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Voice Networks From the January 2005 issue of Communications News |
Is your switch smart? Enterprise networks transport several types of traffic, primarily data and voice. Data traffic usually does not have a pressing delivery deadline, but voice traffic, such as that from a voice-over-IP (VoIP) phone, must progress through the network in real time and arrive within a few milliseconds. The challenge lies in running both real-time voice packets over the same pipes as time-insensitive data packets. Switch intelligence is the part of an enterprise network that enables priority for time-critical packets. Using several queues, an enterprise switch can move voice packets to the front of the line ahead of data packets. Whereas increased bandwidth capacity enables a network to pass more data, intelligence increases the effective use of that bandwidth so that the most important traffic receives priority. Several types of switch intelligence are available for improving overall quality of service (QoS). Many 10/100 (Fast Ethernet) switches support only one or two priority queues per port. Four queues, however, is the bare minimum for an intelligent switch, which is needed to segregate the four basic types of traffic: control, voice, storage and data. Many OEMs are moving to at least eight QoS queues per port for Gigabit Ethernet. The primary reason for this is that network administrators want multiple levels of priority per traffic type so they can differentiate between important storage traffic (such as laptop backup) and mission-critical traffic (such as online order entry). Additional queues can also allow room for new applications and new types of data. Another aspect of switch intelligence is its role in providing network administrators more control over their networks. For example, within a network, control and network-management traffic is typically held in high priority. Most VoIP devices, however, tag voice packets with the highest priority available. Intelligent switches should be able to modify the priority of the traffic, in this case, to the second highest priority–at the edge when it enters the network based on the user’s priority needs and not the needs of the device that initiated the packet. Switch intelligence also reduces the burden of making a network secure. With VoIP, the door is opened to the possibility that someone will access the network without permission. Intelligent switches can deny VoIP to any particular port. Switch intelligence can play an important role in maintaining high availability by having the ability to filter and assist in screening network viruses. With the ability to look into any packet to determine whether it is infected, virus prevention takes the form of never letting unacceptable packets get into the network in the first place. Switch intelligence should not have an impact on performance. Consider that VoIP will double or triple the number of IP addresses in an enterprise system. Compound this with the fact that as functionality is increased in a switch it must have an underlying architecture capable of continuing to operate at wire speed. Intelligence is added to a network to improve quality of service, security and predictability. The point is not served if the added intelligence compromises network performance and slows the network down. For more information from Broadcom: This article was provided by Martin Lund, vice president and general manager, enterprise switching line of business, Broadcom Corp., San Jose, Calif.
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