03-05-2014, 12:46 PM
IMPLEMENTAION OF ROUTERS AND SWITCHES
IMPLEMENTAION OF ROUTERS.docx (Size: 1.45 MB / Downloads: 13)
COMPANY’S PROFILE
Dimension Data is the independent IT services and solutions provider in Asia Pacific & Specialized in customized business solutions. Dimension Data is a wholly owned subsidiary of Dimension Data (LSE: DDT), a US$4 billion leading global IT solutions and services provider. Dimension Data operates in over 50 offices across 13 Asia Pacific countries which helps clients plan, build, support, manage, improve and innovate their IT infrastructures. Dimension Data combines an expertise in networking, security, data centre, storage, Microsoft solutions and contact centre technologies, with advanced skills in consulting, integration, training and managed services to craft IT solutions for businesses.
In January 2008, Dimension Data acquires Security-Assessment.com to provide best-in -class protection to its client’s networks and IT environments across the Asia Pacific region. This acquisition is complementary to Dimension Data's current security practice and this addition will enhance the team's ability to provide the highest level of security advisory and assessment services to clients regionally and globally.
Strong services capabilities
Over half of our employees are networking industry-accredited technical personnel. Dimension Data is the only region wide Cisco Gold Certified Partner, employing over 100 CCIEs (Cisco Certified Internetwork Experts). Dimension Data depth of service expertise is backed by five Global Service Centers (GSCs), which provide 24x7 multivendor support in local languages and local client knowledge. In Asia, Dimension Data GSC is certified to ISO 2000 standard.
Corporate Social Responsibilities
At Dimension Data, we recognize that corporate social responsibilities go hand in hand with corporate achievement. Patting ourselves on the back for the latest sales success is only one part of Dimension Data corporate character. For this reason, sometimes we like to ditch the jackets and ties and take a look at the bigger picture.
Clients
As Asia's pioneer in systems and network integration, Dimension Data has designed, implemented and managed network infrastructure for many global corporations and leading service providers, as well as the equivalent of the Fortune 200 companies in every country throughout Asia Pacific.
Milestones
Dimension Data was founded in 1974 and its growth is the result of our solutions, skills and experience that address issues clients face today and we help them gain competitive advantage. You can gain greater insight into our business and growth from this snapshot of our history and milestones.
Choosing Internetworking Reliability Options
One of the first concerns of most network designers is to determine the required level of application availability. In general, this key consideration is balanced against implementation cost. For most organizations, the cost of making a network completely fault tolerant is prohibitive. Determining the appropriate level of fault tolerance to be included in a network and where redundancy should be used is not trivial.
Redundant Links Versus Meshed Topologies
Typically, WAN links are the least reliable components in an internetwork, usually because of problems in the local loop. In addition to being relatively unreliable, these links are often an order of magnitude slower than the LANs they connect. However, because they are capable of connecting geographically diverse sites, WAN links often make up the backbone network, and are therefore critical to corporate operations. The combination of potentially suspect reliability, lack of speed, and high importance makes the WAN link a good candidate for redundancy.
The primary disadvantage of duplicating WAN links to each remote office is cost. In the example outlined in Figure_1.5, three new WAN links are required. In large star networks with more remote offices, 10 or 20 new WAN links might be needed, as well as new equipment (including new WAN router interfaces). A lower cost alternative that is becoming increasingly popular links the remote offices using a meshed topology, as shown in Figure_1.6 .
Fault-Tolerant Media Implementations
Media failure is another possible network fault. Included in this category are all problems associated with the media and its link to each individual end station. Under this definition, media components include network interface controller failures, lobe or attachment unit interface (AUI) cable failures, transceiver failures, hub failures, and all failures associated with media components (for example, the cable itself, terminators, and other parts). Many media failures are caused by operator negligence and cannot easily be eliminated.
One way to reduce the havoc caused by failed media is to divide existing media into smaller segments and support each segment with different hardware. This minimizes the effect of a failure on a particular segment. For example, if you have 100 stations attached to a single switch, move some of them to other switches.
Backup Hardware
Like all complex devices, routers, switches, and other internetworking devices develop hardware problems. When serious failures occur, the use of dual devices can effectively reduce the adverse effects of a hardware failure. After a failure, discovery protocols help end stations choose new paths with which to communicate across the network. If each network connected to the failed device has an alternative path out of the local area, complete connectivity will still be possible.
For example, when backup routers are used, routing metrics can be set to ensure that the backup routers will not be used unless the primary routers are not functioning. Switchover is automatic and rapid. For example, consider the situation shown in Figure_1.8. In this network, dual routers are used at all sites with dual WAN links. If Router R1 fails, the routers on FDDI 1 will detect the failure by the absence of messages from Router R1. Using any of several dynamic routing protocols, Router A, Router B, and Router C will designate Router R3 as the new next hop on the way to remote resources accessible via Router R4.