Asynchronous Transfer Mode ATM TEL660 Wide Area Networks, Chapter 13 Part 2 of 2

1. Asynchronous Transfer Mode (ATM)TEL660 Wide Area Networks, Chapter 13 Part 2 of 2 February 9 2006 Brian O’Donnell IONA College Rockland Graduate Center Pearl River New York

2. Asynchronous Transfer Mode (ATM)TEL660 Wide Area Networks, Chapter 13 Part 2 of 2 ATM NETWORK FUNCTIONS ATM LAN EMULATION ATM COMMUNICATIONS AND NETWORKS ATM Quality of Service (QoS) APPLICATIONS

3. ATM NETWORK FUNCTIONS ATM moves cells with low delay. ATM-capable devices may include multiplexers, routers, CSUs (Channel Service Units), or switches. Servers can be moved to the ATM backbone by adding an ATM network adapter card.

4. ATM Departmental Architecture for LANs Organizations tend to build ATM networks in phases. In the computer room, a high-end ATM backbone switch is used to link to ATM workgroup switches. For large organizations with a lot of multimedia traffic, ATM provides much faster bandwidth than 100 Mbps Ethernet. If linked together using SONET at the OC-3 level, data transfer between floors occurs at 155Mbps. CAT5 Ethernet cable for desktops may be preferred because it is less expensive. ATM technology is capable of driving 155 Mbps to the desktop if required.

5. ATM Backbone Switch The core of an ATM network is the backbone switch. ATM backbone switches use modular approach to building an ATM network. One switch card or module is called the switch/control point. This module implements cell-switching capabilities and can handle an aggregate capacity of 3 Gbps The other modules (interface cards) in the ATM backbone switch can support speeds of 25, 100, or 155 Mbps The card can be set up with two fiber and two SONET ports at 155 Mbps

6. ATM ROUTING SWITCH FABRIC A routing switch fabric is used to switch cells within the switch The switch fabric is self-routing and can manage the flow of ATM cells through the switch A 3-bit tag is used to send the cell to the appropriate output port Several output queues are located at each port of the switch Buffer management is provided at each output queue to hold traffic temporarily until the device or network switch is ready to receive it

7. ATM Cell Switching Transfer Mode Internally, an ATM switch uses a translation table to manage cell transfer The translation table includes the incoming port number on the switch, the virtual connection ID, and outgoing port, and the virtual connection ID The switch interprets the cell headers and consults its table to determine how to forward the cell ATM switches map the topology of the network to determine the best path to use when establishing a connection Connections can be made “on-the-fly” ATM uses an enhanced version of statistical multiplexing to control switch traffic and network capacity

8. ATM MULTIPLEXING LANs have used Time Division Multiplexing (TDM) techniques for years Time slots are assigned dynamically to individual users or devices Transmission is based on priority and need to transmit Using asynchronous TDM, each user or device can transmit only during its own sequential time slot

9. While the user (or device) #1 might be finished transmitting, users (or devices) on time slot #2 & #3 must continue to wait for their assigned time before they can transmit ATM uses its own multiplexing technique called asynchronous transfer mode multiplexing (ATM multiplexing) Each user or device can use time slots on demand as they become available The user (or device #3) is assigned to every fourth time slot. If user or device #2 requires a lot of bandwidth, the remaining available time slots can be used

10. ATM LAN EMULATION ATM networks were designed to connect LANs together over an ATM backbone Fundamental differences exist: LANs transmit in bits, ATM routes cells ATM Forum developed a standard called LAN emulation (LANE) LANE allows stations attached via ATM the same bit-passing capability as is required on an Ethernet or Token Ring LAN LANE Protocol emulates a LAN on top of an ATM network.

11. ATM LAN Emulation Configuration Servers (LECS) and LAN Emulation Servers (LES) The ATM switch requires a connection to a LES, a LAN Emulation Configuration Server (LECS), and a Broadcast Unknown Server (BUS) LES is responsible for registering and resolving Ethernet MAC addresses to ATM addresses The BUS is responsible for handling broadcast, multicast, and initial unicast frames sent from a LAN emulation client (end node, workstation or device) The LAN emulation software resides between the lower ATM layers and the upper protocol layers and shields the upper layer protocol stack for Ethernet and Token Ring LANs from the ATM network

12. ATM LECS and LES (Cont.) ATM must provide LANs with a connectionless service for the LANs to operate Emulated LANs (ELANs) can be logically separated by an ATM network The LANE protocol defines a service interface for network layer protocols that is identical to that of existing LANs Data is sent across the ATM network encapsulated in the appropriate LAN MAC packet format

13. ATM LECS and LES (Cont.) The LANE system and its components operate the LAN emulation client in stages 1. Performing initialization and configuration 2. Joining and registering with the LES 3. Finding and joining the BUS 4. Performing data transfer

