CHAPTER 5: Signaling in ATM Networks

1. CHAPTER 5: Signaling in ATM Networks Objective: Users must have the capability of signaling connection across the network. 1. Switched Virtual Circuits (SVC) => by Signaling 2. Permanent Virtual Circuits (PVC) => by Network Management

2. THREE CLASSES of SIGNALING PROTOCOLS 1. ITU Protocols (descendent from ISDN protocols) * Q.2931 and related “Recommendations=Standards” e.g., Q.931 used for N-ISDN. 2. ATM FORUM PROTOCOLS * UNI 3.0 (Sept’93) & UNI 3.1 ( Q.2931) (Sept.’94) * UNI 4.0 (April’95) 3. Vendor Specific Protocols (Proprietary) * SPANS (Simple Protocol for ATM Network Signaling from FORE) * Several protocols developed at Research Centers and Universities.

3. THREE CLASSES of SIGNALING PROTOCOLS • Remarks: • * Only Difference between 3.0 and 3.1  • Data link protocol SSCOP used for reliable transport of ATM signaling packets. • Incompatible message formats between UNI 3.0 & • Q.2931 but functionality is very similar. • UNI 3.1 attempts to reconcile UNI 3.0 & Q.2931 but not • completely successful. => Three incompatible standards. • UNI 4.0 attempts supporting QoS. • (Various aspects of an ATM network have been split into Signaling • 4.0, Traffic Management 4.0, the PNNI, the ILMI, and the various • physical interface documents.) •  Need a universal standard to ensure interoperability.

4. UNI and NNI Signaling UNI = “Private” User/Network Interface NNI = “Public” Network/Network Interface UNI signaling NNI signaling UNI signaling Public ATM Switch Private ATM Switch “user” Public ATM Switch Private UNI Public UNI UNI signaling Public ATM Switch Public ATM Switch Public UNI • UNI and NNI signaling protocols are very similar in functionality. • P-NNI is the routing protocol.

5. Setup Setup NETWORK Call Proceeding Call Proceeding (Status Indication but not finished processing) Connect Connect Connect ACK Connect ACK Basic Connection Setup Protocol RECEIVER SENDER Start Call Call Received Setup Complete Call Accepted Local ACK, optional • Connection setup completed in one round-trip. • Signaling performed through dedicated Virtual Channels. • - UNI signaling VC: VPI=0, VCI =5

6. Basic Connection Setup Protocol (Cont.) Remark: Signaling between the end-system and the ATM switch usually takes place over VPI=0 and VCI=5, although this is not always the case. If we implement a feature such as SVC tunneling, the signaling channel will often be over a VPI =/ 0. Also, some proprietary UNI and NNI protocols use VCI =/5 for signaling. Note that the use of more than one VP at an interface does not imply that we require multiple signaling connections, since a single signaling link may service multiple VPCs.

7. Signaling Channels • Reserved VPI/VCI • x/1 = Meta-signaling • x/2 = Broadcast signaling (not used initially) • 0/5 = ATM endpoint to local network signaling both • point-to-point and point-to-multipoint signaling • (NONASSOCIATED SIGNALINGMODE: all VC • connections are created, controlled, released via • this channel) • x/5 = point-to-point signaling with other endpoints and other networks • (ASSOCIATED SIGNALING MODE: only VC connections within the VP x are created, controlled and released via this channel).

8. Meta-Signaling • Used to set up signaling channels • All meta-signaling messages are one cell long and have • VPI/VCI = 0/1 • Sets up 3 types of signaling channels: • - Point-to-point • - General broadcast • - Selective broadcast • Procedures to: • - Set up new signaling channels • - Release channels • - Verify channels

9. Signaling Messages • ATM Signaling is a protocol used to set up, maintain, and clear SVCs between two ATM end users over private or public UNIs. • The protocol is, in fact, an exchange of messages that takes place between the ATM end user (caller or receiver) and adjacent ATM switch. • The messages contain information that is used to build,maintain, or clear the connection. • The messages themselves are segmented into cells at the signaling AAL and then transported over a standard signaling channels, VPI=0, VCI=5.

