Network traffic is handled by both SGSN and GGSN. GPRS network uses its own protocol to encapsulate data. It provides network security and makes data exchange easier.
Mobile data and Open System Interconnection (OSI) model
OSI model is a network standardization created by International Organization for Standardization (ISO), which is a fundamental concept of the Internet infrastructure and operations. Mobile networks use standardized protocols, such as Internet Protocol (IP), from OSI layer 4 and above. The lower level protocols are different from traditional networks, since the network infrastructure is not the same at these levels.
GPRS Tunnel Protocol (GTP) resides at the network layer and is used by GPRS Support Nodes, as was discussed earlier. At the transport layer User Datagram Protocol (UDP) and IP are used. How about Transmission Control Protocol (TCP) that ensures the consistency of data, which is highly important in majority of applications? Since the data consistency and reliability of the transmission is to be handled by the backbone, UDP is preferable in mobile networks. Thus, the backbone should be built accordingly. Although GPRS Support Nodes can be functionally combined under a single unit (just like a home router has an integrated switch), performance wise it is better to keep them separate as independent units. To prevent contention in channel resources Asynchronous Transfer Mode (ATM) or Ethernet protocols can be used according to the network architecture.
Moving down from GTP, Subnetwork Dependent Convergence Protocol (SDCP) is now used to compress user data and encapsulate packets of a network layer for the Logical Link Control (LLC) sublayer at the data link layer. At this stage SGSN can now interact with mobile devices (subscribers) connected to a network, by means of providing data transfer, user identity and data encryption. Radio Link Control / Media Access Control (RLC / MAC) is a lower sublayer that is responsible for transferring user data over channels, defining procedures for having a common transmission medium (several radio channels in a cell tower) between subscribers. The data is transmitted in radio blocks and Automatic Repeat Request (ARQ) resolves errors and missing blocks of data.
Enhanced Data Rates for GSM Evolution (EDGE) is an improvement of GPRS in which the bit rate is increased, hence the bandwidth is improved almost 3 times according to theoretical assumptions.
Universal Mobile Telecommunication System (UMTS) and Long-Term Evolution (LTE)
UMTS is the next successor in mobile network evolution, which uses a completely different radio interface that supports higher bandwidth. The core network did not change, but the radio resources access standard changed, becoming Wideband CDMA. The network has significantly improved with UMTS. Due to design limitations in UMTS, The Third Generation Partnership Project (3GPP) organization decided to redesign radio and core network under a title of LTE. The general architecture is like GSM and UMTS. LTE network is separated into radio network and core network parts.