Ports, Protocols, & the OSI Model

Which types of transmissions use connectionless protocols?

1. Broadcast 2. Multicast

Physical Layer Devices

1. Cables 2. Hubs 3. Repeaters 4. NIC 5. Connectors Notice that there is very little to no programming involved in these devices. They can mostly just be PHYSICALLY set up and they will work.

Presentation Layer Functions

1. Character code translation -ASCII -EBCDIC Translation methods from binary to character 2. Data conversion -Bit order -CR-CR/LF (Carriage return, carriage return line feed which is understanding where Enter key has happened) -Integer-floating point 4. Data Compression (reduce number of bits transmitted on the network) in essence, compression is translation. It uses various sets of characters that represent other sets of characters 5. Data encryption/decryption (encrypt data for security and passwords) though the opposite of compression due to data being much larger, it is much safer because it scrambles characters and uses way more than required

Which type of network activities are handled by the Presentation layer of the OSI Model?

1. Compression and encryption 2. Character code translation

What is involved in the Physical Layer?

1. Definition of Hardware Specifications 2. Encoding and signaling (transforms bits into electrical signals) 3. Topology and Physical Network Design (LAN/WAN - Mesh/Star) 4. Data Transmission / Bit Rate Control in order not to overwhelm the physical media by trying to send too much

ICMP messages are transmitted as datagrams in what two categories?

1. Error reporting 2. Query messages

Presentation Layer Translation

1. Formats data that will be presented in the Application Layer. 2. Translates data into a common format known to the application layer at the receiving station Example: Two different email applications viewing the same email. You have both applications to use different data formats such as if one is in plaintext and the other is in html. The presentation layer is in charge of making sure that the Application Layer knows what to do with the data it receives.

What does the Internet Protocol (IP) specify?

1. Formats of packets 2. Addressing scheme

Which networking functions occur at the Network layer of the OSI Model?

1. Fragmentation 2. Routing 3. Logical addressing

What type of applications ideal for UDP?

1. Gaming 2. Video communication 3. Voice communication 4. Any data that can a) suffer some data loss without affecting overall quality and b) rely on the applications to be responsible for retransmitting lost packets and arranging received packets)

Which protocols are operated at the Application layer of the OSI Model?

1. HTTP 2. DNS 3. FTP

Which statements about the User Datagram Protocol are correct?

1. It is a connectionless protocol 2. It is faster than TCP

Which Statements about the Transmission Control Protocol are correct?

1. It provides guaranteed delivery of packets 2. It uses acknowledgements

What type of communications favors UDP for primary use?

1. Low-latency 2. Tolerable data loss (in favor of speed)

The Data Link layer of the OSI Model is subdivided into which other layers?

1. MAC 2. LLC

Application Layer Examples

1. Mail services Email applications do not need to be consistent in order to send/recieve messages across different environments (SMTP) 2. File transfer, access, and management (FTAM) Multiple types of FTAM applications can be used to access and modify files remotely as long as it supports the FTP protocol 3. Browsers - provides internet access for all types of networking environments as long as it supports HTTP This is where compatibility and easier implementation comes into effect

Transport Layer Functions

1. Manages end-to-end message delivery (Source to destination 2. Provides error checking and ensures no duplication during data transfer and that messages arrive intact and in the correct order 3. Segmentation of Message: Accepts message from Session layer and passes it to network layer (Splits message into packets) 4. Message acknowlegement and traffic control 5. Session multiplexing (Uses one logical link and tracks which message belong to which sessions when a system is talking to multiple other systems) 6. Service point addressing (Ensures that the correct packets arrive to the correct system and processed by the correct application 7. Flow control (Prevents source device from sending data packets at a faster rate than the destination can handle) 8. Error control (Ensures entire message arrives without error) 9. Connection-oriented transmission (Reliable transport method because receiving device sends an acknowledgement upon successfully receiving a packet 10. Connectionless transmission (Reciever does not acknowledge a receipt of packet and sending device assumes packet arrived successfully which enables faster communication between devices)

Which type of network activities are handled by the Session layer of the OSI Model?

1. Name recognition 2. Logins

Which statement about connectionless protocols are correct?

