atm-signaling1 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.

atm-signaling2 Capability Sets for B-ISDN Signaling

atm-signaling3 ATM Forum UNI Signaling ATM Forum UNI signaling specifications are based on the specifications of ITU-T. ATM Forum UNI 3.0 ATM Forum UNI 3.1 ATM Forum UNI 4.0 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.

atm-signaling4 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

atm-signaling5 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

atm-signaling6 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 sublayer Common Part Service-Specific Part

atm-signaling7 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. ITU-T uses AAL5 for Common part.

atm-signaling8 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 ITU-T uses AAL5 for Common part.

atm-signaling9

10 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.)

atm-signaling11 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

atm-signaling12 UNI Point-to-Point Signaling Example Source Destination SETUP CONNECT CONNECT ACK CALL PROCEEDING Network UNI RELEASE RELEASE COMPLETE

atm-signaling13 Point-to-Multipoint Call Setup Example

atm-signaling14 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)

atm-signaling15 SETUP message format

atm-signaling16 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.

atm-signaling17 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.

atm-signaling AFI ICD HO-DSP ESI SEL IDI IDP DSP AFI DCC HO-DSP ESI SEL IDI IDP DSP (a) DCC ATM format (b) ICD ATM format AFI E.164 HO-DSP ESI SEL IDI IDP DSP (c) E.164 ATM format

atm-signaling19 The number is coded in Binary Coded Decimal (BCD) PAD: with zeroes on the left side  15 digits constant length

atm-signaling20 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

atm-signaling21 PNNI Signaling Example Source Switch Transit Switch Destination Switch Source A Destination B SETUP CONNECT CONNECT ACK CALL PROCEEDING RELEASE RELEASE COMPLETE

atm-signaling22 Example of PNNI Hierarchy

atm-signaling23 Topology seen by Switch A.1.1 B A.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]

atm-signaling24 Switch A.1.2 B A.2 A.1.1 A.1.2 A.1.3 When A.1.2 receives the call setup message, it finds that it is 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]

atm-signaling25 Switch A.2.1 B A.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

atm-signaling26 Switch A.2.4 B A.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

atm-signaling27 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

atm-signaling28 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