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Introduction to TCP/IP
Chapter 2
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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
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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
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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
Pro
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Serv
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Moves
Data
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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
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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
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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
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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
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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
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The Network Layer
TCP/IP Structure and Addressing - OSI Model Review
Three-Layer Network Hierarchy
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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
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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
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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
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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
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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
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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
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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Physical
•00-00-23-55-46-78
• Logical
• 10.10.1.2
• Port
•80, 443, 23, etc
TCP/IP address types
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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
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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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OSI Reference Model Review