Cisco Systems 8600 Series manual Functional Description STI Header

Functional Description

Figure 2-10 STI Header

STI Header

8	7	6		5	4	3	2	1
	HCF					VPI
		VPI					VCI
		VCI				Payload class
	CC		F	R		PTI		CLP
					HCS
HCF:	Header Control Field, a 01 indicates an STI Cell

VPI/VCI: Virtual Path/Virtual Channel Identifiers, same as UNI and NNI.

Payload Class:

0001 Non-Timestamped Data/Constant BIt Rate

0010 High Priority/Variable Bit Rate

0011 Voice/Constant BIt Rate

0100 Bursty Data A/Variable BIt Rate

0101 Time-Stamped Data/Constant BIt Rate

0110 Bursty Data B/Variable BIt Rate

CC: Congestion Control

00:	No report	10: Congestion
01:	Uncongested	11: Severe Congestion

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.

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			Description
Bits
432
000	User Data Cell		no congestion experienced	SDU Type 0 (CPE information)
001	User Data Cell		no congestion experienced	SDU Type 1
010	User Data Cell		congestion experienced,	SDU Type 0 (CPE information)
011	User Data Cell		congestion experienced,	SDU Type 1

100Connection Management Cell, OAM F5 Segment Flow Related cell

101Congestion Management Cell, OAM F5 End-to-End Flow related cell

110Connection Management Cell, reserved for future use.

111Connection Management Cell, reserved for future use.

H8149

The most important fields in all three ATM cell header types are the Virtual Path Identifier (VPI) and a Virtual Circuit Identifier (VCI). The VPI identifies the route (path) to be taken by the ATM cell while 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.

A 3-bit Payload Type Indicator (PTI) field indicates the type of data being carried in the payload. The first bit is a “0” if the payload contains user information and is a “1” if it carries connection management information. The second bit indicates if the cell experienced congestion over a path. If the payload is user information, the third bit indicates if the information is from Customer Premises Equipment. The PTI field is identical for UNI/NNI/STI.

2-10Cisco BPX 8600 Series Reference