Applications

1
Applications

• Outline
• Name Service (DNS)
• Traditional Applications

2
Naming

• Outline
• Terminology
• Domain Naming System
• Distributed File Systems

3
Overview

• What do names do?
• identify objects
• help locate objects
• define membership in a group
• specify a role
• convey knowledge of a secret
• Name space
• defines set of possible names
• consists of a set of name to value bindings

4
Properties

• Names versus addresses
• Location transparent versus location-dependent
• Flat (indvisible) versus hierarchical (Unix file
  name)
• Global versus local
• Absolute versus relative
• By architecture versus by convention
• Unique versus ambiguous

5
DNS

• The domain name system (DNS) is the way that
  Internet domain names are located and translated
  into Internet Protocol addresses.
• A domain name is a meaningful and
  easy-to-remember "handle" for an Internet
  address.
• Because maintaining a central list of domain
  name/IP address correspondences would be
  impractical, the lists of domain names and IP
  addresses are distributed throughout the Internet
  in a hierarchy of authority.

6
Examples

• Hosts
• kira.cs.twsu.edu 156.26.10.236
• 156.26.10.236 00C0F030DC8F
• Files
• /usr/llp/tmp/foo (server, fileid)
• Users
• Larry Peterson llp_at_cs.princeton.edu

7
Examples (cont)

• Mailboxes
• Services
• nearby ps printer with short queue and 2MB

8
Domain Naming System

• Hierarchy
• Name
• kira.cs.twsu.edu

9
Name Servers

• Partition hierarchy into zones

edu
com
gov
mil
org
net
uk
fr










princeton
mit
cisco
yahoo
nasa
nsf
arpa
navy
acm
ieee
cs
ee
physics
ux01
ux04

• Each zone implemented by two or more name servers

10
Resource Records

• Each name server maintains a collection of
  resource records which consists of five
  components
• (Name, Value, Type, Class, TTL)
• A Resource record starts with a domain name,
  usually a fully qualified domain name (A domain
  name that extends all the way back to root.
  gomer.gimboid.com. is an FQDN.)
• Second is the record value. It depends on record
  type.
• IP addresses
• If the record data includes a domain name that is
  not a Fully Qualified Domain Name it goes through
  the same appending process as the domain name at
  the start of the record.
• Third is the record type CNAME, PTR, A, etc.
• Fourth is the Record class Internet, Hesiod, or
  Chaos
• Hesiod is only used at M.I.T, and maybe not even
  there anymore.
• Chaos is almost extinct.
• Fifth is the TTL, in seconds.
• Many servers will permit comments as a sixth
  component.

11
Resource Records

• Type
• NS Value gives domain name for host running name
  server that knows how to resolve names within
  specified domain.
• CNAME Value gives canonical name for particular
  host used to define aliases.
• MX Value gives domain name for host running mail
  server that accepts messages for specified
  domain.
• A indicates the value is an IP address.
• Class allow other entities to define types. Only
  widely Class is the one used by the Internet
  denoted as IN.
• TTL Time To Live, the number of seconds
  remaining on a cached record before it is purged.

12
DNS

• A Canonical Name (CNAME) is a host's official
  name as opposed to an alias.
• The official name is the first hostname listed
  for its Internet address in the hostname
  database, /etc/hosts or the Network Information
  Service (NIS).
• Network Information Service (NIS) is Sun
  Microsystems' Yellow Pages (yp) client-server
  protocol for distributing system configuration
  data such as user and host names between
  computers on a network.
• You can find a host's canonical name using
  nslookup if you say
• set querytypeCNAME

13
DNS

• Address Record (A Record), assigns an IP address
  to a domain name. When the domain name system was
  designed it was recommended that no two A records
  refer to the same IP address.
• Pointer Record. Also called a reverse record. A
  PTR record associates an IP address with a
  canonical name.
• PTR records should point to a name that can be
  resolved back to the IP address.
• The name of the pointer record is not the IP
  address itself, but is the IP address four IP
  octets in reverse order followed by IN-ADDR.ARPA.
  
• for Example
• 192.168.0.1 becomes 1.0.168.192.IN-ADDR.ARPA.

