WaveRider Dynamic Polling MAC Loading

WaveRider Dynamic Polling MAC Loading
Introduction
This brief is an example of a current WaveRider wireless system running VPN’s across its airlink.
Terminology
CCU3000 – base station radio or single access point
EUM – subscriber wireless modem, includes antenna
DPMAC – dynamic polling media access control
GoS – Grade of Service
Background
The Media Access Control (MAC) layer determines which EUM may transmit and when it may transmit.
Through the MAC layer, the CCU determines which associated EUM may transmit next and indicates to
the EUM that it can transmit by polling it. The frequency with which an EUM is polled is based on its
assigned Grade of Service (GOS). The CCU transmits a directed poll to the EUM, which immediately
transmits a response to the CCU. After the response is received from the EUM, the CCU transmits the
next poll. In this way, the inbound (EUM-to-CCU) and outbound (CCU-to-EUM) channels are maintained
collision free.
If the CCU has data to send to an EUM, then that data is sent with the directed poll. If the EUM has data
to send to the CCU, then that data is sent with the EUM response to the poll. EUM’s that are not
authorized are not polled.
To optimize polling efficiency, EUM’s that no longer have traffic to send are not polled. EUM’s that are not
being polled can submit a request to be polled by responding to a special random access poll transmitted
regularly by the CCU. Collisions may sometimes occur on this random access channel; however, since
only a small number of users are vying for service through the random access channel at any one time,
the effect on channel performance is negligible.
Recovery from these collisions is made possible by random back-off and retry. Once again, if the EUM
requesting service through the random access channel has data to send to the CCU, it will be included
with the request message. If the CCU has outstanding broadcast messages to send, they will be sent to
all EUM’s with the random access poll.
An automatic repeat request (ARQ) scheme, using acknowledgements and retransmissions to recover
from message losses due to collisions or radio link errors, provides reliable transport. Each transmitted
data payload is numbered in the packet header. Each packet header also contains an acknowledgement
for the last correctly received payload, by number.
If a CCU or EUM does not receive an acknowledgement for a payload that it has transmitted, it
retransmits that payload with the following poll of, or response from, that EUM. A payload is transmitted a
maximum of four times, after which it is discarded. Note that contrary to the 802.11system, MAC-layer
acknowledgements are not transmitted as separate packets, reducing overhead by 33%, on average.
Wireless Network Example – Commercial System
Page 1 of 9
This system is operated by a WiSP with seven CCU3000’s in an area of about 10 square miles. It is in a
town with a population of 10,165. The subscriber mix is one of residential, SOHO and small business.
They currently have approximately 500 subscribers online.
There are 51 registered subscribers on a single access point modem in this example. Of the 51 registered
users, 13 are running a VPN service. Even though the IP address scheme is private, the operator uses
NAT to provide public IP addressees to allow for the VPN service.
The following is a table that depicts the grade of service levels with number of assigned subscribers.
Service Class Label
Best Effort
Bronze
Silver
Gold
Active ftp Rate (kbps)
15 - 394
9 - 1300
9 – 1460
18 - 1460
Number of Subscribers Assigned
2
24
0
25
Registration Table from CCU (access via CLI or SNMP)
REGISTERED EUMs
EUM ID
GOS Class
RSSI dBm SQ
RNA dB
Time s
Rx-Octets
Rx-Packets
Tx-Octets
Tx-Packets
60:05:d9
bronze
-82
9
22
67
11097088
60700
63411780
60:05:ef
bronze
-85
10
9
23949
504926
3816
5658923
4745
60:07:f6
bronze
-77
7
15
14
1411712
10276
9235339
11825
60:08:37
gold
-75
4
27
0
682122218
4274995
2.816E+09
4308820
60:08:e4
bronze
-79
17
27
30145
5003969
19115
12848654
18738
60:09:39
gold
-74
6
29
134
7691192
25417
26748755
28996
60:09:4c
gold
-86
21
19
59
18030439
134256
178145864
173261
60:09:81
bronze
-85
9
22
42
4337659
26937
18327021
28225
60:0a:23
gold
-88
