Computer Networks Week 04 Media and Devices College of Information Science and Engineering Ritsumeikan University
Network Media and Devices l When you build a network, the network hardware may be used for longer than computers or software components l Media is the plural of medium, which means the method of storing or communicating information l In networks, the media is the cables or the radio signals in the physical layer l Devices are the machines that link the media, including the network interface cards (NIC)
Network Media Choices l Selection of network media can determine the physical topology and speed of the network l Connectors connect the ends of cables to devices l The basic types of media in use are: copper, optical fiber, radio waves, and microwaves
Coaxial Cable l l l l You may have seen this type of cable connected to your television Coaxial cable is measured in RG (radio grade) and impedance, which is in ohms Thicknet coaxial is a legacy media Thinnet is a shielded media more expensive than unshielded twisted pair but with reduced interference
Twisted-Pair Cable l Like coaxial, the shield must be grounded l Types of twisted pair range from voice grade to 1000Base-X l Shielding reduces interference and cross-talk l Most Ethernet cables are two or four twisted pairs
Fiber Optic Cable Benefits of fiber are: l High transmission rates, long distances (depending on type) l No EMI (electromagnetic interference) or RFI (radio frequency interference) l Better security Disadvantages include: l It s expensive and difficult to install l Requires integration with electrical circuits
Radio Transmissions l Radio waves generally range from 30 centimeters to 3 kilometers l Most of these bands are reserved for special uses and regulated by agencies such as the FCC l Therefore, each device has a specified frequency (measured in Hz, MHz, or GHz) and bandwidth (which is not the same as internet bandwidth!)
Devices l We have already talked about many of the devices of a network and their differences l Devices are handling more and more layers of the OSI model, not only the Physical and Data Link layers l The types and locations of devices (and media), including the physical topology, determine the network segments, areas of the network bounded by switches, bridges, and routers
Network Interface Cards l Installed in the devices and computers l Each type of network and expansion slot has its own type of NIC so you must select the correct one for the network and the computer l The NIC functions at the Physical and Data Link layers
Repeater l Cleans up interference and noise l Re-times the signal to avoid collisions l Retransmits the signal for longer distances (Shown is a wireless repeater)
l A hub works like a bus l When selecting a hub, consider the type of media, the number of ports, speed, whether or not it has an uplink port (a port for connecting the hub to another hub, repeater, or switch) Hub
l Reduces collisions by dividing the network l Keeps track of devices on each segment with a bridging table l Filters packets based on MAC addresses l Forwards packets that are on the other segments Bridge
Switch l Multiport bridges functioning at the Data Link layer l Divides the network into segments l There are many types, depending on logical topology and type of network
l Present in every type of network from LANs to WANs l Select the best path for each packet based on the IP address in the TCP/IP environment l Can connect different types of networks by altering packet size, etc. Router
Determining the Best Route l Two types: dynamic routing and static routing l Dynamic routing adjusts automatically to the topology and network traffic l The routing table stores information about other networks l Each router makes a decision about where to send a packet based on its routing algorithm
Gateway l Connects different types of networks, translates l Address gateway connects different directory spaces l Protocol gateway connects networks with different protocols l Application gateway examines packets for specific objectives
Uninterrupted Power l UPSs are Uninterruptible Power Supply devices that supplement the current with a battery l Important questions to ask about power Which devices are crucial? How long do you need auxiliary power? How much power will you need for all crucial devices? l UPSs also help condition irregular power sources
Redundancy RAID l Redundancy is a common concept in most fields of engineering: having more than one of a required system to prevent failure l A common disk redundancy system is RAID (Redundant Array of Independent Disks) l RAID has several levels Level 1 is disk mirroring, which requires twice as many disks Level 5 is disk striping with parity, which requires three times as many disks
Levels of RAID
Example of a RAID Array