Chapter 14 communication and internet technologies
What are the functions of a router?
- a router is a networking device whose software and hardware are tailored to the tasks of routing and forwarding information. - connects to or more networks/different types of network/parts of network - it examines the packet's header attached to the message. Reads ip address of destination - a router has access to a routing table which shows all the hardware addresses of the devices which it has a direct connection with, including available hops, netmask... - uses the info in the table to create routes and decide on the next best hop (best route) and sends the packet on its next hop.
What is the BitTorrent protocol?
- peer to peer file sharing protocol - it is used to distribute data over the internet - to send or receive files one uses a BitTorrent client ( a program that implements BitTorrent protocol) -very fast sharing of files between peers. - the user computers are sharing files directly with eachother rather than using a web server similar to a peer to peer network, the main difference is that the BitTorrent protocol allows many computers to share files.
Why are protocols essential for communication?
- so that both devices have the same rules to follow so there is no confusion on which protocols to use. - they allow different network devices to communicate with eachother
Describe the application layer?
- this layer makes sure that the data is sent in a format that will be understandable by the recipient. This means formatting the data in a standard way for that application. E.g: HTTP, FTP... - The application layer contains all the programs that exchange data, such as web browsers or server software; it sends files to the transport layer. This layer allows applications to access the services used in other layers and also defines the protocols that any app uses to allow the exchange of data.
What is circuit switching?
-the circuit functions as if the nodes were physically connected. Connects the sender and receiver directly in an unbroken path. That lasts throughout communication - circuit switching is a method of implementing communication network in which 2 network nodes establish a dedicated channel (circuit) through the network before the nodes may communicate. - the circuit guarantees full bandwidth of the channel and remains connected for the duration of the communication session
How does the TCP/IP stack work? (Outline the steps for sending data)
1. Application layer, data is formatted to be sent in a for,at that will be understood by the recipient. 2. Transport layer, looks at the data to be sent and splits it into chunks that can fit into packets. It then attaches an order number to each, so that the packets can be reassembled. It then attaches a port number dependant on the application being used. 3. transport layer, checks if data has been sent correctly: checks packet port to identify application, checks packet destination socket, checks packet sequence number to ensure reassembly in right order, recalculate checksum if not the same a resend is requested. 4. Network/internet: attaches the ip address of the sender, attaches ip address of host/receiver. These ip addresses with the port number creates a socket. The network port identifies the application or service running on the computer. The use of ports allows devices to use multiple services. 5. Link: attaches the MAC address of the sender and recipient allowing the packets to be directed to a specific network interface on the ip address host machine. Identifies which hardware device the message came from and which device it's going to. These packets can the be sent across the internet and: Reach their destination(socket from network and transport layer) Find the correct network interface(MAC address from link layer. Find the correct service(port no. From transport layer) Be reassembled in the correct order(order no. From transport) Deliver intended message (data from application layer)
What are the steps of packet switching?
1. Data split into chunks (packets) 2. Each packet has a from address, to address and payload (data chunk) 3. If data requires multiple chunks then the order of each packet is noted 4. Packets sent onto the network, moving from router to router taking different paths (set by the router). Each packet's journey time can therefore differ. 5. Once packets arrive they are re-ordered 6. Message sent from recipient to sender indicating that the message has been received 7. If no confirmation message, sender transmits data again
How does bit torrenting work?
1. Initially to share a file the peer creates a Small file called a torrent the torrent contains metadata 2. The actual file is broken into equal pieces. 3. Other peers who want to download the file must first obtain the torrent and connect to the appropriate tracker. 4. As each peer receives a piece of the file they then become a source for that piece. Other peers connected to the tracker will therefore know where to find it when needed. 5. Once a peer has completed the download they make the file available to other peers in the swarm(group of connected peers) they become a seed. The more seeds in the swarm the faster the file downloading process between peers.
What are the benefits and drawbacks of packet switching?
Benefits: - accuracy: ensures accurate delivery of message - better security as packets are sent along different routes -no need to reserve route - can overcome faulty lines by re-routing packets - high data transmission Drawbacks: -if a packet is lost then it has to be retransmitted - more complex protocols are used (more complex protocols) - does not work well for real-time application - takes time to reassemble the packets at the destination
What are the benefits and drawbacks of circuit switching?
Benefits: - uses designated route for transmission - whole bandwidth available - faster transmission - packets arrive in order - packets can't be lost - real time applications Drawbacks: - nobody else can use reserved route - in case of failure there isn't an alternative route. - time required to establish reserved route. - greater bandwidth required for the reserved route
What are the protocols used in the application layer?
HTTP: this is a protocol responsible for correct transfer of files that make up web pages on the world wide web. HTTP protocols define the format of the messages sent and received. HTTP is a client/server protocol. Used to fetch html documents FTP: The file transfer protocol (FTP) is a network protocol used when transferring files from one computer/device to another via the internet or other networks. It is similar to HTTP and SMTP, but FTP's only task is the application protocol for the transfer of files over a network. SMTP: Simple mail transfer protocol (SMTP) is a text-based (and connection-based) protocol used for sending and uploading emails (push protocol). POP3&IMAP: Post office protocol (POP3/4) and internet message access protocol (IMAP) are protocols used when receiving emails from the mail server. Used by email clients to retrieve email messages (pull protocol). BitTorrent(details on other card)
What is packet switching?
Method of transmission where a message is broken into packets which can be sent along paths independently from each other. -latency or lag is the time taken to send data from one device to the other. - as packet switching doesn't have a set route, any disruption in the network can be circumnavigated by rerouting.
What is the difference between POP3/4 and IMAP
POP3 doesn't keep the server and client synchronised so when emails are downloaded by the client they are then deleted from the server. Whereas IMAP does keep the server and client synchronised. Only a copy of the email is downloaded with the original remaining on the server.
What is the purpose of a packet header and the contents?
Purpose: to store data about packet and it's routing - to ensure it reaches destination - to ensure message can be reconstructed CONTENTS: - ip address of sender and destination - number of packets in msg - order number -source port, destination port
What is the TCP/IP protocol?
The main protocol for routing communication packets through the Internet. When sending data the order is 1to4 when receiving its 4to1. It consists of four layers/steps: The TCP/IP protocol suite only operates at the top three layers, the last layers operate with the Ethernet protocol. 1. Application: encodes the data being sent, defines protocols used and handles access to services. protocols: HTTP, SMTP,FTP,POP3 2. Transport: Splits the data into packets, adds port number information. Protocols: TCP,UDP 3. Network/internet: adds IP addresses stating where the data is from and where it is going. Protocols: IP,ARP 4. Link: adds MAC address information to specify which hardware device the message came from, and which hardware device the message is going to.
What is the transport layer and TCP in this layer
The transport layer regulates the network connections; this is where data is broken up into packets which are then sent to the internet/network layer (IP protocol). The transport layer ensures that packets arrive in sequence, without errors, by swapping acknowledgements and retransmitting packets if they become lost or corrupted. The main protocols associated with the transport layer are transmission control protocol (TCP) TCP is responsible for the safe delivery of a message by creating sufficient packets for transmission. It uses positive acknowledgement with retransmission (PAR) which means it automatically re-sends a data packet if it has not received a positive acknowledgement.
What are protocols?
a set of rules governing communication across a network, the rules are agreed by both sender and receiver.
