Download Diapositive 1

VoWLAN:
The Voice over WLAN
Maxime Staszewski
Fall 2008 - CS 484: Network Concept
Agenda
•
Brief overwiew of VoWLAN
•
WLAN:
• Security issue (Virtual Private Network)
•
VoIP:
• Voice Digitization/Compression
• IPv6
• Session Initiation Protocol (SIP)
•
Conclusion
Brief Overwiew of VoWLAN
•
•
•
•
•
•
•
•
VoIP over WLAN
Low-cost communication costs
Add mobility of phone terminals
No permanent connection between the two
sides
transmits information according to the status of
network congestion
Slight degradation of communication compared
to a fixed line
Convergence data/voice
Require 802.11 set by the IEEE
Virtual Private Network (VPN)
•
Virtual: connects two “physical” networks
(WLANs) by an untrusted link (Internet)
•
Private: only computers on both sides of the
VPN can "see" the data.
•
Tunneling Protocol: a protocol allowing data
from one end of the VPN to another to be
secured by encryption algorithms.
Virtual Private Network (VPN)
•
VPN client: the component allowing to encrypt
and decrypt data on the user side (client)
•
VPN server: the component encrypting and
decrypting the data on the other side of the
organization
Virtual Private Network
Point-to-point tunneling protocol (PPTP)
•
•
•
Protocol of PPP encapsulation over IP
designed by Microsoft
Allow to set the virtual private networks (VPNs)
over a public network.
The protocol opens two channels of
communication between the client and server:
• a channel control for the management of the
bond (TCP connection)
• a channel carrying data traffic of private
network (Protocol Generic Routing
Encapsulation)
Internet Protocol Security (IPsec)
•
•
•
•
Set of protocols (Layer 3 of OSI model) using
algorithms allowing the transport of secured
data over an IP network
The purpose of this protocol: authenticate and
encrypt the data
The stream can only be understood by the final
recipient (encryption)
Modification of data through intermediaries may
not be possible (integrity).
Speech digitization methods
•
Waveform coders: utilize algorithms to
produce an output that approximates the input
waveform
•
Vocoding: digitize a compact description of the
voice spectrum in several frequency bands.
Waveform coders
•
Use an algorithm to produce an output that
approximates the input waveform
•
Two processes are required to perform
digitizing of an analog signal:
• Sampling: this discretizes the signal in time
• Quantizing: this discretizes the signal in
amplitude
Pulse Code Modulation (PCM)
An uncompressed sampling technique of an
analog signal
IPv6 (Internet Protocol version 6)
•
Successor of IPv4
• Ensures QoS better than IPv4
• availability, reliability, timeliness
• uses QoS with the help classification and
marking of IP packets to make the VoIP
infrastructure sure
• provides a traffic-class field (8 bits) in the IPv6
header.
• has a 20-bit flow label.
IPv6 (Internet Protocol version 6)
Session Initiation Protocol (SIP)
•
Open standard protocol of management
sessions often used in telecommunications
normalized by IETF
• Most common for Internet telephony (VoIP) since
2007
• Takes the best aspects of the H.323 protocol.
• Handles authentication and location of multiple
participants
• Responsible for negotiating on the types of
media used by the different participants in
encapsulating SDP messages (Session
Description Protocol).
Session Initiation Protocol (SIP)
•
The basic methods are:
• INVITE allows a client to request a new
session
• ACK confirms the establishment of the
session
• CANCEL cancels INVITES in abeyance
•BYE ends a session in progress
• The answer codes are similar to HTTP:
• 100 TRYING
• 200 OK
• 404 not found
Session Initiation Protocol (SIP)
•
The development of SIP is based on three
elements:
• The User Agents designate the agents found
in SIP phones
• The Registrar is a server that handles
REGISTER requests sent by the User Agent to
report their current location
• A SIP Proxy serves as an intermediary
between User Agents who do not know their
respective locations (IP address).
Session Initiation Protocol (SIP)
Proxy Server SIP Call Flow
Conclusion
•
Potential market growth
• Some problems:
• Interferences
• Quality of voice call
•…
• Many opportunities
• Main competitor; DECT
Thank You
For
Your Attention
Questions?