atm signaling

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ATM Signaling

• ATM signaling is mainly used for setup/release of virtual connections.

• A phased approach was taken for the introduction of ATM networks supporting switched services.

• This concept comprises three steps which are called capability sets (CS1, CS2, CS3).

• In CS1, simple switched services with constant bit rates are provided and basic interworking with existing 64 Kb/s ISDN is foreseen.

• More sophisticated services with variable bit rates, point-to-multipoint connections and multi-connections will be supported by CS2.

• With CS2, call and connection control will be separated.

• Finally, CS3 provides full range of services, including multimedia and distributive services.

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Capability Sets for B-ISDN SignalingCS1 CS2 CS3Constant bit rate Variable bit rateConnection-oriented servicewith end-to-end timing

Connection-oriented service Multimedia anddistributive service

QoS indication by the user QoS negotiationPoint-to-point connections Point-to-multipoint

connectionsBroadcast connectionsLeaf-initiated join

Single connection,simultaneously establishment

Multi-connection, delayedestablishedUse of cell loss priority

Third party controlSwitched VPs

Indication of peak bandwidth Negotiation and renegotiationof bandwidth

Peak rate allocation Bandwidth alocation based ontraffic characteristics

Basic interworking with64kbps ISDN

Incorporation of INprinciple into B-ISDN

Point-to-point or point-to-multipoint signaling accessMeta-signalingLimited set of supplementaryservices

Supplementary services Access to the Internet

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ATM Forum UNI Signaling• ATM Forum UNI signaling specifications are based on the

specifications of ITU-T.

• ATM Forum UNI 3.0



• UNI 4.0 provides features such as

- anycast: A user of a specific service need not know which entity in the network actually performs the service, and instead can use a published group address assigned to this service. The network can automatically distribute service requests to the service-providing group members.

- leaf-initiated join: join an already established VCC.

- proxy-signaling: a user performs signaling for one or more other users.

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Protocol Architecture for CS1

• Two signaling access configurations at the UNI:- Point-to-point:

Only one signaling endpoint on the user side.

A single permanently established point-to-point SVC is required.

- Point-to-Multipoint:

Several signaling endpoints are located at the user side.

Meta-signaling is necessary to manage other signaling relations.

S-AAL

Q.2931

ATM

PHY

S-AAL

Q.2931

ATM

PHY

MS

Point-to-point signaling access

Point-to-multipoint signaling access

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Protocol Architecture for CS1

• At the NNI, either the existing STM-based common channel signaling system no. 7 (SS7) or an ATM based network can be used to transport the signaling messages.

MTP-3

B-ISUP

MTP-2

MTP-1

S-AAL

MTP-3

ATM

PHY

STM based signaling network

ATM-based signaling network

B-ISUP

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ATM Adaptation Layer for Signaling• A suitable signaling AAL (S-AAL) is required in order to adapt the signaling

application protocols to the services provided by the underlying ATM layer.

• ITU-T uses AAL5 for Common part.

SAR

SSCF

SSCOP

CP convergence sublayerCommon Part

Service-Specific Part

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S-AAL Service Specific Part• The service-specific connection-oriented protocol (SSCOP) provides mechanisms for the establishment and release of connections

and the reliable exchange of signaling information between signaling entities.• The service-specific coordination functions (SSCFs) map the requirements of the layer above to the requirements of the next lower

layer.• ITU-T uses a common SSCOP for UNI and NNI.• SSCOP could have been designed by using an existing data link layer protocol, with some modifications.• ITU-T decided to specify a new protocol for SSCOP.


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SSCOP Functions• Sequence Integrity: preserve SDU order

• Error correction by retransmission: error detected by sequencing mechanism; corrected by selective retransmission.

• Flow control: receiver controlled; by dynamic window mechanism.

• Error reporting to layer management:

• Keep alive:• Local data retrieval: SDUs can be retrieved which have not yet been delivered

• Link management: establish/release SSCOP connections

• Transfer of Data: assured or unassured

• PCI error detection: errors within PCI are detected

• Status reporting


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Signaling Protocols for CS1• Reuse of existing protocols with some modifications.

• Q.2931 is the layer 3 signaling protocol for B-ISDN.

- UNI: Q.931, layer 3 protocol for 64 Kb/s ISDN- NNI: ISDN User Part (ISUP)

- Q.2931 includes the specification of the signaling messages, information elements and communication procedures between signaling endpoints for the B-ISDN UNI.

- Main modifications from Q.931:- a new information element (IE) for users to select between different AAL classes and the associated protocols.

- a new connection identifier IE consisting of VPCI and VCI. (The Virtual Path Connection Identifier identifies a VPC while a VPI identifies a VP link. VPCI is necessary because a VP cross-connect may exist between the local exchange and the TE.)

