1. Introduction to TCP/IP
Chapter 2

2. TCP/IP Structure and Addressing - OSI Model Review
Primary Functions of the OSI Model Layers
The OSI Model Layers Table provides an overview of each OSI model layer’s primary functions.
OSI Model Layer
Unit of Information
Layer Function
Address type
Application
User Functionality
Program
Presentation
Character representation Compression Security
Character and words
Session
Establishing, conducting, and ending sessions
Transmitting messages from sending computer process to receiving computer process
Message
Process to process between applications
Transport

3. Primary Functions of the OSI Model Layers
TCP/IP Structure and Addressing - OSI Model Review
Primary Functions of the OSI Model Layers
OSI Model Layer
Unit of Information
Layer Function
Address type
Network
Transmitting individual packets across a network
Packet
Packet address identifying receiver’s network and host location
Data Link
Transmitting frames containing a packet across a link en route to final destination
Frame
NIC (next node in network)
Physical
Transmitting bits in the form of signals across physical media
Bit

4. OSI Reference Model Review
Allows users to transfer files, send mail, etc.
Only layer that users can communicate with directly
Key features are ease of use and functionality 7
Application
Provides
Services
Standardized data encoding and decoding
Data compression
Data encryption and decryption 6
Presentation
Manages user sessions
Reports upper-layer errors
Supports Remote Procedure Call activities 5
Session
Connects
processes
Connection management (e.g., TCP)
Error and flow control
Connectionless, unreliable (e.g., UDP) 4
Transport
Internetwork packet routing
Minimizes subnet congestion
Resolves differences between subnets 3
Network
Moves
Data
Network access control - MAC address
Packet framing
Error and flow control
The Open Systems Interconnection Reference Model was developed by the International Organization for Standardization and released in 1984.
Layer 1: Realm of Electrical Engineering. Deals with impedance, signals, connectors.
Layer 2: Understands a frame, what gets to talk on the network, generates or checks the CRC/checksum. Delivers frames based on the DLC address.
Layer 3: Connects networks, unreliable delivery based on the network address, routing.
Layer 4: Guaranteed delivery to an application address. TCP is an example. Can also be connectionless (unreliable). UDP is an example.
Layer 5: Session-oriented conversations. RPC is an example.
Layer 6: ASCII to EBCDIC conversion, video compression, security encryption.
Layer 7: Protocol Application — not the user application.
The OSI model is the key to interoperability between diverse types of environments connected by devices purchased from a variety of vendors. It is also the key enabling Sniffer Portable to make sense of the electrical pulses that fly by on a network cable or phone line.
All layers support the layer above it. When troubleshooting, always start from the bottom up. A problem at a lower layer can create a problem at an upper layer. 2
Data Link
Moves bits across a physical medium
Interface between network medium and network devices
Defines electrical and mechanical characteristics of LAN 1
Physical

5. The Physical Layer operates depending on the chosen network topology.
TCP/IP Structure and Addressing - OSI Model Review
The Physical Layer
The Physical Layer only transmits bits to, and receives bits from, the physical medium, and does not “see” the bits as organized into meaningful patterns, such as an address.
The Physical Layer operates depending on the chosen network topology.

6. A physical address is also referred to as a:
TCP/IP Structure and Addressing - OSI Model Review
Physical Addresses
A physical address is also referred to as a:
Hardware address
Adapter address
Network interface card (NIC) address
Medium Access Control (MAC) address
A physical address is required for network devices to ultimately deliver information to a given network node.

7. TCP/IP Structure and Addressing - OSI Model Review
The Data Link Layer
We can categorize physical addresses, for the purposes of networking, into two general types:
A LAN address is commonly found in an Ethernet or Token Ring LAN environment.
WAN addresses in High-Level Data Link Control (HDLC) or frame relay network protocol addressing
Divided into two distinct parts
MAC
The MAC address of the node – interfaces with lower layers
LLC
Tags and identifies protocols - interfaces with upper layers

8. There are two primary types of logical addresses, as follows:
TCP/IP Structure and Addressing - OSI Model Review
Logical Addresses
A logical address is generally implemented as a software entity rather than a hardware entity.
There are two primary types of logical addresses, as follows:
Network addresses, processed at the Network Layer
Port or process addresses, processed at the Transport Layer

9. The Three-Layer Network Hierarchy Diagram illustrates this concept.
TCP/IP Structure and Addressing - OSI Model Review
The Network Layer
Because layer protocols designate both a host and a network, they allow us to build hierarchical networks.
The Three-Layer Network Hierarchy Diagram illustrates this concept.

