ISDN, BISDN, X.25, FrameRelay, ATM Networks: A Telephony View of Convergence Architectures

1
ISDN, B-ISDN, X.25, Frame-Relay, ATM Networks A
Telephony View of Convergence Architectures

• Shivkumar Kalyanaraman
• Rensselaer Polytechnic Institute
• shivkuma_at_ecse.rpi.edu
• http//www.ecse.rpi.edu/Homepages/shivkuma
• Based in part on slides of Raj Jain (OSU), S.
  Keshav (Ensim)
• Based also on the reference books by U. Black,
  J.C. Bellamy

2
Overview

• Switched Packet-Data Services
• Integrated Services Vision and Concept
  Ingredients
• History X.25, ISDN, Frame Relay
• ATM Networks foundation for B-ISDN
• ATM Key Concepts
• ATM Signaling and PNNI Routing
• ATM Traffic Management
• IP over ATM setting the stage for MPLS

3
A Telephony View of Convergence

• Separate Voice network (PSTN) and Data Networks
  (Frame Relay, SMDS, etc.)
• PSTN sometimes used as a data network backbone,
  but
• PSTN is circuit switched (voice-optimized) and
  PSTN-based WAN not efficient
• Delay sensitive traffic such as voice not
  possible on data networks since no guarantee of
  QoS
• Initial attempts to converge data and voice
  network not too successful, i.e. ISDN
• B-ISDN and ATM networks viewed as the convergence
  end-point leading world-wide domination of
  telephony driven standards

4
Switched Packet-Data Services

• After the success of T1, the telephone carriers
  saw the growth in packet switched networks
• Evolved their own flavors of packet switching,
  notably X.25, ISDN, SMDS, Frame Relay, ATM etc
• Key concept Switched services
• Switched services (aka dial-up service)
• Digital communications that is active only when
  the customer initiates a connection.
• Subsumes both circuit switched and packet
  switched.
• Customer to be billed only when the line is
  active.
• Led to activity-based or average-load-based
  pricing models that did not necessarily have a
  distance-based component
• Vs peak-rate and distance-sensitive T-carrier
  pricing

5
Ingredients

• Signaling and setup of a virtual circuit (I.e.
  nailing down a switched path) is a common feature
• Signaling was heavyweight, and was coupled to
  heavyweight QoS routing
• Contrast this to connectionless, best-effort
  Internet
• Long 20-byte global addresses used only in
  signaling
• Short 4-byte local labels (aka DLCI etc) used in
  packets (cells) label-switching
• Large address space, low per-packet overhead
• ISDN/B-ISDN vision of an end-to-end integrated
  digital network
• Rich QoS capabilities developed support for
  voice, data, video traffic

6
Ingredients (contd)

• X.25 -gt Frame relay/ATM reduction of hop-by-hop
  processing complexities
• Led to the development of high-speed switches and
  networks
• A serious attempt to inter-network with a variety
  of data-networking protocols (IP, Ethernet etc)
• Integration (coupling) of too many features led
  to slow rollout, enormous overall complexity
• Failure to attain the end-to-end market vision
• Current trend is to de-couple building blocks
  of the architecture within the context of
  IP/MPLS, sacrificing strict performance
  guarantees.

7
X.25
8
X.25

• First packet switching interface in the telephony
  world
• Issued in 1976 and revised in 1980, 1984, 1988,
  and 1992.
• Data Terminal Equipment (DTE) to Data
  Communication Equipment (DCE) interface
• User to network interface (UNI)
• Slow speeds, used in point-of-sale apps (eg
  credit-card validation) and several apps abroad

9
X.25 Virtual Circuits

• Circuit Pin a path, reserve resources, use TDM
  based transmission
• Virtual Circuit Virtual Call pin a path,
  optionally reserve resources
• Connection-oriented Setup an end-to-end
  association (data-structure) path not pinned
• Connectionless stateless. No path, no end-to-end
  association
• Two Types of Virtual Circuits
• Switched virtual circuit (SVC) Similar to phone
  call
• Permanent virtual circuit (PVC) Similar to
  leased lines
• Up to 4095 VCs on one X.25 interface

10
X.25 Protocol Layers

• Note the three modular layers were co-specified
  by the same standards body
• Layers
• X.21 replaced by EIA-232 (RS-232C)
• LAP-B Link access procedure - Balanced
• Packet layer Connection-oriented transport over
  virtual circuits

11
X.25 Physical Layer

• Electrical and mechanical specifications of the
  interface
• X.21 15-pin digital recommendation
• X.21bis X.21 twice X.21 second
• Interim analog specification to allow existing
  equipment to be upgraded.
• Now more common than X.21 gt X.21 Rev 2
• RS-232-C developed by Electronics Industries
• Association of America (EIA) is most common
• Uses 25-pin connector. Commonly used in PCs.