14. Steps of Data Transfer in LAN Emulation Client The ATM address of the destination LAN emulation client is resolved before the actual data is transferred The LAN emulation client knows the target ATM address, it sends the frame over an already established connection If the LAN emulation client does not know the target ATM address, the LAN emulation client must issue an LE ARP request to the LES to retrieve the ATM address After the LES responds with the destination ATM address, the source LAN emulation client sets up a direct connection to the target LAN emulation client Finally data begins passing over the direct VC

15. ATM LANEs using LAN emulation Clients and LES Basically the function of the LANE protocol is to resolve MAC addresses to ATM addresses As it progresses through the various stages, the protocol’s intent is to resolve the addresses to set up a direct path Switches negotiate to establish connections with other switches across the network

16. ATM LANE through the OSI Model The figure below illustrates data movement from the source LAN station to the destination LAN station This is a structured process that involves mapping the ATM network layers to the OSI layers of the LAN

17. Steps for data movement within LANE At the LAN station, a MAC frame is created with the traditional headers, trailers, and data The ATM to LAN bridge receives the MAC frame and determines that the frame is destined for the ATM port Bridging software within the ATM to LAN bridge forwards the frame to the LANE software At the convergence sublayer (AAL 5) of the bridging software, a data unit is created using the information from the LAN Emulation layer The data unit is moved to ATM layers where it is segmented into a 48-octet cell payload Each of the cell payload segments are moved to the ATM layer and the correct VPI\VCI is added into the cell header

18. Steps for data movement within LANE (cont.) Each cell is then sent into the network. Each ATM switch in the ATM network handles the switching of the cell using the VPI\VCI defined in the cell header The ATM cell header is read, the cell headers are stripped off and the payload is forwarded on to the ATM layer The segmented 48 octet cell payloads are reassembled into the original data unit and forwarded to the convergence sublayer (AAL 5) At the convergence sublayer (AAL 5), the trailer is read and then forwarded to the LAN Emulation layer The LANE software forwards the frame to the correct LAN port by using the destination’s MAC address The MAC frame is received at the destination ATM station

19. ATM LANE CONFIGURATIONS (1) LANs can be connected with emulation bridges to an ATM network

20. ATM LANE CONFIGURATIONS (2) An ATM station can be connected directly to an ATM network by placing an ATM adapter card directly in the workstation On the LAN side, an emulation bridge is required to connect to the ATM network

21. ATM LANE CONFIGURATIONS (3) A direct ATM-to-ATM connection is possible if workstations at each end have ATM adapters to connect to the ATM network

22. ATM COMMUNICATIONS AND NETWORKS LANs and ATM networks requires ATM-attached equipment The LANE protocol is deployed in ATM NICs and LAN switching equipment The network layer protocols at the end station continue to communicate just as if they were on a regular LAN Unlike a LAN, however, the ATM NICs are capable of using the greater bandwidth offered by the ATM network ATM-attached LAN switches and routers can be directly attached to ATM hosts equipped with ATM NICs to provide a Virtual LAN (VLAN) service

23. ATM COMMUNICATION OPTIONS Multiprotocol over ATM (MPOA), enables devices in different ELANs to communicate without traveling hop by hop Only the first few frames between devices pass through routers The path taken by these frames becomes the default path MPOA devices discover the NSAP address of the destination device and then build a direct connection for subsequent frames in the flow Edge devices that generate the ATM traffic are called multiprotocol clients (MPC) A client can be an ATM-attached workstation or a router Inter-ELAN routers are called multiprotocol servers (MPS) They assist the MPCs in discovering how to build a direct connection to the destination end station

24. ATM COMMUNICATION OPTIONS Native ATM applications, use APIs (application programming interfaces) to communicate directly with the ATM layers When Classical IP is used, IP and ARP are encapsulated and sent over an ATM network When LANE is used, the MAC layer address is mapped to an ATM address, which allows traditional LAN applications to operate across an ATM network

25. ATM Network ATM can successfully use different techniques to communicate with different types of LANs Several devices (servers, hubs, and routers) can be lined together to provide LANs access to an ATM network Three ATM Cell Relay switches are connected in a point-to-point connection through the service provider’s ATM network service Several devices (hubs/routers, PBXs, servers, and desktop networks) are connected directly to the private ATM/Cell Relay switch ATM can provide the connections to route data, voice, video, and image traffic across this network The ATM Back Bone Switch provides several devices (mainframe, PBX (private branch exchange), workstation, and video camera) with access to the ATM network

26. ATM Integration with an FDDI Backbone ATM can keep FDDI and Ethernet segments intact but still offer both a connection to an ATM network ATM must be configured to have the same encoding scheme as FDDI to pass data back and forth to an FDDI LAN Using LANE, the Ethernet LAN hub/switch also is connected into the ATM switch ATM provides a private ATM backbone for both the FDDI and Ethernet LANs

