ADDERLink INFINITY dual 2112T Manual v30 2112T

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APPENDIX C - Tips for success when networking ALIF units
ALIF units use multiple strategies to minimize the amount of data that they send 
across networks. However, data overheads can be quite high, particularly when very 
high resolution video is being transferred, so it is important to take steps to maximize 
network efficiency and help minimize data output. The tips given in this section have been 
proven to produce very beneficial results.  
Summary of steps
• Choose the right kind of switch.
• Create an efficient network layout.
• Configure the switches and devices correctly.
Choosing the right switch
Layer 2 switches are what bind all of the hosts together in the subnet. However, they are 
all not created equally, so choose carefully. In particular look for the following:
• Gigabit (1000Mbps) or faster Ethernet ports,
• Support for IGMP v2 (or v3) snooping,
• Support for Jumbo frames up to 9216-byte size,
• High bandwidth connections between switches, preferably Fiber Channel.
• Look for switches that perform their most onerous tasks (e.g. IGMP snooping) using 
multiple dedicated processors (ASICS).
• Ensure the maximum number of concurrent ‘snoopable groups’ the switch can 
handle meets or exceeds the number of ALIF transmitters that will be used to create 
multicast groups. 
• Check the throughput of the switch: Full duplex, 1Gbps up- and down- stream speeds 
per port.   
• Use the same switch make and model throughout a single subnet.
• You also need a Layer 3 switch. Ensure that it can operate efficiently as an IGMP 
Querier.  
Layer 2 (and Layer 3) switches known to work
• Cisco 2960
• Cisco 3750
• Cisco 4500
• Cisco 6500
• Extreme Networks X480
• HP Procurve 2810
• HP Procurve 2910
Creating an efficient network layout
Network layout is vital. The use of IGMP snooping also introduces certain constraints, so 
take heed:
• Keep it flat. Use a basic line-cascade structure rather than a pyramid or tree 
arrangement.
• Keep the distances between the switches as short as possible.
• Ensure sufficient bandwidth between switches to eliminate bottlenecks.
• Where the A.I.M. server is used to administer multiple ALIF transceivers, ensure the 
A.I.M. server and all ALIF units reside in the same subnet. 
• Do not use VGA to DVI converters, instead replace VGA video cards in older systems 
with suitable DVI replacements. Converters cause ALIF TX units to massively increase 
data output.
• Wherever possible, create a private network.  
The recommended layout
The layout shown below has been found to provide the most efficient network layout for 
rapid throughput when using IGMP snooping:
 Note: From firmware version 3.1, tree and hierarchical structures of network switches are also 
supported. The Transmitter now joins its own multicast group so there is always a route from 
the querier to the transmitter which was previously missing in earlier firmware versions.
• Use no more than two cascade levels.
• Ensure high bandwidth between the two L2 switches and very high bandwidth 
between the top L2 and the L3. Typically 10GB and 20GB, respectively for 48 port L2 
switches.
continued
For the latest list of switches known to work 
with ALIF and setup instructions for them, 
please go to www.adder.com
• H3C 5120
• HuaWei Quidway 
s5328c-E1 (Layer 3)   
						

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Configuring the switches and devices
The layout is vital but so too is the configuration:
• Enable IGMP Snooping on all L2 switches.
• Ensure that IGMP Fast-Leave is enabled on all switches with ALIF units connected 
directly to them.
• Enable the L3 switch as an IGMP Querier.
• Enable Spanning Tree Protocol (STP) on all switches and importantly also enable 
portfast (only) on all switch ports that have ALIF units connected. 
• If any hosts will use any video resolutions using 2048 horizontal pixels (e.g. 2048 x 
1152), ensure that Jumbo Frames are enabled on all switches.
• Choose an appropriate forwarding mode on all switches. Use Cut-through if available, 
otherwise Store and forward.
• Optimize the settings on the ALIF transmitters:
• If moving video images are being shown frequently, then leave Frame Skipping at a 
low percentage and instead reduce the Peak bandwidth limiter.
• Where screens are quite static, try increasing the Background Refresh interval and/
or increasing the Frame skipping percentage setting.
 Make changes to the ALIF transmitters one at a time, in small steps, and view typical 
video images so that you can attribute positive or negative results to the appropriate 
control.
• Ensure that all ALIF units are fully updated to the latest firmware version (at least 
v2.1).   
						

