The fast growth of data traffic, especially the traffic from new network applications such as VoIP, P2P, IPTV, etc., makes people not doubt that the data traffic has become dominating in today’s network. Although traditional voice traffic is still one of major revenue sources for those incumbent network service carriers. They are seeking a way to convert those cheap IP traffic into a big amount cash flow by bringing in various types of service. Such a data traffic evolution also causes the evolution of the carrier networks from the past voice-oriented network architecture to today’s data-oriented network architecture. This evolution mainly manifests in following three aspects.

Huge amount of fibre capacity deployment
When talking about today’s telecommunication networks, nobody will forget to mention fibre communications. As a communication medium, fibre brings a revolution of human communications to carry a huge amount of capacity in a thumb-sized fibre cable. From the initial single wavelength per fibre to today’s multiple wavelengths per fibre WDM technique, optical communications is evolving towards being faster and cheaper. Presently, the most of advanced fibre communication technique based on wavelength division multiplexing has been able to carry more than 100 wavelengths per fibre and each wavelength carries up to 40 Gb/s capacity in a commercially-available system. With more hardware technical breakthrough, people are attempting to further increase the number of wavelength to up to 1000 and the capacity per wavelength up to 100 Gb/s. In the near future, it can be foreseen that each fibre will be more efficiently utilized.

Fibre communication techniques have been widely deployed today’s long-haul backbone transport networks and metro area networks. This technique is now penetrating the access networks based on so-called Fibre To The Home (FTTH) technology, hoping to allow each home to be cheaply connected by a fibre, so as to provide a huge amount capacity to support the future multimedia triple-play services such as IPTV, VoIP, Internet game, etc. It can be expected that in the future fibres will be ubiquitous ranging from a backbone network, a community network, to every home, and the bandwidth will not be a stressed constraint to continue annoying users any more.

Slimmer network layer architecture
Besides the huge increment of network capacity, we are also seeing that the network layer architecture of the today’s network becomes slimmer and slimmer. Such a change again can be attributed to the traffic change in the today’s network. Since the data traffic has dominated today’s communication networks, the traditional network layer architecture that was designed for the past voice-traffic can not efficiently fit today’s data traffic. A more effective layer architecture is necessary to efficiently carry today’s data traffic.

The most traditional network layer architecture contains at least four layers to include (1) optical WDM layer, (2) SDH/SONET layer, (3) ATM, and (4) IP/MPLS layer. Viewing the super-high control overhead of the ATM layer, i.e., each ATM cell has a 10% of control overhead, which wastes the network capacity greatly, it is attractive and reasonable to remove such a layer to directly transport IP traffic over SDH/SONET layer. This technique is called IP over SDH/SONET. Nonetheless, the removal of the ATM layer can lose some functionalities as well, which for example include the support of quality of service, the function of establishing virtual paths or virtual circuits in the network. These lost functions need to be filled by some layer(s) either IP or MPLS layer. According to today’s network technique, it seems that MPLS layer has taken over all the functionalities that were supported by the ATM layer.

Also, current dominating network traffic is IP data traffic, while the SDH/SONET is a network layer that was designed to specifically support the past voice traffic, which has a strict constraint on time delay, so it seems also not necessary for such a network layer to exist in the modern carrier network for efficiency. Thus, to further eliminate the SDH/SONET layer, another slimmer network layer architecture IP over WDM was introduced recently. In this layer architecture, the functionalities supported by the old SDH/SONET layer have to be shifted to other layers, either up to the MPLS layer or down to the optical layer. These functionalities mainly involve the network protection and restoration capability. Now this capability has been proposed to be realized by either the MPLS layer or the optical layer.

Adding intelligence to carrier networks
With the introduction of the concept of Generalized Multiprotocol Label Wwitching (GMPLS), today’s network control system has also incurred a huge evolution, changing from the traditional centralized TMN or SNMP system to a more general distributed control system. GMPLS technique is versatile enough to support almost all the network layers using a common set of network control protocols. The techniques are mainly realized based on a generalized concept called generalized label, which is modelled to cover various types of capacity unit ranging from a single MPLS label, to a SDH/SONET time, to a wavelength, to a wavelength band, or even to an entire fibre. Such a generalized technique also makes the network control so easy to allow different network layers to communicate with each other so as to achieve better network capacity utilization and serve some traffic engineering purpose. Moreover, the GMPLS control technique brings much intelligence to today’s networks, which are mainly reflected in the aspects such as crossing-layer traffic engineering, crossing-layer network recovery, etc. In addition, the distribution of the network control system also enables the control system more robust to survive the failure of a bottleneck central controller in the old day's control system.

Summary
In contrast to the past voice-oriented network implementation, today’s networks can efficiently support IP services while providing a huge amount of capacity in the most scalable and flexible way. They are also much intelligent to handle end-to-end service provisioning, quality of service, and network failure recovery. Meanwhile, the slimmer network layer architecture also helps the today’s networks grow faster but cheaper.