1. No prior arrangements are made between endpoints before sending data 2. It is less reliable but faster 3. UDP is the preferred transport protocol

Presentation Layer

1. Often referred to as the translation layer 2. Presents data in a uniform format to the Application Layer (masks any difference in data between two different systems)

Data Link Layer Functions

1. Physical addressing 2. Frame traffic control 3. Frame sequencing 4. Frame acknowledgement (Detects and recovers errors occurring at the physical layer) 5. Frame delimiting (identifying start and end) 6. Frame error checking (checksum) 7. Establishing and terminating links 8. Media access management 9. Flow control 10. Error control 11. Access control To implement some form of management to the communications

Which statement about connection-oriented protocols are correct?

1. Preliminary negotiations are used to set up and establish end-to-end communication 2. TCP is the preferred transport protocol

Which objects operate at the Physical layer of the OSI model?

1. Repeaters 2. Hubs 3. Cables

Session Layer Functions

1. Responsible for communication between two devices (Beginning, maintenance, and end) 2. Regulates flow of data between two devices 3. Session protocol (Defines parameters for connections) 4. Manages the transfer of data (who can transfer and how long, a connection should never be left open once completed, it should be terminated) 5. Session establishment, maintenance, termination 6. Session support (Security, name recognition, Login) 7. Dialog control (determines which device communicates first and how much data will be sent) 8. Dialog separation (adds checkpoints or markers within a message to clarify end and beginning in order to also know where it might need to be resumed from in case of an interruption) 9. Protocols: NetBIOS, Named pipes, RPC

Data Link Layer

1. Responsible for node-to-node data delivery 2. Recieves data from network layer and passes it on to physical layer 3. In the process it creates frames and adds physical addresses (MAC)

Application Layer

1. Serves as the window for users and application processes accessing network services (interface between program and protocol stack

Types of Dialog Control

1. Simplex 2. Half duplex 3. Full duplex

Network Layer Functions

1. Subnet control (Prevents overloading, allows buffering) 2. Subnet usage accounting (keeps track of frames) 3. Address mapping (translates logical addresses into physical addresses) 4. Internetworking (Providing logical connections between different networks and combining various networks to form a larger network) 5. Logical Addressing (Combines large number of networks and defines addressing scheme to uniquely identify each device on internetwork) 6. Packetizing (Creates packets upon recieving data from upper layers. Packets are created by way of encapsulation. Internet Protocol (IP) defines packet format) 7. Fragmentation (Dividing larger packets into smaller fragments and can then be easily sent out on a physical medium)

Which TCP/IP diagnostic utilities make use of ICMP?

1. Traceroute 2. Ping

What are some main ports that favor UDP as the transport protocol?

1. Trivial File Transfer Protocol (TFTP) 2. Real Time Streaming Protocol (RTSP) 3. Simple Network Protocol (SNP) 4. Domain Name System (DNS) lookups

What are three basic types of transmission?

1. Unicast 2. Broadcast 3. Multicast

The successor of IPv4, IPv6 has how many bits in the address?

128 bits

How many bits are in an IPv4 address?

32 bits (4 bytes)

Match the Protocols to their appropriate ports A - 25 B - 80 C - 69 D - 53 E - 3389 F - 443

A - Simple Mail Transfer Protocol (SMTP) B - Hypertext Transfer Protocol (HTTP) C - Trivial File Transfer Protocol (TFTP) D - Domain Name System (DNS) E - Remote Desktop Protocol (RDP) F - Hypertext Transfer Protocol Secure (HTTPS)

What is the OSI Model?

A 7 layer architectural approach to dividing up tasks so that each layer is responsible for only a subcomponent of the overall communication process. This also allows for consistency when developing new applications, protocols, or devices.

What is a MAC address?

A Media Access Control address is the physical address of a device, the first instance of any kind of address--defining who is the sender and who is the receiver.

Application Layer Functions

Allows users to interact with applications -Application accepts user input and passes data down to lower layers -Allows for easier application compatibility and implementation -Applications do not have to be re-written for different types of network environments User > Application Layer > Data to Presentation > etc Lower Level > Presentation > Application layer > User

ASCII

American Standard Code for Information Interchange

Routing

Moving packets from network to network. This happens entirely in the Network layer and requires logical addresses to implement routing

IP resides at which layer of the OSI Model?

Network

Port 123

Network Time protocol

Which network communication characteristic is determined at the Transport layer of the OSI Model?

