Transcript 3G_Networks_Basics

EA C451
BITS Pilani
Pilani|Dubai|Goa|Hyderabad
Vishal Gupta
BITS Pilani
Pilani|Dubai|Goa|Hyderabad
Agenda: 3G Networks
What is 3G
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3G or 3rd generation mobile telecommunications is a generation of standards for mobile
phones and mobile telecommunication services fulfilling the International Mobile
Telecommunications-2000 (IMT-2000) specifications by the International Telecommunication
Union.
Application services include wide-area wireless voice telephone, mobile Internet access,
video calls and mobile TV, all in a mobile environment.
To meet the IMT-2000 standards, a system is required to provide peak data rates of at least
200 kbit/s.
The following standards are typically branded 3G:
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the UMTS system, first offered in 2001, standardized by 3GPP, used primarily in Europe,
Japan, China (however with a different radio interface) and other regions predominated by
GSM 2G system infrastructure. The cell phones are typically UMTS and GSM hybrids.
the CDMA2000 system, first offered in 2002, standardized by 3GPP2, used especially in North
America and South Korea, sharing infrastructure with the IS-95 2G standard. The cell phones
are typically CDMA2000 and IS-95 hybrids.
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3G Network
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GPRS Core Network
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General packet radio service (GPRS) is a packet oriented mobile data service on the 2G
and 3G cellular communication system's GSM.
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GPRS was originally standardized by European Telecommunications Standards Institute
(ETSI) and is now maintained by the 3rd Generation Partnership Project (3GPP).
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GPRS usage charging is based on volume of data, either as part of a bundle or on a payas-you-use basis. This contrasts with circuit switching data, which is typically billed per
minute of connection time, regardless of whether or not the user transfers data during
that period.
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GPRS is a best-effort service, implying variable throughput and latency that depend on
the number of other users sharing the service concurrently, as opposed to circuit
switching, where a certain quality of service (QoS) is guaranteed during the connection.
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2.5G and 3G systems rely on double core network infrastructures; traditional circuitswitched network nodes (switching points) for telephony, and packet-switched GPRS
nodes for various data services. Dedicated nodes handle the SMS service.
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GPRS Core Network
GPRS supports the following protocols:
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Internet protocol (IP). In practice, built-in mobile browsers use IPv4 since IPv6 is not yet
popular.
• Point-to-point protocol (PPP). In this mode PPP is often not supported by the mobile phone
operator but if the mobile is used as a modem to the connected computer, PPP is used to
tunnel IP to the phone.
• X.25 connections. This is typically used for applications like wireless payment terminals,
although it has been removed from the standard.
• When TCP/IP is used, each phone can have one or more IP addresses allocated. GPRS will
store and forward the IP packets to the phone even during handover. The TCP handles any
packet loss (e.g. due to a radio noise induced pause).
Addressing
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A GPRS connection is established by reference to its access point name (APN).
The APN defines the services such as WAP access, SMS, MMS, and for Internet
communication services such as email and WWW access.
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GPRS Core Network
• The GPRS core network is the central part of the GPRS which allows 2G,
3G and WCDMA mobile networks to transmit IP packets to external
networks such as the Internet.
• The GPRS system is an integrated part of the GSM network switching
subsystem.
• The GPRS core network provides mobility management, session
management and transport for Internet Protocol packet services in GSM
and WCDMA networks.
• The core network also provides support for other additional functions
such as billing.
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GPRS support nodes (GSN)
• A GSN is a network node which supports the use of GPRS in the GSM core
network.
• All GSNs should have a Gn interface and support the GPRS tunneling
protocol.
• There are two key variants of the GSN, namely Gateway GPRS Support
Node (GGSN) and Serving GPRS Support Node (SGSN).
Gateway GPRS Support Node (GGSN)
• The GGSN is responsible for the interworking between the GPRS network
and external packet switched networks, like the Internet.
• From an external network's point of view, the GGSN is a router to a subnetwork, because the GGSN ‘hides’ the GPRS infrastructure from the
external network.
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Gateway GPRS Support Node
(GGSN)
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The GGSN is the anchor point that enables the mobility of the user terminal in the
GPRS/UMTS networks.
It carries out the role in GPRS equivalent to the Home Agent in Mobile IP.
It maintains necessary routing information to tunnel the Protocol Data Units (PDUs) to
the SGSN that service a particular MS.
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The GGSN converts the GPRS packets coming from the SGSN into the appropriate PDP
format (e.g., IP or X.25) and sends them out on the corresponding packet data network.
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In the other direction, PDP addresses of incoming data packets are converted to the
GSM address of the destination user. The readdressed packets are sent to the
responsible SGSN.
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The GGSN is responsible for IP address assignment and is the default router for the
connected user equipment (UE).
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The GGSN also performs authentication and charging functions.
Other functions include subscriber screening, IP Pool management and address
mapping, QoS and PDP context enforcement.
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Serving GPRS Support Node
(SGSN)
• It is responsible for the delivery of data packets from and to the mobile
stations within its geographical service area.
• It provides session management, i.e. mechanisms for establishment,
maintenance, and release of end user PDP contexts.
