Networks

Operating Systems: A Modern Perspective, Chapter 15

Slide 15-1

Copyright © 2004 Pearson Education, Inc.


Slide 15-2


15Networks


Slide 15-3


Connecting Computers Using the Telephone Network

SerialPort

SerialPortMemoryMemory

CPUCPU

SerialPort

SerialPort MemoryMemory

CPUCPU

Switched Telephone NetworkSwitched Telephone Network

Modem Modem

Local Computer Remote Computer


Slide 15-4


Data Networks

NetworkDevice

NetworkDeviceMemoryMemory

CPUCPU

NetworkDevice

NetworkDevice MemoryMemory

CPUCPU

Specialized Data NetworkSpecialized Data Network

•WANs, MANs, and LANs•Specialized communication protocols•Multidrop•Packet oriented•Looks like other devices… make it look like a file ...


Slide 15-5


Multidrop Network

S

RR

S

Network

• Multiple senders• Can address multiple receivers


Slide 15-6


Packet Network

S

RR

S

Circuit Based

Telephone

R

S S

RPacket Based

Data


Slide 15-7


Multidrop Packet Network

• To transmit/receive:– Sender marshals data into a packet– Network interface hardware transforms data for

physical transmission– Network deliver packets to variable destination– Receiver converts physical signal back into a

data packet– Receiver unmarshals packet into data

• Need a widely-agreed upon set of protocols


Slide 15-8


Protocol Tasks• Control information delivery rates

• Pass data across networks

• Provide fast/reliable IPC-like communication

• Support logical byte streams

• Create other models for communication– File transfer– Procedure call paradigm– Shared memory paradigm

• Translate machine-dependent data representations

• … and more …


Slide 15-9


Standardizing Protocols

• ANSI X.25

• ARPAnet

• ISO Open Systems Interconnect (OSI) model– Now widely used as a reference architecture– 7-layer model– Provides framework for specific protocols (such

as IP, TCP, FTP, RPC, RSVP, …)


Slide 15-10


ISO OSI Model

ApplicationPresentation

SessionTransportNetwork

Data LinkPhysical



Data LinkPhysical


Slide 15-11


ISO OSI Model

Data LinkPhysical

Data LinkPhysical

•Physical/Data Link layer networks: Ethernet, Wireless, ATM•Often called the “media access control” (MAC) layer

Examples


Slide 15-12


Low Level Protocols

• Physical layer: Signaling technology

• Data link layer: Frame management

• All done in hardware

• Examples– Ethernet– Token ring– X.25– ATM


Slide 15-13


Ethernet (CSMA/CD)

• Asynchronous• Carrier Sense• Multiple Access• Collision Detection• Backoff


Slide 15-14


Wireless

Backbone

•IEEE 802.11 (“WiFi”)•IEEE 802.15 (“Bluetooth”)

Ad hoc networks


Slide 15-15


Stop-and-wait Flow Control

Sender transmits a frame;Sender sets a time-out on the transmission;Sender waits for an ACKnowledgment;...if (Sender receives ACKnowledgment) continue;if (frame times-out) Retransmit timed-out frame;(a) Transmitter Receiver accepts the frame; Receiver transmit the ACKnowledgment;(b) Receiver


Slide 15-16


ISO OSI Model

NetworkData LinkPhysical

NetworkData LinkPhysical

•Physical/Data Link layer networks: Ethernet, Token Ring, ATM•Network layer net: The Internet

Examples


Slide 15-17


Network Layer

• Primary purpose is to combine networks

• Internet protocol (IP) is dominant protocol

• Creates an internet address space

• Implements packet routing across networks

Host XHost X

Host RHost R Host SHost S Host YHost Y

Network B Network CNetwork A


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Addressing & Routing

Host XHost X

Host RHost R Host YHost Y

Network CNetwork A

3b4e87

3b4e62 3b4e55 3b621a

3b6209

•Host X does not know how to send to Host Y•Can send a frame to Host R for forwarding•What should it tell Host R?


Slide 15-19



Host XHost X


Network CNetwork A

•Host X does not know how to send to Host Y•Can send a frame to Host R for forwarding•What should it tell Host R?•Internet address spans all machines

3b4e87

3b4e62 3b4e55 3b621a

3b6209

128.123.234.033

128.123.234.188 128.229.244.006

128.229.244.109

128.123.234.063

To: 128.229.244.006From: 128.123.234.033Network Layer data


Slide 15-20



Host XHost X


Network CNetwork A

•Host X does not know how to send to Host Y•Can send a frame to Host R for forwarding •What should it tell Host R?•Internet address spans all machines•Send encapsulated packet to Host R with Host Y

