Nice Stuf Chapter 1

LAN (Local Area Network)

A LAN is a privately owned network that operates within and nearby a single building like a home, office or factory. LANs are widely used to connect personal computers and consumer electronics to let them share resources (e.g., printers) and exchange information. When LANs are used by companies, they are called enterprise networks.

communication medium

A computer network can provide a powerful

TCP/IP Reference Model

A four layer model derived from experimentation; omits some OSI layers and uses the IP as the network layer.

protocol stack

A list of the protocols used by a certain system, one protocol per layer

MAN (Metropolitan Area Network)

A network that covers an area equivalent to a city or other municipality. cable television networks

e-commerce (electronic commerce

A third goal for many companies is doing business electronically, especially with customers and suppliers

World Wide Web

A well-known example of a distributed system

TCP/IP Link Layer

All these requirements led to the choice of a packet-switching network based on a connectionless layer that runs across different networks. The lowest layer in the model, the link layer describes what links such as serial lines and classic Ethernet must do to meet the needs of this connectionless internet layer. It is not really a layer at all, in the normal sense of the term, but rather an interface between hosts and transmission links. Early material on the TCP/IP model has little to say about it.

flow control

An allocation problem that occurs at every level is how to keep a fast sender from swamping a slow receiver with data. Feedback from the receiver to the sender is often used.

Network Layer

Controls operation of the subnet. A key design issue is determining how packets are routed from source to destination. Routes can be based on static tables that are ''wired into'' the network and rarely changed, or more often they can be updated automatically to avoid failed components. They can also be determined at the start of each conversation, for example, a terminal session, such as a login to a remote machine. Finally, they can be highly dynamic, being determined anew for each packet to reflect the current network load.

negotiation

In some cases when a connection is established, the sender, receiver, and subnet conduct... ...about the parameters to be used, such as maximum message size, quality of service required, and other issues

Virtual LAN or VLAN

In this design each port is tagged with a ''color,'' say green for engineering and red for finance. The switch then forwards packets so that computers attached to the green ports are separated from the computers attached to the red ports. Broadcast packets sent on a red port, for example, will not be received on a green port, just as though there were two different LANs. We will cover VLANs at the end of Chap. 4

request-reply

In this service the sender transmits a single datagram containing a request; the reply contains the answer

architecture of the mobile phone network

It has several parts, as shown in the simplified version of the UMTS architecture in Fig. 1-31. First, there is the air interface. This term is a fancy name for the radio communication protocol that is used over the air between the mobile device (e.g., the cell phone) and the cellular base station. Advances in the air interface over the past decades have greatly increased wireless data rates. The UMTS air interface is based on Code Division Multiple Access (CDMA), a technique that we will study in Chap. 2. The cellular base station together with its controller forms the radio access network. This part is the wireless side of the mobile phone network. The controller node or RNC (Radio Network Controller) controls how the spectrum is used. The base station implements the air interface. It is called Node B, a temporary label that stuck

TCP/IP transport layer.

It is designed to allow peer entities on the source and destination hosts to carry on a conversation, just as in the OSI transport layer. Two end-to-end transport protocols have been defined here. The first one, TCP (Transmission Control Protocol), is a reliable connection-oriented protocol that allows a byte stream originating on one machine to be delivered without error on any other machine in the internet. It segments the incoming byte stream into discrete messages and passes each one on to the internet layer. At the destination, the receiving TCP process reassembles the received messages into the output stream. TCP also handles flow control to make sure a fast sender cannot swamp a slow receiver with more messages than it can handle.

client-server model.

It is widely used and forms the basis of much network usage. The most popular realization is that of a Web application, in which the server generates Web pages based on its database in response to client requests that may update the database.

communication subnet, or just subnet

The rest of the network that connects these hosts is then called

network service provider

The second variation is that the subnet may be run by a different company.

Ethernet

The topology of many wired LANs is built from point-to-point links. IEEE 802.3. by far, the most common type of wired LAN

DMCA takedown notices

There are now automated systems that search peer-to-peer networks and fire off warnings to network operators and users who are suspected of infringing copyright Digital Millennium Copyright Act

Switching elements, or just switches,

are specialized computers that connect two or more transmission lines

hotspots

based on the 802.11 standard are another kind of wireless network for mobile computers.

VPNs (Virtual Private Networks)

be used to join the individual networks at different sites into one extended network

connectivity

home users can access information, communicate with other people, and buy products and services with e-commerce.

UDP (User Datagram Protocol)

is anunreliable, connectionless protocol for applications that do not want TCP's sequencing or flow control and wish to provide their own. own. It is also widely used for one-shot, client-server-type request-reply queries and applications in which prompt delivery is more important than accurate delivery, such as transmitting speech or video

ARPANET

The NPL system was not a national system (it just connected several computers on the NPL campus), but it demonstrated that packet switching could be made to work. Furthermore, it cited Baran's now discarded earlier work. Roberts came away from Gatlinburg determined to build what later became known as the

TCP/IP Application Layer

The TCP/IP model does not have session or presentation layers. No need for them was perceived. Instead, applications simply include any session and presentation functions that they require. Experience with the OSI model has proven this view correct: these layers are of little use to most applications. On top of the transport layer is the application layer. It contains all the higher- level protocols. The early ones included virtual terminal (TELNET), file transfer (FTP), and electronic mail (SMTP). Many other protocols have been added to these over the years. Some important ones that we will study, shown in Fig. 1-22,

cut-through switching.

