Data Comm and Networking Chapter 1 & 2
Assume a system uses five protocol layers. If the application program creates a message of 100 bytes and each layer (including the fifth and the first) adds a header of 10 bytes to the data unit, what is the efficiency (the ratio of application layer bytes to the number of bytes transmitted) of the system?
The system transmits 150 bytes for a 100-byte message. The efficiency is 100/150 or 66.66%
When a resident uses a dial-up or DLS service to connect to the internet, what is the role of the telephone company?
The telephone company acts as ISP. The connection from the resident to the telephone company is a point to point access WAN that connects the premises to the internet. At the same time, the telephone company needs to provide necessary services such as email.
You have two computers connected by an Ethernet hub at home. Is this a LAN, a MAN, or a WAN. Explain your reason.
This is a LAN. The Ethernet hub cable creates a LAN.
What is the first principle for protocol layering that needs to be followed to make the communication bidirectional?
To develop bidirectional communication each and every layer requires to be able to give two opposite task one in each and every direction.
A host communications with another host using the TCP/IP protocol suite. What is the unit of data sent or received at each of the following layers?
1) Application layer: Messages 2) Network layer: Datagrams or Packets 3) Data-link layer: Frames
A color image uses 16 bits to represent a pixel. What is the maximum numbers of different colors that can be represented?
16 bits. We can represent it by 2^16 different colors.
What is the maximum number of character or symbols that can be represented by Unicode?
32 bits . Therefore 2^32 different characters or symbols.
If a port number is 16 bits, what is the maximum header size at the transport layer of the TCP/IP protocol suite?
8
Assume that the number of hosts connected to the Internet at year 2010 is five hundred million. If the number of hosts increases only 20 percent per year, what is the number of hosts in year 2020?
A = P(1+r/100)n= 500M(1+20/100)10= 500M(1.2)10= 500M(6.19) = 3100M = 3.1B
Which of the following data unit is encapsulated in a frame?
A User Datagram, a Datagram and a Segment
What is an internet? What is the Internet?
An internet is an interconnection of networks. The Internet is the name given to the specifically world wide network.
What are the types of addresses(identifies) used in each of the following layers?
Application: the destination computer name and the name of the file we need to access. An example is [email protected]. the network layer, we use two logical addresses (source and destination) to define the source and destination computers. These addresses are unique universally. At the data-link layer, we use two link-layer addresses (source and destination) to define the source and destination connections to the link
Internet and telephone network. Similarities and Differences
Both are made of interconnections of small networks. Telephone network is mostly circuit switched and the internet is mostly packet switched.
When we use local telephones to talk to a friend, are we using a circuit- switched or packet switched network?
Circuit switched network.
Match the following to one or more layers of the TCP/IP protocol suite:
Creating user datagrams - Transport, and Network b. Responsibility for handling frames between adjacent nodes - Datalink c. Transforming bits to electromagnetic signals - Physical layer
Which layer of the TCP/IP are involved in a link layer switch?
Data link and physical.
Assume we want to connect two isolated hosts together to let each host communicate with the other. Do we need a link-layer switch between the two? Explain
Do not need a link-layer switch because the communication in this case is automatically one-to-one. A link-layer switch is needed when we need to change a one-to-many communication to a one-to-one.
List some application protocols mentioned in this chapter
Hypertext transfer Protocol (HTTP) SimpleMail TransFer Protocol (SMTP) File TransFer Protocol (FTP) Terminal Network (TELNET) Domain Name System (DNS)
IETF and IRTF
IETF identify operational problems and proposing solutions and managed by the internet engineering steering group. IRTF focuses on long term research topics related to internet protocols, apps, architecture and tech and is managed by internet research steering group.
What is the difference between half duplex and full duplex transmission?
In half only one can send at a time and in full both can send at the same time.
What are the advantages of a multipoint over a point to point connection?
Installation and low cost.
Categorize the four basic topologies in terms of line configuration
Mesh, Star and Ring- Point to point Bus: Multi point
For each network topology discuss the consequences if a connection fails. Five devices arranged in each.
Mesh: If one fails others will still work. Star: The other devices will still be able to send data to the hub although there will be no access to the device which has failed. Bus: All stops. Ring: May disable the whole network unless it is a dual ring.
For n devices in a network, what is the number of cable links required for each topology?