12
Link Layer Roots HDLC Family

• Original
• Synchronous Data Link Control (SDLC) IBM
• Derivatives
• High-Level Data Link Control (HDLC) ISO
• Link Access Procedure-Balanced (LAPB) X.25
• Link Access Procedure for the D channel (LAPD)
  ISDN
• Link Access Procedure for modems (LAPM) V.42
• Point-to-Point Protocol (PPP) Internet
• Logical Link Control (LLC) IEEE
• Link Access Procedure for half-duplex links
  (LAPX) Teletex
• Advanced Data Communications Control Procedures
  (ADCCP) ANSI
• V.120 and Frame relay also use HDLC

13
HDLC (contd)

• Primary station Issue commands (master)
• Secondary StationIssue responses (slave)
• Hybrids
• Combined Station Both primary and secondary
  a.k.a Asynchronous Balanced Mode (ABM)
• Balanced Configuration Two combined stations
• Unbalanced Configuration One or more secondary
• Normal Response Mode (NRM) Response from
  secondary
• Asynchronous Response Mode (ARM) Secondary may
  respond before command

14
LAPB

• Uses balanced mode subset of HDLC between DTE and
  DCE
• Uses 01111110 as frame delimiter
• Uses bit stuffing to avoid delimiters inside the
  frames
• Uses HDLC frame format
• Point-to-point Only two stations - DTE (A), DCE
  (B)
• Addresses A00000011, B00000001
• Address Destination Addresses in Commands

15
HDLC frames

• Information Frames User data
• Piggybacked Acks Next frame expected
• Poll/Final Command/Response
• Supervisory Frames Flow and error control
• Go back N and Selective Reject
• Final No more data to send
• Unnumbered Frames Control
• Mode setting commands and responses
• Information transfer commands and responses
• Recovery commands and responses
• Miscellaneous commands and responses

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HDLC Operation
SABM Set Asynchronous Balanced Mode UA
Unnumbered ACK DISC disconnect RR Receiver
Ready RNR Receiver Not Ready I information
frame
Heavyweight Link-Setup and Per-Packet Acking !!
17
HDLC Operation (Contd)
18
X.25 Packet Level Layer 3

• Packet Level End-to-end for X.25 networks
• But really Layer 3 (network layer)
• Packet level procedures
• Establishment and clearing of virtual calls
• Management of PVCs
• Flow Control
• Recovery from error conditions

19
X.25 Packet Level (Layer 3) Signaling Operation
Redundant signaling and reliability functions at
L2 and L3!
20
X.25 Packet Format

• GFI Packet formatting information
• PTI 20 possible packet types (for
  de-multiplexing)
• Logical Channel Group and Channel Numbers
• Virtual circuit identifier

21
(Layer 3) Packet Format (contd)

• Fragmentation/Reassembly support
• M More segments
• Layer 3 reliability
• P(R) and P(S) refer to packet sequence
• Different from N(R) and N(S) - frame sequence

22
(Layer 3) Packet Format (Contd)

• 3-bit and 7-bit sequence number options possible
• Again, note these are layer 3 sequence numbers

23
ISDN Integrated Services Digital Network
24
ISDN End-to-End Digital Services Vision
25
ISDN Configurations
26
BRI and PRI Services
Basic Rate ISDN and Primary Rate ISDN. BRI
can transmit data up to 128 kbps. PRI
(transmitted over a T1 line) can transmit data up
to 1.536 Mbps. An LDN (Local Directory Number)
customer's 7-digit ISDN phone number. A SPID
(Service Profile Identifier) unique ID of an
ISDN line or service provider (10 digits long
and includes the LDN).
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Basic Rate ISDN (BRI) contd

• Basic Rate ISDN service divides a standard
  telephone line into three digital channels
  capable of simultaneous voice and data
  transmission.
• The three channels are comprised of two Bearer
  (B) channels at 64 kpbs each and a data (D)
  channel at 16 kbps, also known as 2BD.
• The B channels are used to carry voice, video,
  and data to the customer's site (hence the term
  integrated services).
• The D channel is used to carry signaling and
  supplementary services.
• Multiple B channels can be used at the same time.
  The D channel can also be used to carry
  packetized data.

28
BRI and Reference Model
29
BRI Reference Model Details

• U-interface U-interface is a 2-wire digital
  telephone line that runs from the telephone
  company's central office to an NT1 device.
• NT1 (Network Termination Type 1) NT1 is a Basic
  Rate ISDN-only device that converts a service
  provider's U-interface to a customer's
  S/T-interface. Stand-alone or integrated into a
  terminal adapter.
• S/T-interface S/T-interface is a common way of
  referring to either an S- or T-interface. This
  can be used to connect directly to an ISDN 2BD
  NT1 or an NT2 device with a terminal adapter.
  This type of interface is often found on Terminal
  Equipment Type 1.
• TE1 TE1 (Terminal Equipment Type 1) is
  ISDN-ready equipment that can directly connect to
  the ISDN line (often using an S/ T-interface).
  Eg ISDN phones, ISDN routers, ISDN computers,
  etc.

30
BRI Ref Model Details Contd

• TA (terminal adapter) TA is a device that allows
  non-ISDN-ready equipment to connect to an ISDN
  line. This device can have an integrated NT1.
• R-interface R-interface is a non-ISDN interface
  such as an EIA-232 or a V.35 interface. This type
  of interface is often found on TE2.
• TE2 (Terminal Equipment Type 2) TE2 is equipment
  that cannot directly connect to an ISDN line. A
  common example of this device is a PC, or a
  non-ISDN-ready router. A TA must be used to
  connect to the ISDN line.

