Layer 3 QoS
Issue 3.4.1 June 2005
315
There is one caution to keep in mind about QoS with regard to the processor load on network
devices. Simple routing and switching technologies have been around for many years and have
advanced significantly. Packet forwarding at Layer 2 and Layer 3 is commonly done in hardware
(Cisco calls this fast switching, with “switching” being used as a generic term here), without
heavy processor intervention. When selection criteria such as QoS and other policies are added
to the routing and switching process, it inherently requires more processing resources from the
network device. Many of the newer devices can handle this additional processing in hardware,
and maintain speed without a significant processor burden. However, to implement QoS, some
devices must take a hardware process and move it to software (Cisco calls this process
“switching”). Process switching not only reduces the speed of packet forwarding, but it also
adds a processor penalty that can be significant. This can result in an overall performance
degradation from the network device, and even device failure. Each network device must be
examined individually to determine if enabling QoS will reduce its overall effectiveness by
moving a hardware function to software, or for any other reason. Since most QoS policies are
implemented on WAN links, the following general points for Cisco routers are offered to
increase the level of confidence that QoS remains in hardware (consult Cisco to be sure):
●
Newer hardware platforms are required: 2600, 3600, 7200, and 7500
●
Newer interface modules (WIC, VIP, and so on) are required. Consult Cisco to determine
which hardware revision is required for any given module.
●
Sufficient memory is required: device dependent.
●
Newer IOS is required: 12.0 or later.
Avaya Layer 3 switches and the X330 WAN module support both 802.1 p/Q and DiffServ QoS.
Several things should be examined whenever QoS is enabled on a network device. First, the
network administrator should examine the processor load on the device, and compare it to
levels before QoS was enabled. It is likely that the levels will have gone up, but the increase
should not be significant. If it is, then it is likely that the QoS process is being done by software.
Also, the processor load must remain at a manageable level (50% average, 80% peak). If the
processor load is manageable, then the IP Telephony response (for example, voice quality)
should be checked to verify that it has improved under stressed conditions (for example, high
congestion). If the IP Telephony response has improved, the other applications should be
checked to verify that their performances have not degraded to unacceptable levels.
Summary of Contents for Application Solutions
Page 1: ...Avaya Application Solutions IP Telephony Deployment Guide 555 245 600 Issue 3 4 1 June 2005 ...
Page 20: ...About This Book 20 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 21: ...Issue 3 4 1 June 2005 21 Section 1 Avaya Application Solutions product guide ...
Page 22: ...22 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 106: ...Call processing 106 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 124: ...Avaya LAN switching products 124 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 139: ...Issue 3 4 1 June 2005 139 Section 2 Deploying IP Telephony ...
Page 140: ...140 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 186: ...Traffic engineering 186 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 204: ...Security 204 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 228: ...Avaya Integrated Management 228 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 274: ...Reliability and Recovery 274 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 275: ...Issue 3 4 1 June 2005 275 Section 3 Getting the IP network ready for telephony ...
Page 276: ...276 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 356: ...Network recovery 356 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 366: ...Network assessment offer 366 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 367: ...Issue 3 4 1 June 2005 367 Appendixes ...
Page 368: ...Appendixes 368 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 394: ...Access list 394 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 414: ...DHCP TFTP 414 Avaya Application Solutions IP Telephony Deployment Guide ...