all of the devices that are connected to the Internet are called ___or ____.

·      a networking infrastructure that provides services to distributed applications.

·      today, close to ------ of the world’s population are active mobile Internet users with the percentage expected to increase to ------ by 2025 [Statista 2019].

·      End systems are connected together by a network of -------- and ----------.

·      Different links can transmit data at different rates, with the -------- of a link measured in bits/second.

·      When one end system has data to send to another end system, the sending end system segments the data and adds ------ to each segment.

·      The resulting packages of information, known as ------- in the jargon of computer networks, are then sent through the network to the destination end system, where they are reassembled into the original data.

·      A ----- takes a packet arriving on one of its incoming communication links and forwards that packet on one of its outgoing communication links.

· packet switches come in many shapes and flavors, but the two most prominent types in today’s Internet are ---- and ---------.

·      ------- are typically used in access networks, while -------- are typically used in the network core.

·      The sequence of communication links and packet switches traversed by a packet from the sending end system to the receiving end system is known as a ------ or ----- through the network.

·      ------- access the Internet ---------- (ISPs), including residential ISPs such as local cable or telephone companies; corporate ISPs; university ISPs; ISPs that provide WiFi access in airports, hotels, coffee shops, and other public places; and cellular data ISPs, providing mobile access to our smartphones and other devices.

·      Each ISP is in itself a network of ----- and ----------.

Cisco predicts annual global IP traffic will reach nearly --------  (10²¹ bytes) by 2022 [Cisco VNI 2020].

·      End systems, packet switches, and other pieces of the Internet run ------ that control the sending and receiving of information within the Internet.

·      The ------- (TCP) and the ------- (IP) are two of the most important protocols in the Internet.

·      The ------ specifies the format of the packets that are sent and received among routers and end systems.

·      The Internet’s principal protocols are collectively known as ------.

·      ---------- are developed by the ------- (IETF) [IETF 2020].

·      The IETF standards documents are called --------- (RFCs).

·      ------- started out as general requests for comments (hence the name) to resolve network and protocol design problems that faced the precursor to the Internet [Allman 2011].

·      They define protocols such as TCP, IP, HTTP (for the Web), and SMTP (for e-mail). There are currently nearly ------- RFCs.

·      The ----- can also be described from an entirely different angle—namely, as an infrastructure that provides services to applications.

·      The applications are said to be --------, since they involve multiple end systems that exchange data with each other.

Internet applications run on ----- —they do not run in the ------ in the network core.

·      Although ------ facilitate the exchange of data among end systems, they are not concerned with the application that is the source or sink of data.

·      End systems attached to the Internet provide a ------- that 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.

·      This ------ is a set of rules that the sending program must follow so that the Internet can deliver the data to the destination program.

·      A ------- 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).

·      All activity in the Internet that involves two or more communicating remote entities is governed by a --------.

·      For example, ------- in two physically connected computers control the flow of bits on the “wire” between the two network interface cards; ------- in end systems control the rate at which packets are transmitted between sender and receiver; -------- determine a packet’s path from source to destination. Protocols are running everywhere in the Internet.

·      A ------ 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.

·      Recall from the previous section that in computer networking jargon, the computers and other devices connected to the Internet are often referred to as ------. They are referred to as ------ because they sit at the ------ of the Internet.

·      End systems are also referred to as ----- because they ---- (that is, run) application programs such as a Web browser program, a Web server program, an e-mail client program, or an e-mail server program.

·      Hosts are sometimes further divided into two categories: ------ and -------.

• Informally, ------ tend to be desktops, laptops, smartphones, and so on, whereas ----- tend to be more powerful machines that store and distribute Web pages, stream video, relay e-mail, and so on.

·      Today, most of the servers from which we receive search results, e-mail, Web pages, videos and mobile app content reside in ____.

·      Having considered the applications and end systems at the “edge of the network,” let’s next consider the ----- —the network that physically connects an end system to the first router (also known as the “-------”) on a path from the end system to any other distant end system.*

Home Access: -----, -------, -----, and -------.

·      Today, the two most prevalent types of broadband residential access are -------- (DSL) and ------.

