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Port-based Priority 
Configure the priority level for each port . With the drop-down selection item of 
Priority Type above being selected as Port -based, this control item will then be 
available to set the queuing policy for each port. 
Figure 5-50:  QoS Configurat ion - Port-Based Priority 
 
This page includes the following fields: 
 
Object Description 
Port x: Each port has 4 priority levels—High, Middle, Low, and Lowest—to 
be chosen. 
 
COS Configuration 
QoS settings allow customization of packet prio
rity in order to facilitate delivery of 
data traffic that might be  affected by latency problems. When CoS / 802.1p Tag 
Priority is applied, the Switch recognizes  802.1Q VLAN tag packets and extracts the 
VLAN tagged packets with User Priority value. 
  
						

							
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Figure 5-51:  802.1p Tag Priority 
 
802.1Q Tag and 802.1p priority 
User Priority CFI  VLAN ID (VID) 
3 bits    1 bits    12 bits  
TPID (Tag Protocol  Identifier)  TCI (Tag Control 
Information) 
2 bytes   2 bytes 
 
Preamble  Destination 
Address  Source 
Address 
VLAN TAG Ethernet  Type  Data FCS 
6 bytes    6 bytes  4 bytes    2 bytes  46-1517 bytes   4 bytes 
Set up the COS priority level. With the dro
p-down selection item of Priority Type above 
being selected as COS only/COS first, this co ntrol item will then be available to set the 
queuing policy for each port. 
Figure 5-52:  QoS Configuration - COS Priority 
 
This page includes the following fields: 
 
Object Description 
COS priority:  Set up the COS priority level 0~7—High, Middle, Low, Lowest. 
NOTE:  802.1p Priority: Priority classifiers of  the Switch forward packet. COS range is 
from 0 to 7. Seven is the high class. Zero  is the less class. The user may configure the 
mapping between COS and Traffic classifiers.  
						

							
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TOS Configuration 
DiffServ Code Point (DSCP) - is the traffic prio ritization bits within an IP header that are 
encoded by certain applications and/or de vices to indicate the level of service 
required by the packet across a network.  
The Quality of Service page provides fields  for defining output queue to specific DSCP 
fields. When TCP/IPs TOS/DSCP mode is  applied, the Switch recognizes TCP/IP 
Differentiated Service Codepoint (DSCP) priori ty information from the DS-field defined 
in RFC2474. Select the QoS mode to TOS,  the TOS to priority mapping page appears, 
as the Figure 5-53 shows. 
Set up the TOS priority. With the drop-down  selection item of Priority Type above 
being selected as TOS only/TOS first, this co ntrol item will then be available to set the 
queuing policy for each port. 
Figure 5-53:  QoS Configuration - TOS Priority 
 
This page includes the following fields: 
 
Object Description 
TOS priority:  The system provides 0~63 TOS priority level. Each level has 4 types 
of priority—High, Middle, Low, and Lowest. The default value is 
‘Lowest’ priority for each level. When the IP packet is received, the 
system will check the TOS level va
lue in the IP packet that has 
received. For example, the user sets the TOS level 25 as high, the 
system will check the TOS value of th e received IP packet. If the TOS 
value of received IP packet is 25 (priority = high), and then the 
packet priority will have highest priority.  
						

							
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IGMP Snooping 
Theory 
The Internet Group Management Protocol (IGMP) lets host and routers share 
information about multicast groups membersh ips. IGMP snooping is a switch feature 
that monitors the exchange of IGMP me ssages and copies them to the CPU for 
feature processing. The overall purpose of IG MP Snooping is to limit the forwarding of 
multicast frames to only ports that  are a member of the multicast group. 
About the Internet Group Management Protocol (IGMP) Snooping 
Computers and network devices that want to  receive multicast transmissions need to 
inform nearby routers that they will be come members of a multicast group. The 
Internet Group Management Protocol (I GMP) is used to communicate this 
information. IGMP is also used to period ically check the multicast group for members 
that are no longer active. In the case where there is more than one multicast router 
on a sub network, one router is elected as  the queried. This router then keeps track 
of the membership of the multicast gr oups that have active members. The 
information received from IGMP is then used  to determine if multicast packets should 
be forwarded to a given sub network or not. The router can check, using IGMP, to see 
if there is at least one memb er of a multicast group on a given subnet work. If there 
are no members on a sub network, packe ts will not be forwarded to that sub 
network. 
Figure 5-54:  Multicast Service 
  
						

							
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Figure 5-55:  Multicast flooding 
 
Figure 5-56:  IGMP Snooping multicast stream control 
 
  
						

							
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IGMP Versions 1 and 2 
Multicast groups allow members to join or leave at any time. IGMP provides the 
method for members and multicast routers  to communicate when joining or leaving 
a multicast group. 
IGMP version 1 is defined in RFC 1112. It ha s a fixed packet size and no optional data. 
The format of an IGMP  packet is shown below: 
 
IGMP Message Format 
Octets 
0             8                                 16                                                                   31 
Type Response Time  Checksum 
Group Address (all zeros if this is a query). 
 
