Sharing Interaction and - ntut.edu.tw
Transcript of Sharing Interaction and - ntut.edu.tw
Overview 1 Overview 2Goal of Computer communications
via
communication networks
(physical communication)
ClientSRC/DEST
ServerDEST/SRC
Rea
l dat
aflo
wReal data flow
(logical communication)
cloud
Since 1970’s . . .
Computernetworks
(to hide the complexity)
Model of Computer CommunicationsModel of Computer Communications
Overview 3
The Goal of Communication
Information Exchangeand
Resource sharing
Since the old time . . .
and now getting . . .
much more Sharing, Interaction , and Fun.
Overview 4
The Four Era of NetworkingThe Four Era of Networking
• Era 1: Mainframe Networks (1965-1975)
– IBM 360/370 + control units + terminals
– Telephone line bandwidth, taking turns
• Era 2: Minicomputer Networks (1975-1985)
– DEC PDP-11/70 VAX + Data PBX + Terminals
– 10Mbps Ethernet + T1 (Muxtiplexed)
• Era 3: Shared-Bandwidth LANs (1985-1995)
– Ethernet bus/hub + routers
• Era 4: Switched Networks (1995 2005 ? )
– LAN switches + ATM switches + routers
Overview 5
Network Structure – A Closer LookNetwork Structure – A Closer Look
• Communication linksi.e., Physical media(selective discussion later)
• Network core:
– Switches/Routers,network of networks
– Switching techniques
• Network edge:- applications and hosts
(end systems)- CO/CL services
(continue . . .)
wireless
AP
• so-called“backbone”
( ( ))
So…• Access networks
Overview 6
NetworkNetwork CoreCore
• Mesh ( )of interconnected routers (mostly) or switches
• The fundamental question:
How do data be transferredHow do data be transferredthrough network(s)?through 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
Overview 7
NetworkNetwork EdgeEdge• 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 DirectoryService) eDonkey, eMule, Gnutella, KaZaA, ezPeer, Kuro
• Edge device(named w.r.t. core device)
AP
Overview 8
AccessAccess NetworksNetworks
Q: How to connect end systems to edge router?
• residential access nets• institutional access
networks (school, company)
• mobile access networks
(click to see the details)
AP
• Keep in mind: the connection- bandwidth (bits per second) ?
(media-dependent)- shared or dedicated ?
(topology-dependent)
Overview 9
Residential Access - I: 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.)
dedicated
Subscriber’sLocal loop(last mile)
Overview 10
ADSL(Asymmetric Digital Subscriber Loop ) Networking
SplitterATUATU--RR
Filter
ATUATU--RR
Filter
ATUATU--RR
Filter
.
.
.
Hinet ISP
DSLAMDSLAM62006200
ATM
Data STM-1 STM-1
TANET
ATMATM
,
PSTN
POTS
POTS: 0 ~ 4KHzUplink: 25 ~ 170KHzDownlink: 200KHz ~ 1.1MHz
POTS
,
1.1MHz
Ex: : 64Kbps - 6Mbps; : 1.5Mbps - 4.1 w/ 26AWG
: 64Kbps – 640Kbps (( ))
Overview 11
xDSL Modem Technology
DSL Service Max. Data Rate
Down/Uplink
(bps)
Copper
Pairs
Required
Analog
Voice
Support
Max. Reach
(km - feet)
VDSL - Very high bit-rate
DSL
25M/1.6M
or 8M/8M
1 Yes .9 - 3,000
ADSL - Asymmetric DSL 7M/1M 1 Yes 5.5 - 18,000
HDSL - High bit rate DSL 1.5M - 2.0M/
1.5M - 2.0M
2 No 4.6 - 15,000
SDSL - Symmetric DSL 784K/784K 1 No 6.9 - 22,000
IDSL - ISDN DSL 144K/144K 1 No 5.5 - 18,000
ISDN 128K/128K 1 No 5.5 - 18,000
PSTN ~ Public Switch Telephone NetworksPOTS ~ Plain Old Telephone Services
Overview 12
Residential Access - II: Cable Modems
• HFC: Hybrid Fiber Coax (network)– asymmetric: up to 10Mbps upstream, 1 Mbps downstream
(by FDM)– Network of cable and fiber attaches homes to ISP router– shared access to links among homes– Deployment: available via cable companies
ONU ~ optical networking unit; SO ~ switching office
SO
SO
SOSOHeadendHeadend