3b4e87

3b4e62 3b4e55 3b621a

3b6209

128.123.234.033

128.123.234.188 128.229.244.006

128.229.244.109

128.123.234.063

To: 3b4e55From: 3b4e87



Slide 15-21



Host XHost X


Network CNetwork A

•Host X does not know how to send to Host Y•Can send a frame to Host R for forwarding •What should it tell Host R?•Internet address spans all machines•Send encapsulated packet to Host R with Host Y

3b4e87

3b4e62 3b4e55 3b621a

3b6209

128.123.234.033

128.123.234.188 128.229.244.006

128.229.244.109

128.123.234.063

Host SHost S

Network B


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Host XHost X


Network CNetwork A

•Host X does not know how to send to Host Y•Can send a frame to Host R for forwarding•What should it tell Host R?•Internet address spans all machines•Send encapsulated packet to Host R with Host Y•Data Link frame is received by Host Y

3b4e87

3b4e62 3b4e55 3b621a

3b6209

128.123.234.033

128.123.234.188 128.229.244.006

128.229.244.109

128.123.234.063

To: 3b621aFrom: ...


Network B


Slide 15-23


More on the Network Layer

• Implements internet addressing & routing

• ARPAnet IP protocol is dominant – the foundation for the Internet

• Intermediate hosts are called gateways– Connected to two or more networks– Runs IP routing software– Read pages 496-501


Slide 15-24


Using Data Link and Network Layer Addresses

NetworkLayer

Data LinkLayer

0x80C31A80837E

128.123.234.012

Dat

a L

ink

Lay

er F

ram

e

Net

wor

k L

ayer

Pac

ket


Slide 15-25


ISO OSI Model

TransportNetwork

Data LinkPhysical

TransportNetwork

Data LinkPhysical

•Physical/Data Link layer networks: Ethernet, Token Ring, ATM•Network layer net: The Internet•Transport layer net: TCP-based network

Examples


Slide 15-26


Transport Layer• Provides yet another address extension

– IP references only networks and hosts– Transport layer adds ports -- logical endpoints– Address form is <net, host, port>

• Two primary protocols (both from ARPAnet)– User Datagram Protocol (UDP)

• User-space interface to IP packets

• No guarantee that packet will be delivered

– Transmission Control Protocol (TCP)• Provides a stream-oriented interface to the network

• Reliable delivery


Slide 15-27


ISO OSI & TCP/IP

MACMAC

ISO OSI NetworkISO OSI Network

ISO OSI TLIISO OSI TLI

ISO OSI SessionISO OSI Session

ISO OSI packet

ISO OSI frame

EthernetEthernet

ARPAnet IPARPAnet IP

ARPAnet TCPARPAnet TCP


ISO OSI packet

IP frame

Ethernet packet


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Domain Name Server (DNS)

• IP uses 32-bit addresses– 128.138.241.1– “anchor.cs.colorado.edu”

• DNS: anchor.cs.colorado.edu128.138.241.1• Huge table

– Distributed/managed according to domain– .edu, .com, .net, .gov, … .us, .ca, are domains– .colorado is a sub domain managed by CU– .cs is a sub domain managed by Computer Sci– anchor is a computer in .cs (in .colorado, in .edu)– anchor is on net 128.138.241, and is host number 1


Slide 15-29


DNS

First-Level Domain

.edu

.colorado

.cs

anchor

pawneeneon

.edu Domain

.colorado Domain

.cs Domain

• Supports TCP• Uses UDP


Slide 15-30


The DNS Protocol Stack

EthernetEthernet

ARPAnet IPARPAnet IP

ARPAnet UDPARPAnet UDP

DNS ResolverDNS Resolver

UDP packet

IP frame

Ethernet packet

UDP packet

MACMAC

ISO OSI NetworkISO OSI Network

ISO OSI TLIISO OSI TLI


ISO OSI packet

ISO OSI frame


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Communication Ports• Global name for a “mailbox”

• Will be many ports at one <net, host>

Transport Layer

Network Layer

Low Layers

P P P P

ports

0 1 2 n

port numbers

mumble.cs.colorado.edu

Host: 34Net: 128.138.34

DN

S r

esol

ve


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Communication Ports• Global name for a “mailbox”

• Will be many ports at one <net, host>

• Each port can be bound to an address

P P P P

Transport Layer

Network Layer

Low LayersHost: 34On Net 128.138.34

128.138.249.34

<128.138.249, 34, 1>

0 1 2 n


Slide 15-33


Sharing Names

(5623, 56, 2046)(3456, 77, 6785)

(9876, 88, 3434)(31978, 12, 1234)

Port 1234

Process A on Host #12 on Net #31978

Bind

The OS on Host #12 on Net #31978

send(…,(31978, 12, 1234), …);