The IGMP Type codes are shown below: 
 
Type Meaning 
0x11  Membership Query (if Group Address is 0.0.0.0). 
0x11  Specific Group Membership Query (if Group Address is Present). 
0x16  Membership Report (version 2). 
0x17  Leave a Group (version 2). 
0x12  Membership Report (version 1). 
 
IGMP packets enable multicast routers to k eep track of the membership of multicast 
groups, on their respective sub networ ks. The following outlines what is 
communicated between a multicast router  and a multicast group member using 
IGMP. 
A host sends an IGMP report to join a group. 
A host will never send a report when it  wants to leave a group (for version 1). 
A host will send a leave report when it  wants to leave a group (for version 2). 
Multicast routers send IGMP queries (to  the all-hosts group address: 224.0.0.1) 
periodically to see whether any group member s exist on their sub networks. If there is 
no response from a particular group, th e router assumes that there are no group 
members on the network. 
The Time-to-Live (TTL) field of query message s is set to 1 so that the queries will not 
be forwarded to other sub networks.  
						

							
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IGMP version 2 introduces some enhanc ements such as a method to elect a 
multicast queried for each LAN, an explic it leave message, and query messages that 
are specific to a given group. 
The states a computer will go  through to join or to leave a multicast group are shown 
below: 
Figure 5-57:  IGMP State Transitions 
 
•  IGMP Querier  
A router, or multicast-enabled switch, can peri odically ask their hosts if they want to 
receive multicast traffic. If there is  more than one router/switch on the LAN 
performing IP multicasting, one of these de vices is elected querier and assumes the 
role of querying the LAN for group members.  It then propagates the service requests 
on to any upstream multicast switch/router to  ensure that it will continue to receive 
the multicast service. 
NOTE:  Multicast routers use this  information, along with a multicast routing protocol 
such as DVMRP or PIM, to support IP  multicasting across the Internet. 
IGMP Configuration 
The Industrial Switch support IP multicas t, you can enable IGMP protocol on web 
managements switch setting advanced page , then the IGMP snooping information 
displays. IP multicast addresses range  are from 224.0.0.0 through 239.255.255.255. 
  
						

							
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Figure 5-58:  IGMP Configuration interface 
 
This page includes the following fields: 
 
Object Description 
IGMP Protocol:  Enable or disable the IGMP protocol. 
IGMP Query: Enable or disable the IGMP query function. The IGMP query 
information will be displayed in IGMP status section. 
X-Ring 
X-Ring provides a faster redundant recovery than Spanning Tree topology. The action 
is similar to STP or RSTP, but the algorith
ms between them are not the same. In the X-
Ring topology, every switch should be en abled with X-Ring function and two ports 
should be assigned as the member ports in  the ring. Only one switch in the X-Ring 
group would be set as the master switch th at one of its two member ports would be 
blocked, called backup port, and another po rt is called working port. Other switches 
in the X-Ring group are called working sw itches and their two member ports are 
called working ports. When the failure of  network connection occurs, the backup port 
of the master switch (Ring Master) will  automatically become a working port to 
recover from the failure. 
X-Ring Application 
The Industrial Switch supports the X-Ring pr otocol that can help the network system 
to recovery from network connection failu re within 20ms or less, and make the 
network system more reliable. The X-Ring  algorithm is similar to spanning tree 
protocol (STP) algorithm but its recovery time  is faster than STP. The following figure is 
a sample X-Ring application.  
						

							
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Figure 5-59:  X-Ring Application 
 
In the network, it may have more than on e X-Ring group. By using the coupling ring 
function, it can connect each X-Ring fo r the redundant backup. It can ensure the 
transmissions between two ring groups not to  fail. The following figure is a sample of 
coupling ring application. 
  
						

							
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Figure 5-60:  Coupling Ring Application 
 
Dual Homing Application 
Dual Homing function is to prevent the connection lose from between X-Ring group 
and upper level/core switch. Assign two port s to be the Dual Homing port that is 
backup port in the X-Ring group. The Dual  Homing function only works when the X-
Ring function is active. Each X-Ring  group only has one Dual Homing port. 
Figure 5-61:  Dual Homing Ring Application 
 
NOTE: In Dual Homing application architectu re, the upper level switches need to 
enable the Rapid Spanning Tree protocol.