Aethra Theseus User Manual download pdf (Page 8)

8/30 Video Conferencing over BGAN

available bandwidth. A Variable bit rate solution has the capability to throttle back when it detects

any packet drop or loss, which typically occurs when IP traffic travels through a series of Internet

routers. This throttling back reduces the speed of data transmission and results in loss of video

quality. Variable bit rate solutions are therefore more suitable for a standard IP connection than a

streaming IP connection.

3.4. Introducing protocols

Inmarsat recommends that you use a streaming IP connection to send and receive video data. A

number of protocols can be used alongside the streaming connection to control the data flow and

provide additional video broadcasting capabilities.

The following two transport protocols are for the general transmission of data over IP:

• TCP

• UDP

Protocols that are specific to video solutions over IP are relatively new, and still evolving. The

following two main sets of call control protocol are in use by the Internet at the time of publication:

• H.323

• SIP

All these protocols are described below.

TCP and UDP

TCP and UDP are transport protocols that are used to transmit data over IP connections. The TCP

protocol is configured to deliver data from end to end in a reliable manner. It is connection-

oriented, and provides flow control and retransmission of lost packets. The UDP protocol is

connectionless, and does not guarantee reliability, flow control or detection of lost packets but

designed for faster delivery.

TCP/IP application will be more effective over Standard IP due to the nature of BGAN Standard IP

service. Typical corporate application i.e. Email, Web browsing, FTP etc uses TCP

UDP is more suited to Streaming IP because if packets are lost, they are ignored and packet

transmission continues. This may cause a slight loss of quality in the transmission, but the

transmission is not interrupted. If the same packets were lost over a TCP connection, TCP would

stop delivery of further packets until the lost packets are successfully been retransmitted. This

would cause an unacceptable break in the flow of the application.

Therefore, UDP thus gives streaming applications greater control over the data flow than TCP.

These characteristics mean that majority of the audio video applications use a combination of TCP

and UDP where needed. Typically, call set-up and data flow control is carried out using TCP. The

audio and video data is sent using UDP.

TIP: BGAN LaunchPad allows the configuration of error correction. Inmarsat

recommends that you disable error correction for UDP applications, and use

UDP applications over streaming IP service. Refer to “BGAN LaunchPad Help”

for details.

H.323

The H.323 protocol is defined by the ITU-T (International Telecommunications Union). It describes

how real-time multimedia communications can be exchanged on packet-based networks. The

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Aethra Theseus User Manual Page 8