1. Network Switches, Key Features & Functions <br />A network switch is a computer networking device that connects network segments. Switches commonly refer to a multi-port network bridge that process and route data at the data link layer (layer 2) of the OSI model. Switches that additionally process data at the network layer (Layer 3) and above are often referred to as Layer 3 switches or multilayer switches. <br />The network switch plays an integral part in most modern Ethernet local area networks (LANs). Mid-to-large sized LANs contain a number of linked managed switches. Small office/home office (SOHO) applications typically use a single switch, or an all-purpose converged device such as a gateway to access small office/home broadband services such as DSL or cable internet. In most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology. User devices may also include a telephone interface for VoIP.<br />Functions and Roles of Switches in Networks<br />An Ethernet switch operates at the data link layer of the OSI model to create a separate collision domain for each switch port. With 4 computers (e.g., A, B, C, and D) on 4 switch ports, A and B can transfer data back and forth, while C and D also do so simultaneously, and the two conversations will not interfere with one another. In the case of a hub, they would all share the bandwidth and run in half duplex, resulting in collisions, which would then necessitate retransmissions. Using a switch is called micro segmentation. This allows computers to have dedicated bandwidth on point-to-point connections to the network and to therefore run in full duplex without collisions.<br />Switches may operate at one or more layers of the OSI model, including data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is known as a multilayer switch.<br />In switches intended for commercial use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet, Fibre Channel, ATM, ITU-T G.hn and 802.11. This connectivity can be at any of the layers mentioned. While Layer 2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet and token ring are easier at Layer 3.<br />Interconnection of different Layer 3 networks is done by routers. If there are any features that characterize quot;
Layer-3 switchesquot;
as opposed to general-purpose routers, it tends to be that they are optimized, in larger switches, for high-density Ethernet connectivity.<br />In some service provider and other environments where there is a need for a great deal of analysis of network performance and security, switches may be connected between WAN routers as places for analytic modules. Some vendors provide firewall, network intrusion detection,[4] and performance analysis modules that can plug into switch ports. Some of these functions may be on combined modules.<br />In other cases, the switch is used to create a mirror image of data that can go to an external device. Since most switch port mirroring provides only one mirrored stream, network hubs can be useful for fanning out data to several read-only analyzers, such as intrusion detection systems and packet sniffers.<br />How to Choose a Suitable/Right Network Switch<br />Tips to consider when selecting a Switch for a Network<br />To select the appropriate switch for a layer in a particular network, you need to have specifications that detail the target traffic flows, user communities, data servers, and data storage servers. Company needs a network that can meet evolving requirements.<br />Traffic flow analysis is the process of measuring the bandwidth usage on a network and analysing the data for the purpose of performance tuning, capacity planning, and making hardware improvement decisions. <br />Future Growth<br />Switches come in different sizes, features and functions, choosing a switch to match a particular network sometimes constitute a daunting task.<br />Consider what will happen if the HR or HQ department grows by five employees or more’ A solid network plan includes the rate of personnel growth over the past five years to be able to anticipate the future growth. With that in mind, you would want to purchase a switch that can accommodate more than 24 ports, such as stackable or modular switches that can scale.<br />Performance<br />When selecting a switch for the* access, **distribution, or ***core layer, consider the ability of the switch to support the port density, forwarding rates, and bandwidth aggregation requirements of your network.<br />Access layer switches facilitate the connection of end node devices to the network e.g. PC, Modems, IP phone, Printers etc. For this reason, they need to support features such as port security, VLANs, Fast Ethernet/Gigabit Ethernet, PoE(power over Internet, and link aggregation. Port security allows the switch to decide how many or what type of devices are permitted to connect to the switch. This is where most Cisco comes in, they all support port layer security. Most renowned network administrator knows this is the first line of defence.<br />Distribution Layer switches plays a very important role on the network. They collect the data from all the access layer switches and forward it to the core layer switches. Traffic that is generated at Layer 2 on a switched network needs to be managed, or segmented into VLANs, Distribution layer switches provides the inter-VLAN routing functions so that one VLAN can communicate with another on the network.