10. Signaling Messages There are four types of messages: • CALL ESTABLISHMENT • CALL STATUS • CALL CLEARING • POINT-TO-MULTIPOINT OPERATIONS

11. SETUP. Sent by calling, or source ATM end user, to network (defined here as nearest ATM switch connected to ATM end user over UNI) and from network (defined here as nearest ATM switch connected to destination ATM end user over UNI) to called, or destination ATM end user. Used to initiate connection setup. Contains information, such as destination ATM address, traffic descriptors, AAL Info, and QoS. ATM End User ATM End User SETUP SETUP CALL PROCEEDING CALL PROCEEDING CONNECT CONNECT CONNECT ACK CONNECT ACK 1.CALL ESTABLISHMENT PROCESS NNI UNI UNI ATM Switch ATM Switch CALL PROCEEDING Accept DATA

12. CALL ESTABLISHMENT PROCESS • CALL PROCEEDING. Sent by destination ATM end user to network and by network to source ATM end user to indicate that call establishment has been initiated. • CONNECT. Sent by destination ATM end user to network and by network to source ATM end user to indicate that destination ATM end user accepts connection request. • CONNECT ACKNOWLEDGE. Sent by network to destination ATM end user to indicate call is accepted. May also flow from source ATM end user to network maintain symmetrical call-control procedures. • ALERTING. Sent by the destination ATM end user to the network and by the network to the source ATM end user to indicate that the destination ATM end user alerting has been initiated. For human interface (e.g., voice). • PROGRESS. Sent by the ATM end user or the network to indicate the progress of a call in the event of inter-working.

13. STATUS. Sent by the ATM end user or network in response to a STATUS ENQUIRY message. STATUS ENQUIRY. Sent by the ATM end user or network to solicit STATUS message. NOTIFY. Sent by the ATM end user or network to indicate information pertaining to a call/connection. 2. CALL STATUS

14. RELEASE. Sent by an ATM end user to request the network to clear the end-to-end connection or is sent by the network to indicate that the VCC is cleared and that the receiving ATM end user should release the VC and prepare to release the call reference after sending a RELEASE COMPLETE. NNI UNI UNI ATM Switch ATM Switch RELEASE RELEASE ATM End User ATM End User RELEASE COMPLETE RELEASE COMPLETE 3. CALL CLEARING RELEASE COMPLETE

15. RELEASE COMPLETE. Sent by an ATM end user or network to indicate that virtual channel and call reference have been released and that the entity receiving the message should release the call reference. RESTART. Sent by the ATM end user or network to request the recipient to restart the indicated virtual channel or all virtual channels controlled by the signaling channel. RESTART ACKNOWLEDGE. Acknowledges restart message and indicates restart is complete. 3. CALL CLEARING

16. Point-to-multipoint SVCs enable a single ATM end user to communicate with one or more ATM end users. Information flowing from the source ATM end user is replicated by the network, not at the source and received by all destination ATM end users attached to the point-to-multipoint connection. The calling or source ATM end user is called the ROOT, and the called or destination ATM end users are called LEAVES. Conceptually viewed, leaves are connected to the root in a tree structure. ATM_2 End User ATM End User ATM_1 End User 4. POINT-TO-MULTIPOINT OPERATIONS UNI UNI NNI ATM Switch ATM Switch ADD PARTY SETUP CALL PROCEEDING ADD PARTY ACK ADD PARTY ACK CONNECT CONNECT ACK

17. The root establishes a connection to the first leaf using standard call-establishment messages as shown in Figure. After that, additional leaves can be added or removed to the point-to-multipoint tree by the root. The leaves have the option of accepting the invitation and unilaterally removing themselves. Point-to-multipoint messages consist of the following: ADD PARTY. Adds party (leaf) to an existing connection. ADD PARTY ACKNOWLEDGE. Acknowledges a successful ADD PARTY. ADD PARTY REJECT. Indicates that ADD PARTY request was unsuccessful. DROP PARTY. Drops or removes party (leaf) from an existing point-to-multipoint connection. DROP PARTY ACKNOWLEDGE. Acknowledges a successful DROP PARTY Figure shows the messages required to be sent by the root to add a leaf (ATM_2) to an existing point-to-multipoint connection. POINT-TO-MULTIPOINT OPERATIONS

18. ATM End User ATM End User ATM End User ATM End User CASE 1 ADD THE NEXT PARTY. THE PARTY REJECTS. UNI NNI UNI ATM Switch ATM Switch ADD PARTY ADD PARTY SETUP CALL PROCEEDING RELEASE ADD PARTY NAK ADD PARTY NAK RELEASE COMPLETE (REJECT) (REJECT) CASE 2 ROOT DROPS A PARTY. UNI NNI UNI ATM Switch ATM Switch DROP PARTY DROP PARTY RELEASE RELEASE COMPLETE DROP PARTY ACK DROP PARTY ACK

