Networking for Home and Small Businesses Lesson 3 Network Transmission Medium
The Internet and How We Connect to It The Internet is a network of networks that connects users in every country in the world.
Internet Service Provider (ISP) An ISP is a company that provides the connections and support to access the Internet. ISPs are essential to gaining access to the Internet. E.g. 香港寬頻, PCCW, etc.
Point of Presence (存在點, POP) Individual computers and local networks connect to the ISP at a Point of Presence (POP). A POP is the connection point between the ISP's network and the particular geographical region that the POP is servicing. POP is a physical location that houses servers, routers, switches, etc. It may be either part of the facilities of a tele- communications provider that the Internet service provider (ISP) rents or a location separate from the telecommunications provider.
Point of Presence (POP) Within an ISP, a network of high-speed routers and switches move data between the various POPs. Multiple links interconnect the POPs to provide alternate routes for the data should one link fail or become overloaded with traffic and congested. ISPs connect to other ISPs in order to send information beyond the boundaries of their own network. The Internet is made up of very high-speed data links that interconnect ISP POPs and ISPs to each other. These interconnections are part of the very large, high capacity network known as the Internet Backbone.
ISP Levels of Service ISP Services Home Service: slower connection speed. Business Class Service: more expensive, provides faster connection speeds, additional services such as e-mail accounts. Business service also includes agreements between the ISP and the customer specifying items such as network availability and service response time. These are known as Service Level Agreements (SLAs).
Service Level Agreements (SLAs)
ISP Levels of Service When data is transferred, it is either uploaded or downloaded. Asymmetric: Most commonly used for the home. Download speeds are faster than upload speeds. Often called ADSL (Asymmetric Digital Subscriber Line) Symmetric: Commonly used for business or individuals hosting servers on the Internet. It can carry large amounts of data in both directions at equal rates. (i.e. download speed is same as upload speed) Often called SDSL (Symmetric digital subscriber line)
Internet Protocol (IP) For hosts to communicate on the Internet, they must be running Internet Protocol (IP). The IP uses packets to carry data, the information you are sending or receiving is encapsulated in the IP packets. Each IP packet must contain a valid source and destination IP address. Without valid address information, packets sent will not reach the destination host. Return packets will not make it back to the original source.
Internet Protocol (IP) The IP Packet (also known as Datagram): Has a header at the beginning containing the source and destination IP addresses. IP addresses must be unique on the Internet. Computers in homes, small businesses and other organizations obtain their IP configuration from their ISP. The data you want to send is divided into smaller pieces and are put into packets. IP packet size is between 64 to 1500 bytes for Ethernet networks. Downloading a single 1 MB song would require around 700 packets of 1500 bytes. Each individual packet must have a source and destination IP address.
How ISPs handle packets Routers in each of the ISP POPs use the destination address of the IP packets to choose the best path through the Internet. The packets you send to the ISP POP are forwarded by routers through the ISP's network and then through the networks of other ISPs. They pass from router to router until they reach their final destination.
Test connectivity to destination device Ping end-to-end connectivity test between source and destination. measure the time that it takes test packets to make a round trip from the source to the destination ping 192.168.1.1
Test connectivity to destination device
Sending Information Across the Internet Traceroute (tracert) Traces the route from source to destination. Displays each hop along the way and the time it takes for each one. Each router through which the packets travel is referred to as a hop.
Sending Information Across the Internet
Internet Cloud When packets travel across the Internet, they pass through many network devices. The Internet can be thought of as a network of routers, interconnected with one another. A diagram that shows all network devices and their interconnections would be very complex. Therefore a cloud is used to represent the Internet or any other complex network.
Networking Media Sending of data from one device to another is called transmission of data Medium (媒介) used to transmit the data is called Media (媒體) Transmission of data through Medium is called Transmission Media Transmission media or communication channels meant that the ‘connecting cables’ or ‘connection media’.
Networking Media Guided (Wired) Twisted Pair Coaxial cable Fiber Optics Unguided (Wireless) Wi-Fi Bluetooth Infrared Microwave Lasers Networking Media Guided Media Twisted Pair Co-Axial Cables Optic fibers Un-Guided Media Microwave Infrared Others
Networking Media : Guided ( Wired ) The medium itself is more important in determining the limitations of transmission. The transmission capacity, in terms of either data rate or bandwidth, depends critically on the distance and on whether the medium is point-to-point or multipoint.
Networking Media There are two kinds of physical cable Metal (copper) using electrical signals Fiber using light signals.
Coaxial cable (同軸電纜)
Coaxial cable (同軸電纜)
Coaxial cable (同軸電纜) BNC Connectors are used for connecting to co-axial cables together at connecting points is when repeaters are required
Coaxial cable (同軸電纜) It consists of solid wire core surrounded by one or more foil or wire shield, each separated by some kind of plastic insulator. the inner core carries the signal , and outer shield provides the ground. the coaxial cable has high electrical properties and is suitable for high speed communication. it is used in television signal.
Coaxial cable (同軸電纜) In general, coaxial cables, or coax, carry signals of higher freq. (100KHz–500MHz) than UTP cables. Outer metallic wrapping serves both as a shield against noise and as the second conductor that completes the circuit. =>Versatile transmission medium, used in a wide variety of applications Television distribution Aerial to TV systems.
