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Page 146 / 344 Scroll up to view Page 141 - 145
Chapter 10 Quality of Service (QoS)
P-2601HN(L)-F1 Series User’s Guide
146
The following table describes the labels in this screen.
10.6
QoS Technical Reference
This section provides some technical background information about the topics
covered in this chapter.
10.6.1
IEEE 802.1Q Tag
The IEEE 802.1Q standard defines an explicit VLAN tag in the MAC header to
identify the VLAN membership of a frame across bridges. A VLAN tag includes the
12-bit VLAN ID and 3-bit user priority. The VLAN ID associates a frame with a
specific VLAN and provides the information that devices need to process the frame
across the network.
Table 33
Network Setting > QoS > Monitor
LABEL
DESCRIPTION
Monitor
Refresh Interval
Select how often you want the ZyXEL Device to update this screen.
Select
No Refresh
to stop refreshing statistics.
Status
#
This is the index number of the entry.
Name
This shows the name of the WAN interface on the ZyXEL Device.
Pass Rate (bps)
This shows how many packets forwarded to this interface are
transmitted successfully.
Queue Monitor
#
This is the index number of the entry.
Name
This shows the name of the queue.
Interface
This shows the interface of the queue.
Pass Rate (bps)
This shows how many packets assigned to this queue are transmitted
successfully.
Drop Rate (bps)
This shows how many packets assigned to this queue are dropped.
Page 147 / 344
Chapter 10 Quality of Service (QoS)
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147
IEEE 802.1p specifies the user priority field and defines up to eight separate traffic
types. The following table describes the traffic types defined in the IEEE 802.1d
standard (which incorporates the 802.1p).
10.6.2
IP Precedence
Similar to IEEE 802.1p prioritization at layer-2, you can use IP precedence to
prioritize packets in a layer-3 network. IP precedence uses three bits of the eight-
bit ToS (Type of Service) field in the IP header. There are eight classes of services
(ranging from zero to seven) in IP precedence. Zero is the lowest priority level and
seven is the highest.
10.6.3
DiffServ
QoS is used to prioritize source-to-destination traffic flows. All packets in the flow
are given the same priority. You can use CoS (class of service) to give different
priorities to different packet types.
DiffServ (Differentiated Services) is a class of service (CoS) model that marks
packets so that they receive specific per-hop treatment at DiffServ-compliant
network devices along the route based on the application types and traffic flow.
Packets are marked with DiffServ Code Points (DSCPs) indicating the level of
service desired. This allows the intermediary DiffServ-compliant network devices
to handle the packets differently depending on the code points without the need to
negotiate paths or remember state information for every flow. In addition,
applications do not have to request a particular service or give advanced notice of
where the traffic is going.
Table 34
IEEE 802.1p Priority Level and Traffic Type
PRIORITY
LEVEL
TRAFFIC TYPE
Level 7
Typically used for network control traffic such as router configuration
messages.
Level 6
Typically used for voice traffic that is especially sensitive to jitter (jitter is the
variations in delay).
Level 5
Typically used for video that consumes high bandwidth and is sensitive to
jitter.
Level 4
Typically used for controlled load, latency-sensitive traffic such as SNA
(Systems Network Architecture) transactions.
Level 3
Typically used for “excellent effort” or better than best effort and would
include important business traffic that can tolerate some delay.
Level 2
This is for “spare bandwidth”.
Level 1
This is typically used for non-critical “background” traffic such as bulk
transfers that are allowed but that should not affect other applications and
users.
Level 0
Typically used for best-effort traffic.
Page 148 / 344
Chapter 10 Quality of Service (QoS)
P-2601HN(L)-F1 Series User’s Guide
148
DSCP and Per-Hop Behavior
DiffServ defines a new DS (Differentiated Services) field to replace the Type of
Service (TOS) field in the IP header. The DS field contains a 2-bit unused field and
a 6-bit DSCP field which can define up to 64 service levels. The following figure
illustrates the DS field.
DSCP is backward compatible with the three precedence bits in the ToS octet so
that non-DiffServ compliant, ToS-enabled network device will not conflict with the
DSCP mapping.
The DSCP value determines the forwarding behavior, the PHB (Per-Hop Behavior),
that each packet gets across the DiffServ network. Based on the marking rule,
different kinds of traffic can be marked for different kinds of forwarding. Resources
can then be allocated according to the DSCP values and the configured policies.
DSCP (6 bits)
Unused (2 bits)
Page 149 / 344
P-2601HN(L)-F1 Series User’s Guide
149
C
HAPTER
11
Network Address Translation
(NAT)
11.1
Overview
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.
11.1.1
What You Can Do in this Chapter
•
Use the
Port Forwarding
screen to configure forward incoming service
requests to the server(s) on your local network (
Section 11.2 on page 150
).
•
Use the
Sessions
screen to limit the number of concurrent NAT sessions each
client can use (
Section 11.3 on page 153
).
11.1.2
What You Need To Know
The following terms and concepts may help as you read this chapter.
Inside/Outside and Global/Local
Inside/outside denotes where a host is located relative to the ZyXEL Device, for
example, the computers of your subscribers are the inside hosts, while the web
servers on the Internet are the outside hosts.
Global/local denotes the IP address of a host in a packet as the packet traverses a
router, for example, the local address refers to the IP address of a host when the
packet is in the local network, while the global address refers to the IP address of
the host when the same packet is traveling in the WAN side.
NAT
In the simplest form, NAT changes the source IP address in a packet received from
a subscriber (the inside local address) to another (the inside global address)
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Chapter 11 Network Address Translation (NAT)
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150
before forwarding the packet to the WAN side. When the response comes back,
NAT translates the destination address (the inside global address) back to the
inside local address before forwarding it to the original inside host.
Port Forwarding
A port forwarding set is a list of inside (behind NAT on the LAN) servers, for
example, web or FTP, that you can make visible to the outside world even though
NAT makes your whole inside network appear as a single computer to the outside
world.
Finding Out More
See
Section 11.4 on page 154
for advanced technical information on NAT.
11.2
The Port Forwarding Screen
Use the
Port Forwarding
screen to forward incoming service requests to the
server(s) on your local network.
You may enter a single port number or a range of port numbers to be forwarded,
and the local IP address of the desired server. The port number identifies a
service; for example, web service is on port 80 and FTP on port 21. In some
cases, such as for unknown services or where one server can support more than
one service (for example both FTP and web service), it might be better to specify
a range of port numbers. You can allocate a server IP address that corresponds to
a port or a range of ports.
The most often used port numbers and services are shown in
Appendix E on page
323
. Please refer to RFC 1700 for further information about port numbers.
Note: Many residential broadband ISP accounts do not allow you to run any server
processes (such as a Web or FTP server) from your location. Your ISP may
periodically check for servers and may suspend your account if it discovers any
active services at your location. If you are unsure, refer to your ISP.
Configuring Servers Behind Port Forwarding (Example)
Let's say you want to assign ports 21-25 to one FTP, Telnet and SMTP server (
A
in
the example), port 80 to another (
B
in the example) and assign a default server IP
address of 192.168.1.35 to a third (
C
in the example). You assign the LAN IP

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