Q-LAN Networking

Q-SYS is a system that performs complex routing, processing and management of audio in a facility. The elements of a Q-SYS system include:

The Core is based on an Intel™ server processor. It runs the system and handles the signal processing and control functions.
I/O Frames are connected to the Core via the network and provide a means for audio signals to be brought into the Core from analog and digital sources as well as sending the processed audio to power amplifiers, powered loudspeakers or other audio devices. The I/O Frames are fitted with cards appropriate to the types of inputs and outputs they receive or send.
Peripheral devices including Page Stations, Touchscreen Controllers, iPads, and iPhones may also be used in a system.
Q-SYS Designer software is used by the audio system designer to create signal flows, processing, and control screens for a system.

Basic Network Layout

Layer-3 Networking

All Q-SYS network protocols are Internet Protocol (IP) based and support advanced networks beyond the simple Ethernet Local Area Network (LAN). Because Q-SYS is a system for live audio, real-time performance is required on both the LAN and the IP environments. In an IP network, routers replace some, or all, of the network switches. Therefore, routers need to provide the same level of performance as the switches they replace.

NOTE: In Q-SYS Designer, you can use the Core’s Network Receive Buffer setting to relax network real-time performance requirements at the expense of increased audio latency through the network.

Layer-3 IP networks have advantages in manageability, scalability, security and convergence over their LAN counterparts. If yours is a large, critical and shared network, it is likely your application will benefit greatly from layer-3 networking.

Layer-3 networks handle QoS and multicast routing in a more engineered manner.

Audio Streaming

Audio is transmitted in streams. A stream is an ongoing series of packets. Each packet contains 16 audio samples for each of up to 16 audio channels. Samples are in 32-bit floating point format. The maximum total payload size, including overhead, for an audio stream packet is therefore 1100 bytes (octets).

A Q-SYS Core may generate and receive up to 128 audio streams. An I/O Frame or Page Station receives and transmits a single stream.

Sample Rate

All streams for a system operate synchronously at the same sample rate. The only sample rate currently supported is 48 kHz. In the future, QSC may add other sample rate and data format options to the protocol.

Networked Hardware

Hardware found in a Q-SYS System, requiring a connection to the Q-LAN network, includes:

Q-SYS Core - One Core is required, a second Core for redundancy is an option. Each core has two Ethernet connections.
Q-SYS I/O Frame - Can have none to many, with optional redundancy for each. Each I/O Frame has two Ethernet connections.
Microsoft Windows-based PC running Q-SYS Designer - optional
Gigabit Ethernet Switch(es)
Q-SYS Touchscreen Controller - optional
About touchscreen LAN connections
The TSC-3 and TSC-47w-G2 touchscreen controllers must be connected to the LAN A network. These touchscreens cannot boot from the LAN B or AUX networks.
QSC Wall Control Plate - optional
Q-SYS Page Station - optional
Third-party Control System - optional

Hard Links

You can configure your PC-based Q-SYS Designer or UCI Viewer, and Apple iPad/iPhone to discover and connect to a remotely located Core. The device must have network connectivity with the Core(s) to which you wish to gain remote access. This can be via VPN or some other method suggested by your friendly network administrator.

A Hard Link is the IP address of the Core to which you wish to connect. You may include multiple IP addresses.

Network Specifications

The Q-SYS Q-LAN network communicates control information, streaming audio, and synchronization for a Q-SYS audio system.

1 Gigabit Ethernet
32-bit floating-point audio format
Redundancy - optional
1 to 16 channels per audio stream

Latency

Configurable from 2.5 to 4.5 ms end-to-end.
Higher latency settings are provided to accommodate larger networks with higher forwarding delay.
To achieve the 2.5 ms system audio latency, audio packets must always get across the network in 234 ms or less. Network equipment must meet the Q-LAN requirements (see Ethernet Switches) and the network must meet the construction requirements (see Network Topology).

