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Figure 36

Network > WAN > WAN Backup

The following table describes the labels in this screen.

Table 22

Network > WAN > WAN Backup

LABEL

DESCRIPTION

WAN Backup Setup

Backup Type

Select the method that the ZyXEL Device uses to check the DSL connection.

Select

DSL Link

to have the ZyXEL Device check if the connection to the DSLAM

is up. Select

ICMP

to have the ZyXEL Device periodically ping the IP addresses

configured in the

Check WAN IP Address

fields.

Check WAN IP

Address1-3

Configure this field to test your ZyXEL Device's WAN accessibility. Type the IP

address of a reliable nearby computer (for example, your ISP's DNS server

address).

Note: If you activate either traffic redirect or dial backup, you must

configure at least one IP address here.

When using a WAN backup connection, the ZyXEL Device periodically pings the

addresses configured here and uses the other WAN backup connection (if

configured) if there is no response.

Fail Tolerance

Type the number of times (2 recommended) that your ZyXEL Device may ping the

IP addresses configured in the

Check WAN IP Address

field without getting a

response before switching to a WAN backup connection (or a different WAN

backup connection).

Recovery Interval

When the ZyXEL Device is using a lower priority connection (usually a WAN

backup connection), it periodically checks whether or not it can use a higher priority

connection.

Type the number of seconds (30 recommended) for the ZyXEL Device to wait

between checks. Allow more time if your destination IP address handles lots of

traffic.

Timeout

Type the number of seconds (3 recommended) for your ZyXEL Device to wait for a

ping response from one of the IP addresses in the

Check WAN IP Address

field

before timing out the request. The WAN connection is considered "down" after the

ZyXEL Device times out the number of times specified in the

Fail Tolerance

field.

Use a higher value in this field if your network is busy or congested.

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5.5

WAN Technical Reference

This section provides some technical background information about the topics covered in this

chapter.

5.5.1

Encapsulation

Be sure to use the encapsulation method required by your ISP. The ZyXEL Device supports

the following methods.

5.5.1.1

ENET ENCAP

The MAC Encapsulated Routing Link Protocol (ENET ENCAP) is only implemented with the

IP network protocol. IP packets are routed between the Ethernet interface and the WAN

interface and then formatted so that they can be understood in a bridged environment. For

instance, it encapsulates routed Ethernet frames into bridged ATM cells. ENET ENCAP

requires that you specify a gateway IP address in the

Gateway IP Address

field in the wizard

or WAN screen. You can get this information from your ISP.

5.5.1.2

PPP over Ethernet

The ZyXEL Device 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).

Traffic Redirect

Traffic redirect forwards traffic to a backup gateway when the ZyXEL Device cannot

connect to the Internet.

Active Traffic

Redirect

Select this check box to have the ZyXEL Device use traffic redirect if the normal

WAN connection goes down.

Note: If you activate traffic redirect, you must configure at least one

Check WAN IP Address.

Metric

This field sets this route's priority among the routes the ZyXEL Device uses.

The metric represents the "cost of transmission". A router determines the best

route for transmission by choosing a path with the lowest "cost". RIP routing uses

hop count as the measurement of cost, with a minimum of "1" for directly

connected networks. The number must be between "1" and "15"; a number greater

than "15" means the link is down. The smaller the number, the lower the "cost".

Backup Gateway

Type the IP address of your backup gateway in dotted decimal notation. The

ZyXEL Device automatically forwards traffic to this IP address if the ZyXEL

Device's Internet connection terminates.

Apply

Click this to save your changes.

Cancel

Click this to restore your previously saved settings.

Table 22

Network > WAN > WAN Backup

LABEL

DESCRIPTION

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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 ZyXEL Device (rather than individual computers),

the computers on the LAN do not need PPPoE software installed, since the ZyXEL Device

does that part of the task. Furthermore, with NAT, all of the LANs’ computers will have

access.

5.5.1.3

PPPoA

PPPoA stands for Point to Point Protocol over ATM Adaptation Layer 5 (AAL5). A PPPoA

connection functions like a dial-up Internet connection. The ZyXEL Device encapsulates the

PPP session based on RFC1483 and sends it through an ATM PVC (Permanent Virtual

Circuit) to the Internet Service Provider’s (ISP) DSLAM (Digital Subscriber Line (DSL)

Access Multiplexer). Please refer to RFC 2364 for more information on PPPoA. Refer to RFC

1661 for more information on PPP.

