HP Survivable Branch Communication zl Module powered by Microsoft Lync Planning and Design Guide 2011-02

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SBM Overview
SBM PSTN Capabilities
Like HDB3, B8ZS was designed to overcome the deficiencies of AMI. To
prevent synchronization loss, B8ZS replaces a string of eight zeros with a
string that includes two logical ones of the same polarity as a timing mark.
Frame Format. You must configure the E1 or T1 interface to use the same
frame format as that used by the public carrier.
E1-carrier lines and T1-carrier lines use different frame formats. E1 interfaces
on the SBM support two frame formats:
■ E1
■ Cyclic Redundancy Check 4 (CRC4)
In the E1 frame format, a channel (or timeslot) is called a TS, and the 32
channels are numbered TS0 to TS31. Two channels are used to establish and
maintain synchronization and signaling: specifically, TS0 is used for synchro-
nization, error detection, and alarms, and TS16 is used for signaling. The other
channels are used to transmit data.
CRC4 is based on the E1 frame format but includes additional error detection.
A checksum bit is included in all even frames of the 16-frame multiframe:
frames 0, 2, 4, 6, 8, 10, 12, and 14. A total of 8 checksum bits are used.
For T1-carrier lines, public carriers use one of two frame formats:
■ D4
■ ESF
D4 framing aggregates 12 DS0 frames into a single superframe. The ESF
standard multiplexes 24 DS0 frames into an extended superframe.
The ESF format has essentially replaced the D4 framing standard because it
frees up bits that can be used to maintain the connection.
Switch Type. The ISDN switch type dictates the ISDN standard used for the
connection.
The E1 interfaces on the SBM support Net5, which is also called European
Telecommunications Standards Institute (ETSI) or Euro ISDN. This is the
ISDN standard used throughout Europe.