Supported Applications
87
The example in Figure 47 shows only one transmission path: the DS3 UNI between
the two PathBuilder S700s. As a result, cells leaving PathBuilder S700 A on VPI/VCI
1/33 arrive at PathBuilder S700 B on VPI/VCI 1/33. If the DS3 trunk were switched
through a standard telephone switching system to interconnect many PathBuilder
S700s, each PathBuilder S700 would have to have the same VPI/VCI designations
assigned. The ATM switch removes this restriction.
Figure 50 shows several PathBuilder S700s in an ATM-switched network. The
switch maps one VPI/VCI into another based on the destination of the packets in
the cell, in the process learning the complete topology of the network. Each
PathBuilder S700 connected to the switch can be configured independently.
Figure 50
Virtual Circuits in a Switched Network
Segmentation
Once the CPU determines that a packet should go across the bridge, it
encapsulates the packet per RFC 1483 and adds a pad and trailer conforming to
AAL5 (ATM Adaption Layer 5) at the end of the packet (see Figure 51). The trailer
is fixed at eight bytes and contains information such as the new length of the
packet and cyclic redundancy check bytes (CRC facilitates error checking at the
receive end). The pad is set to 0 to 47 bytes to make the full packet length
including the trailer divisible by 48 bytes. The packet with the RFC 1483
encapsulation is then segmented into 48-byte (384-bit) cells by the SAR function.
Figure 51
AAL5 Pad and Trailer
PathBuilder S700 A
PathBuilder S700 C
PathBuilder S700 B
ATM
Switch
VPI/VCI 4/6
VPI/VCI 1/3
VPI/VCI 10/23
PathBuilder S700
PathBuilder S700
PathBuilder S700
Ethernet Packet
PAD
(0-47 Bytes)
Reserved
2 Bytes
Length
2 Bytes
CRC
4 Bytes
Trailer
Summary of Contents for 3C63400-3AC-C - PathBuilder S700 Switch
Page 14: ...xiv CHAPTER SUPPLEMENTARY REGULATORY INFORMATION ...
Page 18: ...4 ABOUT THIS GUIDE ...
Page 28: ...14 CHAPTER 1 SYSTEM DESCRIPTION ...
Page 88: ...74 CHAPTER 3 GETTING STARTED ...
Page 260: ...246 CHAPTER 6 PATHBUILDER S700 DIAGNOSTICS AND PERFORMANCE MONITORING ...
Page 270: ...256 INDEX ...