Description Page 61 of 910
IP Line Description, Installation and Maintenance
When a data sequence is packetized and sent from source A to receiver B,
RUDP adds a number to each packet header to indicate its order in the
sequence.
• If the packet is successfully transmitted to B, B sends back an ACK to A,
acknowledging that the packet has been received.
•If A receives no message within a configured time, it retransmits the
packet.
•If B receives a packet without having first received its predecessor, it
discards the packet and all subsequent packets, and a NAK (no
acknowledge) message which includes the number of the missed packet
is sent to A. A retransmits the missed packet and continues.
UNIStim
The Unified Network IP Stimulus protocol (UNIStim) is the single point of
contact between the various server components and the IP Phone.
UNIStim is the stimulus-based protocol used for communication between an
IP Phone and an LTPS on the Voice Gateway Media Card or Signaling
Server.

ELAN TCP transport

Although TCP is used for the signaling protocol between the Call Server and
the Voice Gateway Media Card, RUDP remains for the Keep Alive
mechanism for the link. This means RUDP messages are exchanged to
maintain the link status between the Call Server and the Voice Gateway
Media Card.
There is no change to UNIStim signaling. IP Phones continue to use the
RUDP transport protocol to communicate with the Voice Gateway Media
Card.
The TCP protocol enables messages to be bundled. Unlike the RUDP
transport that creates a separate message for every signaling message (such as
display updates or key messages), the TCP transport bundles a number of
messages and sends them as one packet.