CDMA2000 Mobile Wireless Network ArchitectureCDMA2000 builds on
the inherent advantages of CDMA technologies and introduces other
enhancements, such as Orthogonal Frequency Division Multiplexing
(OFDM and OFDMA), advanced control and signaling mechanisms,
improved interference management techniques, end-to-end Quality of
Service (QoS), and new antenna techniques such as Multiple Inputs
Multiple Outputs (MIMO) and Space Division Multiple Access (SDMA)
to increase data throughput rates and quality of service, while
significantly improving network capacity and reducing delivery
cost. WCDMA and CDMA2000 have the same characteristics (roaming
support, same data rates, wide band, etc). The main difference
between the WCDMA and CDMA2000 is that the WCDMA uses only one wide
band, while CDMA2000, apart from the wide band uses several narrow
bands (low data rate channels).
CDMA2000 network Architecture diagram
CDMA2000 is a hybrid 2.5G / 3G technology of mobile
telecommunications that uses code division multiple access to send
digital radio, voice, data, and signaling data between mobile
phones and cell sites. CDMA2000 is standardized by the 3rd
Generation Partnership Project 2 (3GPP2).
Figure - CDMA2000 Network Architecture in detail
THE
CDMA2000 NETWORK COMPRISES OF THREE MAJOR PARTS
Mobile station (MS) The Core Network (CN) The radio access
network (RAN)
THE
MOBILE STATION
(MS): This is the device which terminates the radio path on
the
user side of the network and enables subscribers to access
network services over the Um interface. In CDMA2000, there is no
need to replace the CDMA MS in order to function in the network;
but in order to receive the full services of the CDMA2000 the MS
should be replaced.
THE
RADIO ACCESS NETWORK
(RAN): In a CDMA2000 access network, two Radio
Access Network technologies are supported; 1xRTT and EV-DO
(Evolution-Data Optimized or Evolution-Data only). CDMA2000 is
considered a 2.5G (or 2.75G) technology when the 1xRTT access
network is used and a 3G technology when the EV-DO access network
is used.
CDMA2000 1xRTT: The core CDMA2000 wireless air interface
standard is also known as 1x, 1xRTT, and IS-2000. The designation
"1x", meaning "1 times Radio Transmission Technology", indicates
the same RF bandwidth as IS-95 (CDMA-One): 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
the original set of 64. Although capable of higher data rates, most
deployments are limited to a peak of 144 Kbit/s. IS-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 (Quality of Service).
CDMA2000
EV-DO:
CDMA2000 EV-DO is a broadband access radio
technology standardized by 3rd Generation Partnership Project 2
(3GPP2), provides access to mobile devices with air interface
speeds of up to 2.4 Mbit/s with Rev. 0 and up to 3.1 Mbit/s with
Rev. A. The industry is working newer generations of EV-DO such as
Rev. B and Rev. C, etc. Characteristics of CDMA2000 Access Network
The CDMA2000 access network may perform mobility management
functions for registering; authorizing, authenticating and paging
IP based terminals, independent of circuit based terminals. The
access network may perform handoffs within an access network and
between access networks of the same technology and may support
handoffs between access networks of differing technologies. The key
components of the cdma2000 access network are: Base Transceiver
System (BTS) Packet Control Function (PCF) Base Station Controller
(BSC)
Base Station Controller (BSC): an entity that provides control
and management for one or more BTSs. Apart from routing the Time
division multiplexing (TDM) traffic to the circuit switched
platform, the BSC routes the packet to and from the PDSN.
