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7 Flow Graphs – Call Transfer

Some Definitions – Call Transfer

There are three actors in a given transfer event, each playing one of the following roles:

Transferee: the party being transferred to the Transfer Target.

Transferor: the party initiating the transfer

Transfer Target: the new party being introduced into a call with the Transferee.

The following roles are used to describe transfer requirements and scenarios:

1. Originator - wishes to place a call to the Recipient. This actor is the source of the first

INVITE in a session, to a Facilitator or a Screener.

2. Facilitator - receives a call or out-of-band request from the Originator, establishes a call to the

Recipient through the Screener, and connects the Originator to the Recipient.

3. Screener - receives a call ultimately intended for the Recipient and transfers the calling party to

the Recipient if appropriate.

4. Recipient - the party the Originator is ultimately connected to.

Call Transfer - Requirements

Any party in a call session is able to transfer any other party in that session at any point in that session.

The Transferor and the Transferee are not removed from a session as part of a transfer transaction.

This requirement is needed so for e.g. ring-back on transfer failure will not be lost.

The Transferor is aware of whether or not the transfer was successful.

Types of Call Transfer

There are three different methods to transferring calls depending on the SIP Server the customer may

be using (most SIP server call transfer method is based on the Refer method). They are as follows and

will be explained in more detail below:

 Basic or Unattended Transfer - Basic Transfer consists of the Transferor providing the Transfer

Target's contact to the Transferee. The Transferee attempts to establish a session using that

contact and reports the results of that attempt to the Transferor. The signalling relationship

between the Transferor and Transferee is not terminated, so the call is recoverable if the Transfer

Target cannot be reached. Note that the Transfer Target's contact information has been exposed

to the Transferee. The provided contact can be used to make new calls in the future.

 Basic or Unattended Transfer with Consultation - Transfer with Consultation Hold is the same as

the Basic Transfer above but involves a session between the transferor and the transfer target

before the transfer actually takes place. This is implemented with SIP Hold and Transfer feature.

 Attended Transfer - The transferor places the transferee on hold, establishes a call with the

transfer target to alert them to the impending transfer, places the target on hold, then proceeds

with transfer.

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RTX 8630 User Manual Page 32