2 Network Models (BOOK)
Assume communication is between a process running at computer A with port address i, and a process running at computer D with port addres j. Show the contents of the packets and frames at the network, data link, and transport layer for each hop. Computer A A/40 LAN1 8/42 LAN2 C/82 Computer D D/80
42 40 - A D - i j - Data - T2 82 80 - A D - i j - Data - T2
Computer A sends a message to computer D via LAN1, router R1, and LAN2. Show the contents of each of the packets and frames at the network and data link layer for each hop interface. Computer A A/40 LAN1 B/42 LAN2 C/82 Computer D D/80
42 40 - D A - Data - T2 82 80 - A D - Data - T2
Which layer in the Internet model is the user support layer?
Application layer
List the layers of the Internet model.
Application layer, Transport layer, Network Layer, Data Link layer, and Physical layer
Name some services provided by the application layer in the Internet model.
Email, remote file access and transfer, shared database management, and other types of distributed information services.
If the data link layer can detect errors between hops, why do you think we need another checking mechanism at the transport layer?
Errors between the nodes can be detected by the data link layer control, but the error at the node (between input port and output port) of the node cannot be detected by the data link layer.
Suppose a computer sends a frame to another computer on a bus topology LAN. The physical destination address of the frame is corrupted during transmission. What happens to the frame? How can sender be informed about the situation?
Frame is delivered to wrong station or packet is lost when corrupted destination address does not match any station address in network. Error detection mechanism in data link protocols used to find error and discard frame. Source computer is informed by using one of data link control mechanisms such as framing, flow control, access control, and error control.
What are the headers and trailers, and how do they get added and removed?
Headers and trailers are control data. At each layer, headers and trailers can be added. Each layer in sending machine adds its own info to the message it receives from the layer above it & passes the whole package to the layer just below it. At receiving machine, headers or trailers attached to the data unit at corresponding sending layers are removed & actions appropriate to that layer are taken. Provide source & destination addresses, synchronization points and info for error detection.
What are the responsibilities of the network layer in the Internet model?
Source-to-destination delivery of a packet Logical addressing (IP) by headers Routing Internetworking
How are OSI and ISO related to each other?
The ISO is the international standards organization. They are a multinational body dedicated to the world wide agreement on international standards. The ISO standard that covers all aspects of network communications is the OSI or Open Systems Interconnection Model.
What are the concerns of the physical layer in the Internet model?
Carry a bit stream over a physical medium Physical characteristics of interfaces and medium. Representation of bits. Transmission rate. Synchronization of bits. Line configuration (multipoint or point-to-point) Physical topology. Transmission mode (duplex)
Suppose a computer sends a packet at the transport layer to another computer somewhere in the Internet. There is no process with the destination port address running at the destination computer. What will happen?
Most protocols issue a "special error message" that is sent back to the source because the transport layer is responsible for the delivery of a message from one process to another.
What are the responsibilities of the data link layer in the Internet model?
Moving frames from one hop to the next Framing Physical addressing (MAC) Error control Flow control Access control (when 2 devices connected to same link)
Which layers in the Internet model are the network support layers?
Network layer, data link layer, and physical layer
What is a peer-to-peer process?
Peer-to-peer processes are processes on two or more devices communicating directly at the same layer.
What are the responsibilities of the transport layer in the Internet model?
Process-to-process delivery of a message. Service-point addressing (port) Segmentation and reassembly Connection control Error control Flow control
How do the layers of the Internet model correlate to the layers of the OSI model?
The correlation between layers of t he Internet model & OSI model are: The host-to-network layer of Internet model correlate to the combination of physical and data link layer in OSI. The internet layers from both correlate with each other. The transport layers from both correlate with each other. The application layer from the Internet model correlate to the session, presentation, and application layer of the OSI model.
What is the difference between network layer delivery and transport layer delivery?
The network layer ensures source to destination delivery of a packet. Provides inter-networking and routing. Transport layer delivery ensures process-to-process delivery of the entire message (segments). Transport layer provides connection, error, and flow control.
How does information get passed from one layer to the next in the Internet model?
The passing of information from one layer to the next is made possible by an interface between each pair of adjacent layers. Each interface defines the information and services of a layer must provide for the layer above it.
What is the difference between a port address, logical address, and a physical address?
The port address identifies a process on a host. The logical address needed for universal communications that are independent of underlying physical networks. IP address is the most common system that contains a combination of Net ID and Host ID. The physical address is the address of a node defined by its LAN or WAN. Included in the frame used by the data link layer. Physical address uniquely defines a host on the internet. Physical address typically changes from node to node, but logical addresses stay the same.
Suppose a computer sends a packet at the network layer to another computer somewhere in the Internet. The logical destination address of the packet is corrupted. What happens to the packet? How can the source computer be informed of the situation?
When destination address of packet is corrupted, the packet is lost. Packet may also reach incorrect destination. When a packet is sent from the network layer, packet is moved down to the data link layer, which further transfers it to reach the destination. Loss is identified at data link layer. Error control mechanism of data link layer identifies packet loss and informs the source computer.
Match the following to one or more layers of the OSI model: a. Route determination b. Flow control c. Interface to transmission media d. Provide access for the end user
a. Network layer b. Data-link & Transport layer c. Physical layer d. Application layer.
Match the following to one or more layers on the OSI model: a. Communicates directly with user's application program b. Error correction and retransmission c. Mechanical, electrical, and functional interface. d. Responsibility for carrying frames between adjacent nodes
a. Presentation b. Transport, session layer c. Physical d. Data link
Match the following to one or more layers of the OSI model: a. Format and code conversion services b. Establishes, manages, and terminates sessions c. Ensures reliable transmission of data d. Log-in and log-out procedures e. Provides independence from differences in data representation
a. Presentation layer b. Session layer c. Transport layer d. Session layer e. Presentation layer
Match the following to one or more layers of the OSI model: a. Reliable process-to-process message delivery b. Route selection c. Defines frames d. Provides user services such as e-mail and file transfer e. Transmission of bit stream across physical medium
a. Transport b. Network c. Data-link d. Application e. Physical
