Kapitel 4 Flashcards
Explain the concepts of TCP/IP and UDP and what the differences are
TCP/IP-protocol suite – a collection of protocol standards used by the internet to implement the four-level communication hierarchy. TCP (Transmission control protocol) defines a version of the transport layer.
UDP – User datagram protocol, another option to TCP to use when sending a package. There are differences between TCP and UDP protocols. UDP is a connectionless protocol and an unreliable protocol since it does not check to see that all segments of a message are successfully transferred.
UDP vs TCP – before sending a message as requested by the app.layer, a transport layer based on TCP sends its own message to the transport layer at the destination telling it that a message is about to be sent. It then waits for this message to be acknowledged before starting to send the application layers message. In this manner a tcp transport layer is said to establish a connection before sending amessage. A message based on UDP does not establish such a connection prior to sending a message. It merely sends the message to the address it was given and forgets about it. For this reason UDP is called a 1. connectionless protocol. TCP transport layers at the origin and destination work together by means of acknowledgements and packet retransmissions to assure that all segments of a message are successfully transferred to the destination. For this reason TCP is called a 2. reliable protocol, whereas UDP does not offer such retransmission services and is therefore said to be an unreliable protocol.TCP provides for both 3. flow control, meaning that a TCP transport layer at a messages origin can reduce the rate at which it transmits segments to keep from overwhelming its counterpart at the destination, as well as 4. congestion control, meaning that a TCP transport layer at a messages origin can adjust it’s transmission rate to alleviate congestion between it and the message’s destination. A transport layer based on UDP is 5. more streamlined than a layer based on TCP, and thus if an application is prepared to handle the potential consequences of UDP, that option might be a better choice. UDP’s efficiency makes it the protocol of choice for DNS lookups and VoIP.
Explain the concepts of Internet, Router and Gateway
Internet – a network of networks
Router – special purpose computers used for forwarding messages. These provide links between netowrks while allowing each network to maintain its uniwue internal characteristics. A router maintans a forwarding table that contains the routers knowledge about the direction in which messages should be sent depending on their destination addresses.
Gateway – th epoint at which one network is linked to an internet. It serves as a passageway between the network and the outside world.
Explain the concept of HTTPS, SSL, public key encryption Certificate authorities, certificates and authentication.
HTTPS – The backbone of HTTPS is the protocol system known as SSL (Secure Sockets Layer).
Public key encryption – Encryption systems are designed so that having knowledge about how messages are encrypted does not allow one to decrypt messages. A public key encryption system involves the use of two values called keys. One key knows as public and one as private. Both are needed to decrypt the messages. TO use the system the public key is first distributed to those who might need to send messages to a particular destination. The private key is held in confidence at this destination. Then, the originator of a message can encrypt the message using the public key and send the message to its destination with assurance that its contents are safe, even if it is handled by intermediaries who also know the public key.
Certificate authorities – exist to maintain accurate lists of parties and their public keys so that impostors cant claim to keep a specific key.
Certificate – a certificate is a package containing a partys name and that partys public key.
Authentication – Making sure that the author of a message is in fact the party it claims to be. The critical point here is that, in some public-key encryption systems the roles of the encryption and decryption keys can be reversed. That is, text can be encrypted with the private key, and because only one party has access to that key any text that is so encrypted must have originated from that party. In this manner, the holder of the private key can produce a bit pattern called a digital signature that only the party knows how to produce.
Explain the hidden terminal problem
Hidden terminal problem – In wireless star networks a machine may be unable to detect that its transmissions are colliding with those of another. For example, the machine may not hear the other because its own signal drowns out that of the other machine. Another cause might be that the signals from the different machines are blocked from each other by objects or distance even though they all can communicate with the central AP. A way to solve this in a star-wifi config is that some wifi networks require that each machine send a short “request” message to the AP and wait until the AP acknowledges that request before transmitting an entire message. If the AP is busy because it is dealing with a hidden terminal it will ignore the request and the requesting machine will know to wait.
Explain the concepts of Bus and Star
if the case of a bus, machines are all connected to a common communication line which is called a bus. In the case of a star one machine servers as a central focal point to which all the others are connected. The star config is popular in wireless networks where communication is conducted by means of radio broadcast and the central machine, called access point (AP) servers as a focal point around which all communication is coordinated.
Explain the four layers of internet software
The four layers of internet software – Communication over the internet involves the interaction of four layers of software. Application layer, transport layer, network layer and link layer. A message originates in the application layer. From there it is passed wodn through the transport and network alyers as it is prepared for transmission, and finally it is transmitted by the link layer. The message is received by the link layer at the destination and passed back up the hierarchy until it is delivered to the application layer at the message’s destination.