Bandwidth

1.65 to 3.31 Mb bandwidth per channel (dependent on the number of channels per stream). Redundant streaming configurations require this bandwidth on two Ethernet ports.
The formula for determining total bandwidth per port is: Mb = ( 1.77 * total stream count ) + ( 1.54 * total channel count )
In most cases control communications consumes less than 1 Mbps. In cases involving redundant Cores and active external controllers (e.g. AMX or Crestron), control bandwidth requirements can be substantially higher, up to 6 Mbps.
You can check your Core's bandwidth calculations on the Check Design dialog in Q-SYS Designer. (File > Check Design... or press Shift-F6)

Q-LAN Protocol Suite

The Q-SYS Q-LAN network uses the following standards:

QoS (Quality of Service)

Quality of service (QoS) allows different traffic streams to receive different treatment on the network depending on their stated relative priorities. QoS is required in the Q-LAN network to prevent non-real-time control and bulk communications from affecting performance of time-sensitive clock and audio-stream traffic. Network performance analysis and specifications are predicated on a QoS mechanism to differentiate and, to a great extent, isolate the different types of traffic on the network.

QoS ensures timely delivery of network data including audio. The Q-LAN network must be configured to prioritize traffic according to Q-SYS QoS classifications.

Prioritization

Q-SYS uses the DSCP field in the IP header to specify traffic priority to the network. The network must inspect, distinguish, and prioritize the following three traffic classes.

Q-SYS Priority	DSCP Assignment	Traffic Type
Highest	46 (101110) - Expedited forwarding (RFC 3246)	Clock distribution
High middle	34 (100010) - Highest priority (AF41) Assured forwarding (see RFC 2597)	Audio streams
Lowest	0 (000000) - Default (best effort) per-hop behavior (RFC 2474)	Control and management traffic (everything else)

Network administrators may choose to trust the DSCP values transmitted by Q-SYS or alternatively reassign new DSCP values based on these values or other distinguishing traffic characteristics. As long as traffic is properly prioritized, it is not necessary to preserve these exact DSCP values through the network.

Flow Control

Flow control protocols (principally 802.3x) are used to prevent input buffer overflows. Modern switches have adequate internal bandwidth such that input buffer overflow is not typically a concern. 802.3x flow control is considered by many network vendors to be a relic. Switches with bandwidth meeting or exceeding wire speed should never have occasion to initiate flow control. The assumption is that the Q-SYS wire-speed requirement implies that switches in a Q-SYS network will never invoke flow control.

Jumbo Packets

Network performance criteria for Q-LAN require no jumbo packet through all audio paths on the network. The presence of jumbo packets on Q-LAN-shared network links, even if on a separate VLAN, introduces additional network latencies making a single switch hop produce the same delay and delay variation as 6 switch hops with standard framing.

Jumbo packets will only be present on a network if network equipment is configured to pass them and end stations are configured to generate them. Fortunately, managed switches typically ship with jumbo-packet support disabled by factory default. End stations such as routers and servers also generally ship with jumbo packets disabled. A concerted and systematic configuration effort is required to enable jumbo packets on a network.

Addressing

Since all Q-SYS networking is IP based, each Q-SYS component must be assigned an IP address. Q-SYS supports several means for IP configuration.

DHCP
IPv4LL (Auto-IP)
Static IP
IP routes may be manually configured

A manually configured static IP assignment is generally preferred for critical equipment such as Q-SYS. Auto-IP adds a significant delay during startup and offers only limited connectivity. When working properly, DHCP does not add significant delay to startup but, depending on configuration of DHCP services on a network, could constitute an (external) single point of failure for your audio system. With either DHCP or Auto-IP, there is the potential for the IP address in use to need to be reassigned. Such reassignment will cause, at minimum, a momentary a disruption in audio service.

End-Point Device Routing

End-point device routing allows a device on one subnet to communicate with a device on separate subnet. There are two methods used to accomplish this task - a static route or the default gateway. A static route defines a specific destination/mask pair. The default gateway is a “catchall” for everything which doesn’t match a static route. Below is an example of a static routing configuration using Q-SYS Configurator in Q-SYS Designer.

Multicast Routing

For Q-SYS to work across a layer-3 network, the network must be configured to route the multicast addresses used by clock distribution and discovery protocols. Q-SYS devices implement the Internet Group Management Protocol (IGMP). IGMP allows network devices to register to receive specific multicast addresses. You can meet Q-SYS multicast routing requirements most easily on a layer-3 network with network equipment supporting IGMP and configured to enable multicast routing. Security policy may require tightening of multicast routing service around Q-SYS requirements. The following IP multicast addresses are used by Q-SYS.

