在做 Video over IP 时候一定要确保双方的 viewstation 以太网口带宽和双工都是一致的，否者会出现有一个方向的视频质量特别差的问题。
这里有个很好的 Video QoS 例子，用的是 2M 的专线，需要在 viewstation 上作优先级设置的，不然 QoS 策略无法被激活的！关于 polycom viewstation 的 QoS precedence 设置请您参考 Polycom Viewstation 的设置。
This is one I did a couple of weeks ago (below)- only acl 100 was getting hit. It did do the trick and the picture was clear. the priority value is actually the bandwidth in Kilobits. You will need to be able to set the precedence on the video traffic to critical - this was done on the viewstations that were sending out the video packets in this case..
class-map match-all video-control
match access-group 101
class-map match-all video
match access-group 100
!
!
policy-map QoS-Policy
class video
priority 800 553058304
class video-control
bandwidth 8
class class-default
fair-queue
!
!
!
!
!
interface Multilink1
ip address 172.22.254.2 255.255.255.0
ip tcp header-compression iphc-format
no ip mroute-cache
load-interval 30
service-policy output QoS-Policy
ppp multilink
ppp multilink fragment-delay 10
ppp multilink interleave
multilink-group 1
ip rtp header-compression iphc-format
!
interface Serial0/0
bandwidth 2048
no ip address
encapsulation ppp
no ip mroute-cache
load-interval 30
no fair-queue
serial restart_delay 0
ppp multilink
multilink-group 1
!
access-list 100 permit ip any any precedence critical
access-list 101 permit ip any any precedence flash
access-list 101 permit ip any any dscp af31