27. ATM Integration with Frame Relay and SMDS Frame Relay and SMDS can also be connected to an ATM network Each require different interfaces to an ATM network Frame Relay switch uses an NNI to connect to the ATM network SMDS switch can use either a SMDS ICI or a B-ICI (Broadband intercarrier interface) to connect to the ATM network Traffic can be submitted to the ATM network as ATM cells, Frame Relay frames, or SMDS PDUs (Protocol Data Units) Frame Relay and SMDS traffic can both be sent across the B-ICI in an encapsulated format SMDS PDUs can be either encapsulated or directly mapped into specific VCC or VPC values

28. ATM Quality of Service (QoS)and Traffic Management ATM has specified QoS parameters for measuring the performance of the network QoS is concerned with the delivery of the cell to the destination Four service classes have been defined for different types of traffic The QoS parameters are defined at connection setup on a connection-by-connection basis

29. QoS Parameters per Class of Service For each class of service, different QoS parameters are specified These QoS parameters can include a bandwidth guarantee, delay variation guarantee, cell loss guarantee, or congestion feedback guarantee CBR – Constant Bit Rate VBR – Variable Bit Rate ABR – Available Bit Rate UBR – Unspecified Bit Rate

30. ATM Adaptation Layer (AAL) Classes AALs are service classes that are selected based on the application type: Voice, video, high-priority data, low-priority data

31. ATM Adaptation Layer Classes Services are classified by the timing required between the source and destination, bit rate whether it is constant or variable Connection type, whether it is connectionless or connection-oriented

32. QoS Parameters Service providers prepare SLAs to finalize the QoS parameters required Depending on the type of traffic, some services are specified and others are unspecified QoS agreements improve traffic management and data loss prevention QoS parameters are defined in the header of each cell Each VCI has a different cell loss priority (CLP) The actions of CLP and QoS are considered together

33. ATM Congestion / Traffic Control ATM traffic management includes ways to control traffic and provide notification to ATM switches when congestion is expected to occur ATM uses Explicit Forward Congestion Control Indicator, EFCI ATM uses Resource Management (RM) cells to provide information concerning congestion and send notification when transmission needs to be slowed down The ATM switches passively forward these RM cells If congestion is detected, the switch sets the EFCI in the cell header The source and the end user or device responds to the notification by either raising or lowering its rate of transmission QoS enables better traffic management for core networks used by ISPs and telephone company service providers With all-optical networks, QoS may soon be offered per wavelength. This may solve future congestion problems.

34. ATM Applications ATM technologies, standards, and services are being applied in a wide range of networking environments ATM services—Service providers globally are introducing or already offering ATM services to their business users. ATM workgroup and campus networks—Enterprise users are deploying ATM campus networks based on the ATM LANE standards. ATM enterprise network consolidation—A new class of product has evolved as an ATM multimedia network-consolidation vehicle. The ATM enterprise network offers a broad range of in-building (voice, video, LAN, and ATM) and wide-area interfaces (leased line, circuit switched, frame relay, and ATM at narrowband and broadband speeds) and supports ATM switching, voice networking, frame-relay SVCs, and integrated multiprotocol routing. Multimedia virtual private networks (VPN) and managed services—Service providers offer a broad range of services. Examples include managed ATM, LAN, voice and video services and full-service virtual private-networking capabilities (these including integrated multimedia access and network management). Frame-relay backbones—Frame-relay service providers are deploying ATM backbones to meet the rapid growth of their frame-relay services to use as a networking infrastructure for a range of data services and to enable frame relay to ATM service interworking services. Internet backbones—Internet service providers are likewise deploying ATM backbones to meet the rapid growth of their frame-relay services, to use as a networking infrastructure for a range of data services, and to enable Internet class-of-service offerings and virtual private intranet services. Residential broadband networks—ATM is the networking infrastructure of choice for carriers establishing residential broadband services, driven by the need for highly scalable solutions. Carrier infrastructures for the telephone and private-line networks—Some carriers have identified opportunities to make more-effective use of their SONET/SDH fiber infrastructures by building an ATM infrastructure to carry their telephony and private-line traffic.

35. The benefits of ATM high performance via hardware switching dynamic bandwidth for bursty traffic class-of-service support for multimedia scalability in speed and network size common LAN/WAN architecture opportunities for simplification via Virtual Channel architecture international standards compliance

36. Summery ATM is a high-performance, cell-oriented switching and multiplexing technology. ATM utilizes fixed-length packets to carry different types of traffic ATM can provide reserved, permanent , or bandwidth on demand services. ATM is a technology that will enable carriers to capitalize on a number of revenue opportunities through multiple ATM classes of services; high-speed local-area network (LAN) interconnection; data, voice, video, and future multimedia applications in business markets in the short term; community and residential markets in the long term.

37. Resources & References http://www.iec.org/online/tutorials/ (International Engineering Consortium) http://www.webopedia.com http://www.mfaforum.org MFA (ATM) Forum. http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/atm.htm Wide Area Networks, Carol Trivedi, EMC Paradigm 2004