Networking: The OSI Layers

What is data on the Data Link Layer referred to as?

A Frame.

What function does a Dynamic Host Configuration Protocol (DHCP) server perform?

A DHCP server assigns IP addresses to systems.

What is a protocol?

A protocol is a rule or set of rules and standards for communication that computers use to send data back and forth.

What is the purpose of the Session Layer?

It manages the connections. It starts the session, manages the traffic, and terminates the session when appropriate. The session layer checks for transmission errors and adds control headers to packets during exchange the exchange of data.

What are 3 protocol suites in use today?

Novell-Internetwork Packet Exchange/Sequenced Packet Exchange(IPX/SPX). Used with the Novell O/S. Apple Talk used in Apple O/S. Transmission Control/Internet Protocol (TCP/IP).

What is a Service Data Unit (SDU)?

Service Data Unit (SDU) a unit of data that has been passed down from an OSI layer to a lower layer and that has not yet been encapsulated into a protocol data unit (PDU) by the lower layer.

What other functions does the Network Layer provide?

The network layer provides the functional and procedural means of transferring variable length data sequences (called a datagram) from one node to another connected to the same network.

What is Routing Information Protocol (RIP)?

a basic routing protocol used by routers in internal networks. RIP is easy to configure, because it does not require any parameters unlike other routing protocols.

What is Simple Mail Transfer Protocol (SMTP)?

a mail protocol for sending messages between servers

What is Address Resolution Protocol (ARP)?

a protocol that resolves an IP address to the Media Access Control (MAC) address. Also known as the physical address.

What is Internet Group Multicast Protocol (IGMP)?

a protocol used for multi-casting traffic. Multicast traffic goes from one computer to multiple computers.

What is Trivial File Transfer Protocol (TFTP)?

an Internet software utility for transferring files that is simpler to use than the File Transfer Protocol (FTP) but less capable. It is used where user authentication and directory visibility are not required.

What is Dynamic Host Configuration Protocol (DHCP) ?

is a protocol used to automatically assign and manage dynamic IP addresses to devices on a network

IEEE 802 divides the Data Link layer into two sub-layers. What are they?

802.3 Media Access Control (MAC) layer - defines how packets are placed onto the physical media at the Physical Layer. 802.3 defines Carrier Sense Multiple Access/Collision Detection (CSMA/CD) 802.2 Logical Link Control (LLC) layer - responsible for identifying Network layer protocols and then encapsulating them. Controls error checking and frame synchronization. Allows multiple protocols to work simultaneously.

What is data on the Network Layer called?

A Packet.

What is a group or combination of protocols called?

A Protocol suite or Protocol stack.

What is Simple Network Management Protocol (SNMP)?

A network management protocol. It is used for collecting information from, and configuring, network devices, such as servers, printers, hubs, switches, and routers on an Internet Protocol (IP) network

What common methods of formatting are used in the Presentation Layer?

American Standard Code for Information Interchange (ASCII) 128 characters Extended Binary Coded Decimal Interchange Code (EBCDIC) 256 characters Audio and Video files :GIF, JPEG, MP3

What other functions is the Presentation Layer responsible for?

Data Encryption and Decryption Data Compression and Decompression

What is a key difference between POP3 server and IMAP 4 server?

POP3 is designed to delete mail on the server as soon as the user has downloaded it. POP3 can be thought of as a "store-and-forward" service. IMAP can be thought of as a remote file server. IMAP provides the user more capabilities for retaining e-mail on the server and for organizing it in folders on the server.

What does Routing Information Protocol (RIP) do?

RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from source to destination. The maximum number of hops allowed for RIP is 15, which limits the size of networks that RIP can support. A hop count of 16 is considered an infinite distance and the route is considered unreachable.

Define Simplex, Half-Duplex and Full Duplex modes of transmission?

Simplex- Data can be sent only one way. Half-Duplex- Data can be sent both ways but only one way at a time. Full Duplex- Data can be sent and received at the same time.

What kind of ports are TCP and UDP ports?

TCP and UDP ports are logical ports. They are simply numbers used to indicate how data is handled when it reaches its destination.

What is Transmission Control Protocol (TCP)?

TCP provides a guaranteed delivery of data. TCP is connection oriented. This means that it establishes a session before transmitting data.

What is the purpose of the Network Layer?

The Network Layer is responsible for routing packets based on its logical address. It translates a logical network address into a physical machine address.

What does the OSI model identify?

The OSI model identifies how data is handled at several different layers. It also identifies the framework of TCP/IP protocols and hardware used on networks.

Who created the OSI model?

The OSI model was created by the International Organization for Standardization (ISO). ( It is derived from the word "Isos" which is Greek for equal.)

What is the purpose of the Data Link Layer?

The data link layer provides node-to-node data transfer—a link between two directly connected nodes. It detects and possibly corrects errors that may occur in the physical layer. It defines the protocols to establish and terminate a connection between two physically connected devices. It also defines the protocol for flow control between them.

How many ports identify details about data on the Transport Layer?

There are 65,535 possible TCP ports and another 65,535 possible UDP ports. In this context a port is a number from 0 to 65,535 utilized by a protocol for connection purposes. It does not represent a physical port.

What is Post Office Protocol (POP3)

a client/server mail protocol in which e-mail is received and held for you by your Internet server

What is the function of the Application Layer?

To manage communications between applications. Applications receive and request data at this layer. This layer interacts with software applications that implement a communicating component. Application-layer functions typically include identifying communication partners, determining resource availability, and synchronizing communication. Everything at this layer is application-specific.

What is User Datagram Protocol (UDP) commonly used for?

UDP is commonly used for media streaming and diagnostic messages.

