CCCNA R&S-02-The TCP-IP and OSI Networking Models

©2015 Amir Jafari – www.amir-Jafari.com
Routing and Switching 200-120
2 - The TCP/IP and OSI Networking Models

The TCP/IP and OSI Networking
Models
Agenda
 Basic Ideas About Computer Networking
 TCP/IP Networking Model
 OSI Networking Model
 Comparing OSI and TCP/IP

TCP/IP Networking Model
Perspectives on Networking
 How you use the Internet from home
 high-speed Internet connection like DSL or cable TV

Perspectives on Networking
 Enterprise Network
 Small Office Home Office (SOHO)

Networking Model
 Also called either a networking architecture or networking blueprint
 Networks require all the devices to follow the rules
 The networking model defines rules about how each part of the network
should work, as well as how the parts should work together
 The networking model refers to a comprehensive set of documents
 Protocol: set of logical rules that devices must follow to communicate
 Like an architectural blueprint for building a house
 Vendors build their products with some networking model

History Leading to TCP/IP
 Systems Network Architecture (SNA) published by IBM in 1974
 Open Systems Interconnection (OSI) networking model
 International Organization for Standardization (ISO)
 To standardize data networking protocols to allow communication between
all computers across the entire planet
 TCP/IP (Transmission Control Protocol/Internet Protocol)
 Department of Defense (DoD)
 Researchers at various universities volunteered to help further develop the
protocols
 OSI has slower formal standardization process as compared with TCP/IP

History Leading to TCP/IP

Overview of the TCP/IP Networking Model
 References a large collection of protocols that allow computers to
communicate
 Requests for Comments (RFC): define a protocol
 Referring to standards or protocols created by other standards body or vendor
consortium
 Layers:
 Help people understand a networking model,
 Each model breaks the functions into a small number of categories

 TCP/IP actually has two alternative models
 The model on the left shows the original TCP/IP model listed in RFC 1122
 The TCP/IP model on the right is a common method used today

TCP/IP Architectural Model and Example
Protocols

TCP/IP Application Layer
 Provide services to the application software running on a computer
 The application layer does not define the application itself
 Provides an interface between software running on a computer and the
network itself

HTTP Overview
 HTTP (Hyper Text Transfer Protocol)
 HTTP defines how web browsers can pull the contents of a web page from a
web server

HTTP Protocol Mechanisms
 Uniform Resource Locators (URL)
 The full version of most web addresses
 begins with the letters “http,” which means that HTTP is used to transfer
the web pages

TCP/IP Transport Layer
 Transport layer protocols provide services to the application layer protocols
that reside one layer higher in the TCP/IP model
 The two most commonly used transport layer protocols :
1. Transmission Control Protocol (TCP)
2. User Datagram Protocol (UDP)

TCP Error Recovery Basics
 TCP/IP needs a mechanism to guarantee delivery of data across a network
 To recover from errors, TCP uses the concept of acknowledgments

Same-Layer and Adjacent-Layer Interactions

TCP/IP Network Layer
 One major protocol: the Internet Protocol (IP)
 Provides several features, most importantly, addressing and routing
 TCP/IP defines two versions of IP: IP Version 4 (IPv4) and IP Version 6 (IPv6).

Internet Protocol and the Postal Service

Internet Protocol Addressing Basics
 TCP/IP host—needs a unique address so that it can be identified in the
network
 Defines how to group addresses together

Internet Protocol Addressing Basics
 This style of number is called a dotted-decimal notation (DDN)
 Routers are networking devices that connect the parts of the TCP/IP network
together for the purpose of routing (forwarding) IP packets to the correct
destination
 Routers make decisions based on the IP address included with the packet
 IP host refers to any device, regardless of size or power, that has an IP
address and connects to any TCP/IP network.

IP Routing Basics
 The TCP/IP network layer, using the IP protocol, provides a service of
forwarding IP packets from one device to another
 The process of forwarding the IP packet is called IP routing.

TCP/IP Link Layer (Data Link Plus Physical)
 defines the protocols and hardware required to deliver data across some
physical network
 Ethernet network, implements link-layer protocols

TCP/IP Link Layer (Data Link Plus Physical)
 The link layer includes all the variations of Ethernet protocols, along with
several other LAN standards
 The link layer includes wide-area network (WAN) standards for different
physical media, such as the Point-to-Point Protocol (PPP) and Frame Relay
 The TCP/IP link layer includes two distinct functions
1. Functions related to the physical transmission of the data
2. Protocols and rules that control the use of the physical media

Comparing the Original and Modern TCP/IP Models

Data Encapsulation Terminology)
 Each layer adds its own header to the data supplied by the higher layer
 Encapsulation: the process of putting headers (and sometimes trailers) around
some data

Names of TCP/IP Messages)

OSI Networking Model
 The first large effort to create a vendor-neutral networking model
 OSI no longer exists as a networking model
 Although some of the original protocols referenced by the OSI model still exist
 The OSI model has many similarities to the TCP/IP model from a basic
conceptual perspective

Comparing OSI and TCP/IP

Describing Protocols by Referencing the OSI Layers
 The comparison of OSI layers to other protocol models is a general
comparison of major goals, and not a comparison of the specific methods
 For Example, both the OSI and TCP/IP network layers define logical
addressing and routing. However, the addresses have a different size, and
the routing logic even works differently.

OSI Layers and Their Functions

OSI Layering Concepts and Benefits
Benefits of layered protocol specifications:
 Less complex
 Standard interfaces
 Easier to learn
 Easier to develop
 Multivendor interoperability
 Modular engineering

OSI Encapsulation Terminology
OSI uses a more generic term: protocol data unit (PDU)

The TCP/IP and OSI Networking
Models
References
1) Cisco Systems, Inc, www.cisco.com/
2) Wendell Odom ,”Cisco CCENT/CCNA ICND1 100-101 Official Cert Guide”,
Cisco Press, USA, 2013

CCCNA R&S-02-The TCP-IP and OSI Networking Models

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CCCNA R&S-02-The TCP-IP and OSI Networking Models

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