j'c'westlakestaffs'ac'uk

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Network Systems and Technologies(NST)

• Lecture 10
• Review of Layer 4 and above networking
  technologies and trends (mainly VoIP)

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Format

• Context
• Quick review of OSI layer 4 and above
• Layer 4 and above technologies
• TCP
• UDP
• Trends for Layer 4 and above
• VoIP
• Summary

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TCP A Reminder of the OSI 7-Layer Model
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Transport Layer

• The transport layer
• has no concept of routing
• does not know about any intermediate nodes

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(No Transcript)
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User Datagram Protocol (UDP)

• Connectionless unreliable datagram delivery
  service
• Adds only port number for multiplexing delivery
  to application checksum
• If checksum fails on receipt, packet is simply
  discarded

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UDP (cont.)

• If application can't accept data, packet is
  discarded
• Low overhead only 8 bytes of header added
• Used for broadcasts
• NFS
• DNS

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Reliable Delivery - TCP

• TCP works on top of IP, which supplies a
  connectionless, unreliable network
• TCP is connection-oriented. It corrects lost,
  corrupted, out-of-order delayed packets

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Transport Control Protocol (TCP)

• Guaranteed delivery service
• Virtual circuit between end systems
• Positive acknowledgment with time-out
  retransmission

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How TCP Ensures Reliability

• Every message has a sequence no. The receiver
  can tell if a message is missing or out of order
• Corrupted messages are detected by means of
  checksums
• TCP acknowledges all correctly received messages
  (sends ACK to the sender)

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Well-Known Port Numbers

• Servers listen on port numbers for clients
  requesting a connection
• Telnet 23
• FTP 21
• SMTP 25
• Echo 7
• SNMP 161
• Well known port numbers lt 256

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Telnet

• Used for remote terminal sessions
• Can also be used for terminal to terminal
  communication IPC
• Uses TCP (WKP 23) to provide reliable byte
  streams
• Based on Network Virtual Terminal (NVT) model
• 7 bit USASCII over 8-bit path, half duplex, a
  line at a time

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File Transfer Protocol (FTP)

• Used to transfer files between hosts
• Data control information are passed over
  separate connections
• Default mode is ASCII, 7-bit transfer of text
  files
• BINARY/IMAGE mode 8 bit for host- dependent
  transfer of binary files

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Voice over IP (VoIP)

• VoIP let you make toll-free long distance voice
  and fax calls over existing IP data networks
  instead of public switched telephone network
  (PSTN).
• VoIP solution can dramatically cut long distance
  call charges between two or more locations.

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Voice over IP

• Enable users to transmit voice traffic over an IP
  network
• Open standards H.323, SIP
• Toll bypass
• Interoperability

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Small Business Networks today
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Reducing Cost, complexity and adding services
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Integrated WEB Search and Calls
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Issues on VoIP

• SPIT Spam over Internet Telephony
• Voice mail attacks
• Mass marketing
• Spoofing

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ITUH.323 Standard

• Application Layer Protocol
• Full detail of H.323 standard on
  http//www.protocols.com/pbook/h323.htm

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SIP Standard

• SIP Session Initiation Protocol
• Open source standard
• Text based protocol, similar to HTTP transmitting
  over TCP/UDP.
• Support voice, video, chat, interactive game ,
  virtual reality and 3G.

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SIP addressing

• The SIP address is identified by a SIP URL, in
  the format user_at_host.
• Examples of SIP URLs
• siphostname_at_vovida.org
• sipm28_at_192.168.0.5
• sip294284_at_www.staffs.ac.uk

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Comparing H.323 and SIP

• Reliability control
• H323 has failure control if one of the components
  fails alternative gatekeepers
• SIP protocol doesnt support failure control but
  depend on the endpoint/user agent to work out
• Flexibility Traffic control
• H323 has ability to define the load balancing
  endpoints but not SIP.
• Addressing mechanisms
• H323 uses many formats like URL or email address.
• SIP only use URI-style addresses
• Video and data conferencing
• H323 fully supports video and data conferencing
• SIP supports basic functions no control features

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Useful SIP server and IP soft phone

• SIP Server
• OnDo SIP server
• Router with build-in VoIP features
• IP soft phones
• Windows Messenger 5.0 or higher
• SJPhone

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Summary

• We have discussed the technology in VoIP
• VoIP is the new technology and the features are
  still expanding
• Demonstration of VoIP will be next