ISDN, B-ISDN, X.25, Frame-Relay, ATM Networks: A Telephony ... · Evolved their own flavors of...

Shivkumar KalyanaramanRensselaer Polytechnic Institute

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ISDN, B-ISDN, X.25, Frame-Relay, ATM Networks:

A Telephony View of Convergence Architectures


[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

http://www.ecse.rpi.edu/Homepages/shivkuma


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Overview

Switched Packet-Data ServicesIntegrated Services Vision and Concept IngredientsHistory: X.25, ISDN, Frame RelayATM Networks: foundation for B-ISDN

ATM Key ConceptsATM Signaling and PNNI RoutingATM Traffic Management

IP over ATM: setting the stage for MPLS


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A Telephony View of ConvergenceSeparate 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 efficientDelay sensitive traffic such as voice not possible on data networks since no guarantee of QoSInitial 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


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Switched Packet-Data ServicesAfter 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


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IngredientsSignaling 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 routingContrast this to “connectionless, best-effort” Internet

Long 20-byte global addresses used only in signalingShort 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


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Ingredients (contd)X.25 -> Frame relay/ATM: reduction of hop-by-hop processing complexities

Led to the development of high-speed switches and networksA 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 visionCurrent trend is to “de-couple” building blocks of the architecture within the context of IP/MPLS, sacrificing strict performance guarantees.


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X.25


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X.25First packet switching interface in the telephony worldIssued in 1976 and revised in 1980, 1984, 1988, and 1992.Data Terminal Equipment (DTE) to Data Communication Equipment (DCE) interfaceUser to network interface (UNI)Slow speeds, used in point-of-sale apps (eg: credit-card validation) and several apps abroad


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X.25 Virtual Circuits

Circuit: Pin a path, reserve resources, use TDM based transmissionVirtual Circuit = Virtual Call: pin a path, optionally reserve resourcesConnection-oriented: Setup an end-to-end association (data-structure); path not pinnedConnectionless: stateless. No path, no end-to-end associationTwo Types of Virtual Circuits:

Switched virtual circuit (SVC): Similar to phone callPermanent virtual circuit (PVC): Similar to leased lines

Up to 4095 VCs on one X.25 interface


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X.25 Protocol Layers

Note: the three modular layers were co-specified by the same standards bodyLayers:

X.21 replaced by EIA-232 (RS-232C)LAP-B = Link access procedure - BalancedPacket layer = Connection-oriented transport over virtual circuits


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X.25 Physical Layer

Electrical and mechanical specifications of the interfaceX.21 = 15-pin digital recommendationX.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 IndustriesAssociation of America (EIA) is most commonUses 25-pin connector. Commonly used in PCs.


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Link Layer Roots: HDLC FamilyOriginal:

Synchronous Data Link Control (SDLC): IBMDerivatives:

High-Level Data Link Control (HDLC): ISOLink Access Procedure-Balanced (LAPB): X.25Link Access Procedure for the D channel (LAPD): ISDNLink Access Procedure for modems (LAPM): V.42Point-to-Point Protocol (PPP): InternetLogical Link Control (LLC): IEEELink Access Procedure for half-duplex links (LAPX): TeletexAdvanced Data Communications Control Procedures (ADCCP): ANSIV.120 and Frame relay also use HDLC


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HDLC (contd)Primary station: Issue commands (master)Secondary Station:Issue responses (slave)

Hybrids:Combined Station: Both primary and secondary: a.k.a Asynchronous Balanced Mode (ABM)

Balanced Configuration: Two combined stationsUnbalanced Configuration: One or more secondary

Normal Response Mode (NRM): Response from secondaryAsynchronous Response Mode (ARM): Secondary may respond before command


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LAPBUses balanced mode subset of HDLC between DTE and DCE

Uses 01111110 as frame delimiterUses bit stuffing to avoid delimiters inside the framesUses HDLC frame formatPoint-to-point: Only two stations - DTE (A), DCE (B)

Addresses: A=00000011, B=00000001Address = Destination Addresses in Commands


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HDLC framesInformation Frames: User dataPiggybacked Acks: Next frame expectedPoll/Final = Command/ResponseSupervisory Frames: Flow and error controlGo back N and Selective RejectFinal No more data to sendUnnumbered Frames: ControlMode setting commands and responsesInformation transfer commands and responsesRecovery commands and responsesMiscellaneous commands and responses


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HDLC OperationSABM: Set Asynchronous Balanced Mode

UA: Unnumbered ACK

DISC: disconnect

RR: Receiver Ready

RNR: Receiver Not Ready

I: information frameHeavyweight Link-Setup and Per-Packet Acking !!


