QoS & DNS

1. 25.1
QoS,
Application Layer
Paradigms, DNS
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2. QUALITYOFSERVICE
Quality of service (QoS) is an internetworking issue
that has been discussed more than defined. We can
informally define quality of service as something a
flow seeks to attain.
Topics discussed in this section:
Flow Characteristics Flow Classes
24.23

3. Figure 24.15 Flow characteristics
24.24

4. TECHNIQUES TO IMPROVE QoS
In Section 24.5 we tried to define QoS in terms of its
characteristics. In this section, we discuss some
techniques that can be used to improve the quality of
service. We briefly discuss four common methods:
scheduling, traffic shaping, admission control, and
resource reservation.
Topics discussed in this section:
Scheduling Traffic Shaping
Resource Reservation Admission Control
24.25

5. Figure 24.16 FIFO queue
24.26

6. Figure 24.17 Priority queuing
24.27

7. Figure 24.18 Weighted fair queuing
24.28

8. Figure 24.19 Leaky bucket
24.29

9. Figure 24.20 Leaky bucket implementation
24.30

10. A leaky bucket algorithm shapes bursty
traffic into fixed-rate traffic by averaging
the data rate. It may drop the packets if
the bucket is full.
Note
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11. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
The token bucket allows bursty traffic at
a regulated maximum rate.
Note
24.32

12. Figure 24.21 Token bucket
24.33

13. INTEGRATED SERVICES
Two models have been designed to provide quality of
service in the Internet: Integrated Services and
Differentiated Services. We discuss the first model
here.
Topics discussed in this section:
Signaling
Flow Specification Admission
Service Classes RSVP
Problems with Integrated Services
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14. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Integrated Services is a flow-based QoS
model designed for IP.
Note
24.35

15. Figure 24.22 Path messages
24.36

16. Figure 24.23 Resv messages
24.37

17. Figure 24.24 Reservation merging
24.38

18. Figure 24.25 Reservation styles
24.39

19. DIFFERENTIATED SERVICES
Differentiated Services (DS or Diffserv) was
introduced by the IETF (Internet Engineering Task
Force) to handle the shortcomings of Integrated
Services.
Topics discussed in this section:
DS Field
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20. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Differentiated Services is a class-based
QoS model designed for IP.
Note
24.41

21. Figure 24.26 DS field
24.42

22. Figure 24.27 Traffic
conditioner
24.43

23. 24-9 QoS IN SWITCHED NETWORKS
Let us now discuss QoS as used in two switched
networks: Frame Relay and ATM. These two networks
are virtual-circuit networks that need a signaling
protocol such as RSVP.
Topics discussed in this section:
QoS in Frame Relay QoS in ATM
24.44

24. Figure 24.28 Relationship between traffic control attributes
24.45

25. Figure 24.29 User rate in relation to Bc and Bc + Be
24.46

26. Figure 24.30 Service
classes
24.47

27. Relationship of service classes to the total capacity of the network
24.48

28. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Application Layer
• The application layer provides services to the user.
• Communication is provided using a logical connection, which
means that the two application layers assume that there is an
imaginary direct connection through which they can send and
receive the messages.
• Application Layer provides a facility by which users can forward
several emails and it also provides a storage facility.
• This layer allows users to access, retrieve and manage files in a
remote computer.
• It allows users to log on as a remote host.
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29. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Providing Services
• The Internet was originally designed for the same purpose: to provide service
to users around the world.
• New protocols can be added or some protocols can be removed or replaced
by the Internet authorities.
• Since the application layer is the only layer that provides services to the
Internet user, it allows new application protocols to be easily added to the
Internet.
Standard Application-Layer Protocols
• There are several application-layer protocols that have been standardized and
documented by the Internet authority.
• Each standard protocol is a pair of computer programs that interact with the
user and the transport layer to provide a specific service to the user.
• Ex: Telnet, FTP, TFTP, SMTP, SNMP, DNS, DHCP.
Nonstandard Application-Layer Protocols
• A programmer can create a nonstandard application-layer program.
• It is the creation of a nonstandard (proprietary) protocol, which does not even
need the approval of the Internet authorities if privately used.
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30. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Application-Layer Paradigms
Two paradigms have been developed during the lifetime of the Internet:
1. the client-server paradigm
2. the peer-to-peer paradigm.
Traditional Paradigm: Client-Server
• The traditional paradigm is called the client-server paradigm.
• Service provider is an application program, called the server process; it runs continuously, waiting
for another application program, called the client process, to make a connection through the
Internet and ask for service.
• The server process must be running all the time; the client process is started when the client
needs to receive service.
• Several traditional services are still using this paradigm, including the World Wide Web (WWW)
and its vehicle HyperText Transfer Protocol (HTTP), file transfer proto- col (FTP), secure shell (SSH),
e-mail, and so on.
5/14/2024 Dr. Shivashankar, E&CE, RRIT 30
Figure 25.2 Example of a client-
server paradigm

31. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Peer-to-Peer
• A new paradigm, called the peer-to-peer paradigm (P2P paradigm) has emerged to
respond to the needs of some new applications.
• In this paradigm, there is no need for a server process to be running all the time and
waiting for the client processes to connect.
• The responsibility is shared between peers.
• A computer connected to the Internet can provide service at one time and receive
service at another time.
• A computer can even provide and receive services at the same time.
• There are some new applications, such as BitTorrent, Skype, IPTV, and Internet
telephony.
5/14/2024 Dr. Shivashankar, E&CE, RRIT 31
Figure 25.3 Example of a peer-
to-peer paradigm

32. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Mixed Paradigm
• An application may choose to use a mixture of the two
paradigms by combining the advantages of both.
• For example, a light-load client-server communication can be
used to find the address of the peer that can offer a service.
• When the address of the peer is found, the actual service can be
received from the peer by using the peer-to- peer paradigm.
5/14/2024 Dr. Shivashankar, E&CE, RRIT 32

33. 25.33
Figure 25.1 Example of using the DNS service
server
Typo in textbook

34. 25.34
25-1 NAME SPACE
To be unambiguous, the names assigned to machines
must be carefully selected from a name space with
complete control over the binding between the names
and IP addresses.
Flat Name Space: hard to manage for large-scale system
Hierarchical Name Space: name has several parts
Topics discussed in this section:

35. 25.35
25-2 DOMAIN NAME SPACE
To have a hierarchical name space, a domain name
space was designed. In this design the names are
defined in an inverted-tree structure with the root at
the top. The tree can have only 128 levels: level 0
(root) to level 127.
Label
Domain Name
Domain
Topics discussed in this section:

36. 25.36
Figure 25.2 Domain name space
root

37. 25.37
Figure 25.3 Domain names and labels

38. 25.38
Figure 25.5 Domains: subtree of the domain name space

39. 25.39
25-3 DISTRIBUTION OF NAME SPACE
The information contained in the domain name space
must be stored. However, it is very inefficient and also
unreliable to have just one computer store such a huge
amount of information. In this section, we discuss the
distribution of the domain name space.
Hierarchy of Name Servers
Zone
Root Server
Primary and Secondary Servers
Topics discussed in this section:

40. 25.40
Figure 25.6 Hierarchy of name servers

41. DNS: Root name servers
b USC-ISI Marina del Rey, CA
l ICANN Los Angeles, CA
e NASA Mt View, CA
f Internet Software C. Palo Alto, CA
(and 17 other locations)
i Autonomica, Stockholm (plus 3 other
locations)
k RIPE London (also Amsterdam, Frankfurt)
m WIDE Tokyo
a Verisign, Dulles, VA
c Cogent, Herndon, VA (also Los Angeles)
d U Maryland College Park, MD
g US DoD Vienna, VA
h ARL Aberdeen, MD
j Verisign, ( 11 locations)
13 root name
servers
worldwide

42. TLD and Authoritative Servers
 Top-level domain (TLD) servers: responsible for
com, org, net, edu, etc, and all top-level country
domains uk, fr, ca, jp.
 Network solutions maintains servers for com TLD
 Educause for edu TLD
 Authoritative DNS servers: organization’s DNS
servers, providing authoritative hostname to IP
mappings for organization’s servers (e.g., Web
and mail).
 Can be maintained by organization or service
provider (paid by the organization)

