Bob Baker Communications Bob Baker September 1999.
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Transcript of Bob Baker Communications Bob Baker September 1999.
Bob Baker
Communications
Bob Baker
September 1999
Bob Baker
Section 1
• Communications and networks
• Communications services
• Data equipment
• OSI reference model
• Encapsulation
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Communications and Networks
• Data Communications– Sender– Receiver– Channel (medium)– Message
• Telecommunications– At a distance
Sender
Receiver
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Communications Services
Network
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Services
• Sharing files (databases, applications)• Sending messages (e-mail, chat)• Collecting information (remote sensing)• Controlling devices (home automation)• Transferring funds (EFTPOS, E-commerce)• Transaction processing (ordering, booking)• Sharing information (WWW, libraries)• Sharing resources (printers, storage)
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medium
Data Equipment
Data Terminal (hosts)
Data Switching
Data Communication
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Data Terminal Equipment
• Workstations
• PCs
• Printers
• File Servers
• Application Servers
DTE
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Data Communications Equipment
• Modems
• ISDN adapters
• Satellite (and base stations)
• Microwave stations
• Network Interface Cards (NICs)
DCE
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Data Switching Equipment
• Hubs
• Bridges
• Switches
• Routers
• Gateways
DSE
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A campus network
http://www.comms.unsw.EDU.AU/net98/images/h_diagrm.jpg
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Open Systems Interconnection
• OSI Reference model– Layer 7 application– Layer 6 presentation– Layer 5 session– Layer 4 transport– Layer 3 network– Layer 2 data link– Layer 1 physical
Channel
Sender Receiver
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Services
– Layer 7 application
– Layer 6 presentation
– Layer 5 session
– Layer 4 transport
– Layer 3 network
– Layer 2 data link
– Layer 1 physical
– Identification, authentication
– Format conversion
– Set-up and coordinate conversation
– Ensures complete, error-free transfer
– Routing of data through network
– Error control and synchronisation
– Placing signals on the carrier
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Sample- Internet protocol suite
– Layer 7 application
– Layer 6 presentation
– Layer 5 session
– Layer 4 transport
– Layer 3 network
– Layer 2 data link
– Layer 1 physical
– E-mail, Web browser, Directory
– POP, SMTP, FTP, HTTP, DNS
– Sockets
– TCP
– IP
– PPP, Ethernet, Token ring
– 100baseT
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Encapsulation
Application
Presentation
Session
Transport
Network
Data Link
Physical
dataDevice 1 Device 2
dataH6 T6
dataH5 T5
dataH4 T4
(packet)H3 data T3
H2 data T2
H1 data T1
carrier frame
Application
Presentation
Session
Transport
Network
Data Link
Physical
frameframe frame
A typical frame DestinationAddress
SourceAddress
Data Padding CRCPreamble
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Section 2
• Layer 1 (Physical)– Media and Bandwidth– Speeds– Handling errors in signal transmission
• Dial up connections– Modulation/Demodulation
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Data format
1 0 0 0 0 1 001
(7E1) (7bits Even parity 1 stop bit)
B
Parity bitStop bit
Data bits
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Section 3
• Layer 2 (Data Link)– Local Area Network topologies
• Bus
• Ring
• Star
– Hardware addresses– Line access
• Polling
• Token passing
• CSMA/CD
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LAN topologies
• Three common topologies
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Hardware addresses
• At Data Link level
• Each Host (actually the interface) has a unique number
• Usually 48 bits and built in by manufacturer
• Example is the Ethernet Interface number
• Different to Internet Address
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Line access
• Polling– Each station is given a turn at accessing the line
• Token passing (as in Token Ring)– Token passed, only access the line when you have the
token
• CSMA/CD (as in Ethernet)– Carrier sense– Multiple access– Collision detection
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Media access and addressing
Data linkAA:F1 Data link Data link Data linkAB:F3 AA:C2 A1:53
A1:53 AB:F3 data
Each node only has to check the destination address of the frame
This happens at the Data link level
data
data
data
A1:53 AB:F3 data A1:53 AB:F3 data
data
data
data
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Servers
• Peer-to-peer– All nodes have equal status.