Mesh: n(n-1)/2 Star: n Ring: n-1 Bus: one back bone and n drop lines
Name the four basic topologies and cite an advantage of each
Mesh: secure Bus: easy installation Star: Robust Ring: Easy fault isolation
Which of the following data unit is decapsulated from a user data gram?
Message
In the TCP/IP protocol suite, what are the identical objects at the sender and receiver sites when we think about the logical connection at the application layer?
Messages are the identical objects at the sender and the receiver sites when we think about the logical connection at the application layer.
What are the two types of line configuration?
Multi point and point to point.
In an internet, we change the LAN technology to a new one. Which layers in the TCP/IP protocol suite need to be changed?
Network....
Assume that a private internet requires that the messages at the application layer be encrypted and decrypted for security purposes. If we need to add some information about the encryption/decryption process (such as the algorithms used in the process), does it mean that we are adding one layer to the TCP/IP protocol suite? Redraw the TCP/IP layers if you think so
No it does not mean that we are adding another layer to the protocol suite, it just means that the transport layer has taken another function and now contains the encryption/decryption process. This process could be contained and handled within the transport layer to be able to encrypt and decrypt data
What are the three criteria necessary for an effective and efficient network?
Performance Reliability Security
A router connects 3 links(network). How many of each of following layers can the router be involved with?
Physical: 3 Data link layer: 3 Network: 1
Why are protocols needed?
Protocol defines what is communicated, in what way and when. This provides accurate and timely transfer of information between different devices on a network.
What is the difference between required RFC and recommended RFC?
Required RFC must be implemented by all internet systems to achieve minimum conformance. Recommended RFC is not required but is recommended because of usefulness.
What are the advantages of distributed processing?
Security, access to distributed databases, collanorative processing and faster problem solving
Identify the 5 components of a data communication system.
Sender Receiver Message Tranmission medium Protocol
What are some of the factors that determine whether a communication system is a LAN or WAN?
Size, distance, structure, ownership.
Why are standards needed?
Standards are needed to create and maintain an open and competitive market for manufacturers, to coordinate protocol rules, and thus guarantee compatibility of data communication technologies.
Performance is inversely related to delay. When you use the Internet, which of the delay following application are more sensitive to delay?
Surfing the internet.
Assume that an application-layer protocol is written to use the services of UDP. Can the application-layer protocol use the services of TCP without change?
That depends. SInce UDP is not handshaked, it can be used for things like video streaming across long distances where low jitter is more important than retry-till-success. Using TCP in such as case would not work well.
Assume we have created a packet-switched internet. Using the TCP/IP protocol suite, we need to transfer a huge file. What are the advantage and disadvantage of sending large packets?
The advantage is that the packet is routed along the fastest available route by routers that read the destination address and forwards each IP packet independently. The disadvantage is that larger packets take longer to transmit as they contain more data
When we say that the transport layer multiplexes and demultiplexes application layer messages, do we mean that a transport-layer protocol can combine several messages from the application layer in one packet? Explain.
The answer is no. Multiplexing/demultiplexing at the transport layer does not mean combining several upper-layer packets (from the same or different applications) into one transport-layer packet. It only means that each of the transport-layer protocols (such as TCP or UDP) can carry a packet from any application-layer protocol that needs its service. However, a transport-layer packet can carry one, and only one, packet from an application-layer protocol. For example, UDP can carry a message from FTP in one user datagram and a message from HTTP in another user datagram
When a party makes a local telephone call to another party, is this a point to point or multipoint connection.
The communication is only between caller and callee, therefore a dedicated line is established between them. It is point to point.
Which of the following data units has an application layer message plus the header from layer 4?
User datagram
If there is a single path between the source host and the destination host, do we need a router between the two hosts?
We do not need a router in this case because a router is needed when there is more than one path between the two hosts; the router is responsible for choosing the best path at each moment.
Assume six devices are arranged in a mesh topology. How many cables are needed? How many ports are needed for each device?
a. Cable links: n(n-1)/2 = (6*5)/2=15. b. Number of ports: (n-1)=5 ports needed.
Match the following to one or more layers of the TCP/IP protocol suite
a. Route determination - data-link, network, b. Connection to transmission data - network, physical, c. Providing services for the end user - Physical
How many point to point WANs are needed to connect n LANs if each LAN should be able to directly commnuicate with any other LAN?
n-1. Which means that we will have n times n minus 1 connections. However, if each connection can be used in both direction we need only n times n minus 1 divided by 2.
