Integrators' Reference Manual for For ViewStation EX, ViewStation FX, and VS4000

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

(Speed)

Bandwidth Required over

ISDN (H.320)

Bandwidth Required

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

Rate ISDN (PRI) line

922 Kbps