An Investigation into Transport Protocols and Data Transport ...

2.4. Data Transfer Requirements 37
2.4.2 Tier-1 to Tier-2
Traffic between Tier-1 and Tier-2 sites are likely to be relatively local, with
latencies in the range of 10msec to 50msec. Typical data transfers are likely
to pass through existing infrastructures such as that of Janet, Abilene etc
between the Tier-1 and Tier-2 sites. Currently most of these networks are
built upon 10Gb/sec backbones with relatively light loading (typically around
10% [ST]). If the network is shared (Internet), then it will be important to
maintain fairness between the LHC and commodity traffic.
2.4.3 Tier-2 to Tier-3/4
The ‘last hop’ of the LHC data transport will be from the Tier-2 centres to
that of local workgroup machines and desktop computers where physicists
will perform the analysis of data. As such, this will typically be what users
will perceive as the raw performance of the data transfer. Due to the locality
of the Tier-2 to Tier-3/4 sites, latencies are likely to be relatively small (less
than 20msec). However, the networks at this edge are generally likely to
be bottlenecked by the local MAN and campus networks, and will likely
need to be shared between all users on the campus and or local area and
thus fairness becomes an important issue. Therefore, is will be important to
sustain a balance between affecting other network users (and the network in
general) and achieving high throughput to enable the users to do their work.
2.4.4 Summary
Table 2.2 shows a matrix of TCP performance metrics according to the type
of end-to-end connection with a relation to that of the Tiers in the MONARC
architecture.