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APPENDIX D - Troubleshooting
Problem: The video image of the ALIF receiver shows horizontal lines across 
the screen. 
This issue is known as Blinding because the resulting video image looks as though you’re 
viewing it through a venetian blind. 
When video is transmitted by ALIF units, the various lines of each screen are divided up 
and transmitted as separate data packets. If the reception of those packets is disturbed, 
then blinding is caused. The lines are displayed in place of the missing video data packets. 
There are several possible causes for the loss of data packets:
• Incorrect switch configuration. The problem could be caused by multicast flooding, 
which causes unnecessary network traffic. This is what IGMP snooping is designed to 
combat, however, there can be numerous causes of the flooding. 
• Speed/memory bandwidth issues within one or more switches. The speed and 
capabilities of different switch models varies greatly. If a switch cannot maintain pace 
with the quantity of data being sent through it, then it will inevitably start dropping 
packets.
• One or more ALIF units may be outputting Jumbo frames due to the video resolution 
(2048 horizontal pixels) being used. If jumbo frames are output by an ALIF unit, but 
the network switches have not been configured to use jumbo frames, the switches 
will attempt to break the large packets down into standard packets. This process 
introduces a certain latency and could be a cause for dropped packets.
• One or more ALIF units may be using an old firmware version. Firmware versions 
prior to v2.1 exhibited an issue with the timing of IGMP join and lea ve commands that 
caused multicast flooding in certain configurations.
Remedies: 
• Ensure that IGMP snooping is enabled on all switches within the subnet.
• Where each ALIF unit is connected as the sole device on a port connection to 
a switch, enable IGMP Fast-Leave (aka Immediate Leave) to reduce unnecessary 
processing on each switch.    
• Check the video resolution(s) being fed into the ALIF transmitters. If resolutions using 
2048 horizontal pixels are unavoidable then ensure that Jumbo frames are enabled on 
all switches.
• Check the forwarding mode on the switches. If Store and forward is being used, try 
selecting Cut-through as this mode causes reduced latency on lesser switch designs.  
• Ensure that one device within the subnet is correctly configured as an IGMP Querier, 
usually a layer 3 switch or multicast router.
• Ensure that the firmware in every ALIF unit is version 2.1 or greater.
• Try adjusting the transmitter settings on each ALIF to make the output data stream as 
efficient as possible. See ALIF transmitter video settings for details.
continued   
						

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Problem: The mouse pointer of the ALIF receiver is slow or sluggish when 
moved across the screen.
This issue is often related to either using dithering on the video output of one or more 
transmitting computers or using VGA-to-DVI video converters.
Dithering is used to improve the perceived quality and color depth of images by diffusing 
or altering the color of pixels between video frames. This practice is commonly used 
on Apple Mac computers using ATI or Nvidia graphics cards. VGAto-DVI converters 
unwittingly produce a similar issue by creating high levels of pixel background noise.
ALIF units attempt to considerably reduce network traffic by transmitting only the pixels 
that change between successive video frames. When dithering is enabled and/or VGA-to-
DVI converters are used, this can have the effect of changing almost every pixel between 
each frame, thus forcing the ALIF transmitter to send the whole of every frame: resulting 
in greatly increased network traffic and what’s perceived as sluggish performance.
Remedies:
•  Linux PCs 
 Check the video settings on the PC. If the Dither video box option is enabled, disable 
it.
•  Apple Mac with Nvidia graphics
 Use the Adder utility for Mac’s – Contact technical support.
•  Apple Mac with ATI graphics
 Enable the Magic Eye dither removal feature.
•  Windows PCs
 If you suspect these issues with PC’s, contact technical support for assistance.
• Replace old VGA adapters on host computers with DVI video cards.
Problem: The audio output of the ALIF receiver sounds like a scratched re-
cord.
This issue is called Audio crackle and is a symptom of the same problem that produces 
blinding (see previous page). The issue is related to missing data packets.
Remedies: 
As per blinding discussed previously. 
Problem: A.I.M. cannot locate working ALIF units.
There are a few possible causes:
• The ALIF units must be reset back to their zero config IP addresses for A.I.M. 
discovery. If you have a working network of ALIF’s without A.I.M. and then add A.I.M. to 
the network A.I.M. will not discover the ALIFs until they are reset to the zero config IP 
addresses. 
• This could be caused by Layer 2 Cisco switches that have Spanning Tree  Protocol 
(STP) enabled but do not also have portfast enabled on the ports to which ALIF units 
are connected. Without portfast enabled, ALIF units will all be assigned the same 
zero config IP address at reboot and A.I.M. will only acquire them one at a time on a 
random basis. 
 You can easily tell whether portfast is enabled on a switch that is running STP: When 
you plug the link cable from a working ALIF unit into the switch port, check how long 
it takes for the port indicator to change from orange to green. If it takes roughly one 
second, portfast is on; if it takes roughly thirty seconds then portfast is disabled.             
Remedies: 
• Ensure that the ALIF units and the A.I.M. server are located within the same subnet 
because A.I.M. cannot cross subnet boundaries.
• Manually reset the ALIF units to their zero config IP addresses. 
• Enable portfast on all switch ports that have ALIF units attached to them or try 
temporarily disabling STP on the switches while A.I.M. is attempting to locate ALIF 
units.   
						