31
Primary Rate ISDN (PRI)

• Primary Rate Interface (PRI) ISDN is a
  user-to-network interface (UNI) consisting of
• Twenty-three 64 kbps bearer (B) channels, and
• One 64 kbps signaling (D) channel (aka 23BD)
• Cumulatively carried over a 1.544 Mbps DS-1
  circuit.
• The B channels carry data, voice or video
  traffic. The D channel is used to set up calls on
  the B channels.

32
ISDN Reference Model
33
LAPD Framing in ISDN
34
Q.931 ISDN Signaling
35
Frame Relay
36
Dis-economics of Leased Lines

• Multiple logical links gt Multiple connections
• Four nodes gt 12 ports (full mesh!!)
• 12 local exchange carrier (LEC) access lines,
• 6 inter-exchange carrier (IXC) connections
• One more node gt 8 more ports, 8 more LEC lines,
  4 more IXC circuits (same issues as full mesh in
  LANs)
• Charged both by bandwidth and by the mile!

37
X.25/Frame Relay Niche

• 6 IXC circuits (star vs full mesh FR network is
  like a hub or switch in a star-topology)
• One more node 1 more port,
• 1 more access line, 4 more IXC circuits
• Share local leased lines to LECs (aka Virtual
  Private Networks (VPNs) or closed-user groups
  (CUGs))
• Tradeoffs
• Packetized L2 (FR) or L3 (X.25) service instead
  of digital L1 service (T-carrier)
• Service guarantees weaker (delay, jitter, loss
  PIR/CIR vs peak rate)

38
X.25 vs Frame Relay
X.25 Message Exchanges
Frame Relay Message Exchanges
FR obviously more efficient from a protocol
standpoint than X.25, in addition to the
compelling economics vs leased lines
39
X.25 vs Frame Relay

• X.25 interface between host and packet-switching
  network
• 3 layers phy, link, packet
• Heavyweight error control at every link as well
  as layer 3 twelve messages for one packet
  transfer!!
• X.25 offers no QoS capability
• Frame relay breaks up link-layer into two parts
• LAPF-core and LAPF-control
• Network nodes only implement LAPF-core
• Frame Switching is a service that implements both
• Frame relay uses a separate VC for control
  channel in vs in-band control approach used in
  X.25

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Frame Relay Overview

• Frame Relay digital packet network providing
  benefits dedicated T-1 link, but without the
  expense of multiple dedicated circuits.
• Frame Relay leverages the underlying telephone
  network
• Frame Relay distance-insensitive and average-rate
  pricing is an ideal, cost-effective solution for
  networks with bursty traffic
• Especially those that require connections to
  multiple locations and where a certain degree of
  delay is acceptable.
• FR also allows a voice circuit to share the same
  virtual connection as a data circuit, again,
  saving money.
• Frame Relay assumes higher-speed, low error-rate
  underlying PHY.
• Switches do not perform hop-by-hop error
  correction (other than discarding corrupted
  frames) or flow control (other than setting
  FECN/BECN bits)

41
Frame Relay Key Features

• X.25 simplified
• No flow and error control
• Out-of-band signaling
• Two layers
• Protocol multiplexing in the second layer
• Congestion control added
• Higher speed possible.
• X.25 suitable to 200 kbps vs
• Frame relay suitable to 2.048 Mbps.
• Frame Relay Unreliable multiplexing service
• X.25 Switching Relaying Ack Flow control
  Error recovery loss recovery

42
Frame Relay Reference Model Lingo

• PVC Permanent Virtual Circuit
• DLCI Data Link Connection Identifier
• CIR Committed Information Rate
• CSU Channel Service Unit
• UNI User-to-Network Interface
• NNI Network-to-Network Interface
• DTE Data Terminal Equipment
• DE Discard Eligible
• FRAD Frame Relay Access Device
• DSU Data Service Unit

43
Frame Relay Lingo (contd)

• Frame Relay Access Device FRAD generic name
  for a device that multiplexes/formats traffic for
  entering a Frame Relay network.
• Access Line A communications line
  interconnecting a Frame Relay-compatible device
  to a Frame Relay switch.
• Bursty/burstiness Sporadic use of bandwidth that
  does not use the total bandwidth of a circuit
  100 of the time.
• CIR (Committed Information Rate) The committed
  rate (usually lt the access/peak rate) which the
  carrier guarantees to be available
• DE (Discard Eligibility) A user-set bit frame
  may be discarded
• DLCI (Data Link Connection Identifier) A unique
  number IDing a particular PVC endpoint has local
  significance only to that channel.
• BECN (Backward Explicit Congestion Notification)
  A bit set by a FR network to notify an interface
  device (DTE) that congestion avoidance procedures
  should be initiated by the sending device.
• FECN (Forward Explicit Congestion Notification)
  A bit set by a FR network to notify an interface
  device (DTE) that congestion avoidance procedures
  should be initiated by the receiving device.

