Title: 2.2 Network Devices
Course: Information and Communication Technology: Module B > Section: Section 2 - Network Addressing Basics

2.2.1

Signals can only travel through media a certain distance before they weaken and become garbled. This weakening of signals is called attenuation. Attenuation increases when:

- media distances are lengthened
- nodes are added to the media

A collision occurs when devices on the same media try to transmit data at the same time. A collision domain is created when more than one device shares the same media.

Layer 1 devices do not make any decisions. They are “dumb” devices and transmit data at half-duplex. They do NOT look at Layer 2, Data Link (MAC) addresses or Layer 3, IP Addresses. They create a shared media and are vulnerable to collisions.

There are three common layer 1 devices:

- A repeater is a Layer 1 internetwork device used to combat attenuation. Repeaters take in weakened signals, clean them up, regenerate them, and send them on their way along the network. By using repeaters, the distance over which a network can operate is extended.

- A hub is essentially just a multiport repeater. Data that comes in one port is sent out from all other ports, except for the port it came in on. Hubs use the Bus topology, meaning they share the same media. This causes a lot of unwanted traffic on the media. Hubs operate at 10 Mbps and were meant to connect no more than ten devices. They are considered legacy devices on our network today.

- A transceiver is a device used to change one transmission media type to another—for example, from copper to fiber.

2.2.2 Network Devices

Layer 2 devices make decisions and provide filters based on MAC address or physical address. Unlike layer 1 devices, layer 2 devices do not share the media and work at full-duplex. They help solve network congestion by creating a virtual private path between the host and the layer 2 device.

Less traffic means fewer collisions. Frames are not forwarded throughout the whole network, but are contained in the appropriate network segment.

There are three main networking devices on Layer 2:

- A bridge has two ports. It examines Layer 2 Data Link addresses (MAC addresses) and keeps tables of those MAC addresses. It holds traffic destined for one side of the bridge to that side.

- A switch is like a multiport bridge. Switches are one of the core devices in today’s modern LANs. Switches learn about devices on each port and “decide” whether or not to forward the traffic. Unlike layer 1 devices, layer 2 devices do not share the media. Each port of a switch is considered its own collision domain. It micro-segments the network. The number of segments depends on the number of ports. Several ports can be grouped together into a VLAN (virtual local area network). VLANS can be used to secure certain parts of the network.

- A network interface card (NIC) is a computer circuit board that has a network connection and is used to connect the transmission media to the computer. Computers and other devices on a local area network (LAN) typically contain a network interface card specifically designed for the LAN transmission technology such as Ethernet. NICs provide device network connectivity. The can operate at speeds of 10 Mbps, 10/100 Mbps, or 10/100/1000 Mbps.

2.2.3 Network Devices

Layer 3 devices make decisions based on IP addresses or logical address. They are considered more intelligent than Layer 2 devices because they make logical decisions based on assigned network addresses. The main device at this layer is called a router.

A router serves these purposes:

- It examines incoming packets, choose the best path through the network, and then switch them to the proper outgoing port. This in known as path determination.

- It interconnects different networks or subnets. A router connects:
  - LANs to LANs
  - LANs to WANs
  - WANs to WANs

Routers can also connect different LAN technologies (such as Ethernet), and different WAN technologies (such as ISDN or PPP). Because of their ability to route packets based on Layer 3 information, routers have become the backbone of the Internet, running the IP protocol.

2.2.4 Network Devices

Layer 4 devices make decisions based on the incoming or outgoing port numbers and provide a reliable connection to the destination. Port numbers are used to keep track of the different “conversations” going on.

The main device at this layer is called a firewall. Firewalls are devices designed to permit or deny network access using rules set by the network administrator. They are frequently used to protect networks from unauthorized access.