15.1 Network Evolution Overview

15.1.1 Fixed Transport Network Evolution

The fixed transport network has been evolving rapidly in the last few years . The optical technology revolution of the late 1990s has resulted in deployment of long-haul as well as metro networks based on wavelength division multiplexing (WDM) and dense wavelength division multiplexing (DWDM) technologies, which has increased the available bandwidth and network capacity to a great degree. Technologies that are having an impact on the transport network evolution include Gigabit Ethernet among others. The increased availability of bandwidth directly translates to lower costs for carrying the bits.

Asynchronous transfer mode (ATM) was predominantly deployed in the backbone networks in the early 1990s. However with the development of multi-protocol label switching (MPLS), the growth of ATM has slowed down and MPLS is now in the process of cohabiting with ATM switches in some places and in many instances replacing it altogether. Technologies such as packet over sonet (PoS) are also changing the way data networks interface to the backbone networks.

One of the major costs of operating a wireless network is the backhaul network cost. Base stations and cell sites need to be connected to a centralized controller. Generally this has been done using T1s and E1s as well as microwave links. With the availability of high-capacity optical networks in metro areas, it is possible that the base stations could be connected to the optical networks directly, and traffic to and from the central controller routed through such networks. Hence, instead of having point-to-point connections between the controller and the base stations, a large number of base stations could be connected to a fiber ring and share the resources of the transport network with other traffic, thereby reducing the cost of the backhaul networks. The availability of technologies such as xDSL will also allow different models and networking technology to be used for the transport networks used by cellular systems. The proliferation of IP will also have an impact on the transport network architectures in the radio network and the core network. Currently these are based primarily on ATM and use dedicated circuits. These may evolve in the future to use packet switched networks and utilize shared networks (as opposed to dedicated circuits) with guaranteed service.

15.1.2 Wireless Network Evolution

On the mobile networking side, third-generation WCDMA technology will dominate the wide area access networks as well as licensed band hotspots. 802.11a and 802.11b wireless LAN technologies provide high data rates (on the order of 11 Mbps and 54 Mbps) and are ideally suited for hotspots such as airports, convention centers, and other public places. New WLAN security standard increases WLAN's significance, especially if the access provider does not have a license to operate a cellular network. Cellular operators are also interested in WLAN technologies and are in the process of building such networks to complement their wide area cellular service. A nominal air interface bit rate of 2 Mbps in WCDMA hotspots is clearly less than WLAN can provide. However, direct bit rate comparison does not reflect the end user experience since WLAN lacks the QoS and smooth handover features that are standard in the WCDMA air interface. Advanced WCDMA radio resource control optimizes the access bandwidth usage, thus lowering operator costs and giving indirect savings to the subscriber.

In the short term , the evolution of wireless networks is based on the technology path chosen . Third-generation license ownership is one of the major control points here (thus the high European auction prices). Existing second-generation GSM, TDMA, or CDMA networks are another crucial factor when selecting a new technology. In the longer run one or two technologies will dominate the market. A small number of technologies can provide better economies of scale than multiple heterogeneous networks. Global roaming and other features are also easier to achieve when only a few interfaces must be matched. UMTS networks, WCDMA radio technology, and global radio band allocation have been major steps toward harmonizing the networks. The IETF Mobile IP working group is attempting to specify a universal mobility management mechanism with IPv6 technology.

Personal area networks (PANs) are an interesting future development. A single node ("personal base station" or "mobile router") passes traffic between the subscriber's personal area and the wide area, which is in the operator's domain. Technically a small-scale gateway between the domains is not that difficult as low-power integrated circuits can do most of the user plane processing, but the deployment scenarios are much harder: PAN management is a totally new issue; how trusted is the mobile router from the WAN perspective (and vice versa), and will the development lead to a peer-to-peer network where WAN has only a minor significance? Bluetooth devices already implement the required radio technology. Several control technologies related to security, QoS, and addressing are still under study in Bluetooth Forum and IETF Mobile ad hoc networks working groups. PAN use cases vary from cooperation of a mobile phone and embedded intelligence in an automobile to mobile phone-wireless earpiece-laptop communication.

15.1.3 Wireless Applications

This book focuses on Internet technologies in wireless networks. Internet and IP networking especially concentrate on carrying messages from the source to the destination. But in the end the applications ”mail, news, chat, messaging, Web browsing, presence services ”is what subscribers ask for. The applications in turn set the quality and security requirements for the network. So far circuit switched voice has been the dominating application in cellular networks, and data traffic has been transported on top of the circuits. The ratio of voice and data will be reversed , which means that it will be more economical to adjust voice traffic into the packet switched data networks than vice versa.

Unfortunately the applications are the part that is hardest to predict. We have seen this many times: GSM short message service (SMS) is limited to low bandwidth and 160-character messages since it was considered a niche application when design decisions were made. Open System Interconnection (OSI) protocols were an alternative to TCP/IP data networking until the WWW applications termed the latter the definitive winner. Browsing and user experience (graphical user interface included) had the key position here, not the http, ftp, DNS, or IP protocols.

Mobile phones with embedded digital cameras and color displays were launched in 2001. These features in the terminals will enable new services like multimedia messaging (MMS) with mixed data and images. 3GPP selected the IETF Session Initiation Protocol to control IP multimedia services in future mobile networks. SIP is a flexible, text-based signaling protocol for connection setup and teardown . In the IMS model the network holds the connection status for each user. Peer-to-peer connection directly between the hosts (e.g., mobile terminals), is also possible, but it will be a later development when terminals become capable. Even then certain kinds of centralized directories, proxies, and portals will be in place so peer-to-peer is only an additional form of communication between the hosts .