Computer Networks and the Internet - Chapter 1
Clients
A category of a host (aka end system). Such devices tend to be desktop and mobile PCs, smartphones and so on.
Servers
A category of a host (aka end system). Such devices tend to be more powerful machines that store and distribute Web pages, stream video, relay e-mail and so on.
Satellite radio
A communication satellite links two or more Earth-based microwave transmitter/receivers, known as ground stations. The satellite receives transmissions on one frequency band, regenerates a signal using a repeater and transmits the signal on another frequency.
Shared Medium
A medium or channel of information transfer that serves more than one user at a time.
Network protocols
A network protocol is similar to a human protocol, except that the entities exchanging messages and taking actions are hardware or software components of some device (for example, computer, smartphone, tablet, router, or other network-capable device).
Packet Switching
A packet it sent into the network without reserving any link resources whatsoever. If one of the links is congested because other packets need to be transmitted over the link at the same time, then the packet will have to wait in a buffer at the sending side of the transmission link and suffer a delay.
Fiber Optics
A thin, flexible medium that conduct pulses of light, with each pulse representing a bit. A single optical fiber can support tremendous bit rates, up to tens or even hundreds of gigabits per second. They are immune to electromagnetic interference, have very low signal attenuation of up to 100 kilometers and are very hard to tap. These characteristics have made fiber optics the preferred long-haul guided transmission media.
Link-layer switch
A type of switch that is typically used in access networks.
Routers
A type of switch that is typically used in the network core.
Distributed applications
Applications that are provided service by the infrastructure that is the internet. Such applications involve multiple end systems that exchange data with each other. Importantly, Internet applications run on end systems - they do not run in the packet switches in the network core.
Circuit
Bona fide connection established by a network before a sender can even send the information. Switches on the path between the sender and receiver maintain connection state for that connection.
messages
Can contain anything the application designer wants. May perform a control function or contain data.
Unshielded Twister Pair (UTP)
Commonly used for computer networks within a building, that is, for LANs. Data rates for such range from 10Mbps to 10Gbps.
Hosts/End Systems
Computing devices throughout the world that are interconnected by the internet - a global computer network.
Coaxial Cable
Consist of two copper conductors like twister pair, but the two conductors are concentric rather than parallel. With this construction and special insulation/shielding, coaxial cable can achieve high data transmission rates.
Silent periods
Dedicated circuits are idle during this time (an argument made by proponents of packet switching to circuit switching). When one person in a telephone call stops talking, the idle network resources - frequency bands or time slots in the links along the connection's route - cannot be used by other ongoing connections.
Internet standards
Developed by the Internet Engineering Task Force. Given the importance of protocols to the Internet, it's important that everyone agree on what each and every protocol does, so that people can create systems and products that interoperate.
Output buffer
Each packet switch has this for each attached link, which stores packets that the router is about to send into that link. Plays a key role in packet switching. Also known as output queue.
Forwarding Table
Each router has this, which maps destination addresses to that router's outbound links. When a packet arrives at a router, the router examines the address and searches this, using the destination address, to find the appropriate outbound link. The packet is then redirected by the router to that outbound link.
HFC (Hybrid Fiber Coax)
Fiber and coaxial cable are employed in a cable-based internet access system, hence this other name given to cable internet access.
Physical Medium
For each transmitter-receiver pair, a bit is sent by propagating electromagnetic waves or optical pulses across such. Such can take many shapes and forms and does not have to be the same type for each transmitter-receiver pair along the path.
FDM (Frequency division multiplexing)
Frequency spectrum of a link is divided up among the connections established across the link. Specifically, the link dedicates a frequency bad to each connection for the duration of the connection.
Circuit Switching
In these networks, the resources needed along a path to provide for communication between the end systems are reserved for the duration of the communication session between the end systems.
WiFi
In this setting, wireless users transmit/receive packets to/from an access point that is connected into the enterprise's network (most likely including wired Ethernet), which in turn, is connected to the wired Internet. A user in this setting must typically be within a few tens of meters of the access point.
LEO satellite
Low-earth orbiting satellites are placed much closer to Earth and do not remain permanently above one spot on Earth. They rotate around Earth and may communicate with each other as well as with ground stations. To provide continuous coverage to an area, many satellites need to be placed in orbit.
Transmission rate
Measured in bits/second. These are rates of data transmission, which vary based on the type of the communication link.
Ethernet
Most prevalent access technology in corporate, university and home networks. Users of such, use twisted-pair copper wire to connect to an Ethernet switch. The Ethernet switch, or a network of such interconnected switches, is then in turn connected into the larger Internet. With Ethernet access, users typically have 100Mbps access to the Ethernet switch, whereas servers may have 1Gbps or even 10Gbps access.
End-to-end connection
Network establishes this dedicated connection between hosts, when two hosts wants to communicate.
Transmission Control Protocol (TCP)
One of the most important protocols in the Internet.