Packet Control Function (PCF): an entity that provides interface
function between the access network and the packet switched core
network. It is located in the radio access network and manages the
relay of packets between the BS and the PDSN. The PCF is generally
part of the BSC. In order to provide the feel of always connected,
if there are packets from the Internet to a certain MS that
currently doesnt have radio resources allocated, the packet is held
on the PCF until the user is allocated a channel. The PDSN does not
hold the packets but the PCF. The PCF may be HW and/or SW. The
CDMA2000 may introduce firewalls to protect the network and
application servers to support packet services. The PDSNs, AAA and
the connection to the RAN (BSCs) are via a private IP network for
security and for providing different QoS levels. Mobile IP (not an
entity)- supports moving between two different PDSNs without
needing to reconnect. It is the PDSNs responsibility to either
update the IP of the user when they move to another PDSN area (it
is implying the packet sessions need to turn down and restart), or
to implement the Mobile IP mechanism for a transparent move. In the
Mobile IP mechanism the FA and HA are required. Simple IP (not an
entity) does not support mobility between different PDSNs. The PDSN
is the owner of the User IP (DHCP). If in the middle of a page
loading the MS moves between two different PDSNs, the MS will have
to reconnect Base Transceiver System (BTS): an entity that provides
transmission capabilities across the Um reference point. The BTS
consists of radio devices, antenna and equipment and its
responsibilities include: a) Assigning the Fundamental channel
(FCHs) - the number of physical resources available. b) The FCH
forward power (the power already allocated and available). c) The
Walsh codes required and those available. d) SDU function: The SDU
function (Selection/Distribution Unit function) includes the
following functions: Traffic Handler: This function exchanges
traffic bits with the associated vocoder or CDMA RLP function, and
is directly connected to the A5 interface.
Signaling Layer 2: This function performs the layer 2
functionality of the air interface signaling protocol and is
responsible for the reliable delivery of layer 3 signaling messages
between the base station and the mobile station.
Multiplex Sub-layer: This function multiplexes and demultiplexes
user traffic and signaling traffic for the air interface. Power
Control: This function administrates the forward and reverse link
power control in a CDMA system. This function and the channel
element provide the power control function for the CDMA operation.
As part of this function, it generates or utilizes relevant power
control information that is exchanged over the air interface or
with the channel element.
Frame Selection/Distribution: This function is responsible for
selecting the best incoming air interface reverse link frame from
the channel elements involved in the soft handoff. It also
distributes forward air interface frames to all channel elements
involved in a call.
Backhaul
Frame
Handler:
This
function
demultiplexes
the
control
information and the air interface reverse frame from the frame
received over the backhaul network. It also multiplexes the control
information and the air interface frames in the forward
direction.
THE CORE NETWORK (CN): This is further decomposed in two parts,
one interfacingto external networks such as the Public Switched
Telephone Network (PSTN) which is called the Circuit switched
domain (that based on voice) and the other interfacing to the IP
based network such as Internet, which is called the Packet switched
domains (that is based on data).
Figure-CDMA2000 Packet Core Network (PCN) Architecture
A. The Circuit Switch Core Network(CS-CN) In any mobile services
network, the most important circuit switched core network elements
are the Mobile Switching Center / Visitor Location Register (MSC /
VLR) and the Home Location Register (HLR). All the other network
elements, required for other supplementary or value added services
are called as Adjunct Network elements (like SMSC, SCP, VMS, OTAF
etc.) The circuit-switching network interfaces with the
radio/access network via the mobile switching center (MSC), which
provides the typical wire-line interface to the PSTN. The MSC-VLR
and HLR (All the circuit switched Core networks) need software
upgrades in order to support the authentication and authorization
of the packet data network. Note that, it is still the CS-CN
(Circuit Switched Core Network) which authenticates and authorizes
the wireless access of the user during packet session initiation.
The MSC-VLR and HLR are updated with the Packet data user profile
information. The information is then downloaded from the HLR to the
VLR of the associated network switch during the successful
registration process. The HLR: It is responsible to keep track of
the current location of a Mobile Station. The HLR is a database
used for storage and management of subscriptions. The HLR is
considered the most important database, as it stores permanent
data about subscribers, including a subscriber's service profile,
location information, and activity status. When an individual buys
a subscription from one of the mobile services switching center
(MSC) - The MSC performs the telephony switching functions of the
system. It controls calls to and from other telephone and data
systems. It also performs such functions as toll ticketing, network
interfacing, common channel signaling, and others. MSC: VLR: The
VLR is always integrated with the MSC, and it is a database that
contains temporary information about subscribers that are needed by
the MSC in order to service visiting subscribers.. When a mobile
station roams into a new MSC area, the VLR connected to that MSC
will request data about the mobile station from the HLR. Later, if
the mobile station makes a call, the VLR will have the information
needed for call setup without having to interrogate the HLR each
time. Its the combined responsibility of the MS (Mobile Station)
and the MSC that, they should keep the HLR updated about the MSs
current location. This is done by virtue of Registration process.