10. Three-Layer Network Hierarchy
TCP/IP Structure and Addressing - OSI Model Review
The Network Layer
Three-Layer Network Hierarchy

11. TCP/IP Structure and Addressing - OSI Model Review
The Transport Layer
The Well-Known Port Numbers Table lists some of the more commonly used TCP and User Datagram Protocol (UDP) addresses.
Decimal
Protocol-Description 20 21 23 25 53 67 69
161
TCP-FTP Data
TCP-FTP
TCP-TELNET
TCP-SMTP
TCP/UDP-DNS
UDP-BOOTP/DHCP
UDP-TFTP
UDP-SNMP

12. The Transport Layer provides:
TCP/IP Structure and Addressing - OSI Model Review
The Transport Layer
The Transport Layer is responsible not only for application addressing, but also for providing reliable communications over the best effort Layer 3 protocols.
The Transport Layer provides:
Flow control
Windowing
Data sequencing
Recovery

13. TCP/IP Structure and Addressing - OSI Model Review
Layers 5 through 7
The remaining OSI model layers work with the data itself. These layers leave the end-to-end data transport issues to the lower four layers:
The Session Layer
The Presentation Layer
The Application Layer

14. TCP/IP Structure and Addressing - OSI Model Review
The Session Layer
The Session Layer:
establishes, manages, and terminates sessions between applications.
provides its services to the Presentation Layer.
synchronizes dialog between Presentation Layer entities and manages their data exchange.

15. The Presentation Layer:
TCP/IP Structure and Addressing - OSI Model Review
The Presentation Layer
The Presentation Layer:
ensures that information sent by the Application Layer of one system is formatted in a manner in which the destination system’s Application Layer can read it.
can translate between multiple data representation formats, if necessary.

16. The Application Layer:
TCP/IP Structure and Addressing - OSI Model Review
The Application Layer
The Application Layer:
is the layer closest to the user.
provides user application services to application processes outside the OSI model’s scope and does not support the other layers.
identifies and establishes the intended communication partners availability, synchronizes cooperating applications, and establishes agreed procedures for application error recovery and data integrity control.
determines whether sufficient resources exist for the intended communications.

17. Lesson 2.3 – The TCP/IP protocol suite
TCP/IP Structure and Addressing - Internet Protocol Suite
This lesson covers important aspects and protocols of a TCP/IP system.
Lesson 2.3 – The TCP/IP protocol suite
TCP/IP suite pre-dates the OSI model
The TCP/IP model is the defacto model in use on the internet
KEY POINT
Each TCP/IP architecture layer has a specific purpose.

18. TCP/IP Structure and Addressing - Internet Protocol Suite
Overview of the TCP/IP Protocol Suite
The TCP/IP Protocols Diagram shows a detailed picture of the TCP/IP layers.
TCP/IP Protocols

19. The TCP/IP model layers function as follows:
TCP/IP Structure and Addressing - Internet Protocol Suite
Overview of the TCP/IP Protocol Suite
The TCP/IP model layers function as follows:
Network Interface Layer
Internetwork Layer
Transport Layer
Application Layer

20. These low-level protocols define how a host connects to the network.
TCP/IP Structure and Addressing - Internet Protocol Suite
Network Interface Layer Protocols
The Network Interface Layer protocols define rules that determine how a host accesses a LAN.
These low-level protocols define how a host connects to the network.

21. IP, in its current version 4, provides the following functions:
TCP/IP Structure and Addressing - Internet Protocol Suite
Internetwork Layer Protocols
The Internetwork Layer protocols define the basic unit of transfer across a network and provide support for a global addressing scheme and routing.
IP, in its current version 4, provides the following functions:
A global addressing structure
Service type requests
Packet fragmentation
Packet reassembly

22. Other protocols at the Internetwork Layer include:
TCP/IP Structure and Addressing - Internet Protocol Suite
Internetwork Layer Protocols
Other protocols at the Internetwork Layer include:
Address Resolution Protocol (ARP)/ Reverse ARP (RARP)
Internet Control Message Protocol (ICMP)
Internet Group Management Protocol (IGMP)

23. TCP/IP provides applications two different levels of service:
TCP/IP Structure and Addressing - Internet Protocol Suite
Transport Layer Protocols
The Transport Layer’s primary function is to provide communication from one application program to another.
TCP/IP provides applications two different levels of service:
TCP
UDP

24. TCP/IP Structure and Addressing - Internet Protocol Suite
Application Layer Protocols
An application passes data to the Transport Layer protocols, which sequence the data into messages, or byte streams, for transport across the network.
The TCP/IP protocol suite includes the following Application Layer protocols:
Telnet
File Transfer Protocol (FTP)
Simple Mail Transfer Protocol (SMTP)
Simple Network Management Protocol (SNMP)

25. Post Office Protocol 3 (POP3) Hypertext Transfer Protocol (HTTP)
TCP/IP Structure and Addressing - Internet Protocol Suite
Application Layer Protocols
DNS
Post Office Protocol 3 (POP3)
Hypertext Transfer Protocol (HTTP)
Network News Transfer Protocol (NNTP)
UNIX-to-UNIX Copy Program (UUCP) protocol

26. TCP/IP address types Physical 00-00-23-55-46-78 Logical 10.10.1.2 Port
80, 443, 23, etc

27. Multiplexing Using TCP Port Numbers
Multiplexing relies on the use of a concept called a socket. A socket consists of three things:
An IP address
A transport protocol
A port number

28. Overview of TCP/IP Applications - Port Numbers
Jessie receives 3 packets:
A UDP-based ad application
A TCP-based wire-transfer application
A TCP web server application
…Jessie needs to know which application to give the data to, but all three packets are from the same Ethernet and IP address. You might think that Jessie could look at whether the packet contains a UDP or a TCP header, but, as you see in the figure, two applications (wire transfer and web) both are using TCP.

29. OSI Reference Model Review