CNT4713 Chapter 1

FDM

...Frequency-division multiplexing: A circuit in a link is implemented by having the frequency spectrum of a link be 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.

average throughput

...If the file consists of F bits and the transfer takes T seconds for Host B to receive all F bits from Host A, then the average throughput of the file transfer if F/T bits/sec.

circuit

...In a circuit switching network, the sender can sender can send the information after the network has established a connection between the sender and the receive. In the jargon of telephony, this connection is called a circuit.

end-to-end connection

...In a circuit-switching network, the dedicated link(s) make up the end-to-end connection between two end systems.

circuit switching

...In circuit-switched 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. In use the resources on demand, and as a consequences, may have to wait( that is queue) for access to a communication link.

malware

...Malicious software that can infect an end system that can do all kinds of devious things, including deleting our files; installing spyware that collects our private information such as social security numbers, passwords, and keystrokes, and then sends this over the internet back to the bad guys.

worm

...Malware that can center a device without any explicit user interaction. For example, a user may be running a vulnerable network application to which an attacker can send malware.

virus

...Malware that require some form of user interaction to infect the user's device. Such as an e-mail attachment containing malicious executable code.

network-layer datagram

...The Internet's network layer is responsible for moving network-layer packets known as datagrams from one host to another. The Internet trasport-layer protocol (TCP or UDP) in a source host passes a transport-layer segment and a destination address to the network layer. The network layer then provides the service of delivering the segment to the transport layer in the destination host.

traffic intensity

...The Ratio La/R where a packet consists of L bits, R is the transmission rate (bits/sec) and a denotes the average rate at which packets arrive. If La/R > 1, then the average rate at which bits arrive at the queue exceed the rate at which the bits can be transmitted from the queue.

IP spoofing

...The ability to inject packets into the Internet with a false source address is known as IP spoofing, and is but one of many ways in which one user can masquerade as another user.

DDos

...The attacker controls multiple sources and has each source blast traffic at the target. With this approach, the aggregate traffic rate across all the controlled sources need to be approximately R to cripple the service.

instantaneous throughput

...The instantaneous throughput at any instant of a time is the rate (in bit/set) at which Host B is receiving the file from Host A.

transport-layer segment

...The internet's transport layer transports application-layer messages between application endpoints. In the Internet there are two transport protocols, TCP and UDP, either of which can transport application-layer messages. In this book, a transport-layer packet will be known as a segment.

link-layer frame

...The link layer moves a packet from one node to another. The services provided by the link layer depend on the specific link-layer protocol that is employed over the link. For example, some link-layer protocols provide reliable delivery, from transmitting node, over one link, to receiving node. Examples include Ethernet, Wifi, and cable access network. Link-layer packets are known as frames.

bottleneck link

...The link that significantly decreases the rate at which a file will transfer from Host A to Host B.

nodal processing delay

...The time required to examine the packet's header and determine where to direct the packet is part of the processing delay. It can include other factors, such as the time needed to check for bit-level errors in the packet that occurred in transmitting the packet's bits from the upstream node to router A.

propagation delay

...The time required to propogate from the beginning of the link to the next switch. The propogation speed depends on the physical medium of the link and is in the range of 2x10^8 m/s to 3x10^8 m/s which is equal to, or a little less than, the speed of light. The propogation delay d/s, is the distance between two routers (d) divided by (s) which is the propogation speed of the link.

bandwich

...The width of a frequency band.

TDM

...Time-division multiplexing: A circuit in a link 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.

traceroute

...Traceroute is a simple program that can run in any Internet host. When the user specifies a destination hostname, the program in the source host sends multiple, special packets toward that destination. As these packets work their way toward the destination, they pass through a series of routers. When a router receives one of these special packets, it sends back to the source a short mes- sage that contains the name and address of the router.

service model

...Way of describing what services a lay provides to the layer above.

packet loss

...When an incoming packet reaches a full buffer, either the incoming packet or one of the already-queued packets will be dropped.

peer

...When two networks directly connect together so that all the traffic between them passes over the direct connections rather than through upstream intermediaries.

cable internet access

cable Internet access 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.

coaxial cable

coaxial cable consists of two copper conductors, but the two conductors are concentric rather than parallel. With this construction and special insulation and shielding, coaxial cable can achieve high data transmission rates. Coaxial cable is quite common in cable television systems.

