Tandberg | Video on Frame Relay |
Cell based systems cut packet into fixed sizes
Dropped frames are potentially a more serious problem. The frame relay standard allows the network service provider to control congestion by simply disposing of any frames which exceed the users CIR. In other words, if you contract for a CIR of 128 kbps but send a burst at 192 kbps, frames which exceed the 128 kbps CIR will have a DE (Discard Eligible) bit set. If some intermediate switch on the network becomes congested, these frames may be discarded. While an occasional lost frame will not seriously degrade video quality, too many will cause a noticeable loss of video quality.
In most networks, dropped frames are unlikely to occur. This depends, of course, on the capacity of the network, the actual traffic load at any given time, how the load varies, and other factors beyond the control of the end user.
The only certain way is to have enough CIR to cover all usage.
This is unnecessary in most cases, as the majority of installed public networks are not oversubscribed. Most carriers are now offering QoS (Quality of Service) or SLA (Service Level Agreement) guarantees, which categorically provide an end user with confidence that more than 99% of frames will arrive at their destination. For the Video over Frame Relay user, there are other ways of reducing the threat of frame loss.
1.The first is the configuration of the frame size. Frame relay allows the payload portion of the frame to be adjusted to carry larger or smaller amounts of information. This allows network administrators to adjust the frame size for optimal network performance. If a small frame packet is lost, it is not carrying too much information as to critically impair video function.
D11624 rev.01 | 6 |
