The following table identifies the bandwidth of FAX, modem, TTY, and clear channel calls based on the following factors:

• Packet sizes

• Redundancy

• Relay or Pass-Through method

The values are approximate because bandwidth can vary during each call for multiple reasons.

Table 1: Bandwidth for FAX, modem, and TTY calls over IP networks

Packet Size (in msec)	Bandwidth (in kbps) (bidirectional)
	Redundancy = 0						Redundancy = 1		Red. = 2	Red. = 3
	TTY at G.711	TTY at G.729	TTY at G.723	FAX Relay	Modem Relay at 9600 Baud	Clear Channel FAX/Modem pass-through	FAX Relay	Clear Channel FAX/Modem pass-through	FAX Relay3 4	FAX Relay3 4
10	110	54	-	-	-	110	-	221	-	-
20	87	31	-	-	-	87	-	174	-	-
30	79	23	22	25	22.9	-	50	-	75	100
40	76	20	-	-	19.6	-	-	-	-	-
50	73	17	-	-	17.6	-	-	-	-	-
60	72	16	14	-	16.3	-	-	-	-	-

TTY, Modem Relay, Modem pass-through, and FAX pass-through calls are full duplex. Multiply the bandwidth of the mode by 2 to get the network bandwidth usage.

TTY at G723 supports 30 and 60 ms packet size.

FAX Relay supports 30 ms packet size.

Nonzero redundancy options increase the bandwidth usage by a linear factor of the bandwidth usage when the redundancy is zero.

FAX and Modem pass-through support 10 and 20 ms packet size.

Clear Channel transport supports a packet size of 20 ms.