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ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
Voice over packet transport technologies
Format of lecture:Follow up week 9 and week 10 lecture on VoIPTo look at the packet efficiency of VoIPVoIP practical tonight
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
Definition of a good voice packet
High BandwidthHigh QuantitativeHigh QualitativeHigh SpeedNo bottleneck
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
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
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
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
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
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
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
Voice over IP
In IP network, voice is transported over RTPEither PPP or SONET/SDH for data link layerPPP adds a fixed amount of overhead per IP packetSONET/SDH overhead per IP packet depends on the length
of IP packet
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
Voice over Frame Relay
Voice over Frame Relay includes the multiplexing of several voice packets from a single call into a subframe
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
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.
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
Voice over MPLS
There are 3 alternatives for data link layer for MPLSPPPEthernetATM
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
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
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
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
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
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.
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
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 speechCompress header informationMore encoded frame encapsulated into the packet
ACT Week 11
Version 1 Feb 2005 Slide [email protected] &
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.