shared
Overview 13
Cable Network Architecture: OverviewCable Network Architecture: Overview
cable distributionnetwork (simplified)
(500~5000 homes)
server(s)
Channels
VIDEO
VIDEO
VIDEO
VIDEO
VIDEO
VIDEO
DATA
DATA
CONTROL
1 2 3 4 5 6 7 8 9
Ref: http://www.cabledatacomnews.com/cmic/diagram.html
cable headend
home
Overview 14
Institutional Access: Local Area NetworksInstitutional Access: Local Area Networks• Company/university’s local
area network (LAN) connects end systems to edge router
• Ethernet: (a popular example)
– shared or dedicated cableconnects end system(s) and router(s), with somethingelse in between
– 10 Mbs, 100Mbps, Gigabit Ethernet
• Deployment: institutions, homeLANs (soon)
• LANs: (discussed later)
Port/interface
Shared/dedicated
Overview 15
Mobile Access NetworksMobile Access Networks
• Shared wireless access networkconnects end systems to router
• Wireless LANs: (hot spot)– radio spectrum replaces wire– e.g., Lucent Wavelan 10Mbps
• Wider-area wireless access– CDPD: wireless access to ISP
router via cellular network(Cellular Digital Packet Data)over Advance Mobile Phone (AMP) Service
- SM/MMS/EMS/WAP over GSM/GPRS/3G (WirelessApplication Protocol, General Packet Radio Service) overMobile phone
basestation
mobilehosts
router
AP ~ access point
AP
shared
Overview 16
Communication LinksCommunication Links -- MediaMedia
• Transmission media
~ physical path (wired or wireless) between transmitter
and receiver
(Propagation is in the form of electromagnetic (EM) waves.)
• Media
GuidedGuided media ~ media ~ waves are guided along a physical path
Twisted pair, Coaxial cable, Optical fiber
UnguidedUnguided media ~ media ~ offering a means of transmittingEM waves but do not guide them
Radio, Laser, Infrared, Microwave
Overview 17
Signals TerminologySignals Terminology Related to T.M.
• Information ~ an abstract object
Message ~ a concrete form of information
Data ~ an entity that convey meaning
Signal ~ an electric or an electromagnetic
encoding of data for being transmitted
Transmission ~ the communication of data by the
propagation and processing of signals
• Analog continuous
Digital discrete Data, signal, Transmissionvs
value/amplitude vs time scaleOverview 18
• Analog data ~ take on continuous (real number) values
on some interval (e.g., voice and video)
Digital data ~ take on discrete values
(e.g., text and integers/numbers in Telegraph)
• Analog signal
~ represent data with continuously varying voltage or
electromagnetic wave
Digital signal
~ represent data with sequence of voltage/current/light pulses
Overview 19
Signal, Harmonics, and Spectra
))1052sin((
))1032sin(())102sin((4)(
651
6316
t
ttts
(Line) spectra
Overview 20
BandwidthBandwidth andand Data RateData Rate
• Harmonic and Signal bandwidth
Harmonics byFourier analysis
(one cycle)
• # of harmonics better approximation of signals(composite of harmonics)
Overview 21
• Data rate ~ the rate/speed in bit per sec (bps) at which
data can be communicated
• Bandwidth ~ frequency range/width of a signal or
a system (e.g., for a transmission medium)
- Max # of times /sec the signal can change (baud rate)
• Relation between data rate and bandwidth
– Data rate = R bps, Time for sending 8-bit = T = 8 (1/R)
then, the first harmonic (fundamental) freq. = 1/T = R/8
– Consider a voice-grade channel with BW = 3000 Hz
No of harmonics (can be sent) = 3000/(R/8) = 24000/R
(or the system allows it to change)
i.e., getting through the channelOverview 22
Data Rate vs Harmonics
limited (system) BW limiting maximum data rate
(due to larger distortion)Channel capacity