44
Frame Relay Lingo (Contd)

• DTE (Data Terminal Equipment) User terminal
  equipment which creates information for
  transmission for example, a user's PC or a
  router.
• CSU/DSU A customer owned, physical layer device
  that connects DTE (eg router) to an access line
  (eg T1), from the network service provider.
• Traditionally, DSUs were network-owned equipment
  used in conjunction with customer-owned CSUs to
  terminate access lines.
• Because of regulatory changes, there is no need
  for physical separation of CSU and DSU any longer
  gt combination CSU/DSUs.

45
Datalink Control Identifiers (DLCI)
Similar to X.25 DLCI Only local significance
Multiple logical connections over one physical
circuit Some ranges pre-assigned Eg DLCI 0
is used for signaling
46
Frame Relay UNI (aka FUNI)

• UNI User-network Interface
• LAPF Link Access Protocol - Frame Mode Services
• LAPD Link Access Protocol - D Channel
• Control Plane
• Signaling over D channel (D Delta Signaling)
• Data transfer over B, D, or H (B Bearer)
• LAPD used for reliable signaling
• ISDN Signaling Q.933 Q.931 re-used for
  signaling messages
• Service Access Point Identifier (SAPI) in LAPD
  0
• gt Q.933 Q.931 Frame relay message

47
Frame Relay Data (User) Plane

• Link Access Procedure for Frame-Mode bearer
  services (LAPF)
• Q.922 Enhanced LAPD (Q.921) LAPD Congestion
  Control
• Functions
• Frame delimiting, alignment, and flag
  transparency
• Virtual circuit multiplexing and de-multiplexing
• Octet alignment gt Integer number of octets
  before zero-bit insertion
• Checking min and max frame sizes
• Error detection, Sequence and non-duplication
• Congestion control
• LAPF control may be used for end-to-end signaling
  
• A FR-variant called frame-switching uses this
  at every hop

48
Frame Relay LAPF-Core Protocol

• LAPF is similar to LAPD Flag, bit stuffing, FCS
• No control frames in LAPF-Core gt No control
  field
• No in-band signaling unlike X.25
• No flow control, no error control, no sequence
  numbers
• Logical Link Control (LLC) may be used on the top
  of LAPF core

49
LAPF Address Field
50
Frame Relay Traffic Management

• Minimum rate guarantee Committed Information
  Rate (CIR)
• Maximum burst rate Peak Information Rate (PIR)
• TM enforcement model
• Discard Control (DE Bit) set on all packets when
  CIR lt user rate lt PIR
• Network usually over-provisioned for ?CIR, but
  under-provisioned for ?PIR
• Can drop packets with DE set during congestion
  (I.e. when absolutely necessary)
• Congestion control hooks
• Backward Explicit Congestion Notification (BECN)
• Forward Explicit Congestion Notification (FECN)
• Very nice ideas later proposed as ECN in TCP/IP
• But generally ignored in practice by CPE equipment

51
CIR/PIR Service Example
52
Leaky Bucket Policing _at_ Network Edge
53
Leaky Bucket Parameters

• Committed Information Rate (CIR)
• Committed Burst Size (Bc)
• Excess Burst Size (Be)
• Measurement interval T
• T Bc/CIR
• Policing actions
• Between Bc and Bc Be gt Mark DE bit
• Over Be gt Discard

54
FECN

• Forward Explicit Congestion Notification (FECN)
• Source sets FECN 0
• Networks set FECN if avg Q gt1
• Dest tells source to inc/dec the rate (or window)
• Start with R CIR (or W1)
• If more than 50 bits set gt decrease to 0.875
  R (or 0.875W)
• If less than 50 bits set gt increase to 1.0625
  R (or minW1, Wmax)
• If idle for a long time, reset R CIR (or W1)

55
BECN

• Backward Explicit Congestion Notification (BECN)
• Set BECN bit in reverse traffic or send
  Consolidated Link-Layer Management (CLLM) message
  to source
• On first BECN bit Set R CIR
• On further "S" BECNs R0.675 CIR, 0.5 CIR, 0.25
  CIR
• On S/2 BECNs clear Slowly increase R 1.125 R
• If idle for long, R CIR

56
BECN (Contd)

• For window based control
• S One frame interval
• Start with W1
• First BECN W max(0.625W,1)
• Next S BECNs W max(0.625W,1)
• S/2 clear BECNs gt W max(W1, Wmax)
• CLLM contains a list of congested DLCIs

57
ATM Asynchronous Transfer Mode
58
Why ATM networks?

• Driven by the integration of services and
  performance requirements of both telephony and
  data networking
• broadband integrated service vision (B-ISDN)
• Telephone networks support a single quality of
  service
• and is expensive to boot
• Internet supports no quality of service
• but is flexible and cheap
• ATM networks are meant to support a range of
  service qualities at a reasonable cost
• Intended to subsume both the telephone network
  and the Internet

59
ATM Concepts

• 1. Virtual circuits
• 2. Fixed-size packets (cells) allowed fast h/w
  switching
• 3. Small packet size
• 4. Statistical multiplexing
• 5. Integrated services
• 6. Good management and traffic engineering
  features
• 7. Scalability in speed and network size
• Together
• can carry multiple types of traffic
• with end-to-end quality of service