The Registration Process Registration is the process of a mobile
associating itself with a particular cell in a particular network.
There are nine types of registration. 1. Power on: when a mobile is
turned on 2. Power off: just before a mobile is turned off 3.
Timer-based: after a certain timer expires 4. Distance-based: if
the mobile moves to a further cell 5. Zone-based: if a mobile moves
in or out of a zone 6. Ordered: base station requests the
registration 7. Parameter change: if the mobiles parameters change
8. Implicit: base station infers the mobiles position 9. Traffic
channel: for registration in active mode Of these the first five
are autonomous type of registration. They are called so, because
the base station informs the mobile station at power on, to
register if any of the events happen.
a. Mobile Station moves from MSC/VLR2 to MSC/VLR1. The Mobile
Station requests for Location Update to the network. The MSC/VLR-1
sends IS-41 message called Registration Notification (or REGNOT in
short) to the HLR with different parameters included in it. Most
important parameter being the MIN. MIN is used as the primary key
by the HLR to find the subscribers record in its database. b. HLR
compares the received MSCID / PC_SSN parameter against the value of
these parameters stored in its dynamic database. As the HLR finds
that the MS (identified by the MIN) was registered at MSC/VLR-2,
earlier, it sends a message called as Registration Cancellation
(REGCANC) to the MSC/VLR-2. c. The MSC/VLR-2 deletes the record of
this MIN from its database and sends the response to REGCANC to the
HLR. The HLR stores the new MSCID / PC_SSN parameter in its dynamic
data. d. On receipt of regcanc from MSC/VLR-2, the HLR sends the
regnot response to the MSC/VLR-1 with the subscribers profile
included in it. The profile includes the MDN of the subscriber,
Call Origination / Termination capabilities, SMS
origination/termination capabilities, Data Services capabilities,
other supplementary service like Call Waiting, Call Conferencing,
Call Forward etc. For further details about Registration Process
visit Authentication center (AUC): A unit called the AUC provides
authentication and encryption parameters that verify the user's
identity and ensure the confidentiality of each call. The AUC
protects network operators from different types of fraud found in
today's cellular world. Authentication is the process by which
information is exchanged between a mobile station and base station
for the purpose of confirming the identity of the mobile station. A
successful outcome of the authentication process occurs only when
it can be demonstrated that the mobile station and base station
possess identical sets of shared secret data. This is done so as to
prevent what is called Phone Cloning.
The standards use the CAVE (Cellular Authentication Voice
Privacy Encryption) Algorithm and CMEA (Cellular Message Encryption
Algorithm) for the maintaining security. Uses of the CAVE and CMEA
Algorithm i. CAVE is also used to generate a set of
crypto-variables for the Cellular Message Encryption Algorithm
(CMEA) message encryption process. ii. CAVE is used in the
generation of 520 bits for the duplex voice privacy masks. iii.CAVE
is used in the generation of a subscriber's "shared secret data"
from his unique A-key. Also used in verifying the manual entry of
the A-key. iv.CMEA is used in encrypting certain type specific
fields. Encryption: In an effort to enhance the authentication
process and to protect sensitive information (example PINs sent as
DTMF tones), certain fields which carry these sensitive information
in Traffic Channel messages are encrypted. Equipment identity
register (EIR): The EIR is a database that contains information
about the identity of mobile equipment that prevents calls from
stolen, unauthorized, or defective mobile stations. Note: The AUC
and EIR can implemented as stand-alone nodes or as a combined
AUC/EIR node
B. The Packet Switch core network (PS-CN) This is a network
architecture based on third-generation cdma2000 mobile/cellular
networks, being promoted by TIA as the packet-data standard. Packet
data calls allow users to exchange data between the MS and an IP
data network. For all calls supporting packet data services, a
Packet Data Serving Node (PDSN) exists that interfaces between the
transmission of the data in the fixed network and the transmission
of the data over the air interface. The PDSN interfaces to the BS
through a Packet Control Function (PCF), which may or may not be
co-located with the BS.
