What’s Data Communications

Microsoft PowerPoint - 1. Introduction - Data communications and NetworkingConcerning directly-connected information exchange (hop-by-hop) Generation of the information is not part of data communications
Interested in the transfer of data, the method of transfer and the preservation of the data during the transfer process. Purpose to provide the rules (protocols) and regulations (standards) that allow computers to exchange information and share resources. Networking focuses on the connectivity via data
communications technologies.
Introduction 3
Goal of Computer communications
• Communication links i.e., Physical media (selective discussion later)
• Network core: – Switches/Routers,
(end systems) - CO/CL services
Network Network CoreCore Mesh ()of interconnected routers (mostly) or switches The fundamental question:
How do data be transferred through How do data be transferred through network(s)?network(s)?
Circuit-switching: dedicated circuit/path per call(?), e.g., telephone network (Plain Old Telephone Service)
Packet-switching: data sent through net in discrete “chunks”
AP
Introduction 6
End systems (hosts): run application programs e.g., WWW, email at “edge of network”
Client/serverClient/server model (CS): client host requests, receives service from server e.g., WWW client (browser)/ server; email client/server
PeerPeer--toto--peerpeer model (P2P): host interaction symmetric Since Napster, 1999 e.g., (video) teleconferencing, file-sharing (New Internet Directory Service) eDonkey, eMule, Gnutella, KaZaA, ezPeer, Kuro
Network Network EdgeEdge • Edge device
(named w.r.t. core device)
Introduction 7
AccessAccess NetworksNetworks
Q: How to connect end systems to edge router? residential access nets institutional access networks (school, company) mobile access networks
AP
AP– access point
dedicated shared
Introduction 8
Residential Access : point to point accessResidential Access : point to point access
Dialup via modem
- up to 56Kbps direct access to router (conceptually)
ISDN: - Integrated Services Digital Network - BRI~64x2+16, PRI~1544 Kbps all-digital connect to router
xDSL: digital subscriber line (e.g., Asymmetric ADSL)
up to 1 Mbps home-to-router up to 8 Mbps router-to-home
(Speed is continuously enhancing.)
Subscriber’s Local loop
Introduction 9



: 64Kbps – 640Kbps (())
P O T S
Introduction 10
Message Switching & digit(al) transmission Telephone Networks - PSTN
Circuit Switching Analog transmission (SL) → digital transmission (DSL) Mobile communications (WLP)
Computer Networks - Internet Packet Switching & computer applications
Next-Generation Internet Multiservice, Mobile, Plug&Play packet switching network Switching
Techniques Switching
Consists of MANY pieces : devices (computers/hosts/peripherals/IA) nodes (repeaters/switches/routers/computers) links (various media: wired or wireless) Lots of Protocols (layered in stack, standarization) Various of Applications
(FTP/Web/Videoconferencing/…) * Miscellaneous hardwares and softwares
• Two key elements: - Network topology ()
- Protocols () and Network architecture
Sooooo…
A Computer Network interconnects computers over a wide geographical area
Communications between computers requires very specific unambiguous rules in every tier
A protocolprotocol is a set of rulesa set of rules that governs how two or more communicating parties are to interact, e.g.,
Transport/delivery rules: • Internet Protocol (IP) • Transmission Control Protocol (TCP)
Even Application rules: • HyperText Transfer Protocol (HTTP) ~ for web services • Simple Mail Transfer Protocol (SMTP) ~ for E-mail services
Introduction 13
“Do you have a first name or street?”
