Computer Networks – Multimedia
October 22, 2009 Leave a comment
What is Multimedia?
So what exactly is multimedia? well the truth is – nobody knows!! This is because its nothing but binary data – except for audio and video which varies, and is commonly in analogue.
Text and Pictures, which in there basic form is often digital.
Animations, Movies and Sounds, which – like mentioned above, there common form is often analogue – to merge them with text and images, then it must be converted to digital.
Some of the farfetched multimedia’s could include sense of smell and sight – yeah right -.-‘
There are loads of types of multimedia networks, but some of the basic types are:
- Telephones ( like the old, old, old phones )
- Broadcast Television
- All of this converges to Broadband Multiservice Networks.
All transfer of media takes time, and is very delay sensitive. With this comes loss of tolerant.
Now, this should be obvious, but media transfer is obviously different to:
- Web, Email, FTP and Telnet / RSH / SSH
A telephone network is known as Plain Old Telephone Service – POTS. This is from the old phones back in the day, when the phones were connected directly to the exchange via a copper wire. Then, at the exchange, the calls would be met by a Circuit Switch – contiguous circuit from source to sink.
Cellular Mobile Phones
Unlike the phones back in the day, phones – especially mobile phones – are all digital, with a high (ish…) bit rate.
This really should be obvious… the Internet! As well as things such as LANs, WANs and MANs.
All the data that is sent over these networks are in “packet mode”.
a simple approach is a client-server system.
Things such as audio or video is stored inside a file. These files are transferred as HTTP objects that are imbedded in TCP.
This kind of approach sucks for streaming, as there is a huge delay before playback, so it would suck for YouTube!
Streaming Live Multimedia
All live multimedia is streamed, and this involves a playback buffer. This playback can lag tens of seconds after transmission.
Because this form of media is Live, it is impossible to fast forward – unless you’re Hiro from Heroes o_O. However, we can pause and rewind this live streaming.
The rest of the streaming slides are a little…. meh….
Real-Time Interactive Multimedia
Such applications of this type of multimedia are IP telephony, video conferencing and distributed interactive worlds.
End to end delay requirements:
- Audio: <150ms and Video: <400ms
Internet Phone: Packet Loss and Delay
All Internet Phones have problems, such as Skype and Ventrilo. Such things that can be lost are:
- Network Loss: IP datagram lost due to network congestion (router buffer overflow)
- Delay Loss: IP datagram arrives too late for play out at the receiver. This delays things such as processing and queuing in networks
- Loss Tolerance: depending on voice encoding, losses concealed, packet loss rates between 1% and 10% can be tolerated.
This continues inside “Play-Out Delay”