B-ISDN & ATM

1. B-ISDN & ATM

2. Bit Rates for Different Applications

3. OVERVIEW • BISDN is an extension of ISDN in terms of capabilities, i.e. it not only has the narrowband capability of ISDN but also the broadband capability. Definition • “A service requiring transmission channels capable of supporting rates greater than the primary rate.” • Any service inquiry with a speed greater than 1.544 Mbps is defined as broadband, and any communications based on this speed are called broadband communications.

4. BISDN is an extension of ISDN only in term of the name. Everything is different including protocol, architecture, transmission, and switching technology. • The Goal of BISDN is to achieve complete integration of services, ranging from low-bit-rate bursty signals to high-bit-rate continuous real-time signals.

5. Broadband ISDN Second generation (broadband) ISDN • Supports very high data rate (600 Mbps) • It uses fiber optic cable at all levels • Has packet switching orientation • It uses ATM to move data from one end point to another.

6. Services include voice-band services such as telemetry, low-speed data, telephone, and facsimile and broadband services, such as high quality video conferencing, high-definition television (HDTV) video transmission and high speed data transmission. • Thus BISDN must adapt the characteristics of each of the different services and integrate them into a common transmission and switching platform. • For instance, the packet switching concept is used for data- transmission and the circuit switching concept is used for voice transmission. In BISDN both these concepts are used so that both type of traffic can be handled.

8. Interactive Services: Two-way exchange of information (other than control signaling information) between two subscribers or between a subscriber and a service provider. Distribution Services: Primarily one way transfer of information, from service provider to B-ISDN subscriber.

9. Interactive services: • Conversational • Services that support real time data exchange ( phone class, video conferencing, real time data transfer) • Messaging • These services are store-and-forward services (voice mail, data mail, video mail) • Retrieval: • Information are retrieved from a central source (libraries, shared resources)

10. Distribution Services Without User Presentation Control • Referred also as broadcast services • Provide a continuous flow of information, which is distributed from a central source to an unlimited number of authorized receivers connected to the Network. • User can access this flow of information but has no control over it. • Example: High definition television (HDTV) • Commercial TV, programming contents and times are decided by provider.

11. Distribution Services With User Presentation Control • Distribute information from a central source to a large number of users. • Information is provided as a sequence of information entities (e.g. , frames) with cyclical repetition. • User has the ability of individual access to the cyclical distributed information and can control start and order of presentation. • Example: cable text • Pay TV • Educational broadcasting

12. Functional Architecture • Control of B-ISDN based on common-channel signaling • B-ISDN must support all the 64-kbps transmission services, both circuit switching and packet switching. • In addition it should support higher-data-rate transmission services. Example: high resolution video (150 Mbps), video-on-demand (600 Mbps) • At the user-network interface, higher-data-rate transmission are provided using ATM. • Needs fiber subscriber loops.

14. Broadband ISDN Access Methods • Symmetrical: • 155.52 Mbps full-duplex • Suitable for residential and small businesses subscribers • 622 .08 Mbps full-duplex • Suitable for businesses subscribers that provide and receive distributive services • Asymmetrical: • 155.52 Mbps output/622.08 Mbps input full-duplex

15. B-ISDN Access Methods

16. Protocols: ATM used for transfer of information across the user-network interface. This implies that B-ISDN is a packet-based network ( at the interface and internal switching) B-ISDN also supports circuit mode applications over a packet based transport mechanism.

17. ATM: What it is • Asynchronous Transfer Mode • A low-layer networking technology based on fast packet-switching of small fixed size packets called cells • ATM provides a single transport mechanism for integrated services traffic: data, voice, video, image, graphics. • All statistically multiplexed at ATM layer

18. ATM: What it isn’t • Synchronous Transfer Mode (STM) • STM relies on pre-assigned “slots” for each user within a frame, and global timing information to mark frame boundaries • Example: T1 transmission (1.544 Mbps)

19. Synchronous Transfer Mode • STM relies on positional association: slots are identified by their relative position from the start of the frame (global timing info) • Each user knows which slot(s) to use • All slots are the same size (e.g., 8 bits) • Bandwidth allocated in multiples of slots • Efficient for Constant Bit Rate traffic • Inefficient for Variable Bit Rate traffic

20. Asynchronous Transfer Mode • ATM does not use a priori assignment of slots to users • Slots are assigned “on demand” on an as needed basis • Users can use whichever slots are empty

21. Slotted transmission scheme All slots are the same size (53 bytes = 1 ATM cell) Any user can use any empty slot No notion of specific slots assigned to specific users Bandwidth allocation in ATM may reserve a certain percentage of the total slots for a given call, but which slots you get is determined at time of transmission ATM Transmission Can support arbitrary bit rates

22. Asynchronous Transfer Mode • No global timing relationship between slots (i.e., cells) of different users (asynchronous) • Efficient for Variable Bit Rate traffic • Implication: the cell in each slot has to be completely self-identifying (i.e., overhead)

23. Advantages of ATM • Better for bursty traffic (i.e., VBR) • Statistical multiplexing gain • Better network utilization • Same mechanism works for all traffic types • Simple and fast hardware switching

