Transcript Lecture 7 - Egan Family

ATM Signalling
Philip Branch
Centre for Telecommunications and Information
Engineering (CTIE)
Monash University
http://www.anspag.monash.edu.au/~pbranch/masters.ppt
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Signalling Overview
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Description of Signalling
Signalling between the User and Network
Signalling within Private ATM Networks
Signalling between ATM networks
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What is Signalling?
• Call and Connection Control
• Means by which calls are
– established, maintained, terminated
• In Channel Signalling
– in and out of band
• Common Channel Signalling
– One shared, dedicated signalling channel
– N-ISDN and ATM
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Requirements of ATM Signalling
• Establish connection
– Routing
– Quality of Service
– Point to point, multipoint
• Clear connection
• Status information
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Establishment of a Connection
• Find destination node
• Determine path through network
• Establish connection between each node
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Signalling Standards
• User-Network Interface
– UNI 3.0, UNI 3.1, UNI 4.0
– Q.93B, Q.2931
– ILMI
• Network to Network Interface
– IISP, P-NNI, IPNNI, AINI, BICI, B-ISUP
• Other important standards
– LANE, MPOA
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ATM Signalling Standards
Evolution
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Q.931 - Q.93B - UNI 3.0
Q.931 - Q.2931 - UNI 3.1
Q.931 - Q.2931 - UNI 4.0
Q.931 - Q.2931 - IISP - PNNI
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Signalling within Private ATM
Networks
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Private and public network standards
ATM Forum, ITU-T main standards bodies
Connection of CPE to network
Connection across the network
Passing of reachability information between
switches
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ATM Addressing
• Two formats
– OSI NSAP for private networks
– E.164 for public networks (ISDN numbers)
• Format
– Network part
– User part
• Network part hierarchical structure
• User part similar to Ethernet MAC address
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ILMI and Addressing
• Interim Local Management Interface
Specification
• Management plane of ATM protocol stack
• Built around SNMP
• Management Information Base
• Monitoring and Control across the UNI
• Key function is address registration
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User-Network Interface
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Access Signalling
Connection between CPE and network
UNI 3.0, 3.1, 4.0
Q.2931
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UNI 3.1
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ATM Forum Standard
Similar to N-ISDN Q.931
Signalling between CPE and network
Specify point to point and multipoint
Signalling ATM Adaptation Layer
Signalling over PVC
– VPI = 0, VCI = 5
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Signalling Protocol Stack
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UNI,
UNI SSCF,
SSCOP Q.2110,
AAL5
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UNI 3.1 Signalling Messages
• Fewer messages than Q.931
• Call establishment
– setup, proceeding, connect, connect
acknowledge
• Call Clearing
– release, relase complete
• Status
– status, status enquiry
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SETUP Signalling Message
• Similar to SETUP in N-ISDN Q.931
• Additional functions in SETUP
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AAL type
Bearer (CBR, VBR-nrt, Unkown)
ATM traffic descriptor
QoS parameter
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Traffic Descriptor in SETUP
• Forward and backwards traffic
• CLP priorities
• Token Bucket Parameters
– Peak Cell Rate
– Sustainable Cell Rate
– Maximum Burst Size
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Quality of Service Parameter
• Predefined in 3.1
• Parameterised in 4.0
• Parameters
– Cell Loss Ratio
– Maximum Cell Delay Time
– Maximum Cell Delay Variation
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Call Progression
Calling Party
VPI 0, VCI 5
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SETUP (Call Ref, AAL, Address, Cell Rates, QoS)
Various timers
used during call
connection phase
CONNECT (Call Ref, AAL, Connection ID - VPCI, VCI)
Active
State
ATM Network/Switch
Various timers
used during call
connection phase
CONNECT ACK (Call Ref)
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Switch to Switch Signalling
• Routing
– How to find destination
• Resource allocation
– Quality of Service guarantees
– Connection Admission Control
• Signalling Protocol
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Interim Inter-Switch Protocol
(IISP)
• Precursor to PNNI
– PNNI phase 0
• Based on UNI 3.1
• Static Routing
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P-NNI Standard
• Private Network to Network Interface
• ATM Forum Standard
• Communications between switches in a
private network
• Scalability
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P-NNI Protocol Stack
• PNNI
• UNI SSCF (Q.2130) and SSCOP (Q.2110)
– Signalling Specific Coordinating Functions
– Service Specific Connection-oriented Control
– Data Link protocol
• AAL5
• SSCF, SSCOP, AAL5 = SAAL
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Functions of P-NNI
• Signalling protocol
– Based on UNI 3.1
• Routing
– Most important function of P-NNI
– Designated Transit List(DTL)
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Routing in P-NNI
• Source based routing protocol
• Source specifies route to destination
– Designated Transit List
• Transfer of topology information between
switches
• Uses hierarchy and summarisation
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Source Routing
• Source needs complete topology
information
• Broadcast id on all paths
• Copy and transfer other nodes
• Scales poorly
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P-NNI Topology Construction
• Hierarchy of Peer Groups
– overcomes scalability problems of Source
Routing
• Every member of Peer Group knows route
to every other member
– DTL in Setup message
• New DTL constructed whenever message
leaves peer group
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Exchange of information at first
level within a PG
• PNNI topology state packets (PTSP)
– reachable destinations within PG
– current capabilities of nodes and links
• All members of Peer group flooded with
PTSPs
• New PTSPs exchanged when
– major events
– information aged
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Topology State Information
• Information transferred in PTSPs
• Attributes of Switch
– total capacity
• Metrics
– number of connections
– used capacity
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Reachability Information
• Based on Address prefixes
• Designated Transit List
– Source route at each level
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Exchange of information at
higher level PGs
• Designated Peer Group Leader
– Elected by other nodes
– Election ongoing
– Represents PG at next layer
• PGL summarises topology state and
reachability information
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GCAC and Crankback
• Generic Connection Admission Control
(GCAC)
– Indication only as to whether connection can be
admitted
• Crankback enables alternate path to be
found without abandoning complete call
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Example of P-NNI connection
establishment
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Summary of Functions of PNNI
Routing
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Discovery of neighbours and link status
Synchronisation of topology databases
Flooding of PTSPs
Election of PGLs
Summarisation of topology information
Construction of routing hierarchy
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Broadband ISDN User Part
• ITU-T standard
• Public carrier standard
• Connectionless, Hop-by-hop routing
– similar to IP
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Signalling between ATM
Networks
• Interconnection between both public and
private networks
• Private to private eg. Monash University /
Melbourne University
• Private to public eg. Monash / Telstra
• Public to Public eg. Telstra / Optus
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Issues with signalling between
ATM networks
• Different network signalling standards
• Large amounts of topology information
• Confidential information
– topology, metrics
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Standards for Signalling between
ATM Networks
• Broadband Inter-Carrier Interface
– ATM Forum
– Based on SS7, B-ISUP
– Interworking between B-ISUP networks
• ATM Internetwork Interface (AINI)
– Interworking between PNNI, B-ISUP
– PNNI signalling with static routing
– Connecting non-PNNI / PNNI networks
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Conclusion
• Signalling functions
• User network interface signalling
– UNI 3.0, 3.1
• Switch to switch signalling
– IISP, P-NNI
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Questions
• Why is there no contention algorithm for
access to the signalling channel in ATM?
• In the worked example of PNNI routing,
what is the next DTL to be pushed onto the
stack?
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