Influence of the IP Traffic Asymmetry on the Cost of the Optical Network Layer

The main traffic to be carried by a backbone network in the future (or even now) will be (is) IP traffic, which is unidirectional and asymmetric in nature. Today, most backbone networks are still designed for bidirectional, symmetrical services like SDH/SONET. In the future, the transmission links in the optical layer will probably still be symmetric (same amount of capacity installed in both directions of the optical link), and operators will probably continue to lease bidirectional capacity to their customers. However, the traffic that will be conveyed over those bidirectional transmission links will be mainly unidirectional and asymmetric. This paper studies the influence of the asymmetric nature of IP traffic on the underlying optical layer. In case the optical layer contains bidirectional symmetric capacity (as is almost always the case nowadays), it shows how cost(in)efficient this optical capacity is used for IP traffic patterns with varying asymmetry. The comparison is also made with a unidirectional optical layer, in which the capacity (line-systems) installed in the network is asymmetric (more capacity can be present in one direction of an optical link than in the other direction), or in which the capacity that is leased by operators is asymmetric (e.g., an ISP can choose to lease two wavelengths from city A to city B and five wavelengths in the other direction, from city B to city A).