Zyxel P-791R v2 Рекомендации по настройке онлайн [15/98] 154425

P-791R v2 Support Notes

PCR as the maximum value according to the line rate (for example, 2.3 Mbps

line rate will result PCR as 5424 cell/sec.)

12. What do ATM QoS Types (CBR, UBR, VBR-nRT, VBR-RT) mean?

Constant bit rate(CBR): An ATM bandwidth-allocation service that requires

the user to determine a fixed bandwidth requirement at the time the connection

is set up so that the data can be sent in a steady stream. CBR service is often

used when transmitting fixed-rate uncompressed video.

Unspecified bit rate(UBR): An ATM bandwidth-allocation service that does

not guarantee any throughput levels and uses only available bandwidth. UBR

is often used when transmitting data that can tolerate delays, such as e-mail.

Variable bit rate(VBR): An ATM bandwidth-allocation service that allows

users to specify a throughput capacity (i.e., a peak rate) and a sustained rate

but data is not sent evenly. You can select VBR for bursty traffic and

bandwidth sharing with other applications. It contains two subclasses:

Variable bit rate nonreal time (VBR-nRT) and Variable bit rate real time

(VBR-RT).

13. Why do we perform traffic shaping in the P-791R v2?

The P-791R v2 must manage traffic fairly and provide bandwidth allocation for

different sorts of applications, such as voice, video, and data. All applications

have their own natural bit rate. Large data transactions have a fluctuating

natural bit rate. The P-791R v2 is able to support variable traffic among

different virtual connections. Certain traffic may be discarded if the virtual

connection experiences congestion. Traffic shaping defines a set of actions

taken by the P-791R v2 to avoid congestion; traffic shaping takes measures to

adapt to unpredictable fluctuations in traffic flows and other problems among

virtual connections.

14. The P-791R v2 supports Bridge and Router mode, what's the

difference between them?

When the ISP limits some specific computers to access Internet, which means

only the traffic to/from these computers will be forwarded and the other will be

filtered. In this case, we use bridge mode which works as an DSL modem to

connect to the ISP. The ISP will generally give one Internet account and limit

only one computer to access the Internet.

For most Internet users having multiple computers want to share an Internet

account for Internet access, they have to add another Internet sharing device,