An Investigation into Transport Protocols and Data Transport ...

2.4. Data Transfer Requirements 38
Internet
Dedicated
(sole)
Dedicated
(shared)
Tier-0 to
Tier-1
1) Fairness
2) Throughput
3) Low Overhead
Tier-1 to
Tier-2
Tier-2 to
Tier-3/4
1) Fairness
2) Low Overhead
3) Throughput
1) Throughput
2) Low Overhead
1) Throughput
2) Fairness
3) Convergence
Time
Table 2.2: Overview of Transport requirements for different Tiers based upon the
type of end-to-end connection.
For an in-depth discussion of the definitions of the various metrics presented,
please refer to Chapter 7.
When the large scale data transfers are competing over the commodity
Internet, it will be very important that the transfer will not adversely affect
the existing traffic on the network, therefore the most important metric to
consider is that of Fairness. In order to aid efficient replication to the Tier-1
and Tier-2 locations, throughput becomes the next important factor to consider
such that very large scale caching will not be required at the Tier-0 and
Tier-1 sites respectively. It will also be important to minimise the amount
of data that needs to be retransmitted as such traffic on the commodity Internet
may lead to congestion collapse [FF99]. As such it is important for
the transport algorithms to have low overhead. This is especially important
at the bottom of the hierarchy due to the high possibility of bottlenecked
systems which are more likely to be located in Tier-3 and Tier-4 locations
(due to less hardware and or staff investment in tuning and optimisation).
When considering the move to dedicated circuits for the transport of LHC