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ISDN, B-ISDN, X.25, Frame-Relay,
ATM Networks:
A Telephony View of Convergence
Architectures
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
[email protected]
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
1
Overview
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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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
2
A Telephony View of Convergence
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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 PSTNbased 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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
3
Switched Packet-Data Services
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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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
4
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, Institute
video traffic
Shivkumar Kalyanaraman
Rensselaer Polytechnic
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5
Ingredients (contd)
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X.25 -> 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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
6
X.25
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
7
X.25
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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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
8
X.25 Virtual Circuits
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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 (datastructure); 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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
9
X.25 Protocol Layers
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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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
10
X.25 Physical Layer
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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 => 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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
11
Link Layer Roots: HDLC Family
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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
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Link Access Procedure for half-duplex links (LAPX): Teletex
Advanced Data Communications Control Procedures (ADCCP):
ANSI
V.120 and Frame relay also use HDLC
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
12
HDLC (contd)
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Primary station: Issue commands (master)
Secondary Station:Issue responses (slave)
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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
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Normal Response Mode (NRM): Response from
secondary
Asynchronous Response Mode (ARM): Secondary may
respond before command
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Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
13
LAPB
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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: A=00000011, B=00000001
Address = Destination Addresses in Commands
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
14
HDLC frames
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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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
15
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 !!
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
16
HDLC Operation (Contd)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
17
X.25 Packet Level: Layer 3
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Packet Level = “End-to-end” for X.25 networks
 But really Layer 3 (network layer)
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Packet level procedures:
 Establishment and clearing of virtual calls
 Management of PVCs
 Flow Control
 Recovery from error conditions
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
18
X.25 Packet Level (Layer 3) Signaling Operation
Redundant signaling and reliability functions at L2 and L3!
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
19
X.25 Packet Format
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GFI = Packet formatting information
 PTI = 20 possible packet types (for de-multiplexing)
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Logical Channel Group and Channel Numbers:
 Virtual circuit identifier
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
20
(Layer 3) Packet Format (contd)
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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 #
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
21
(Layer 3) Packet Format (Contd)
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3-bit and 7-bit sequence number options possible
Again, note: these are layer 3 sequence numbers…
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
22
ISDN: Integrated Services Digital Network
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
23
ISDN: End-to-End Digital Services Vision
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
24
ISDN Configurations
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
25
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).
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
26
Basic Rate ISDN (BRI): contd
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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 2B+D.
 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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
27
BRI and Reference Model
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
28
BRI Reference Model Details
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U-interface: U-interface is a 2-wire digital telephone line that runs
from the telephone company's central office to an NT1 device.
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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.
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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
2B+D NT1 or an NT2 device with a terminal adapter. This type of
interface is often found on Terminal Equipment Type 1.
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TE1: TE1 (Terminal Equipment Type 1) is ISDN-ready equipment
that can directly connect to the ISDN line (often using an S/ Tinterface). Eg: ISDN phones, ISDN routers, ISDN computers, etc.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
29
BRI Ref Model Details: Contd
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TA (terminal adapter): TA is a device that allows nonISDN-ready equipment to connect to an ISDN line. This
device can have an integrated NT1.
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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.
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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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
30
Primary Rate ISDN (PRI)
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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 23B+D)
 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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
31
ISDN Reference Model
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
32
LAPD Framing in ISDN
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
33
Q.931: ISDN Signaling
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
34
Frame Relay
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
35
Dis-economics of Leased Lines…
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Multiple logical links => Multiple connections
Four nodes => 12 ports (full mesh!!)
 12 local exchange carrier (LEC) access lines,
 6 inter-exchange carrier (IXC) connections
 One more node => 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!
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
36
X.25/Frame Relay Niche
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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)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
37
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
38
X.25 vs Frame Relay
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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
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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
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Frame relay uses a separate VC for control channel in vs
in-band control approach used in X.25
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
39
Frame Relay Overview
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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
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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)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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40
Frame Relay: Key Features
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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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
41
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
Rensselaer
Polytechnic
Institute
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42
Shivkumar Kalyanaraman
Frame Relay Lingo (contd)
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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 <
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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
43
Frame Relay Lingo (Contd)
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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 =>
combination CSU/DSUs.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
44
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
45
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
=> Q.933 + Q.931 Frame relay message
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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46
Frame Relay: Data (User) Plane
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Link Access Procedure for Frame-Mode bearer services
(LAPF)
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Functions:
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Q.922 = Enhanced LAPD (Q.921) = LAPD + Congestion Control
Frame delimiting, alignment, and flag transparency
Virtual circuit multiplexing and de-multiplexing
Octet alignment => 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
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A FR-variant called “frame-switching” uses this at every hop
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
47
Frame Relay: LAPF-Core Protocol
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LAPF is similar to LAPD: Flag, bit stuffing, FCS
 No control frames in LAPF-Core => 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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
48
LAPF Address Field
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
49
Frame Relay Traffic Management
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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 <
user rate < PIR
 Network usually over-provisioned for CIR, but underprovisioned for PIR
 Can drop packets with DE set during congestion (I.e.
when absolutely necessary)
Congestion control hooks:
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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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
50
CIR/PIR Service Example
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
51
Leaky Bucket Policing @ Network Edge
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
52
Leaky Bucket Parameters
Committed Information Rate (CIR)
 Committed Burst Size (Bc):
 Excess Burst Size (Be)
 Measurement interval T
 T = Bc/CIR
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Policing actions:
 Between Bc and Bc + Be => Mark DE bit
 Over Be => Discard
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
53
FECN
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Forward Explicit Congestion Notification (FECN)
Source sets FECN = 0
Networks set FECN if avg Q >1
Dest tells source to inc/dec the rate (or window)
Start with R = CIR (or W=1)
If more than 50% bits set => decrease to 0.875 × R (or
0.875W)
If less than 50% bits set => increase to 1.0625 × R (or
min{W+1, Wmax})
If idle for a long time, reset R = CIR (or W=1)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
54
BECN
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Backward Explicit Congestion Notification (BECN)
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Set BECN bit in reverse traffic or send Consolidated LinkLayer Management (CLLM) message to source
 On first BECN bit: Set R = CIR
 On further "S" BECNs: R=0.675 CIR, 0.5 CIR, 0.25
CIR
 On S/2 BECNs clear: Slowly increase R = 1.125 R
 If idle for long, R = CIR
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
55
BECN (Contd)
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For window based control:
 S = One frame interval
 Start with W=1
 First BECN W = max(0.625W,1)
 Next S BECNs W = max(0.625W,1)
 S/2 clear BECNs => W = max(W+1, Wmax)
CLLM contains a list of congested DLCIs
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
56
ATM: Asynchronous Transfer Mode
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
57
Why ATM networks?
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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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
58
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
59
ATM Applications

