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Internet and Intranet Fundamentals
Class 5
Session B
Topics
• NNTP
• Mid-Term Review
NNTP
• NNTP = Network News Transfer Protocol– Internet bulletin board system
• 1986– RFC 977 (Kantor & Lapsley)
• “News” means bulletins, information, data, messages from individuals– not news agencies (although this is not
precluded)
NNTP
• Facilitates rapid dissemination of software bug fixes, technical tips, product reviews, discussions, rumors– distribution– inquiry– retrieval– posting
• USENET News System
NNTP
• Model: Centralized storage of postings or news articles– clients / server model
• USENET News
• TCP– Port 119
NNTP
• Info Organized into Newsgroups– hierarchical, like a file directory system
• rec.sports.football.nfl
• Master-Slave Relationship between News Servers– dependent news servers can request that only
certain postings (e.g., since a certain time) are transmitted
– equivalent of caching
NNTPCommands
• ARTICLE <message-id> or [nnn]
Responses: 220 n <a> article retrieved - head and body follow (n = article number, <a> = message-id)221 n <a> article retrieved - head follows222 n <a> article retrieved - body follows223 n <a> article retrieved - request text separately412 no newsgroup has been selected420 no current article has been selected423 no such article number in this group430 no such article found
NNTPCommands
• LIST– lists valid newsgroups
• GROUP ggg– selects a valid newsgroup– response returns first and last article numbers
• LAST– current article pointer set to previous article
• NEXT
NNTPCommands
• NEWSGROUPS date time– list of newsgroups created since date and time
• NEWNEWS newsgroups date time– returns list of articles posted to any one of the
newsgroups specified since date and time
• POST– post article in format specified by RFC 850
NNTPUSENET News-Related Services
• http://www.dejanews.com
• http://www.intellinews.com
Mid-Term Review
• Covers Everything Up Through Class 5
• Selections from Previous Presentations
Open Systems Interconnection Model
• Seven Layers– Application (S/W)– Presentation (S/W)– Session (S/W)– Transport (S/W)– Network (S/W and H/W)– Data Link (F/W and H/W)– Physical (H/W)
OSI Reference Model
Application
Presentation
Session
Network
Transport
Data Link
Physical
Application
Presentation
Session
Network
Transport
Data Link
Physical
Network
Data Link
Physical
OSI Application Layer
• Application and User Interfaces
• File Transfer
• Database Access
• Program to Program Communication
• http, ftp, gopher, smtp, telnet
OSI Transport Layer
• Host-to-Host Layer
• Error Free End-to-End Connections– virtual connections– doesn’t know about intervening routers
• TCP in TCP/IP
• Often Implemented in Operating System
OSI Network Layer
• Communications Subnet Layer
• Network Routing
• Packets
• Congestion and Flow Control
• Accounting
• IP in TCP/IP
• Typically Implemented as I/O Driver
OSI Data Link Layer
• Breaks Up Input Data from Network Layer and Transmits as Data Frames
• Typically an Interface Card with Firmware– Ethernet card
• Acknowledgement
• Error Handling– Retransmission
• Flow Control
OSI Physical Layer
• Transmits Raw Bits• Includes Communication Channel
– copper wire– fiber– microwave
• Signaling Levels– voltages, timing
• Pin Configurations
DefinitionsClient / Server
• Client– makes request– initiates communication– may have a GUI and human
• but not always
• Server– fulfills request– passively waits for requests– usually multitasking machine
DefinitionsClient / Server
• Fat Clients– full-featured, large applications– use servers as data servers– not much computational power on the server
side
• Thin Clients– small applications– downloaded from the network– relies on computational power of server
DefinitionsClient / Server
• Fat Client Example– Web Browser– Eudora– Visio
• Thin Client– Java Applets– JavaScript Applications inside of HTML Pages– Note dependence on Fat Client (i.e., the
browser)
DefinitionsTCP / IP Berkeley Sockets
• Five Basic Attributes of a Socket Connection– Local Port (chosen by OS on client side)– Local IP Address– Remote Port– Remote IP Address– Protocol (“tcp”, “udp”, etc.)
