applications like voice and video can’t wait for recovery mechanisms such as retransmissions and therefore use UDP to transport their packets. UDP performance across a satellite network is generalized as having:

  • Large delay dependent on the height of the satellite’s orbit and the number of satellite hops
  • fading RF channel environment resulting in a bursty and high BER data communications channel

Unlike UDP, TCP guarantees delivery and order of packets to the higher layers of the communications stack. TCP applications include disaster recovery, data transfers, and branch office communicationssuch as e-mail. TCP performance across a satellite network is generalized as having:

  • Large variations in round trip packet time resulting in false TCP windowing time-outs and false retransmissions
  • fading RF channel environment resulting in a bursty and high BER data communications channel

The most likely impairments to occur in a satellite link are: delay, jitter, lost packets, and bit errors. To emulate the real world as closely as possible, the jitter needs to be random without any packets getting out of order. This is true because packets have only one path between the transmitter and receiver of the satellite link. Ideally, the inter-packet jitter should be specified to accurately test the satellite receiver.

No matter if the application is for homeland security, IT infrastructure, or media broadcast, satellite systems severely stress Internet Protocol applications with delay, jitter, loss, and bit errors. PacketStorm emulators provide a repeatable and accurate method to optimize the satellite application or network in the lab. By emulating real life measurements, PacketStorm emulators thoroughly test applications before they’re utilized in the satellite network.

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