Network ServicesNetworking for Home & Small Business

Introduction

• Everyday we communicate across the Internet– What kinds of activities?

• What’s in common with all of these?– Servers

• All these interactions use standards & protocols

Client-Server

• Web Page Request– Client has web client software

• Browser- widely used client software

– Server• Host running an application that provides info or

services to a client

Client-Server

Web Site domain names to IP address translation

Remote login to device to control it

Send/Receive email

Assigns IP addresses

Web Site File Transfer

Activity

• Complete 6.1.1.1

Standardized Communication

• Different computers & operating systems across the Internet– Communication not possible if they didn’t

share a protocol

• Phone call China to US– We have connectivity– A Chinese sales person couldn’t be understood

by an English speaking person– That’s why there’s protocols (rules) to follow

Licklider• DoD• Saw the need for

networked computers• 3 bidders w/ different

systems– They couldn’t

communicate with each other

– Came up with the idea of ARPAnet, which later became the Internet

Client Server Interaction

• A web server & client use specific protocols and standards in exchanging info to ensure that the messages are received & understood.

• Application, transport, Internetwork and network access protocols

Client Server Interaction

• Application Protocol• HTTP

– Rules for how browser & web server interact

• You request web page• Another protocol delivers it

Client Server Interaction

• Transport Protocol• TCP

– Manages the conversations/packet exchange– Splits message into segments– Flow control & acknowledgments between the

hosts– Retransmission

Client Server Interaction

• Internetwork Protocol• IP

– Assigns IP addresses– Encapsulate into packets for routing

Client Server Interaction

• Network Access Protocols– Get on the Ethernet cable!!!

• Data Link Management– Takes packets & encaps them into frames– MAC addresses are attached here

• Physical Transmission– How bits go on media (wired, wireless)

Overview

Review

• Which server…– Translates names to IP addresses?– Used for remote login?– Assigns IP addresses?

• Which protocol…– Splits data into segments?– Controls flow of data?– Acknowledges receipt of data?– Requests retransmission if a piece is missing?

End of Day One

Review

• Which protocol adds the IP addresses?

• Which category of protocols encapsulates packets into frames?

• Which protocol is for the rules of how a browser & web server communicate?

Transport Protocols

• IP addresses & routes data for all protocols

• Different applications use different protocols for transport of the data– How data is sent/exchanged

• TCP or UDP

Transmission Control Protocol

• Used when an application requires an acknowledgement– Like a registered letter in the mail

• Breaks messages into small numbered segments– If sender doesn’t get an ACK of message received, it

retransmits – Only portion lost is resent

• On receiving host, TCP reassembles data• FTP & HTTP are examples of protocols using

TCP• Look at 6.1.3.2 Example

User Datagram Protocol

• Used for faster transmissions• “Best effort delivery”

– Standard postal letter• No ACK or retransmission• Used for streaming audio or video, Internet

radio, VoIP

UDP & Internet Radio• If some of the message is lost, it is not

retransmitted. – You might hear a slight break in the sound.

• If TCP were used and the lost packets were resent, the transmission would pause to receive them and the disruption would be more noticeable.

Comparing TCP & UDP

• TCP– Slower– Segments– Acknowledgements– Retransmission– Reassembles– Connection-

oriented

• UDP– Faster– Best effort delivery– No

acknowledgements– No retransmit– Connectionless

Review

Port Numbers & Communication

• When message is delivered, port # assigned

• Used to keep track of conversations and destination services requested

• Each message sent, has a source & destination port number

Port Numbers, Communication & Sockets

• The combo of the source & destination IP AND the source & destination port number is known as a socket. – Used to identify the server and service being

requested by the client. – Thousands of requests per day are tracked by this

Port Numbers

• Destination- tells about service requested– 80- HTTP– 25- SMTP– 53- DNS– 21- FTP– 23- Telnet

• Source Port– Random– Allows multiple conversations

Application Protocols

& Services

Domain Name Service• Server with table of IP & host names• Request sent to port 53 (DNS)

– DNS server looks in table to translate it– If there, it lets client know– If not there, forwards to another DNS server

• If no learn, time out

Lab

• DNS Lab• 6.2.1.3

Review

• What does www.gcit.org represent?– An IP address

• Which server would translate that name to an IP address?– DNS server

• Which server would assign IP addresses?– DHCP server

• Which Application protocol does FTP use?– TCP

Review• Why would an application use UDP?

