24.11.2012 Views

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

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

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

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

9.2 The ERICA Switch Scheme: Renotated<br />

In this section, we <strong>in</strong>troduce some new notation <strong>for</strong> <strong>the</strong> ERICA algorithm which<br />

we use later <strong>in</strong> this section to expla<strong>in</strong> its implementation <strong>in</strong> a VS/VD switch.<br />

The ERICA target rate is set as follows:<br />

Target <strong>Rate</strong> = Target Utilization L<strong>in</strong>k <strong>Rate</strong> - VBR (high priority) <strong>Rate</strong>.<br />

ERICA measures <strong>the</strong> <strong>in</strong>put rate to <strong>the</strong> <strong>ABR</strong> queue and <strong>the</strong> number of active <strong>ABR</strong><br />

sources.<br />

To achieve fairness, <strong>the</strong> VC's Allocation (VA) has a component:<br />

VA fairness = Target <strong>Rate</strong> /Number of Active VCs<br />

To achieve e ciency, <strong>the</strong> VC's Allocation (VA) has a component:<br />

VA e ciency = VC's Current Cell <strong>Rate</strong> / Overload, where Overload = Input <strong>Rate</strong> /<br />

Target <strong>Rate</strong>�<br />

F<strong>in</strong>ally, <strong>the</strong>VC's allocation on this l<strong>in</strong>k (VAL) is calculated as:<br />

VAL =Maxf VA e ciency ,VA fairness g =Functionf Input <strong>Rate</strong>, VC's current rate<br />

g<br />

We use this basic algorithm to illustrate <strong>the</strong> VS/VD implementation. The imple-<br />

mentation of <strong>the</strong> full scheme can be derived as a simple extension to <strong>the</strong> description<br />

given <strong>in</strong> this section.<br />

9.2.1 <strong>Rate</strong> Calculations <strong>in</strong> a non-VS/VD Switch<br />

The non-VS/VD switch calculates <strong>the</strong> rate (VAL) <strong>for</strong> sources when <strong>the</strong> BRMs are<br />

processed <strong>in</strong> <strong>the</strong> reverse direction and enters it <strong>in</strong> <strong>the</strong> BRM eld as follows:<br />

ER <strong>in</strong> BRM = M<strong>in</strong>f ER <strong>in</strong> BRM, VAL g<br />

344

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!