Communication llinks

connect two or more end systems. made of copper wire, optical fiber, ...

PON

passive optical networks. each fiber leaving the central office is actually shared by many homes; it is not until the fiber gets relatively close to the homes that it is split into individual customer-specific fibers. PON performs this splitting.

packet

when one end system sends data to another end system, the sending end system segments the data and add a header to each segment. the resulting packages of information know as packets.

AON

active optical networks. each fiber leaving the central office is actually shared by many homes; it is not until the fiber gets relatively close to the homes that it is split into individual customer-specific fibers. AON performs this splitting.

Physical medium

A medium is a third-party or element through which a message is communicated. Examples of physical media include twisted-pair copper wire, coaxial cable, multimode fiber-optic cable, terrestrial radio spectrum, and satellite radio spectrum. Physical media fall into two categories: guided media and unguided media.

network protoclos

A protocol 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.

path

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 route or path through the network.

distributed applications

The applications are said to be distributed applications, since they involve multiple end systems that exchange data with each other. ex: electronic mail, Web surfing, social networks, instant messaging, Voice-over-IP (VoIP), video streaming, distributed games, peer-to-peer (P2P) file sharing, television over the Internet, remote login

UTP

Unshielded twisted pair 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.

output buffer

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

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ISO OSI protocol stack

... Application Presentation Session Transport Network Link Physical

transmission delay

... The transmission delay is L/R. This is the amount of time required to push (that is, transmit) all of the packet's bits into the link. Transmission delays are typically on the order of microseconds to milliseconds in practice.

output queue

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

regional ISP

...A ISP which many access isp connect to, and itself may connect to a tier-1 isp.

Pop for ISP

...A PoP is simply a group of one or more routers (at the same location) in the provider's network where customers ISPs can connect into the provider ISP.

layered architecture

...A layered architecture allows us to discuss a well-defined, specific part of a large and complex system. This simplification itself is of considerable value by providing modularity, making it much easier to change the implementation of the service provided by the layer. As long as the layer provides the same service to the layer above it, and uses the same services from the layer below it, the remainder of the system remains unchanged when a layer's implementation is changed.

botnet

...A network of many to thousands of similarly compromised devices due to malware, that bad guys control and leverage for spam e-ail distribution or distributed denial-of-service attacks.

content provider networks

...A network that behaves much like an ISP, but independent at the same time. They may house their own data centers where all traffic may come to and from their servers directly without interaction to other ISPs

store-and-forward transmission

...A packet switch must receive the entire packet before it can begin to transmit the first bit of packet onto the outbound link.

packet sniffer

...A passive receive that records a copy of every packet that flies by is called a packet sniffer.

self-replication

...A property of malware: once it infects one host, from that host it seeks into entry into other hosts over the Internet, and from the newly infected hosts, it seeks entry into yet more hosts.

IXP

...A stand-alone building with its own switches that acts as a meeting point where multiple ISPs can peer together.

tier-1 ISP

...An ISP that are much bigger than regional ISP but do not have a presence in every city, such as AT&T, Sprint, and NTT.

customer

...An entity that pays for internet access.

provider

...An entity that provides internet access as a service.

multi-homed ISP

...Any ISP (except for tier-1 ISP) may choose to multi-home, that is, to connect to two or more provider ISPs. So, for example, an access ISP may multi-home with two regional ISPs, or it may multi-home with two regional ISPs and also with a tier-1 ISP.

queuing delay

...At the queue, the packet experiences a queuing delay as it waits to be transmitted onto the link. The length of the queuing delay of a specific packet will depend on the number of earlier-arriving packets that are queued and waiting for transmission onto the link. If the queue is empty and no other packet is currently being transmitted, then our packet's queuing delay will be zero.

