Cisco BPX-BXM-155-8DX Installation And Configuration Manual page 594

Figure C-5
STI Header
8
HCF
CC
HCF:
VPI/VCI: Virtual Path/Virtual Channel Identifiers, same
Payload Class:
0001
0010
0011
0100
0101
0110
CC: Congestion Control
00: No report
01: Uncongested
PTI, bits 4,3, and 2:
bit 4 = 0, user data cell;
bit 4 = 1, connection management cell
bit 3 = 0, No congestion experienced
bit 3 = 1, Congestion experienced
bit 2 = 0, for user data cell, indicates CPE information
bit 2 = 1, not used
PTI
Bits
432
000
001
010
011
100
101
110
111
The most important fields in all three ATM cell header types are:
• Virtual Path Identifier (VPI)
The VPI identifies the route (path) to be taken by the ATM cell
• Virtual Circuit Identifier (VCI)
the VCI identifies the circuit or connection number on that path.
The VPI and VCI are translated at each ATM switch, they are unique only for a given physical link.
A 4-bit Generic Flow Control (GFC) field in the UNI header is intended to be used for controlling user
access and flow control. At present, it is not defined by the standards committees and is generally set
to all zeros.
Cisco BPX 8600 Series Installation and Configuration
C-4
STI Header
7 6 5 4 3
VPI
VPI
VCI Payload class
F R PTI
HCS
Header Control Field, a 01 indicates an STI Cell
as UNI and NNI.
Non-Timestamped Data/Constant BIt Rate
High Priority/Variable Bit Rate
Voice/Constant BIt Rate
Bursty Data A/Variable BIt Rate
Time-Stamped Data/Constant BIt Rate
Bursty Data B/Variable BIt Rate
10: Congestion
11: Severe Congestion
Description
User Data Cell no congestion experienced
User Data Cell no congestion experienced
User Data Cell congestion experienced,
User Data Cell congestion experienced,
Connection Management Cell, OAM F5 Segment Flow Related cell
Congestion Management Cell, OAM F5 End-to-End Flow related cell
Connection Management Cell, reserved for future use.
Connection Management Cell, reserved for future use.
2 1
VCI
CLP
F: ForeSIght Forward Congestion
Indication (FFCI).
Set to 1 if FECN in Frame is a 1.
or if incoming cell FFCI is a 1, or
egress queue experiences congestion.
R: Reserved
PTI: Payload Type Indicator
CLP: Cell Loss Priority. Same as for UNI
or NNI. The CLP bit is set to 1 if the
DE is set for a frame, or if the first
FastPacket in a frame has its CLP set.
SDU Type 0 (CPE information)
SDU Type 1
SDU Type 0 (CPE information)
SDU Type 1
Release 9.3.0, Part Number 78-10674-01 Rev. D0, July 2001
Appendix C ATM: An Overview