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HDLC Operation (Contd)


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X.25 Packet Level: Layer 3Packet Level = “End-to-end” for X.25 networks

But really Layer 3 (network layer)

Packet level procedures:Establishment and clearing of virtual callsManagement of PVCsFlow ControlRecovery from error conditions


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X.25 Packet Level (Layer 3) Signaling Operation

Redundant signaling and reliability functions at L2 and L3!


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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


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(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 #


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(Layer 3) Packet Format (Contd)

3-bit and 7-bit sequence number options possibleAgain, note: these are layer 3 sequence numbers…


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ISDN: Integrated Services Digital Network


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ISDN: End-to-End Digital Services Vision


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ISDN Configurations


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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): contdBasic 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 packetizeddata.


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BRI and Reference Model


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BRI Reference Model DetailsU-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 2B+D 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.


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BRI Ref Model Details: ContdTA (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.


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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 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.


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ISDN Reference Model


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LAPD Framing in ISDN


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Q.931: ISDN Signaling


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Frame Relay


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Dis-economics of Leased Lines…Multiple logical links => Multiple connectionsFour nodes => 12 ports (full mesh!!)

12 local exchange carrier (LEC) access lines,6 inter-exchange carrier (IXC) connectionsOne 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!


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X.25/Frame Relay Niche6 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 circuitsShare 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)


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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


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X.25 vs Frame Relay X.25: interface between host and packet-switching network

3 layers: phy, link, packetHeavyweight: 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-controlNetwork nodes only implement LAPF-core Frame Switching is a service that implements both

Frame relay uses a separate VC for control channel in vsin-band control approach used in X.25


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Frame Relay OverviewFrame Relay: “digital packet network” providing benefits dedicated T-1 link, but without the expense of multiple dedicated circuits. Frame Relay leverages the underlying telephone networkFrame 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)


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Frame Relay: Key FeaturesX.25 simplifiedNo flow and error controlOut-of-band signalingTwo layersProtocol multiplexing in the second layerCongestion control addedHigher speed possible.X.25 suitable to 200 kbps vsFrame relay suitable to 2.048 Mbps.Frame Relay = Unreliable multiplexing serviceX.25 Switching = Relaying + Ack + Flow control + Error recovery +loss recovery


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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


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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 < the access/peak rate) which the carrier guarantees to be available DE (Discard Eligibility): A user-set bit: frame may be discardedDLCI (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.


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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 => combination CSU/DSUs.


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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


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Frame Relay UNI (aka FUNI)

UNI = User-network InterfaceLAPF = Link Access Protocol - Frame Mode ServicesLAPD = Link Access Protocol - D ChannelControl Plane:

Signaling over D channel (D = Delta = Signaling)Data transfer over B, D, or H (B = Bearer)LAPD used for reliable signalingISDN Signaling Q.933 + Q.931 re-used for signaling messagesService Access Point Identifier (SAPI) in LAPD = 0

=> Q.933 + Q.931 Frame relay message


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Frame Relay: Data (User) PlaneLink Access Procedure for Frame-Mode bearer services (LAPF)

Q.922 = Enhanced LAPD (Q.921) = LAPD + Congestion Control

Functions:Frame delimiting, alignment, and flag transparencyVirtual circuit multiplexing and de-multiplexingOctet alignment => Integer number of octets before zero-bit insertionChecking min and max frame sizesError detection, Sequence and non-duplicationCongestion control

LAPF control may be used for end-to-end signaling A FR-variant called “frame-switching” uses this at every hop


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Frame Relay: LAPF-Core Protocol

LAPF is similar to LAPD: Flag, bit stuffing, FCSNo control frames in LAPF-Core => No control fieldNo in-band signaling unlike X.25No flow control, no error control, no sequence numbers

Logical Link Control (LLC) may be used on the top of LAPF core


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LAPF Address Field


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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 < user rate < PIRNetwork usually over-provisioned for ΣCIR, but under-provisioned for ΣPIRCan 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/IPBut generally ignored in practice by CPE equipment


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CIR/PIR Service Example


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Leaky Bucket Policing @ Network Edge


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Leaky Bucket ParametersCommitted Information Rate (CIR)Committed Burst Size (Bc):Excess Burst Size (Be)Measurement interval T

