An Investigation into Transport Protocols and Data Transport ...

2.3. Data Volumes and Regional Centres 35
• Tier-2
Tier 2 centres will service single nations or regions, caching popular
data in their local storage. There will be approximately 60 sites worldwide.
• Tier-3 / 4
The local computing resources at member institutions make up Tier-3
of the model, with Tier-4 consisting of individual machines.
The initial storage and processing of event data will be located at the Tier-
0 site. In the case of the LHC, this will be CERN. The data is then replicated
to various Tier-1 centers around the world where they are further processed.
Approximately sixty Tier-2 regional centers, each serving a medium-sized
country, or one region of a larger country (e.g. USA, UK, Italy, etc), will
then replicate data from the Tier-1 centers. Physicists will then typically
access and further analyse data using one of hundreds of Tier-3 and Tier-4
workgroup servers and/or desktops.
The design of such a system ensures that a physicist should not need to
wait more than 10 minutes [LN00] to transfer relevant data for analysis.
The estimated data rates between Tiers are based on having a very wellordered,
group orientated and scheduled approach to the transfer of data. As
such, the data transfer rates are expected to actually be higher in practice.
An important development in being able to realise the transport requirements
of such data intensive science applications is that of a shift from the
typical shared ‘best-effort’ services of the Internet to dedicated connection
oriented end-to-end paths to facilitate the separation (and hence impact) of
such large scale traffic to that of standard Internet traffic. This is apparent
in projects such as Terapaths [Gib04], OSCARS [Guo04] and LHCnet