AUDIO NETWORKING OVERVIEW by Canford Audio

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AUDIO NETWORKING OVERVIEW Multimedia networks synopsis Long distance communications have been an obsession of humanity for a long time, with the earliest methods of relaying messages consisting of smoke signals or drumming. Although primitive these methods use an agreed standard between transmitter and receiver, encoding and decoding a message which is the basic principle still used today. In 1451 Johannes Gutenberg invented the printing press, allowing widespread access to mobile information, exampling the “one-to-many” motive in communication. 1844 introduced the Telegraph, after Samuel Morse and his colleague’s relayed electrical impulses “Morse code”. The telephone, developed by Graham Bell in 1876, domesticated by the 1940s, transmitted the human voice on shared party lines. The journey to modern telecommunications is punctuated not only with major milestones but also with ideas that were ahead of their time. For instance, Bell’s wireless telephone call in 1880 eventually led to today’s fibre optics. Traditionally in the analogue world, sending an audio signal from one device to another requires cables capable of transporting the voltage differentiation of a transduced signal. Consisting of one physical line of one way traffic from each source to their respective destinations. In the digital networking domain, the same is true but signals are transcoded into a binary format, which is then wrapped in a codex protocol. Allowing multiple channels of data to not only be sent down the same line but generally, a line of smaller size, substituting the use of bulky multicores with one or two low profile data cables. Basics of networking There are now several AoIP’s (Audio over Internet protocol) available, each provides a different service depending upon

the application for different infrastructure and bandwidth requirements. It is therefore important to understand the nuances of each, ensuring we have appropriate networks before embarking on any AoIP deployment. Based on the French scientific network “Cyclades“, developed in the 1970s, a modern network is a group of devices that can communicate with each other. With each device acting as a node, inter-connected between network types. The underlying theoretical model for networking is the Open Systems Interconnection (OSI), developed by the International Organization for Standardization (ISO) that splits up the functions of network communication into seven layers. TCP/IP is also a layered protocol, with equivalent operation and function to the ISO model. Developed by the Department of Defence’s (DoD) Advanced Research Projects Agency (ARPA). Today, it is the main protocol used for all Internet operations. TCP/IP

OSI

Defines interface to user processes for communication and data transfer.

7 Application 6 Presentatio

Applicatio

Translates data between a networking service and an application. Managing communication sessions exchange of information between two nodes.

5 Session 4 Transport

Internet

Outlines reliable and sequential packet delivery of end-to-end message delivery.

3 Networ

Transport

Under the umbrella of IP internet protocol, it structures and manages a multi-node network.

2 Data link 1 Physical

Network

Utilises the MAC address with the transmission of data frames between two physically connected nodes. Depicts the transmission and reception of raw bit streams over physical medium between devices.

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canford.co.uk As protocols, TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are used to control data in the 3rd Layer of OSI model, determining what kind of connection is to be established whether ConnectionOriented or Connection-Less. Connection-Oriented or TCP/IP protocol is used when there is an established session retransmitting lost packets. Whereas Connection-Less or UDP/IP (User Datagram Protocol) protocol provides constant streams with no retransmission. Networked audio standards Since the evolution of digital transmission thus the inerrant implementation of audio across a network, there have been many protocols designed to tackle handling audio across a network. Minimising packet loss and or buffer time that would be more acceptable to straight data transferring examples. To date, networks are Standardised by SMTPE 2022-6 allowing deployment of IP infrastructures and realizing operational efficiencies such as SMPTE 2110, which provides an ‘essence based’ approach by separating audio, video and metadata into separate streams. The most common audio protocols occupying layers 1, 2 and 3 of the ISO model are: Layer 1: AES10 “MADI” (Multichannel Audio Digital Interface), developed in 1991 by AES (Audio Engineering Society) as a means to transport bi-directional audio. Layer 2: IEEE802, Audio Video Bridging (AVB), developed in 2011 by the Institute of Electrical and Electronics Engineers (IEEE) specifies the operation of Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networked audio. Layer 3: AES67 encompassing: Ravenna, developed in 2010 by ALC NetworX is a technology for real-time transport of audio and other media data in IP-based network environments. DANTE (Digital Audio Network through Ethernet), developed in 2006 by Audinate, as a combination of hardware and software used to transport multi-channel, digital audio over a standard Ethernet network. Whilst AES67 looks set to be the preferred AoIP standard, broadcasters use a variety of protocols across the industry and see the importance to continued development and support for AoIP solutions such as Dante networks. Cabling, bandwidths & data rates Networks generally use CAT5 or higher cables, with the original CAT5 standard was designed to carry 10 Mb and 100 Mb signals, yet the demand quickly grew for 1 GB compatibility, consequently, CAT5e offers 1 GB support as an enhanced standard. Sequentially the introduction of CAT6 offered a more stable 1 GB line, achieved through more twist per meter and separation between twisted pairs. The latest standard, CAT7 adding an individual shield for each pair, boasting 10 GB compatibilities.

When caballing for AoIP networks the use of gigabit switches in a dedicated network is recommended, while MADI, Ether Sound, and many other formats are 100 Mb, Dante is 1 GB of which the best results are found from a dedicated network, using switches with a capacity equalled to two times the number of ports. Cabling to a maximum length of 60 meters between nodes when using copper stranded cable and up to 100m (suggested the best performance at 70 meters) for solid copper core cabling, CAT5e or higher. Greater distances can be achieved through the implementation of additional switches and or active optical cabling, yet the actual potential transmission distance varies, dependant on factors such as the cable environment and termination quality.

100Mbps

Audio channels: bi-directional:

Gigabit

48 x 48 48 kHz/24bit

512 x 512 48 kHz/24bit

1024

For 96 kHz 24 bit audio the channel capacity is halved. When installing an AoIP system, a dedicated network infrastructure is recommended but not required. As an example, Dante-enabled devices can happily co-exist on an existing converged data network. Using standard Voice over IP (VoIP) Quality of Service (QoS) switch features to prioritize audio traffic using what are called DSCP/Diffserv values. In contrast, a low load on a full Gigabit network will function without QoS. As load increases, QoS will aid in a better system performance, outlined by the following procedure table. However, for the best performance, a dedicated network is suggested.

Priority

Usage

DSCP Label

HEX

Decimal

Binary

High

Time critical PTP

CS7

0x38

111000

Medium

Audio, PTP

0x2E

101110

Low

(Reserved)

CS1

0X08

001000

None

Other traffic

Best effort

0X00

000000

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