– No disruption if dropped packets (fast)– Slight interruption, but it keeps going

• Which protocol is used for web sites?– HTTP

• Which port # is…– FTP

• 21– HTTP

• 80

Web Communication• You want www.cisco.com• DNS gets you the IP address of it• Your browser uses that IP & port 80 to request the

web page• Socket connection made with server• Web page comes back to your browser encoded

in HTML

Web Clients & Servers

• HTTP is not secure• Secure HTTP (https:) is port 443

Lab

• Packet Tracer 6.2.2.2

FTP Clients & Servers

• Transfer files from host to host• Built in to OS & browsers• Also GUI based software available

• Client/Server• Uses TCP• Request to server on port 21• Port 20 to send files to client

FTP• Up/downloading of

files, music, web site

Email

• Email server receives & stores emails• You email client allows access to view

messages• user@company.domain • Protocols used in email include SMTP,

POP3, IMAP4

Email Protocols- SMTP

• SMTP (25)– Used to send email from client to server– Email server to email server

Email Protocols- POP3

• POP3 (110)– Used to send client messages & deleted from

storage on the server• Mail on server until collected from client

Email Protocols- IMAP4

• IMAP4 (143)– Like POP3, but it keeps messages on server

until user deleted them

Configuring Email

IM Protocols: Clients & Servers

• Real-time communication• Each IM service may use different

protocols & destination ports– So you must have compatible IM software

Voice Protocols: Clients & Servers

• VoIP• Can call similar clients

– Calls to landlines need public phone network

More About Port Numbers- 6.2.7.2

• 1-65,535• Well-known ports

– 1- 1023– Common applications

• Registered ports– 1024- 49,151– Can be source or destination ports– Used for specific applications like IM

• Private ports– 49,152 & above – For source ports

Port # Review

• 6.2.7.2

Review• Which email service protocol…

– Is used to send mail to server?• SMTP

– Is used to get mail from the server & keep it there until deleted?• IMAP4

– Is used to communicate from email server to email server?• SMTP

– Is used to get mail from the server & delete it?• POP3

Layered Model &

Protocols

Protocol Interaction

• They interact with each other– Protocol Stack

• Some protocols focus on content of message

• Others focus on moving the data

• Protocols visualized in layers

TCP/IP Model

Sending a Message

• Web Server to client (you)– Application data broken into TCP segments

• Each segment has a header w/ source & dest ports

– Segment encapsulates HTTP & HTML data– Encapsulates into a packet w/ IP header

• IP header has source & dest IP addresses

– IP Packet sent to Ethernet protocol• Encapsulates into frame header & trailer• Source & destination MAC AND error checking

– Bits encoded onto the media

Sending

Receiving a Message• Last process in reverse

– Bits received by NIC & decoded• Destination MAC recognized

– Ethernet header & trailer removed• Source & dest MAC removed

– IP header removed• Source & dest IP removed

– TCP header removed• Source & dest ports removed

– Web page data passed to HTTP & browser– TCP segment received, reassembled, & page

displays

Receiving

TCP/IP Model Match

OSI Model

• Primary model for protocol development• Unlike TCP/IP model, this is for all

protocols

Activity• 192.168.5.101

• 80 or TCP or UDP

• 01-5A-FF-65-80-DC

• 1100101101000010

• DHCP or POP3 or HTTP

Activity

• Handout 6.3.3.4• Packet Tracer 6.3.3.5

Review

Network ServicesNetworking for Home & Small Business