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APPENDIX E - Glossary
Internet Group Management Protocol
Where an ALIF transmitter is required to stream video to 
two or more receivers, multicasting is the method used. 
Multicasting involves the delivery of identical data to 
multiple receivers simultaneously without the need to 
maintain individual links. When multicast data packets enter 
a subnet, the natural reaction of the switches that bind 
all the hosts together within the subnet, is to spread the 
multicast data to all of their ports. This is referred to as 
Multicast flooding and means that the hosts (or at least 
their network interfaces) are required to process plenty of 
data that they didn’t request. IGMP offers a partial solution.
The Internet Group Management Protocol (IGMP) is 
designed to prevent multicast flooding by allowing Layer 
3 switches to check whether host computers within 
their care are interested in receiving particular multicast 
transmissions. They can then direct multicast data only to 
those points that require it and can shut off a multicast 
stream if the subnet has no recipients.
There are currently three IGMP versions: 1, 2 and 3, with 
each version building upon the capabilities of the previous 
one: 
• IGMPv1 allows host computers to opt into a multicast 
transmission using a Join Group message, it is then 
incumbent on the router to discover when they no 
longer wish to receive; this is achieved by polling them 
(see IGMP Querier below) until they no longer respond.
• IGMPv2 includes the means for hosts to opt out as well 
as in, using a Leave Group message. 
• IGMPv3 encompasses the abilities of versions 1 and 2 
but also adds the ability for hosts to specify particular 
sources of multicast data. 
AdderLink Infinity units make use of IGMPv2 when 
performing multicasts to ensure that no unnecessary 
congestion is caused.
IGMP Snooping
The IGMP messages are effective but only operate at 
layer 2 - intended for routers to determine whether 
multicast data should enter a subnet. A relatively recent 
development has taken place within the switches that 
glue together all of the hosts within each subnet: IGMP 
Snooping. IGMP snooping means these layer 2 devices now 
have the ability to take a peek at the IGMP messages. As a 
result, the switches can then determine exactly which of 
their own hosts have requested to receive a multicast – 
and only pass on multicast data to those hosts. 
IGMP Querier
When IGMP is used, each subnet requires one Layer 3 
switch to act as a Querier. In this lead role, the switch 
periodically sends out IGMP Query messages and in 
response all hosts report which multicast streams they 
wish to receive. The Querier device and all snooping Layer 
2 switches, then update their lists accordingly (the lists are 
also updated when Join Group and Leave Group (IGMPv2) 
messages are received).  
IGMP Fast-Leave (aka Immediate Leave)
When a device/host no longer wishes to receive a 
multicast transmission, it can issue an IGMP Leave Group 
message as mentioned above. This causes the switch to 
issue an IGMP Group-Specific Query message on the port 
(that the Leave Group was received on) to check no other 
receivers exist on that connection that wish to remain a 
part of the multicast. This process has a cost in terms of 
switch processor activity and time. 
Where ALIF units are connected directly to the switch 
(with no other devices on the same port) then enabling 
IGMP Fast-Leave mode means that switches can 
immediately remove receivers without going through 
a full checking procedure. Where multiple units are 
regularly joining and leaving multicasts, this can speed up 
performance considerably. 
Jumbo frames (Jumbo packets)
Since its commercial introduction in 1980, the Ethernet 
standard has been successfully extended and adapted to 
keep pace with the ever improving capabilities of computer 
systems. The achievable data rates, for instance, have risen 
in ten-fold leaps from the original 10Mbit/s to a current 
maximum of 100Gbit/s. 
While data speeds have increased massively, the standard 
defining the number of bytes (known as the Payload) 
placed into each data packet has remained resolutely stuck 
at its original level of 1500 bytes. This standard was set 
during the original speed era (10Mbits/s) and offered the 
best compromise at that speed between the time taken to 
process each packet and the time required to resend faulty 
packets due to transmission errors. 
But now networks are much faster and files/data streams 
are much larger; so time for a change? Unfortunately, a 
wholesale change to the packet size is not straightforward 
as it is a fundamental standard and changing it would mean 
a loss of backward compatibility with older systems.
Larger payload options have been around for a while, 
however, they have often been vendor specific and at 
present they remain outside the official standard. There 
is, however, increased consensus on an optional ‘Jumbo’ 
payload size of 9000 bytes and this is fully supported by 
the AdderLink Infinity (ALIF) units.
Jumbo frames (or Jumbo packets) offer advantages for 
ALIF units when transmitting certain high resolution video 
signals across a network. This is because the increased data 
in each packet reduces the number of packets that need to 
be transferred and dealt with - thus reducing latency times.
The main problem is that for jumbo frames to be possible 
on a network, all of the devices on the network must 
support them.   
						

