Transcript Chapter 6 2007

Network Services
Networking for Home & Small Business
Client-Server
• Server
– Host running an application that provides info
or services to a client
• Web Server
• Email Server
• File Server
• Browser- widely used client software
Client-Server
Web Site
Remote login
Send/Receive
Assigns IPWeb Site
domain namesto device to
email
addresses
to IP address control it
translation
File Transfer
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
Roles of Protocols in
Communication
• A web server & client use specific protocols and
standards in exchanging info to ensure that the
messages are received & understood.
• HTTP
– An Application protocol
– Rules of how a web server/client interact
– Relies on other protocols to deliver the messages
• TCP
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Transmission Control Protocol
A Transport protocol
Manages the individual conversations
Formats messages
Acknowledgements, retransmissions
Roles of Protocols in
Communication
• IP
– Internet protocol
– Assigns addresses, encapsulates message
into packets
Roles of Protocols in
Communication
• Network Access Protocols
– Data Link Management
– Takes packets from IP and formats them into
frames for your network
– Assigns the MAC address so it can be sent
over the network
• Physical Network Transmission
– How the bits go on media
• Electricity, light, radio…ones & zeros
TCP & UDP
• Transport Protocols
• The IP protocol uses these transport
protocols to enable hosts to communicate
and transfer data.
Transmission Control Protocol
• Used when an application requires an
acknowledgement
– Like a registered letter in the mail
• Breaks messages into small numbered
segments & ready to become packets
• 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
• 6.1.3.2 Example
User Datagram Protocol
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Used for faster transmissions
“Best effort delivery”
No ACK
No retransmission
– Standard postal letter
• 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.
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
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
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
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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
• [email protected]
• 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 Numbers6.2.7.2
• 1-65,535
• Well-known ports
– 1- 1023
– Common applications
• Registered ports
– 1024- 49,151
– Used for specific applications like IM
– Source/dest ports
• Private ports
– 49,152 & above
– For source ports
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
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
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
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
• Complete 6.3.3.4
• 6.3.3.5
Network Services
Networking for Home & Small Business