chapter 2 communicating over the network -...

Chapter 2 Communicating Over the Network

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Elements of Communication

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Communicating the Messages

  Single communications (e.g. video, e-mail message) could be:   Continuous stream of bits   Take over (hog) the network.   Significant delays   Inefficient use   Any loss - resend entire message

00101010100101010101010101010101010

I have to wait…

Continuous stream of bits

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  Better approach – segmentation.

Multiplexing:   Different conversations can be interleaved.

Segmentation

001010

001010

001010

001010

001010

001010

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Benefits Reliability (3)

  Different paths   Alternate path   Only the missing segments need to be retransmitted

X

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Disadvantage of Segmentation

  Disadvantage – added level of complexity.   Analogy: 100 page letter one page at a time

  Separate envelopes   Sequencing

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Components of the Network

  Devices (hardware)   End devices, switch, router, firewall, hub

  Media (wired, wireless)   Cables, wireless mediums

  Services (software)   Network applications, routing protocols, processes, algorithms

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End devices

  End devices or hosts:   The source or destination of a message.

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  Each host is identified by an address.   IP (Internet Protocol) address (later)

Source Address: 209.67.102.55 Destination Address: 107.16.4.21

209.67.102.55 107.16.4.21

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Servers and Clients

  A host   Client, Server, or both.   Software determines the role.

  Servers provide information and services to clients   e-mail or web pages

  Clients request information from the server.

Server

Client

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Intermediary Devices

  Intermediary devices:   Connectivity to and between networks

  Examples (4):   Network Access Devices (Hubs, switches, and wireless access points)   Internetworking Devices (routers)   Communication Servers and Modems   Security Devices (firewalls)

routers

switch or hub

switch or hub

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Network Media

  Network media: The medium over which the message travels.   Metallic wires - electrical impulses.   Fiber optics – pulses of light   Wireless – electromagnetic waves.

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Network Media

  Different media considerations (4):   Distance it will carry signal   Environment it works in   Bandwidth (speed)   Cost

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Local Area Network (LAN)

  Local Area Network (LAN)   An individual network usually spans a single geographical area, providing

services and applications to people within a common organizational structure, such as a single business, campus or region.

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Wide Area Network (WAN)

  Wide Area Networks (WANs)   Leased connections through a telecommunications service provider

network.   Networks that connect LANs in geographically separated locations

  Telecommunications service provider (TSP) interconnect the LANs at the different locations.   Voice and data on separate networks or converged networks

  T1, DS3, OC3   PPP, HDLC   Frame Relay, ATM   ISDN, POTS

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The Internet – A Network of Networks

  ISPs (Internet Service Providers)   Often also TSPs   Connect their customers to the Internet.

  The Internet – ISPs connected to other ISPs

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Network Representations

  Network Interface Card (NIC)   Ports and interfaces (used interchangeably)

  Physical Port   Interface - Connect to individual networks.

Protocols

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Protocol

  Protocol – Rules that govern communications.   Protocol suite - A group of inter-related protocols - Example: TCP/IP

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Message uses Multiple protocols (encapsulated)

  Message:   Data   Multiple protocols

HTTP Header Data

Frame Header IP Header TCP Header App Header Frame Trailer Data

Protocols

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Multiple protocols (encapsulated)

  Encapsulation – Process of adding a header to the data or any previous set of headers.

  Decapsulation – Process of removing a header.

HTTP Header Data


Protocols

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Example: Protocol – IPv4

Frame Header IP Header TCP Header Frame Trailer Data HTTP Header

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209.67.102.55 107.16.4.21

Frame Header IP Header TCP Header Frame Trailer

Data

209.67.102.55 107.16.4.21

HTTP Header

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Protocols

  Networking protocols suites include rules for: (4)   Format   Accessing the media   Error detection   Setup and termination

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  Early days – proprietary network equipment and protocols.   Now – Industry standards   Institute of Electrical and Electronics Engineers (IEEE)

  Examples: 802.3 (Ethernet), 802.11 (WLAN)   Internet Engineering Task Force (IETF)

  Internet standards   RFCs (Request for Comments)   Example: TCP, IP, HTTP, FTP

Protocol Suites and Standards

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Example: RFC 791 IPv4

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Interaction of Protocols

Hypertext Transfer Protocol (HTTP)   Protocol that governs interaction between web server and a web client.

HTTP Header Data


Protocols

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Transmission Control Protocol (TCP)   Responsible for controlling the information exchanged between the server and

the client:   Size of data   Flow control   Reliability

segment

HTTP Header Data Protocols

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Internetwork Protocol (IP)   Assigns the appropriate source and destination addresses,

  Original source address of host   Final destination address of host   Used by routers in selecting the best path

packet


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Network access protocols (Data link and Physical layer protocols)   Format and physical transmission of data on the media.

frame


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Technology-Independent Protocols

  IP is a protocol that will travel over different types of media.

Frame Header IP Header TCP Header Frame Trailer HTTP Header

  T1, DS3, OC3   PPP, HDLC   Frame Relay, ATM   ISDN, POTS

Ethernet Ethernet

IP Packet IP Packet

data

Using Layered Protocols

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  Using a layered model:   Fosters competition   Prevents changes in one layer from affecting other layers above and

below.   Provides a common language to describe networking functions and

capabilities.

Benefits of a Layered Model HTTP Header Data Protocols

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Protocol and Reference Models

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Protocol and Reference Models

  The Open Systems Interconnection (OSI) model is the most widely known internetwork reference model.

  The International Organization for Standardization (ISO) released the OSI reference model in 1984, was the descriptive scheme they created.

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TCP/IP Model

  TCP/IP Model and Protocol Suite is an open standard.

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The Communication Process - Encapsulation

Server

Data HTTP Header

TCP Header

IP Header

Data Link Header

Data Link Trailer

HTTP Data

  Encapsulation – Process of adding control information as it passes down through the layered model.

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The Communication Process - Decapsulation Data HTTP

Header TCP Header

IP Header

Data Link Header

Data Link Trailer

Client

HTTP Data

  Decapsulation – Process of removing control information as it passes upwards through the layered model.

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Wireshark will let us examine protocols!

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The Communication Process

  Protocol Data Unit (PDU) - The form that a piece of data takes at any layer.   PDUs are named according to the protocols of the TCP/IP suite.

  Data - Application layer PDU   Segment - Transport Layer PDU   Packet - Internetwork Layer PDU   Frame - Network Access Layer PDU   Bits - A PDU used when physically transmitting data over the medium

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  The sending host builds message with multiple encapsulations.

Dest. MAC 00-10

Source MAC 0A-10

Type 800

Trailer

Layer 2 Data Link Frame

Dest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields Data

Layer 3 IP Packet

Dest. MAC 0B-31

Source MAC 00-20

Type 800

Trailer Dest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields Data Dest. Add FF-FF

Source Add Type 800

Trailer Dest. MAC 0B-20

Source MAC 0C-22

Type 800

Trailer

Data HTTP Header

TCP Header

IP Header

Data Link Header

Data Link Trailer

Data HTTP Header

TCP Header

IP Header

Data Link Header

Data Link Trailer

  The receiving host receives the message with multiple decapsulations.

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Getting Data to the Right Application

  Layer 4 (TCP/UDP) contains a port number which represents the application or service carried in the IP packet.   Destination port – destination application   Source port – source application


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Getting Data to the Right Application

  Destination port number tells the OS (TCP/IP) stack which application to hand the data to.

  Examples:   80 = HTTP (www)   23 = Telnet   20, 21 = FTP   25 = SMTP

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