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Signaling Messages• Call establishment messages

• Call clear messages

• Status Messages

• Global Call Reference Related Messages

• Point-to-Multipoint Connection Control- Add Party- Add Party Acknowledge- Add Party Reject- Drop Party- Drop Party Acknowledge

- Status Enquiry- Status (Response)

- Release- Release Complete

- Call Proceeding- Connect- Connect Acknowledge- Setup

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UNI Point-to-Point Signaling Example

Source Destination

SETUP

SETUP

CONNECT

CONNECT

CONNECT ACK

CONNECT ACK

CALL PROCEEDING

CALL PROCEEDING

Network

UNI UNI

RELEASE

RELEASERELEASE COMPLETE

RELEASE COMPLETE

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Point-to-Multipoint Call Setup Example

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Signaling Message • Each message contains several common mandatory

information elements:

protocol discriminator (1)

call reference (4)

variable length info elements, as required (1)

message length (2)

message type (2)

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SETUP message format

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ATM Addressing• ATM uses two basic types of addresses: E.164 and AESA

(ATM end system addresses).• Telecom uses the global ISDN numbering plan specified in

ITU-T E.164.• AESAs are based on ISO NSAP (network service access

point).• Computer networks mostly employ the OSI NSAP

addressing mechanism.• E.164 addresses comprise 15 digits (8 bytes): country code

+ area or city code + subscriber number.• ATM Forum chose 20-octet NSAP address format and

encoding for addressing of ATM systems connected to a private network; systems connected to an public network can use either NSAP or E.164 addresses.

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ATM Addressing

• Current version of the NSAP addressing planes• Three addressing formats

– DCC (Data Country Code): the country with an address is registered

– ICD (International Code Designator): an international organization– E.164: ISDN & telephone numbers

• Each address is composed of IDP (Initial Domain Part) & DSP (Domain Specific Part).

• AFI (Authority and Format Identifier): Which of the formats• IDI (Initial Domain Identifier): specifies the Authority that allocates the

DSP that follows.

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1 3 13 19 20

AFI ICD HO-DSP ESI SEL

IDI

IDP DSP

1 3 13 19 20

AFI DCC HO-DSP ESI SEL

IDI

IDP DSP

(a) DCC ATM format

(b) ICD ATM format

1 9 13 19 20

AFI E.164 HO-DSP ESI SEL

IDI

IDP DSP

(c) E.164 ATM format

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• The number is coded in Binary Coded Decimal (BCD)• PAD: with zeroes on the left side 15 digits constant length

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PNNI• The private network-network interface (PNNI) is a

trunking, routing and signaling protocol specified by the ATM Forum. It is an inter-switch protocol which supports SVC between switches of multiple vendors.

PNNI

Network A Network B

PNNI

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PNNI Signaling Example

Source Switch

Transit Switch

Destination Switch

Source A Destination BSETUP

SETUPSETUP

SETUP

CONNECTCONNECT

CONNECTCONNECT

CONNECT ACK CONNECT ACKCONNECT ACK

CONNECT ACK

CALL PROCEEDINGCALL PROCEEDING

CALL PROCEEDING CALL PROCEEDING

RELEASE

RELEASERELEASE

RELEASE

RELEASE COMPLETERELEASE COMPLETE

RELEASE COMPLETERELEASE COMPLETE

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Example of PNNI Hierarchy

A B

PG(A)

PG(B)

A.1A.2

PG(A.1) PG(A.2)

A.1.1

A.1.2

A.1.3A.2.1

A.2.2

A.2.3A.2.4

B.1

B.2

B.3

B.4

Peer Group Leader

Logical Link

Physical Link

Logical Group Node

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Topology seen by Switch A.1.1

BA.2

A.1.1

A.1.2

A.1.3

DTL: Designated Transit List

DTL: [A.1.1, A.1.2]DTL: [A.1, A.2]DTL: [A, B]

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Switch A.1.2

BA.2

A.1.1

A.1.2

A.1.3

When A.1.2 receives the call setup message, it finds that itis at the end of top DTL, so it removes the top DTL and sends The message to A.2 (via A.2.1).

DTL: [A.1.1, A.1.2]

DTL: [A.1, A.2]DTL: [A, B]

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Switch A.2.1

BA.1

A.2.1

A.2.2

A.2.4

When A.2.1 receives the call setup message, it finds that A.2 has been reached. So it builds a route to B (say via A.2.3 and A.2.4) and pushes a new DTL onto the stack.

DTL: [A.2.1, A.2.3, A.2.4]DTL: [A.1, A.2]DTL: [A, B]

A.2.3

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Switch A.2.4

BA.1

A.2.1

A.2.2

A.2.4

When A.2.4 receives the call setup message, it finds that the targets at the top two DTLs have been reached. So it removes the top two DTLs and forwards the message with the following DTL to its neighbor:

DTL: [A.2.1, A.2.3, A.2.4]DTL: [A.1, A.2]DTL: [A, B]

A.2.3

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Switch B.1

A

B.2

B.1

B.3

When B.1 receives the call setup message, it finds that the current DTL has been reached.B.1 builds a new DTL, resulting in

DTL: [B.1, B.3]DTL: [A, B]

B.4

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Switch B.3

A

B.2

B.1

B.3

When B.3 receives the call setup message, it finds that it is the DTL terminator since all DTLs are at the end.

DTL: [B.1, B.3]DTL: [A, B]

B.4

atm signaling

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