Traffic Management for the Available Bit Rate (ABR) Service in ...

st link, VC 15 is limited to a throughput of less than 1/15 the link rate. VC 16 and
VC 17 should, therefore, each converge to a little less than 7/15 of the second link
rate. The con guration is called an upstream con guration because the bottleneck
link is the rst link (upstream link). A WAN con guration (1000 Km links) is used
in this situation to illustrate the scalability of ERICA to long distances.
Figure 6.17 shows that the original ERICA algorithm was unfair in this situation,
and gure 6.18 shows that ERICA, after the modi cation discussed in section 6.2, is
fair. As seen in gure 6.18, the modi ed algorithm converges to max-min allocations.
Regardless of the initial load factor value, after a short transient period, all sources
contending for bandwidth are allocated equal rates, and the two curves in gure
6.18(b) (number of cells received at the destination) have the same slope (compare
with gure 6.17(b)). The transient responseisslightly worse than the original ERICA
algorithm due to the temporary over-allocation needed to equalize the shares, but the
steady state performance is as good as with the original ERICA algorithm.
6.22.5 Transient and Steady State Performance
To test the transient response of the system, we use a modi ed two source con-
guration. The con guration is similar to the two source con guration because two
sources share the same link, but one of the sources is only active from 10 ms to
20 ms while the other source is active throughout. Besides illustrating the transient
response of the system, this con guration also illustrates the e ect of the \fairshare
rst" algorithm discussed in section 6.3. That algorithm (see section 6.3) prevents a
low rate VC to rise above F airShare. This VC takes an extra round trip compared
to the basic ERICA because it rst comes to F airShare before rising further. The
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