• Each Connection Has Own 5-tuple
DefinitionsTCP / IP Berkeley Sockets
• Server Listens on (Well-Known) Port
• Clients Attempts Make a Connection
• Server Accepts the Connection
• Server Receives Request from Client
• Server Interprets Request– performs some action
• Sends Response to Client
• Shuts Down the Connection
Internet ProtoclsTCP/IP Overview
• TCP / IP = Transmission Control Protocol / Internet Protocol
• Early 1970s– ARPANET
• Distributed with UC Berkeley UNIX in Early 1980s
• Public Domain, Non-Proprietary, Open Source
Internet ProtocolsLayers
• Five Layer Model– Application– Transport (TCP / UDP)
• contains some Session features
– Network (IP)• actually there are three sublayers
– internet (IP)– convergence– subnet
– Data Link and Physical
Internet ProtocolsLayers
• Packet Switching– datagrams
• Nodes– hosts
• end-user machines• clients or servers
– routers• connecting different networks• a router is also a host of sorts
Internet ProtocolsLayers
• Connection-Oriented– TCP– reliable two-way, byte stream protocol
• Connectionless– UDP = User Datagram Protocol
• also known as the “Unreliable Datagram Protocol”
Internet ProtocolsTCP
• Reliable, Bidirectional Byte Stream– like a UNIX pipe
• End-to-End Reliability
• Bandwidth Optimization (flow control)
• Ports– source– destination
Internet ProtocolsUDP
• User Datagram Protocol
• Ports (like TCP)
• Length, Checksum, Data– no sequencing or acknowledgment structure– error handling left to applications protocol
• DNS uses UDP
Internet ProtocolsDNS
• Domain Name System
• Distributed– database scattered across thousands of
nameservers
• Top-Level Domains– root domain: .– net, edu, com, org, mil, and country codes (jp)
• FQDN: Fully Qualified Domain Name
TCP / IP
• ICMP = Internet Control Message Protocol– routers generate most ICMP traffic– most common types
• destination unreachable: can’t find routing table entry
• routing redirect: better route exists
• time expired: ttl = 0; traceroute uses this
• echo request / echo reply: ping uses this
TCP / IPRouting Architecture
• Autonomous Systems (AS)– collection of routers under single administration– use same routing protocol
• Interior Gateway Protocol (IGP)
• keeps routers informed of interior routes
– AS-to-AS connection uses a different protocol• Exterior Gateway Protocol
• policy routing, transit traffic, local traffic (originating within)
TCP / IPRouting Architecture
• Routing Protocols
• Reachability Protocols– whether path exists
• EGPs and BGPs (Border Gateway Protocol)
• Distance Vector Protocol– distance metric to remote network
• RIP = Routing Information Protocol– broadcast exchange of routing information
– uses UDP
• OSPF = Open Shortest Path First
Internet ArchitectureOverview
• A Network of Networks– internetworking
• The Big Picture– http://navigators.com/internet_architecture.html
ISPs
• Points of Presence (POPs)
• Dial-Up and Dedicated Network Connections– variety of underlying technologies– PPP (Point-to-Point Protocol)
• modems
– ISDN (Integrated Services Digital Network)– Frame Relay, Dedicated T-1– ADSL and Cable Modems
Regional Networks
• BARRNet: Northern Central California (CA)
• CERFnet: Western US and International
• CICnet: Midwest US (MN, WI, IA, IN, IL, MI, OH)
• MIDnet: Mid-US (NE, OK, AR, MO, IA, KS, SD)
• NEARNET: Northeastern US (ME, NH, VT, CT, RI, MA)
• NYSERNet: Northeastern US (NY...)