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Spanning Tree Protocol (STP)
In order to build a robust network, it is necessary 
to include certain levels of redundancy within the 
interconnections between switches. This will help to 
ensure that a failure of one link does not lead to a 
complete failure of the whole network.
The danger of multiple links is that data packets, especially 
multicast packets, become involved in continual loops as 
neighbouring switches use the duplicated links to send and 
resend them to each other. 
To prevent such bridging loops from occurring, the 
Spanning Tree Protocol (STP), operating at layer 2, is 
used within each switch. STP encourages all switches 
to communicate and learn about each other. It prevents 
bridging loops by blocking newly discovered links until it 
can discover the nature of the link: is it a new host or a 
new switch? 
The problem with this is that the discovery process can 
take up to 50 seconds before the block is lifted, causing 
problematic timeouts.
The answer to this issue is to enable the portfast variable 
for all host links on a switch. This will cause any new 
connection to go immediately into forwarding mode. 
However, take particular care not to enable portfast on 
any switch to switch connections as this will result in 
bridging loops.   
						

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Forwarding modes
In essence, the job of a layer 2 switch is to transfer as 
fast as possible, data packets arriving at one port out to 
another port as determined by the destination address. 
This is known as data forwarding and most switches offer 
a choice of methods to achieve this. Choosing the most 
appropriate forwarding method can often have a sizeable 
impact on the overall speed of switching:
• Store and forward is the original method and requires 
the switch to save each entire data packet to buffer 
memory, run an error check and then forward if no 
error is found (or otherwise discard it).
• Cut-through was developed to address the latency 
issues suffered by some store and forward switches. 
The switch begins interpreting each data packet as it 
arrives. Once the initial addressing information has been 
read, the switch immediately begins forwarding the 
data packet while the remainder is still arriving. Once 
all of the packet has been received, an error check is 
performed and, if necessary, the packet is tagged as 
being in error. This checking ‘on-the-fly’ means that 
cut-through switches cannot discard faulty packets 
themselves. However, on receipt of the marked packet, a 
host will carry out the discard process.     
• Fragment-free is a hybrid of the above two methods. 
It waits until the first 64 bits have been received before 
beginning to forward each data packet. This way the 
switch is more likely to locate and discard faulty packets 
that are fragmented due to collisions with other data 
packets.  
• Adaptive switches automatically choose between the 
above methods. Usually they start out as a cut-through 
switches and change to store and forward or fragment-
free methods if large number of errors or collisions are 
detected. 
So which one to choose? The Cut-through method has the 
least latency so is usually the best to use with AdderLink 
Infinity units. However, if the network components and/
or cabling generate a lot of errors, the Store and forward 
method should probably be used. On higher end store and 
forward switches, latency is rarely an issue.
Layer 2 and Layer 3: The OSI model
When discussing network switches, the terms Layer 2 and 
Layer 3 are very often used. These refer to parts of the 
Open System Interconnection (OSI) model, a standardized 
way to categorize the necessary functions of any standard 
network. 
There are seven layers in the OSI model and these define 
the steps needed to get the data created by you (imagine 
that you are Layer 8) reliably down onto the transmission 
medium (the cable, optical fiber, radio wave, etc.) that 
So why are Layer 2 and Layer 3 of particular importance 
when discussing AdderLink Infinity? Because the successful 
transmission of data relies upon fast and reliable passage 
through network switches – and most of these operate at 
either Layer 2 or Layer 3.
The job of any network switch is to receive each incoming 
network packet, strip away only the first few wrappers to 
discover the intended destination then rewrap the packet 
and send it in the correct direction. 
In simplified terms, the wrapper that is added at Layer 2 
(by the sending system) includes the physical address of 
the intended recipient system, i.e. the unique MAC address 
(for example, 09:f8:33:d7:66:12) that is assigned to every 
networking device at manufacture. Deciphering recipients 
at this level is more straightforward than at Layer 3, where 
the address of the recipient is represented by a logical IP 
address (e.g. 192.168.0.10) and requires greater knowledge 
of the surrounding network structure. Due to their more 
complex circuitry, Layer 3 switches are more expensive 
than Layer 2 switches of a similar build quality and are 
used more sparingly within installations.
carries the data to another user; to complete the picture, 
consider the transmission medium is Layer 0. In general, 
think of the functions carried out by the layers at the top 
as being complex, becoming less complex as you go lower 
down. 
As your data travel down from you towards the 
transmission medium (the cable), they are successively 
encapsulated at each layer within a new wrapper (along 
with a few instructions), ready for transport. Once 
transmission has been made to the intended destination, 
the reverse occurs: Each wrapper is stripped away and the 
instructions examined until finally only the original data are 
left.   
						

