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Chapter 4 Broadband
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41
Figure 17
Network Setting
>
Broadband > 3G Backup
The following table describes the labels in this screen.
Table 6
Network Setting
>
Broadband > 3G Backup
LABEL
DESCRIPTION
General
3G Backup
Select
Enable
to have the Device use the 3G connection as your WAN or a backup when the
wired WAN connection fails.
Card
description
This field displays the manufacturer and model name of your 3G card if you inserted one in
the Device. Otherwise, it displays
N/A
.
Username
Type the user name (of up to 64 ASCII printable characters) given to you by your service
provider.
Password
Type the password (of up to 64 ASCII printable characters) associated with the user name
above.
PIN
A PIN (Personal Identification Number) code is a key to a 3G card. Without the PIN code,
you cannot use the 3G card.
If your ISP enabled PIN code authentication, enter the 4-digit PIN code (0000 for example)
provided by your ISP. If you enter the PIN code incorrectly, the 3G card may be blocked by
your ISP and you cannot use the account to access the Internet.
If your ISP disabled PIN code authentication, leave this field blank.
Dial string
Enter the phone number (dial string) used to dial up a connection to your service provider’s
base station. Your ISP should provide the phone number.
For example, *99# is the dial string to establish a GPRS or 3G connection in Taiwan.
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4.5
WAN Technical Reference
This section provides some technical background information about the topics covered in this
chapter.
4.5.1
Encapsulation
Be sure to use the encapsulation method required by your ISP. The Device supports the following
methods.
4.5.1.1
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
APN
Enter the APN (Access Point Name) provided by your service provider. Connections with
different APNs may provide different services (such as Internet access or MMS (Multi-Media
Messaging Service)) and charge method.
You can enter up to 32 ASCII printable characters. Spaces are allowed.
Obtain an IP
Address
Automatically
Select this option If your ISP did not assign you a fixed IP address.
Use the
following static
IP address
Select this option If the ISP assigned a fixed IP address.
IP Address
Enter your WAN IP address in this field if you selected
Use the following static IP
address
.
Obtain DNS
info
dynamically
Select this to have the Device get the DNS server addresses from the ISP automatically.
Use the
following static
DNS IP address
Select this to have the Device use the DNS server addresses you configure manually.
Primary DNS
server
Enter the first DNS server address assigned by the ISP.
Secondary DNS
server
Enter the second DNS server address assigned by the ISP.
Connection
Select
Keep Alive
if you do not want the connection to time out.
Select
Connect on Demand
if you do not want the connection up all the time and specify
an idle time-out in the
Max Idle Timeout
field.
Max Idle
Timeout
This value specifies the time in minutes that elapses before the Device automatically
disconnects from the ISP.
Apply
Click
Apply
to save your changes back to the Device.
Cancel
Click
Cancel
to return to the previous configuration.
Table 6
Network Setting
>
Broadband > 3G Backup (continued)
LABEL
DESCRIPTION
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43
a gateway IP address in the
Gateway IP Address
field in the wizard or WAN screen. You can get
this information from your ISP.
4.5.1.2
PPP over Ethernet
The 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).
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 Device (rather than individual computers), the computers on
the LAN do not need PPPoE software installed, since the Device does that part of the task.
Furthermore, with NAT, all of the LANs’ computers will have access.
4.5.1.3
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 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.
4.5.1.4
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.
4.5.2
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.
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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.
4.5.3
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.
4.5.4
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 Address
assigned by your ISP, then they should also assign you a
Subnet Mask
and a
Gateway IP Address
.
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
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 Device.
4.5.5
Nailed-Up Connection (PPP)
A nailed-up connection is a dial-up line where the connection is always up regardless of traffic
demand. The Device does two things when you specify a nailed-up connection. The first is that idle
timeout is disabled. The second is that the 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.
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4.5.6
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.
4.6
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 18
Example of Traffic Shaping
4.6.1
ATM Traffic Classes
These are the basic ATM traffic classes defined by the ATM Forum Traffic Management 4.0
Specification.

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