Application layer – Consists of those software units such as clients and servers that use the internet communication to carry out their tasks. The application layer uses the transport layer to send and receive messages over the internet in much the same way that you would use a shipping company to send and receive packages. The application layers responsibility to provde an address that is compatible with the internet infrastructure.
Transport layer – An important task of the transport layer is to accept messages from the application layer and to ensure that the messages are properly formatted for transmission over the internet. The transport layer divides long messages into small segments, which are transmitted over the internet as individual units. This division is necessary because a single long message can obstruct the flow of other messages at the internet routers where numerous messages cross paths. Indeed, small segments of messages can interweave at these points, whereas long message forces others to wait while it passes (much like cars waiting for a long train to pass at a railroad crossing) The segments (packets) reveives sequence-numbers so that they can be reassembled at the destination.
Network layer and link layer – The network layer devices in which direction a packet should be sent. The combination of the network layer and the link layer below it constitutes the software residing on the internet routers. The network layer is in charge of maintaining the routers forwarding table and using that table to determine the direction in which to forward packets. The link layer at the router is in charge of receiving and transmitting the packets.
Explain the different variants of computer networks that exist
Either a PAN (personal area network), LAN (local area network), a MAN (Metropolitan area network) or a WAN (wide area network). PAN – Short range, wireless mouse and PC. LAN – a collections of computers in a single building. MAN – a network spanning a local community. WAN – links machines over a greater distance – perhaps in neighboring cities or on opposite sides of the world.
What does the following acronyms stand for: ICANN TLD DNS HTTP SMTP MIME POP3 IMAP VoIP HTML XML
ICANN – Internet corporation for assigned names and numbers
TLD – Top-level domains .com, .gov .net, etc.
Country-code TLD - .se, .us etc.
DNS – Domain name server (system?)
HTTP – Hyper Text Transfer Protocol, a protocol used to transfer hypertext documents between browsers and webservers.
SMTP – Simple Mail Transfer Protocol
MIME – multipurpose internet mail extensions
POP3 – Post office protocol version 3
IMAP – Internet Mail access protocol
VoIP – Voice over Internet Protocol.
HTML – Hypertext markup language
XML – eXtensible Markup Language, a standardized style for designing notational systems for representing data as text files.
Explain the two protocols CSMA/CD and CSMA/CA and when they are used.
CSMA/CD – Carrier sense, Multiple access with collision detection, a protocol controlling a bus network with the ethernet standards. This protocol dictates each message be broadcast to all the machines of the bus. Not compatible with wireless star networks in which all machines communicate through a central AP.
CSMA/CA – Carrier Sense, Multiple Access with collision avoidance – Instead of detecting collisions this protocol rather just avoids them. When collisions do occur, messages bust be retransmitted. This protocol is used within wifis (Star networks)
Explain the two Interprocess communications P2P and Client/server
Interprocess communication (cient/server and p2p) – The communication that takes place between processes executing on different computers within a network. A popular convention used for this is the client/server model. A client makes requests of other processes and a server satisfies these requests. Other means of interprocess communications is the peer-to-peer model. This model involves processes that provide service to and receive service from each other. The collections of peers participating in distributions of files is sometimes called a swarm.
What is a CDN, and how does it work?
CDN – content delivery networks, used by streaming-sites, groups of servers distributed strategically around the internet that specialize in syreaming copies of content to nearby end users in their network “neighborhood”. A networking technology called anycast enables an end user to automatically connect to the closest server out of a defined group of servers.
What is an ISP and what types of ISP’s are there?
ISP – Internet service provider, organizations that construct and maintains networks that are connected to the internet. Tier-1 ISPs highspeed-wans. Backbone of the internet. Tier-2 ISPs tend to be more reginal in scope and less potent in their capabilities. Tier-3 ISP is what grants access to tier 2ISPs. An access ISP is essentially an independent internet, sometimes called an intranet, operated by a signle authority. Cable and telephone companies. End system/hosts are the devices that individual users use to connect to the ISPs.
Explain Multicast and unicast
Unicast and multicast – Unicast refers to one senced sending messages to one reveicer, multicast refers to a server transmitting a message to multiple clients by means of a single address and relies on the routers in the Internet to recognize the significance of that address and to produce and forward copies of the message to the appropriate destinations. This has not yet been implemented to the global internet since the routers are required to expand its functionality beyond their original duties.
