105
Bandwidth, Inter-Switch Links and Larger Networks
Network topology and bandwidth management are impacted not just by the quantity, but also by the physical location of devices.
Each copper Ethernet cable should be less than 100m total length (factoring in cable routing and looming, so often 90m is quoted).
Fibre SFP ports or additional switch hops need to be used to extend the range beyond 100m.
Where switches are connected together, one should be mindful of the bandwidth available on the inter-switch links.
Multiple links can be fitted between switches as trunks to increase bandwidth (switches need to be appropriately configured to
support such connections using LACP link aggregation), and many switches have a pair or more of SFP slots that are capable of
higher bandwidth, intended to be used to connect to other switches.
On the 10 (8+2) port Quarra switches that Calrec currently use, 2 of the ports are SFP slots that can be fitted with either 1Gbps or
2.5Gbps SFP interfaces. Note that switches are not supplied with the SFP interfaces.
As a general rule of thumb for AoIP, audio traffic should not exceed roughly 50% of the capacity on a link.
This broadly equates to 256 channels of audio over a 1Gbps link. This is a somewhat conservative guideline, but it is a safe
recommendation for critical live audio application such as broadcast.
Audio is not the only data being passed, even on a dedicated audio network there is still additional traffic. Higher channel counts can
be achieved, but deterministic network conditions are required to successfully exceed the safe working recommendations.
Type R Cores can pass up to 256 audio channels over each AoIP Interface card.
Using 32 x 8 channel streams (at 32 bit / 48kHz / 125us packet time), the bandwidth consumption of audio for each port would be
554Mbps. With 2 cards fitted, the overall audio consumption of a Type R core can potentially be more than 1Gbps
If large amounts of audio/data have to pass over a given network segment such as an inter-switch link, then higher bandwidth SFPs
should be used for those segments (or multiple aggregated links).
Type R I/O boxes have a single redundant pair of AoIP ports, capable of passing up to 64 channels of audio.
As the largest Type R I/O boxes only have 16 channels of physical audio I/O ports, typical actual usage would be only 35Mbps.
If required, audio bandwidth can be reduced by using a 1ms packet time (at the cost of increased latency), or by using 24 bit audio
(sacrificing the additional headroom we provide for our mic inputs).
For larger networks with lots of switches, instead of daisy-chaining them together, they should connect via an additional switch, as
shown in Examples 6, 7, 11, 12 and 13, in order to limit the number of switches that data has to pass through to get from point A to
point B, providing more uniform latency, and making bandwidth simpler to manage.
The dotted lines shown in Example 6 represent the option to increase bandwidth on switch links through aggregation if needed.
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