Intro to ATM Asynchronous Transfer Mode Text References Sect 2.6

ATM Background Outgrowth of TELCO transition to integrated services Only “real” >100Mbit standard Offers multiservice (voice video data) potential Switched architecture familiar to TELCOs, not to high speed data networks

What is ATM? Note: Tanenbaum considers this more a network layer technology.

ATM - A layered standard AAL - ATM Adaptation Layer • Assembles and disassembles broadband servicesinto a stream of cells • Each cell has a header that contains routing information ATM - Asynchronous Transfer Mode • Switches the cells around the network based on the routing information in the header Physical Layer • Provides the physical transportation of cells across the network (Note: CCITT reference model, p. 63)

ATM - A Switched Architecture Cells (small, fixed length packets) are switched in a connection-oriented manner but not using circuits like today’s voice. Switch Switch Edge Device Edge Device

What is ATM Switching? Why small cells? (32+64)/2=48 + 5 header bytes Mixed Traffic Packet (random)vs Circuit (TDM) Switching Q.2931 SVC, PVC

Physical Layer Options • SONET (US)/ SDH (Europe) • SMDS • DQDB • Speeds from DS3 on up! (45Mbs to Gbps) OC-3c => 155.52Mbps => 149.76Mbps ^ optical carrier ^ 3rd level in heirarchy ^ full duplex (two strands of fiber) Also OC-12c (622Mbps), OC-48c (2048Mbps) [Look at the interesting way to frame cells]

ATM Adaptation Layer (AAL) • Classes of Service: 1, 2, 3/4, 5 1: circuit emulation 2: variable bit rate service 3/4: connection oriented data service 5: connectionless data service • SAR - Segmentation and Reassembly • Convergence Sublayer the miscellaneous category

ATM Cell • ATM cells are constant size packets of 53 bytes size. -- 48 bytes payload, 5 bytes header/overhead. VPI - Virtual Path ID VCI - Virtual Channel ID Type - Payload type (internal) Res - reserved CLP- Cell loss priority HEC- Header Error Control

VCI/VPI Operation • A Virtual Channel exists between two switching points • A Virtual Path contains 'bundles' of VCs

ATM Switch Architecture Crossbar Banyan TDM busses Buffering Input Output Both?

ATM Protocols UNI, NNI Services “LAN” Stuff

ATM Services CBR VBR (RT, NRT) UBR ABR

ATM Quality of Service QoS: A contract Traffic Descriptors Cell Rate Options (pg 462) Traffic Shaping Traffic Policing

ATM Congestion Control Admission Policy Reservation System Rate Based Control Other

ATM Flow Control • The leaky bucket algorithm • CLP in ATM header • Frame Relay comparisons

Routing IISP (Interim Inter-switch Signaling Protocol) PNNI (Private Network-Network Interface) Phase 1 Phase 2

IISP Interim Signaling Routing via manually configured NSAP prefixes Allowed multi-vendor interoperability before completion of NNI Signaling Routing via manually configured NSAP prefixes

PNNI Topology abstraction Peer group(group of nodes) One switch elected Peer Group Leader All nodes in group have identical view of group Hierarchy of logical groups Up to 105 levels of hierarchy

PNNI Routing NSAP Domain A117 A13 A12 A11 B25 A1 B A2 B3 B2 B1 A23 A22 View from A117 at A11

Sequence of Events A117 -> B25 Forward to switch (A11) Switch knows topology of A1 group B reachable by A2 - A2 reachable by either A12 or A13 DTL (Designated Transit List) [A12][A2][B] [A22][A23][B] [B2]

ATM “LAN” Stuff LAN == Link Layer Domain ELANs & VLANs LANE & MPOA LECS, LES, BUS

LANE v1 LAN Emulation No QoS (Quality of Service) Support Uses AAL5 signaling optimized for data transport entire cell payload available for user data LEC - LAN Emulation Client LAN Emulation Service LECS - LAN Emulation Configuration Server LES - LAN Emulation Server BUS - Broadcast and Unknown Server STP (Spanning Tree Protocol) supported

LEC - LAN Emulation Client Software process on any ATM-connected LAN switch, router, PC, or workstation Layer 2 process Prior knowledge of certain parameters LEC’s ATM address LAN type to be emulated maximum data frame size any route descriptors (for SR bridging) whether it is willing to proxy (respond to LE-ARP) LAN name - SNMPv2 display string

LECS - LAN Emulation Configuration Server One per administrative domain Gives identity of ELAN (Emulated LAN) Returns ATM address of LES, type of LAN emulated, and maximum PDU size of ELAN Controls which physical LANs are combined to form VLANs (Virtual LAN) LECS address known via ILMI or its well-known NSAP address

LES- LAN Emulation Server Adds LEC’s to ELAN Assigns LECID to joining LEC Table of address information of LEC MAC address proxy for MAC address Token Ring route descriptors LECs can communicate directly with each other only when they are connected to the same LES Multiple LESs on the same physical ATM LAN Answers LE-ARP requests from LECs

BUS- Broadcast and Unknown Server During address resolution LEC forwards all frames to the BUS floods frames to all LECs after address resolved flush protocol used to guarantee order of cells All multicast and broadcast traffic sent through BUS Traffic limited to 10 frames/second Intelligent BUS resolve destinations CLS- connectionless server

LANE Setup

Connections All SVC (switched virtual circuits) SVCs required: LECs and LECS LES and LECS Control Direct - LECs and LES pt-mpt Control Distribute - LES to LECs Multicast Send - LECs and BUS pt-mpt Multicast Forward - BUS to LECs Data Direct - LEC and LEC PVC (permanent virtual circuit) possible to connect LEC and LECS

Virtual Channel Connections LANE Server (LES) Broadcast and Unknown Server (BUS) Control Direct VCC Control Direct VCC Multicast Send VCC Multicast Send VCC LANE Client (LEC) LANE Client (LEC) LANE Client (LEC) LANE Client (LEC) Control Distribute VCC Multicast Forward VCC LAN Switch Data Direct VCC LAN Switch ATM Host ATM Host Configuration Direct VCC Configuration Direct VCC LANE Configuration Server (LECS)

NHRP Next Hop Resolution Protocol Grew out of ATMARP Only IP Allows shortcut routes (pt-pt) direct VCCs across ATM network Address resolution across multiple IP networks If network unknown, request forwarded to other NHSs (Next-hop Server) NHS with knowledge will forward response to source router Router must have ability to bypass default route

RSVP Resource Reservation Protocol Provides QoS (Quality of Service) guarantees Operates in simplex each direction has separate reservation maps well to ATM (two individual VCCs) Built on IP, but no data transport built-in Only if resources available and does not conflict with policy Flowspec (bandwidth and delay) and filterspec (type of packets) transmitted downstream hop by hop

MPOA Multiprotocol over ATM EDFG (Edge Device Functional Groups) existing LAN segments via LAN switches AHFG (ATM-attached Host Functional Groups) ATM-connected host Layer 3 Only supports IP for now Uses LANE for Layer 2 forwarding within a single Layer 3 subnet Adaptation of NHRP to provide connectivity between hosts in different subnets

MPOA Operation

Competing Technologies “Fast Ethernet” 100BASE-TX, 100BASE-FX,100BASE-T4, 100BASE-VG FDDI, FDDI- II HPPI Gigabit Ethernet (IEEE 802.3z)

ATM Issues • SONET/SDH duplication of services • ATM overhead • ATM granularity and bandwidth management • ATM & connectionless service • End point synchronization • Flow Control !!! (bandwidth allocation, correlated traffic) ATM Forum