DoS

...Denial of Service: an attack that renders a network, host, or other piece of infrastructure unusable by legitimate users.

vulnerability attack

...DoS AttacK: This involves sending well-crafted messages to a vulnerable application or operating system running on a targeted host. If the right sequence of packets is sent to a vulnerable application or operating system, the service can stop, or worse, the host can crash.

connection flooding

...DoS Attack: The attacker establishes a large number of half-open or fully open TCP connections at the target host. The host can become so bogged down with these bogus connections that it stops accepting legitimate connections.

bandwidth flooding

...DoS Attack: The attacker sends a deluge of packets to the targeted host - so many packets that the target's access link becomes clogged, preventing legitimate packets from reaching the server.

packet drop

...Due to finite storage capacity of queues, when it becomes full it will drop any extra incoming packets.

internet protocol stack

...Five layers: Application Transport Network Link Physical

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 the signal using a repeater, and transmits the signal on another frequency.

forwarding table

A table inside each router that maps destination addresses (or portions of the destination addresses of packets) to the router's outbound links.

application-layer message

An application-layer protocol is distributed over multiple end systems, with the application in one end system using 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 message.

fiber optics

An optical fiber is a thin, flexible medium that conducts 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 up to 100 kilometers, and are very hard to tap.

API

Application Programming Interface. This Internet API is a set of rules that the sending program must follow so that the Internet can deliver the data to the destination program. ex: Alice wants to mail a letter to Bob. she can not write a letter and drop it out her window. She has to put the letter in the envelope, write Bob's address, zip code, in the center of the envelope, seal it, put a stamp in the right-hand corner, and drop it to postal service mail box. this is postal service API.

clients

Clients are hosts(end system). clients tend to be desktop and mobile PCs, smartphones, and so on.

shared medium

Coaxial cable can be used as a guided shared medium

DSL

Digital Subscriber Line. it's a broadband residential access. The home's 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. • A high-speed downstream channel, in the 50 kHz to 1 MHz band • A medium-speed upstream channel, in the 4 kHz to 50 kHz band • An ordinary two-way telephone channel, in the 0 to 4 kHz band This approach makes the single DSL link appear as if there were three separate links, so that a telephone call and an Internet connection can share the DSL link at the same time.

ISP

End systems access the Internet through Internet Service Providers (ISPs). Each ISP is in itself a network of packet switches and communication links. ex: residential ISPs such as local cable or telephone companies; corporate ISPs; university ISPs; and ISPs that provide WiFi access in airports, hotels, coffee shops, and other public places.

FTTH

Fiber To The Home. the FTTH concept is simple— provide an optical fiber path from the Central Office directly to the home.

geostationary satellite

Geostationary satellites 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. Nevertheless, satellite links, which can operate at speeds of hundreds of Mbps, are often used in areas without access to DSL or cable-based Internet access.

messages

In a network application, end systems exchange messages with each other. Messages can contain anything the application designer wants. Messages may perform a control function .

host / end system

In the internet, all devices are called host and end system. ex: PC, servers, wireless laptop, smartphones, TVs. Two Categories: clients, servers.

IP

Internet Protocol. The IP protocol specifies the format of the packets that are sent and received among routers and end systems.

routers

It's one type of packet switch. they typically used in the network core

internet standards (STD)

It's specification that has been approved by the Internet Engineering Task Force (IETF). Such standard helps to promote a consistent and universal use of the Internet worldwide.

terrestrial radio

Radio channels carry signals in the electromagnetic spectrum. ex: -short distance: wireless headsets, keyboards, -local areas: wireless LAN technologies -wide area: the cellular access technologies

servers

Servers are hosts(end system). servers tend to be more powerful machines that store and distribute Web pages, stream video, relay e-mail, and so on.

RFC

The IETF standards documents are called Requests For Comments. They define protocols such as TCP, IP, HTTP (for the Web), and SMTP (for e-mail).

silent periods

Time intervals in circuit-switching networks for which the dedicated circuits are idle.

TCP

Transmission Control Protocol. Provides reliable transport, flow control, congestion control, does not provide timing, minimum throughput guarantee, security, it is connection-oriented (setup required between client and server processes).

guided media

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

unguided media

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

HFC

hybrid fiber coax. Because both fiber and coaxial cable are employed in cable internet access, it is often referred to as hybrid fiber coax (HFC).

link-layer swtich

it's one type of packet switch. they typically used in access networks.

LEO satellite

low-earth orbiting. LEO satellites 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.

protocol

sets of rules. a protocol is the special set of rules that end systems in a telecommunication connection use when they communicate. Protocols specify interactions between the communicating entities. ex: TCP, IP.

packet switches

takes the arriving packets by one of its incoming communication links and send it to the end system by one of its outgoing communication links. ex: routers, Link-layer switches

access network

the network that physically connects an 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.

Ethernet

uses copper wire.