CDMA2000 Packet data network Architecture
There are three packet data service states: Active/Connected,
Dormant, and Null/Inactive In the Active/Connected State, a
physical traffic channel exists between the MS and the BS, and
either side may send data. In the Dormant State, no physical
traffic channel exists between the MS and the BS, but the PPP link
between the MS and the PDSN is maintained. In the Null/Inactive
State, there is no traffic channel between the MS and the BS and no
PPP link between the MS and the PDSN.
Figure 3-1: Packet data service transitions
The mobile may cross Packet Zone boundaries while in the Dormant
State. This is referred to as Dormant Handoff. The Dormant handoff
procedures allow the A10 connections between the PCF and PDSN to be
moved (or established) for the mobile when it enters a new packet
zone. The mobile may re-enter Active state (e.g., if the user has
data to send) at any time. This transition is referred to as
Re-Activation from Dormant, and is not related to Dormant Handoff
(i.e., Re-Activation from Dormant is not related to a mobility
event). Packet data is typically transmitted over the air on
dedicated traffic channels. Mechanisms also exist for transmitting
data over the common channels. Short Data Burst (SDB) is a part of
the 3G Packet Data feature that enables small amounts of data to be
transmitted over the common channels. Common Channel Packet Data is
a mode of 3G Packet Data where all data is transmitted using Short
Data Bursts. A1 and A8 connections are maintained during the Active
/ Connected State and released during transition to Dormant or
Null/Inactive State. The A10 connection is maintained during the
Active/Connected and the Dormant State. PCN is a collection of
logical and physical entities that provide; IP-centric
packet-data-based registration, roaming, and Forwarding services
for mobile nodes.IN
NEW ENTITIESPDSN:
CDMA2000-1X COMPARED
TO
CDMA (IS-95)
Establishes, maintains and terminates Point-to-Point protocol
(PPP) session with the MS. Establishes, maintains and terminates
the logical link to the Radio network across the radio-packet (R-P)
interface. Initiates Authentication, Authorization and Accounting
(AAA) for the MS to the packet data network (Internet) via the AAA
Server. Receives service parameters for the MS from the AAA. Routes
packet data between the RAN and the Internet (like NAS in the
Internet). Collects usage data that is related to the AAA Server.
Supports both Simple and Mobile IP.
For Mobile IP the FA (foreign agent) should be implemented on
the PDSN (also a HA (home agent) is needed). One BSC can
interconnect to a few PDSNs for load balancing.
AAA: The AAA server, also called the RADIUS server,
authenticates only the user Internet access and not a user wireless
access (same entity used in the Internet). RADIUS Remote Access
Dial-In User Service communicates with the PDSN via IP.
Authentication associated with PPP and Mobile IP connection. HA:
One of the tasks of the HA is to track the location of the Mobile
IP subscriber as it moves from one packet zone to another. In
tracking the Mobile, the HA ensures that the packets are forwarded
to the mobile itself. An HA is a router on the Mobile nodes home
network. It uses a tunneling mechanism to forward Internet traffic
so that the devices IP address does not have to be changed each
time it connects from a different location. The HA works in
conjunction with the FA, which is the router on the visited
network. The HA identifies the IPv4 address of the PDSN that
terminates the A10 connection. FA: Works in conjunction with the HA
in order to perform internet traffic forwarding to a device
connecting to the Internet from any location other than its home
network. The HA tunnels datagram packets intended for the mobile
node to either the IP address for the FA, or to an IP address
acquired through DHCP. The FA detunnels the packets and delivers
them to the mobile node. In general, Mobile IPv6 (MIPv6) minimizes
the use of FA.
NEW ENTITIES
AND
FEATURES
FOR
CDMA 1X-EV-DO
Access Network This is the network equipment providing data
connectivity between a packet switched data network (typically the
Internet) and the access terminals. An access network is equivalent
to a base station in CDMA2000 systems. Access Terminal (AT) : This
is a device that provides data connectivity to a user. An access
terminal may be connected to a computing device such as a laptop or
it
may be a self-contained data device such as a personal digital
assistant. An access terminal is equivalent to a mobile station in
CDMA2000 systems. Access Network (AN): This is the network
equipment that provides data connectivity between a packet switched
data network (typically the Internet) and the access terminals. An
access network is equivalent to a base station in
GSM/CDMA2000-1xRTT. AN AAA: An entity that performs terminal
authentication and authorization functions for the Access Network.
