1X EVDO Rev A (3G)
CDMA2000 1X (IS-2000), also known as
1x and
1xRTT, is the core CDMA2000 wireless air interface standard. The designation "1x", meaning
1 times Radio Transmission Technology, indicates the same RF bandwidth as
IS-95: a
duplex pair of 1.25 MHz radio channels. 1xRTT almost doubles the capacity of IS-95 by adding 64 more traffic channels to the
forward link,
orthogonal to (in
quadrature with) the original set of 64. The 1X standard supports packet data speeds of up to 153
kbps with real world data transmission averaging 60–100 kbps in most commercial applications.
[5] IMT-2000 also made changes to the
data link layer for the greater use of data services, including medium and link access control protocols and
QoS. The IS-95 data link layer only provided "best effort delivery" for data and circuit switched channel for voice (i.e., a voice frame once every 20 ms).
EVDO Rev A (3G)
Revision A of EV-DO makes several additions to the protocol while keeping it completely backwards compatible with Revision 0.
These changes included the introduction of several new forward link data rates that increase the maximum burst rate from 2.45 Mbit/s to 3.1 Mbit/s. Also included were protocols that would decrease connection establishment time (called enhanced access channel MAC), the ability for more than one mobile to share the same timeslot (multi-user packets) and the introduction of
QoS flags. All of these were put in place to allow for low latency, low bit rate communications such as
VoIP.
[7]
In the
United States,
Verizon Wireless and
Sprint Nextel have migrated 100% of their EV-DO Rev.0 networks to EV-DO Rev. A.
