CELLULAR DATA NETWORKS Mr. Husnain Sherazi [email protected] Lecture 5

CELLULAR DATA NETWORKS

Mr. Husnain Sherazi [email protected]

Lecture 5

Cellular Data Network

• In the absence of Wi-Fi, the network which can help in

internet connectivity is Cellular Network.

• Cellular networks were designed to carry voice.

• However with the increase in the usage of internet, Cellular

Networks are now used to carry data along with voice.

• Users can communicate with each other on-the-go while

moving which makes Cellular Networks a good choice to be

used while moving within a distance of kilometers.

• Wi-Fi can operate within few meters which limits its usage

as far as distance / range is concerned.

Cellular Data Network

Internet

Generations of Cellular Network

• Cellular Networks have different generations

• 1G (First Generation)

• 2G (Second Generation)

• 2.5G (Second Generation)

• 3G (Third Generation)

• 4G (Long Term Evolution)


• 1G (First Generation)

• It was the first generation of Cellular Networks.

• It came into being in around 1978.

• Japanese Telecom company (NTT) first used it for voice

communication.

• No Data communication is done through 1G.

• It is an analog technology.


• 2G (Second Generation)

• 1G was replaced by 2G in around 1980.

• It is a faster cellular network than 1G.

• Europe made a standard for this technology and

named it Global System for Mobile Communication

(GSM).

• It’s a digital form of wireless technology.

• Protocols used by 2G are

• TDMA

• CDMA


• 2.5G (Second Generation)

• 2.5G is enhanced form of 2G networks.

• It is the first form of data communication over the

cellular network which is always on.

• It is not defined as a standard but normally used as an

interim generation between 2G and 3G.

• Protocols used in 2.5G are

• GPRS (General Packet Radio Service)


• 3G (Third Generation)

• 3G is considered as a third form of cellular networks.

• They carry high data at a high speed.

• Video conferencing is one of the major breakthroughs

cellular networks have seen using 3G networks.

• NTT Docomo (A Japanese company) launched first

commercial 3G enabled system in 2001.


• 4G (Long Term Evolution)

• It is even faster than 3G networks.

• High speed is the major advantage of 4G networks.

• This is still a new technology.

Cellular Network Architecture

• 2G Network Architecture

• Cellular networks are called Cellular networks because

coverage area of a cellular network is divided into Cells.

• Each cell is a hexagon.

• Each cell contains a BTS (Base Transceiver Station).

• This BTS can send and receive signals.

• Coverage area of Cell depends upon

• Transmitting power of BTS

• Transmitting power of User Device

• Line of Sight

• Characteristics of BTS Antenna

2G Network Architecture



• BTS in some networks were used to be in the middle of

each cell so that coverage area is well spread.

• In new systems, BTS are used at one corner and cells

are arranged in such a way that BTS can cover all the

three cells.

• A Base Station Controller (BSC) provides channels to

BTS.

• Mobile Switching Center (MSC) makes authentications

of whether a user can connect to network or not.



• 3G networks use 2G network architecture to extend it

to use it for data communication.

• It leaves the existing architecture as it is and add

some additional functionality that works in parallel.

• It used Radio Network Controller (RNC) to control

several cells just like BSC in 2G.

3G Network Architecture



• There are two nodes in 3G core network

• SGSN (Serving GPRS Support Nodes)

• It sends and receives datagrams to and from mobile nodes.

• It interacts with area specific RNC for authorization.

• GGSN (Gateway GPRS Support Nodes)

• It serves as a Gateway connecting multiple SGSNs.

• It is the last component to which datagram is exposed before

entering the Internet.

Mobility Management

• How a user is Mobile?

• Network layer perspective

• A user is not mobile if he is moving within the same

network.

• User is some what mobile if he moves from one network to

another by shutting down his device.

• User is highly mobile if he moves from one wireless access

network to another without shutting down his device.

Mobility Management

• How a user is Mobile?

• Network layer perspective

Mobility Management

• Addressing

• If a node is moving in a way that its IP Address remains

the same, it does not matter to an application which

deals directly with the IP Address of the node.

• When a node moves to a Foreign network, this network

advertises to all other neighboring network about this

node.

