Comtech EF Data CDM-840 - Manual (Page 237)

CDM-840 Remote Router Revision 2
Appendix G MN-CDM840
G–5
G.2.2 WAN Link Dimensioning and Pre-emptive Bandwidth Management
RAN traffic varies over time – variations during the day that peak at certain time(s), and longer
term variation as user density/profile(s) changes. The WAN link can be dimensioned to
accommodate the peak traffic, or it can be dimensioned to meet a statistically derived value
(e.g. average traffic).
Dimensioning the WAN link for peak traffic may not be economically viable. However,
dimensioning the WAN link for average traffic has its challenges. Specifically: What happens
when the optimized traffic exceeds WAN capacity?
Typical of most other vendors’ RAN optimization solutions, Figure G-4 shows the optimized Abis
traffic as a function of time, depending on the BTS traffic load. The red line is the pre-defined
WAN link capacity (assuming 35% target optimization). Each time the optimized Abis traffic
exceeds WAN capacity, packets are dropped and the voice quality degrades dramatically – even
leading to dropped calls or in the worst case, causing BTS drop.
Figure G-4. Optimized Abis Traffic without Pre-emptive BW Management
The simplistic packet drop employed by most vendors in case of WAN congestion has potentially
disastrous effects on voice quality and call handling – the results can include clicks, blank calls,
and eventually call drops, especially if the BCCH channel of the TRX is impacted. In the worst
case, it may even lead to BTS drop.
To compensate, most other vendor solutions are forced to over-dimension the WAN link, which
leads to significant inefficiencies. This methodology should not be acceptable to mobile
operators. A good RAN optimization solution should be nearly transparent, and should provide
the same level of service to the mobile customers as when there is no RAN Optimization while
providing a significant reduction in RAN transmission bandwidth.