Coaxial cable (同軸電纜) There are two types . 1.Thicknet: It is a thicker than thinner. It is used upto 500 meters long. 2. Thinner: It is used upto 185 meters long.
Optical fiber cables Light travels at 3108 ms-1 in free space and is the fastest possible speed in the Universe Light slows down in denser media, e.g. glass Refraction occurs at interface, with light bending away from the normal when it enters a less dense medium Beyond the critical angle total internal reflection
Optical fiber cables An optical fiber consists of a core (denser material) and a cladding (less dense material) Light bounces back and forth along the core Common light sources: LEDs and lasers
Optical fiber cables
Common Optical Fiber Connectors
Twisted Pair Cables A twisted pair consists of two insulated copper wires arranged in a regular spiral pattern. The twisting tends to decrease the crosstalk interference between adjacent pairs in a cable. Twisted pair may be used to transmit both analog and digital transmission. Twisted pair is limited in distance, bandwidth, and data rate.
Twisted Pair Cables If the pair of wires are not twisted, electromagnetic noises from, e.g., motors, will affect the closer wire more than the further one, thereby causing errors
Twisted pair cables common problem Data transmission is sensitive to interference or noise, which can reduce the data rate that a cable can provide. A twisted pair cable is susceptible (易受影響) to electromagnetic interference (EMI), a type of noise. A source of interference, known as crosstalk ( 線 與 線 串 擾 ), occurs when cables are bundled together for long lengths. The signal from one cable can leak out to adjacent cables. When data transmission is corrupted due to interference such as crosstalk, the data must be retransmitted. This can degrade the data carrying capacity of the medium. In twisted pair cabling, the number of twists per unit length affects the amount of resistance that the cable has to interference.
Twisted Pair Cables Unshielded Twisted Pair (UTP) ordinary telephone wire cheapest easiest to install suffers from external EM interference Shielded Twisted Pair (STP) metal braid or sheathing that reduces interference more expensive easiest to install harder to handle (thick, heavy)
Twisted Pair Cables Modern Ethernet technology generally uses a type of copper cable known as twisted pair (TP) to interconnect devices. unshielded twisted pair Screened twisted pair Shielded Twisted-pair Cable (STP)
Categories of Twisted Pair Category 3 (10-16 Mbps) Used of Voice communication Most often used for phone lines Category 5 and 5e Used for Data transmission Cat 5 supports 100 Mbps and can support 1000 Mbps but it is not recommended Cat 5e can support 1000 Mbps Category 6 An added separator is between each pair of wires allowing it to function at higher speeds Supports 1000 Mbps (1 Gbps) – 10 Gbps, though 10 Gbps is not recommended
Working with Twisted Pair Cabling
Working with Twisted Pair Cabling All Categories of data grade UTP cable are traditionally terminated into an RJ-45 connector. 所有可傳輸Data的UTP Cable都使用RJ45連接頭
TIA-568A: 白綠、綠、白橙、藍、白藍、橙、白啡、啡 TIA-568B: 白橙、橙、白綠、藍、白藍、綠、白啡、啡
Working with Twisted Pair Cabling
Straight-Through vs Crossover UTP Implementation: Straight-Through vs Crossover connect between dissimilar devices connect between similar devices
Rollover Cable
Rollover Cable
Patch panels Patch panels and cables allow quick rearrangement of network connections.
Patch panels A patch panel is used to house cable connections. One typically shorter patch cable will plug into the front side (connect to host), whereas the back holds the connection of a much longer and more permanent cable (connect to switch).
Patch panels Example (without a patch panel): An office spans 5 floors in a building. The switch is located in the server room on the first floor. To connect every workstations in each floor, they have to measure, cut, crimp and pull across the floors to reach switches.
Structural Cabling Video 1 Video 2
Cable faults Short: A short occurs when the copper conductors touch each other. As the electric pulse travels down the wire, it will cross onto the touching wire. This creates an unintended path in the flow of the signal to its destination. Open: An open circuit occurs when the wire is not properly pushed into the connector and there is no electrical contact. An open can also occur if there is a break in the wire.
Cable faults Split Pair: A split-pair fault occurs when one wire from one pair is switched with one wire from a different pair at both ends. A split pair creates two transmit or receive pairs each with two wires that are not twisted together. This mixing hampers the cross-cancellation process and makes the cable more susceptible to crosstalk and interference. Reversed-Pair: The reversed-pair fault occurs when a wire pair is correctly installed on one connector, but reversed on the other connector. For example if the white/green wire is terminated on pin 1 and the green wire is terminated on pin 2 at one end of a cable, but reversed at the other end, then the cable has a reversed-pair fault.
Working with Twisted Pair Cabling UTP signal degradation cause by cable distance, low quality cables, and poor terminations. Attenuation (衰減): drop in signal strength over distance Crosstalk (Pair與Pair串擾): Crosstalk is the leakage of signals between pairs. Near-end crosstalk (NEXT): If this is measured near the transmitting end it is termed near-end crosstalk (NEXT). Far-end crosstalk (FEXT): If measured at the receiving end of the cable it is termed far-end crosstalk (FEXT).