,R
Any transmission system/media has a limited band offrequencies (i.e., the system bandwidth)
This limits the data rate that can be carried
Overview 23
MediaMedia –– Twisted PairsTwisted Pairs
Shielded TP (STP)Unshielded TP (UTP)
• Twisted Pair
Help reduce interference
- Copper wire, 24AWG (Diameter = 0.5mm)- used in telephone and intrabuilding LAN connection
- USA : Category 1 (1MHz) ~ Cat. 5 (100MHz)
- UL (Underwriting Laboratories, Inc) :
Level 1 ~ Level 5
- IEEE EIA 568-A/B (=AT&T 258A) : Wiring standard for LAN
- Ex: AT&T Power Sum Enhance Cat. 5
UTP
RJ-45
8.1
Overview 24
UTP ClassificationsUTP Classifications
Category 1 2Mbps Voice application
Category 2 4Mbps voice 4Mbps token ring
Category 3 16Mbps 100BaseT 16Mbps token ring
Category 4 20Mbps 100BaseT4 16Mbps token ring
Category 5 100Mbps 100BaseTX
Category 5E 1000Mbps 1000BaseT
Category 6 2.4Gbps 1000BaseT
E ~ enhanced NEXT = 1/4 of Cat5’s; Power sum NEXT = 1/8 of Cat. 5’s
• Some notations marked on UTP jacket: (Defined by Article 800, National Electric Codes)CM (Communication): Horizontal cabling, e.g., room to roomCMR (Communication Riser): Vertical cabling, e.g., floor to floorCMP (Communication Plenum ): Horizontal and vertical cabling
Overview 25
AttenuationAttenuation~ the amount of signal loss in a transmission link/media
• Examples:
1/1 0 dB1/2 - 6 dB 1/10 - 20 dB
lossvrec/vsrc
src
rec
v
vlossdB 10log20
• Measurement
Signalsource
Signalreception
dB loss
Just sending Receiving atFar-end
vrecvsrc
Overview 26
NEXT
• Near-End CrossTalk (NEXT)
the coupling of the signal from one
pair of conductors to another pair
the near-transmitted signal is picked up
by the near-receiver pair
- The biggest noise in twisted-pair wiring system
NEXT = 10*log10(Pinterfering / Pcrosstalk_in_interfered_end)
(NEXT measured in dB; The higher, the better.)
TX
RX
measured at the RX-end
• In addition, FARNEXT (FEXT) and Power Sum NEXT
Overview 27
Comparisons of UTP and STP
Overview 28
EIA/TIA 568A/B 8P8C Pin AssignmentEIA/TIA 568A EIA/TIA 568B, AT&T 258A
1
8
RJ-45
P ~ positionC ~ contact
Tx-Rx-6
Tx+Rx+3
Rx-Tx-2
Rx+Tx+1
HubNICPin #
Overview 29
• PC – Hub : use straight cable
•
Interconnection for PCs (Hubs)(review)
(pin)RJ-45 RJ-45
1 (Tx+) (Rx+)
2 (Tx-) (Rx-)
3 (Rx+) (Tx+)
4
5
6 (Rx-) (Tx-)
7
8
• PC – PC or Hub – Hub :
~ use crossover cable
Overview 30
(review)
MediaMedia –– Coaxial CableCoaxial Cable
- shielded, concentric construction much lesssusceptible to interference and cross talk (than in TP)
- used over longer distance and support multiple-stationconnections (multidrop); Ex: bus network - 10Base2
Cross-section view
(outer)
(protective)
RG-58 cableBNC type
• Coaxial Cable structure
Overview 31
(review)
MediaMedia –– Fiber opticsFiber optics
- Use optical instead of electrical signaling(free from interference)(Transmitting light sources : laser Diode or LED) (Detection light-pulse : photoelectric diodes)
- Light transmission dep. on “propagation mode” & “index profile”- Operating frequency: 1014 Hz ~ 1015 Hz
Straight-Connected Straight-Twisted Overview 32
• Best wavelength “windows” for light propagation in FO:centered on 850, 1300, and 1550 nm (infrared frequency)
Wavelength ~ 200 um, BW ~ 30 THz (1012)
• Wavelength window ~ 200nm max.- Attenuation of light through the fiber in the infrared region
Overview 33
Refraction and Reflection at the Boundary
n1sin = n2sin~
• Snell’s law :
Refraction
Absorbedby claddingor jactet
• Total internal Reflection( needs: n1 > n2 )
v
cnindexRefraction
n = 1.0 for air,
1.5 for glass
normal
(more dense)
(less dense)
Overview 34