60
ATM Applications

• ATM Deployments
• Frame Relay backbones
• Internet backbones
• Aggregating Residential broadband networks
  (Cable, DSL, ISDN)
• Carrier infrastructures for the telephone and
  private-line networks
• Failed market tests of ATM
• ATM workgroup and campus networks
• ATM enterprise network consolidation
• End-to-end ATM

61
ATM vs Synchronous (Phone) Networks

• Phone networks are synchronous (periodic).
• ATM Asynchronous Transfer Mode
• Phone networks use circuit-switching.
• ATM networks use Packet or cell Switching
• In phone networks, all rates are multiple of 64
  kbps.
• With ATM service, you can get any rate, and you
  can vary your rate with time.
• With current phone networks, all high speed
  circuits are manually setup.
• ATM allows dialing any speed rapid
  provisioning

62
ATM vs Data Networks (Internet)

• ATM is virtual circuit based the path (and
  optionally resources on the path) is reserved
  before transmission
• Internet Protocol (IP) is connectionless, and
  end-to-end resource reservations not possible
• RSVP is a new signaling protocol in the Internet
• ATM Cells Fixed/small size tradeoff between
  voice/data
• IP packets variable size
• ATM provides QoS routing coupled to signaling
  (PNNI)
• Internet provides best-effort routing
  (combination of RIP/OSPF/IS-IS/BGP-4), aiming
  only for connectivity
• Addressing
• ATM uses 20-byte global NSAP addresses for
  signaling and 32-bit locally-assigned labels in
  cells
• IP uses 32-bit global addresses in all packets
• ATM offers sophisticated traffic management
• TCP/IP congestion control is packet-loss-based

63
Brief History of ATM

• 1996 death of ATM in the enterprise, rollouts
  in carrier networks

64
ATM Interfaces

• UNI User-Network Interface (Private Public)
• NNI Network Node Interface (Private and Public)
• B-ICI Broadband Inter-Carrier Interface
• DXI Data Exchange Interface

65
ATM Forum Standards
66
ATM Switch Hierarchy
67
ATM Layers

• Adaptation mapping apps (eg voice, data) to ATM
  cells
• Physical layer SONET etc
• ATM Layer Transmission/Switching/Reception,
  Congestion Control, Cell header processing,
  Sequential delivery etc

68
AAL Sublayers and AAL5

• AAL Sublayers
• Convergence Sublayer (CS)
• Determines Class of Service (CoS) for incoming
  traffic
• Provides a specific AAL service at an AAL network
  service access point (NSAP)
• Segmentation and Reassembly Sublayer (SAR)
• Segments higher-level user data into 48-byte
  cells at the sending node and reassembles cells
  at receiving node

69
AAL Lingo.
70
AAL Types

• AAL1 CBR voice
• AAL5 data

71
ATM Physical Layer Functions

• Transports ATM cells on a communications channel
  and defines mechanical specs (connectors, etc.)
• 2 Sub-layers
• Transmission Convergence Sub-layer
• Maps cells into the physical layer frame format
  (e.g. DS1, STS3) on transmit and delineates ATM
  cells in the received bit stream
• Generates HEC on transmit
• Generates idle cells for cell rate decoupling, or
  speed matching
• Physical Medium Sub-layer
• Medium dependent functions like bit transfer, bit
  alignment, OEO

72
Physical Layers

• Multimode Fiber 100 Mbps using 4b/5b,
• 155 Mbps SONET STS-3c, 155 Mbps 8b/10b
• Single-mode Fiber 155 Mbps STS-3c, 622 Mbps
• Plastic Optical Fiber 155 Mbps
• Shielded Twisted Pair (STP) 155 Mbps 8b/10b
• Coax 45 Mbps, DS3, 155 Mbps
• Unshielded Twisted Pair (UTP)
• UTP-3 (phone wire) at 25.6, 51.84, 155 Mbps
• UTP-5 (Data grade UTP) at 155 Mbps
• DS1, DS3, STS-3c, STM-1, E1, E3, J2, n T1
• Take-home message Serious attempt to
  inter-operate with several L1, L2 and L3
  technologies

73
ATM-SONET Mapping
Cells are mapped row-wise into the frame Cells
could contain data or be empty
74
ATM Concepts Virtual Paths Virtual Channels

• VCs way to dial up and get bandwidth

75
Virtual circuits Label Concept Rationale for
Signaling

• Two ways to use packets
• carry entire destination address in header
• carry only an identifier, a.k.a label
• Labels have local significance, addresses have
  global significance
• Signaling protocol fundamentally maps global
  addresses or paths (sequence of addresses) to
  local labels

Data
Sample ATM cell Datagram
Data
VCI
Data
Addr.
76
VPI/VCI Assignment and Use

• All packets must follow the same path (why?)
• Switches store per-VCI state eg QoS info
• Signaling gt separation of data and control
• Small Ids can be looked up (exact match) quickly
  in hardware
• harder to do this with IP addresses
  (longest-prefix match)
• Setup must precede data transfer
• delays short messages
• Switched vs. Permanent virtual circuits

