Radio over IP (RoIP) is a generic term that describes
the application of Voice over IP (VoIP) on two-way
radio networks. So all digital radio networks with IP
connectivity use RoIP.
For radio fleet operators, RoIP can lower costs, improve
reliability and increase interoperability in the following
• access to remote radios,
• point-to-point, point-to-multipoint and cross-band
• radio-to-dispatch console links,
• radio-to-telephone gateway,
• by reducing cabling.
All of these applications utilize IP infrastructure –
the IP backbones that make up both local and wide
Originally designed as a telephone replacement, VoIP
allowed large service providers to connect many users
for voice communications on demand. VoIP and RoIP
use the same mechanism to transmit voice or audio data.
However, radio has additional capabilities when it comes
to signalling and control.
• Push-to-Talk (PTT) indicates the radio should
transmit and must be synchronized with the audio,
• Carrier Operated Switch (COS) from the radio
generates a busy signal or keys up another
• Type of call in progress (Broadcast, Group or
• Radio identification,
• Advanced radio features (Stun, Revive, Remote
• Channel profile change (can include frequency and
other operating parameters).
Using VoIP standards to implement RoIP provides
several advantages. They improve vendor-independent
interoperability and integrate radio networks easily with
existing phone and voice systems. They are compatible
with off-the-shelf voice recorders, routers, firewalls and
There are many standards that are relevant to voice
and multimedia communications, none of which are
interoperable. However, SIP and RTP are common
protocols. DMR (AIS) and APCO P25 (DFSI, ISSI and
CSSI) standards use both RTP and SIP.
Session Initiated Protocol (SIP)
SIP is a standard protocol used to set up and disconnect
VoIP calls. It determines IP addresses of remote devices
and UDP Port Numbers for RTP and negotiates which
features can be used. No audio is transmitted via SIP.