Converged networks are networks with the capacity to transport a multitude of applications and data, including high-quality video and delay-sensitive data such as real-time voice. Although bandwidth-intensive applications stretch network capabilities and resources, they also complement, add value, and enhance every business process.
Converged networks must provide secure, predictable, measurable, and sometimes guaranteed services. In order to ensure successful end-to-end business solutions, Quality of Service (QoS) is required to manage network resources. Most networks experience the following:
- Delay Issues
- Bandwidth Issues
- Jitter Issues
- Packet Loss Issues
All packets in a network experience some kind of delay from the time the packet is first sent to when it arrives at its intended destination. This total delay, from start to finish, is referred to as latency. There are several types of delay that may be experienced by packets or frames.
While delving into the specifics on each one of them is beyond the scope of the SWITCH exam requirements, some common causes of delay include serialization delay (which is the time it takes to send bits, one-at-a-time, across the wire), queuing delay (which is the delay experienced when packets wait for other packets to be sent), and forwarding delay (which includes the processing time from when a frame and when the packet has been placed in the output queue).
Generally speaking, bandwidth refers to the number of bits per second (bps) that are expected to be delivered successfully across some medium. Based on this definition, bandwidth is equal to the physical link speed or clock rate of the interface. In switching terms, however, the term bandwidth refers to the capacity of the switch fabric. Therefore, the bandwidth considerations for WAN connections, for example, are not necessarily the same for LAN connections.
Jitter is the variation in delay between consecutive packets. Jitter is often referred to as variation delay. While such variations may be acceptable for applications and data traffic, they can severely impact isochronous traffic, such as digitized voice, which requires that packets are transmitted in a consistent, uniform manner.
Packet loss occurs when one or more packets traversing the network fail to reach their intended destination. This may occur for several reasons, such as bit errors or lack of space in queues, for example. While this does not generally affect connection-oriented protocols, such as TCP, packet loss can cause major issues for real-time traffic such as voice and streaming video traffic