77
ATM Switches
78
ATM Cell Structure
79
ATM Cell Structure Different View
80
ATM Concepts Fixed-size packets

• Pros
• Simpler buffer hardware
• packet arrival and departure requires us to
  manage fixed buffer sizes
• Simpler line scheduling
• each cell takes a constant chunk of bandwidth to
  transmit
• Easier to build large parallel packet switches
• Cons
• overhead for sending small amounts of data
• segmentation and reassembly cost
• last unfilled cell after segmentation wastes
  bandwidth

81
ATM Concepts Small packet size

• At 8KHz, each byte is 125 microseconds
• The smaller the cell, the less an endpoint has to
  wait to fill it
• Low packetization delay
• The smaller the packet, the larger the header
  overhead
• Standards body balanced the two to prescribe 48
  bytes 5 byte header 53 bytes
• gt maximal efficiency of 90.57

82
Error Characteristics Header Protection
83
ATM Concepts Statistical multiplexing with QoS

• Trade off worst-case delay against speed of
  output trunk
• Whenever long term average rate differs from
  peak, we can trade off service rate for delay
• Build scheduling, buffer management, policing
  entities to manage the zero-sum games of delay
  and bandwidth
• Key to building packet-switched networks with QoS

84
QoS Big Picture Control/Data Planes
85
ATM Concepts Service Categories

• ABR (Available bit rate)
• Source follows network feedback.
• Max throughput with minimum loss.
• UBR (Unspecified bit rate)
• User sends whenever it wants. No feedback. No
  guarantee. Cells may be dropped during
  congestion.
• CBR (Constant bit rate) User declares required
  rate.
• Throughput, delay and delay variation guaranteed.
• VBR (Variable bit rate) Declare avg and max
  rate.
• rt-VBR (Real-time) Conferencing.
• Max delay guaranteed.
• nrt-VBR (non-real time) Stored video.

86
CBR and VBR
87
Classes of Service

• The Convergence Sublayer (CS) interprets the type
  and format of incoming information based on 1 of
  4 classes of service assigned by the application
• Class A Constant bit rate (CBR), Connection
  oriented, strict timing relationship between
  source and destination, i.e voice
• Class B Variable bit rate (VBR), Connection
  oriented, strict timing, e.g. packet-mode video
  for video conferencing
• Class C Connection oriented VBR, not strict
  timing, e.g. LAN
• data transfer applications such as Frame Relay
• Class D Connectionless VBR, not strict timing,
  e.g. LAN data
• transfer applications such as IP

88
ABR vs UBR

• ABR
• Queue in the source
• Pushes congestion to edges
• Good if end-to-end ATM
• Fair
• Good for the provider
• UBR
• Queue in the network
• No backpressure
• Same end-to-end or backbone
• Generally unfair
• Simple for user

89
Guaranteed Frame Rate (GFR)

• UBR with minimum cell rate (MCR) Þ UBR
• Frame based service
• Complete frames are accepted or discarded in the
  switch
• Traffic shaping is frame-based.
• All cells of the frame have the same cell loss
  priority (CLP)
• All frames below MCR are given CLP 0 service.
• All frames above MCR are given best effort
• (CLP 1) service.

90
ATM Signaling and QoS Routing (PNNI)
91
ATM Connection Setup
92
ATM Control/Data/Management Planes
93
ATM Control Plane
94
Protocol Stacks for ATM Signaling
95
Q.931 Message Format
96
Sample Q.931 Message Types
97
Information Element Formats
98
Sample Information Elements
99
ATM Bandwidth Contract
100
ATM Addresses Basis for Signaling

• Three NSAP-like (Network Service Access Point)
  address formats
• DCC ATM Format,
• ICD ATM Format,
• E.164 ATM Format

101
Address Hierarchy in ATM

• Multiple formats.
• All 20 Bytes long addresses.
• Left-to-right hierarchical
• Level boundaries can be put in any bit position
• 13-byte prefix gt 104 levels of hierarchy
  possible

102
Recall Flat vs Structured Addresses

• Flat addresses no structure in them to
  facilitate scalable routing
• Eg IEEE 802 LAN addresses
• Hierarchical addresses
• Network part (prefix) and host part
• Helps identify direct or indirectly connected
  nodes

103
ATM Address Formats

• Authority and Format Identifier (AFI) IDI
• 39 ISO DCC, 47 British Stds Institute ICD, 45
  ITU ISDN
• ISDN uses E.164 numbers (up to 15 BCD digits)
• ATM forum extended E.164 addresses to NSAP
  format.
• E.164 number is filled with leading zeros to make
  15 digits. A F16 is padded to make 8 bytes.
• End System Identifier (ESI) 48-bit IEEE MAC
  address.
• Selector is for use inside the host and is not
  used for routing.
• All ATM addresses are 20 bytes long.

104
NSAP vs SNPA Addressing A Clarification

• NSAP Network Service Access Point. Identifies
  network layer service entry
• SNPA Sub-network point of attachment.
  Identifies the interface to sub-network
• SNPA address (or part of it) is used to carry the
  packet across the network.
• CLNP uses NSAP to deliver the packet to the right
  entity in the host.
• ATM uses NSAP-like encoding but ATM addresses
  identify SNPA and not NSAP.