<br />Distribution layer switches provides advanced security policies that can be applied to network traffic using Access Control Lists (ACL). This type of security allows the switch to prevent certain types of traffic and permit others. ACLs also allow you to control, which network devices can communicate on the network.<br />Core layer switches: These types of switches at the core layer of a topology, which is the high-speed backbone of the network and requires switches that can handle very high forwarding rates. The switch that operates in this area also needs to support link aggregation (10GbE connections which is currently the fastest available Ethernet connectivity.) to ensure adequate bandwidth coming into the core from the distribution layer switches.<br /> Also, core layer switches support additional hardware redundancy features like redundant power supplies that can be swapped while the switch continues to operate. Because of the high workload carried by core layer switches, they tend to operate hotter than access or distribution layer switches, so they should have more sophisticated cooling options. Many true, core layer-capable switches have the ability to swap cooling fans without having to turn the switch off.<br />For example, it would be disruptive to shut down a switch at the core layer to change a power supply or a fan in the middle of the day when the network usage is at its Peak. To perform a hardware replacement, you could expect to have at least a 10 to 15 minute network shutdown, and that is if you are very fast at performing the maintenance. In more realistic circumstances, the switch could be down for 30 to 45 minutes or more, which most likely is not acceptable. With hot-swappable hardware, there is no downtime during switch maintenance.<br />Port Speed<br />Another characteristic one needs to put into consideration is port speed, which at times depend on performance requirements, choosing between fast Ethernet and Gigabit Ethernet Switch Ports. <br />Fast Ethernet allows up to 100 Mb/s of traffic per switch port while Gigabit Ethernet allows up to 1000 Mb/s of traffic per switch port. Fast Ethernet is adequate for IP telephony and data traffic on most business networks; however, performance is slower than Gigabit Ethernet ports.. <br />Port Density<br />Port density is the number of ports available on a single switch. Fixed configuration switches support up to 48 ports on a single device, with options for up to four additional ports.<br />High port densities allow for better use of space and power when both are in limited supply. If you have two switches that each contain 24 ports, you would be able to support up to 46 devices, because you lose at least one port per switch to connect each switch to the rest of the network. In addition, two power outlets are required. On the other hand, if you have a single 48-port switch, 47 devices can be supported, with only one port used to connect the switch to the rest of the network, and only one power outlet needed to accommodate the single switch.<br />Modular switches can support very high port densities through the addition of multiple switch port line cards, as shown in the figure. For example, the Cisco Catalyst 6500 switch can support in excess of 1,000 switch ports on a single device. <br />Forwarding Rates<br />Switches have different processing capabilities at the rate in which they process data per second. Processing and forwarding data rates are very important when selecting a switch, the lower the processing, the slower the forwarding this results to the switch unable to accommodate full wire-speed communication across all its ports. A normal fast Ethernet port attains a 100Mb/s , while Gigabit Ethernet does 1000Mb/s.<br />For example, a 48-port gigabit switch operating at full wire speed generates 48 Gb/s of traffic. If the switch only supports a forwarding rate of 32 Gb/s, it cannot run at full wire speed across all ports simultaneously.<br />Link Aggregation<br />The more ports you have on a switch to support bandwidth aggregation, the more speed you have on your network traffic,. e.g. , consider a Gigabit Ethernet port, which carries up to 1 Gb/s of traffic in a network. If you have a 24-port switch, with all its ports capable of running at gigabit speeds, you could generate up to 24 Gb/s of network traffic. If the switch is connected to the rest of the network by a single network cable, it can only forward 1 Gb/s of the data to the rest of that network. Due to the contention for bandwidth, the data would forward more slowly. That results in 1 out of 24 wire speed available to each of the 24 devices connected to the switch.<br />Power over Ethernet (PoE)<br />Another characteristic you consider when choosing a switch is Power over Ethernet (PoE). This is the ability of the switch to deliver power to a device over the existing Ethernet cabling. IP phones and some wireless access points can use this feature, you can be able to install them anywhere you can run an Ethernet cable.<br />