The alternative, in which the onward transmission of a message at a node starts before it is completely received by the node

Application Layer

The application layer contains a variety of protocols that are commonly needed by users. One widely used application protocol is HTTP (HyperText Transfer Protocol), which is the basis for the World Wide Web. When a browser wants a Web page, it sends the name of the page it wants to the server hosting the page using HTTP. The server then sends the page back. Other application protocols are used for file transfer, electronic mail, and network news.

Session Layer

The fifth layer in the OSI model. This layer establishes and maintains communication between two nodes on the network. It can be considered the "traffic cop" for network communications.

Transport Layer

The fourth layer of the OSI model. In this layer protocols ensure that data are transferred from point A to point B reliably and without errors. this layer services include flow control, acknowledgment, error correction, segmentation, reassembly, and sequencing.

resource sharing

The goal is to make all programs, equipment, and especially data available to anyone on the network without regard to the physical location of the resource or the user.

IP(Internet Protocol), plus a companion protocol called ICMP (Internet Control) Message Protocol

The job of the internet layer is to deliver IP packets where they are supposed to go. Packet routing is clearly a major issue here, as is congestion (though IP has not proven effective at avoiding congestion)

interface

Between each pair of adjacent layers. The interface defines which primitive operations and services the lower layer makes available to the upper one.

social network

Between person-to-person communications and accessing information. Facebook

Medium Access Control

Broadcast networks have an additional issue in the data link layer: how to control access to the shared channel. A special sublayer of the data link layer, the medium access control sublayer, deals with this problem.

broadcasting(multicasting)

Broadcast systems usually also allow the possibility of addressing a packet to all destinations by using a special code in the address field

scalable

Designs that continue to work well when the network gets large are said to be

power-line networks

Devices such as televisions that plug into the wall... to send information throughout the house over the wires that carry electricity

switched Ethernet

Each computer speaks the Ethernet protocol and connects to a box called a switch with a point-to-point link. Hence the name. A switch has multiple ports, each of which can connect to one computer. The job of the switch is to relay packets between computers that are attached to it, using the address in each packet to determine which computer to send it to.

wiki

Even more loosely, groups of people can work together to create content. Wikipedia

profiling

For example, small files called cookies that Web browsers store on users' computers allow companies to track users' activities in cyberspace and may also allow credit card numbers, social security numbers, and other confidential information to leak all over the Internet (Berghel, 2001).

forwarding algorithm

How each router makes the decision as to where to send a packet next

routing algorithm

How the network makes the decision as to which path

network neutrality

It should now come only as a slight surprise to learn that some network operators block content for their own reasons. Some users of peer-to-peer applications had their network service cut off because the network operators did not find it profitable to carry the large amounts of traffic sent by those applications. Those same operators would probably like to treat different companies differently. If you are a big company and pay well then you get good service, but if you are a small-time player, you get poor service. Opponents of this practice argue that peer-to-peer and other content should be treated in the same way because they are all just bits to the network

ISP (Internet Service Provider)

Its customers who connect to the ISP receive Internet service.

confidentiality

Mechanisms that provide... ...defend against this threat, and they are used in multiple layers.

error correction

More powerful codes allow... ...where the correct message is recovered from the possibly incorrect bits that were originally received

Middleware

Often a layer of software on top of the operating system.

servers

Often these are centrally housed and maintained by a system administrator.

error detection

One mechanism for finding errors in received information uses codes

point-to-point (unicasting)

Point-to-point links connect individual pairs of machines. source to the destination on a network made up of point-to-point links, short messages, called packets

addressing or naming

Since there are many computers on the network, every layer needs a mechanism for identifying the senders and receivers that are involved in a particular message.

congestion

Sometimes the problem is that the network is oversubscribed because too many computers want to send too much traffic, and the network cannot deliver it all. This overloading of the network is called

IEEE 802.11

There is a standard for wireless LANs. 802.11, popularly known as WiFi, which has become very widespread

primitives

These primitives tell the service to perform some action or report on an action taken by a peer entity.

router

These switching computers have been called by various names in the past

botnet

They might be used to steal your bank account passwords, or to have your computer send spam

layers or levels

To reduce their design complexity, most networks are organized as a stack of

Presentation Layer (Layer 6)

Unlike the lower layers, which are mostly concerned with moving bits around, the presentation layer is concerned with the syntax and semantics of the information transmitted. In order to make it possible for computers with different internal data representations to communicate, the data structures to be exchanged can be defined in an abstract way, along with a standard encoding to be used ''on the wire.'' The presentation layer manages these abstract data structures and allows higher-level data structures (e.g., banking records) to be defined and exchanged.

