Transcript Voice over other technologies

ACT Week 11
Voice over packet transport technologies
Format of lecture:
Follow up week 9 and week 10 lecture on VoIP
To look at the packet efficiency of VoIP
VoIP practical tonight
Version 1 Feb 2005
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Slide 1
ACT Week 11
Definition of a good voice packet
High Bandwidth
High Quantitative
High Qualitative
High Speed
No bottleneck
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Slide 2
ACT Week 11
Layer 2 OSI model
Layer 2 of OSI model is an important layer for
Voice over packet.
This layer provide information how available
bandwidth can be shared.
Point-to-Point Protocol (PPP) is a method of
transmitting packet between an ISP and a
home user over a dial-up link.
Frame relay and ATM are other faster
methods for WAN
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Slide 3
ACT Week 11
Multiprotocol Label Switching (MPLS)
 MPLS integrates Layer 2 information about network
links (bandwidth, latency, utilization) into Layer 3 (IP).
 It provide better information for the router for routing
efficiency.
 It includes the more information on the packet which
are called MPLS shim.
 These are extra information labels for the routers
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Slide 4
ACT Week 11
Real time Protocol (RTP)
IP protocol provides only means to transmit
data packet between source and destination
Transmission time may vary from packet to
packet, therefore RTP is needed to provide
timing information to ensure correct
reconstruction at the receiver
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Slide 5
ACT Week 11
Voice over IP
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In IP network, voice is transported over RTP
Either PPP or SONET/SDH for data link layer
PPP adds a fixed amount of overhead per IP packet
SONET/SDH overhead per IP packet depends on the length
of IP packet
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Slide 6
ACT Week 11
Voice over Frame Relay
Voice over Frame Relay includes the
multiplexing of several voice packets from a
single call into a subframe
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Slide 7
ACT Week 11
Voice over ATM
Voice can be transported over ATM using
AAL1
AAL5 which are suited to constant bit rate
voice therefore not benefit for silence removal.
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Slide 8
ACT Week 11
Voice over MPLS
There are 3 alternatives for data link layer for
MPLS
PPP
Ethernet
ATM
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Slide 9
ACT Week 11
Advantages of each Voice packet
 VoIP has the benefits of mature networks, good
software available to use and required only low
bandwidth that header compression can be used.
 VoATM has the advantage that it is standardised for
voice over DSL.
 VoFR has the advantage that it is a widely used
access technology for enterprise users
 MPLS has the advantages of software upgrade,
efficient routing and better security as MPLS VPN
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Slide 10
ACT Week 11
Overhead for each voice transport
The variable overhead is the transport
overhead per voice packet
The fixed overhead is the transport overhead
independent of the number f voice packets
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Slide 11
ACT Week 11
Voice over GPRS
In total, the data header is 50 bytes and 10-35
bytes of encoded speech for normal voice
packet on a network.
Efficiency is less than 50%.
Further overheads are needed in GPRS and
in total more than 60 byte and this cause the
efficiency is much less.
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Slide 12
ACT Week 11
Voice over GPRS
GPRS was designed for non-real time data
and does not as such provide the same
efficiency for speech as circuit switched GSM
Some modification to GPRS standards are
needed in order to reach good quality of
speech
Compress header information
More encoded frame encapsulated into the packet
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Slide 13
ACT Week 11
Summary of voice over packet
 VoMPLS give good QoS on aggregated traffic and
high bandwidth efficiency.
 VoIP has scalable with qualitative guarantee but no
QoS on quantitative.
 VoATM has quantitative guarantees and network
widely available and proven management.
 VoFr has very high bandwidth efficiency.
 VoGPRS lacks of packet efficiency, too many
overhead included in GRPS frame compared to
encoded frame.
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Slide 14