ARCHITECTURE 

ANSP’s PTTA comprises a virtual switch-router, configured within the peering matrix(an actual switch-router, dedicated to the exchange of traffic) of NAP do Brasil. This matrix is the principal private PTT in the country, to which the major Brazilian networks are connected, including those of the largest national and international telecommunications operators. As earlier mentioned in the section on network topology, the PTTA works with the BGP protocol and, were it not a subprotocol of the TCP/IP, we could classify ANSP as a BGP network rather than an IP network. The PTTA is ANSP’s logical center, and that is where everything decisive on the network occurs.

The use of virtual switch-routers is supported under the BGP protocol and, although little used in the world, it is a resource that is easy to use and with surprising results. ANSP began using it in 2005. Its construction consists entirely of the manipulation of the properties of the BGP and does not need any extra resources (neither software nor hardware) from the peering matrix used. It begins by defining all network participants as autonomous networks (AS - Autonomous System, in BGP jargon) and each one is assigned an address (ASN - Autonomous System Number). BGP provides for the use of public and private ASNs. Networks maintained by telecommunications companies and Internet providers have their own ASNs. Large research and education networks such as the RNP, ANSP, USP and Unesp, also. The networks of the institutions connected to ANSP that do not have public ASNs, are given private ASNs.

To set up the virtual switch-router, a default route to the outside is defined and each participant announces its ASN only to its ANSP peers, and to the rest of the peering matrix it announces ANSP’s public ASN. Thus, the internal traffic is isolated from the external traffic by the ANSP ASN. The result is that ANSP participants exchange traffic among themselves without interference from networks external to ANSP, as if they were connected to a router, and exchange traffic with the external networks as if they were connected to a gateway. And they do so independently!

The same applies to the relationship of ANSP with the commodity Internet and with Brazilian and foreign research and education networks. Every traffic exchange is performed by BGP. Therefore, perhaps the best definition for ANSP today would be to classify it not as a network, but as a point of Distributed Traffic Exchange!