1. Hybrid Mode Operation
Author Name Department Contact Information
Anit Lohtia Core RF Engineering (972) 685-4124
1. Overview
A hybrid access terminal supports operation on both IS-2000 and IS-856 access networks, and
can hand off between the two types of access network as required to support the connection of
services provided by both types of access networks. To support mobile-terminated services on
both types of access networks, a hybrid access terminal is capable of maintaining registration and
receiving page messages on both types of access networks concurrently. To support mobile-
originated services on both types of access networks, a hybrid access terminal is capable of
originating services on either type of access network, and can hand off an existing packet data
session between the two types of access networks to avoid unnecessary packet data session
renegotiation.
The operational states of a hybrid access terminal::
• No system acquired
• Idle on IS-2000 system, no data session
• Idle on IS-2000 system, dormant data session on IS-2000 system
• Idle on both IS-856 and IS-2000 systems, dormant data session on IS-856 system
• Active data session on IS-2000 system
• Active data session on IS-856 system, idle on IS-2000 system
An access terminal is considered to be idle if it does not have an active connection over the air
interface but is maintaining registration on the system and monitoring the signaling messages
received on the overhead channels. An access terminal is considered to be dormant if it is idle and
has a packet data service session established with a PDSN in the network. An access terminal is
considered to be active when it has an active connection over the air interface.
2. Slotted Mode Operation
To maximize standby time while idle, an access terminal performs slotted operation while in the
idle state as specified in the IS-2000 and IS-856 air interface standards. Slotted operation allows
an idle access terminal to receive page messages over the air at specified intervals and to conserve
battery capacity by placing electronic components into a low power state when not receiving.
To ensure that mobile-terminated IS-2000 services can be supported whenever an IS-2000 access
network is available, a hybrid access terminal performs IS-2000 idle state slotted operation
regardless of whether the hybrid access terminal is idle or active on an IS-856 access network. By
continuing to perform IS-2000 idle state slotted operation even when active on an IS-856 access
network, a hybrid access terminal maintains current registration and overhead information for the
IS-2000 access network; it is also able to continue to receive page messages for mobile-
terminated IS-2000 services, even while actively providing packet data service on an IS-856
access network. A hybrid access terminal may also originate services on the IS-2000 access
network regardless of the operational state on the IS-856 access network. To originate a

2. connection on the IS-2000 access network, any active IS-856 packet data service must be
interrupted.
3. IS-2000 and IS-856 Dual Mode Slotted Operation
When idle on an IS-856 access network, a hybrid access terminal performs slotted operation on
the IS-856 access network to receive overhead and paging messages and maintain registration on
the IS-856 access network. Mobile-originated and mobile-terminated packet data services on the
IS-856 access network are supported by a hybrid access terminal operating in this mode. When a
hybrid access terminal is performing slotted operation on an IS-856 access network, the hybrid
access terminal also continues to perform slotted operation on the IS-2000 access network to
receive overhead and paging messages and maintain registration on the IS-2000 access network.
Mobile- originated and mobile-terminated IS-2000 services are supported by a hybrid access
terminal operating in this mode. If a hybrid access terminal receives a page message from the IS-
2000 access network when operating in this mode, the hybrid access terminal performs the
necessary connection setup procedures on the IS-2000 access network and discontinues slotted
operation on the IS-856 access network until the IS-2000 service has been disconnected.
Provisions in the IS-856 standard make it possible for a hybrid access terminal to concurrently
monitor the paging slots of an IS-2000 access network and an IS-856 access network without
missing pages on either system. When performing dual-system slotted operation, the sleep
timelines for the IS-2000 access network and the IS-856 access network are effectively overlaid.
