Network Services Networking for Home & Small Business

Client-Server Server –Host running an application that provides info or services to a client Web Server Server File Server Browser- widely used client software

Client-Server Web Site domain names to IP address translation Remote login to device to control it Send/Receive Assigns IP addresses Web SiteFile 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 –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 Example

User Datagram Protocol 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 source & destination IP source & destination port numberThe 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

Review What does 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 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 ( is port 443

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

server receives & stores s You client allows access to view messages Protocols used in include SMTP, POP3, IMAP4

Protocols- SMTP SMTP (25) –Used to send from client to server – server to server

Protocols- POP3 POP3 (110) –Used to send client messages & deleted from storage on the server Mail on server until collected from client

Protocols- IMAP4 IMAP4 (143) –Like POP3, but it keeps messages on server until user deleted them

Configuring

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 ,535 Well-known ports – –Common applications Registered ports – ,151 –Used for specific applications like IM –Source/dest ports Private ports –49,152 & above –For source ports

Review Which 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 server to 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 or TCP or UDP 01-5A-FF DC DHCP or POP3 or HTTP

Activity Complete

Network Services Networking for Home & Small Business