• Client/server– Server provides services for clients– Web servers, print servers, mail servers etc
• Master/slave– Master processor controls operation of many slave
processors.– Eg slave robots.
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Client / Server
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Section 4
• Connecting and segmenting LANS– Physical level [Hubs]– Data Link level [Bridge] / [LAN Switch] /
[Switching Hub]– Network level [Routers] / [Multilayer Switch]– Application level [Gateways]
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HUB / BRIDGE / ROUTER / GATEWAY
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Segmenting LANS• Why
– Reduce wiring– Reduce and restrict traffic– Extend distance, maintain speed– Use same protocols
• How– Hub (layer 1)– Bridge (layer 2)– LAN Switch (layer 2)
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Hubs
Hub passes packets at physical layer without processing
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Hubs/Bridge
Bridge checks packets at data link layer
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Bridged rings
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Switched rings
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Bridge Tables
345
127
H
265H
215
614299
B/S1
2
3
387
H122
345 437
132
portMAC345215299127614132
1331
Bridge table
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Wide Area Networks
• Point to Point
• Uses PPP• Usually an ISDN or dedicated line
B/S
H345
127
265B/S
H122
345 437
132387
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Section 5
• Layer 3 (Network level)
• Internet Protocol– Internet addresses– TCP/IP
• Routers and Gateways
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Sample hybrid topology
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Hybrid Network
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Internet connectivity
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Hub/Switch/Router
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Bridging and Routing Internets
• Bridge same network
• Route across different networks
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Domains
• WWW.edfac.usyd.edu.au
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Internet (IP) Addresses
• Addresses 32 bit binary written as “dotted quad”• 11000000101010000000000100000000 = 192.168.1.0
• Class C addresses (network part in blue)– 192.0.0.0 to – 223.0.0.0
• Private Intranet addresses– 192.168.0.0 to– 192.168.255.0
– Allows 254 hosts on each network
• Network numbers assigned by ISP or interNIC
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Internet Protocol
• IP Operates at the Network Layer (3)
• Packages up data into packets
• Each packet has a source IP address and a destination IP address
• Packet passed to Data Link layer where machine address is determined
• Packaged into a frame at Physical level
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Address Resolution
• Address Resolution Protocol• Hardware address from IP address
– Each Interface has two addresses• Hardware address and Internet address
– ARP Matches Machine address to IP address– Table kept in ARP cache on each machine
Internet address192.168.1.1 AA:12:34:21
Machine address
192.168.1.4 12:11:7A:12192.168.1.n AA:12:23:A6
192.168.1.2
This is a router
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Routers
• Operate at Network Layer
• Connect networks
• Have an interface for each network they connect– Each of these interfaces has:
• An IP address
• A machine address
• Forward IP packets based on routing table and algorithms
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Routers (continued)
• Generally Hardware & Software
• Can filter packets
• Can convert protocols between different networks– Eg can link an Ethernet to a token ring
• Can be managed, secured and set up to “sniff” packets passing through.
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Routers (concluded)
PhysicalData Link Data Link
PhysicalData LinkPhysical
Network Layer
A router with three interfaces
Net 1
Net 2
Net 3
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Gateways
• Operate up to Layer 7
• Many of the functions of Routers
• Include security, authentication, access
• Firewalls, Cache servers, Proxy servers
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An Intranet
• With two subnets
192.168.1.4
192.168.1.1
192.168.1.2
H
192.168.1.0
H192.168.1.37
192.168.1.36 192.168.1.40
192.168.1.41192.168.1.33
192.168.1.32
R192.168.1.8
192.168.1.44
Internet
192.168.1.65
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Section 6
• Transport Layer
• Transmission Control Protocol– Handshaking– Sequencing– Error checking
• Effectively creates a connection between hosts
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What TCP does
• Handshaking– Does the destination exist– Establish port connection– Establish appropriate size of packet
• Create and send packets– Break up message– Create and number packet– Pass to IP and wait for acknowledgement
• Terminate connection
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TCP processes
Sender Receiver
SynAckAck
PacAck
FinAck
AckFin
PacAck
PacAck
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