Avaya 38DHB0002UKDD manual Bandwidth Requirements Calculations, Variable, Value

How Do I? Part 2 Voice Over IP - Page 101

Bandwidth Requirements Calculations

When considering the deployment of VoIP, establish the goals for data and voice integration and determine the main traffic types the integrated network is expected to support. Determine if baseline data networking requirements can be met when the INDeX solution is in place on the network. Within this section the calculation to determine to load of VoIP call is given.

In a correctly designed network, VOIP traffic is prioritised over non-voice traffic. The bandwidth for VOIP must be available in the networking, when congestion occurs non-voice traffic will be dropped in favour of voice traffic. The TCP/IP protocol will handle the re transmission of non-voice packets. In the absence of VoIP traffic non-voice traffic will have full occupancy of the link. Congestion mainly occurs on slow speed WAN links. Ethernet switches can be used to ensure congestion does not occur on the LAN.

The Bandwidth used by a given compression type can be calculated using the formula shown below.

(Layer2 Header + IP_ header + UDP_header + RTP_Header + Payload) X Num_Sample_per_sec X 8

The variables in this formula are detailed in the proceeding table.

Variable		Description	Value
Layer2_Header		VoIP may be encapsulated using	Type	Bytes
		Ethernet or PPP.
			LAN	14
			PPP	4
IP_Header			20 bytes
UDP_header			8 bytes
RTP_Header			12 bytes
Payload			Type	Size
			G711	160
			G729	20
			G723	24
num_Sample_per_sec	The IPNC generates one sample		G711/729	G723
		(payload) either every 20ms (50 per	50 per sec.	33 per sec.
		sec.) or 30ms (33 per sec.).

Notes: 1. Multiplication factor of 8 (i.e. X 8) is used to convert the calculation to bits per seconds. Transmission speed is expressed in bits per second or Kbps).

2.The effect of running IPHC is to reduce the total byte size of the IP, UDP and RTP headers. For the purposes of general calculations when running IPHC a nominal value of 7 bytes should be used to represent the sum of IP, UDP and RTP headers.

3.The LAN calculation does not include the 4-byte CRC of the Ethernet frame.

INDeX IPNC Cassette Administration Manual	How Do I? - Page 101
38DHB0002UKDD – Issue 7 (22/11/02)	Part 2 Voice Over IP