**1. Introduction**

328 Telecommunications Networks – Current Status and Future Trends

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Spurred by the vision of seamless connectivity anywhere and anytime, ubiquitous and pervasive communications are playing increasingly important role in our daily lives. New types of applications are also affecting behaviour of users and changing their habits, essentially reinforcing the need for being always connected. This clearly represents a challenge for the telecommunications community especially for operating scenarios characterised by high dynamics of the network requiring appropriate routing and traffic engineering.

Routing and traffic engineering are cornerstones of every future telecommunication system, thus, this chapter is concerned with an adaptive routing and traffic engineering in highly dynamic packet-oriented networks such as mobile ad hoc networks, mobile sensor networks or non-geostationary satellite communication systems with intersatellite links (ISL). The first two cases are recently particularly popular for smaller scale computer or data networks, where scarce energy resources represent the main optimisation parameter both for traffic engineering and routing. However, they require a significantly different approach, typically based on clustering, which exceeds the scope of this chapter. The third case, on the other hand, is particularly interesting from the aspect of routing and traffic engineering in large scale telecommunication networks. Even more so, since it exhibits a high degree of regularity, predictability and periodicity. It combines different segments of communication network and generally requires distinction between different types of traffic. Different restrictions and requirements in different segments typically require separate optimization of resource management.

So, in order to explain all routing functions and different techniques used for traffic engineering in highly dynamic networks we use as an example the ISL network, characterized by highly dynamic conditions. Nonetheless, wherever possible the discussion is intentionally kept independent of the type of underlying network or particular communication protocols and mechanisms (e.g. IP, RIP, OSPF, MPLS, IntServ, DiffServ, etc.), although some presented techniques are an integral part of those protocols. Thus, this chapter is focusing on general routing and traffic engineering techniques that are suitable for the provision of QoS in packet-oriented ISL networks. Furthermore, most concepts,

Routing and Traffic Engineering in Dynamic Packet-Oriented Networks 331

network and traffic conditions but also for their simulation, testing and benchmarking. To this end this chapter is complemented by description of a methodology for developing a global traffic model suitable for the non-geostationary ISL networks, which consists of modules describing distribution of sources, their traffic intensity and its temporal variation,

The main task of any routing is to find suitable paths for user traffic from the source node to destination node in accordance with the traffic's service requirements and the network's service restrictions. Paths should accommodate all different types of services using different optimisation metrics (e.g. delay, bandwidth, etc.). Thus, different types of traffic can be routed over different routes. Routing functionality can be in general split in four core routing functions, (i) acquiring information about the network and user traffic state, and link cost calculation, (ii) distributing the acquired information, (iii) computing routes according to the traffic state information and chosen optimization criteria, and (iv)

For each of these functions, several policies exist. Generally speaking, the selection of a given policy will impact (i) the performance of the routing protocol and (ii) the cost of running the protocol. These two aspects are dual and a careful design in the routing algorithm must achieve a suitable balance between the two. The following sub-sections will

The parameters of the link-cost metric should directly represent the fundamental network characteristics and the changing dynamics of the network status. Furthermore, they should be orthogonal to each other, in order to eliminate unnecessary redundant information and inter-dependence among the variables (Wang & Crowcroft, 1996). Depending on the composition rule we distinguish additive, multiplicative, concave and convex link-cost metrics (Wang, 1999). In additive link-cost metrics the total cost of the path is a sum of costs on every hop. Additive link costs include delay, jitter, cost and hop-count. Total cost of the path in the case of multiplicative link-cost metrics is a product of individual costs of links. A typical example of multiplicative link cost is link reliability. In concave and convex link-cost metrics the total cost of the path equals the cost on the hop with the minimum and maximum link cost respectively, and a typical example of link-cost metric is the available

We show the use of the additive link-cost metric as an example for the link-cost function for the delay sensitive traffic, considering two dynamically changing parameters. The first is the intersatellite distance between neighbouring satellites, while the second is the traffic load on a particular satellite. They have a significant effect on the routing performance and are scalable with the network load and link capacity, thus being well suited for link-cost metric.

forwarding the user traffic along the routes to the destination node.

**2.1 Acquiring information about the network and link cost calculation** 

as well as traffic flow patterns.

discuss the four core routing functions.

**2.1.1 Link cost for delay sensitive traffic** 

(Mohorcic et al., 2004; Svigelj et al., 2004a).

bandwidth.

**2. Routing functions** 

described techniques, procedures and algorithms, even if explained on an example of ISL network, can be generalised and used also in other types of networks exhibiting high level of dynamics (Liu et al., 2011; Long et al., 2010; Rao & Wang, 2010, 2011). The modular approach allows easy (re)usage of presented procedures and techniques, thus, only particular or entire procedures can be used.

ISL network exhibits several useful properties which support the development of routing procedures. These properties include (Wood et al., 2001):


The above properties are incorporated in the described routing and traffic modelling techniques and procedures. Special attention is given to properties which support the development of efficient, yet not excessively complex, adaptive routing and traffic engineering techniques.

However, for the verification, validation and performance evaluation of algorithms, protocols, or whole telecommunication systems, the development of suitable traffic models, which serve as a vital input parameter in any simulation model, is of paramount importance. Thus, at the end of the chapter we are presenting the methodology for modelling global aggregate traffic comprising of four main modules. It can be used as a whole or only selected modules can be used for particular purposes connected with simulation of particular models.

Routing and traffic engineering on one side require good knowledge of the type of network and its characteristics and on the other side also of the type of traffic in the network. This is needed not only for adapting particular techniques, procedures and algorithms to the network and traffic conditions but also for their simulation, testing and benchmarking. To this end this chapter is complemented by description of a methodology for developing a global traffic model suitable for the non-geostationary ISL networks, which consists of modules describing distribution of sources, their traffic intensity and its temporal variation, as well as traffic flow patterns.