Connection oriented vs connectionless communication

The OSI Model was designed to facilitate which objective?

Consistency and compatibility when developing new network applications, protocols, and devices

Port 22

Secure Shell (SSH) (commonly used in Linux and UNIX communication)

Error-free Transfer

Data Link Layer handles error-free transfer which allows other layers can assume error-free transmission over medium.

Port 443

Secured implementation of Hypertext Transfer Protocol (HTTPS) (often used in online banking or credic card transactions)

Port 53

Domain Name System (DNS)

Port 67/68

Dynamic Host Configuration Protocol (DHCP) used to assign IP addresses

EBCDIC

Extended Binary Coded Decimal Interchange Code

Port 20/21

File Transfer Protocol (FTP)

Port 445

Server Message Block (SMB)

Full Duplex

Full duplex is bi-directional two at time ex: Phone call Fastest network communication

Port 80

Hypertext Transfer Protocol (HTTP)

Port 443

Hypertext Transfer Protocol Secure (HTTPS)

Examples of Connectionless Protocols

IP UDP ICMP IPX

Why is IP used in conjunction with TCP?

IP is a connectionless protocol and packets are treated as an independent unit of data. These packets are assembled in the correct order using TCP. It is normal for packets to take different paths across the internet and arrive at various times which is why TCP is critical in assembling these packets correctly when required.

What is a Frame?

Identifies the beginning and the end of any given transmission.

Port 143

Interactive Mail Access Protocol (IMAP)

Port 389

Lightweight Directory Access Protocol (LDAP) Used for querying directory services for things like usernames or computers

Port 636

Lightweight Directory Access Protocol over SSL (LDAPS)

LLC

Logical Link Control sublayer is the interface between media access methods and network layer protocols. It determines if communication will connectionless or connection-oriented 1. Certain rules defined for connection-oriented communicaation is implemented by LLC 2. It is more concerned with the formal and control mechanisms

MAC sublayer

Media Access Control 1. Responsible for connection to physical media 2. MAC Address (A 12 digit hexadecimal number unique to every computer and every device)

Multicast

Message is sent to multiple hosts which may belong to a specific multicast group.

Simplex

One-way communication one at a time ex: Radios, walkie-talkies (You can either only receive, or only send)

OSI meaning

Open Systems Interconnect

Port 110

Post Office Protocol (POP)

Purpose of Data Link sublayers

Provides interface between the media access methods down in the Physical layer and the Network Layer protocols in Layer 3

Port 3389

Remote Desktop Protocol (RDP)

Port 3389

Remote Desktop Protocol (RDP) (when you want to initiate a remote session to another system and take over its desktop)

Network Layer

Responsible for 1. Packet addressing 2. Converting addresses (logical to physical) 3. Source-to-destination delivery 4. Routing

Physical Layer

Responsible for transmission of digital data bits from the source device to the destination device over the physical network communications media

Port 5060/5061

Session Initiation Protocol (SIP)

Port 25

Simple Mail Transfer Protocol (SMTP)

Port 161

Simple Network Management Protocol (SNMP)

Broadacst

Single message is sent to ALL hosts on a network simultaneously.

What state is a connectionless communication referred as due to there being no ngeotiation, no set up, and no rules?

Stateless Communication

Port 23

Telnet (used for configuring network devices)

Checksum

The Data Link Layer implements a checksum which is a mathematical calculation applied that says if you have this value and that value, it should add up this value. If that other value is added and the outcome value is not obtained, you can assume a value was missed and must be retransmitted.

Logical Addresses

The logical address, the IP address can be changed at anytime and reside entirely in the Network layer. An IP address in one network can be the same as an IP address in another network only because they are in SEPARATED in different networks.

Application Layer Protocols

These protocols provide the following network services: FTP DHCP DNS SMTP HTTP POP3 NFS Example: A Browser application is directly dependent on the HTTP protocol to request the website that the server hosts

Data Link Layer Identification

This layer is where we start to see the specific identification of a sender and a reciever which the physical layer is unaware of.

What are ports used for?

To identify the specific type of service being requested from a system

Purpose of Bit Rate Control

To not overwhelm the physical media by sending too much at once.

Port 69

Trivial File Transfer Protocol (TFTP)

Half Duplex

Two-way or bi-directional communication but still one at a time