Internet Protocol (IP)
One of the most important protocols in the Internet. Specifies the format of the packets that are sent and received among routes and end systems.
Digital Subscriber Line (DSL)
One of the most prevalent types of broadband residential access. A residence typically obtains DSL Internet access from the same local telephone company that provided its wired local phone access. Each customer's DSL model uses the existing telephone line (twisted pair copper wire) to exchange data with a digital subscriber line access multiplexer (DSLAM) located in the telephone company's local central office. The home DSL modem takes digital data and translates it to high frequency tones for transmission over telephone wires to the central office. The analog signals from many such houses are translated back into digital format at the DSLAM.
Active Optical Networks (AONs)
One of the two competing optical-distribution network architectures that perform the splitting of customer-specific finders when the fiber leaving the central office gets relatively close to the homes that are sharing a piece of that fiber.
Geostationary satellite
One of the two types of satellites that are used in communications. Permanently remain above the same spot on Earth. This stationary presence is achieved by placing the satellite in orbit at 36,000 kilometers above Earth's surface. This huge distance from ground station through satellite back to ground station introduces a substantial signal propagation delay of 280 milliseconds.
Packet
Packages of information that are packaged when one end system has data to send to another end system. When one end system has data to send to another end system, the sending end system segments the data and adds header bytes to each segment. Such packages are sent through the network to the destination end system, where they are reassembled into the original data.
Queuing delays
Packets suffer this kind of a delay. These delays are variable and depend on the level of congestion in the network - the arriving packet must wait in the output buffer if it finds the link busy with the transmission of another packet.
Application Programming Interface (API)
Provided by the end systems that are attached to the Internet. Such specifies how a program running on one end system asks the Internet infrastructure to deliver data to a specific destination program running on another end system.
Internet Service Providers (ISPs)
Provides internet access for end systems. Each of such is in itself, a network of packet switches and communication links.
Terrestrial radio
Radio channels carry signals in the electromagnetic spectrum. They are an attractive medium because they require no physical wire to be installed, can penetrate walls, provide connectivity to a mobile user and can potentially carry a signal for long distances. Can be classified to 3 groups: those that operate over very short distance, those that operate in local areas and those that operate in the wide area.
Protocols
Ran by end systems, packet switches and other pieces of the internet that control the sending and receiving of information within the Internet. Defines the format and the order of messages exchanged between two or more communicating entities as well as the actions taken on the transmission and/or receipt of a message or other event.
Network edge
Section at the edge of a network that are made up of familiar components such as computers, smartphones and other devices that we use on a daily basis.
Packet Switches
Takes a packet arriving on one of its incoming communication links and forwards that packet on one of its outgoing communication links.
Request For Comments (RFCs)
The name for IETF standards documents, which started out as general requests for comments (hence the name) to resolve network and protocol design problems that faced the precursor to the Internet.
Communication Links
The network of such devices connect end systems together. There are different types of physical media for such, which include coaxial cable, copper wire, optical fiber and radio spectrum.
Access Networks
The network that physically connects and end system to the first router (also known as the "edge router") on a path from the end system to any other distant end system.
Route/Path
The sequence of communication links and packet switches traversed by a packet from the sending end system to the receiving end system.
Guided Media
The waves are guided along a solid medium, such as fiber-optic cable, a twisted-pair copper wire or a coaxial cable.
Unguided media
The waves propagate in the atmosphere and in outer space, such as in a wireless LAN or a digital satellite channel.
TMD (Time division multiplexing)
Time is divided into frames of fixed duration and each frame is divided into a fixed number of time slots. When the network establishes a connection across a link, the network dedicates one time slot in every frame to this connection. These slots are dedicated for the sole use of that connection, with one time slot available for use (in every frame) to transmit the connection's data.
Store-and-forward
Transmission used by most packet switches at the inputs to the links. This transmission means that the packet switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.
Fiber to the home (FTTH)
Up-and-coming technology that promises even higher speeds. This provides an optical fiber path from the central office directly to the home. Verizon has been aggressive with this with its FIOS service.
Passive Optical Networks (PONs)
Used in Verizon's FIOS service. Each home has an optical network terminator, which is connected by a dedicated optical fiber to a neighborhood splitter. The splitter combines a number of homes onto a single, shared optical fiber, which connect to an optical line terminator in the in the telephone company's central office. The optical line terminator (in the company's central office) provides conversion between optical and electrical signals. In the home, users connect a home router to the optical network terminator and access the Internet via this home router.
Cable Internet Access
While DSL makes use of the telephone company's existing local telephone infrastructure, this makes use of the cable television company's existing cable television infrastructure. A residence obtains cable Internet access from the same company that provides its cable television. A residence obtains cable internet access from the same company that provides its cable television. Fiber optics connect the cable head end to neighborhood-level junctions, from which traditional coaxial cable is then used to reach individual houses and apartments. Because both fiber and coaxial cable are employed in this system, it is often referred to as hybrid fiber coax (HFC)
Bandwidth
Width of the band (frequency band)
