Bob Baker Communications Bob Baker September 1999

Bob Baker Section 1 Communications and networks Communications services Data equipment OSI reference model Encapsulation

Bob Baker Communications and Networks Data Communications –Sender –Receiver –Channel (medium) –Message Telecommunications –At a distance Sender Receiver

Bob Baker Communications Services Network

Bob Baker Services Sharing files (databases, applications) Sending messages ( , 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)

Bob Baker medium Data Equipment Data Terminal (hosts) Data Switching Data Communication

Bob Baker Data Terminal Equipment Workstations PCs Printers File Servers Application Servers DTE

Bob Baker Data Communications Equipment Modems ISDN adapters Satellite (and base stations) Microwave stations Network Interface Cards (NICs) DCE

Bob Baker Data Switching Equipment Hubs Bridges Switches Routers Gateways DSE

Bob Baker A campus network

Bob Baker 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 SenderReceiver

Bob Baker 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

Bob Baker 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 – , Web browser, Directory –POP, SMTP, FTP, HTTP, DNS –Sockets –TCP –IP –PPP, Ethernet, Token ring –100baseT

Bob Baker Encapsulation Application Presentation Session Transport Network Data Link Physical data Device 1Device 2 data H6T6 data H5T5 data H4T4 (packet) H3 data T3 H2 data T2H1 data T1 carrier frame Application Presentation Session Transport Network Data Link Physical frame A typical frame Destination Address Source Address DataPaddingCRCPreamble

Bob Baker Section 2 Layer 1 (Physical) –Media and Bandwidth –Speeds –Handling errors in signal transmission Dial up connections –Modulation/Demodulation

Bob Baker Data format (7E1)(7bits Even parity 1 stop bit) B Parity bit Stop bit Data bits

Bob Baker Section 3 Layer 2 (Data Link) –Local Area Network topologies Bus Ring Star –Hardware addresses –Line access Polling Token passing CSMA/CD

Bob Baker LAN topologies Three common topologies

Bob Baker 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

Bob Baker 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

Bob Baker Media access and addressing Data link AA:F1 Data link AB:F3AA:C2A1:53 AB:F3data Each node only has to check the destination address of the frame This happens at the Data link level data A1:53AB:F3dataA1:53AB:F3data

Bob Baker 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.

Bob Baker Client / Server

Bob Baker 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]

Bob Baker HUB / BRIDGE / ROUTER / GATEWAY

Bob Baker 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)

Bob Baker Hubs Hub passes packets at physical layer without processing

Bob Baker Hubs/Bridge Bridge checks packets at data link layer

Bob Baker Bridged rings

Bob Baker Switched rings

Bob Baker Bridge Tables H 265 H B/S H portMAC Bridge table

Bob Baker Wide Area Networks Point to Point Uses PPP Usually an ISDN or dedicated line B/S H B/SH

Bob Baker Section 5 Layer 3 (Network level) Internet Protocol –Internet addresses –TCP/IP Routers and Gateways

Bob Baker Sample hybrid topology

Bob Baker Hybrid Network

Bob Baker Internet connectivity

Bob Baker Hub/Switch/Router

Bob Baker Bridging and Routing Internets Bridge same network Route across different networks

Bob Baker Domains

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Internet (IP) Addresses Addresses 32 bit binary written as “dotted quad” = Class C addresses (network part in blue) – to – Private Intranet addresses – to – –Allows 254 hosts on each network Network numbers assigned by ISP or interNIC

Bob Baker 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

Bob Baker 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 address AA:12:34:21 Machine address :11:7A: nAA:12:23:A This is a router

Bob Baker 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

Bob Baker 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.

Bob Baker Routers (concluded) Physical Data Link Physical Data Link Physical Network Layer A router with three interfaces Net 1 Net 2 Net 3

Bob Baker Gateways Operate up to Layer 7 Many of the functions of Routers Include security, authentication, access Firewalls, Cache servers, Proxy servers

Bob Baker An Intranet With two subnets H H R Internet

Bob Baker Section 6 Transport Layer Transmission Control Protocol –Handshaking –Sequencing –Error checking Effectively creates a connection between hosts

Bob Baker 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

Bob Baker TCP processes Sender Receiver SynAck PacAckFinAck Fin Pac Ack Pac Ack

Bob Baker