ZyXEL Communications ADSL2+ Ethernet/USB Gateway 660RU-Tx Series, Руководство пользователя

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Prestige 660RU-Tx Series User’s Guide
65 Chapter 6 WAN Setup
6.3 PPPoE Encapsulation
The Prestige supports PPPoE (Point-to-Point Protocol over Ethernet). PPPoE is an IETF Draft
standard (RFC 2516) specifying how a personal computer (PC) interacts with a broadband
modem (DSL, cable, wireless, etc.) connection. The
PPPoE option is for a dial-up connection
using PPPoE.
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.