ATM Deployments:
 Frame Relay backbones
 Internet backbones
 Aggregating Residential broadband networks (Cable,
DSL, ISDN)
 Carrier infrastructures for the telephone and privateline networks

Failed market tests of ATM:
 ATM workgroup and campus networks
 ATM enterprise network consolidation
 End-to-end ATM…
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
60
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
61
ATM vs Data Networks (Internet)

ATM is “virtual circuit” based: the path (and optionally
resources on the path) is reserved before transmission



ATM Cells: Fixed/small size: tradeoff between voice/data


Internet provides “best-effort” routing (combination of
RIP/OSPF/IS-IS/BGP-4), aiming only for connectivity
Addressing:



IP packets: variable size
ATM provides QoS routing coupled to signaling (PNNI)


Internet Protocol (IP) is connectionless, and end-to-end resource
reservations not possible
RSVP is a new signaling protocol in the Internet
ATM uses 20-byte global NSAP addresses for signaling and 32bit 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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
62
Brief History of ATM

1996+: death of ATM in the enterprise, rollouts in
carrier networks
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
63
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute

64
ATM Forum Standards
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
65
ATM Switch Hierarchy
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
66
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
67
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 Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute

68
AAL Lingo….
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
69
AAL Types
AAL1: CBR voice
 AAL5: data…

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
70
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
71
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 Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute

72
ATM-SONET Mapping
Cells are mapped row-wise into the frame
Cells could contain data or be empty
Rensselaer Polytechnic Institute
73
Shivkumar Kalyanaraman
ATM Concepts: Virtual Paths & Virtual Channels

