ACT Week 11

Version 1 Feb 2005 Slide 1j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

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 2j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

Definition of a good voice packet

High BandwidthHigh QuantitativeHigh QualitativeHigh SpeedNo bottleneck

ACT Week 11

Version 1 Feb 2005 Slide 3j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

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 4j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

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 5j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

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 6j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

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 7j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

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 8j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

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 9j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

Voice over MPLS

There are 3 alternatives for data link layer for MPLSPPPEthernetATM

ACT Week 11

Version 1 Feb 2005 Slide 10j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

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 11j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

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 12j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

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 13j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

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 14j.c.westlake@staffs.ac.uk &

k.k.chai@staffs.ac.uk

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.