Caller
“please dial . . . ”
Introduction 14
Data Communications ProtocolsData Communications ProtocolsData Communications Protocols Connection-Oriented (CO) Protocol
Sending and receiving station establish a real/virtual connection before data is transmitted All frames/packets are guaranteed to arrive and are to arrive in order Ex: VCPS(at NL), TCP(at TL), FTP(at APL), ATM(at DLL)
(between end-systems)
Connectionless (CL) Protocol - Sending station sends a sequence of independent frames/packets to
the receiving station with no dedicated/fixed path - Intermediate nodes are forwarding packets with their best-effort - can be acknowledged (with retransmission) or no acknowledged
(with no retransmission) ACK by the receiver - Ex: DGPS(at NL), UDP(at TL), SNMP(at APL), IP (at NL)
Introduction 16
• Protocols ~ a set of (standard) rules that specifies - Format of messages - Meaning of messages - Rules of exchange - Procedures for handling problems
~ Designed in Layers (layered communications) - separation of networking functions to simplify
network design (reducing complexity and more …) • Layers + Protocols form a Protocol stack/suite
( several software modules) ~ called Network Architecture
• Protocols ~ a set of (standard) rules that specifies - Format of messages - Meaning of messages - Rules of exchange - Procedures for handling problems
~ Designed in LayersLayers (layered communications)(layered communications) -- separation of networking functions to simplify
network design (reducing complexity and more …) • Layers + Protocols form a Protocol stack/suite
( several software modules) ~ called Network ArchitectureNetwork Architecture
Introduction 17
- above ~ to provide services - below ~ to ask for (receive) services
(2) peer layer entity via peer protocols protocols ()
~ to logically transfer messages for a session to be built-up
* ServiceService interface ~ define the physical data flow between layers * Peer protocolprotocol ~ define the logical data exchange and
peer-to-peer logicallogical communications (Q: How to approach this goal ?)
•• In LayeredIn Layered communicationscommunications - an entityentity of a particular layerlayer can only communicate with :
(1) adjacent layer entities via serviceservice interfacesinterfaces
(service viewpoint) or Service Access Point, SAPSAP)
?
??
Introduction 18
Layer and Peer Protocol InteractionLayer and Peer Protocol Interaction • For each layer , it will communicate
to above service provider; to below service user; and adjacent through service interface point (SAP) address
protocolprotocol
• Standardizing interfaces (physical) ~ define interfaces for PnP compatibility and multivendor integration
• Facilitating modular engineering ~ specialize development/implementation efforts on modular functions
• Accelerating technique evolution ~ prevent change dependency, so each layer can evolve quickly
• Simplifying teaching and learning ~ divide internetworking into discrete and easily learned subsets
Why a layered Network Model ? (advantages ?)Why a layered Network Model ? (advantages ?)Why a layered Network Model ? (advantages ?)
• Layers: each layer implements a service . . . - via its own internal-layer actions - relying on services provided by layer below
Introduction 20
OSI 7-Layer Reference ModelOSI 7OSI 7--Layer Reference ModelLayer Reference Model
Proposed by ISO for OSI (Open System Interconnection) Started in 1977; completed in 1983
“ISO standard 7498” A reference model for computer communication architecture and protocol development
Introduction 21
~ Provides network access to application programs and users ~ Issues: everything is application specific ~ Example: Telnet (Remote login), File Transfer Protocol (FTP)
Electronic mail service, X-terminal (terminal emulation)
OSI 7-layer : A Top-Down View
Introduction 22
Presentation layer (Layer 6) ~ Responsible for the format/transformation of data to be
exchanged between applications ~ Issues: - Syntax (character code) & semantics conversion
- Data compression(encoding)/decompression - Cryptography (Encryption & Decryption)
~ Example: ASN.1, OSI presentation protocol, data types
Introduction 23
~ Issues: - Session/dialog establishment/maintenance/termination - Synchronization of dialog - Recovery (from error) or backup via checkpoints
~ Example: ISO session protocol, RPC (Remote Procedure Call)
Introduction 24
- Error control and/or flow/congestion control(if required) ~ Example: TCP, UDP, SPX (Netware’s Sequenced Packet eXchange)
Introduction 25
~ transfer of data between end systems across communication networks
~ Issues: - Addressing (locating a host in the network) - Routing (data packet forwarding) & Congestion control
~ Example: IP (Internet Protocol), IPX(InterPacket eXchange Protocol), CCITT X.25 (network layer)
Introduction 26
Data Link layer (Layer 2)
~ Provides reliable transfer of block information (the frame) over a link (between two physically connected end system on a link basis)
~ Issues: - Synchronization (framing) - Error control* - Flow control
~ Example: ISO HDLC (High Level Data Control), IEEE 802.2 LLC CCITT LAPD (Link Access Procedure-D channel), X-modem
Switch/bridge
~ Concerned with (only) transmission of bits over a communication channel (transmission media)
~ Issues: - Conversion of bits into electrical or optical signal - Encoding & Decoding - Scrambling & Descrambling
~ Example: CCITT X.21, RS-232(unbalanced), RS-449 (balanced)
blue lines - links Introduction 28
Layer 4 and above (referred to “higher layer”) are end-to- end protocols (executed only on a host computer/end-system) The lower four layers provide reliable data exchange and quality of information transmission. Not all 7 layers are needed.
