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has stabilized and the routing information has been
disseminated.
Using this picture, each IS traverses the entire graph
using Dijkstra's Shortest Path First (SPF) algorithm. It
finds, for each destination, the next hop to use on the
best path to that destination. Level 1 ISs also find the
shortest path to the nearest Level 2 IS. For Level 1
routing, the destination is a system ID; for Level 2
routing the destination is an area address.
It is necessary for all ISs in the area (for Level 1) or
domain (for Level 2) to have the same picture of the area
or domain. Otherwise, routing loops can occur because
two ISs may each think that the other is on the shortest
path to the destination, sending packets back and forth
between each other until the packet lifetime expires.
SONET SDCC SPECIFICATIONS
This section specifies the characteristics of the SONET
SDCC as implemented in the OC-3 MUX module.
7-Layer OSI Stack
• Physical Layer
– SONET SDCC, a 192 Kbps channel carried in 3
section overhead bytes of the first STS-1
– A separate stack exists per OC-3 MUX; one
MUX will be selected to contain the active stack
enabling the SDCC to be protected from all
facility-related protection switches. Active TL1
sessions will be lost if the MUX containing the
active stack is unplugged or is re-initialized after
a program download.
• Data Link Layer
– The protocol is the Link Access Protocol on the
D-channel (LAPD) as specified in ITU-T
Recommendation Q.921, ISDN user-network
interface – Data link layer specification.
– Acknowledged information transfer service
(AITS) is supported. Unacknowledged Infor-
mation Transfer Service (UITS) is not supported.
– The SAPI value is fixed at 62. It cannot be
changed.
– Maximum packet size set to 512 octets.
• Network Layer
– Two NSAP address formats are supported: the
ISO DCC format, as defined in GR-253-CORE,
and the Private format. The ISO DCC format is
26 hex characters indicated by an Authority
Format Identifier (AFI) value of 39 (e.g.,
3940F0000000000000000000). The Private
A-2
format is a variable length field indicated by an
AFI value of 49 (e.g., 490000).
– The NSAP area address is user-definable. No
default value is supported.
– The system ID is a fixed-size hex number 12-
characters long. It is user definable and has no
default value.
– The Globally Unique Network Layer Quality of
Service (QoS) option is not supported.
• Transport Layer
– Supports both end system (ES) and intermediate
system (IS).
• Session Layer
– Standard implementation.
• Presentation Layer
– Standard implementation.
• Application Layer
– TL1 is supported.
– ACSE, ROSE/CMISE, FTAM, Name/Address
Translation Services are not supported.
TOTAL ACCESS DCC REQUIREMENTS
Initial turnup procedures must be performed locally
through the craft interface provided on the front (or
rear) of the SCU. For simplex configurations, the SCU
provisioning must have the MUX Auto Provisioning
Option enabled, which will result in a copy of the provi-
sioning on the SCU. Failure to do this will require the
DCC system provisioning options to be manually
entered whenever the MUX board is replaced.
For duplex configurations, the MUX Provisioning
should have the Linked Provisioning and the MUX
Auto Provisioning Options enabled on both cards. The
Linked Provisioning option will enable changes to
"linked parameters" entered on one MUX module to be
updated on the other MUX module. If Linked Provi-
sioning is not enabled, changes in the DCC provisioning
will have to be made to both copies.
When a MUX board is replaced, it will obtain provi-
sioning from its mate MUX board (if Linked Provi-
sioning is enabled) and/or the SCU (if MUX Auto
Provisioning is enabled).
SCU Provisioning Data
The SCU has provisioning that defines the Common
Language Location Identifier (CLLI) code. The MUX
uses the CLLI code as the TL1 target identifier (TID).
61181031L3-5A
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