Communication Flashcards
What are the requirements of a data communication system?
Sender, Receiver, Transmission Medium, Message and a Protocol
What is meant by a message?
Any type of transmitted data
When can a message only be transmitted?
When there is an agreed protocol
Where can data communications systems be used?
For any network, including an isolated network
What are the different topologies that can be also used for an isolated network?
Point-to-Point Connection Star Network Bus Network Ring Network Mesh Network
What is a computer that is connected to one of these networks called?
End system
What is the cable called that connects end systems?
network link
State what is meant by a bus topology?
One network link
Shared by a number of end systems
Has multi-point connections
No direct connections between any pair of end-systems
State what is meant by a ring topology?
Each end system has a point to point connection to the two adjacent end systems
State what is meant by a mesh topology
Each end system has a point to point connection to each of the other end systems
State what is meant by a star topology
Each end system has a point to point connection to the central device
What did old systems use?
BUS/RING networks that had servers and workstations
How is a star topology structured?
Workstations/servers but it uses a central device - router/switch/hub.
The central device can be used to connect the network to other networks such as the internet.
A specialised application is to use the star topology to function logically as a ring. With the appropriate software installed, each end system can function as though it has 2 directly connected neighbours.
What is meant by HTTP?
Underpins the world wide web - it is an application layer protocol that is used everytime a website is accessed using a browser.
What type of protocol is HTTP?
a transaction-oriented, client-server protocol
What does a transaction involving HTTP look like?
It involves the client sending a request message and the server sending back a response message. The HTTP protocol defines the format of the message.
What does a message request look like in HTTP?
1st line is the request line. It can be followed by header lines. They all use ASCII coding. <> CRLF CR = carriage return LF = line feed The method is normally GET (not POST). Many versions of HTTP as time has evolved
Describe the events of when a browser accesses a web page.
- HTTP transmits a request message
- TCP creates 1 or more packets and sends the first 1 to IP using port 80 for the destination port and a temporary port number for the sending port.
- IP uses the URL in the message to get an IP address using DNS and sends a datagram.
- At the server, IP forwards datagram to TCP
- The server TCP sends an acknowledgement
- When a connection has been established, TCP sends remaining packets, if any, to IP which forwards them through server and TCP to the server application layer.
- HTTP transmits a response message which is transmitted via TCP->IP->IP->TCP->Client browser application
State the different types of email protocols that are responsible for receiving an email
POP3 (pull)
IMAP
HTTP (browser)
State the different types of email protocols that are responsible for sending emails
SMTP (push)
How does an email protocol work?
Email sender sends an email via SMTP.
The mail server has a server and client. It will send the email out over the internet via SMTP.
The receiver has a mail server which has a server. It passes the email onto another server, which is then passed onto the receiver client using POP3
How does an email protocol work?
What is the difference between IMAP and POP3?
IMAP allows for synchronisation between different inboxes. The email is not downloaded onto individual machines
POP3 does allow for emails to be downloaded. POP3 also takes up more storage space.
What is meant by FTP?
It is a protocol that is responsible for transferring files from one computer to another. Attaching a file to an email is FTP
How does FTP handle different operating systems with different file systems?
It has 2 channels. A data channel as well as a communication (control) channel.
What is meant by a protocol?
It is a set of rules for data transmission which are agreed by the sender and receiver.
State what is meant by TCP/IP?
It is a protocol suite for internet usage
TCP/IP contains a number of stacks of layers. List them all
Application Transport Network Data Link Physical
List the layers that are a part of the TCP/IP suite
Application
Transport
Network
What does each layer apart from physical have?
Software installed on them and the router
What does the software on each layer provide?
The capability to receive and transmit data in a full duplex mode to an adjacent layer
What is meant by full duplex data transmission?
Data that travels in both directions at the same time
How are protocols in the upper layers serviced?
By the protocols in the lower level
What is the aim/result of TCP/IP?
That an application on one-end system can behave as though there was a direct connection with an application running on a different end-system.
What are the protocols used on each of the TCP/IP suite layers?
Application - HTTP, SMTP,
POP3, FTP, DNS
Transport - TCP, UDP, SCTP
Network: IP, IGMP, ICMP, ARP
What is TCP not concerned with when sending data packets?
The address of the receiving end
What happens if more than one packet is to be sent?
A sequence number is included on the data packet so that the end user can reassemble the packets
What is meant by TCP being connection oriented?
That it will put reliability over speed by putting into place rules to ensure that packets arrive in the right data
How are the packets sent to ensure there are few difficulties?
Only one packet is sent to the network layer. Once the connection has been established, the TCP sends the other packets and receive response packets containing acknowledgements. This allows missing packets to be identified and resent.
What is the purpose of the network layer?
To ensure correct routing is made over the internet
How does the network layer work?
It uses IP.
It takes the packet received from the transport layer and adds a further header = IP addresses of both the sender and the receiver.
To find the IP address of the receiver, it is likely DNS systems are used to find the correct address matching the URL supplied in the user data.
What is another name for a data packet?
datagram
Where is a datagram sent after it is has been in the network layer?
The data link layer
What happens at the data link layer?
The data link layer assembles data grams into frames.
This is when transmission begins.
What occurs to the IP layer during the data link layer?
Once the IP packet has been sent to this layer, IP plays no further role as IP functions as a connectionless service.
If IP receives a packet which contains an acknowledgement of a previously sent packet, it will simply pass the packet on to TCP with no awareness of content.
State what is meant by the ethernet protocol
Ethernet protocol is responsible for the rules transmitting of packets especially in local area networks. It uses connectionless service.
What is meant by ethernet?
It transmits data in frames. Each frame contains a source address and a destination address. The address is the physical/MAc address which is used to identify a NIC