224.0.1.129 - 224.0.1.132– IEEE 1588 - registered to IEEE
224.0.23.175 - QDP Device Discovery - registered to QSC

Ethernet Switch Requirements

For a list of Qualified and Unqualified Switches, refer to the Ethernet Switches topic.

Switches used with a Q-SYS system must meet the following minimum requirements:

Non-blocking wire-speed gigabit Ethernet bridging
- No dropped packets due to internal bandwidth constraints
- Generates no 802.3x flow control messages
At least 80 kB total egress buffering available for audio class of service with minimum of 40 kB dynamically available, for the audio class, per port.
Packet forwarding decision time of 10 ms or less ¹
DiffServ (DSCP) support
- Minimum four egress queues per port
- Ability to recognize and prioritize two high priority traffic classes by DSCP values or other means in addition to best-effort traffic. Refer to Prioritization for details.
- Strict priority queuing support (weighted round robin, weighted fair queuing, or other selection methods do not provide the latency guarantees required by Q-LAN)

1. Forwarding decision time is defined as the time from end of the packet on ingress to the beginning of the packet on egress. Forwarding decidion time excludes the store-forward time due to packet length.

Network Topology

No more than 7 hops between any two points with up to 100 meters between switches (Refer to the table below for more detail)
Network diameter limit of 29 kilometers for three-hop Core-switched network

NOTE: To measure the network diameter, measure between the two nodes with the longest physical path in the network.

Network diameter limit of 22 kilometers for four-hop redundant Core-switched network.
Backbone bandwidth
- 1-Gigabit backbone bandwidth for systems not utilizing audio stream redundancy (no LAN B connections)
- 1-Gigabit backbone bandwidth on each network for installations using separate networks for redundancy
- 2-Gigabit backbone bandwidth required for installations using redundant connections to a single audio network
No jumbo frames on any Q-LAN paths

Example Network Configurations

The following are general examples of networks meeting the network topology requirements. Other configurations are possible and would have different requirements based on the individual configuration.

Designers are free to use 10 Gigabit in place of 1 Gigabit while following the 1 Gigabit design rules.

Hop count is defined as how many switches there are between two system nodes.

System Limitations

Channel Capacity

Core Type	Core Model	Local I/O Channels	Network Audio Channels	AEC Processors	Multitrack Audio Players	Local I/O Card Capacity	VoIP Instances
Unified Core (small scale)	Core 110	24 8 analog in, 8 analog out, 8 analog flex in/out, 16x16 USB audio	128 x 128¹	16	16 (upgradable to 32)	N/A (Built-in I/O on this model)	4
Integrated Cores (medium scale)	Core 500i	Up to 32 analog, up to 128x128 AES/CobraNet/ Dante/AVB	128 flex in/out	24	16 (upgradable to 128)	8	64
Integrated Cores (medium scale)	Core 510i	Up to 32 analog, up to 128x128 AES/CobraNet/ Dante/AVB	256 x 256	64	16 (upgradable to 128)	8	64
Enterprise Cores (large scale)	Core 1100	Up to 4 analog, up to 16 AES, up to 64x64 CobraNet/Dante/AVB	256 x 256	72	16 (upgradable to 128)	1	64
Enterprise Cores (large scale)	Core 3100	Up to 4 analog, up to 16 AES, up to 64x64 CobraNet/Dante/AVB	512 x 512	144	16 (upgradable to 128)	1	64
Dell Enterprise Cores (IT friendly)	Core 5200	N / A	512 x 512	160	16 (upgradable to 128	N / A	64
1. When using the Core 110f on-board USB Device Port for video bridging, the Q-LAN / AES67 maximum audio channel count is 64 x 64.

The Core has the following capacity constraints:

Core channel capacity is as listed in the table above.
Core capacity (Core 4000) is further constrained to 128 streams in and 128 streams out. 128 streams correspond to 384,000 packets/second.
Streams may carry 1 to 16 channels of audio each.
An arbitrary mixture of different sized streams is permitted.
It is a considered a configuration error for a GbE link to be burdened at greater than 90% utilization. Overhead in headers becomes significant for smaller streams and therefore the 90% limit becomes a significant constraint for smaller streams.

NOTE: You can check your design for these parameters by selecting File > Check Design... or by pressing Shift-F6.