105
ATM Connection Types

• Permanent and Switched
• Point to point
• Symmetric or asymmetric bandwidth (Uni- or
  bi-directional)
• Point-to-multipoint Data flow in one direction
  only.
• Data replicated by network.
• Leaf Initiated Join (LIJ) or non-LIJ

106
ATM Switch Model Call Processing
107
ATM Connection Setup
108
ATM Connection Release
109
ATM Connection Release (contd)
110
ATM Routing PNNI

• Private Network-to-network Interface
• Private Network Node Interface

111
Private Network to Node Interface (PNNI)

• Link State Routing Protocol for ATM Networks
• A hierarchy mechanism ensures that this protocol
  scales well for large world-wide ATM networks. A
  key feature of the PNNI hierarchy mechanism is
  its ability to automatically configure itself in
  networks in which the address structure reflects
  the topology

112
PNNI Features

• Scales to very large networks.
• Supports hierarchical routing.
• Supports QoS.
• Supports multiple routing metrics and attributes.
• Uses source routed connection setup.
• Operates in the presence of partitioned areas.
• Provides dynamic routing, responsive to changes
  in resource availability.
• Separates the routing protocol used within a peer
  group from that used among peer groups.
• Interoperates with external routing domains, not
  necessarily using PNNI.
• Supports both physical links and tunneling over
  VPCs.

113
PNNI Terminology (partial)

• Peer group A group of nodes at the same
  hierarchy
• Border node one link crosses the boundary
• Logical group node Representation of a group as
  a single point
• Child node Any node at the next lower hierarchy
  level
• Parent node LGN at the next higher hierarchy
  level
• Logical links links between logical nodes
• Peer group leader (PGL) Represents a group at
  the next higher level.
• Node with the highest "leadership priority" and
  highest ATM address is elected as a leader.
• PGL acts as a logical group node.
• Uses same ATM address with a different selector
  value.
• Peer group ID Address prefixes up to 13 bytes

114
PNNI Terminology
115
Hierarchical Routing PNNI
116
Hierarchical Routing (contd)
117
Topology State (QoS) Parameters
118
Call Admission Control
119
Source Routing

• Source specifies route as a list of all
  intermediate systems in the route (original idea
  in token ring)
• Designated Transit List (DTL) (next slide)
• Source route across each level of hierarchy
• Entry switch of each peer group specifies
  complete route through that group
• Set of DTLs and manipulations implemented as a
  stack

120
DTL Example
121
Crank back and Alternate Path Routing

• If a call fails along a particular route
• It is cranked back to the originator of the top
  DTL
• The originator finds another route or
• Cranks back to the generator of the higher level
  source route

122
Traffic Management ATM
123
Traffic Management Functions

• Connection Admission Control (CAC) Can requested
  bandwidth and quality of service be supported?
• Traffic Shaping Limit burst length. Space-out
  cells.
• Usage Parameter Control (UPC) Monitor and
  control traffic at the network entrance.
• Network Resource Management Scheduling,
  Queueing, virtual path resource reservation
• Selective cell discard
• Cell Loss Priority (CLP) 1 cells may be dropped
• Cells of non-compliant connections may be dropped
• Frame Discarding
• Feedback Control ABR schemes

124
CAC and UPC
125
Traffic Contract Parameters

• Peak Cell Rate (PCR) 1/T
• Sustained Cell Rate (SCR) Average over a long
  period
• Burst Tolerance (BT) ts GCRA limit parameter
  wrt SCR GCRA(1/Ts, ts)
• Maximum Burst Size MBS ?1BT/(1/SCR-1/PCR) ?
• BT ?(MBS-1)(1/SCR-1/PCR), MBS(1/SCR- 1/PCR)
• Cell Transfer Delay (CTD) First bit in to last
  bit out
• Cell Delay Variation (CDV) Max CTD - Min CTD
• Peak-to-peak CDV
• Cell Delay Variation Tolerance (CDVT) t GCRA
  limit parameter wrt PCR Þ GCRA(T, t)
• Cell Loss Ratio (CLR) Cells lost /Totals cells
  sent
• Minimum cell rate (MCR)

126
Peak-to-Peak CDV
127
Service Categories
128
Leaky Bucket Basis for Policing

• Provides traffic shaping I.e. smooth bursty
  arrivals
• Provides traffic policing Ensure that users are
  sending traffic within specified limits
• Excess traffic discarded or admitted with CLP 1
• GCRA in ATM requires increment (inter-cell
  arrival time) and limit (on earliness)
• Two implementations Virtual scheduling and leaky
  bucket

129
Generic Cell Rate Algorithm
130
GCRA Virtual Scheduling Algorithm
131
GCRA Leaky Bucket Algorithm
132
GCRA Examples
133
Maximum Burst Size
134
ATM ABR Binary Rate Scheme

• DECbit scheme in many standards since 1986.
• Forward explicit congestion notification (FECN)
  in
• Frame relay
• Explicit forward congestion indicator (EFCI) set
  to 0 at source. Congested switches set EFCI to 1
• Every nth cell, destination sends an resource
  management (RM) cell to the source

135
ABR Explicit Rate Scheme
136
ABR Segment-by-Segment Control
137
Guaranteed Frame Rate (GFR)

• UBR with minimum cell rate (MCR) Þ UBR
• Frame based service
• Complete frames are accepted or discarded in the
  switch
• Traffic shaping is frame based.
• All cells of the frame have the same cell loss
  priority (CLP)
• All frames below MCR are given CLP 0 service.
• All frames above MCR are given best effort (CLP
  1) service.

