CELLULAR DATA NETWORKS Mr. Husnain Sherazi 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)

Generations of Cellular Network 1G (First Generation) It was the first generation of Cellular Networks. It came into being in around Japanese Telecom company (NTT) first used it for voice communication. No Data communication is done through 1G. It is an analog technology.

Generations of Cellular Network 2G (Second Generation) 1G was replaced by 2G in around 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

Generations of Cellular Network 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)

Generations of Cellular Network 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.

Generations of Cellular Network 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

Cellular Network Architecture 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.

Cellular Network Architecture 3G Network Architecture 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

Cellular Network Architecture 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 LahoreNew House in Karachi Post Office in LahorePost Office in Karachi

Mobile IP Home NetworkForeign 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)

Managing Mobility for Voice Calls A special switch called G ateway M obile service S witching C enter (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 V isitor L ocation R egister (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 generated Roaming number is like COA Call is made through PSTN Call is made through BS Roaming number is temporary

Managing Mobility for Voice Calls

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