data transmission rates. New functionality or enhancement to an existing release is also added in each subsequent release. The Release 99, shown in Figure 2.10, was the first version where UMTS came into existence which evolved from the GSM/GPRS system in terms of the new RAN, UTRAN. Subsequent releases of the UMTS UTRAN introduced new features offering increased data transmission rates. Similarly, 3GPP Release 8 was the first version of the LTE system, and Release 15 was the first version of the 5G system.
Table 2.3 Summary of 3GPP Releases and their features.
| 3GPP Releases | Features |
|---|---|
| Release 99 [Year: 2000] | UMTS First Release, combination of GSM and UMTS, voice call through E1 interface. |
| Release 4 [Year: 2001] | UMTS core called Bearer‐Independent Core Network (BICN)/Next‐Generation Network,Splitting architecture, separating control plane and data plane |
| Release 5 [Year: 2002] | IMS, HSDPA, all IP network |
| Release 6 [Year: 2005] | HSUPA |
| Release 7 [Year: 2007] | HSPA+ |
| Release 8/9 [Year: 2010] | LTE E‐UTRA/LTE Baseline Release |
| Release 10 [Year: 2011] and beyond | LTE‐Advanced, Career Aggregation |
| Release 15 and Beyond | 5G System |
Prior to Release 99, 3GPP technical specifications releases were known by the corresponding year such as Release 1997 and Release 1998. However, after the Release 99, 3GPP technical specifications releases are known by the corresponding version number only such as Release 4 Release 5 and beyond. A new 3GPP release details are described through its own and dedicated technical specifications series. However, because of a new feature or functionality, an existing technical specification from a previous release version may be also impacted. Details of such information can be derived from the 3GPP release descriptions document available on the 3GPP site [3].
Apart from the introduction of a new feature in each 3GPP release, a new message(s) or a new information element(s) or a new type of channel, either in DL or UL, to an existing protocol layer may be also added. For further details on each of the above releases, visit this 3GPP site [3].
Chapter Summary
In this chapter, we have presented the introductory architectures, the various domains or areas, and the network elements of mobile communications networks based on the GSM, UMTS, and LTE systems. The 5G system is also covered in appropriate sections of this chapter. We then presented the global 3GPP standardizations process of various technical specifications based on which mobile communications systems and networks are designed and built. The evolutions of mobile communications systems and networks in terms of 3GPP system architectures release are also discussed.
The reader is advised to get familiar with the various aspects of a 3GPP TS. To start with, select a particular mobile communications system and then use the 3GPP specification series [2] as the guiding resources to download and study the technical specifications of a particular series and the subject area of interest. Get an overview of the various protocol layers, interfaces, procedures, and functions performed by a particular network element.
This chapter was the introductory one, for the reader, whose contents are general in nature and thus applicable to the 5G system also. The various protocols, procedures, and functions performed by a mobile communications network and its elements/entities shall be described in detail in the subsequent chapters of this book. Design, development, and implementation aspects of a network element in the software code shall be also presented in the subsequent chapter.
3 Protocols, Interfaces, and Architectures
Introduction
This chapter covers the protocol architectures of network elements of mobile communications networks based on the Global System for Mobile Communication (GSM), Universal Mobile Telecommunication System (UMTS), Long‐Term Evolution (LTE), and 5G systems as defined by the 3rd Generation Partnership Project (3GPP). The protocol stack, its layer, and the architecture of a mobile communications network are different from the traditional Internet Protocol (IP) networks. Nevertheless, the protocol stack and layers of a mobile communications network can be studied in parlance with the OSI‐7‐layer reference network architecture. Developers must have understandings of the architectural aspects of protocol stack and its layers as it is core to the design and development of network elements of mobile communications systems and networks.
We begin with the basic means of communication between two peer protocol layers of network elements irrespective of the mobile communications system and network being used. Following this, we present the concept of sublayering of a protocol layer performing different functions and procedures of each protocol sublayer. We then present how protocol layers are grouped in case of the UMTS, LTE, and 5G systems based on the peer‐to‐peer communication between a User Equipment (UE) and the radio access network (RAN) and between UE and core network (CN). Classification of individual protocol layers is also presented based on the nature of functions performed by each layer. We also present the working model of a protocol layer based on which it provides services to its upper layer or uses the services from a layer below it. We close this chapter with another aspect of peer‐to‐peer protocol layer communications, which is protocol layer termination.
3.1 Protocol Interface and Its Stack
Network elements of mobile communications networks are designed and developed based on a set of standard protocols and specifications as defined by the 3GPP. A protocol interface is a communication path that is established between two network elements. Each network element and its protocol layers communicate with the peer network element and its protocol layers through a particular interface. The related protocol layers or the protocol stack, supported by a network element, are organized into a protocol interface. Over a particular protocol interface between two network elements, they exchange various signaling messages corresponding to a particular function and procedure such as the following ones:
Call Control Management, i.e. a call establishment, maintenance, and its releasing;
Mobility Management and Session Management (SM);
Radio Resource Management, Handover, and Power Control Management; and
Interworking, Interoperations, Roaming Management, and so on.
A protocol interface also carries user data or traffic between two network elements. A protocol interface between two network elements could be physical as well as logical as described below. A logical interface may be a point to point, i.e. direct, or may span through several network elements. A logical interface works on top of a physical interface.
3.1.1 Physical Interface
The physical interface defines the electrical characteristic of the physical transmission media being used for the actual transmission and reception of information between a sender and receiver. Consider the physical Cat5 cable or its other variants used in a Local Area Network to transmit and receive upper/lower layers information. Application data received from the upper layers are converted into