OSI Model

What is a protocol

“In networking, a protocol is a set of rules for formatting and processing data. Network protocols are like a common language for computers. The computers within a network may use vastly different software and hardware; software and hardware; however, the use of protocols enables them to communicate with each other regardless.”

Common Protocols:

• HTTP

• HTTPS

• SMTP

• FTP

• TCP

• UDP

(OSI) Model

(OSI) Model Layers

• Internetworking models are used to organize and describe network functions. Each layer describes a different set of unique functions.

• The Open System Interconnection (OSI) Model is made up of seven layers containing various types of hardware and software.

• Created to achieve interoperability of diverse vendor devices

• Partitions communication systems into abstraction layers

• Protocols are the standard terms that computers use to understand each other

Mnemonics

• All People Seem To Need Data Processing

• Please Do Not Throw Sausage Pizza Away

OSI Model Layers (Example)

(OSI) Model Layers (Example 2)

Encapsulation / De-encapsulation

Layer 7 - Application

• This is the entry door to network services at a lower level

• Apps uses this layer to get services when they TX or RX data over a network

• Applications sit on top of this layer

• Responsible for interfacing user applications, network mgmt. services, remote access etc.

• The playground of hackers today

Layer 7 - Application pt 2.

• Simple Mail Transfer Protocol (SMTP) – 25

• Simple Network Management Protocol (SNMP) - 161

• Hypertext Transfer Protocol (HTTP) – 80

• Line Printer Daemon (LPD)

• File Transfer Protocol (FTP) – 21

• Telnet – 23

• Trivial File Transfer Protocol (TFTP) – 69

• Electronic Data Interchange (EDI)

• Post Office Protocol version 3 (POP3) – 110

• Internet Message Access Protocol (IMAP) –143

• Network News Transport Protocol (NNTP)

• Secure Remote Procedure Call (S-RPC) RPC - Session

• Secure Electronic Transaction (SET)

Layer 6 - Presentation Layer

Concerned about the format

Apps must use a common format

The main services are:

• Data Conversion

• Character Code Translation

• Compression

• Encryption & Decryption

Layer 6 - Presentation Layer pt.2

• American Standard Code For Information Interchange (ASCII)

• Extended Binary-Coded Decimal Interchange Mode (EBCDIC)

• Tagged Image file Format (TIFF)

• Joint Photographic Experts Group (JPEG)

• Motion Picture Experts Group (MPEG)

• Musical Instrument Digital Interface (MIDI)

Layer 5 - Session

Provides Logical persistent

connection between peer

hosts

Conversation between

applications exchanging

information

Creates, monitors, tears down

sessions

Full Duplex, Half Duplex,

Simplex

Layer 5 - Session pt 2.

• Network File System (NFS)

• Structured Query Language (SQL)

• NetBIOS

• Remote Procedure Call (RPC)

Layer 4 - Transport

One of the busiest layers

Creates an End-to-End transport between peer hosts

UDP and TCP are at this layer

UDP is connectionless, best

effort

TCP is connection oriented &

reliable

TCP uses Flags

Layer 4 - Transport p 2.

Transmission Control Protocol

(TCP)•full-duplex connection-oriented

•User Datagram Protocol (UDP) •simplex connectionless

•Secure Sockets Layer (SSL)

•Transport Layer Security (TLS)

•Sequenced Packet Exchange (SPX)

•TCP and UDP Ports

•Well-Known Ports: Ports 0 - 1023

•Registered Ports: Ports 1024 -

49151

•Dynamic or Private Ports: Ports

49152 – 65535

Layer 3 - Network

Move data between two hosts not physically connected

Use logical addresses (IP)

IP is at this layer

Addressing (uses IP addresses)

IP does not guarantee delivery

It only finds the best delivery

route

Uses routing tables to deliver

the info

Devices: Routers

Layer 3 - Network pt 2.

Internet Protocol (IP)

•connectionless

•Internet Control Message Protocol (ICMP)

•Routing Information Protocol (RIP)

•Open Shortest Path First (OSPF)

•Border Gateway Protocol (BGP)

•Internet Group Management Protocol (IGMP)

•Supports multicasting

•Internetwork Packet Exchange (IPX)

•Internet Protocol Security (IPSec)

•Network Address Translation (NAT)

•Simple Key Management for Internet Protocols (SKIP)

Layer 2 - Data Link Layer

Get packets from the Network Layer

Transmit frames

Detects errors within frames

Converts information into bits

Use MAC/Hardware addresses to communicate

Move data to the next physically connected device

Two Sub Layers

• Logical Link Layer (LLC)

• Media Access Control (MAC)

Devices: Switches and bridges

Media Access Control layer

The Media Access Control (MAC) layer is a sublayer of the OSI model's Data Link Layer that manages protocol access to the physical network medium.

It is responsible for the addressing and channel access control mechanisms that enable several nodes to communicate within a network, typically using MAC addresses.

Logical Link Control layer

The Logical Link Control (LLC) layer is the upper sublayer of the OSI model's Data Link Layer that provides flow control and error control.

Layer 2 - Data Link Layer p.2

• Address Resolution Protocol (ARP)

•Resolves IP into MAC

• Reverse Address Resolution Protocol

(RARP)

•Resolves MAC into IP addresses

• Point-to-Point Protocol (PPP)

• Serial Line Internet Protocol (SLIP)

• Layer 2 Forwarding (L2F)

• Layer 2 Tunneling Protocol (L2TP) 

• Point to Point Tunneling Protocol (PPTP)

• Ethernet (IEEE 802.3) – only remaining

• Token Ring (IEEE 802.5)

• Fiber Distributed Data Interface (FDDI)

• Asynchronous Transfer Mode (ATM)

• Copper DDI (CDDI)

Layer 1 - Physical

Receive bits from the Data Link

Layer

Bits converted into electrical

signals

Photons or beam of light if on

Fiber

Physical Topologies

Devices: Cables, Connectors,

wireless access point, hub,

modems etc…

Layer 1 - Physical

EIA/TIA-232 and EIA/TIA-449

• X.21

• (HSSI)

• High-Speed Serial Interface • Networking (SONET)

Synchronous Optical

• V.24 and V.35

• Network (ISDN)

Integrated Services Digital • Digital Subscriber Line (DSL)

• 10BASE-T, 10BASE2, 10BASE5,

100BASE-TX, 100BASE-FX,

100BASE-T, 1000BASE-T,

1000BASE-SX