43. 25.43
Figure 25.7 Zones and domains

44. 25.44
Two types of DNS server: A primary server
loads all information from the disk file; the
secondary server loads all information from
the primary server. Reason: redundancy
When the secondary downloads
information from the primary, it is called zone
transfer.
Note

45. 25.45
25-4 DNS IN THE INTERNET
DNS is a protocol that can be used in different
platforms. In the Internet, the domain name space
(tree) is divided into three different sections: generic
domains, country domains, and the inverse domain.
Generic Domains
Country Domains
Inverse Domain
Topics discussed in this section:

46. 25.46
Unix: nslookup, dig
Windows: nslookup
DNS Query Commands

47. 25.47
Figure 25.8 DNS IN THE INTERNET

48. 25.48
Figure 25.9 Generic domains

49. 25.49
Table 25.1 Generic domain labels

50. 25.50
Figure 25.10 Country domains

51. 25.51
25-5 RESOLUTION
Mapping a name to an address or an address to a
name is called name-address resolution.
Resolver
Mapping Names to Addresses
Mapping Addresses to Names
Recursive Resolution
Caching
Topics discussed in this section:

52. 25.52
Figure 25.12 Recursive resolution

53. 25.53
Figure 25.13 Iterative resolution

54. 25.54
Caching: Main Reason for the Efficiency of DNS
All DNS servers cache prior query results
Normal DNS query will not go through the
full steps of recursive/iterative resolution

55. 25.55
25-6 DNS MESSAGES
DNS has two types of messages: query and response.
Both types have the same format. The query message
consists of a header and question records; the
response message consists of a header, question
records, answer records, authoritative records, and
additional records.
Header
Topics discussed in this section:

56. 25.56
Figure 25.14 Query and response messages

57. 25.57
Figure 25.15 Header format

58. 25.58
25-7 TYPES OF RECORDS
As we saw in Section 25.6, two types of records are
used in DNS. The question records are used in the
question section of the query and response messages.
The resource records are used in the answer,
authoritative, and additional information sections of
the response message.
Question Record
Resource Record
Topics discussed in this section:

59. DNS records
DNS: distributed db storing Resource Records (RR)
 Type=NS
 name is domain (e.g.
foo.com)
 value is name of
authoritative DNS server
for this domain
RR format: (name, value, type, ttl)
 Type=A
 name is hostname
 value is IP address
 Type=CNAME
 name is alias name for some
“canonical” (the real) name
www.ibm.com is really
servereast.backup2.ibm.com
 value is canonical name
 Type=MX
 value is name of mailserver
associated with name
25.59

60. DNS protocol, messages
DNS protocol : query and reply messages, both with
same message format
msg header
 identification: 16 bit # for
query, reply to query
uses same #
 flags:
 query or reply
 recursion desired
 recursion available
 reply is authoritative
25.60

61. DNS protocol, messages (UDP 53)
Name, type fields
for a query
RRs in
response
to query
records for
authoritative servers
additional “helpful”
info that may be used
Let’s check a web example using Wireshark!
(MX record: nslookup –type=MX cs.ucf.edu or
dig mx cs.ucf.edu)
25.61

62. Inserting records into DNS
 Example: just created startup “netwar”
 Register name netwar.com at a registrar (e.g., Network
Solutions)
 Need to provide registrar with names and IP addresses of your
authoritative name server (primary and secondary)
 Registrar inserts two RRs into the com TLD server:
(netwar.com, dns1.netwar.com, NS)
(dns1.netwar.com, 212.212.212.1, A)
 Put in authoritative server dns1.netwar.com
 Type A record for www.netwar.com
 Type CName for netwar.com (alias)
 Type MX record for netwar.com (email)
 Type A record for the email server
 How do people get the IP address of your Web site?
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63. 25.63
DNS can use the services of UDP or TCP
using the well-known port 53.
Note