14
Root Server

• (princeton.edu, cit.princeton.edu, NS, IN)
• (cit.princeton.edu, 128.196.128.233, A, IN)
• (cisco.com, thumper.cisco.com, NS, IN)
• (thumper.ciscoe.com, 128.96.32.20, A, IN)

15
Princeton Server

• (cs.princeton.edu, optima.cs.princeton.edu, NS,
  IN)
• (optima.cs.princeton.edu, 192.12.69.5, A, IN)
• (ee.princeton.edu, helios.ee.princeton.edu, NS,
  IN)
• (helios.ee.princeton.edu, 128.196.28.166, A, IN)
• (jupiter.physics.princeton.edu, 128.196.4.1, A,
  IN)
• (saturn.physics.princeton.edu, 128.196.4.2, A,
  IN)
• (mars.physics.princeton.edu, 128.196.4.3, A, IN)
• (venus.physics.princeton.edu, 128.196.4.4, A, IN)

16
CS Server

• (cs.princeton.edu, optima.cs.princeton.edu, MX,
  IN)
• (cheltenham.cs.princeton.edu, 192.12.69.60, A,
  IN)
• (che.cs.princeton.edu, cheltenham.cs.princeton.edu
  , CNAME, IN)
• (optima.cs.princeton.edu, 192.12.69.5, A, IN)
• (opt.cs.princeton.edu, optima.cs.princeton.edu,
  CNAME, IN)
• (baskerville.cs.princeton.edu, 192.12.69.35, A,
  IN)
• (bas.cs.princeton.edu, baskerville.cs.princeton.ed
  u, CNAME, IN)

17
Name Resolution

• Strategies
• forward
• iterative
• recursive
• Local server
• need to know root at only one place (not each
  host)
• site-wide cache

18
Distributed File Systems

• Network File System (NFS)
• Provides transparent file access for client
  applications.
• Built on top of Sun RPC.
• NFS is used predominately with UDP. The NFS
  server receives a clients request on port 2049.
• It is common to start multiple instances of the
  server (nfsd).

19
Distributed File Systems

• No Transparency
• Global AFS /cs.princeton.edu/usr/llp/tmp/foo
• Windows f/usr/llp/tmp/foo
• Transparency by Convention
• NFS /usr/llp/tmp/foo
• Or Not /n/fs/fac5/llp/tmp/foo
• Transparency by Architecture
• Sprite /usr/llp/tmp/foo
• Private versus Shared
• ASF /usr/llp/tmp/foo versus /afs/shared

20
Applications

• File Transfer Protocol (FTP)
• FTP uses two TCP connections to transfer a file.
• The control connection is established on port
  number 21.
• The data connection is established through port
  20.
• SMTP (Simple Mail Transfer Protocol) is a TCP/IP
  protocol used in sending and receiving e-mail.
• The Hypertext Transfer Protocol (HTTP) is the set
  of rules for exchanging files (text, graphic
  images, sound, video, and other multimedia files)
  on the World Wide Web.
• Simple Network Management Protocol (SNMP) is the
  protocol governing network management and the
  monitoring of network devices and their
  functions.

21
RTP

• The Real-Time Transport Protocol (RTP) is an
  Internet protocol standard that specifies a way
  for programs to manage the real-time transmission
  of multimedia data over either unicast or
  multicast network services.
• RTP is commonly used in Internet telephony
  applications. RTP does not in itself guarantee
  real-time delivery of multimedia data.
• RTP combines its data transport with a control
  protocol (RTCP), which makes it possible to
  monitor data delivery for large multicast
  networks.

22
Real-Time Transport Protocol (RTP)

• Monitoring allows the receiver to detect
• A sequence number is used to detect lost packets.
  
• A timestamp detects different delay jitter.
• Control Packets is sent periodically.
• Measure loss rate (fraction of packets received
  since last report)
• measure jitter .
• RTP runs on top of the User Datagram Protocol
  (UDP), although it can use other transport
  protocols.

23
Session Control

• Video conferencing requires session control.
• The Session Initiation Protocol (SIP) is an
  Internet Engineering Task Force (IETF) standard
  protocol for initiating an interactive user
  session that involves multimedia elements such as
  video, voice, chat, gaming, and virtual reality.
• SIP can establish multimedia sessions or Internet
  telephony calls, and modify, or terminate them.
• SIP uses RTP.
• H.323 is a standard built on top of RTP and
  approved by the International Telecommunication
  Union (ITU) in 1996 to promote compatibility in
  videoconference transmissions over IP networks.