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51
P
ART
II
Advanced
WAN Setup
(53)
LAN Setup
(75)
Network Address Translation (NAT)
Screens
(83)
Security
(93)
Quality of Service (QoS)
(103)
Routing
(115)
RIP
(119)
DNS Setup
(121)
Dynamic DNS Setup
(123)
DSL Setup
(127)
Interface Group
(129)
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52
Page 53 / 300
P-663HN-51 User’s Guide
53
C
HAPTER
5
WAN Setup
5.1
WAN Overview
A WAN (Wide Area Network) is an outside connection to another network or the
Internet.
5.1.1
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.
5.1.2
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.
5.1.2.1
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.
5.1.2.2
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.
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Chapter 5 WAN Setup
P-663HN-51 User’s Guide
54
5.2
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.
Note: Traffic shaping controls outgoing (upstream) traffic, not incoming (downstream).
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 21
Example of Traffic Shaping
5.2.1
ATM Traffic Classes
These are the basic ATM traffic classes defined by the ATM Forum Traffic
Management 4.0 Specification.
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Chapter 5 WAN Setup
P-663HN-51 User’s Guide
55
5.2.1.1
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.
5.2.1.2
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
realtime or non realtime
connections.
The realtime VBR 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 realtime VBR 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 non realtime VBR 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 non realtime VBR connection would be non-time
sensitive data file transfers.
5.2.1.3
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.
5.3
WAN
Click
Advanced Setup > WAN
to open the following screen.
This screen displays
your ZyXEL Device’s WAN Internet access settings. You can also edit those
settings and add more settings. The screen differs by the encapsulation.

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