Connection: A connection is a particular state of the air-link in
which the access terminal is assigned a Forward Traffic Channel, a
Reverse Traffic Channel and associated Medium Access Control (MAC)
Channels. During a single HRPD session the access terminal and the
access network can open and can close a connection multiple times.
Hybrid MS/AT : This device is capable of operating on both CDMA2000
and HRPD access networks. Service Stream: The HRPD stream is used
when exchanging data between the access terminal and the PDSN. HRPD
session: An HRPD (High Rate Packet Data (1xEV-DO)) session refers
to a shared state between the access terminal and the Access
network. This shared state stores the protocols and protocol
configurations that were negotiated and are used for communications
between the access terminal and the access network. Other than to
open a session, an access terminal cannot communicate with an
access network without having an open session. Note, that it is
possible that the A10/A11 connection is not established even though
the HRPD session is established. PCF: The PCF enhancement for EV-DO
logically contains the SC/MM function and is capable of HRPD
specific operation. The original PCF function and procedure may
also be optimized or enhanced using information obtained from these
additional functions. Packet Data Session: This is an instance of
the use of packet data service by a mobile user. A packet data
session begins when the user invokes a packet data service. A
packet data session ends when the user or the network terminates
the
packet data service. During a particular packet data session,
the user may change locations but the same IP address is
maintained. SC/MM function: SC/MM (Session Control and Mobility
Management) is logically located in the PCF and includes the
following functions: Storage of HRPD session related information:
This function keeps HRPD session related information (e.g., Keep
Alive timer, MNID, mapping between MNID and UATI, etc.) for dormant
ATs. Assignment of UATI (Unicast AT identifier): This function
assigns a new UATI to an AT. Terminal Authentication: This function
performs the terminal authentication procedure. This function
judges whether an AT (access terminal) should be authenticated or
not when the AT is accessing the HRPD RAN. The SC/MM performs PPP
procedures for terminal authentication. Mobility Management: This
function manages the location of an AT. The location information of
the AT is obtained via distance-based registration. This function
may perform a paging procedure based on the information. Terminal
Authentication: A procedure in which the AT is authenticated by the
ANAAA
Note Multimedia Domain (MMD), a new all IP network defined by
the 3GPP2, is the latest architecture of the CDMA2000 core network,
which is intended to provide multimedia services based on the IP
technologies. For a UMTS based 3G mobile/cellular wireless network,
the basic Core Network architecture is based on GSM network with
GPRS. All equipment has to be modified for UMTS operation and
services. The UTRAN provides the air interface access method for
User Equipment. Base Station is referred as Node-B and control
equipment for Node-B's is called Radio Network Controller (RNC).
Some of the circuit switched elements in the UMTS core network are
Mobile services Switching Centre (MSC), Visitor location register
(VLR) and Gateway MSC. Packet switched elements are Serving GPRS
Support Node (SGSN) and Gateway GPRS
Support Node (GGSN). Some network elements, like EIR, HLR, VLR
and AUC are shared by both domains. The architecture of the UMTS
Core Network may change when new services and features are
introduced. Number Portability Database (NPDB) will be used to
enable user to change the network while keeping their old phone
number. Gateway Location Register (GLR) may be used to optimize the
subscriber handling between network boundaries. MSC, VLR and SGSN
can merge to become a UMTS MSC. CDMA2000 Network Interfaces and
Protocol Stack CDMA2000, also known as IMT-CDMA Multi-Carrier or
IS-2000 is the main 2.5 and 3G technology for CDMA based 2G
networks (cdmaOne). The CDMA2000 technologies and protocols are
defined by the Third Generation Partnership Project 2 (3GPP2).
CDMA2000 provides enhanced services to cdmaOne subscribers, as well
as forward and backward capabilities in terminals.