24. Characteristics of ATM • Point to point technology • Connection-oriented: an end-to-end connection (called a virtual channel) must be set up using a signalling protocol before any data cells can be sent on that VC • “Bandwidth on demand” • Statistical multiplexing • Integrated services

25. ATM is a scalable technology • scalable in bandwidth • scalable in distance • scalable in deployment

26. ATM: Scalable Bandwidth • ATM is not tied to any particular bit rate or physical layer network technology • ATM is simply the abstract concept of fast packet switching with small fixed size cells • Can do low speed ATM (e.g., 1.5 Mbps) • Can do high speed ATM (e.g., 155 Mbps) • Primary interest: high speed ATM networks

27. ATM: Scalable Distance • ATM can be used for LANs • ATM can be used for MANs • ATM can be used for WANs • Initial market: ATM LANs, enterprise area networks, LAN backbones • Future: wide area network backbone, ATM to the desktop, wireless ATM

28. ATM: Scalable Deployment • Emphasis on interoperability, compatibility • Incremental evolutionary path to ATM • Ethernet => switched Ethernet => ATM hub • Start with one switch, N ports, plus NICs • Add more ports as needed • Add more switches as needed • Hierarchical cascading structure

29. The B-ISDN ATM reference protocol model consists of three planes: Management Plane User Plane Control Plane

30. B-ISDN ATM Reference Model

31. Management Plane: Two types of functions exist in this plane Layer management: All the management functions related to the resources and parameters residing in its protocol entities such as signaling are performed by layer management. Plane management: All the management functions that relate to the whole system are located in the plane management.

32. USER PLANE: The function of the user plane is to transfer the user information from point A to point B in the network. All associated mechanisms, such as flow control congestion control, or recovery from errors are included. CONTROL OR SIGNALING PLANE: This plane is responsible for call control and connection control functions related to setting up and tearing down a connection.

34. ATM Physical Layer

35. Physical Layer in ATM • B-ISDN service : Compromise between circuit and packet switching • Virtual Circuits • Connection oriented • Implemented internally with packet switching • Connection Types • Permanent virtual circuits (No setup time) • Switched virtual circuits (Like telephone call) • Circuit establishment • The route is chosen from source to destination • All switch along the way make table entries so they can route any packet on that virtual circuit

37. Data Link Layer in ATM TC(Transmission Convergence) sublayer • Cell Transmission • takes a sequence of cells • add HEC to each one ( HEC : Header Error Control ) • convert the result to bit stream • match the bit stream to the speed of the underlying physical transmission system by inserting OAM cells as filler • OAM : Operation And Maintenance • Cell Reception • takes an incoming bit stream • locates cell boundaries • verifies the header • processes the OAM cells • passes the data cell up to the ATM layer

38. Locating the cell boundaries • HUNT : Shifting bits into the shift registers one at a time looking for a valid HEC • PRESYNCH : shifts in the next 424 bits(5-bytes) without examining them

39. Cell Payload Scrambling • At source, scramble the cell payload • At receiver, descramble the cell payload • To increase the security and robustness • To protect against malicious users or unintended simulation of a correct HEC in the information field

40. Header Error Control • 8-bit field calculated based on remaining 32 bits of header error detection • in some cases, error correction of single-bit errors in header • 2 modes: • error detection • Error correction

41. Figure 5.6

42. ATM Layer

43. Cell Formats • UNI(User-Network Interface) • Define boundary between a host and an ATM network(between the customer and the carrier) • NNI(Network-Network Interface) • Define boundary between two ATM switches GFC : General Flow Control PTI : Payload Type VPI : Virtual Path Identifier CLP : Cell Loss Priority VCI : Virtual Channel Identification HEC : Header Error Check 40 bits 40 bits

44. GFC : flow control or priority • VPI : select a particular virtual path • VCI : select a particular virtual circuit • PTI : define the type of payload • CLP : set by host to differentiate between high-priority traffic and low-priority traffic • HEC : checksum over the header

45. Virtual Circuits in ATM Virtual Circuit Identifier is represented jointly by: • Virtual Channel Identifier (VCI) • Virtual Path Identifier (VPI) Virtual Channel (VC) • Path for cell associated with a connection • Supports transportation of a data stream • Each VC is assigned a unique VCI on a link

46. Virtual Channels in ATM Virtual Path (VP) • Grouping of virtual channels on a physical link • Switching can be performed on the path basis: • reduced overheads • Each virtual path is assigned Virtual Path Identifier (VPI)

47. Virtual Path Transmission Path Virtual Channel VCs In ATM

48. VP - Switch VP4 VP1 VC3 VC4 VC5 VC1 VC2 VP5 VP2 VC! VC2 VC3 VC4 VC5 VP3 VP6 VC6 VC7 VC6 VC7 Virtual Path Switch (VP - Switch)

49. VC3 VC3 VC1 VC1 VC2 VC2 VP3 VP1 VC2 VC3 VC1 VP4 VP2 VP5 VC4 VC5 VC4 VC5 VP/VC Switch VP / VC Switch

50. Why VPI / VCI rather than a single VC number? • Semi-permanent VP reduces the setup time • VCs can be easily added to the existing VPs • Reduced size of the routing table • Separate groups for different types of streams: voice, data, and video • Different QoS can be applied to different VPs