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3Com IntelliJack NJ200 Supplementary Manual

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TECHNICAL BRIEF

3Com

®

NJ200 

Network Jack
Management
Feature:

Virtual LANs 
and Traffic
Prioritization

 


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A VLAN is a logical subnet grouping that can be assigned to users, logins, or systems—
independently of the physical network infrastructure. An IEEE 802.1Q-compliant
VLAN is equivalent to a Layer 2 broadcast domain.

Systems or users associated with a particular VLAN subnet can communicate freely.
Network logins and end systems can be centrally managed as though they were physi-
cally located in the same site, regardless of the actual topology of the network.

Benefits

Support for port-based VLANs enables the 3Com

®

NJ200 Network Jack to deliver signif-

icant IT and business benefits. For example, it can help:

• Reduce the costs of IT equipment moves, upgrades, and other changes

• Centralize and automate network administration

• Create and monitor virtual workgroups for a specific department or section, with most

of the traffic staying in the same VLAN broadcast domain

• Isolate broadcast, multicast, and unicast traffic to a single subnet domain

• Reduce traffic congestion and prevent network flooding 

• Accelerate network performance without expensive router hardware

• Control communication among broadcast domains 

How VLANS Work

In order to properly forward VLAN traffic, core network switches and management
platforms check each Ethernet frame for an IEEE 802.1Q VLAN tag. Each tag is identi-
fied by a unique VLAN ID (VID), which can be a number between 1 and 4095. 

IEEE 802.1Q-compliant NJ200 Network Jacks support the following VLAN functionality:

Forwarding Inbound-Traffic from the LAN

The NJ200 Network Jack forwards voice, data, and video packets based on their MAC
addresses, not Ethernet frame tags. However, this 802.1Q-compliant Ethernet-data
switch can be configured to: 

• Check incoming traffic for VLAN tags

• Modify outbound traffic to include VLAN tags

• Forward VLAN-tagged traffic

This supports other devices that rely on Ethernet frame tags to correctly recognize and
forward VLAN traffic. The section titled, Setting the Ingress and Egress Modes, provides
step-by-step details on how to configure these capabilities.

Forwarding Traffic Among PAN Ports 

Port Associations regulate traffic between the PAN (device) ports on the same switch.
Port Associations only distribute traffic at the four PAN ports and have no effect on
traffic entering or leaving the switch, or going out to the LAN. 

Port Associations can be configured in any combination among PAN ports belonging to
the same switch. For example, Port #1 can be associated to any other port, all three, or
none of them. For details on how to set up Port Associations, refer to the section titled,
Setting PAN Port Associations.

Table 1. Summary of 802.1Q VLAN Functionality

Feature

Function

Ingress/egress rules

Applied at the LAN port (uplink port) only

VLAN tags

One VLAN tag can be set per PAN port

Traffic prioritization

802.1p traffic prioritization supported through four, port-based hardware queues

Inbound unicast traffic

Ethernet frames forwarded based on the MAC addresses; no exceptions

Inbound multicast traffic

All Ethernet frames forwarded to all ports regardless of tags

Inbound broadcast traffic

All Ethernet frames forwarded to all ports regardless of tags

2

What is a Virtual LAN
(VLAN)?

C O N T E N T S

What is a Virtual LAN (VLAN)?................2

Benefits ...............................................2

How VLANS Work ...............................2

VLAN Configuration and Setup ..............3

Setting the Ingress and Egress Modes .3

Setting the PAN Port Associations........5

Setting Outgoing and 
Incoming Tag Schemes ........................6

What is Traffic Prioritization? ..................8

Benefits ...............................................8

How Traffic Prioritization Works ..........8

Traffic Prioritization 
Configuration and Setup ........................9

Setting Priority Tag Values ...................9

Setting Up Traffic Priority 
Schedule Policy..................................11

Business Application .............................12

For More Information ...........................12

Appendix A: Default Settings................13

Appendix B: Additional Notes...............14

 


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Forwarding Outbound-Traffic to the LAN

For most outbound data traffic, the PAN ports add VID tags to the Ethernet frames prior
to them reaching the LAN (uplink) port. In this case, the LAN port simply delivers the
outbound traffic to the network. Once on the network, the VID-tagged traffic can be
forwarded and segmented by any 802.1Q enabled switch port.

For broadcast, multicast, and unicast traffic, the outgoing Ethernet frames are tagged at
the LAN port. This tagged traffic is subsequently identified and forwarded by 802.1Q-
enabled upstream network switches. 