• Foreign network will assign a specific route to this

node which is used to reach this node.

Mobility Management

• Addressing

• A second approach is that when a node enters the

Foreign network, it will assign it a Care of Address.

• A node will also have a permanent address along with

the Care of Address.

• The Foreign Network will inform the Home Network

that the node is in its network.

Mobility Management

• Routing

• When a node moves from its home network to a foreign

network, the process of communicating with the node

becomes complex.

• The node is not directly accessible from its home network

so some routing scheme should be used to send and

receive data to and from the node in the foreign network.

• Two types of routing are used for this purpose

• Indirect Routing

• Direct Routing

Mobility Management

• Indirect Routing

• The data is first sent to the home network of the

mobile node using its permanent address.

• The home network will send the packet to the foreign

network using COA of the mobile node.

• After the packet is in the foreign network, the packet is

then sent to the node using its permanent address.

Indirect Routing

Mobility Management

• Direct Routing

• Indirect routing can create problem of time and speed.

• Even if the nodes are close to each other, the data is

to be passed to home network and then to the foreign

network which is inefficient.

• To overcome this problem, Direct Routing is used.

• In Direct Routing, Correspondent queries Home

Network about the COA of the node.

• The information is then sent directly to the node from

the correspondent using the COA.

Direct Routing

Mobility Management

• Direct Routing with Multiple Foreign Agents

• What if node is moving from one foreign agent to another?

• Correspondent will ask about COA of the node only once

when starting the session so if foreign agent is changed,

the updated COA is not available for the correspondent.

• To overcome this problem, COA for mobile node is

maintained at foreign agent called Anchor Foreign

Agent.

• As soon as node enters the new foreign network, it will

register with the new Foreign agent which will send the

COA of the node to the Anchor Foreign Agent.

Direct Routing

Mobile IP

• Mobile IP is a standard which is used when nodes

are moving from one network (Home Network) to

another (Foreign Network).

• Mobile IP protocol is used to inform Home Network

about the COA when a node enters the Foreign

Network, so all packets are now sent from Home

Network to Foreign Network and then to the node.

• Mobile IP is used in large Wireless WANs.

Mobile IP Post Office Analogy

Old House in Lahore New House in Karachi

Post Office in Lahore Post Office in Karachi

Mobile IP

Home Network Foreign Network

Mobile IP Components

• Agent Discovery

• Used for advertising the service by Home and Foreign

Agent.

• Registration with Home Agent

• Used for registering or deregistering of COA for a node.

• Indirect Routing of Datagrams

• Rule for transferring datagrams to nodes

• Rules for error conditions

• Rules for encapsulation

Managing Mobility for Voice Calls

• In Cellular network same concept of Home and

Foreign network are used for managing calls.

• Foreign networks are some times also called Visited

Networks.

• Home network maintains the database for each

mobile node

• Permanent Number

• Profile

• Current Location (Even if node is in Visited Network)


• A special switch called Gateway Mobile service

Switching Center (GMSC) is contacted when a call is

made to the node from a correspondent.

• Visited Network maintains a database for the

location of each node currently available in its

network. This is called Visitor Location Register

(VLR).

• Visited Network also contains a MSC.

Routing calls to Mobile User

Correspondent Calls a Mobile User

Calls moves to Home MSC

Home MSC checks HLR

A roaming number is returned to Home

Call is established through Visited MSC

Node is in Visited Network

A roaming number is generatedRoaming number

is like COA

Call is made through PSTN

Call is made through BS

Roaming number

is temporary


Handoffs in GSM

• A Handoff occurs when mobile node changes its

association from one Base Station (BS) to other.

• An association occurs in such a way that Old BS

association is no longer valid and resources are

released.

• An association with new BS occurs so that all the

calls are routed using new BS.

• MSC is the central part for this association.

Handoffs in GSM

Old BS informs MSC for handoff

MSC initiates setup with new BS

New BS allocates a channel

New BS informs MSC and Old BS

Mobile is informed about Handoffs

Mobile and new BS exchanges messages

Handoff complete message

Resources released from old BS

Handoffs in GSM

Documents

CELLULAR DATA NETWORKS Mr. Husnain Sherazi [email protected] Lecture 5