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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.
6.4.5
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.
6.4.6
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.
6.5
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.
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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 35
Example of Traffic Shaping
6.5.1
ATM Traffic Classes
These are the basic ATM traffic classes defined by the ATM Forum Traffic
Management 4.0 Specification.
Constant Bit Rate (CBR)
Constant Bit Rate (CBR) provides fixed bandwidth that is always available even if
no data is being sent. CBR traffic is generally time-sensitive (doesn't tolerate
delay). CBR is used for connections that continuously require a specific amount of
bandwidth. A PCR is specified and if traffic exceeds this rate, cells may be
dropped. Examples of connections that need CBR would be high-resolution video
and voice.
Variable Bit Rate (VBR)
The Variable Bit Rate (VBR) ATM traffic class is used with bursty connections.
Connections that use the Variable Bit Rate (VBR) traffic class can be grouped into
real time (VBR-RT) or non-real time (VBR-nRT) connections.
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The VBR-RT (real-time Variable Bit Rate) type is used with bursty connections that
require closely controlled delay and delay variation. It also provides a fixed
amount of bandwidth (a PCR is specified) but is only available when data is being
sent. An example of an VBR-RT connection would be video conferencing. Video
conferencing requires real-time data transfers and the bandwidth requirement
varies in proportion to the video image's changing dynamics.
The VBR-nRT (non real-time Variable Bit Rate) type is used with bursty
connections that do not require closely controlled delay and delay variation. It is
commonly used for "bursty" traffic typical on LANs. PCR and MBS define the burst
levels, SCR defines the minimum level. An example of an VBR-nRT connection
would be non-time sensitive data file transfers.
Unspecified Bit Rate (UBR)
The Unspecified Bit Rate (UBR) ATM traffic class is for bursty data transfers.
However, UBR doesn't guarantee any bandwidth and only delivers traffic when the
network has spare bandwidth. An example application is background file transfer.
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C
HAPTER
7
LAN Setup
7.1
Overview
A Local Area Network (LAN) is a shared communication system to which many
networking devices are connected. It is usually located in one immediate area
such as a building or floor of a building.
Use the LAN screens to help you configure a LAN DHCP server and manage IP
addresses.
7.1.1
What You Can Do in the LAN Screens
Use the
LAN IP
screen (
Section 7.2 on page 91
) to set the LAN IP address and
subnet mask of your ZyXEL device. You can also edit your ZyXEL Device's RIP,
multicast and Windows Networking settings from this screen.
Use the
DHCP Setup
screen (
Section 7.3 on page 93
) to configure the ZyXEL
Device’s DHCP settings.
Use the
Client List
screen (
Section 7.4 on page 94
) to assign IP addresses on
the LAN to specific individual computers based on their MAC Addresses.
Use the
IP Alias
screen (
Section 7.5 on page 95
) to change your ZyXEL
Device’s IP alias settings.
DSL
LAN
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7.1.2
What You Need To Know About LAN
IP Address
IP addresses identify individual devices on a network. Every networking device
(including computers, servers, routers, printers, etc.) needs an IP address to
communicate across the network. These networking devices are also known as
hosts.
Subnet Mask
Subnet masks determine the maximum number of possible hosts on a network.
You can also use subnet masks to divide one network into multiple sub-networks.
DHCP
A DHCP (Dynamic Host Configuration Protocol) server can assign your ZyXEL
Device an IP address, subnet mask, DNS and other routing information when it's
turned on.
RIP
RIP (Routing Information Protocol) allows a router to exchange routing
information with other routers.
Multicast
Traditionally, IP packets are transmitted in one of either two ways - Unicast (1
sender - 1 recipient) or Broadcast (1 sender - everybody on the network).
Multicast delivers IP packets to a group of hosts on the network - not everybody
and not just 1.
IGMP
IGMP (Internet Group Multicast Protocol) is a network-layer protocol used to
establish membership in a Multicast group - it is not used to carry user data.
There are three versions of IGMP. IGMP version 2 and 3 are improvements over
version 1, but IGMP version 1 is still in wide use.
DNS
DNS (Domain Name System) is for mapping a domain name to its corresponding
IP address and vice versa. The DNS server is extremely important because
without it, you must know the IP address of a networking device before you can
access it.

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