Primary Rate Interface 167
In traditional E1 implementations, there are 30 timeslots, leaving 2 timeslots for signaling and
framing. Timeslot 0 is used for framing and timeslot 16 is used for signaling (counting 031).
E1 PRI makes use of this same principal. Timeslot 16 is the D channel, and timeslot 0 is used
for framing information. Figure 6-12 depicts T1 and E1 PRI.
Figure 6-12
T1 and E1 PRI
ISDN Switch Type
The PRI installation procedure is similar to its BRI counterpart. A service call is placed, and
then the demarc is determined and extended, if necessary. The carrier provides the basic
information necessary for connectivity, but it will be necessary to configure the router with the
appropriate switch type. Table 6-4 shows the Cisco-supported switch types.
T1/E1 Framing and Line Coding
Although it is ISDN, PRI uses T1 framing and line coding. These technologies are based on the
same model, represented in a number of 64-kbps channels.
The original use of digital facilities was the transport of voice traffic. Because analog
technologies were not adequate for long distance transmission due to attenuation, another form
of transmission--digitizing--was necessary. Digitizing the voice traffic for transmission
enabled it to travel very long distances with no attenuation.
Table 6-4
Cisco-Supported Primary Rate Switch Types
Switch Type
Description
primary-4ess
AT&T 4ESS switch type for the U.S.
primary-5ess
AT&T 5ESS switch type for the U.S.
primary-dms100
Northern Telecom switch type for the U.S.
primary-net5
European switch type for NET5
primary-ni
National ISDN switch type for the U.S.
primary-ntt
Japanese switch type
primary-ts014
Australian switch type
*Check with the provider for the appropriate switch type. A change of switch type requires a reload of the router.
23 x 64 kbps B channels
1 x 64 kbps D channel
BRI
T1 PRI
BRI
E1 PRI
30 x 64 kbps channels
1 x 64 kbps D channel (signaling)