Bandwidth is the fundamental requirement that there be enough space in a network path for all of your packets to get through unimpeded. When it comes to bandwidth and conferencing more is always better. IP-based H.323 video calls typically use bandwidth of around 384-768Kbps plus overhead because of the packetizing overhead of IP. This bandwidth should be symmetric — meaning each end should be able to both send and receive the same amount of data for the call.

Here are some guidelines for IP videoconferencing and video call quality.

Circuits are full-duplex. You need to add about 30% for overhead to call speeds desired.

• 384 Kbps + 30% = 499.2 Kbps
• 512 Kbps + 30% = 665.6 Kbps
• 768 Kbps + 30% = 998.4 Kbps
• 1536 Kbps + 30% = 1.996 Mbps
• 1920 Kbps + 30% = 2.496 Mbps

Multiply by the number of simultaneous sessions that you desire.

Packet loss is when packets fail to arrive correctly. This can be due to insufficient bandwidth along the path (when congestion occurs, routers will drop packets), or perhaps errors in transmission. Packet loss results in effects such as "tiling" within the video window, missing pieces or blank areas within the video window, and/or disruptions in audio.

Latency is the time delay between an event occurring and the remote end seeing it. Latency is introduced both by the encoding/decoding process, and hence depends on the equipment used, and also by the time it takes packets to traverse the network.

Excessive latency increases the chances of people "talking over one another" because they don't realize that the person at the other end has started speaking too. This is less significant in calls with less than 50ms of network latency. It can become very troublesome in calls with more than 150ms. Another problem is that the latency for the audio and video may be different, and hence lip movements don’t appear synchronized with the audio.

Jitter is the random variation in latency due to things like competing processes running on the terminal (for example on your desktop PC), other traffic temporarily blocking the path through routers along the way, or even the network path changing during a videoconference. This random variation is one of several things that cause packets to arrive out of order from their transmitted order. Jitter results in uneven and unpredictable quality within a videoconference and the endstation client will try to compensate for it by buffering the traffic up to some finite time, before playing it out to you. This increases the latency even further.

Network Address Translation (NAT), is an Internet standard that enables a local-area network (LAN) to use one set of IP addresses (usually private) for internal traffic and a second set of addresses for external traffic (usually public). A NAT box located where the LAN meets the Internet makes all necessary IP address translations.

NAT serves three main purposes:

• Provides a type of firewall by hiding internal IP addresses
• Enables a you to use more internal IP addresses. Since they're used internally only, there's no possibility of conflict with IP addresses used by other companies and organizations.
• Allows a users to share connections into a single Internet connection (public IP address).

Usually the private IP addresses used internally when NAT is used are non-routeable private IP addresses and sometimes used in conjunction with DHCP (Dynamic Host Configuration Protocol) which uses a "server" (many times embedded in a router) to hand out IP addresses to computers or end points as needed. This means the IP addresses assigned to computers, devices or end points as dynamic and can change. NAT and DHCP offer challenges to videoconferencing.

Dynamic Host Configuration Protocol (DHCP), is a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device's IP address can even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses.

Dynamic addressing simplifies network administration because the software keeps track of IP addresses rather than requiring an administrator to manage the task. This means that a new computer can be added to a network without the hassle of manually assigning it a unique IP address.

As you may realize since in videoconferencing the IP address is sometimes used like a "telephone number" to dial video end points, DHCP can be a challenge for setting up videoconferencing.