Weighted fair queuing (WFQ) is another queuing technique, and is the default used on router interfaces with less that 2.048 Mbps of bandwidth. Weighted fair queuing is concerned with ensuring that all traffic flows receive predictable bandwidth to meet their needs. For example, it will place smaller, interactive traffic (like telnet) at the front of […]

Packet loss can occur on any network for a variety of reasons including congested links (packets dropped when buffers are full), routing problems, incorrect equipment configuration issues, and more. Because voice traffic uses UDP as its transport protocol, dropped packets are lost, and obviously not resent. On a voice conversation, this is recognized by what […]

The bullet points below each type of variable delay encountered with VoIP traffic, and how these issues can be compensated for where possible.

Queuing Delay. When a WAN interface is congested, traffic must be queued using any of the various methods looked at in this chapter. Although a method like LLQ can prioritize voice traffic, another […]

In order for a queuing mechanism like LLQ or IP RTP Priority to queue voice packets into a priority queue correctly, they must be able to identify the traffic as VoIP. With IP RTP Priority, packets are matched and priority queued according to the UDP port numbers used by RTP voice traffic, which fall into […]

Implementing QoS mechanisms is another key consideration in order to ensure that VoIP traffic is forwarded across a network in a timely manner. A variety of different queuing mechanisms can be used on WAN interfaces to help prioritize voice traffic in order to ensure that it is serviced in this manner, and not delayed by […]

Network congestion is an issue that can lead to a variety of problems on any data network; when the data network is also supporting voice traffic, these issues are even more serious. For example, WAN interfaces on a router may already be at or very near to capacity, leading to queuing issues that may result […]

ATM maps to the Data Link and Physical layers of the OSI model, but uses its own reference model to describe its functions. This model consists of three layers, which map to the OSI model as shown in the figure below.
The ATM reference model maps to the Data Link and Physical layers of the OSI […]

Now that you’re familiar with Layer 3 switching, you’re probably curious about what Layer 4 switching represents. Well, the answer isn’t as difficult as you might have imagined. Quite simply, a Layer 4 switch is typically just a Layer 3 switch that is also capable of making decisions based on Layer 4 information. Layer 4 […]

When terminal devices like IP phones wish to communicate, call processing software like Cisco CallManager is typically involved in the process. While some calls will be between two IP phones on the same subnet, some may be on a remote IP network (for example, across a WAN link), while others will be to traditional phones […]

A traditional voice network relies upon 64 kbps circuit-switched connections between the originator and the recipient of a call. While this dedicated bandwidth helps to ensure the quality of a call, it is also somewhat wasteful. At many points in any conversation, voice traffic is not crossing the circuit, since natural silences occur in human […]