Figure-CDMA2000 Interfaces and Protocol stacks
The main communication interfaces and protocols in the CDMA2000
network are listed below: Reference Points A, Ater, Aquinter, and
Aquater The A reference point is implemented by A1, A2, A5. The
Ater reference point is implemented by A3 and A7. The Aquinter
reference point is implemented by A8 and A9. The Aquater reference
point is implemented by A10 and A11. Interfaces Description
CDMA2000 1xRTT A1: The A1 interface carries signaling information
between the Call Control and Mobility Management functions of the
MSC and the call control component of the BS (BSC). A2: The A2
interface carries 64/56 kbps PCM information or 64 kbps
Unrestricted Digital Information (UDI, for ISDN) between the Switch
component of the MSC and the Selection/Distribution Unit (SDU)
function of the BS. A3: The A3 interface carries coded user
information (voice/data) and signaling information between the
source BS SDU function and the channel element component (BTS) of
the target BS. This is a logical description of the endpoints
of
the A3 interface. The A3 interface is composed of two parts:
signaling and user traffic. The signaling information is carried
across a separate logical channel from the user traffic channel,
and controls the allocation and use of channels for transporting
user traffic. A5: The A5 interface carries a full duplex stream of
bytes between the MSC and the SDU function of the BSC. A7: The A7
interface carries signaling information between a source BS and a
target BS. A8: The A8 interface carries user traffic between the BS
and the PCF. A9: The A9 interface carries signaling information
between the BS and the PCF. A10: The A10 interface carries user
traffic between the PCF and the PDSN. A11: The A11 interface
carries signaling information between the PCF and the PDSN.
Interfaces Description CDMA20001xEV-DO A8: The A8 interface carries
user traffic between the Access Network (AN) and the Packet Control
Function (PCF). A9: The A9 interface carries signaling information
between the AN and the PCF. A10: The A10 interface carries user
traffic between the PCF and the PDSN. A11: The A11 interface
carries signaling information between the PCF and the PDSN. A12:
The A12 interface carries signaling information related to terminal
authentication between the SC/MM function in the PCF and the AN AAA
(Authentication, Authorization and Accounting entity for 1x-EV-DO).
A13: The A13 interface carries signaling information between the
SC/MM function in the source PCF and the SC/MM function in the
target PCF. A14: The A14 interface carries signaling information
between the SC/MM function in the PCF and the AN. A15: The A15
interface carries signaling information between ANs when
interANpaging is used. Ax The Ax interface carries user traffic
between the SC/MM function in the PCF and the AN. Mobility
Management
The responsibility for keeping the MS connected while moving on
the network (between different MSCs, etc.) is divided into two
different cases: While in active session, the RAN is responsible
for the Handoff (in general for the Low data rate channel we will
always have SHO (Soft hand off), and as much as the data increases
in the SCH the SHO for SCH will decrease (the SHO for SCH is
limited). While the mobile moves between BTSs but not in a session,
and than between BSCs and MSCs and PDSNs (while idle) it is the
mobiles responsibility to update the network that it has moved by
registering to a new MSC or PDSN. It is important that the MS
updates the system in the CS in order for the system to be able to
route the circuit voice calls to the mobile. In idle mode the MS
runs the mobility management procedure, and in active the MS
assists the RAN. The A8/A9 interfaces supports mobility between
BSCs under the same PCF. The A10/A11 interfaces supports mobility
between PCFs under the same PDSN. Mobile IP supports mobility
between PDSN/FA under the same Home Agent. Hard handoff and soft
handoff procedures realize the mobility between BTSs.
Packet Data Micro-Mobility and Macro-Mobility Concepts -
CDMA2000 1x The figure below provides a conceptual view of levels
of packet data mobility.
Figure 3-2: Levels of packet data mobility
The A8/A9 interfaces support mobility between BSCs under the
same PCFs. The A10/A11 interfaces support mobility between PCFs
under the same PDSN. Mobile IP supports mobility between PDSN/FA
under the same Home Agent. Hard handoff and soft handoff procedures
realize the mobility between BTSs.
HRPD Micro-Mobility and Macro-Mobility Concepts - CDMA2000
1x-EV-DO The figure below provides a conceptual view of levels of
HRPD packet data mobility.
Figure 3-3: HRPD Packet data mobility
The A8/A9/A14 interfaces support mobility between ANs under the
same PCF. The A10/A11/A13 interfaces support mobility between PCFs
under the same PDSN. Mobile IP supports mobility between PDSNs
under the same Home Agent.