Define sublayers if necessary: DLL LLC (logic link control) & MAC (medium
access control) Many layered protocol architectures do not define the session or the presentation layer. ( Example )
Remarks
Internetwork
AP L.C.
PL L.C.
SL L.C.
- Physical ~ transmission of bits over communication channel (transmission media)
- Data link ~ Provides reliable transfer of block information (the frame) over a link
- Network ~ packet forwarding (addressing + routing)
- Transport ~ Controls the way of data delivery between stations/nodes
- Session ~ dialog between cooperating application programs (login and password)
- Presentation ~ data representation of information and compatibility
- Application ~ individual application program for users
Summary Summary -- OSI LayersOSI Layers
Introduction 32
Introduction 33
te ra
ct io
Introduction 34
PDU
Data
Message
overhead
Transport
network
IS (Intermediate System) : L7 Gateway* L3 Router L2 Switch/Bridge L1 Hub/Repeater
Data Link Physical
Network(protocol stack in One computer)
IS - so called Intermediate Message Processor, IMP (refer to ISO Network Hierarchy)
L3 L2 L1
Calls for Addressing ()Calls for Addressing Calls for Addressing (())
• Mechanisms needed to distinguish among . . .
- multiple networks on the Internet (internetworking)
- multiple computers on a network
- multiple applications (software) on a computer
- multiple copies of specific single application on a computer
(entity,) End-point (in TCP/IP-based Internet)
. . .
Introduction 37
Addressing ConceptsAddressing Concepts
A SAP is unique only within a system but need not be globally unique. Introduction 38
Physical/MAC Address Physical/MAC Address –– the NICthe NIC’’s IDs ID
RJ-45 Jack
DFE 540TX
NIC ~ Network Interface Card () ID ~ identifier ()
uniquely identifies each physical network connection of a device also referred to as physical or hardware address usually exist within a flat address
space preestablished and typically fixed
relationship to a specific device
Introduction 39
Manufacturer’s ID
NIC’s ID/Serial number
(a) point to point(a) point to point (b) star(b) star
(c) bus(c) bus (d) ring(d) ring
(e) mesh(e) mesh
•WAN
•MAN
•GAN
Introduction 44
Standard Organization for Data and Standard Organization for Data and Network Communications Network Communications
ISO (Institute of Standardization Organization) ITU-T (International Telecommunication Union – Telecommunications sectors) formally the CCITT ANSI (America National Standard Institute) IEEE (Institute of Electrical and Electronic Engineering) Electronic/Telecommunications Industrial Associations Others: ATM forum, Gigabit/10GE Alliance, etc.
Introduction 45
IAB - Internet Activities/Architecture Board IETF - Internet Engineering Task Force
(the most important one) IRTF - Internet Research Task Force
Introduction 46
Network of networks (inter-connected set of networks) To interconnect different computers used by various organizations via the same TCP/IP protocol it treats all networks (e.g., LAN, WAN, etc.) equally (i.e., a flat network)
What is the What is the ““ InternetInternet ”” ??
NBP A
NBP B
NAP NAP
regional ISP
regional ISP
local ISP
Service) Providers
* roughly hierarchical
• New computers added to the Internet > ONE per second • Internet ~ Doubling in size every nine to twelve months
Introduction 47
• NIC ~ Network Information Center APNIC (TWNIC, etc.), EURNIC, etc.
RFC ~ Request For Comments FYI ~ For Your Information (RFC # > 1500)
IRTF - Internet Research Task Force - Responsible for research and deve- lopment of the Internet protocol suite
IETF - Internet Engineering Task Force - Responsible for solving short-term engineering needs of the Internet. It has over 40 Working Groups.
IAB, 1983
TWNIC
Application: supporting network applications
TCP, UDP Network: routing of datagrams from source to destination
IP,ICMP, IGMP, RIP,OSPF, BGP4 Link: data transfer between neighboring network elements
PPP/SLIP, Ethernet, Token-Ring Physical: bits “on the wire” - transmission
Network Access
Physical Layer
Introduction 49 Higher-layer see nothing pealed off; Lower-layer cannot see misunderstood
Protocol layering and dataProtocol layering and data Each layer takes data from upper (lower)
Adds (take off) header information to create new data unit Does what the action(s) indicated by the header passes new data unit to layer below (above)
application transport network
Ht
Introduction 51
IP headerTCP header
Protocol Data Unit (Protocol Data Unit (PDUPDU) in TCP/IP Architecture) in TCP/IP Architecture
Meaningful to appropriate peer protocol software module
DLL Frame
Introduction 52
Windows> telnet 140.124.70.26 (showing the first packet transmitted by the src PC)
PDU Decomposition in TCP/IP Scenario
Protocol #: Network--Transport layer
Protocol type: DLC--Network layer
Introduction 53
Src port # (randomly generated by the src PC) Dest port # (an well-known for well-known application)
Port #: Transport--Application layer
(PDU cont’d)
How to get RFC ?