(review)Two FO Transmission Modes
• Single-mode (SMF)- core diameter (1.5~10um) < wavelength one transmission path- used for longer distance (Ex: 2 Gbps over 30 km)
Inner core
Light ray out
Light ray in
claddingMode = path
(propagates light ray by refraction)
• Multimode (MMF)- multiple reflection angles of ray internally (various modes/paths)- signal element spreading out limits the distance & speed
Direct rayHigher-Order
mode Inner coreCladding (jacket)
air
squeeze
Overview 35
(review)
Different Index Profiles
Step-indexSMF
n
Graded-indexMMF
n
Step-indexMMF
air
n
large
Overview 36
Focusing Effect of Different ModesFocusing Effect of Different Modes(review)
Axial ray
( with higher refraction index at center)
(different modes take different times to traval)
timedispersion
Overview 37
(review)
Some comments on FO
Graded-index MMF – with good focusing effect~ Because the refractive index decreases with
distance from the center and the velocity is Inversely proportional to the refraction index.
The propagation speed of light inside a FO is NOT as fast as light speed in vacuum. How fast is it ?
~ 194,865 km/sec in glass or optic fiber
( vs 224,844 km/sec in copper)
The factor limiting the use of FO is not the cost of FO itself but the cost of installation.
Overview 38
(review)
Comparisons of Guided Media
1000GHz/km
HighlightHighHighFO
HighheavyMediumHighCoax
lowmediumlowLowTP
safetyweightratecostitemsmedia
Overview 39
(review)
Unguided Transmission Media
~ transmission and reception are achieved by antenna forradiation and pickup EM (ElectroMagnetic) energy into/from medium with no physical connection (wireless)
- Radio Frequency (RF) :
* freq. < 2 MHz : via ground wave propagation
- follow creature of the earth; pass through obstacle/building
* 2 ~ 30 MHz : via sky wave propagation
- bounce back by ionosphere layer; may absorbed by rain
* freq. > 30 MHz: Line-Of-Sight (LOS) propagation (straight)- Blocked by obstacles and diverges in space (multipath
fading : signals arrived via different paths and cancels/destroys to one another)
Overview 40
Telecommunication Spectrum – by FCCTelecommunication Spectrum – by FCC(review)
3 3
VF ~ voice Freq., E - Extremely; V – Very; U – Ultra; S - Super
|Ultravioletlight
Overview 41
(brief)
Two types of wireless transmission
- Infrared (IR) : 3 1011 ~ 2 1014 Hz
~ wireless communication w/o antenna (portable)
~ limited to small area (single room)
1. Omni-directional Electromagnetic (EM) waves
- Broadcast radio : 30 MHz ~ 1 GHz
2. Directional EM waves
- Point-to-Point Satellite Channel :Varieties: 4/6 , 12/14 , and 19/29 GHz (downlink/uplink frequency)
- Satellite Microwave : 2 GHz ~ 40 GHz, Optimal: 1~10GHz
- Limited broadcast (spot beam)
- Laser beam : straight line and may be blockedOverview 42
(review)
Effects of Signal Propagation
• Propagation in free space always like light (straight line)
• Receiving power proportional to 1/d² power law
(d = distance between sender and receiver)
• Receiving power additionally influenced by
– fading (frequency dependent)
– Shadowing (or even worse, blocking)
– reflection at large obstacles
– scattering at small obstacles
– diffraction at edges
shadowing reflection scattering diffraction
Overview 43
(review)
Multipath propagation
• Signal can take many different paths between sender and
receiver due to reflection, scattering, and diffraction
(spreading effect)
signal at sendersignal at receiver
~ dispersion effect in optic fiber
Overview 44
Network ComponentsNetwork ComponentsSooooo…
• Networks are COMPLEX
• Consists of MANY pieces . . .
