Communications System Design
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The most compelling reason to consider basing the next radio control system upgrade on VoIP technology is the simplification
in wiring requirements. Instead of needing to bring a pair or more of wires, per channel, to each console, only a single
connection to the Ethernet is required. Since Ethernet can easily handle dozens of simultaneous connections, it becomes the
only pipeline required for all communications.
Network Requirements
IP Operation Overview
The network options today have essentially converged on Ethernet. A local electronics store may sell many of the components
for both a wired or wireless network solution. For more advanced network applications, an in-house or external network
hardware source may be required. These sources of information can also help with the design of the network, as well as
provide sources for advanced networking equipment, such as routers and hubs from Cisco and other network vendors. This
section is an overview of the protocols operating on the top of the Ethernet network.
Ethernet as Physical Layer
Ethernet is a network and has a low level method for transferring data from one (1) location to another. Source and
destinations are based on the MAC (Media Access Control) which is embedded in the Ethernet interface. The MAC Address
is unique for all devices in the world and cannot be changed. The IEEE (Institute of Electrical and Electronics Engineers)
controls the allocation of the MAC Addresses. The definition for Ethernet includes requirements for inter-operation at speeds
of 10 and 100 Mbps. Higher speeds are available, but generally have not filtered down into end-user equipment.
Bandwidth
Each VoIP (Voice Over Internet Protocol) channel requires 50kBit of bandwidth while active. Full-duplex conversation (audio
in each direction) requires 100kBit of bandwidth.
NOTE: Most radio voice communications are half-duplex (audio in only one direction at any one time), thus requiring
50kbits.
Some radio systems transmit go-ahead beeps when it is clear to talk. In order for the console operator to hear the beeps, the
system must support full-duplex communication. Full-duplex bandwidth may only be required for the first few seconds of a
conversation, due to the brief nature of the go-ahead beeps at the beginning of the transmission.
When using a PIB, TDI, C-6200, or the NI-223 for a telephone connection, 100kBit is required since it is a constant,
full-duplex conversation.
Multicast
In general, Telex systems require Multicast to function. The network must be able to support the multicast traffic generated by
the system.
It is common for networks to enable Multicast after an IGMP (Internet Group Management Protocol) join message is sent out,
and then prune off branches after a period of time. Due to the intermittent usage patterns of two-way radios, a system can
appear to work flawlessly for a period of time and then no longer work.
NOTE: When using Cisco technology, IP PIM dense mode is generally recommended. Generally speaking, sparse-dense-
mode can also be implemented effectively. We recommend explicitly joining the multicast group with an IP
IGMP static-join X.X.X.X command. For more information on Cisco and IGMP, visit www.cisco.com.
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