topic
1. RFC1700 - assigned numbers (including all port numbers and constants) 2. RFC2700 - State (standard, draft standard, proposed standard, experimental,
informational, or historic) of standardization of various internet protocols
• Other RFCs:
RFC 1577
RFC 1700
Introduction 56
Protocol Full
Name RFC #
Dynamic Host Configuration
Protocol V.3 1939
IP Network Address


-



Optical (Visual) TelegraphOptical (Visual) Telegraph
Claude Chappe invented optical telegraph in the 1790’s Semaphore mimicked a person with outstretched arms with flags in each hand Different angle combinations of arms & hands generated hundreds of possible signals Code for enciphering messages kept secret (code book) Signal could propagate 800 km in 3 minutes!
Introduction 60
ChappeChappe TelegraphTelegraph
Principle of operation
The telegraph of the Chappe brothers is a 5 m height mechanical device made up: - of two wings or indicators, 2 meters length and 30 cm broad. - counterweight to ensure the balance of the unit. - of a manipulator to put moving the wings.
Claude Chappe (1763 - 1805)
Electric TelegraphElectric Telegraph William Sturgeon Electro-magnet (1825)
Electric current in a wire wrapped around a piece of iron generates a magnetic force
Joseph Henry (1830) Current over 1 mile of wire to ring a bell
Samuel Morse (1835, 1791-1872) Pulses of current deflect electromagnetPulses of current deflect electromagnet to generate to generate dotsdots & & dashesdashes Experimental telegraph line (wire) over 40 miles (1840)
Signal propagates at the speed of light (~ 2 x 108 m/s in cable)
Introduction 62
Morse code converts text message into sequence of dots and dashes
Use transmission system designed to convey dots and dashes
Morse Code: 1st Digital CommunicationsMorse Code: 1st Digital Communications
Introduction 63
Morse register Introduction 64
Rate: 25~30words/min or 20bit/s20bit/s (5 char/word, 8bit/char) Optical telegraph networks disappeared since then (1832)
Electric Telegraph NetworksElectric Telegraph Networks
Q: How to increase the transmission rate over a telegraph circuit?
Switches
Message
Destination
Introduction 65
BellBell’’s Telephones Telephone Alexander Graham Bell (1875) working on harmonic telegraph to multiplex telegraph signals Discovered voice signals can be transmitted directly
Microphone converts voice pressure variation (sound) into analogous electrical signal Loudspeaker converts electrical signal back into sound
Telephone patent granted in 1876 Bell Telephone Company founded in 1877
Signal for “ae” as in cat
Microphone Loudspeaker analog
electrical signalsound sound
Introduction 67
The NThe N22 ProblemProblem
For N users to be fully connected directly Requires N(N – 1)/2 connections Requires too much space for cables Inefficient & costly since connections not always on
N = 1000 N(N – 1)/2 = 499500
1
2
34
N
Solution?
1950s: Telegraph technology adapted to computers 1960s: Dumb terminals access shared host computer
SABRE airline reservation system (terminal-oriented ntwk) 1970s: Computers connect directly to each other
ARPANET (1970s) packet switching network TCP/IP internet protocols Ethernet local area network
1980s & 1990s: New applications and Internet growth Commercialization of Internet E-mail, file transfer, Telnet, WWW, firewall, P2P, . . . Internet traffic surpasses voice traffic
Introduction 70
ARPANET ApplicationsARPANET Applications 1957, ARPA(Advanced Research Project Agency) of DoD
in response to the Soviet Unions’ Sputnik Intiated in the lat of 1970s, Introduced many new applications : Email, remote login, file transfer, … Formed a committee, 1983 IAB (Internet Activity Board) Intelligence at the edge
UCLA RAND TINKER
CARN
MITRE
ETAC
MIT