For a step-by-step guide on setting up outbound traffic tags for the LAN port, please
refer to the section titled, Setting the Outgoing Tag Scheme.

3

VLAN Configuration 
and Setup

Setting the Ingress and Egress Modes

Although the NJ200 switch does not use VLAN tags, these tags are needed by many
other network devices—such as upstream switches or a VoIP phone connected to a PAN
port. To ensure traffic is appropriately tagged as it enters and exits, the NJ200 Network
Jack can be configured to add tags, remove tags, or leave frames unmodified. 

The ingress mode uses the receiving port buffer to inspect and process inbound traffic.
The egress mode uses the transmitting port buffer to inspect and process outbound traf-
fic. The four settings are summarized in Table 2.

Table 2. Ingress and Egress Control Settings

Inbound

Outbound 

Ingress Mode 

Egress Mode

Traffic

Traffic

Setting

Setting

Tagged

Tagged

Frames received unmodified

Frames transmitted unmodified

Tagged

Untagged

Remove 802.1 tag if present

Frames transmitted unmodified

Untagged

Untagged

Frames received unmodified

Frames transmitted unmodified

Untagged

Tagged

Frames received unmodified

Add 802.1 tag to untagged frame

 


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Figure 1 provides a two-key schematic of the traffic-control process, including where
ingress and egress rules are applied. Configuring the ingress and egress modes is 
accomplished using 3Com Central Configuration Manager: 

1. Open the 

Central Configuration Manager

. From the list of devices, select an NJ200

Network Jack and then select 

Property

. You can also right-click on its IP address

and select 

Property 

from the menu.

4

YES

YES

NO

NO

NO

NO

YES

YES

Inspect 

Ethernet

frame

Inspect 

Ethernet

frame

802.1 VLAN Tag Set?

802.1 VLAN Tag Set?

Egress rule set  

to add tag?

Ingress rule set  
to remove tag?

Do not modify

tag information

Forward frame 

to PAN port

Forward frame 

to PAN port

Add VLAN tag

information

Remove all tag

information

Do not modify

tag information

Do not modify

tag information

Do not modify

tag information

Figure 1. The ingress mode is applied to VLAN
traffic coming from the LAN before it gets sent
downstream to the PAN ports. The egress mode is
applied to VLAN traffic coming from the PAN ports
before it gets sent upstream to the LAN.

Figure 2. 3Com Central Configuration Manager
GUI enables point-and-click remote administration
of NJ200 Network Jacks.

How the LAN port handles traffic coming from the LAN

How the LAN port handles traffic coming from the PAN

 


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5

Figure 3. Ingress and egress modes can be viewed
and configured using 3Com Central Configuration
Manager. 

3. Use the pull-down menu to set the desired 

LAN Egress Mode

, either:

a) Frames transmitted unmodified

b) Add 802.1 tag to untagged frame

4. Use the pull-down menu to set the desired 

LAN Ingress Mode

, either:

a) Frames received unmodified

b) Remove 802.1 tag if present

5. Click on 

Apply

to proceed to the password-request window. Once a password is

entered and accepted, the next window will show a summary of the new settings. 

6. Click 

OK

to finalize and exit the configuration window.

Setting the PAN Port Associations

The PAN (device) ports can support up to four different VLAN domains. 3Com Central
Configuration Manager lets you assign individual ports to four separate VLANs, all
ports to the same VLAN, or any combination in between. The following example illus-
trates how the Port Associations are used to create two port groups assigned to separate
VLANs—where the ports in one group cannot share traffic with ports in the other. 

1. Open 

3Com Central Configuration Manager

and select 

Devices

from the main menu.

2. From the list of devices, select an NJ200 Network Jack and then select

Configuration

. You can also highlight and right-click on the switch and select

Configuration

.

2. Click on the 

Hardware Settings

tab to view the LAN (uplink) port ingress and

egress modes. You should see a window like this: 

 


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3. Click on the 

VLAN

tab to open a window that displays port-based settings for

VLANs, outgoing tags, and incoming tags: 

6

Figure 4. Port associations enable you to assign a
VLAN broadcast domain to a single PAN port or
group of associated ports.

4. Under 

Port-based VLANs

, make sure the 

Port Association

box is checked. 