·      A residence typically obtains DSL Internet access from the same local ------ (telco) that provides its wired local phone access. Thus, when DSL is used, a customer’s telco is also its ISP.*

·      each customer’s DSL modem uses the existing telephone line exchange data with a ------- (DSLAM) located in the telco’s local central office (CO).*

·      The home’s ------  takes digital data and translates it to high- frequency tones for transmission over telephone wires to the CO; the analog signals from many such houses are translated back into digital format at the -----.*

·      The --------- carries both data and traditional telephone signals simultaneously, which are encoded at different frequencies:*

A high-speed downstream channel, in the ----- to ------ band*

·      A medium-speed upstream channel, in the ----- to ------ band*

An ordinary two-way telephone channel, in the --- to --- band*

·      On the customer side, a ------ separates the data and telephone signals arriving to the home and forwards the data signal to the DSL modem.*

·      On the telco side, in the CO, the ------ separates the data and phone signals and sends the data into the Internet.*

·      The DSL standards define multiple transmission rates, including downstream transmission rates of ---Mbs and ----- Mbs, and upstream rates of ---- Mbps and ----- Mbps; the newest standard provides for aggregate upstream plus downstream rates of ----- Gbps [ITU 2014].*

·      Because the downstream and upstream rates are different, the access is said to be ------. *

·      While DSL makes use of the telco’s existing local telephone infrastructure, -------- makes use of the cable television company’s existing cable television infrastructure.

·      Each neighborhood junction typically supports ---- to ----- homes. Because both fiber and coaxial cable are employed in this system, it is often referred to as ------ (HFC). *

·      Cable internet access requires special modems, called -------. As with a DSL modem, the ----- is typically an external device and connects to the home PC through an Ethernet port.*

·      At the cable head end, the ------ (CMTS) serves a similar function as the DSL network’s DSLAM—turning the analog signal sent from the cable modems in many downstream homes back into digital format.*

·      As with DSL, access is typically -------, with the downstream channel typically allocated a higher transmission rate than the upstream channel.*

·      The ------ ----- and ----- standards define downstream bitrates of 40 Mbps and 1.2 Gbps, and upstream rates of 30 Mbps and 100 Mbps, respectively. As in the case of DSL networks, the maximum achievable rate may not be realized due to lower contracted data rates or media impairments.*

·      In cable internet, because the upstream channel is also shared, a ----------- is needed to coordinate transmissions and avoid collisions.*

·      Although DSL and cable networks currently represent the majority of residential broadband access in the United States, an up-and-coming technology that provides even higher speeds is ---------.

   As the name suggests, the ------ concept is simple—provide an optical fiber path from the CO directly to the home.
·      ----- can potentially provide Internet access rates in the gigabits per second range.

·      The simplest optical distribution network is called --------, with one fiber leaving the CO for each home.

·      There are two competing optical-distribution network architectures that perform this splitting: ------ and ---------.

·      ------- is essentially switched Ethernet.

·      ------ is used in Verizon FiOS service.*

In the ----- architecture, all packets sent from OLT to the splitter are replicated at the splitter (similar to a cable head end).

·      -------- not only promises high-speed residential access, but will do so without installing costly and failure-prone cabling from the telco’s CO to the home.*

·      Access in the Enterprise (and the Home): --------- and ---------

·      -------- is by far the most prevalent access technology in corporate, university, and home networks.*

·      As shown in the figure, Ethernet users use twisted-pair copper wire to connect to an -------. The --------, or a network of such interconnected switches, is then in turn connected into the larger Internet.*

·      With Ethernet access, users typically have ------ Mbps to ------ of Gbps access to the Ethernet switch, whereas servers may have ---- Gbps ---- Gbps access.*

·      Wireless lan access based on ----- technology, more colloquially known as ------, is now just about everywhere—universities, business offices, cafes, airports, homes, and even in airplanes. ------- today provides a shared transmission rate of up to more than 100 Mbps.*

·      ------- employ the same wireless infrastructure used for -------- to send/receive packets through a base station that is operated by the cellular network provider.

·      Unlike WiFi, a user need only be within a few ----- of kilometers (as opposed to a few tens of meters) of the base station.

·      Telecommunications companies have made enormous investments in so-called ------  wireless, which provides real-world download speeds of up to -------.

·      But even higher-speed wide-area access technologies—a ------ of wide-area wireless networks—are already being deployed. *

·      For each transmitter-receiver pair, the bit is sent by propagating electromagnetic waves or optical pulses across a --------.

·      The ------- can take many shapes and forms and does not have to be of the same type for each transmitter-receiver pair along the path.

·      Physical media fall into two categories: ------- and -------.

