3Com S330 manual Illustrates AAL1 structured DS1

CBR Module 235

These frames are then followed by the ABCD bits of each active DS0. Two DS0’s ABCD bits are provided in each byte after the last DS0 group. Figure 174 shows an example of three DS0s and their ABCD bits sent in a structured encapsulation.

Figure 174 Multiframe Structure for 3x64kbit/s DS1 with CAS

AAL1 Pointer First Transported Octet of Multiframe

Second Transported Octet of Multiframe

First 125 µsec Frame of Multiframe for

DS1

		Second 125 µsec Frame of Multiframe for
		DS1
	. . .
ABCD for		Last 125 µsec Frame of Multiframe for
First
Transported		DS1
Timeslot
ABCD for		Signaling
		Substructure
Third
Transported
Timeslot
	ABCD for Second
	Transported Timeslot

Figure 175 illustrates AAL1 structured DS1.

Figure 175 AAL1 Structured DS1

FEC for SN/CSI

Lost Cell

Detection

Clock Recovery

		CSI	SN	SNP	SAR-SDU
		1 Bit	3 Bits	4 Bits	47 Bytes
AAL 1	ATM Header			AAL 1 Data
VCC	5 Bytes			48 Bytes

CSI - Convergence Sublayer Indicator

FEC - Forward Error Correction

SNP - Sequence Number Protection

SN - Sequence Number

SAR - SDU - Segmentation and Reassembly Service Data Unit

VCC - V irtual Channel Connection

AAL Layer SAR

ATM Layer