5. You should see four tabs, one for each PAN port. Select the 

Port 1

tab and check the

Port 2

box. This configures Ports 1 and 2 to share traffic with each other but not

ports 3 or 4.

6. Next, select the 

Port 3

tab and check the 

Port 4

box. This configures Ports 3 and 4

to share traffic with each other but not ports 1 or 2.

Note: It is possible to override these port configurations with a higher-level device, such as a core switch
that supports Layer 3 IP forwarding between VLANs.

Setting Outgoing and Incoming Tag Schemes

Once the Port Associations have been set up, the PAN ports can be assigned to VLANs
using the appropriate VLAN ID (VID) numbers. The PAN-port VIDs can be any number
from 0 to 4095 and must match the core-switching VIDs, which are typically assigned
by the enterprise network management platform.

IMPORTANT: If any PAN port is configured with a VID that has no corresponding upstream match, the
entire switch may lose network connectivity. To reset the LAN port and recover network communications,
the NJ200 Network Jack must be connected to a hub or flat VLAN. It can then be reconfigured with the
proper VID using 3Com Central Configuration Manager.

 


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7

1. Put a check the 

Outgoing Tag Scheme

box. 

Note: This setting affects both VLAN and traffic priority sorting on a bridge-wide basis.

2. Select the 

Port 1

tab and from the pull-down menu, select 

Add tag to any 

untagged frame

.

3. Put a check in the 

VLAN ID

box and type 

1

in the 

VLAN ID

field. PAN ports 1 and 2

are now configured as part of the “VLAN 1” subnet. 

4. Repeat the last two steps to configure PAN ports 3 and 4 as part of the “VLAN 2”

subnet. Click 

OK

to exit configuration window.

5. Put a check in the 

Incoming Tag Scheme

box. 

Note: This setting affects both VLAN and priority traffic sorting on a bridge-wide basis.

6. From the pull-down menu, select 

Frames received are unmodified

.

7. Click 

OK

to exit configuration window.

Figure 5. Setting the outgoing and incoming tag
schemes assigns the PAN ports to one or more VLANs.

 


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IEEE 802.1D/D17 (which incorporates IEEE 802.1p) traffic prioritization lets IT staff
establish packet-based control over network traffic. These advanced features allow high-
priority packets containing time-sensitive or system-critical data to be transmitted with
minimal delay. 

Traffic prioritization can also help differentiate network traffic by type—such as multi-
media, video, protocol-specific, time critical, and file-backup.

Benefits

Traffic prioritization can significantly reduce bandwidth limitations, network delay,
data loss, and jitter (interference). Traffic prioritization is most useful for critical appli-
cations that require a high Class of Service (CoS) from the network. 

In addition to delivering the above capabilities, the NJ200 Network Jack can help
increase the reliability of data delivery, allow specific applications to be prioritized
across the network, and define exactly how to treat selected applications and types of
traffic. The following are a few of the many applications that can benefit from being
connected through this standard-compliant switch:

Converged network applications

enable voice, video, and data traffic to share the same

physical infrastructure. These sophisticated applications require maximum bandwidth
and minimal latency in order to deliver high-quality voice and video transmissions.

Resource planning applications

rely on time-sensitive communications and on-demand

access to core enterprise servers such as SAP.

Financial applications

are used by accounting departments to handle AR/AP, taxes,

interest payments, and other business-critical processes. These powerful programs need
immediate and reliable access to large datasets and bulky spreadsheets.

CAD/CAM design applications

take up enormous amounts of network bandwidth—for

accessing server farms and transferring very large graphics files.

How Traffic Prioritization Works

IEEE 802.1D/p traffic prioritization differentiates data packets into classes that are used
to automatically select and forward high-priority transmissions over less critical traffic.
This helps ensure that time-sensitive and business-critical communications get the high-
est level of service. Traffic prioritization also separates the queuing of time-critical
frames to help reduce jitter.

Table 3 shows the range of priority tag values, with 7 having the highest importance
and 1 the lowest. 

Note: The NJ200 Network Jack default priority tag setting is 0. This has a higher priority than 2, which is
used for nonessential traffic. 

Table 3. IEEE 802.1D/p Traffic Prioritization Tag Values 

Value

Tag

Traffic Type

Best Effort 

Default setting

Background

Background system processes

2

Standard

Spare, nonessential

3 Excellent 

Effort 

Business-critical

4

Controlled Load

Streaming multimedia

5

Video

Interactive media; latency <100 ms; jitter-control queuing

6

Voice

Interactive voice; latency <10 ms; jitter-control queuing

7

Network Control

Reserved network processes 

The 802.1D/p-compliant switch gives preference to Ethernet frames with higher prior-
ity tag values. High-priority traffic is directed through hardware-based queues that are
kept separate from queues for lower priority traffic. 