Process BProcess A

Transport Layer Global Address Space

0x001a4772


Slide 15-34


BSD Sockets

• Sockets are comm ports in UNIX, Windows, etc.• Semantics resemble pipes (files)• Bidirectional

int socket(int addressFamily, int socketType, int protocolNo)

ss = socket(…)


Slide 15-35


BSD Sockets (cont)• Once a socket has been created, it can be

bound to an internet port

P

s


Slide 15-36


BSD Sockets (cont)• Once a socket has been created, it can be

bound to an internet port

int bind(int skt, struct sockadrr *addr, int addrLength)

P

s


Slide 15-37


UDP

• Datagram (“connectionless”) service– Similar to disk I/O level of service

• Logically associated with an IP packet & Data Link frame (but not physically)

• Best-effort delivery of datagrams, but:– Datagram may be dropped (lost)– Datagrams may be delivered out of order

• Efficient, relative to TCP


Slide 15-38


Using UDP/* Set up a socket to talk to the server */ skt = socket(AF_INET, SOCK_DGRAM, 0); host = gethostbyname(remoteHostName); bzero(&remote, sizeof(remote)); remote.sin_family = host->h_addrtype; remote.sin_port = htons(remotePort); bcopy(host->h_addr, &remote.sin_addr, host->h_length);/* Export the socket to a port (and IP address) */ host = gethostbyname(localHostName); bzero(&local, sizeof(local)); local.sin_family = host->h_addrtype; local.sin_port = htons(localPort); bcopy(host->h_addr, &local.sin_addr, host->h_length); if(bind(skt, &local, sizeof(local))) { printf("Bind error ... restart\n"); exit(1); } . . . sendto(s, outBuf, strlen(outBuf), 0, remote, sizeof(remote)); if((len = recv(s, inBuf, BUFLEN, 0)) > 0) {. . .}


Slide 15-39


TCP

• Connected (or virtual circuit) protocol

• Interface allows programmer to read/write a byte stream over the network

• Byte stream is mapped into a series of packets– Reliable delivery– Each packet must be acknowledged– Effectively 2 packets per transmission

• Must open/close a connection before use


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Using TCP -- Client

skt = socket(AF_INET, SOCK_STREAM, 0);host = gethostbyname(serverHostName);bzero(&listener, sizeof(listener));listener.sin_family = host->h_addrtype;listener.sin_port = htons(port);bcopy(host->h_addr, &listener.sin_addr, host->h_length);if(connect(skt, &listener, sizeof(listener))) { printf("Connect error ... restart\n"); printf("(Must start Server end first)\n"); exit(1);};. . .write(s, outBuf, BUFLEN);if((len = read(s, inBuf, BUFLEN)) > 0) {. . .}


Slide 15-41


Using TCP -- Serverskt = socket(AF_INET, SOCK_STREAM, 0); /* Produce an inet address */host = gethostbyname(serverHostName);bzero(&listener, sizeof(listener));listener.sin_family = host->h_addrtype;listener.sin_port = htons(port);bcopy(host->h_addr, &listener.sin_addr, host->h_length);if(bind(skt, &listener, sizeof(listener))) { printf("Bind error ... restart\n"); exit(1);}listen(skt, BACKLOG); /* Listen for a request */newSkt = accept(skt, &client, &clientLen);if (fork() == 0) { close(skt); /* Child doesn't need listener socket */ . . .}close(newSkt); /* Parent doesn't need the new socket */

if((len = read(s, inBuf, BUFLEN)) > 0) { . . .}write(s, outBuf, BUFLEN);


Slide 15-42


ISO OSI Model

PresentationSession

TransportNetwork

Data LinkPhysical

PresentationSession

TransportNetwork

Data LinkPhysical

•Physical/Data Link layer networks: Ethernet, Token Ring, ATM•Network layer net: The Internet•Transport layer net: TCP-based network•Presentation/Session layer net: http/html, RPC, PVM, MPI

Examples


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ISO OSI ModelApplicationPresentation


Data LinkPhysical



Data LinkPhysical

•Physical/Data Link layer networks: Ethernet, Token Ring, ATM•Network layer net: The Internet•Transport layer net: TCP-based network•Presentation/Session layer net: http/html, RPC, PVM, MPI•Applications, e.g., WWW, window system, numerical algorithm

Examples


Slide 15-44


A Firewall

Organization’sIntranet

FirewallFirewall

Internal HostInternal Host

Internal HostInternal Host Internal HostInternal Host

Internal HostInternal Host

Internet


Slide 15-45


Client-Server Paradigm

• Making a connection in TCP is an example of the client-server paradigm for distributed computing– Active component is the client

• Runs autonomously

• Decides when it wants to use server

– Passive component is the server• Persistent

• Always waiting for a client to request service

• Not a machine -- just software

Documents

Networks