Third,a distinct variation can occur in the delay times of outgoing traffic and incoming traffic.This delay variation can be detrimental to some delay-sensitive application such as voice and live video.

 

Classless interdomain routing(CIDR)--originally introduced in RFC1517 in 1993,finalized in RFC 1519 in the same year as a standard proposal,and amended by RFC 1520--was created for this purpose,and BGP-4 was created to support CIDR.

 

CIDR is merely a polictically sanctioned address summarization scheme that takes advantage of the hierarchical stucture of the Internet.

 

A result of the transition to commercial control of the Internet is that the topology of the modern Internet is far from the tidy picture drawn by the preceding paragraphs.

 

5、bilateral　双面的　multilateral　多边的、多国的

A　peering aggrement may be established directly between two providers(a bilateral peering aggrement) or between a group of similar-sized providers (a multilateral peering aggrement,or MLPA)

 

The peering is equitable for the two partners.

 

Private peering is encouraged because it helps relieve congestion at the national NAPs,adds to route diversity,and can decrease delay for some traffic.