Network Active Devices

1- HUB & Switch HUB & Router

3Com® SuperStack® 3 Switch 3870, 48-Port

A vital difference between a hub and a switch is that all the nodes connected to a hub share the bandwidth among themselves, while a device connected to a switch port has the full bandwidth all to itself. For example, if 10 nodes are communicating using a hub on a 10-Mbps network, then each node may only get a portion of the 10 Mbps if other nodes on the hub want to communicate as well. But with a switch, each node could possibly communicate at the full 10 Mbps.

In a fully switched network, switches replace all the hubs of an Ethernet network with a dedicated segment for every node. These segments connect to a switch, which supports multiple dedicated segments (sometimes in the hundreds). Since the only devices on each segment are the switch and the node, the switch picks up every transmission before it reaches another node. The switch then forwards the frame over the appropriate segment. Since any segment contains only a single node, the frame only reaches the intended recipient. This allows many conversations to occur simultaneously on a switched network.

An example of a network using a switch
 

Switching allows a network to maintain full-duplex Ethernet. Before switching, Ethernet was half-duplex, which means that data could be transmitted in only one direction at a time. In a fully switched network, each node communicates only with the switch, not directly with other nodes. Information can travel from node to switch and from switch to node simultaneously.

Fully switched networks employ either twisted-pair or fiber-optic cabling, both of which use separate conductors for sending and receiving data. In this type of environment, Ethernet nodes can forgo the collision detection process and transmit at will, since they are the only potential devices that can access the medium. In other words, traffic flowing in each direction has a lane to itself. This allows nodes to transmit to the switch as the switch transmits to them -- it's a collision-free environment. Transmitting in both directions can effectively double the apparent speed of the network when two nodes are exchanging information. If the speed of the network is 10 Mbps, then each node can transmit simultaneously at 10 Mbps.

Routers and Switches

You can see that a switch has the potential to radically change the way nodes communicate with each other. But you may be wondering what makes it different from a router. Switches usually work at Layer 2 (Data or Datalink) of the OSI Reference Model, using MAC addresses, while routers work at Layer 3 (Network) with Layer 3 addresses (IP, IPX or Appletalk, depending on which Layer 3 protocols are being used). The algorithm that switches use to decide how to forward packets is different from the algorithms used by routers to forward packets.

One of these differences in the algorithms between switches and routers is how broadcasts are handled. On any network, the concept of a broadcast packet is vital to the operability of a network. Whenever a device needs to send out information but doesn't know who it should send it to, it sends out a broadcast. For example, every time a new computer or other device comes on to the network, it sends out a broadcast packet to announce its presence. The other nodes (such as a domain server) can add the computer to their browser list (kind of like an address directory) and communicate directly with that computer from that point on. Broadcasts are used any time a device needs to make an announcement to the rest of the network or is unsure of who the recipient of the information should be.

 
 

Transparent Bridging

Most Ethernet LAN switches use a very cool system called transparent bridging to create their address lookup tables. Transparent bridging is a technology that allows a switch to learn everything it needs to know about the location of nodes on the network without the network administrator having to do anything. Transparent bridging has five parts:

Types of switches

Form Factor

  • Rack mounted
  • Non rack mounted

Possibility of configuration

  • Non managed
  • Managed
  • Smart / intelligent

Unmanaged switches have no configuration interface. They are typically found in SOHO environment. Configuration options for managed switches vary with manufacturers and models. You can access the configuration interface for managing your switch (hence the name). Older models use a serial console, more recent devices use a web interface. (Sometimes you can configure them via pushing buttons on the switch also.) They are found in medium/large network environment and come at a higher price and quality (eg. backplane with higher transfer speeds). The task of managing usually requires understanding of Layer 2 networks (eg. Ethernet). Smart (or intelligent) switches are usually managed switches with a limited set of features.

Possible features (slightly in the order of basic to advanced features):

  • Turn some particular port on or off
  • Link speed and duplex settings
  • Priority settings for ports
  • MAC filtering
  • Use of Spanning Tree Protocol
  • SNMP monitoring of device and link health
  • Port mirroring (also named: monitoring port, spanning port, SPAN port, Roving Analysis Port, link mode port)
  • Link aggregation (also called: bonding/trunking)
  • VLAN settings

Performance specs? - Switch Fabric (definition needed) - MAC table size - RAM buffer size - Network Protocol and Standards - optional ports (fiber, SFP Expansion Slots, etc) - auto port speed detection, configuration

Frame capturing (and other network administration tasks) can be difficult in a switched ethernet. Port monitoring addresses this problem with replicating the traffic from all ports (or VLANs) onto a single port, on which you can set up an isolated monitoring network. Link aggregation allows you to use multiple ports for the same connection achieving higher data transfer speeds. Creating VLANs can solve collision problems and serve security goals (by reducing the broadcast/collision domain).

Form of power source

  • Standard
  • Power over Ethernet

Multilayer switch

A multilayer switch (MLS) is a computer networking device that switches on OSI layer 2 like an ordinary network switch and provides extra functions on higher OSI layers.

The major difference between the packet switching operation of a router and that of a Layer 3 switch is the physical implementation. In general-purpose routers, packet switching takes place using a microprocessor, whereas a Layer 3 switch performs this using application-specific integrated circuit (ASIC) hardware.

Network Bridge

A network bridge connects multiple network segments at the data link layer. Bridges are similar to repeaters or network hubs, devices that connect network segments at the physical layer, however a bridge works by using bridging where traffic from one network is managed rather than simply rebroadcast to adjacent network segments. In Ethernet networks, the term "bridge" formally means a device that behaves according to the IEEE 802.1D standard - this is most often referred to as a network switch in marketing literature.

 2- Network card

A network card, network adapter or NIC (network interface controller) is a piece of computer hardware designed to allow computers to communicate over a computer network. It is an OSI model layer 2 item because it has a MAC address. It allows users to connect to each other using cables.

Every network card has a unique 48-bit serial number called a MAC address, which is written to ROM carried on the card. Every computer on a network must have a card with a unique MAC address. No two cards ever manufactured should share the same address. This is because the Institute of Electrical and Electronics Engineers (The IEEE) is responsible for assigning unique MAC addresses to the vendors of network interface controllers.

manufacturers

3Com - AMD - Intel - Micronet - Novell - Realtek