ZyXEL Communications ZyXEL Prestige 660R, Руководство пользователя

Страница: 62 / 297

Prestige 660R ADSL 2+ Access Gateway
6-2 WAN Setup
For the service provider, PPPoE offers an access and authentication method that works with existing access
control systems (for example Radius). PPPoE provides a login and authentication method that the existing
Microsoft Dial-Up Networking software can activate, and therefore requires no new learning or procedures
for Windows users.
One of the benefits of PPPoE is the ability to let you access one of multiple network services, a function
known as dynamic service selection. This enables the service provider to easily create and offer new IP
services for individuals.
Operationally, PPPoE saves significant effort for both you and the ISP or carrier, as it requires no specific
configuration of the broadband modem at the customer site.
By implementing PPPoE directly on the Prestige (rather than individual computers), the computers on the
LAN do not need PPPoE software installed, since the Prestige does that part of the task. Furthermore, with
NAT, all of the LANs’ computers will have access.
6.4 Traffic Shaping
Traffic Shaping is an agreement between the carrier and the subscriber to regulate the average rate and
fluctuations of data transmission over an ATM network. This agreement helps eliminate congestion, which is
important for transmission of real time data such as audio and video connections.
Peak Cell Rate (PCR) is the maximum rate at which the sender can send cells. This parameter may be lower
(but not higher) than the maximum line speed. 1 ATM cell is 53 bytes (424 bits), so a maximum speed of
832Kbps gives a maximum PCR of 1962 cells/sec. This rate is not guaranteed because it is dependent on the
line speed.
Sustained Cell Rate (SCR) is the mean cell rate of each bursty traffic source. It specifies the maximum
average rate at which cells can be sent over the virtual connection. SCR may not be greater than the PCR.
Maximum Burst Size (MBS) is the maximum number of cells that can be sent at the PCR. After MBS is
reached, cell rates fall below SCR until cell rate averages to the SCR again. At this time, more cells (up to
the MBS) can be sent at the PCR again.
If the PCR, SCR or MBS is set to the default of “0”, the system will assign a
maximum value that correlates to your upstream line rate.
The following figure illustrates the relationship between PCR, SCR and MBS.