·      With -------, the waves are guided along a solid medium, such as a fiber-optic cable, a twisted-pair copper wire, or a coaxial cable.

·      With --------, the waves propagate in the atmosphere and in outer space, such as in a wireless LAN or a digital satellite channel.

·      The least expensive and most commonly used guided transmission medium is --------.

·      ----- consists of two insulated copper wires, each about ----- thick, arranged in a regular spiral pattern.

·      A ------ constitutes a single communication link.

·      For over a hundred years it has been used by telephone networks. In fact, more than ----- of the wired connections from the telephone handset to the local telephone switch use twisted-pair copper wire. Most of us have seen twisted pair in our homes (or those of our parents or grandparents!) and work environments. *

·      ------- is commonly used for computer networks within a building, that is, for LANs. Data rates for LANs using twisted pair today range from 10 Mbps to 10 Gbps. The data rates that can be achieved depend on the thickness of the wire and the distance between transmitter and receiver.

Modern twisted-pair technology, such as category 6a cable, can achieve data rates of ------ for distances up to a ------.

·      Like twisted pair, ------ consists of two copper conductors, but the two conductors are concentric rather than parallel.

·      With this construction and special insulation and shielding, ---- can achieve high data transmission rates.

·      -------- is quite common in cable television systems.

·      Coaxial Cable can be used as a guided ------. Specifically, a number of end systems can be connected directly to the cable, with each of the end systems receiving whatever is sent by the other end systems.*

·      An ----- is a thin, flexible medium that conducts pulses of light, with each pulse representing a bit. A single ------ 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 up to 100 kilometers, and are very hard to tap.

·      The Optical Carrier (OC) standard link speeds range from ---- Mbps to ---- Gbps; these specifications are often referred to as OC-n, where the link speed equals n × 51.8 Mbps.

·      OC-x stands for -------, is a set of signaling rates designed for transmission over ---- (SONET) networks.

·      ------- 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.

·      Environmental considerations determine ----- and ---- (which decrease the signal strength as the signal travels over a distance and around/through obstructing objects), ------ (due to signal reflection off of interfering objects), and ------ (due to other transmissions and electromagnetic signals).

can be broadly classified into three groups: those that operate over very short distance (e.g., with one or two meters); those that operate in local areas, typically spanning from ten to a few hundred meters; and those that operate in the wide area, spanning tens of kilometers.

·      A ------- links two or more Earth-based microwave transmitter/ receivers, known as ground stations.

·      The ------ receives transmissions on one frequency band, regenerates the signal using a repeater, and transmits the signal on another frequency.

·      Two types of satellites are used in communications: ------ and ------ satellites.

·      ---------- permanently remain above the same spot on Earth.

·      This stationary presence is achieved by placing the satellite in orbit at ------- above Earth’s surface.

·        This huge distance from ground station through satellite back to ground station introduces a substantial signal propagation delay of -------.

·      ------ are placed much closer to Earth and do not remain permanently above one spot on Earth. They rotate around Earth (just as the Moon does) 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.

·      In a network application, end systems exchange ----- with each other.

·      To send a message from a source end system to a destination end system, the source breaks long messages into smaller chunks of data known as ------.

-------- 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.

·      For each attached link, the packet switch has an ------ (also called an ------), which stores packets that the router is about to send into that link.

·      In addition to the store-and-forward delays, packets suffer --------. These delays are variable and depend on the level of congestion in the network.

·      In the Internet, every end system has an address called an -------.

·      When a source end system wants to send a packet to a destination end system, the source includes the destination’s ------- in the packet’s ------. When a packet arrives at a router in the network, the router examines a portion of the packet’s destination address and forwards the packet to an adjacent router.

·      each router has a -------- that maps destination addresses (or portions of the destination addresses) to that router’s outbound links.

·      When a packet arrives at a router, the router examines the address and searches its --------, using this destination address, to find the appropriate outbound link. The router then directs the packet to this outbound link.

·      There are two fundamental approaches to moving data through a network of links and switches: ------- and -------.

·      In -------- networks, the resources needed along a path (buffers, link transmission rate) to provide for communication between the end systems are reserved for the duration of the communication session between the end systems.

·      ------ networks are examples of circuit-switched networks.

·      When the network establishes the ------, it also reserves a constant transmission rate in the network’s links (representing a fraction of each link’s transmission capacity) for the duration of the connection. Since a given transmission rate has been reserved for this sender-to-receiver connection, the sender can transfer the data to the receiver at the guaranteed constant rate.