• SURAnet: Southeastern US (WV, VA, SC, NC, TN, KY, LA, MS, AL, GA, FL, Washington, D.C., MD, DE)
• Westnet: Western US (AZ, CO, ID, NM, UT, WY)
NAPs and MAEs
• NAP = Network Access Point– originally NFS
• MAE = Metropolitan Area Exchange– MCI Worldcom has a service mark on this– Tier-1
• MAE-East (D.C.) and MAE-West (San Jose)
– Tier-2• LA, Chicago, Dallas, Houston, New York
– Giant LAN switch (FDDI)
DNS
• Function of DNS?
• Function of central registry and what does it hold.
• Why aren’t we drowning in DNS requests?
• What is a “root domain”, a “fully qualified domain name”.
TopicsRegulation
• Documentation– RFCs and STD
• Organizations– ISOC (IAB, IESG)– IETF– W3C– InterNic
• IAB Standards Process
DocumentationRFCs
• RFC = Request for Comments– series of notes– ARPANET 1969– anyone can write an RFC– two paths
• as Internet Draft• through IETF• through RFC Editor
– http://www.rfc-editor.org/
Organizational Hierarchy
ISOC
IESG
IETF
IAB
Working Group Working Group Working Group
Areas
OrganizationsIETF
• IETF = Internet Engineering Task Force– technical worker bees
• Applications Area
• General Area
• Internet Area
• Operations and Management Area
• Routing Area
• Security Area
• Transport Area
• User Services Area
IAB Standards Process
• Informational
• Experimental
• Proposed Standard
• Draft Standard
• Internet Standard
HTTPOverview
• HyperText Transfer Protocol
• Applications Layer Protocol– Generic Protocol
• gateway to SMTP, NNTP, FTP, Gopher, WAIS
• Uses TCP Port 80 (by default)– presumes reliable transport
HTTPOverview
• Language of the World Wide Web
• Provides Open-Ended Set of Methods– indicating purpose of request
• Builds on URI, URL, URN disciplines
HTTPOverview
• URI = Uniform Resource Identifier– identifies points of content– mechanism used to access resource – specific computer housing the resource – specific name of resource on computer– formatted strings which indicate characteristics
of a resource
HTTPOverview
• URL = Uniform Resource Locator– a particular form of URI– Web page address
• URN = Uniform Resource Name– institutional persistence– identifies agency responsible for a definition,
for example, but not the location
HTTP/1.0
• Shortcomings of HTTP/1.0– weak on proxies, caching, persistent
connections, and virtual hosts– proliferation of imposters:
• incompletely implemented applications
– stateless• new connection for each request/response exchange
How HTTP WorksRequest/Response Protocol
• Response from server contains …– status line
• message protocol version
• success or error code
– MIME-like message• server info
• entity meta-information
• possible entity body content
How HTTP WorksRequest/Response Protocol
• More Sophisticated Interactions– proxies
• forwarding agent
– gateways• receiving agent
– tunnels• relay point between two connections• firewalls• non-caching
How HTTP Works Media Types
• Type / Subtype– followed by 0 or more optional parameters
delimited on the left by “;”• parameter are of form attribute=value
– Content-type: text/html– Content-type: text/plain (default)– Content-Type: multipart/mixed;
boundary=gc0p4Jq0M2Yt08jU534c0p
• Assigned by IANA
HTTP
• Authentication– .htaccess files
• Secure Sockets Layer (SSL)– https– RSA Encryption
• public key / private key
– not really part of HTTP
HTML
• Main Tags– <html> </html> starts HTML stream– <head> </head> delimits HEAD of document– <title> </title> title that appears at top of
browser frame– <body> </body> delimits document BODY– <a href=“…URL…”>Text</a> creates a
hyperlink– <img src=“…”> inserts an image into a file
Misc.
• What is an application server, when would you use it, when would you not use one?
• What are html “cookies”, what problem do they solve?
• What is the difference between a Get and a Post request?
• How is an https page secured?