19. ATM End User ATM End User ATM End User ATM End User CASE 3: ROOT DROPS LAST PARTY. UNI NNI UNI ATM Switch ATM Switch RELEASE RELEASE RELEASE RELEASE COMPLETE RELEASE RELEASE COMPLETE COMPLETE CASE 4: A PARTY DROPS OUT. UNI NNI UNI ATM Switch ATM Switch RELEASE DROP PARTY DROP PARTY DROP PARTY ACK DROP PARTY ACK RELEASE COMPLETE

20. ATM End User ATM End User CASE 5 NETWORK CLEARS THE CALL. UNI NNI UNI ATM Switch ATM Switch CONNECTION DROP PARTY TERMINATED RELEASE DROP PARTY ACK RELEASE RELEASE COMPLETE RELEASE COMPLETE

21. Leaf Initiated Join (LIJ) UNI 3.1 only allowed the root the option of adding leaves to an existing point-to-multipoint connection. This was deemed restrictive and would not provide the flexibility for applications to take full advantage of this capability. Therefore, UNI Signaling 4.0 added a capability for leaves to join a point-to-multipoint connection without intervention from the root. This is called leaf initiated join (LIJ). LIJ is supported in one of the FOLLOWING MODES.

22. Leaf Initiated Join (LIJ) MODE 1. ROOT SETS UP A NETWORK LIJ CALL (ROOT PROMPTED JOIN) (ROOT LIJ CONNECTION) MODE 2.LEAF PROMPTED JOIN WITHOUT ROOT NOTIFICATION MODE 3: LEAF JOIN TO AN INACTIVE LIJ CALL (I.e., No MulticastGroup Exists and a leaf wants to initiate a multicast group) MODE 4: LEAF JOIN TO A NON-LIJ CALL (A multicast group exists but notcreated by a LIJ procedure. A Leaf wants to join that existing multicast group.)

23. LIJ EXTENSION IN UNI 4.0 Two new messages were added to support LIJ in Signaling 4.0: LEAF SETUP REQUEST. Sent by leaf to initiate leaf-joining procedures. LEAF SETUP FAILURE. Sent to leaf by root or network to indicate failure to join the point-to-multipoint connection.

24. ATM End User ATM End User ATM End User MODE 1: ROOT SETS UP A NETWORK LIJ CALL. (The set up message contains LIJ parameters.) Also known asRoot-prompted Join. In this model the leaf generates and sends a request over the UNI to join a point-to-multipoint connection. This request, in turn, is forwarded up to the root which then invokes established procedures for adding a leaf to an existing connection. This is also called a root LIJ connection. UNI NNI UNI ATM Switch ATM Switch LIJ SET UP REQUEST LIJ SET UP REQUEST LIJ SET UP REQUEST ADD PARTY SET UP ADD PARTY CALL PROCEEDING CALL PROCEEDING CALL PROCEEDING ADD PARTY ACK CONNECT ADD PARTY ACK CONNECT ACK CONNECT ACK CONNECT ACK

25. ATM End User ATM End User ATM End User MODE 2: LEAF JOINS TO AN ACTIVE LIJ CALL. UNI NNI UNI ATM Switch ATM Switch LIJ SETUP REQ SETUP CALL PROCEEDING CONNECT NO ROOT NOTIFICATION CONNECT ACK Also known as Leaf-prompted Join without root notification. In this model a leaf generates and sends a request over the UNI to join a point-to-multipoint connection. The network handles the request and the leaf joins the connection without notifying the root. This is called a NETWORK LIJ CONNECTION.

26. ATM End User ATM_1 End User MODE 3: LEAF JOIN TO AN INACTIVE LIJ CALL NNI UNI UNI ATM Switch ATM Switch Leaf Setup Leaf Setup Leaf Setup Setup Setup Setup Call Proceeding Call Proceeding Call Proceeding Connect Connect Connect Connect Ack Connect Ack Connect Ack No Multicast Group Exists and a LEAF wants to initiate a MULTICAST GROUP.

27. ATM End User ATM_1 End User ATM_2 End User MODE 4. LEAF JOIN TO A NON-LIJ CALL NNI UNI UNI ATM Switch ATM Switch Leaf Setup Leaf Setup Leaf Setup Add Party Add Party Setup Call Proceeding Connect Add Party Ack Add Party Ack Connect Ack Suppose a MULTICAST GROUP exists but created by a NON-LIJ set-up. Now a LEAF wants to join that existing MULTICAST GROUP by LIJ Set Up Request.