8

What is Traffic Prioritization?

 


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9

Setting Priority Tag Values

The first step in configuring a traffic prioritization scheme is to ensure that the NJ200
Network Jack recognizes the priority tags as traffic passes through the switch. As with
the VLAN scheme, the switch can be configured to add tags, remove tags, or leave
frames unmodified. 

As mentioned in the previous section, the IEEE 802.1D/p standard specifies eight dis-
tinct levels of priority (0 through 7), each of which relates to a particular type (class) of
traffic. The NJ200 Network Jack pairs up the eight tag values into four priority levels,
to match the available traffic queues. Each priority level is determined by the lower
value of each tag-value pair as follows:

Table 4. IEEE 802.1D/p Tags and Switch Values 

Tag Pair 

Priority Value

0 or 1

0

2 or 3

2

4 or 5

4

6 or 7

6

Traffic Prioritization
Configuration and Setup 

YES

YES

NO

NO

NO

NO

YES

YES

Inspect 

Ethernet

frame

Inspect 

Ethernet

frame

802.1 Priority Tag Set?

802.1 Priority Tag Set?

Egress rule set  

to add tag?

Ingress rule set  

to add tag?

Do not modify

tag information

Forward frame 

to PAN port

Forward frame 

to PAN port

Add priority tag

information

Remove all tag

information

Do not modify

tag information

Do not modify

tag information

Do not modify

tag information

Figure 6. The ingress mode is applied to prioritized
traffic coming from the LAN before they are sent
downstream to the PAN ports. The egress mode is
applied to prioritzed traffic coming from the PAN
ports before they are sent upstream to the LAN.

The traffic prioritization process is similar to that of the VLAN scheme. The switch
applies ingress rules at the receiving-port buffer and egress rules at the transmitting
port buffer. (Figure 6.) 

How the LAN port handles traffic coming from the LAN

How the LAN port handles traffic coming from the PAN

 


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Configuring traffic priority levels is accomplished using 3Com Central Configuration
Manager: 

1. Open 3Com 

Central Configuration Manager

and select 

Devices

from the main

menu. 

2. From the list of devices, select an NJ200 Network Jack and then select 

Property

.

You can also right-click on its IP address and select 

Property

from the menu.

3. Click on the 

Priority

tab and select a PAN (device) port to configure. For example,

the configuration window for Port 2 will look similar to this:

10

4. Under 

Priority Lookup Scheme

, choose one of the following settings:

a) None

b) 802.1p Traffic Class fields

c)

Use IP TOS, Diffserv fields

d) Both

To ignore the priority tags on incoming Ethernet frames, set the 

Priority Look up

Scheme

to 

None

.

Note: Priority Lookup Scheme specifically instructs the NJ200/NJ205 to inspect Ethernet frames at the LAN
port for 802.1p, Diffserv, or both. If the incoming traffic will not be Diffserv or 802.1p, the Priority Lookup
Scheme should be set at “None.” 

5. Under 

Default Priority Level

, set what priority level to associate with the PAN port: 

a) 802.1p Priority 0 or 1

b) 802.1p Priority 2 or 3

c)

802.1p Priority 4 or 5

d) 802.1p Priority 6 or 7

6. Click 

OK

to exit the configuration window. Repeat these steps for the other PAN ports.

Figure 7. Traffic priority levels are individually 
configured for each PAN port.

 


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11

Setting Up Traffic Priority Schedule Policy

Use this setting to modify how the switch will receive frames from each queue:

1. Open 

3Com Central Configuration Manager

and select 

Devices

from the main menu.

2. From the list of devices, select an NJ200/NJ205 and then select 

Property

. You can

also highlight and right-click on the NJ200/NJ205 and select 

Property

.

3. Click on the 

Hardware Settings

tab to view and configure the 

Priority Schedule

Policy

settings. You should see a window like this:

4. Under 

Priority Schedule Policy

, choose one of the following:

a) 8,4,2,1 weighted fair queuing  (default)

b) Strict Priority Scheme (all queues weighted the same)

5. When all configuration settings are complete, click on the 

Apply

button, which

opens a password-prompt window. After the password is accepted a screen will
appear summarizing the new settings. Click 

OK

to accept and close configuration

window.

