Many broadcast networks have already transitioned from copper Telco infrastructure to IP networks for provision of trunks used for broadcast communications. However, in some countries many links are still provided over POTS or ISDN copper services, but with rising service costs, and diminishing availability, these need to be migrated to maintain connectivity. Thankfully, there are many proven IP solutions that will facilitate a smooth transition and deliver better quality, higher reliability, and increased flexibility.
SIP Trunk Gateways
AoIP infrastructure within the broadcast plant operates over managed AES67, ST 2110-30 and ST 2022-7 compliant multicast networks. Devices at the edge of the network, like audio codecs, bridge between the broadcast plant, other studios (inter-studio links), production facilities and live events. These codecs are often associated with facilitating studio-to-transmitter links, outside broadcast links and other audio contribution use cases. They support IP streams traversing lossy WANs like the internet and integrate with managed AoIP networks at the studio.
With POTS and ISDN lines being deprecated, IP audio codecs are ideal to use as SIP trunks that handle audio encoding and decoding, bridging between studio AoIP audio infrastructure and VoIP infrastructure like SIP servers or cloud-based PBXs. Codecs using SIP (Session Initiation Protocol) can:
- Register to SIP server accounts or cloud PBXs for routing of calls
- Dial directly peer-to-peer with SIP
- Integrate flexibly with existing IP communications systems, e.g. Riedel, Clear-Com and RTS at the studio
Tieline Gateway IP codecs support up to 16 bidirectional SIP connections using Opus or a variety of other algorithms. Each connection can be registered with, and routed via, different SIP server accounts. Gateway is also compliant with I3P EBU334 requirements for interoperability of AoIP production intercoms.
SIP Trunk Options
Traditionally, trunks referred to physical copper phone lines. In the context of audio codecs, SIP trunks are virtual lines that replace copper phone lines as follows:
- Replacement of old POTS and ISDN 4-wire circuits for outside broadcasts and at stadia for live events.
- Replacement of fixed-line POTS and ISDN lines providing IFB circuits for live crosses.
- Integrating bidirectional communication circuits using cell-phones with SIP apps or proprietary apps like Tieline’s Report-IT Enterprise.
- Using SIP apps or Report-IT Enterprise to provide IFB to reporters for live crosses.
SIP calls received at the studio can be routed into existing IP communications systems for direct communications between endpoints, or integration into 4-wire communications. Codec GPIOs can also deliver flexible routing and control functionality.
Protocol flexibility is important when selecting a codec. This facilitates connecting and streaming between equipment from different vendors using a variety of open standard and proprietary protocols. Look for codecs that support RAVENNA, Dante, Livewire+, Ember+, NMOS, and WheatNet-IP. This will deliver more flexibility when integrating IP audio streams into the broadcast plant from a range of sources.
SIP Trunk Benefits
There are several benefits of using codecs for SIP trunks compared to traditional POTS and ISDN lines. These include:
- Flexibility and scalability: Setup and maintenance of links is simpler – add additional SIP trunks as required.
- Lower Operational Costs: IP connections are cheaper than expensive fixed line Telco charges.
- Higher Audio Quality: SIP can improve audio quality when compared to phone lines.
- Redundancy: SIP trunks can be configured with failover and backup connections.
When increased flexibility and operational cost savings are considered, the advantages of SIP over legacy copper networks are significant. The other major advantage is the ability to remotely control and configure connections using codec management software. There is no need to contact telcos to install or book lines with all links transmitted over regular IP network connections. For example, Tieline codecs offer HTML5 browser-based control of individual codecs and optional Cloud Codec Controller software can manage an entire network of codecs from anywhere with an internet connection.
In summary, IP connections are now so reliable over WANs that they are widely accepted as the primary way to distribute audio. Therefore, it’s wise to consider SIP to replace your soon-to-be obsolete copper lines before it’s too late.
(“Gateway Provides SIP Trunk Flexibility” first published in InBroadcast magazine September, 2025)
