The SEEREN physical and logical network topologies are depicted in Figure 12-13 and Figure 12-14, respectively. The MPLS-enabled core network infrastructure, which is provided by a consortium of operators in SE Europe, has Points of Presence (PoPs) in all the SE European capital cities. Interconnection between the SEEREN NRENs is achieved with the Carrier supporting Carrier (CsC) technique (see Figure 12-15), which enables an MPLS VPN-based service provider, called the carrier provider, to allow other IP (or MPLS) service providers, called customers carriers (SEEREN NRENs1), to use a segment of its backbone network.

The access links of SEEREN NRENs range from 2Mbps up to 34Mbps, while connectivity is achieved by using diverse technologies from ATM to Ethernet over PPP (EoPPP). The SEEREN primary connection to GÉANT is a 95Mbps ATM PVC crossing GRNET. A secondary (backup) 34Mbps ATM connection diverts traffic to RoduNET (Bucharest GÉANT PoP) in case of failure in the primary connection.