Figure 15.1 A distributed multimedia system

Figure 15.1 A distributed multimedia system

Slides for Chapter 9: Name Services
From Coulouris, Dollimore and Kindberg
Distributed Systems:
Concepts and Design
Edition 4, © Pearson Education 2005
Figure 9.1
Composed naming domains used to access a resource from a UR
URL
http://www.cdk3.net:8888/WebExamples/earth.html
DNS lookup
Resource ID (IP number, port number, pathname)
55.55.55.55
8888 WebExamples/earth.html
Web server
Network address
file
2:60:8c:2:b0:5a
Socket
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Figure 9.2
Iterative navigation
NS2
2
Client
1
NS1
Name
servers
3
NS3
A client iteratively contacts name servers NS1–NS3 in order to resolve a name
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Figure 9.3
Non­recursive and recursive server­controlled navigation
NS2
NS2
2
2
1
client
4
NS1
client
3
1
4
NS1
3
5
NS3
NS3
Non­recursive
server­controlled
Recursive
server­controlled
A name server NS1 communicates with other name servers on behalf of a client
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Figure 9.4
DNS name servers
a.root­servers.net
(root)
Note: Name server names are in italics, and the corresponding domains are in parentheses. Arrows denote name server entries ns1.nic.uk
(uk)
co.uk
ac.uk
uk
purdue.edu
yahoo.com
ns0.ja.net
(ac.uk)
ns.purdue.edu
(purdue.edu)
* .purdue.edu
ic.ac.uk
qmw.ac.uk
dcs.qmw.ac.uk
*.qmw.ac.uk
*.dcs.qmw.ac.uk
alpha.qmw.ac.uk
(qmw.ac.uk)
dns0.dcs.qmw.ac.uk
(dcs.qmw.ac.uk)
*.ic.ac.uk
dns0­doc.ic.ac.uk
(ic.ac.uk)
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Figure 9.5
DNS resource records
Record type Meaning
Main contents
A
NS
CNAME
SOA
WKS
PTR
IP number
Domain name for server
Domain name for alias
Parameters governing the zone
List of service names and protocols
Domain name
HINFO
A computer address
An authoritative name server
The canonical name for an alias
Marks the start of data for a zone
A well­known service description
Domain name pointer (reverse
lookups)
Host information
MX
TXT
Mail exchange
Text string
Machine architecture and operating
system
List of < preference, host> pairs
Arbitrary text
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Figure 9.6
DNS zone data records
domain name time to live
1D
1D
1D
1D
1D
class
type
value
IN
IN
IN
IN
IN
NS
NS
NS
MX
MX
dns0
dns1
cancer.ucs.ed.ac.uk
1 mail1.qmul.ac.uk
2 mail2.qmul.ac.uk
domain name
time to live class
type value www apricot 1D 1D IN IN CNAME A apricot 138.37.88.248 dcs dns0.dcs dcs dns1.dcs dcs 1D 1D 1D 1D 1D IN IN IN IN IN NS A NS A NS dns0.dcs
138.37.88.249
dns1.dcs
138.37.94.248
cancer.ucs.ed.ac.uk
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Figure 9.7
GNS directory tree and value tree for user Peter.Smith
DI: 599 (EC)
DI: 543
DI: 574
AC
DI: 437
DI: 322
UK FR
QMW
Peter.Smith
mailboxes
Alpha
Beta
password
Gamma
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Figure 9.8
Merging trees under a new root
DI: 633 (WORLD)
Well­known directories:
#599 = #633/EC
#642 = #633/NORTH AMERICA
NORTH AMERICA
EC
DI: 599
DI: 543
UK
DI: 642
FR
DI: 574
DI: 732
US
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 CANADA
DI: 457
Figure 9.9
Restructuring the directory
DI: 633 (WORLD)
Well­known directories:
#599 = #633/EC
#642 = #633/NORTH AMERICA
EC
DI: 599
DI: 543
UK
NORTH AMERICA
DI: 642
FR
US
DI: 574
DI: 732
US
CANADA
DI: 457
#633/EC/US
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Figure 9.10
X.500 service architecture
DUA
DUA
DSA
DSA
DSA
DSA
DUA
DSA
DSA
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Figure 9.11
Part of the X.500 Directory Information Tree
X.500 Service (root)
... France (country)Great Britain (country)Greece (country)
...
... BT Plc (organization)University of Gormenghast (organization)
...
... Computing Service (organizationalUnit)
Department of Computer Science (organizationalUnit)
Engineering Department (organizationalUnit)
...
... Departmental Staff (organizationalUnit)
ely (applicationProcess)
Research Students (organizationalUnit)
...
... Alice Flintstone (person)... Pat King (person)James Healey (person)
Janet Papworth (person) ...
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Figure 9.12
An X.500 DIB Entry
info
Alice Flintstone, Departmental Staff, Department of Computer Science, University of Gormenghast, GB
commonName
Alice.L.Flintstone
Alice.Flintstone
Alice Flintstone
A. Flintstone
surname
Flintstone
telephoneNumber
+44 986 33 4604
uid
alf mail [email protected]
[email protected]
roomNumber
Z42
userClass
Research Fellow
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Exercícios (Cap. 9)
1. Como a técnica de caching ajuda a disponibilidade de um serviço?
2. Qual a diferença entre navegação recursiva e iterativa? Qual das duas é mais eficiente em termos de velocidade de resposta e sobrecarga dos servidores?
3. Quando um servidor DNS provê várias respostas como resultado de uma consulta e porquê?
4. Qual a diferença entre X.500 e LDAP ? (especificação x protocolo?)
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Exercícios (Cap. 9)
5. Qual a semelhança entre as árvores de diretório do sistema de arquivos UNIX e a do serviço de diretórios GNS?
6. Qual a semelhança entre xPath e expressão do filtro para mecanismo de busca no X.500?
7. O que é uma entrada MX no DNS?
8. Explique a diferença entre: navegação recursiva controlada pelo servidor e navegação não­
recursiva controlada pelo servidor.
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000 Exercícios (Cap. 6)
9. Conceitue Processo e Thread
10.Quais são as arquiteturas multi­thread para servidores? (Thread por requisição....)
11.EXTRA (Cap. 7):
A. Qual o papel de um Firewall?
B. O que é criptografia?
C. O que é chave em criptografia?
D. O significa chave pública e privada?
E. O que é criptografia simétrica e assimétrica?
F. O que é autenticação?
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Addison­Wesley Publishers 2000