28. SIGNALING PROTOCOL STACK (S-AAL) SSCS: Service Specific Common Part Sub-layer UNI 4.0 UNI 3.1 Q.2931 SSCF: Service Specific Coordination Function SSCOP: Service Specific Connection-Oriented Protocol SAP SSCF SSCS SAAL CPCS: Common Part Convergence Sub-layer SSCOP CPCS SAR: Segmentation & Reassembly SAR

29. Signaling Protocol Service-Specific Coordination Function (SSCF) AAL service-specific part (SSCS) Signaling AAL (SAAL) Service-Specific Connection- Oriented Protocol (SSCOP) CPCS AAL 5 SAR ATM Layer Physical Layer UNI Signaling Protocol Stack • Signaling messages transported over ATM network using Signaling AAL (SAAL) • Based on AAL 5 • SSCOP provides reliable transport

30. Signaling AAL (SAAL) Provides a structured & reliable means to transport signaling traffic between two ATM end users. As part of the C_PLANE (Control Plane), it serves as the interface between higher layer control & signaling functions such as UNI 3.1/Q.2931 and the ATM layer. SSCF: responsible for mapping the higher layer application to SSCOP. SSCOP: a powerful connection-oriented data link protocol that provides a reliable transport for signaling messages. It supports end-to-end error detection, correction, frame sequencing & selective framerecovery.

31. SSCOP Operation SSCOP can be used as general Transport Layer over ATM • Flow control based on sliding window • Window size can be dynamically controlled by receiver (buffer size) • Error control by selective retransmission of frames (only lost frame is retransmitted; AAL5 packets which consist of multiple ATM cells). • Separate frames for control and data • Data frames up to 64 Kbytes

32. SSCOP Control Frames {POLL, STAT, USTAT} used for reliable delivery TCP uses a timer, whereas SSCOP uses explicit delivery • POLL(Next): Periodically used by SOURCE to request status of receiver (DESTINATION) • Contains sequence number (SN) of next frame (NEXT) to be transmitted and timestamp --- if frames #1, #2, and #3 sent, POLL will send number for frame #4. • Receiver responds with sequence number of next sequential frame expected and list of any outstanding frames.

33. SSCOP Control Frames • STAT(Next;Missing): Status ACKing next and list of missing data. Response to POLL frame generated by receiver • SOURCE uses STAT frame to: • Retransmit lost frames • Release ACKed frames from the retransmission buffer • Advance transmission window to last sequential frame received by receiver • USTAT (Unsolicited Status): Sent by receiver upon detecting a “hole” in the received sequence of frames • Enables fast retransmission in the presence of random loss • Used to improve performance. Can have in-frequent POLLs, yet not send too many frames following a lost frame.

34. SSCOP Operation: Example Transmitter POLL POLL 0 1 2 3 4 5 6 7 8 9 7 10 11 12 X Receiver Transmitter does not Retransmit frame 7 Because POLL transmitted Before first retransmission STAT(5) Acknowledges Frames 0-4 USTAT Receiver detects Loss of frame 7 time STAT(10;7) Again requests Retransmission Of frame 7 Transmitter buffer size determined by frame rate and round trip delay between POLL and Receiver STAT

35. ATM Addressing PEER MODEL: Use existing IP or MAC Addresses. IP routing protocols (OSPF) could be used. Advantages: Simplifies end system address administration. Disadvantages: Increases the complexity of ATM switches since they must act like multiprotocol routers and support address tables for all current protocols. OVERLAY MODEL: Decouple ATM from existing Infrastructure and have unique addressing mechanism. Accordingly new routing protocols were needed + Address resolution protocols from IP to ATM or from LANs to ATM address conversions. Advantages: Decoupling of ATM from higher layers allows independent development, applications and ATM technology. OVERLAY MODEL  CHOSEN!!!

36. Each ATM end user must have a UNIQUE ADDRESS. There is a STANDARDIZED ADDRESSING STRUCTURE for both PUBLIC and PRIVATE ATM NETWORKS!!! Private Networks: (based on HIERARCHICAL ADDRESSING DOMAINS) - 20-byte format based on syntax of OSI Network Service Access Point (NSAP) address -Two different formats: 1. DCC (Data Country Code) 2. ICD (International Code Designator) ATM Host Addressing

37. ATM Host Addressing Public Networks: - 8-byte (64 bits) E.164 format defined by ITU-T (has 16 digits each code with Binary Coded Decimal (BCD) using 4 bits.) - Can be extended to a 20-byte private address format by appending end-system address (e.g., MAC address) Make Compatible With Private Network address

38. Authority& Format Identifier(39) “BD” Data Country Code High-order Domain Specific Part End-System Identifier Selector 1 byte 2 bytes 10 bytes 1 byte 6 bytes ATM Network Address Formats ATM Forum specifies 3 NSAP (Network Service Access Points) – like Address Formats DCC ATM Format Private Not used In Routing EndSystem Supplied Network Supplied IDP DSP IDI Multiple addresses assigned to the same ATM adapter.

