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EDGE

The Evolution of the GSM Network

The existing mobile digital communications network continues to develop, in order to increase capacity, coverage, quality and data transmission rates. There have been a series of developments that are now starting to be deployed with the aim of enhancing the GSM network functionality.

The next section shows the enhancements planned for the next few years, starting off with High Speed Circuit Switched Data (HSCD). The next development is General Packet Radio Services (GPRS), this is a packet-switched service that allows full mobility and wide-area coverage. Enhanced Data rates for GSM Evolution (EDGE) will use enhanced modulation and related techniques, further improving local mobility. Universal Mobile Telecommunications System (UMTS) will include second and third generation services.

Figure 18 Evolution of GSM Data Service

Figure 18 Evolution of GSM Data Service
(Adapted from Ericsson Document EN/LZT 123 5374 R1B)

Cell Selection and Reselection

Comparing GPRS with circuit switched In a GSM network the BSC governs the cell selection behavior of the MS when in idle and active mode by different methods. Idle mode MSs autonomously performs cell reselection by using the C1/C2 criteria. In active mode, non-GPRS MSs are steered by the locating functionality implemented in the BSC. …

Dedicated PDCH

Dedicated PDCHs can only be used for GPRS, the operator can specify between zero and eight dedicated PDCHs per cell, the reason for dedicated PDCHs is to ensure that there is always the GPRS resources in a cell. To some extent the operators can specify to where they dedicated PDCH(s) to be located. However from …

EDGE Chapter Summary and Key Points

In GSM Circuit switched data, the typical maximum data rate of data throughput was officially 9.6 kbit/s, however when the overhead of control, guard data, encryption keys and error correction, are taken into account the typically user data throughput was only 1 – 1.5 kbit/s. The first phase of the GSM evolution to higher speed …

General Packet Radio Service (GPRS)

The parts of the GPRS system that carry out the switch of packet data are called the Serving GPRS Support Node (SGSN) and the Gateway GPRS Node (GGSN). The SGSN provides a packet routing to and from the geographical SGSN service area. The GGSN makes up the interface towards the external IP packet networks, the …

GPRS Air Interface

The air interface (Um) is the logical link between the MS and the BSS. Figure 25 shows the GPRS Protocol Stack from the perspective of the BSS.

GPRS IP Connectivity

One of the main advantages of GPRS is that it provides IP connectivity, this means that communication between the different parts of the operators GPRS system, the GGSN, administrative hosts and hosts providing Internet Services. Further more the IP connectivity enables easy communication with the Internet. However is should be noted that GPRS has two …

GPRS Logical Channels

Within GPRS there are a number of new logical channels, similar to the existing ones, but these are only for GPRS. (NB These logical channels have been standardized.) The new logical channels have been mapped onto the physical channels that have been assigned for packet data, the physical channels denoted as Packet Data Channels (PDCH), …

GPRS Support Node (GSN)

The GSN is a general purpose, high-performance packet switching platform, the GSN combines features usually more associated with data communications (features such as compactness and high functionality) with features from telecommunications such as robustness and scalability. The GSN is designed for non-stop operation, the platform incorporates 1+n redundant hardware, and also the software is of …

High Speed Circuit Switched Data (HSCSD)

HSCSD is basically an upgrade of the original GSM CS data transmission system, by using HSCSD the speed at which data is transmitted is greatly improved. The higher data transmission rates are achieved by making use of bundled Traffic Channels (TCH). The way that this works is the MS requests one or more TCHs from …

Interconnection Principles

In this section the connection between GSNs and their operating environment, the interfaces used in the GPRSN network and the GSNs, and their contexts are shown in Figure 29, the interface names are part of the ETSI GSM standard for GPRS.

Master PDCH

A master PDCH (MPDCH), is a PDCH carrying a PBCCH and PCCCH, as well as GPRS traffic. The PCCCH carries all the necessary control signaling to initiate packet traffic. In the standard, the MPDCH is called “the PDCH carrying the PBCCH”. NB the abbreviation MPDCH is only used within Ericsson systems. The first directed PDCH …

On Demand Dedicated PDCH

On-demand PDCH can be pre-empted by incoming circuit switched calls in congested cells, it should be noted that in a HSCSD, a user can never get more than a single channel through the pre-emption procedure. There is no physical limit on how many on-demand PDCHs there can be in a cell. However the number of …

PDCH Allocation

The following section will explain how the PDCH is allocated. Traffic Channels and packet data channels basically create a common pool of resources, utilising the existing resources in an efficient way. See Figure 26   The PDCHs are allocated to the PCU, the PCU is responsible for assigning channels to different GPRS MSs. The PDCHs …

PDP Context Activation and Deactivation

In order for the MS to send and receive GPRS data the MS must perform a PDP context activation after the GPRS attach (Shown in Figure 23). The PDP context activation makes the MS known in the concerned GGSN and communication to external networks is made possible. The PDP context activation corresponds from the end …

System Overview

Terminal Equipment (TE) The TE is the computer terminal that the end user uses. This is the component used for the GPRS system to transmit and receive end user packet data. For example, the TE could be a laptop computer. The GPRS system provides for IP connectivity between the TE and an Internet Service Provider …

The users IP communication

The latter is the communication between a GPRS MS and an ISP, for example. The GPRS system provides IP connectivity between MS and ISPs, using the GSM standard, data transfer is based on the common internet protocol (IP), which means that packet data transmission is carried out on an end-to-end basis (including the air interface). …

Traffic Case – GPRS Attach

In order for the GPRS MS to receive or transmit data the end user needs to perform a two-step procedure, GPRS attach (Figure 21) ND PDP context activation (Figure 22) At GPRS attach a logical link is established between MS and SGSN, the GPRS attachment procedure in Figure 23.     MS sends message to …

Traffic Case – IMSI Attach

In order to make or receive calls on the GSM system an MS needs to perform one procedure, an IMSI attach. The IMSI attach is shown in Figure 21, at IMSI attach a connection between the MS and the GSM network is established. The end user does not need to specify which fixed networks he …

Traffic Case Combined GPRS/IMSI Attach

In a combined GPRS/IMSI attach, both of the previous procedures are carried out simultaneously, shown in Figure 24.

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