T = Bc/CIR

Policing actions:Between Bc and Bc + Be => Mark DE bitOver Be => Discard


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FECN

Forward Explicit Congestion Notification (FECN)Source sets FECN = 0Networks set FECN if avg Q >1Dest 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)


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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 = CIROn further "S" BECNs: R=0.675 CIR, 0.5 CIR, 0.25 CIROn S/2 BECNs clear: Slowly increase R = 1.125 RIf idle for long, R = CIR


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BECN (Contd)For window based control:

S = One frame intervalStart with W=1First 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


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ATM: Asynchronous Transfer Mode


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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 bootInternet supports no quality of service

but is flexible and cheapATM networks are meant to support a range of service qualities at a reasonable cost

Intended to subsume both the telephone network and the Internet


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ATM Concepts 1. Virtual circuits2. Fixed-size packets (cells): allowed fast h/w switching3. Small packet size4. Statistical multiplexing5. Integrated services6. Good management and traffic engineering features7. Scalability in speed and network size

Togethercan carry multiple types of trafficwith end-to-end quality of service


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ATM ApplicationsATM Deployments:

Frame Relay backbonesInternet backbonesAggregating Residential broadband networks (Cable, DSL, ISDN)Carrier infrastructures for the telephone and private-line networks

Failed market tests of ATM:ATM workgroup and campus networksATM enterprise network consolidationEnd-to-end ATM…


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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


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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 possibleRSVP is a new signaling protocol in the Internet

ATM Cells: Fixed/small size: tradeoff between voice/dataIP 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 cellsIP uses 32-bit global addresses in all packets

ATM offers sophisticated traffic managementTCP/IP: congestion control is packet-loss-based


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Brief History of ATM

1996+: death of ATM in the enterprise, rollouts in carrier networks


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ATM Interfaces

UNI = User-Network Interface (Private & Public)NNI = Network Node Interface (Private and Public)B-ICI = Broadband Inter-Carrier InterfaceDXI = Data Exchange Interface


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ATM Forum Standards


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ATM Switch Hierarchy


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ATM Layers

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


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AAL Sublayers and AAL5:

AAL SublayersConvergence Sublayer (CS)

Determines Class of Service (CoS) for incoming trafficProvides 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


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AAL Lingo….


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AAL Types

AAL1: CBR voiceAAL5: data…


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ATM Physical Layer FunctionsTransports ATM cells on a communications channel and defines mechanical specs (connectors, etc.)2 Sub-layersTransmission 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 streamGenerates HEC on transmitGenerates idle cells for cell rate decoupling, or speed matching

Physical Medium Sub-layerMedium dependent functions like bit transfer, bit alignment, OEO


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Physical LayersMultimode Fiber: 100 Mbps using 4b/5b,155 Mbps SONET STS-3c, 155 Mbps 8b/10bSingle-mode Fiber: 155 Mbps STS-3c, 622 MbpsPlastic Optical Fiber: 155 MbpsShielded Twisted Pair (STP): 155 Mbps 8b/10bCoax: 45 Mbps, DS3, 155 MbpsUnshielded Twisted Pair (UTP)UTP-3 (phone wire) at 25.6, 51.84, 155 MbpsUTP-5 (Data grade UTP) at 155 MbpsDS1, 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


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ATM-SONET Mapping

Cells are mapped row-wise into the frame

Cells could contain data or be empty


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ATM Concepts: Virtual Paths & Virtual Channels

VCs: way to ‘dial’ up and get bandwidth


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Virtual circuits: Label Concept & Rationale for Signaling

Two ways to use “packets”carry entire destination address in headercarry only an identifier, a.k.a “label”

Labels have “local” significance, addresses have “global” significanceSignaling protocol: fundamentally maps “global addresses” or paths (sequence of addresses) to local labels

Data

Data

DataVCI

Addr.

