January 28, 2013

Is IPv6 Good for VoIP?

Internet Protocol, Version 6 (IPv6) is here to stay. We hear many good things about the values that IPv6 will bring to the Internet and private IPv6 networks. There are about 40 Request for Comment (RFC) documents describing different aspects of IPv6. Not all of these RFCs will be implemented in the Internet and private IP networks. IPv6 will have costs associated with it besides hardware and software to implement. You will need anywhere from 10% to 46% more bandwidth for VoIP calls. 

Expanded IP Header

The one value everyone seems to agree on is the vastly expanded IP address space. The address field expands from 32 to 128 bits. Most experts do not expect that the address field will ever have to be expanded again. This larger address field expands the IP header from 20 to 40 bytes. This will affect the bandwidth requirements for VoIP calls.

The IPv6 header is at minimum 40 bytes but can be expanded for other functions. There are several optional IPv6 header extensions that further expand the IP header for hop-by-hop options, destination options, routing, fragment headers, plus four other header extensions. These extensions facilitate a wider range of functions and features. They also add a requirement for greater bandwidth to carry the expanded IPv6 header. 

The IPv6 header can be far longer than today's IPv4 IP header. The smallest header extensions are 8 or 12 bytes in length. They can be far longer depending on the options chosen. The focus of this TechNote is on the VoIP bandwidth requirements for IPv6 voice calls.

VoIP Bandwidth Requirements

The additional IP header overhead will impact the VoIP call bandwidth requirements. There is no doubt that the enterprise will have to procure expanded IP network bandwidth to compensate for the IPv6 header overhead. The chart below summarizes what bandwidth expansion will be required when VoIP calls are carried over an IPv6 connection. 

The chart compares the bandwidth requirements of IPv4 to IPv6. Only the three most commonly implemented voice codecs are presented. G.711, operating at 64 kbps, is the common default for VoIP. G.722 also consumes 64 kbps but delivers HD voice. G.729 is the most popular compressed voice codec standard. Most VoIP implementations use a 20 ms voice sample to fill the packet. Although a larger voice sample packet, 30 to 40 ms, uses less bandwidth, the smaller packet produces less delay. When a smaller packet is lost, it is easier to compensate for the lost packet. 

The effect of the IPv6 header on Ethernet connections is higher bandwidth consumption. However, LAN bandwidth is so great that there really is no measurable impact. Likewise, when Compressed Real Time Protocol (cRTP) is applied, there is a small difference in the bandwidth requirements. 

The Point to Point Protocol (PPP) and uncompressed Real Time Protocol (RTP) connections will require more bandwidth. The enterprise will need 10% more bandwidth per G.711/G.722 call when no header extensions are applied. The G.711/G.722 VoIP call will need 15% more bandwidth when the minimum header extension (eight more bytes) is used. The amount of VoIP bandwidth consumption grows substantially when the G.729 codec is used. The IPv6 header consumes 31% more bandwidth while the IPv6 header plus minimum header extension will require 46% more bandwidth per VoIP call.

VoIP during the Transition to IPv6

The migration to IPv6 will take 5 to 10 years. One Internet Service Provider (ISP) has set the date of 2020 as the cut off of IPv4 access. It will probably be longer. During the transition to IPv6, many enterprises will still be operating IPv4 networks. There will have to be some translation device between the private IPv4 network and IPv6 networks. If this device is the responsibility of the enterprise and IPv6 traffic will only be accepted by the ISP, then the enterprise has to increase its bandwidth to the IPv6 network for VoIP calls. However, if the ISP performs this translation, then the enterprise need not buy more bandwidth since the VoIP traffic will be delivered in IPv4 packets.

Impact on the Enterprise

Bandwidth has become cheaper over the years. But you still have to pay for it. The use of SIP trunks and connections to MultiProtocol Label Switching (MPLS) networks will be affected by the larger IPv6 header deployment. The enterprise does not have to do anything in the near term. But eventually, more bandwidth will be required for IPv6 VoIP calls. 

For small business locations, the expanded bandwidth may produce a small cost increase. Call centers on the other hand, will have to budget for the expanded bandwidth. Most enterprises are concerned with the hardware and software costs of migrating to IPv6. They should also plan on a higher bandwidth bill. 

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Gary- good article and thanks for the hard data. Related to bandwidth and protocol overhead with IPv6 is the issue of NAT. Especially with hosted providers, this is a persistent headache. While we'll certainly take an IPv6 hit with bandwidth, especially in the G.729 case so many of us use for Internet-facing transport, the offset of reduced NAT issues, obviously depending on implementation and network topology, should play into the discussion too.


In the near term you will probably still have to have a NAT or other device for IPv4 to IPv6 address translation. In the long run as private networks migrate to IPv6, there will be issues like the NAT that will disappear. There will be other issues, less obvious but producing new problems. See the IEEE Computing article "Future Internet Protocols".

Gary, while the IPv6 fixed size header is 40 octets vs 20 octets + options for IPv4, your chart is unclear on your assumed header sizes. It says you added extension header (which is not header BTW it is considered payload) but you did not state which one was used nor why? It is not clear to me why any of the extension headers would be used in normal VoIP in IPv6. Thanks.

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