- devices (computers/hosts)
- nodes (switches/routers/computers)
- links (various media: wired or wireless)
- Lots of (layered) Protocols
- Various of Applications
- Miscellaneous hardwares and softwares
• Two key elements:- Network topology- Protocols and Network architecture
Overview 45
• 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 Architecture
裏
Network ArchitectureOverview 46
•• 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)
?
??
(for your information)
- above ~ to provide services- below ~ to ask for (receive) services
(2) peer layer entity via peer protocolsprotocols
~ 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 the goal ?)
Overview 47
Layer and Peer Protocol InteractionLayer and Peer Protocol Interaction
To sum up, for each layer : to above--service providerto below--service userin between--service interface
• Service Protocol; (can be) totally separated
• Service object descriptions w/o specifying “how to do it?”• Protocol rules for (monitoring) entities’ communication• Entity uses protocols (which can be changed) to define its
services (which is unchanged, i.e., invisible to users).
N layer entityN layer entity
Layer N+1protocol
Layer N-1 protocol
Layer N/N-1interface
Layer N+1/Ninterface
Layer N protocol
Peer-to-peer
N+1 layer entity N+1 layer entity
N-1 layer entity N-1 layer entity
Overview 48
OSI Reference ModelOSI Reference Model
• Proposed by ISO for OSI (OpenSystem Interconnection)
• Started in 1977; completed in 1983 “ISO standard 7498”
• A reference model for computercommunication architecture andprotocol development
• Layered model just provides aframework, but not defines or constrains an implementation
• Developed per-layer protocol/
standard, but not very successful.
OSI 7OSI 7--layer modellayer model
Reg
ardi
ngto
dat
atr
ansp
ort
Reg
ardi
ngto
app
licat
ions
Overview 49
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
• Reducing complexity~ divide interrelated aspects of networking
• 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
Overview 50
OSI 7-layer : A Top-Down ViewOSI 7-layer : A Top-Down View
• Application layer (Layer 7)
~ 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)
• 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
Overview 51
• Session layer (Layer 5)
~ Supports the dialog between cooperating application programs
~ Issues: - Session/dialog establishment/maintenance/termination
- Synchronization of dialog
- Recovery (from error) or backup via checkpoints
~ Example: ISO session protocol, RPC (Remote Procedure Call)
(The lower four layers provide reliable data exchange and quality of service.)
• Transport layer (Layer 4)
~ Controls the delivery of messages/data between the end stations
(at a pre-negotiated service quality) (e.g., reliable ?)
~ Issues: - Connection establishment/management/termination
- Error control and/or flow/congestion control(if required)
~ Example: TCP, UDP, SPX (Netware’s Sequenced Packet eXchange)Overview 52
• Network layer (Layer 3)
~ transfer of data between end systems across a communication
network
~ Issues: - Addressing (locating a host in the network)- Routing (data packet forwarding) & Congestion control
~ Example: IP (Internet Protocol), IPX, CCITT X.25 (network layer)
• 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
(InterPacket eXchange Protocol)
Overview 53
Remark:
- Layer 4 and above (referred to “higher layer”) are End-to-End
protocols (executed only on host computer)
- Not all 7 layers are needed
- Many layered protocol architectures do not define the session
or the presentation layer. ( Example )
- Define sublayers if necessary (later on)
• Physical layer (Layer 1)
~ Concerned with (only) transmission of bits over a communicationchannel (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)
Overview 54
MODEM Example
Overview 55
FTP Operation - Combining higher layers
Host A (FTP client) Host B (FTP server)
Internetwork
Control connection (at initial)
Data connection (by request)
AP L.C.
PL L.C.
