1. Intro to ATM Asynchronous Transfer Mode Text References Sect 2.6

2. 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

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

4. 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)

5. 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

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

7. Physical Layer Options
• SONET (US)/ SDH (Europe)
• SMDS
• DQDB
• Speeds from DS3 on up! (45Mbs to Gbps)
OC-3c => Mbps => Mbps
^ 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]

8. 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

9. 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

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

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

12. ATM Protocols
UNI, NNI
Services
“LAN” Stuff

13. ATM Services
CBR
VBR (RT, NRT)
UBR
ABR

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

15. ATM Congestion Control
Admission Policy
Reservation System
Rate Based Control
Other

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

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

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

19. 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

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

21. 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]

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

23. 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

24. 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

25. 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

26. 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

27. 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

28. LANE Setup

29. 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

30. 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)

31. 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

32. 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

33. 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

34. MPOA Operation

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

36. 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