39. ICD ATM Format Private Authority& Format Identifier(47) “C5” Int’l Code Designator High-order Domain Specific Part End-System Identifier Selector 1 byte 2 bytes 10 bytes 1 byte 6 bytes IDP DSP IDI ETHERNET & Token Ring address field length for IEEE assigned addresses ICD codes identify particular international organizations.

40. Authority& Format Identifier(45) “C3” E.164 Address High-order Domain Specific Part End-System Identifier Selector 1 byte 8 bytes 4 bytes 1 byte 6 bytes NSAP-Encoded E.164 Format Public IDP DSP (Domain Specific Part) IDI High order domain specific part addresses can be assigned by “hand”.

41. The IDP specifies an administration authority which has the responsibility for allocating and assigning values for the DSP. IDP has AFI (Authority and Format Identifier (AFI)) and IDI (Initial Domain Identifier (IDI). AFI specifies the format of the IDI, and the abstract syntax of the DSP field. IDI specifies the network addressing domain, from which DSPs are allocated and the network addressing authority responsible for allocating values of the DSP from that domain. DCC (Data Country Code) Specifies the country in which the address is registered. These addresses are administered by the ISO’s national member body in each country. The digits of data country code are encoded using BCD. Addressing

42. ICD (International Code Designator) Identifies an authority which administers a coding scheme. This authority is responsible for the allocation of identifiers within this coding scheme to organizations. The registration authority for the international code designator is maintained by the British Standards Institute. The digits of ICD are encoded using BCD. Addressing

43. ATM Forum extended E.164 address to NSAP format. E.164 number is filled with leading zeroes to make 15 digits. A F16 is padded to make 8 bytes. High Order DSP (HO-DSP) field will be used to construct multi-level address hierarchies for routing. Remark: In real NSAPs, DSP is subdivided into a hierarchy of Routing Domain (RD) and an Area Identifier (AREA) and an End System Identifier (ESI). ATM Forum combined the RD and AREA fields into HO-DSP. A range of addressing hierarchies will be supported -> increases the scalability.

44. End System Identifier (ESI): 48-bit IEEE MAC address (to identify a specific host within an ATM subnet) (Token Ring, Ethernet LAN MAC addresses) SELECTOR is for use inside the host and is not used for routing (used for local multiplexing within end stations and has no network significance). This is used to distinguish between different destinations reachable at the end device. All ATM addresses are 20 bytes long.

45. Addressing • Private networks must support all three formats • Type of Number field = Unknown • Numbering Plan Indication field = ISO NSAP • Public networks must support native E.164 and may optionally support three NSAP-encoded formats. • For E.164: • Type of Number field = International Number • Numbering Plan Indication field = Recommendation E.164 • If only native E.164 addresses, subaddress field in signaling messages used to convey private ATM address across. • One Transit network selection possible using carrier identification code field

46. E.164 Addresses (ITU-T) • North American Numbering Plan (NANP): 1(614)-555-1212 • E.163 numbering plan for telephony: 12 digits • E.164 numbering plan for ISDN: 15 digits • Defined in ITU-T recommendation E.164 for ISDN • ISDN numbers uniquely identify interfaces to public networks • Several ISDN numbers can identify the same interface • ISDN signaling allows ISDN number followed by a sub-address (extension) of up to 40 digits • Administrated by public networks (Therefore, are not easily available for private network use)

47. EXAMPLE ATM Address for SVC connecting BWN Lab Testbed (GCATT) to OIT-OC-3 (Rich Building) 39.840F.8001.BC88.2280.4110.4002.4000.OC80.0020.00

48. . . . ATM Signaling Message Format(Q.2931, UNI 3.0, UNI 3.1) • Each message includes the following components: Bits 8 7 6 5 4 3 2 1 Octets Protocol Discriminator 1 Length of call reference value (in octets) 0 0 0 0 2 Flag Call reference value 3 Call reference value (continued) 4 Call reference value (continued) 5 Message type 6 Message type (continued) 7 Message length 8 Message length (continued) 9 Information Elements 10 Information Elements 11

49. Message Format • Protocol Discriminator (1 byte):Distinguishes Q.2931 messages from other messages. • 08 = Q.931 • 09 = Q.2931 • Call Reference (4 bytes):Identifies call to which this message is related to. One user may have many calls simultaneously. • Flag = 1 : Message is from call reference originator • Flag = 0 : Message is to call reference originator • Message Type (2 bytes): Many types, e.g., connect, call proceeding, setup, release, etc. • Message Length (2 bytes): Length of contents of this message

50. Sample Message Types