Introduction to TCP/IP

Chapter 2

The OSI Model Layers Table provides an overview of each OSI model layer’s primary functions.

Primary Functions of the OSI Model Layers

TCP/IP Structure and Addressing - OSI Model Review

OSI Model LayerLayer Function

Unit of Information Address type

Application User Functionality Program

Presentation Character representation Compression Security

Character and words

Session Establishing, conducting, and ending sessions

TransportTransmitting messages from sending computer process to receiving computer process

Message Process to process between applications

Primary Functions of the OSI Model Layers

TCP/IP Structure and Addressing - OSI Model Review

OSI Model LayerLayer Function

Unit of Information Address type

Network Transmitting individual packets across a network

Packet

Data Link

Transmitting bits in the form of signals across physical media

Physical

Transmitting frames containing a packet across a link en route to final destination

Packet address identifying receiver’s network and host location

Frame NIC (next node in network)

Bit

OSI Reference Model ReviewAllows users to transfer files, send mail, etc.Only layer that users can communicate with directlyKey features are ease of use and functionalityStandardized data encoding and decodingData compressionData encryption and decryption

Manages user sessionsReports upper-layer errorsSupports Remote Procedure Call activities

Connection management (e.g., TCP)Error and flow controlConnectionless, unreliable (e.g., UDP)

Internetwork packet routingMinimizes subnet congestionResolves differences between subnetsNetwork access control - MAC addressPacket framingError and flow control

ApplicationApplication77

66 PresentatioPresentationn

55 SessionSession

44 TransporTransportt

33 NetworkNetwork

22 Data LinkData Link

11 PhysicalPhysicalMoves bits across a physical mediumInterface between network medium and network devicesDefines electrical and mechanical characteristics of LAN

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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.

The Physical Layer

TCP/IP Structure and Addressing - OSI Model Review

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.

Physical Addresses

TCP/IP Structure and Addressing - OSI Model Review

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

The Data Link Layer

TCP/IP Structure and Addressing - OSI Model Review

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

Logical Addresses

TCP/IP Structure and Addressing - OSI Model Review

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.

The Network Layer

TCP/IP Structure and Addressing - OSI Model Review

The Network Layer

TCP/IP Structure and Addressing - OSI Model Review

Three-Layer Network Hierarchy

The Well-Known Port Numbers Table lists some of the more commonly used TCP and User Datagram Protocol (UDP) addresses.

The Transport Layer

TCP/IP Structure and Addressing - OSI Model Review

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

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

The Transport Layer

TCP/IP Structure and Addressing - OSI Model Review

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

Layers 5 through 7

TCP/IP Structure and Addressing - OSI Model Review

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.

The Session Layer

TCP/IP Structure and Addressing - OSI Model Review

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.

The Presentation Layer

TCP/IP Structure and Addressing - OSI Model Review

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.

The Application Layer

TCP/IP Structure and Addressing - OSI Model Review

TCP/IP Structure and Addressing - Internet Protocol Suite

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

This lesson covers important aspects and protocols of a TCP/IP system.

KEY POINT

Each TCP/IP architecture layer has a specific purpose.

TCP/IP Structure and Addressing - Internet Protocol Suite

The TCP/IP Protocols Diagram shows a detailed picture of the TCP/IP layers.

Overview of the TCP/IP Protocol Suite

TCP/IP Protocols

TCP/IP Structure and Addressing - Internet Protocol Suite

The TCP/IP model layers function as follows:– Network Interface Layer– Internetwork Layer– Transport Layer– Application Layer

Overview of the TCP/IP Protocol Suite

TCP/IP Structure and Addressing - Internet Protocol Suite

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.

Network Interface Layer Protocols

TCP/IP Structure and Addressing - Internet Protocol Suite

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

Internetwork Layer Protocols

TCP/IP Structure and Addressing - Internet Protocol Suite

Other protocols at the Internetwork Layer include:– Address Resolution Protocol (ARP)/

Reverse ARP (RARP)– Internet Control Message Protocol (ICMP)– Internet Group Management Protocol

(IGMP)

Internetwork Layer Protocols

TCP/IP Structure and Addressing - Internet Protocol Suite

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

Transport Layer Protocols

TCP/IP Structure and Addressing - Internet Protocol Suite

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)

Application Layer Protocols

TCP/IP Structure and Addressing - Internet Protocol Suite

– DNS– Post Office Protocol 3 (POP3)– Hypertext Transfer Protocol (HTTP)– Network News Transfer Protocol (NNTP)– UNIX-to-UNIX Copy Program (UUCP)

protocol

Application Layer Protocols

Physical

•00-00-23-55-46-78

• Logical

• 10.10.1.2

• Port

•80, 443, 23, etc

TCP/IP address types

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

Multiplexing Using TCP Port Numbers

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.

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