WHITE PAPER August 2012 Successful AdderLink Infinity Implementation Optimising your network for AdderLink Infinity 1
Successful Implementation: Optimising your network Successful AdderLink Infinity Implementation Optimising your network for AdderLink Infinity S INCE ITS INTRODUCTION IN 2010, the AdderLink Infinity system (otherwise known as ALIF), has provided new levels of flexibility in the distribution of high performance computing power.
Choosing layer 2 switches The trouble with multicasting 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.
Implementing IGMP snooping on a low end switch with a slow processor can cause severe performance problems when data is transmitted at high data rates and/or there are multiple IGMP groups to be monitored. If a switch cannot keep pace, it will cause backlogs where large numbers of data packets are arbitrarily discarded and/or it resorts to sending all multicasts to all ports - causing multicast flooding. Either way, this results in slow video updates and a poor user experience.
Designing the network layout Selecting the right kind of switches is the first stage; ensuring they are laid out correctly is the next. General recommendations • The general rule is: Keep it flat. This means adopting a basic line cascade structure with a flat 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.
The advantage of arranging switches as a line cascade is that the communication links between them effectively form a simple bus structure that avoids the IGMP traps encountered by the pyramid arrangement.
Configuring switches and ALIFs The correct configuration of each switch can have a significant impact on overall performance, so in this section we’ll take a look at the various issues. The precise configuration details for each switch vary with make and model, so please also check the Switch setups section where a selection of specific configuration details are made available for a limited number of common switches.
Choose the most appropriate switch forwarding mode Every switch is built to transfer data from any one of its ports to any other as quickly as possible. Of the numerous factors involved to make this possible is the forwarding mode: the precise manner in which data packets are deciphered, checked and transferred. For use with ALIF units, the Cut-through method generally produces the fastest results.
Troubleshooting Problem: The video image of the ALIF receiver shows horizontal lines across the screen. Problem: AIM cannot locate working ALIF units. There are a few possible causes: This issue is known as Blinding because the resulting video image looks as though you’re viewing it through a venetian blind. Remedies: When video is transmitted by ALIF units, the various lines of each screen are divided up and transmitted as separate data packets.
Troubleshooting 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 colour depth of images by diffusing or altering the colour of pixels between video frames. This practice is commonly used on Apple Mac computers using ATI or Nvidia graphics cards.
Glossary Internet Group Management Protocol IGMP Querier Jumbo frames (Jumbo packets) 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.
Glossary Spanning Tree Protocol (STP) Layer 2 and Layer 3: The OSI model 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. When discussing network switches, the terms Layer 2 and Layer 3 are very often used.
Glossary Protocols and ports In order to achieve the feat of sending high resolution DVI video, audio, RS232 serial and four USB streams across a standard Gigabit Ethernet network, ALIF units rely upon a combination of industry standard protocols. These protocols operate at Layer 4 (the Transport layer) in the OSI model, i.e. another level of sophistication above the Layer 2 and 3 techniques enacted by the switches and routers through which it travels.
Glossary 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.
Switch setups Cisco Catalyst 2960S and 3750 Cisco 6500 You need to configure the following settings: On VLAN1: • Assign switch IP address and default gateway 2 ip igmp snooping vlan 1 • Assign VLAN1 with an IP address • Enable IGMP snooping • Enable IGMP querier • Enable Jumbo packets and choose the Max setting.
Switch setups Extreme X460-24t For example: Enable IGMP Snooping • Assign VLAN1 with an IP address configure vlan default ipaddress 123.45.67.8 255.255.255.0 To enable or disable IGMP snooping, use the following commands: • Enable IGMP Snooping The changes take effect immediately. • Enable IGMP Fast Leave NOTE: As a general rule, when configuring any IP addresses for the switch, you can express a subnet mask by using dotted decimal notation or by using classless inter domain routing notation (CIDR).
Switch setups HP ProCurve 2810 and 2910 H3C 5120 HuaWei Quidway s5328c-EI (Layer 3) Using Command Line Interface (CLI) will provide access to the switch’s full set of commands. dis cur You need to configure the following: # version 5.20, Release 2202P06 • Assign switch IP address The settings below affect multicast operation on the switch.
Index A L Adaptive 14 AIM 10 ASIC 3 Layer 2 and 3 12 B Background refresh 8, 13 Bandwidth 6 C CGMP 7 Colourdepth 8 Colour Depth 13 Configuration browser-based utility 8 Cut-through 14 D Dithering 9 F Fast-Leave 9, 11 Forwarding modes 8, 14 Fragment-free 14 Frame Skipping 8, 13 G M MAC address 12 Multicasting 3 Multicast router 6 O OSI model 12 P Payload 11 Peak bandwidth limiter 8, 13 Portfast 7 Protocols 13 Q Querier 5, 6 S Snooping 3, 9 Spanning Tree Protocol 7, 12 Store and forwa
About Adder Adder is a leading developer and manufacturer of KVM switches, video and audio extenders, KVM-over-IP devices, and remote management solutions. By empowering IT professionals to securely manage technology resources anywhere in the world, Adder solutions help customers make the best use of those resources while driving down total cost of ownership. In addition, through its advanced video and audio extension solutions, Adder is enabling the next generation of digital signage.
