Network Devices: Repeaters, Hubs, Routers, Switches, Bridges
Repeaters
A repeater is an electronic device that operates on the physical layer of the OSI model. An amplifier cannot differentiate between the original signal and a noise signal. Repeaters do not amplify the signal; they regenerate it. When a repeater receives a signal affected by noise, it creates a copy, bit by bit, restoring it to its original strength.
Advantages of Repeaters
- Extend the physical distance of a network.
- Do not seriously affect network performance.
Disadvantages of Repeaters
- Cannot connect different network architectures.
- Do not filter data.
- Repeat everything without discrimination.
- The number of repeaters must be limited.
Hubs
A hub operates on the physical layer of the OSI model. Hubs are central network devices that connect network nodes and provide central management. They connect devices centrally in a star topology. They cannot filter network traffic.
Types of Hubs
Active Hubs: Active hubs work similarly to repeaters. They need electrical power to run and are also called multiport repeaters.
Passive Hubs: A passive hub simply provides a connection between devices, enabling data to go from one device (or segment) to another. They do not need electrical power to run.
Intelligent Hubs: These hubs read the destination address of each packet and then forward the packet to the correct port. Intelligent hubs are also called manageable hubs.
Routers: Static and Dynamic
A router operates on the physical, data link, and network layers of the OSI model. It is most active in the network layer. It stores the IP addresses of the devices on the network in a table called the routing table. The function of a router is to receive packets from one network and forward them to another network based on the information stored in the routing table.
Advantages of Routers
- Can connect networks of different architectures.
- Choose the best path through or to a network.
- Create smaller collision domains.
- Create smaller broadcast domains.
Disadvantages of Routers
- Only work with routable protocols such as RIP, OSPF, or BGP.
- More expensive than hubs, bridges, and switches.
- Routing table updates consume bandwidth.
Switches: Store and Forward, Cut-Through
A switch works on the data link layer of the OSI model. It provides bridging with greater efficiency. Switches have a buffer for each link to which they are connected.
Advantages of Switches
- Increase available network bandwidth.
- Increase network performance.
- Smaller collision domains.
Disadvantages of Switches
- More expensive than hubs and bridges.
- Difficult to trace network connectivity problems through a switch.
- Do not filter broadcast traffic.
Bridges
Bridges work at the data link layer of the OSI model. They are designed to connect two or more LAN segments. At layer 1, a bridge is used to regenerate a signal. At layer 2, it is used to filter traffic on a LAN, keep local traffic local, and allow connectivity to other segments of the network. To provide security, a bridge filters traffic by looking at the MAC address and preventing unauthorized access.
Types of Bridges
Simple Bridge: Links two segments only. It has the lowest cost among other types. It requires manual updating of the bridging table and more time to maintain devices.
Multiport Bridges: Links more than two segments. Three tables are created, each storing the physical addresses of stations reachable through the corresponding port.
Transparent Bridges: Builds its tables of physical station addresses on its own. It performs bridge functions independently. The table is automatically built by frame movement in a network.
Advantages of Using a Bridge
- Extend the physical network.
- Reduce network traffic with minor segmentation.
- Create separate collision domains.
- Reduce collisions.
- Connect different architectures.
Disadvantages of Using Bridges
- Slower than repeaters due to filtering.
- Do not filter broadcasts.
- Broadcast packets are passed across bridges.
- More expensive than repeaters.