SL L.C.
Overview 56
SummarySummary -- OSI LayersOSI Layers
- Physical ~ transmission of bits over communicationchannel (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 betweenstations/nodes
- Session ~ dialog between cooperating application programs(login and password)
- Presentation ~ data representation of information and compatibility
- Application ~ individual application program for users
Overview 57
OSI model in Point-to-Point Communication
• How are data transmitted under the OSI model ?
PDU
Encapsulation Decapsulation
100110101101010201101000010 . . .
Physical (transmission media)(via channel or network)
Data
Message
Information
bits
Frame
Packet
Segment
Signal
Overview 58
Protocol Layering Networked Communication
Transport
Presentation
Session
Data Link
Physical
Network
Application
Transport
Presentation
Session
Data Link
Physical
Network
Application
Station/Host A Station/Host B
IS or Node
network
IS (Intermediate System) :L7 Gateway*L3 RouterL2 Switch/BridgeL1 Hub/Repeater
Data Link
Physical
Network
Data Link
Physical
Network
Data Link
Physical
Network
Data Link
Physical
Network(protocol stack inOne computer)
IS - so called Intermediate Message Processor,IMP (refer to ISO Network Hierarchy)
L3L2L1
datadata datadata
datadata
Overview 59
Internet Protocol StackInternet Protocol Stack
• Application: supporting networkapplications– FTP, SMTP, HTTP, SMTP, POP3
• Transport: host-host data transfer– TCP, UDP
• Network: routing of datagrams fromsource to destination– IP,ICMP, IGMP, RIP,OSPF, BGP4
• Link: data transfer between neighboringnetwork elements– PPP/SLIP, Ethernet, Token-Ring
• Physical: bits “on the wire” - transmission
application
transport
network
link
physical
Network Access
Overview 60
Layering: logical communication
Ex: transport layer• take data from appl.
• add addressing, reliability check info to form “datagram”
• send datagram to peer
• wait for peer to Ackreceipt
applicationtransportnetwork
linkphysical
transport
applicationtransportnetwork
linkphysical
transport
applicationtransportnetwork
linkphysical application
transportnetwork
linkphysical
networklink
physical
data
data
Logical comm.
data
ack
Overview 61
Layering: physical communication
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
networklink
physical
data
dataHost A
Host B
Overview 62
Protocol 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)
Higher-layer see nothing pealed off; Lower-layer cannot see misunderstood
applicationtransportnetwork
linkphysical
source
applicationtransportnetwork
linkphysical
destinationMMMM
Ht
HtHnHtHnHl
MMMM
Ht
HtHnHtHnHl
messagesegmentdatagramframe
Encapsulation Decapsulation
network(s)
Overview 63
Protocol Data Unit (PDU) in TCP/IP Architecture
TCP header IP header
DLL Frame
InternetProtocolStack
DLL header
Host A
NIC
Meaningful to appropriate peerprotocol software module Overview 64
PDU Decomposition in TCP/IP Scenario
Windows> telnet 140.124.70.26 (showing the first packet transmitted by the src PC)
Protocol #: Network--Transport layer
Source’s MAC addressDest.’s MAC address
Protocol type: DLC--Network layer
Overview 65
(PDU cont’d)
Src port # (randomly generated by the src PC)Dest port # (an well-known for well-known application)
Port #: Transport--Application layer
(More on Layer communication)Overview 66
Layering: internetworking communication(summary)
(Layer 3 device)(Layer 2 device)
hostIS (Intermediate Systems) :
L7 Gateway*L3 RouterL2 Switch/BridgeL1 Hub/Repeater
Anything below 2 or above 3 ?
• Hosts, routers, switches, and bridges; each contains a different set of layers, reflecting their differences in functionality.
