Post on 22-Dec-2015
Intro to ATM
• Asynchronous Transfer Mode
• Text References– Sect 2.6– Sect 3.6.3– Sect 5.6– Sect 6.5
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?
AAL
ATM
PLPhysical
Data/Link
Network
Transport
Session
Presentation
Application Note: Tanenbaum considersthis more a network layertechnology.
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.
(8 bits wide)VPI
VPI VCI
VCI
VCI
HEC
Type Res CLP
VPI - Virtual Path IDVCI - Virtual Channel IDType - Payload type (internal)Res - reservedCLP- Cell loss priorityHEC- Header Error Control
VCI/VPI Operation
• A Virtual Channel exists between two switching points
VCI = a VCI = b
• A Virtual Path contains 'bundles' of VCs
ATM Quality of Service
• QoS: A contract
• Traffic Descriptors
• Cell Rate Options (pg 462)
• Traffic Shaping
• Traffic Policing
Routing
•IISP (Interim Inter-switch Signaling Protocol)
•PNNI (Private Network-Network Interface)
•Phase 1•Phase 2
IISP
• Interim– 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
A117
A13
A12
A11
B25
A1BA2
B3
B2B1A23
A22
A21
NSAP Domain
A11
A12
A13
A2 B
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]
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
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 ConnectionsVirtual Channel Connections
LANE Client (LEC) LANE Client
(LEC)
LANE Server (LES)
LANE Configuration Server (LECS)
ATM Host
LAN Switch
Configuration Direct VCC
Configuration Direct VCC
Control Direct VCC
Control Direct VCC
Control Distribute VCC
LAN Switch
ATM Host
LANE Client (LEC) LANE Client
(LEC)
Multicast Forward VCC
Data Direct VCC
Multicast Send VCC
Multicast Send VCC
Broadcast and Unknown Server (BUS)
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
Competing Technologies
• “Fast Ethernet”– 100BASE-TX, 100BASE-FX,100BASE-T4,
100BASE-VG
• FDDI, FDDI- II
• HPPI
• Gigabit Ethernet (IEEE 802.3z)