1. ACT Week 11 Version 1 Feb 2005Slide 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 VoIP To look at the packet efficiency of VoIP VoIP practical tonight

2. ACT Week 11 Version 1 Feb 2005Slide 2j.c.westlake@staffs.ac.uk & k.k.chai@staffs.ac.uk Definition of a good voice packet High Bandwidth High Quantitative High Qualitative High Speed No bottleneck

3. ACT Week 11 Version 1 Feb 2005Slide 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

4. ACT Week 11 Version 1 Feb 2005Slide 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

5. ACT Week 11 Version 1 Feb 2005Slide 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

6. ACT Week 11 Version 1 Feb 2005Slide 6j.c.westlake@staffs.ac.uk & k.k.chai@staffs.ac.uk Voice over IP 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

7. ACT Week 11 Version 1 Feb 2005Slide 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

8. ACT Week 11 Version 1 Feb 2005Slide 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.

9. ACT Week 11 Version 1 Feb 2005Slide 9j.c.westlake@staffs.ac.uk & k.k.chai@staffs.ac.uk Voice over MPLS There are 3 alternatives for data link layer for MPLS PPP Ethernet ATM

10. ACT Week 11 Version 1 Feb 2005Slide 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

11. ACT Week 11 Version 1 Feb 2005Slide 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

12. ACT Week 11 Version 1 Feb 2005Slide 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.

13. ACT Week 11 Version 1 Feb 2005Slide 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 speech Compress header information More encoded frame encapsulated into the packet

14. ACT Week 11 Version 1 Feb 2005Slide 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.