VCs: way to ‘dial’ up and get bandwidth
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
74
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
VCI
Addr.
Data
Sample
Data
ATM cell
Data
Datagram
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
75
VPI/VCI Assignment and Use






All packets must follow the same
path (why?)
Switches store per-VCI state: eg:
QoS info
Signaling => 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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
76
ATM Switches
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
77
ATM Cell Structure
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
78
ATM Cell Structure: Different View
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
79
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
80
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
 => maximal efficiency of 90.57%

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
81
Error Characteristics & Header Protection
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
82
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
83
QoS Big Picture: Control/Data Planes
Control Plane: Signaling + Admission Control or
SLA (Contracting) + Provisioning/Traffic Engineering
Router
Workstation
Router
Internetwork or WAN
Router
Workstation
Data Plane: Traffic conditioning (shaping, policing, marking
etc) + Traffic Classification + Scheduling, Buffer management
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
84
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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
85
CBR and VBR
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
86
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





Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
87
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
88
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.

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
89
ATM Signaling and QoS Routing (PNNI)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
90
ATM: Connection Setup
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
91
ATM: Control/Data/Management Planes
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
92
ATM: Control Plane
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
93
Protocol Stacks for ATM Signaling
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
94
Q.931 Message Format
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
95
Sample Q.931 Message Types
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
96
Information Element Formats
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
97
Sample Information Elements
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
98
ATM Bandwidth Contract
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
99
ATM Addresses: Basis for Signaling
Three NSAP-like (Network Service Access Point) address
formats:
 DCC ATM Format,
 ICD ATM Format,
 Polytechnic
E.164Institute
ATM Format
Shivkumar Kalyanaraman
Rensselaer

100
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 => 104 levels of hierarchy possible

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Rensselaer Polytechnic Institute
101
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
102
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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
103
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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
104
ATM Connection Types






Permanent and Switched
Point to point
Symmetric or asymmetric bandwidth (Uni- or bidirectional)
Point-to-multipoint: Data flow in one direction only.
Data replicated by network.
Leaf Initiated Join (LIJ) or non-LIJ
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
105
ATM Switch: Model & Call Processing
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
106
ATM Connection Setup
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
107
ATM Connection Release
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
108
ATM Connection Release (contd)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
109
ATM Routing: PNNI


Private Network-to-network Interface
Private Network Node Interface
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110
Shivkumar Kalyanaraman
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…”
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
111
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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
112
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
113
PNNI Terminology
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
114
Hierarchical Routing: PNNI
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
115
Hierarchical Routing (contd)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
116
Topology State (QoS) Parameters
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
117
Call Admission Control
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
118
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
119
DTL Example
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
120
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
121
Traffic Management: ATM
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
122
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
123
CAC and UPC
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
124
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 = 1+BT/(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)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
125
Peak-to-Peak CDV
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
126
Service Categories
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
127
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
128
Generic Cell Rate Algorithm
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
129
GCRA: Virtual Scheduling Algorithm
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
130
GCRA: Leaky Bucket Algorithm
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
131
GCRA: Examples
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
132
Maximum Burst Size
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
133
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute

134
ABR: Explicit Rate Scheme
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
135
ABR: Segment-by-Segment Control
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
136
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.

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
137
IP OVER ATM
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
138
ATM: Lan Emulation
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
139
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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
140
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
141
LAN Emulation (Contd)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
142
Protocol Layering w/ LAN Emulation
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
143
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)

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
144
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.

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
145
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

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
146
ATM Virtual LANs
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
147
IP over ATM






How many VC’s 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]
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
148
IP over ATM: RFCs 1483, 1577
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
149
RFC 1483: Packet Encapsulation
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Question: Given an ATM link between two routers,how
many VC’s should we setup?
Answer 1: One VC per Layer 3 protocol. Null
Encapsulation: No sharing. VC based multiplexing.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
150
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
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Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
151
Address Resolution: ATMARP
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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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
152
RFC 1577: Classical IP over ATM
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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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
153
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
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Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
154
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.
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Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
155
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
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Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
156
MPOA (contd)
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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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
157
ATM interfaces w/ Internetworking
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
158