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APPENDIX F - Configuration menus (via VNC)
When viewing remotely via VNC, the unit has a main configuration menu through which 
you can access various sub menus to configure particular items.
To view the main configuration menu
1 Using VNC viewer or a browser, log on as the ‘admin’ user.
2 Click the ‘Configure’ button in the top right corner. The main configuration menu will 
be displayed:
The various configuration pages are covered within this appendix:
• User accounts
• Gui edit configuration
• Unit configuration
• Advanced unit configuration
• Time & date configuration
• Network configuration 
• Serial port configuration
• Host configuration
• Power switching configuration
• Logging and status   
						

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User accounts
Up to 16 users can be created by the admin user, each with their password. One of the 
16 users can be the admin user. This user has access to the units configuration menu. 
Ticking the ‘IsAdmin’ box creates the Admin user. The admin user can also determine 
whether the users are allowed access to the power control menu in order to turn 
servers on and off.
To get here
1 Using VNC viewer or a browser, log on as the ‘admin’ user.
2 Click the ‘Configure’ button in the top right corner.
3 Click the ‘User Accounts’ option.
User Name     
All user names must consist of lower case characters or numbers only. No symbols 
or upper case characters are permissible. The user name can be between 1 and 32 
characters in length but cannot contain foreign characters.
Password
Each password can be between 1 and 16 characters in length. A suitable password is best 
constructed using a mixture of more than 6 letters, numbers and punctuation characters.
Local
This column is greyed out as this feature is not available on ALIF 2112T.
Remote
When ticked, the selected user can gain access via an IP network link (such as a local 
intranet or the wider Internet, depending on how the ALIF 2112T is connected) and/or 
Console Server access.
Pow e r
When ticked, the selected user will be permitted to control the power input to host 
systems (requires optional power control switch unit(s) to be fitted).
Menu Bar
Optionally click to customize the menu bar for each user. See next page. 
Enable Password Hashing 
This enables the storing of passwords in an encrypted format, which provides added 
security.
      
						

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Gui edit configuration
If required, you can customize the menu bar of the viewer window to ensure that it 
contains only the necessary options. 
The menu bar can be edited locally by each user or edited singly by the admin or 
alternatively, the admin can globally alter the menu bar for all users.
To globally edit the menu bar via admin
1 Using VNC viewer or a browser, log on as the ‘admin’ user.
2 Click the ‘Configure’ button in the top right corner.
3  Click on User Configuration
4  Click on the relevant Edit button.
To edit the menu bar locally
1 Login remotely via VNC viewer and display the viewer window.
2  Place the mouse pointer on the menu bar and click the right mouse button. A popup 
will be displayed:   
3 Click on any option within the popup to add it to or remove it from the menu bar.
4 When all changes have been made, click anywhere else within the viewer window.
Changes made in this way will affect the individual user only.