5.5.1.4

RFC 1483

RFC 1483 describes two methods for Multiprotocol Encapsulation over ATM Adaptation

Layer 5 (AAL5). The first method allows multiplexing of multiple protocols over a single

ATM virtual circuit (LLC-based multiplexing) and the second method assumes that each

protocol is carried over a separate ATM virtual circuit (VC-based multiplexing). Please refer

to RFC 1483 for more detailed information.

5.5.2

Multiplexing

There are two conventions to identify what protocols the virtual circuit (VC) is carrying. Be

sure to use the multiplexing method required by your ISP.

VC-based Multiplexing

In this case, by prior mutual agreement, each protocol is assigned to a specific virtual circuit;

for example, VC1 carries IP, etc. VC-based multiplexing may be dominant in environments

where dynamic creation of large numbers of ATM VCs is fast and economical.

LLC-based Multiplexing

In this case one VC carries multiple protocols with protocol identifying information being

contained in each packet header. Despite the extra bandwidth and processing overhead, this

method may be advantageous if it is not practical to have a separate VC for each carried

protocol, for example, if charging heavily depends on the number of simultaneous VCs.

5.5.3

VPI and VCI

Be sure to use the correct Virtual Path Identifier (VPI) and Virtual Channel Identifier (VCI)

numbers assigned to you. The valid range for the VPI is 0 to 255 and for the VCI is 32 to

65535 (0 to 31 is reserved for local management of ATM traffic). Please see the appendix for

more information.

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5.5.4

IP Address Assignment

A static IP is a fixed IP that your ISP gives you. A dynamic IP is not fixed; the ISP assigns you

a different one each time. The Single User Account feature can be enabled or disabled if you

have either a dynamic or static IP. However the encapsulation method assigned influences

your choices for IP address and ENET ENCAP gateway.

IP Assignment with PPPoA or PPPoE Encapsulation

If you have a dynamic IP, then the

IP Address

and

Gateway IP Address

fields are not

applicable (N/A). If you have a static IP, then you only need to fill in the

IP Address

field and

not the

Gateway IP Address

field.

IP Assignment with RFC 1483 Encapsulation

In this case the IP address assignment must be static.

IP Assignment with ENET ENCAP Encapsulation

In this case you can have either a static or dynamic IP. For a static IP you must fill in all the

IP

Address

and

Gateway IP Address

fields as supplied by your ISP. However for a dynamic IP,

the ZyXEL Device acts as a DHCP client on the WAN port and so the

IP Address

and

Gateway IP Address

fields are not applicable (N/A) as the DHCP server assigns them to the

ZyXEL Device.

5.5.5

Nailed-Up Connection (PPP)

A nailed-up connection is a dial-up line where the connection is always up regardless of traffic

demand. The ZyXEL Device does two things when you specify a nailed-up connection. The

first is that idle timeout is disabled. The second is that the ZyXEL Device will try to bring up

the connection when turned on and whenever the connection is down. A nailed-up connection

can be very expensive for obvious reasons.

Do not specify a nailed-up connection unless your telephone company offers flat-rate service

or you need a constant connection and the cost is of no concern.

5.5.6

NAT

NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP address of a

host in a packet, for example, the source address of an outgoing packet, used within one

network to a different IP address known within another network.

5.6

Metric

The metric represents the "cost of transmission". A router determines the best route for

transmission by choosing a path with the lowest "cost". RIP routing uses hop count as the

measurement of cost, with a minimum of "1" for directly connected networks. The number

must be between "1" and "15"; a number greater than "15" means the link is down. The

smaller the number, the lower the "cost".

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The metric sets the priority for the ZyXEL Device’s routes to the Internet. If any two of the

default routes have the same metric, the ZyXEL Device uses the following pre-defined

priorities:

•

Normal route: designated by the ISP (see

Section 5.2 on page 70

)

•

Traffic-redirect route (see

Section 5.8 on page 86

)

For example, if the normal route has a metric of "1" and the traffic-redirect route has a metric

of "2", then the normal route acts as the primary default route. If the normal route fails to

connect to the Internet, the ZyXEL Device tries the traffic-redirect route next.

5.7

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.

Figure 37

Example of Traffic Shaping