• Its tasks include packet routing and transfer, mobility management
(attach/detach and location management), logical link management, and
authentication and charging functions.
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– Detunnel GTP packets from the GGSN (downlink)
– Tunnel IP packets toward the GGSN (uplink)
– Carry out mobility management as Standby mode mobile moves from one Routing Area
to another Routing Area
– Billing user data
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GPRS tunnelling protocol (GTP)
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GTP is a group of IP-based communications protocols used to carry GPRS within
GSM, UMTS and LTE networks.
• It is the protocol which allows end users of a GSM or UMTS network to move from
place to place whilst continuing to connect to the Internet as if from one location
at the GGSN.
• It does this by carrying the subscriber's data from the subscriber's current SGSN to
the GGSN which is handling the subscriber's session.
Three forms of GTP are used by the GPRS core network.
• GTP-U for transfer of user data in separated tunnels for each PDP context.
• GTP-C for control reasons including:
– setup and deletion of PDP contexts
– verification of GSN reachability
– updates; e.g., as subscribers move from one SGSN to another.
• GTP' for transfer of charging data from GSNs to the charging function.
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PDP (Packet Data protocol)
Context
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When a GPRS mobile phone sets up a PDP context, the access point (An IP
network to which a mobile can be connected) is selected. At this point an
access point name (APN) is determined.
The PDP (e.g., IP, X.25, FrameRelay) context is a data structure present on
both the SGSN and the GGSN which contains the subscriber's session
information when the subscriber has an active session.
When a mobile wants to use GPRS, it must first attach and then activate a
PDP context. This allocates a PDP context data structure in the SGSN that the
subscriber is currently visiting and the GGSN serving the subscriber's access
point. The data recorded includes:
Subscriber's IP address
Subscriber's IMSI
Subscriber's
– Tunnel Endpoint ID (TEID) at the GGSN
– Tunnel Endpoint ID (TEID) at the SGSN
The Tunnel Endpoint ID (TEID) is a number allocated by the GSN which
identifies the tunnelled data related to a particular PDP context.
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3G Network
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BITS Pilani, Deemed to be University under Section 3 of UGC Act, 1956
3GPP – WLAN Interworking
Scenarios
• 3GPP 22.934 specifies six 3GPP-WLAN interworking scenarios.
• Each scenario realises an additional step in integrating WLAN in the 3GPP
service offering and naturally includes the previous level of integration of
the previous scenario.
• 3GPP -WLAN interworking scenarios may be considered with the aid of the
simplified reference diagram shown in next slide.
• This reference diagram illustrates the elements of the 3GPP system and
WLANs being interworked. These may be interconnected in a variety of
ways to develop the progressive scenarios outlined in this section
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BITS Pilani, Deemed to be University under Section 3 of UGC Act, 1956
Scenario 1 - Common Billing and
Customer Care
• The connection between the WLAN and the 3GPP system is that there is a
single customer relationship.
• The customer receives one bill from the mobile operator for the usage of
both 3GPP and WLAN services.
• Integrated Customer Care allows for a simplified service offering from
both the operator and the subscribers perspective.
• The security level of the two systems may be independent.
• This scenario does not pose any new requirements on 3GPP specifications.
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Scenario 2 - 3GPP system based
Access Control and Charging
• This is the scenario where authentication, authorization and accounting
are provided by the 3GPP system.
• The security level of these functions applied to WLAN is in line with that of
the 3GPP system. This provide means for the operator to charge access in
a consistent manner over the two platforms.
Benefits of reusing the 3GPP system access control principles:
• The 3GPP system operator may easily allow subscribers within his existing
3GPP system customer base to access the WLAN with a minimum effort
both for the subscriber and the operator.
• The maintenance of the subscriber may also be simplified.
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Scenario 3: Access to 3GPP system
PS based services
• The goal of this scenario is to allow the operator to extend 3GPP system PS
based services to the WLAN.
• These services may include, for example, APNs, IMS based services,
location based services, instant messaging, presence based services etc.
• Even though this scenario allows access to all services, it is an
implementation question whether only a subset of the services is actually
provided.
• However, service continuity between the 3GPP system part and the WLAN
part is not required.
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Scenario 4: Service Continuity
• The goal of this scenario is to allow the services supported in Scenario 3 to
survive a change of access between WLAN and 3GPP systems.
• The change of access may be noticeable to the user, but there will be no
need for the user/UE to reestablish the service.
• There may be a change in service quality as a consequence of the
transition between systems due to the varying capabilities and
characteristics of the access technologies and their associated networks.
• It is also possible that some services may not survive, as the continuing
network may not support an equivalent service.
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Scenario 5: Seamless services
• The goal of this scenario is to provide seamless service continuity between
the access technologies, for the services supported in Scenario 3.
• By seamless service continuity is meant minimizing aspects such as data
loss and break time during the switch between access technologies.
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Scenario 6: Access to 3GPP CS
Services
• This scenario allows access to services provided by the entities of the
3GPP Circuit Switched Core Network over WLAN.
• This scenario does not imply any circuit-switched type of characteristics to
be included into WLAN.
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