Use the following table to get familiar with some of the ATM usage concepts:
|
Category of Service |
CBR |
VBR-nrt/UBR |
|
AAL Type |
AAL 1 |
AAL 5 |
|
Bytes per ATM cell |
47 bytes |
48 bytes |
|
Bytes per ATM Megacell |
47 million bytes |
48 million bytes |
|
Bits per ATM cell |
376 bits |
384 bits |
|
Bits per ATM Megacell |
376 million bits |
384 million bits |
The provider has noticed that customers are typically uncertain about their usage patterns and almost always overestimate their usage volume, since they usually have not had to track actual usage across the WAN (private lines and frame relay are billed a flat rate).
The following table estimates monthly megacell usage based on assumptions about PVC utilization. This table assumes a 48 byte payload for VBR-nrt service, 18 hours per day, 22 business days per month equals 100% utilization.
|
|
Megacell Usage Per Month (Kbps or Mbps) |
|||||
|
Estimated Utilization |
64 K |
384 K |
2 M |
5 M |
10 M |
20 M |
|
1% |
2 |
14 |
74 |
186 |
371 |
743 |
|
3% |
7 |
43 |
223 |
557 |
1,114 |
2,228 |
|
5% |
12 |
71 |
371 |
928 |
1,856 |
3,713 |
|
10% |
24 |
143 |
743 |
1,856 |
3,713 |
7,425 |
|
15% |
36 |
214 |
1,114 |
2,784 |
5,569 |
11,138 |
|
20% |
48 |
286 |
1,485 |
3,713 |
7,425 |
14,850 |
|
25% |
60 |
357 |
1,856 |
4,641 |
9,281 |
18,563 |
|
30% |
71 |
428 |
2,228 |
5,569 |
11,138 |
22,275 |
|
50% |
119 |
714 |
3,713 |
9,281 |
18,563 |
37,125 |
|
100% |
238 |
1,428 |
7,425 |
18,563 |
37,125 |
74,250 |
The following examples are intended to show how to work with customer-provided information to estimate monthly megacell usage. They are not representative of true application performance. Factors such as latency and retransmissions, will affect actual data delivery and may increase the amount of cells actually transferred. For these examples, a ‘work month’ of 22 days is used.