11
14
623
754139
12328
2052359
17819
60:0a:37
gold
-84
9
21
0
38089746
288503
152281594
284675
60:0b:52
bronze
-82
7
19
7312
5796968
39420
54373564
52076
60:0b:a1
bronze
-85
6
20
1883
16791188
109709
114112886
138766
60:0d:a4
gold
-85
7
21
28321
1148088
7445
4432872
7502
60:0e:05
bronze
-75
9
30
0
28188255
62325
17952197
60185
60:0e:34
gold
-85
7
22
20769
216572
1028
900922
1180
69192
60:0f:bb
gold
-85
7
22
1
44944010
228757
189667518
239250
60:12:12
bronze
-80
7
25
28
1312727
9319
10014769
10897
60:12:4a
bronze
-85
8
22
2
54800
547
70387
535
60:12:59
bronze
-84
7
22
12223
4629153
33329
37661734
41539
60:13:05
bronze
-86
6
7
8202
706134
6959
12676525
10035
60:13:16
gold
-85
4
21
761
623150
8125
13701507
11829
60:15:3c
gold
-85
9
21
25
8524168
57432
45830596
58091
60:15:99
gold
-84
8
22
688
5811789
45384
66802783
59531
60:18:50
gold
-78
16
28
11
56797333
366734
522116239
481368
60:18:6f
gold
-84
11
21
4972
214575639
949650
316932699
837441
60:18:70
gold
-84
12
22
1356
573237
4631
1075082
4569
60:18:96
gold
-80
10
25
3
407844600
3369046
3.474E+09
4065926
60:18:dc
bronze
-85
10
21
8823
76738
105
34097
85
60:18:ef
gold
-85
21
21
4
1864438
14826
16518864
18458
60:19:5e
bronze
-86
5
21
181
4500879
29168
29692847
33070
Page 2 of 9
60:25:0e
gold
-81
7
25
2
957424
14564
64329
350
60:25:7d
bronze
-76
8
31
3521
8600649
63448
42830548
65033
60:27:af
gold
-79
6
27
144
15272422
86618
73919147
99400
60:28:75
bronze
-79
11
26
16077
358266
2495
2380617
2762
60:2a:45
bronze
-78
6
28
5313
2510854
16866
19742870
22339
60:2a:87
gold
-77
7
29
11
187173958
1523630
2.178E+09
1978023
60:2a:8f
gold
-81
6
25
5438
4946980
20461
12951304
20991
60:8a:d8
bronze
-87
7
18
387
199160
2122
5178752
3553
60:8b:0b
gold
-83
8
22
224
4663547
9189
5523869
9141
60:8e:61
gold
-84
7
22
0
53396617
124353
10086007
83368
60:95:60
bronze
-77
5
28
4267
113612
396
259788
394
60:95:e0
bronze
-84
6
22
2742
892846
2579
2101421
2614
60:96:37
bronze
-79
4
12
995
2114609
13353
11767281
14067
60:a4:5f
gold
-78
6
27
22
1822271
11419
16402399
14173
60:ab:73
bronze
-76
7
29
20333
77203
725
1176594
999
60:af:a4
gold
-83
5
23
5
10396408
67860
68844587
77447
60:af:ba
gold
-79
4
26
1
2975915
29124
20387662
29567
60:b0:7d
bronze
-84
5
22
5967
1428986
13394
19301251
17895
60:b0:ed
bronze
-80
5
25
17472
610113
3660
6662504
5172
60:c8:e9
be
-86
8
20
20597
617152
3649
5134762
4632
60:c9:53
be
-88
8
14
3283
71040397
250109
29787543
254736
Monitoring Channel Loading
Using WaveRider’s radiometer, the following charts show the dynamic capability of the polling MAC in
real life use.
1) Instantaneous polling rate: the polling rate is steady at the maximum allowed throughout the
display.
Page 3 of 9
Page 4 of 9
2) Active traffic shows that the system is seldom loaded above 1/3 capacity and averages less than
1/10. The most interesting thing to note is the #EUM’s total doesn't go above 13 and averages 3
to 4.
Page 5 of 9
3) Activations shows EUM’s getting to active state - this is how dynamic the system is, 2 to 4 EUM’s
becoming active every second.
Page 6 of 9
4) % Empty polls indicates that users are not being limited by the GOS cap - lots of small,
transaction type traffic going on.
Page 7 of 9
:4
0
15 :00
:4
0
15 :07
:4
0
15 :13
:4
0
15 :19
:4
0
15 :25
:4
0
15 :31
:4
0
15 :37
:4
0
15 :43
:4
0
15 :49
:4
0
15 :55
:4
1
15 :01
:4
1
15 :07
:4
1
15 :13
:4
1
15 :19
:4
1
15 :25
:4
1
15 :31
:4
1
15 :37
:4
1
15 :43
:4
1
15 :49
:4
1
15 :55
:4
2
15 :01
:4
2
15 :07
:4
2
15 :14
:4
2
15 :21
:4
2
15 :27
:4
2
15 :33
:4
2
15 :39
:4
2
15 :46
:4
2
15 :52
:4
2:
58
15
16:04:35
16:03:40
16:02:46
16:01:52
16:00:58
16:00:03
15:59:09
15:58:15
15:57:20
15:56:26
15:55:32
15:54:38
15:53:43
15:52:47
15:51:53
15:50:59
15:50:04
15:49:10
15:48:16
15:47:21
15:46:27
15:45:32
15:44:38
15:43:44
15:42:50
15:41:53
15:40:59
15:40:04
15:39:10
15:38:16
15:37:21
15:36:27
15:35:33
15:34:39
15:33:45
5) Channel utilization, the first chart shows 30 minutes of monitoring; the second chart shows over 3
minutes.
1
0.9
0.8
0.7
0.6
0.5
GO Util
BR Util
BE Util
BC Util
0.4
0.3
0.2
0.1
0
0.5
0.45
0.4
0.35
0.3
0.25
0.2
GO Util
SI Util
BR Util
BE Util
BC Util
0.15
0.1
0.05
0
Page 8 of 9
Conclusion
The system is very lightly loaded with 51 users. The number sharing the bandwidth averages 3 to 4.
Page 9 of 9