138
IP OVER ATM
139
ATM Lan Emulation
140
ATM Lan Emulation (LANE)

• One ATM LAN can be n virtual LANs
• Logical subnets interconnected via routers
• Need drivers in hosts to support each LAN
• Only IEEE 802.3 and IEEE 802.5 frame formats
  supported. (FDDI can be easily done.)
• Doesn't allow passive monitoring
• No token management (SMT), collisions, beacon
  frames.
• Allows larger frames.

141
LAN Emulation (Contd)

• LAN Emulation driver replaces Ethernet driver and
  passes the networking layer packets to ATM
  driver.
• Each ATM host is assigned an Ethernet address.
• LAN Emulation Server translates Ethernet
  addresses to ATM addresses
• Hosts set up a VC and exchange packets
• All software that runs of Ethernet can run on LANE

142
LAN Emulation (Contd)
143
Protocol Layering w/ LAN Emulation
144
Terminology

• NDIS Network Driver Interface Specification
• ODI Open Datalink Interface
• IPX NetWare Internetworking Protocol
• LAN Emulation Software
• LAN Emulation Clients in each host
• LAN Emulation Servers
• LAN Emulation Configuration server (LECS)
• LAN Emulation Server (LES)
• Broadcast and unknown server (BUS)

145
LAN Emulation Process

• Initialization
• Client gets address of LAN Emulation
• Configuration Server (LECS) from its switch, uses
  well-known LECS address, or well known LECS PVC
• Client gets Server's address from LECS
• Registration
• Client sends a list of its MAC addresses to
  Server.
• Declares whether it wants ARP requests.

146
LANE Process

• Address Resolution
• Client sends ARP request to Server.
• Unresolved requests sent to clients, bridges.
• Server, Clients, Bridges answer ARP
• Client setups a direct connection
• Broadcast/Unknown Server (BUS)
• Forwards multicast traffic to all members
• Clients can also send unicast frames for unknown
  addresses

147
ATM Virtual LANs
148
IP over ATM

• How many VCs do we need for n protocols?
• Packet encapsulation RFC1483
• How to find ATM addresses from IP addresses
• Address resolution RFC1577
• How to handle multicast? MARS, RFC 2022
• How do we go through n subnets on a large ATM
  network? NHRP

149
IP over ATM RFCs 1483, 1577
150
RFC 1483 Packet Encapsulation

• Question Given an ATM link between two
  routers,how many VCs should we setup?
• Answer 1 One VC per Layer 3 protocol. Null
  Encapsulation No sharing. VC based multiplexing.

151
Encapsulation (RFC 1483) Contd

• Answer 2 Share a VC using Logical Link Control
  (LLC) Subnetwork Access Protocol (SNAP). LLC
  Encapsulation
• Protocol Types 0x0800 IP, 0x0806 ARP, 0x809B
  AppleTalk, 0x8137 IPX

152
Address Resolution ATMARP

• IP address 123.145.134.65
• ATM address 47.0000 1 614 999 2345.00.00.AA....
• Issue IP Address Û ATM Address translation
• Address Resolution Protocol (ARP)
• Inverse ATM ARP VC Þ IP Address
• Solution ATMARP servers

153
RFC 1577 Classical IP over ATM

• ATM stations are divided in to Logical IP Subnets
  (LIS)
• ATMARP server translates IP addresses to ATM
  addresses.
• Each LIS has an ATMARP server for resolution
• IP stations set up a direct VC with the
  destination or the router and exchange packets.

154
IP Multicast over ATM

• Multicast Address Resolution Servers (MARS)
• Internet Group Multicast Protocol (IGMP)
• Multicast group members send IGMP join/leave
  messages to MARS
• Hosts wishing to send a multicast send a
  resolution request to MARS
• MARS returns the list of addresses
• MARS distributes membership update information to
  all cluster members

155
Next-Hop Resolution Protocol (NHRP)

• Routers assemble packets Þ Slow
• NHRP servers can provide ATM address for the edge
  device to any IP host
• Can avoid routers if both source and destination
  are on the same ATM network.

156
Multi-Protocol over ATM (MPOA)

• MPOA LANE NHRP
• Extension of LANE
• Uses NHRP to find the shortcut to the next hop
• No routing (reassembly) in the ATM network

157
MPOA (contd)

• LANE operates at layer 2
• RFC 1577 operates at layer 3
• MPOA operates at both layer 2 and layer 3 Þ MPOA
  can handle non-routable as well as routable
  protocols
• Layer 3 protocol runs directly over ATM Þ Can use
  ATM QoS
• MPOA uses LANE for its layer 2 forwarding

158
ATM interfaces w/ Internetworking