Figure 8. Traffic priority schedules are individually
configured for each PAN port.

 


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IT staff can use VLANs to partition traffic streams into easily manageable and securable
groups. Automated traffic prioritization can significantly improve network and applica-
tion performance, particularly for time-sensitive transmissions such as voice and video.
The following scenario, while fictional, demonstrates how these two advanced switch-
ing features can solve real-world problems and deliver significant time and cost savings.

In an effort to converge and consolidate, a large aerospace corporation had successfully
migrated business-critical resources onto the network. The core switching infrastructure
was upgraded, DSL Internet router installed, and PSTN phones were replaced by a VoIP
telephony system.

News of an upcoming satellite launch sent draftpersons and engineers dashing to their
desktops to watch via the live webcast. All this Internet traffic sent network loads soar-
ing—creating access bottlenecks and slowing application response. In particular, a
telephone conference with a trans-Pacific client suffered in quality and usability. The
meeting ended up being postponed until the next day, a 24-hour delay that cost the
company many thousands of dollars.

This disaster might have been avoided if IT staff had installed 3Com NJ200 Network
Jacks in all offices and conference rooms as part of the infrastructure upgrade. Using
port-based VLANs, all VoIP transmissions could have been directed through their own
subnet, regardless of what conference room was being used. In addition, the Default
Priority Level could be set to recognize the IEEE priority tag for VoIP (value = 6), which
would help ensure that this extremely time-sensitive traffic gets preference over stream-
ing video (value = 4).

12

Business Application

For More Information

3Com NJ200 Network Jacks work in almost any network environment—including
small-office or enterprise businesses, government offices, dormitories, hospitals, school
classrooms, universities, laboratories, public kiosks, conference rooms, and shared office
spaces.

For more information on how these managed “in the wall” switches can resolve common
networking problems and significantly lower IT costs, please visit

www.3com.com/networkjack

.

 


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13

Global Switch Setting

Default Value

Max Frame Size

1518 or 1522 if tagged

Counter Mode

Count good frames

Priority Scheduling Mode

8, 4, 2, 1 weighted

VLAN Tag for LAN Port (egress)

Egress frame unmodified

VLAN Tag for LAN Port (ingress)

Ingress frame unmodified

Power Forward

Autodetection

SNMP “Set” Permission

Not allowed

Port Setting

Default Value

State

Forwarding

Link

Autonegotiation

Flow Control

Off

MDI[X]

Force MDI

Multicast Limit

3%

Priority Lookup

Tag and IPV4

Port Priority

1

VLAN ID

1

Port based VLAN

All ports on same VLAN

Unchanged Values After Restoring to Factory Default Settings

Some configuration values remain unchanged when you click 

Restore Factory Default

Settings

. The following values must be changed manually:

• Group Name

• Location ID

• Password

• IP Address

• DHCP Settings

• SNMP Community Strings

• SNMP Trap Settings

Appendix A: Default Settings

 


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3Com Corporation, Corporate Headquarters, 350 Campus Drive, Marlborough, MA  01752-3064

To learn more about 3Com solutions, visit www.3com.com. 3Com is publicly traded on NASDAQ under the symbol COMS.

Copyright © 2003 3Com Corporation. All rights reserved. 3Com and the 3Com logo are registered trademarks of 3Com
Corporation. IntelliJack and Possible made practical are trademarks of 3Com Corporation. All other company and prod-
uct names may be trademarks of their respective companies. While every effort is made to ensure the information given
is accurate, 3Com does not accept liability for any errors or mistakes which may arise. Specifications and other informa-
tion in this document may be subject to change without notice.

NJ_VirtualLANs   09/03

• 3Com NJ200 Network Jack is compliant with SNMPv.1 and supports most SNMP

management platforms

• Multicast packets are handled the same as broadcast packets

• The autonegotiation setting on the LAN port (uplink port) cannot be changed

• NJ200 Network Jack does not support spanning tree protocol (STP)

• MAC table is capable of 512 addresses at any given time; timeout in 300 seconds/5

minutes of inactivity; these settings are permanent and cannot be changed

• Ethernet switching uses store-and-forward—receives complete frame in switch buffer,

checks CRC, looks up destination address in MAC filter table, and forwards frame

Appendix B: Additional Notes