Sample

ATM cell

Datagram


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VPI/VCI Assignment and UseAll packets must follow the same path (why?)Switches store per-VCI state: eg:QoS infoSignaling => separation of data and controlSmall Ids can be looked up (exact match) quickly in hardware

harder to do this with IP addresses (longest-prefix match)

Setup must precede data transferdelays short messages

Switched vs. Permanent virtual circuits


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ATM Switches


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ATM Cell Structure


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ATM Cell Structure: Different View


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ATM Concepts: Fixed-size packetsPros

Simpler buffer hardwarepacket arrival and departure requires us to manage fixed buffer sizes

Simpler line schedulingeach cell takes a constant chunk of bandwidth to transmit

Easier to build large parallel packet switchesCons

overhead for sending small amounts of datasegmentation and reassembly costlast unfilled cell after segmentation wastes bandwidth


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ATM Concepts: Small packet sizeAt 8KHz, each byte is 125 microsecondsThe smaller the cell, the less an endpoint has to wait to fill it

Low packetization delayThe smaller the packet, the larger the header overheadStandards body balanced the two to prescribe 48 bytes + 5 byte header = 53 bytes

=> maximal efficiency of 90.57%


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Error Characteristics & Header Protection


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ATM Concepts: Statistical multiplexing with QoS

Trade off worst-case delay against speed of output trunkWhenever long term average rate differs from peak, we can trade off service rate for delay

Build scheduling, buffer management, policing entities to managethe zero-sum games of delay and bandwidth

Key to building packet-switched networks with QoS


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QoS Big Picture: Control/Data Planes

Internetwork or WANWorkstationRouter

Router

RouterWorkstation

Control Plane: Signaling + Admission Control orSLA (Contracting) + Provisioning/Traffic Engineering

Data Plane: Traffic conditioning (shaping, policing, markingetc) + Traffic Classification + Scheduling, Buffer management


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ATM Concepts: Service CategoriesABR (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.


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CBR and VBR


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Classes of ServiceThe 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 voiceClass B: Variable bit rate (VBR), Connection oriented, strict timing, e.g. packet-mode video for video conferencingClass C: Connection oriented VBR, not strict timing, e.g. LANdata transfer applications such as Frame RelayClass D: Connectionless VBR, not strict timing, e.g. LAN datatransfer applications such as IP


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ABR vs UBRABR

Queue in the sourcePushes congestion to edgesGood if end-to-end ATMFairGood for the provider

UBRQueue in the networkNo backpressureSame end-to-end or backboneGenerally unfairSimple for user


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Guaranteed Frame Rate (GFR)UBR with minimum cell rate (MCR) Þ UBR+Frame based serviceComplete frames are accepted or discarded in the switchTraffic 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.


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ATM Signaling and QoS Routing (PNNI)


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ATM: Connection Setup


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ATM: Control/Data/Management Planes


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ATM: Control Plane


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Protocol Stacks for ATM Signaling


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Q.931 Message Format


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Sample Q.931 Message Types


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Information Element Formats


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Sample Information Elements


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ATM Bandwidth Contract


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ATM Addresses: Basis for Signaling

Three NSAP-like (Network Service Access Point) address formats:

DCC ATM Format, ICD ATM Format, E.164 ATM Format


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Address Hierarchy in ATMMultiple formats.All 20 Bytes long addresses.Left-to-right hierarchicalLevel boundaries can be put in any bit position13-byte prefix => 104 levels of hierarchy possible


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Recall: Flat vs Structured AddressesFlat addresses: no structure in them to facilitate scalable routing

Eg: IEEE 802 LAN addressesHierarchical addresses:

Network part (prefix) and host partHelps identify direct or indirectly connected nodes


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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 F16is 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.


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NSAP vs SNPA Addressing: A ClarificationNSAP = Network Service Access Point. Identifies network layer service entrySNPA = 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.


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ATM Connection TypesPermanent and SwitchedPoint to pointSymmetric 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


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ATM Switch: Model & Call Processing


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ATM Connection Setup


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ATM Connection Release


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ATM Connection Release (contd)


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ATM Routing: PNNI

Private Network-to-network InterfacePrivate Network Node Interface


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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…”


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PNNI FeaturesScales 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.


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PNNI Terminology (partial)Peer group: A group of nodes at the same hierarchyBorder node: one link crosses the boundaryLogical group node: Representation of a group as a single pointChild node: Any node at the next lower hierarchy levelParent node: LGN at the next higher hierarchy levelLogical links: links between logical nodesPeer 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


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PNNI Terminology


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Hierarchical Routing: PNNI


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Hierarchical Routing (contd)


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Topology State (QoS) Parameters


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Call Admission Control


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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 hierarchyEntry switch of each peer group specifies complete route through that groupSet of DTLs and manipulations implemented as a stack


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DTL Example


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Crank back and Alternate Path RoutingIf a call fails along a particular route:

It is cranked back to the originator of the top DTLThe originator finds another route orCranks back to the generator of the higher level source route