Overview 67
IEEE 802 ProjectIEEE 802 Project
• IEEE 802.1 High Level Interface
• IEEE 802.2 LLC (Logical Link Control) Working Group
• IEEE 802.3 CSMA/CD (Carrier Sense Multiple Access with
Collision Detection)**
• IEEE 802.4 Token-Bus WG
• IEEE 802.5 Token-Ring WG
• IEEE 802.6 DQDB (Distributed Queue Dual Bus) [MANWG]
• IEEE 802.7 Broadband Technical Advisory Group
• IEEE 802.8 Fiber Optic Technical Advisory Group
• IEEE 802.9 Integrated Voice and Data LAN Working Group
• IEEE 802.10 LAN Security Working Group
• IEEE 802.11 Wireless LAN (WLAN)**
• IEEE 802.12 Demand-Priority (100VG-AnyLAN)
Ethernet
ARCnet
IBM token-ring
LM
SG
Overview 68
More on IEEE 802.xMore on IEEE 802.x• IEEE 802.14
– Cable-TV based broadband communication network• IEEE 802.15
– Wireless personal area network (WPAN) **• IEEE 802.16
– Broadband wireless access (BBWA) **• IEEE 802.17
– Resilient Packet Ring Working Group• IEEE 802.18
– Radio Regulatory TAG• IEEE 802.19
– Coexistence Technical Advisory Group (coexistence with existing standards and other standards)
• IEEE 802.20– Wide area broadband wireless access (WBWA)
(Most of them are in hibernation.)
Overview 69
Issues of DLC in DLLIssues of DLC in DLL
• Physical layer
~ concerns sending signalssignals over a transmission (physical) link
• Data link layer
~ a logic added above physical interface~ concerns sending datadata over a communication link
• With a Data Link Control protocol, the transmission media between systems is referred to as a data link.
• Major issues
- Framing (Frame synchronization) - Flow control- Error detection and error control - Addressing- Exchange of data, control Link and management
Sublayer concept
Overview 70
Medium Access ControlMedium Access Control
• Why separate DLL to sublayers - LLC and MAC ?
- many DLL w/o access mechanism to a sharedshared--accessaccess medium
- under the same LLC, several MAC options may be provided
• MAC sublayer appends control information at the front and back
of LLC PDU, forming a MAC frame
• Multiple Access
- a set of rules to control the access to a sharedcommunication medium(called channel)
- conflicting access to the channel may be happened- mostly for broadcasting channels- Ex: shared-media LANs (such as Ethernet-Bus, wireless)
Overview 71
OSI’s DLL vs IEEE 802.2 (LLC and MAC)OSI’s DLL vs IEEE 802.2 (LLC and MAC)
• LLC (Logical Link Control (LLC) ) sublayer- refers upward to higher-layer software functions (using IEEE 802.2)
- provides for environments that need connectionless and connection-oriented
• MAC (Media Access Control (MAC) ) sublayer
- refers downward to lower-layer hardware functions (using IEEE 802.3x )
- provides access to the LAN medium in an orderly manner.- several MAC options may be provided for the same LLC
Medium Access Control (MAC)
DLLsublayers
Logical link Logical link ControlControl (LLC)(LLC)Data
LinkLayer
Splitting
Especially in LAN environments
Overview 72
Calls for Addressing ( )Calls for AddressingCalls 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 ona computer
(entity, )
. . .
End-point (in TCP/IP-based Internet)
Overview 73
Data Link Layer’s Address
• Data-link layer address
- uniquely identifies each physical network connection of a device
- also referred to as physical or hardware address
- usually exist within a flat address space
Data Link Layer’s Address
pre-established and typically fixed relationship to a specific device
MAC/NIC address in a LAN Overview 74
Physical/MAC Address – the NIC’s ID
DFE 540TX
RJ-45 Jack NIC ~ Network Interface Card ( )ID ~ identifier ( )
Overview 75
Check with your MAC Address via “ winipcfg ”
Manufacturer’s ID NIC’s ID/Serial number
242 's
IEEE’s EIU-48 rule
* Alternate: “ipconfig -all”, “netstat –r” command under MS NT/2000/XP Overview 76
Connection-Oriented and Connectionless ServicesConnection-Oriented and Connectionless Services
• Connection-Oriented (CO) service- 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)
• Connectionless (CL) service- 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- Receiving of frame/Packet 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)
(between end-systems)