Welcome to this course on Layer 2 Multimedia Network transmission. In this course we shall look at the two most important standards-based layer 2 technologies for the transmission of audio and video data, namely Firewire (IEEE 1394) and Ethernet AVB (IEEE 802.1(x) and IEEE 1722(x)). Ethernet AVB has been adopted by most major Ethernet switch manufacturers, who are manufacturing switches that comply with the Ethernet AVB standards documents. We shall also look at the Audio Engineering Society's draft standard X170 for the connection management and control of devices on either of the above-mentioned layer 2 technologies. We shall focus particularly on the transmission of audio, since the transmission of digital audio presents a number of interesting challenges.

Course Layout

Configurations:

To start with we shall look at a simple Firewire configuration and a simple Ethernet AVB configuration and see how to manage the streaming of stereo audio between two devices. We shall use the Unos Creator application to set up the streams. We shall look at the high level use of Ethernet AVB switches and Firewire routers.

Stream formats:

Following this, we shall have a close look at the nature of the Firewire and Ethernet AVB streams that carry the audio and video data between end points, via bridges and routers. We shall relate our low level knowledge of stream formats to the high level connection management concepts seen in Unos Creator.

Bandwidth reservation:

A major feature of both Firewire and Ethernet AVB is that they enable the deterministic transmission of multimedia streams – audio samples will reach their destination within a prescribed time frame. We shall look at mechanisms in both Firewire and Ethernet AVB to reserve bandwidth and thereby guarantee deterministic transmission.

Global time:

When a Firewire or Ethernet AVB transmitter sends multimedia data to a receiver, it time stamps this data with a time at which the data should be played out by the receiver device. The intervals between the time stamps will reflect the intervals between the receipt of chunks of multimedia data by the transmitter. These intervals can be relayed to the receiver, allowing for example a word clock to be reconstituted on the receiver side. For this time stamping mechanism to work, all devices must have the same global time. We shall look at the mechanisms within Firewire and Ethernet AVB systems to enable this common time.

Device Discovery:

When a control application such as Unos Creator starts up, it has to discover devices on the network. We shall look at the approach that AES X170 takes to device discovery. We shall then look at the IEEE 1722.1 specification and its approach to device discovery.

Connection management and control parameters provided by AES X170:

There are a number of connection management and control protocols for the routing of multimedia and the control of various parameters within devices. We shall look at the features provided by the X170 connection management and control protocol. In particular we shall look at the connection management parameters provided for Firewire and Ethernet AVB connection management. We shall look at the capabilities of the X170 stack that allow for the creation of such parameters and the receipt of messages to access the parameters.