ITG Engineering Guidelines Page 85 of 378
ITG Trunk 2.0 ISDN Signaling Link (ISL) Description, Installation and Operation
Because of its high capacity, 100BaseT Ethernet does not experi ence
bottlenecks.
WAN links are normally based on PSTN standards such as DS0, DS1, DS3,
SONET STS-3c, or Frame Relay. These standards are full-duplex
communication channels
With standard PCM encoding (G.711 codec), a two-way conversation
channel has a rate of 128 kbit/s (i.e., 64 kbit/s in each direction). The same
conversation on WAN (e.g, T1) requires a 64 kbit/s channel only, because a
WAN channel is a full duplex channel.
When ITG cards share a segm ent of Ethernet in the si mp le x mode, the
average loading on Ethernet should not exceed 30%.
When simplex/duplex Ethernet links terminate on the ports of an Ethernet
switch (e.g., Baystack 450), the fully duplex Ethernet up-link to the
router/WAN can be loaded to 60% on each direction of the link.
A WAN route with bandwidth of 1.536 Mbit/s or more can be loaded up to
80% (voice packets must have priority over data), a single DS0 WAN pipe
(64 kbit/s) is recommended to a loading of 50%.
When the WAN route prioritizes VoIP applicati on ov er d ata t raff ic, t he route
bandwidth can be engineered to 90% loading level, otherwise 80%.
Fax engineering considerations
Fax calculation is based on 30 bytes packet size and data rate of 6 4 kbit/s (no
compression). The frame duration (payload) is calculated by using the
equation: 30*8/14400=16.6 ms, where 14,400 bit/s is the modem data rate.
Bandwidth output is calculated by the equation: 108*8*1000/16.6=52.0
kbit/s. Bandwidth output to WAN is: 70*8*1000/16.6=33.7 kbit/s.
Payload and bandwidth output for other pa cket sizes or modem dat a rates wil l
have to go through similar calculations.
Fax traffic is always one-way. Fax pag es sent and fax pages received generate
data traffic to the T- LAN. For WAN calcula tion, only the larger tr affic parcel
of the two needs to be considered.