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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

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