An Investigation into Transport Protocols and Data Transport ...

9.2. Preferential Flow Handling Using DiffServ 216
The DiffServ architecture offers new opportunities for building preferential
macro-flow handling for end-to-end networks. However, it also introduces
new challenges. [FKSS98, YR99b, YR99a] show that it is difficult to guarantee
requested throughputs for TCP flows, because of the flow and congestion
control mechanisms used by TCP, which result, for example, in bursty traffic.
Two recent developments can significantly contribute to tackle the problems
of high capacity service differentiation: Proposals for high throughput
TCP algorithms and the availability of DiffServ enabled networks at gigabit
speeds.
9.2.1 Methodology
Sections 9.1.3 and 9.1.6 and suggests that a mechanism for segregating traffic
sharing the same packet-switched path would be beneficial. The reasons for
this are two fold:
• To protect traditional traffic from the possible aggression of the New-
TCP algorithms and hence be more ‘fair’ to existing Internet users.
• To provide a guarantee on the level of end-to-end service predictability
for the New-TCP proposals.
As such, DiffServ provides a facility to offer protection of the background
traffic whilst maintaining a predefined pipe whereby the high-speed New-
TCP flow can fully utilise the link.
Two PHB classes were configured: BE for traditional Best Effort [CF98]
traffic and Assured Forwarding (AF) [HFB + 99] to provide network resources
for the New-TCP flows. Traffic was marked with an appropriate Diffserv
codepoint (DSCP) [BBC + 98] at the sending host and each class is put in