Evaluation of network parameters at the stage of optical transport system designing

O.V. Krasko

Lviv Polytechnic National University

Since the primary network is nothing more than a set of channels, behavior and standards do not go beyond the network layer protocols, which includes a description of channels and methods of switching. Emerging of new solutions for access network FFTx and wideband mobile access network brings on a rapid growing of packet traffic, transmitted over transport network.  
For successful interaction between different access networks, the channels of the backbone network should be standardize according to the PDH and SDH hierarchy. Initially, the development of transport networks assumed that there are only primary channels data. The backbone network considered as a set of channels. Further separation of network traffic segments and segments greatly enhanced the access network scalability. Solutions for transport networks and access networks have become less formal and less standardized, compared with the solutions for the primary and secondary networks.
The main problem that arises when transmitting packet traffic over SDH network is inconsistency throughputs of Gigabit Ethernet networks with a capacity of payload that can be transport by STM. This mismatch significantly reduce the efficiency of channel resources while packet traffic transmitted. One of the possible mechanisms of solving this problem is to use virtual concatenation (VCAT) in conjunction with general framing procedure (GFP) and link capacity adjustment scheme (LCAS).
The concatenation principle leads in combining of multiple virtual containers. As result, their combined capacity used as a block for transmission of data, which size exceeds the size of single container. There are two types of concatenation – contiguous and virtual. Concatenation of both types forms a path of bandwidth is n times greater than the rate of a single container CVC, but with different principle of transmission between two nodes. The set of containers that deliver IP-traffic between two nodes A and B called contiguous concatenation (CCG) or virtual concatenation (VCG) group. The disadvantage of contiguous concatenation is that permissible speed transmission is strictly defined standard SDH hierarchy. The virtual concatenation utilizing channel resources more flexible by non-hierarchical speeds.
The paper presents a hybrid mechanism for virtual concatenation (H-VCAT), which allows increasing channel utilizing by 10% compared with virtual concatenation and by 50-70% in comparison with contiguous concatenation. The evaluation of network parameters at the stage of optical transport system designing provided. The optimum set of containers for transferring traffic from FTTx access networks with 99.7% channel utilizing was proposed.