During slotted operation on the IS-2000 access network, the access terminal receives the paging
channel once every slot cycle. During slotted operation on the IS-856 access network, the access
terminal receives the synchronous control channel capsule in the designated IS-856 control
channel slot. The IS-856 control channel slot duration is 5.12 sec, which is identical to the IS-
2000 slot cycle index 2 duration. To avoid collision of the paging slots on the two access
networks, the specific IS-856 paging slot assigned to an access terminal can be changed at the
request of the access terminal if the IS-856 paging slot conflicts with the IS-2000 paging slot
assigned to the same access terminal.
Since concurrent slotted operation on both the IS-2000 and IS-856 access networks has a greater
impact on battery capacity than slotted operation on a single system, the amount of time that a
hybrid access terminal spends performing concurrent slotted operation while dormant on an IS-
856 access network is limited. If a hybrid access terminal has been dormant on an IS-856 access
network for an extended period of time, the hybrid access terminal reverts to slotted operation on
the IS-2000 access network only. Reverting to slotted operation on the IS-2000 access network
includes handing off the existing packet data session to the IS-2000 access network to allow the
access terminal to maintain the existing packet data session with the corresponding PDSN. The
amount of time allowed for simultaneous slotted operation on the IS-2000 and IS-856 access
networks is a configurable parameter.
4. IS-2000 slotted operation during IS-856 connected state
When active on an IS-856 access network, a hybrid access terminal continues to perform slotted
operation on the IS-2000 access network to receive overhead and paging messages and maintain
registration on the IS-2000 access network. Mobile-originated and mobile-terminated packet data
services on the IS-856 access network are supported by a hybrid access terminal operating in this
mode. Mobile-originated and mobile-terminated IS-2000 services are also supported by a hybrid

3. access terminal operating in this mode. During this mode of operation, a hybrid access terminal
periodically tunes to the frequency of the IS-2000 access network to receive the appropriate
paging slot, and then tunes back to the IS-856 frequency to resume the active packet data
connection.
To avoid negative impact to the forward link sector capacity of the IS-856 access network while
receiving the IS-2000 paging channel, a hybrid access terminal sets the cover of the IS-856
reverse link data rate control channel to the null value prior to tuning to the IS-2000 access
network. By doing so, a hybrid access terminal ensures that the IS-856 access network will not
schedule packets for that 1access terminal while it is tuned to the IS-2000 frequency. Upon
returning to the frequency of the IS-856 access network, a hybrid access terminal resumes normal
operation of the data rate control channel to resume IS-856 packet data service. Prolonged
absence of the access terminal from the IS-856 access network for IS-2000 operations, such as
registration maintenance, overhead update, or connection setup, should be treated by the IS-856
access network in the same way as an extended fade, and should result in the release of the
assigned air interface resources by the IS-856 access network. To ensure operation compliant
with the IS-856 standard, a hybrid access terminal continues to perform IS-856 supervision
procedures, even when operating on an IS-2000 access network.
5. Key Points to Remember about Hybrid Terminal
• A hybrid terminal is a voice terminal first, and a data device second i.e. voice services
get preference over the data services in a hybrid terminal.
• A hybrid terminal will always go to 1xEV-DO carrier for data services if a 1xEV-DO
carrier is in the preferred roaming list (PRL) of the terminal, and is present. If a
1xEV-DO carrier is not available, only then the terminal will use 1xRTT carrier for
data service. This is also applicable to a dual-mode data only terminal that supports
both 1xRTT and 1xEV-DO.
• A hybrid terminal will not support a 1xEV-DO data call and a voice call concurrently.
In the event of a call origination/terminal during a 1xEV-DO data connection being
active, the data RF connection is terminated on 1xEV-DO carrier, and reestablished
after completion of the voice call.
• To force a hybrid terminal or dual mode data terminal to use 1xRTT for data service,
don’t add any 1xEV-DO carrier in the PRL of the terminal.
• 1xRTT and 1xEV-DO are two separate access networks. There is no physical layer
interaction between two networks i.e. there are no soft handoffs between two
networks. There is only R-P session handoffs between two networks through a PDSN.