Polycom EX, FX, VS4000, EX4000, FX4000, VS4000 manual Capacity Planning

Chapter 3 - Before You Deploy

Capacity Planning

H.323 traffic uses more bandwidth than the selected call quality or H.320 equivalent. Polycom recommends that you allow 20% overhead for the H.323 signaling traffic. ISDN networks do not include signaling in the payload calculations, but in TCP/IP networks all signaling must also be accounted for. For example, a 384-Kbps video call would require approximately 384 Kbps + 20% = 460 Kbps of bandwidth on a TCP/IP network. These figures assume a full-duplex network.

If H.323 traffic starts out on a half-duplex network segment, it will require twice the bandwidth indicated by the bandwidth calculations described above. It will, however, take advantage of full-duplex segments as soon as it reaches them. For full-duplex segments, the calculations above remain valid. WAN segments (T1, Frame Relay, ATM) are typically full-duplex.

The following equations will help in determining the bandwidth required for H.323 traffic across various network segments:

❑Full-duplex Ethernet = (Call Speed + 20%) x 1

❑Half-duplex Ethernet = (Call Speed + 20%) x 2

❑Wide Area Network = (Call Speed + 20%) x 1

❑ATM (Using LANE) = (Call Speed + 35%) x 1

The table below provides a comparison between H.320 and H.323 point-to-point calls.

Table 3-2. Bandwidth Requirements

Call Quality	Bandwidth Required over		Bandwidth Required
(Speed)	ISDN (H.320)		over IP (H.323)
128 Kbps	1	Basic Rate ISDN (BRI) line	153 Kbps
256 Kbps	2	BRI lines	307 Kbps
384 Kbps	3	BRI lines	460 Kbps
512 Kbps	4	BRI lines	614 Kbps
768 Kbps	Fractional T1 or full Primary		922 Kbps
	Rate ISDN (PRI) line

© Polycom, Inc. 53