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Traffic Management: ATM


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Traffic Management FunctionsConnection 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 droppedCells of non-compliant connections may be droppedFrame Discarding

Feedback Control: ABR schemes


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CAC and UPC


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Traffic Contract Parameters

Peak Cell Rate (PCR): 1/TSustained 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 outCell Delay Variation (CDV): ~ Max CTD - Min CTD

Peak-to-peak CDVCell Delay Variation Tolerance (CDVT) t = GCRA limit parameter wrtPCR Þ GCRA(T, t)

Cell Loss Ratio (CLR): Cells lost /Totals cells sentMinimum cell rate (MCR)


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Peak-to-Peak CDV


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Service Categories


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Leaky Bucket: Basis for Policing

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


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Generic Cell Rate Algorithm


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GCRA: Virtual Scheduling Algorithm


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GCRA: Leaky Bucket Algorithm


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GCRA: Examples


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Maximum Burst Size


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ATM ABR: Binary Rate Scheme

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


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ABR: Explicit Rate Scheme


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ABR: Segment-by-Segment Control


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Guaranteed Frame Rate (GFR)UBR with minimum cell rate (MCR) Þ UBR+Frame based serviceComplete frames are accepted or discarded in the switchTraffic 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.


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IP OVER ATM


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ATM: Lan Emulation


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ATM Lan Emulation (LANE)One ATM LAN can be n virtual LANsLogical subnets interconnected via routersNeed drivers in hosts to support each LANOnly IEEE 802.3 and IEEE 802.5 frame formats supported. (FDDI can be easily done.)Doesn't allow passive monitoringNo token management (SMT), collisions, beacon frames.Allows larger frames.


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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 addressesHosts set up a VC and exchange packetsAll software that runs of Ethernet can run on LANE


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LAN Emulation (Contd)


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Protocol Layering w/ LAN Emulation


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TerminologyNDIS = Network Driver Interface SpecificationODI = Open Datalink InterfaceIPX = NetWare Internetworking ProtocolLAN Emulation Software:

LAN Emulation Clients in each hostLAN Emulation ServersLAN Emulation Configuration server (LECS)LAN Emulation Server (LES)Broadcast and unknown server (BUS)


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LAN Emulation ProcessInitialization:

Client gets address of LAN EmulationConfiguration Server (LECS) from its switch, uses well-known LECS address, or well known LECS PVCClient gets Server's address from LECS

Registration:Client sends a list of its MAC addresses to Server.Declares whether it wants ARP requests.


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LANE ProcessAddress Resolution:

Client sends ARP request to Server.Unresolved requests sent to clients, bridges.Server, Clients, Bridges answer ARPClient setups a direct connection

Broadcast/Unknown Server (BUS):Forwards multicast traffic to all membersClients can also send unicast frames for unknown addresses


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ATM Virtual LANs


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IP over ATM

How many VC’s do we need for n protocols?Packet encapsulation [RFC1483]How to find ATM addresses from IP addressesAddress resolution [RFC1577]How to handle multicast? [MARS, RFC 2022]How do we go through n subnets on a large ATM network? [NHRP]


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IP over ATM: RFCs 1483, 1577


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RFC 1483: Packet Encapsulation

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.


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Encapsulation (RFC 1483): Contd

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


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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 translationAddress Resolution Protocol (ARP)Inverse ATM ARP: VC Þ IP AddressSolution: ATMARP servers


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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 resolutionIP stations set up a direct VC with the destination or the router and exchange packets.


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IP Multicast over ATMMulticast Address Resolution Servers (MARS)Internet Group Multicast Protocol (IGMP)Multicast group members send IGMP join/leave messages to MARSHosts wishing to send a multicast send a resolution request to MARSMARS returns the list of addressesMARS distributes membership update information to all cluster members


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Next-Hop Resolution Protocol (NHRP)

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


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Multi-Protocol over ATM (MPOA)

MPOA= LANE + “NHRP+”Extension of LANEUses NHRP to find the shortcut to the next hopNo routing (reassembly) in the ATM network


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MPOA (contd)LANE operates at layer 2RFC 1577 operates at layer 3MPOA operates at both layer 2 and layer 3 Þ MPOA can handle non-routable as well as routable protocolsLayer 3 protocol runs directly over ATM Þ Can use ATMQoSMPOA uses LANE for its layer 2 forwarding


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ATM interfaces w/ Internetworking

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