·      A circuit in a link is implemented with either ------ or -------- .

·      With -----, the frequency spectrum of a link is divided up among the connections established across the link. Specifically, the link dedicates a frequency band to each connection for the duration of the connection.

·      In telephone networks, this frequency band typically has a width of ------ (that is, ------ hertz or ----- cycles per second).

·      The width of the band is called, not surprisingly, the -------.

·      For a -----, 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.

·        To provide structure to the design of network protocols, network designers organize protocols—and the network hardware and software that implement the protocols—in _____.

·        We are again interested in the ------ that a layer offers to the layer above—the so-called ------ of a layer.

·        A ----------- can be implemented in software, in hardware, or in a combination of the two.

·        Application-layer protocols, such as ------ and -----, are almost always implemented in software in the end systems; so are ----------.

·        Because the ------ layer and --------- layers are responsible for handling communication over a specific link, they are typically implemented in a network interface card (for example, Ethernet or WiFi interface cards) associated with a given link. The network layer is often a mixed implementation of hardware and software.

·        Protocol layering has conceptual and structural advantages. As we have seen, layering provides a structured way to discuss system components. ----------- makes it easier to update system components.

·        What are included in the Five-Layer Internet protocol stack?

When taken together, the protocols of the various layers are called the

·        The ----------- is where network applications and their application-layer protocols reside.

·        The Internet’s application layer includes many protocols, such as the ------ protocol (which provides for Web document request and transfer), -------- (which provides for the transfer of e-mail messages), and ------- (which provides for the transfer of files between two end systems).

·        Certain network functions, such as the translation of human-friendly names for Internet end systems like www.ietf.org to a 32-bit network address, are also done with the help of a specific application-layer protocol, namely, the --------.

·        An application-layer protocol is distributed over multiple end systems, with the application in one end system using the protocol to exchange packets of information with the application in another end system. We’ll refer to this packet of information at the application layer as a --------.

·        The Internet’s ---------- transports application-layer messages between application endpoints.

·        In the Internet, there are two transport protocols, ----- and -----, either of which can transport application-layer messages.

·        ------ protocol provides a  connection-oriented service to its applications. This service includes guaranteed delivery of application-layer messages to the destination and flow control (that is, sender/receiver speed matching). It also breaks long messages into shorter segments and provides a congestion-control mechanism, so that a source throttles its transmission rate when the network is congested.

·        The ------- protocol provides a connectionless service to its applications. This is a no-frills service that provides no reliability, no flow control, and no congestion control.

·        A transport-layer packet is referred to as a -------.

·        The Internet’s network layer is responsible for moving network-layer packets known as -------- from one host to another.

·        The Internet’s network layer includes the celebrated ----- protocol, which defines the fields in the datagram as well as how the end systems and routers act on these fields. There is only 1 of it and all Internet components that have a network layer must run it.

·        The Internet’s network layer routes a datagram through a series of routers between the source and destination. To move a packet from one node (host or router) to the next node in the route, the network layer relies on the services of the -----------.

·        At each node, the -------- passes the datagram down to the ---------, which delivers the datagram to the next node along the route.

·        Examples of link-layer protocols include ------, ------, and the cable access network’s ----- protocol.

·        Link-layer packets are referred to as --------.

·        While the job of the link layer is to move entire frames from one network element to an adjacent network element, the job of the -------- is to move the -------- within the frame from one node to the next.

·        The protocols in this layer are again link dependent and further depend on the actual transmission medium of the link (for example, -------, -------).

·        Figure 4 also illustrates the important concept of encapsulation. At the sending host, an -------, M, is passed to the transport layer.

In the simplest case, the transport layer takes the message and appends additional information, H_t, that will be used by the receiver-side transport layer. The application-layer message and the transport-layer header information together constitute the -----------.

·        The transport-layer segment thus encapsulates the ---------. The added information might include information allowing the receiver-side transport layer to deliver the message up to the appropriate application, and error-detection bits that allow the receiver to determine whether bits in the message have been changed in route.

·        The transport layer then passes the segment to the network layer, which adds ----------, H_n, such as source and destination end system addresses, creating a ----------.

The datagram is then passed to the link layer, which will add its own ----, H_l, and create a --------.

·        Thus, we see that at each layer, a packet has two types of fields: ----- and a -----.

·        The ------- is typically a packet from the layer above.