GPRS Network Operations
The GPRS Network Operations consists of the attachment and detachment procedure. The GPRS attach is for the mobile station to register itself with SGSN. It establishes a logical link between mobile station and SGSN. The network checks if the mobile station is authorised, then it copies the user profile from the Home Location Register (HLR) to SGSN, assigns a temporary mobile station identity (P-TMSI). The mobile station asks for the address to exchange packets with the external packet data network (PDN). It gets PDP (Packet Data Protocol) address. A PDP context is created for each session, which is stored in the mobile station, SGSN,and GGSN. A user can have several simultaneous contexts. The allocation of PDP address can be either static (permanent address) or dynamic (given upon activation of context). The GPRS detach is the procedure of disconnection from the network. It is initiated by mobile station or network. All resources are released in the detach process.
Mobility Management
SGSN communicates with each other to update mobile station's location. The mobile station profiles stored in Visitor Location Register (VLR) are accessible to SGSN via local mobile switching center. When a mobile station moves out, resources and logical link with the specific SGSN are released.
Routing
The intra-PLMN networks are connected with the Inter-PLMN backbone. A roaming agreement is necessary between the PLMN networks. A GRPS mobile station sends a data packet, the associated SGSN encapsulates it, examines the PDP context, and then routes them through the intra-PLMN GPRS backbone to the appropriate GGSN. The GGSN then decapsulates the packet, sends them to the network, like IP, where routing mechanisms are used to transfer packets to the access router of the destination network, which then delivers packets to host.
Communicating with the IP networks
GPRS can connect to the IP network. It supports IPv4 and IPv6. From the external IP network's view, GPRS looks like the IP subnetwork, GGSN looks like router. Each user gets IP address from the address space of GPRS operator, maintained by DHCP (Dynamic Host Configuration Protocol) server. Address resolution between IP address and GSM address is performed by GGSN using appropriate PDP context. DNS (Domain Name Server) is managed by GPRS operator to resolve host names. Firewall is used to protect from unauthorised access between external IP network and private GPRS network.
Data Services in GPRS
There are two modes of GPRS network. These are-
- Application Mode: access to applications on phone. example, WAP browser embedded in phone to access websites. The operating execution environments include Symbian and J2ME. The applications are developed in C, C++ and Java.
- Tunneling Mode: for mobile computing where user uses the GPRS interface to access the network. The device acts as modem for laptops, PDAs etc. to access wireless data network, by connecting to mobile phones. The device is like black box, different from mobile phone.
GPRS Handsets
There are three classes of a GPRS terminal:
- Class A: It supports GPRS data and GSM services like SMS simultaneously. It includes simultaneous attach, activation, monitor and traffic. It can make or receive calls, SMS etc. on two services simultaneously. When using circuit switched service, virtual switched network (GPRS) will be placed on busy.
- Class B: It can monitor GSM and GPRS simultaneously, but support only one at a time. It can support simultaneous attach, activation, monitor but not simultaneous traffic. It can make or receive calls, SMS etc. on two services simultaneously. When using circuit switched service, virtual switched network (GPRS) will be placed on busy.
- Class C: It supports only non-simultaneous attach. The user selects which service to connect to. It can make/receive calls from only manually selected network service. A service that is not selected is not reachable. SMS support is optional.
Bearers in GPRS
GPRS offers end-to-end packet switched data transfer. There are two kinds of data transport services, PTM (Point to Multipoint) which is available in future releases, and PTP (Point to Point), which is available now, and offers transfer of data packets between two users.
Services Supported by GPRS
- SMS: Short Message Service. Originally designed for GSM. GPRS supports SMS as a bearer.
- WAP: Wireless Application Protocol. It is the data bearer service over HTTP protocol. WAP uses WML (Wireless Markup Language) and a WAP gateway.
- MMS: Multimedia Messaging Service. It supports multimedia messages. It uses WAP and SMS as its lower layer transport to transport video, audio, clips etc.
Applications for GPRS
Generic Apps
Information Services, internet access, email, web browsing. Generic mass marketing apps: sports, news, weather, flight, reminders, horoscope, traffic information etc. Due to higher bandwidth, mobile internet browsing is more suited to GPRS. Mobile commerce, banking app.
GPRS Specific Apps
Chat: GPRS offers ubiquitous chat by integrating internet chat and wireless chat using SMS and WAP.
Multimedia Service: Phone and Camera apps, sharing apps for multimedia- monitor locations, parking lot information for crime etc., sending images of accident by journalists etc., remote medical help, virtual private network. Banks use VSAT (very small aperture terminal) to connect ATM to bank server.
Personal Information Management: Persona diary, calendar etc.
Job Sheet Dispatch: design and communicate job sheets from office based staff to mobile file staff. Example, vehicle positioning apps, like Uber, to dispatch nearest available personnel to serve the customer.
Unified Messaging: single mailbox for email, fax, SMS, MMS, voice email etc.
Vehicle Positioning: Integrates GPS for car rental tariffs, stolen vehicle tracking.
Location Based Services and Telemetrics: hotel and restaurant finders, news and weather etc.
Limitations of GPRS
- Limited Cell Capacity for all users - because of limited radio resources, as voice and call use same network resources.
- Speed lower in reality - the theoretical maximum of 172 KBps is not achievable as all time slots cannot be used by single user.
- No Support of GPRS Mobile Terminated Connection for Mobile Server - GPRS terminal can only act as client, not server.
