Does the VOICE Priority Class borrow bandwidth from the non priority classes like the default-Class , does it !!!!!!
Scenario
-QoS is configured on SITE_A
-Will monitor the voice traffic as it leaves SITE_A
-Fa 0/1 is the INPUT(traffic entering the SITE_A router from the LAN ) interface
-Fa 0/0 is the OUTPUT(traffic existing the SITE_A router into the WAN ) interface
-The bandwidth on Fa0/0 and Fa0/1 is 10Mbps
-The Voice class is assigned 8kbps bandwidth
-The rest of the bandwidth is assigned to the default-class
Configs ;
INPUT
interface Fast Ethernet0/1
service-policy input CE-INPUT
policy-map CE-INPUT
class CE-INPUT-VOICE
set dscp ef
class class-default
set dscp default
class-map match-any CE-INPUT-VOICE
match access-group name VOICE
ip access-list extended VOICE
permit ip 10.80.80.0 0.0.0.255 any
OUTPUT
interface FastEthernet0/0
service-policy output CE-OUTPUT
policy-map CE-OUTPUT
class CE-OUTPUT-VOICE
priority 8
class class-default
bandwidth 9992
random-detect dscp-based
class-map match-any CE-OUTPUT-VOICE
match ip dscp ef
Results
-Phone call is made between SITE_A and SITE_B , see below QoS stats on Site_A’s router.
SiteA#sh policy-map int fa 0/0
FastEthernet0/0
Service-policy output: CE-OUTPUT
Class-map: CE-OUTPUT-VOICE (match-any)
36100 packets, 3035978 bytes
30 second offered rate 22000 bps, drop rate 0 bps
Match: ip dscp ef
36100 packets, 3035978 bytes
30 second rate 22000 bps
Queueing
Strict Priority
Output Queue: Conversation 264
Bandwidth 8 (kbps) Burst 200 (Bytes)
(pkts matched/bytes matched) 1/84
(total drops/bytes drops) 0/0
Class-map: class-default (match-any)
360 packets, 30117 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: any
Queueing
Output Queue: Conversation 265
Bandwidth 9992 (kbps)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0
exponential weight: 9
mean queue depth: 0
dscp Transmitted Random drop Tail drop Minimum Maximum Mark
pkts/bytes pkts/bytes pkts/bytes thresh thresh prob
cs6 235/17390 0/0 0/0 32 40 1/10
default 128/12935 0/0 0/0 20 40 1/10
-If you look at the VOICE class the offered rate is 22kbps , this means the voice class requires 22Kbps bandwidth.
-But we have 8kbps allocated clearly that’s not enough bandwidth but we don’t see any voice drops.
Conclusion:
Does the VOICE Priority Class borrow bandwidth from the non priority classes like the default-Class : YES it does
The priority queue can burst into other non-priority classes but not vise versa.
DOVICHNETWORKS 