protocol layering

We have recently seen the key structuring mechanism used to support change by dividing the overall problem and hiding implementation details:

store-and-forward switching

When the intermediate nodes receive a message in full before sending it on to the next node

distributed system

a collection of independent computers appears to its users as a single coherent system

computer networks

a large number of separate but interconnected computers do the job

protocol

an agreement between the communicating parties on how communication is to proceed

circuit

another name for a connection with associated resources, such as a fixed bandwidth. This dates from the telephone network in which a circuit was a path over copper wire that carried a phone conversation

internetwork

composite networks that are made up of more than one network

physical layer

concerned with transmitting raw bits over a communication channel.43

OSI (Open Systems Interconnection) model

deals with connecting open systems—that is, systems that are open for communication with other systems. We will just call it the OSI model for short

header

front of the message to identify the message and passes the result to layer 3. The header includes control information, such as addresses, to allow layer 4 on the destination machine to deliver the message. Other examples of control information used in some layers are sequence numbers (in case the lower layer does not preserve message order), sizes, and times.

RFID (Radio Frequency IDentification)

future. RFID tags are passive (i.e., have no battery) chips the size of stamps and they can already be affixed to books, passports, pets, credit cards, and other items in the home and out. This lets RFID readers locate and communicate with the items over a distance of up to several meters, depending on the kind of RFID. Originally, RFID was commercialized to replace barcodes. It has not succeeded yet because barcodes are free and RFID tags cost a few cents. Of course, RFID tags offer much more and their price is rapidly declining. They may turn the real world into the Internet of things (ITU, 2005).

datagram service,

guarantee. Unreliable (meaning not acknowledged) connectionless service

data link layer

is to transform a raw transmission facility into a line that appears free of undetected transmission errors. It does so by masking the real errors so the network layer does not see them. It accomplishes this task by having the sender break up the input data into data frames (typically a few hundred or a few thousand bytes) and transmit the frames sequentially. If the service is reliable, the receiver confirms correct receipt of each frame by sending back an acknowledgement frame.

PANs (Personal Area Networks)

let devices communicate over the range of a person Bluetooth

statistical multiplexing

meaning sharing based on the statistics of demand. It can be applied at low layers or a single link, or at high layers for a network or even applications that use the network.

packet

message at the network layer

Phishing

messages masquerade as originating from a trustworthy party, for example, your bank, to try to trick you into revealing sensitive information, for example, credit card numbers

Transmission lines

move bits between machines. They can be made of copper wire, optical fiber, or even radio links. Most companies do not have transmission lines lying about, so instead they lease the lines from a telecommunications company.

Quality of service

name given to mechanisms that reconcile these competing demands

authentication

prevent someone from impersonating someone else

integrity

prevent surreptitious changes to messages, such as altering ''debit my account $10'' to ''debit my account $1000.'' All of these designs are based on cryptography, which we shall study in Chap. 8.

AP (Access Point), wireless router, or base station,

relays packets between the wireless computers and also between them and the Internet.

connectionless

service is modeled after the postal system. Each message (letter) carries the full destination address. and each one is routed through the intermediate nodes inside the system independent of all the subsequent messages.

Connection-oriented

service is modeled after the telephone system

network architecture

set of layers and protocols. The specification of an architecture must contain enough information to allow an implementer to write the program or build the hardware for each layer so that it will correctly obey the appropriate protocol

Acknowledged Datagram

situations, the convenience of not having to establish a connection to send one message is desired, but reliability is essential. It is like sending a registered letter and requesting a return receipt. When the receipt comes back, the sender is absolutely sure that the letter was delivered to the intended party and not lost along the way. Text messaging on mobile phones is an example.

WAN (Wide Area Network)

spans a large geographical area, often a country or continent

dialog control (keeping track of whose turn it is to transmit), token management (preventing two parties from attempting the same critical operation simultaneously), and synchronization

ssss

IPTV (IP TeleVision)

systems that are based on IP technology instead of cable TV or radio transmissions

broadcast links

the communication channel is shared by all the machines on the network; packets sent by any machine are received by all the others. An address field within each packet specifies the intended recipient

TCP/IP Internet Layer

the linchpin that holds the whole architecture together. It is shown in Fig. 1-21 as corresponding roughly to the OSI network layer. Its job is to permit hosts to inject packets into any network and have them travel independently to the destination (potentially on a different network). They may even arrive in a completely different order than they were sent, in which case it is the job of higher layers to rearrange them, if in-order delivery is desired. Note that ''internet'' is used here in a generic sense, even though this layer is present in the Internet

internetworking

the linking of separate networks into an interconnected network, where each network retains its own identity

NFC (Near Field Communication)

the mobile can act as an RFID smartcard and interact with a nearby reader for payment

Internet

the most well-known example of a network of networks

physical medium

through which actual communication occurs

ubiquitous computing

which computing is embedded into everyday life, as in the vision of Mark Weiser (1991

email (electronic mail)

which employees generally use for a great deal of daily communication

clients

with which they access remote data, for example, to include in spreadsheets they are constructing.