Important points about the OSI layer

1)Layers only interact with adjoining layers. 2)Functions at each layer are standardized. Different operating systems are able to communicate with each other. 3)Network communications are segmented. Instead of a single protocol that does everything, multiple protocols are used.

What is Hypertext Transfer Protocol (HTTP)?

defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands

What other functions does the Session Layer Provide

ensures data from different applications are kept separate for each application at the application layer. Ensures that resources are available for each session and kept separate from each other. It coordinates the communication, tracks the mode of transmission used by the computer and determines which mode to use. Simplex, 1/2 Duplex, Full-Duplex.

What do network protocols do?

Network Protocols define: all the operations within a network, and also how entities outside the network must interact. How data gets from point A to Point B How computers and devices communicate For example: How a file is printed on a printer How data is transmitted over a telephone line.

What are two protocols that operate on the Session Layer?

Network Basic Input/Output System (NetBios) Remote Procedure Call (RPC)

What functions does Dynamic Host Configuration Protocol (DHCP) perform?

DHCP assigns the Subnet Mask, the address of the default gateway (a router), the address of a DNS server, the domain name and more.

What is a Media Access Control Address (MAC)?

A physical or hardware address stored on the Network Interface Cards (NIC) firmware. A MAC address is represented with 12 Hexadecimal characters for 6 pairs of Hexadecimal characters ( 4 bits per character by 12 characters long or 48 bits)

What is the OSI Model?

A seven layer frame work or set of guidelines for network communication.

What does Internet Protocol Security (IPSec) do?

IPsec can be used in protecting data flows between a pair of hosts (host-to-host), between a pair of security gateways (network-to-network), or between a security gateway and a host (network-to-host). Internet Protocol security (IPsec) uses cryptographic security services to protect communications over Internet Protocol (IP) networks. IPsec supports network-level peer authentication, data origin authentication, data integrity, data confidentiality (encryption), and replay protection.

What is Internet Protocol v4 (IPv4)?

IPv4 is a 32-bit IP addressing protocol. TCP/IP uses IPv4 addressing to get traffic from one computer to another.

What is a Protocol Data unit (PDU)?

In a layered system, a unit of data which is specified in a protocol of a given layer and which consists of protocol-control information and possibly user data of that layer.

What is one of the primary goals of the OSI model?

Operating System independence. The OSI model allows computers running any operating system to communicate with other computers.

What is the purpose of the Presentation Layer?

The presentation layer is responsible for the delivery and formatting of information to the application layer for further processing or display. The presentation layer ensures the information that the application layer of one system sends out is readable by the application layer of another system. Protocols at this layer may translate data into an understandable syntax and then compress or encrypt the data before passing it on to the session layer.

What is the purpose of the Transport Layer?

The transport layer controls the reliability of a given link through flow control, segmentation/desegmentation, and error control. Some protocols are state- and connection-oriented. This means that the transport layer can keep track of the segments and re-transmit those that fail. The transport layer also provides the acknowledgement of the successful data transmission and sends the next data if no errors occurred.

What other functions does the Transport Layer provide?

The transport layer creates packets out of the message received from the application layer. Packetizing is a process of dividing the long message into smaller messages. (Segments) The transport layer manages the ordering of segments so that when packets arrive the can be returned to the same order.

What is a function of the Simple Network Management Protocol?

To detect and report problems before they become significant.

What is User Datagram Protocol (UDP)?

User Datagram Protocol provides a best- effort method of delivering data. It does not provide guaranteed delivery of data. UDP is referred to as connection-less. Data is sent with out verifying a connection with the other system. UDP accepts that there may be some data loss and simply transmits the data.

What is Internet Message Access Protocol (IMAP4)?

a mail protocol used for accessing email on a remote web server from a local client

What is Hypertext Transfer Protocol Secure (HTTPS)?

a protocol for secure communication over a computer network

What is Internet Protocol Security (IPSec)

a protocol suite for secure Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a communication session. IPsec includes protocols for establishing mutual authentication between agents at the beginning of the session and negotiation of cryptographic keys to be used during the session. IPsec protects all application traffic over an IP network. Applications can be automatically secured by IPsec at the IP layer.

What is Reverse Address Resolution Protocol (RARP)?

a protocol that resolves a Media Access Control (MAC) address (Physical address) to an IP address.

What is Internet Control Message Protocol (ICMP)?

a protocol used for error messages and diagnostic reporting. Diagnostic tools such as Ping, PathPing, TraceRt and others use ICMP.

What is File Transfer Protocol (FTP)?

a standard network protocol used to transfer computer files between a client and server on a computer network

What is Internet Protocol v6 (IPv6)?

an addressing protocol using 128-bit addresses. IPv6 addresses are commonly expressed in hexadecimal format.

What is the purpose of Lightweight Directory Access Protocol?

an application protocol used over an IP network to manage and access the distributed directory information service

What is Server Message Block (SMB)?

an application-layer network protocol mainly used for providing shared access to files, printers, and serial ports and miscellaneous communications between nodes on a network. (NOTE: Most usage of SMB involves computers running Microsoft Windows, where it was known as "Microsoft Windows Network" before the subsequent introduction of Active Directory)

What is Open Shortest Path First (OSPF) Protocol?

an interior gateway protocol (IGP) for routing Internet Protocol (IP) packets solely within a single routing domain, such as an autonomous system. It gathers link state information from available routers and constructs a topology map of the network. The topology is presented as a routing table to the Internet Layer which routes datagrams based solely on the destination IP address found in IP packets.

Why are protocol standards important?

to ensure that hardware and software produced by different vendors can work together. The use of standards makes it much easier to develop software and hardware that link different networks because software and hardware can be developed one layer at a time.

What is the purpose of Domain Name System (DNS)?

translates Internet domain and host names to IP addresses. DNS is also used to locate servers running specific services within a Microsoft Network.