9. Examples
[DESIRE] [DESIRE Web cache] [Web cache Architecture]Contents
9.1 Location
The UNINETT top-level Web cache server is located in Oslo, close to the international connection and national Internet exchange point.
For the universities in the star, connected via high-bandwith lines (Supernett), it makes sense to be neighbors, as the added latency for connections to the other points of the star is (almost) negligible. Whether these institutions use the top-level UNINETT server as parent or neighbor is depending on their caching server. As of this writing, some are children and some are neighbors. We will investigate the optimum configuration for a first-level server when bandwith is plentiful.
These examples are taken from UNINETT, an overview of the network is found at traffic statistics server.
![[UNINETT topology]](http://domen.uninett.no/~im/bilde/nett/llast.max.1996-11-27.gif)
![[UNINETT topology, color codes]](http://domen.uninett.no/~im/bilde/nett/llast-codes.gif)
UNINETT backbone network
The network is built like a star with the center in Trondheim (21). The international connection and national Internet exchange point are in Oslo (15), one of the star points. From the star points and center, connections in a tree (two-level) go to user institutions. The first level is shown in the figure above. Another local Internet exchange point is being added in Bergen (4), at another of the star points.
The UNINETT top-level Web cache server is located in Oslo, close to the international connection and national Internet exchange point.
For the universities in the star, connected via high-bandwidth lines (Supernett), it makes sense to be neighbors, as the added latency for connections to the other points of the star is (almost) negligible. Whether these institutions use the top-level UNINETT server as parent or neighbor depends on their caching server. As this is written some are children and some are neighbors, and we will investigate what is the optimum configuration for a first-level server when bandwidth is plentiful.
For the colleges at the leafnode it makes sense to have the top-level server as their parent, as their connections lead to the star, and as soon as they reach the star bandwidth is plentiful. Using other leafnode institutions as neighbors is not recommended as their tree connections are slow. The bottleneck for the colleges is normally their connection to the star, and for other institutions the bottleneck is mostly their connection to the tree.
Having one single top-level server places high availability demands on that server, and the redundancy added by having two servers is recommended. This is a question of how much money can be spent (which is a function of how much money you save by adding Web caching).
9.2 Relations
SURFnet relations
These are some of the relations of the SURFnet top-level Web cache server. The lower part of the figure shows relations inside SURFnet, the upper left part shows relations with other Dutch ISPs and the upper right shows the dual parent relations with UNINETT, where UNINETT top-level cache is parent for all documents in the .no domain and SURFnet top-level cache is parent for all documents in the .nl domain.
UNINETT relations
These are some of the relations of the UNINETT top-level Web cache server. Note that Telenor (another ISP) is only allowed a sibling relationship. The Universities (UiO, UiB and UiTų) should be siblings, but at the moment they are not. KTH is used as a parent for the .se domain, and as a sibling for everything else. NLANR is actually several servers, and we use one of them as a sibling for the .com domain.
9.3 Statistics
There are a number of different log analyzing programs around, these figures are generated by some home made scripts.
Figure 5: UNINETT top-level
Figure 6: Tromsų first level
Figure 7: UNINETT top-level
Figure 8: Tromsų first level
The figures shows the hit rates for the first-level cache at the University of Tromsų and the UNINETT top-level cache for the period 21. Oct - 1. Dec 1996. The drop in hit rate on 25. Nov is due to a total clean out of the UNINETT cache. More statistics are available for the UNINETT and the University of Tromsų Web caches.
Typical total savings for the two-level cache system are around 50% on the number of connections made to the origin server, and around 55% for bytes downloaded.
Ingrid Melve