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

ISDN, B-ISDN, X.25, Frame-Relay, ATM Networks 1
ISDN, BISDN, X.25, FrameRelay, ATM Networks: A Telephony View of Convergence Architectures Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Overview  Switched PacketData Services  Integrated Services Vision and Concept Ingredients  History: X.25, ISDN, Frame Relay  ATM Networks: foundation for BISDN  ATM Key Concepts  ATM Signaling and PNNI Routing  ATM Traffic Management  IP over ATM: setting the stage for MPLS Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2A Telephony View of Convergence  Separate Voice network (PSTN) and Data Networks (Frame Relay, SMDS, etc.)  PSTN sometimes used as a data network backbone, but  PSTN is circuit switched (voiceoptimized) and PSTN based WAN not efficient  Delay sensitive traffic such as voice not possible on data networks since no guarantee of QoS  Initial attempts to converge data and voice network not too successful, i.e. ISDN  BISDN and ATM networks viewed as the convergence endpoint leading worldwide domination of telephony driven standards Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3Switched PacketData Services  After the success of T1, the telephone carriers saw the growth in packet switched networks  Evolved their own flavors of packet switching, notably X.25, ISDN, SMDS, Frame Relay, ATM etc  Key concept: Switched services  Switched services: (aka dialup 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 activitybased or averageloadbased pricing models that did not necessarily have a distancebased component  Vs peakrate and distancesensitive Tcarrier pricing Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4Ingredients  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, besteffort” Internet  Long 20byte global addresses used only in signaling  Short 4byte local labels (aka DLCI etc) used in packets (cells): “labelswitching”  Large address space, low perpacket overhead  ISDN/BISDN vision of an endtoend integrated digital network:  Rich QoS capabilities developed: support for voice, data, video traffic Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5Ingredients (contd)  X.25 Frame relay/ATM: reduction of hopbyhop processing complexities  Led to the development of highspeed switches and networks  A serious attempt to internetwork with a variety of datanetworking protocols (IP, Ethernet etc)  Integration (“coupling”) of too many features led to slow rollout, enormous overall complexity  Failure to attain the endtoend market vision  Current trend is to “decouple” building blocks of the architecture within the context of IP/MPLS, sacrificing strict performance guarantees. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6X.25 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7X.25  First packet switching interface in the telephony world  Issued in 1976 and revised in 1980, 1984, 1988, and 1992.  Data Terminal Equipment (DTE) to Data Communication Equipment (DCE) interface  User to network interface (UNI)  Slow speeds, used in pointofsale apps (eg: creditcard validation) and several apps abroad Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8X.25 Virtual Circuits  Circuit: Pin a path, reserve resources, use TDM based transmission  Virtual Circuit = Virtual Call: pin a path, optionally reserve resources  Connectionoriented: Setup an endtoend association (data structure); path not pinned  Connectionless: stateless. No path, no endtoend 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 9X.25 Protocol Layers  Note: the three modular layers were cospecified by the same standards body  Layers:  X.21 replaced by EIA232 (RS232C)  LAPB = Link access procedure Balanced  Packet layer = Connectionoriented transport over virtual circuits Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 10X.25 Physical Layer  Electrical and mechanical specifications of the interface  X.21 = 15pin 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  RS232C developed by Electronics Industries  Association of America (EIA) is most common  Uses 25pin connector. Commonly used in PCs. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11Link Layer Roots: HDLC Family  Original:  Synchronous Data Link Control (SDLC): IBM  Derivatives:  HighLevel Data Link Control (HDLC): ISO  Link Access ProcedureBalanced (LAPB): X.25  Link Access Procedure for the D channel (LAPD): ISDN  Link Access Procedure for modems (LAPM): V.42  PointtoPoint Protocol (PPP): Internet  Logical Link Control (LLC): IEEE  Link Access Procedure for halfduplex links (LAPX): Teletex  Advanced Data Communications Control Procedures (ADCCP): ANSI  V.120 and Frame relay also use HDLC Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12HDLC (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 stations  Unbalanced Configuration: One or more secondary  Normal Response Mode (NRM): Response from secondary  Asynchronous Response Mode (ARM): Secondary may respond before command Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13LAPB  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  Pointtopoint: Only two stations DTE (A), DCE (B)  Addresses: A=00000011, B=00000001  Address = Destination Addresses in Commands Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14HDLC frames  Information Frames: User data  Piggybacked Acks: Next frame expected  Poll/Final = Command/Response  Supervisory Frames: Flow and error control  Go back N and Selective Reject  Final No more data to send  Unnumbered Frames: Control  Mode setting commands and responses  Information transfer commands and responses  Recovery commands and responses  Miscellaneous commands and responses Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15HDLC Operation SABM: Set Asynchronous Balanced Mode UA: Unnumbered ACK DISC: disconnect RR: Receiver Ready RNR: Receiver Not Ready I: information frame Heavyweight LinkSetup and PerPacket Acking Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16HDLC Operation (Contd) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17X.25 Packet Level: Layer 3  Packet Level = “Endtoend” for X.25 networks But really Layer 3 (network layer)  Packet level procedures: Establishment and clearing of virtual calls Management of PVCs Flow Control Recovery from error conditions Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18X.25 Packet Level (Layer 3) Signaling Operation Redundant signaling and reliability functions at L2 and L3 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19X.25 Packet Format  GFI = Packet formatting information  PTI = 20 possible packet types (for demultiplexing)  Logical Channel Group and Channel Numbers:  Virtual circuit identifier Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20(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 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 21(Layer 3) Packet Format (Contd)  3bit and 7bit sequence number options possible  Again, note: these are layer 3 sequence numbers… Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 22ISDN: Integrated Services Digital Network Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 23ISDN: EndtoEnd Digital Services Vision Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 24ISDN Configurations Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 25BRI 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 7digit 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 26Basic Rate ISDN (BRI): contd  Basic Rate ISDN service divides a standard telephone line into three digital channels capable of simultaneous voice and data transmission.  The three channels are comprised of two Bearer (B) channels at 64 kpbs each and a data (D) channel at 16 kbps, also known as 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 27BRI and Reference Model Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 28BRI Reference Model Details  Uinterface: Uinterface is a 2wire 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 ISDNonly device that converts a service provider's Uinterface to a customer's S/Tinterface. Standalone or integrated into a terminal adapter.  S/Tinterface: S/Tinterface is a common way of referring to either an S or Tinterface. 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 ISDNready equipment that can directly connect to the ISDN line (often using an S/ T interface). Eg: ISDN phones, ISDN routers, ISDN computers, etc. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 29BRI Ref Model Details: Contd  TA (terminal adapter): TA is a device that allows non ISDNready equipment to connect to an ISDN line. This device can have an integrated NT1.  Rinterface: Rinterface is a nonISDN interface such as an EIA232 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 nonISDNready router. A TA must be used to connect to the ISDN line. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 30Primary Rate ISDN (PRI)  Primary Rate Interface (PRI) ISDN is a usertonetwork interface (UNI) consisting of:  Twentythree 64 kbps bearer (B) channels, and  One 64 kbps signaling (D) channel (aka 23B+D)  Cumulatively carried over a 1.544 Mbps DS1 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 31ISDN Reference Model Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 32LAPD Framing in ISDN Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 33Q.931: ISDN Signaling Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 34Frame Relay Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 35Diseconomics of Leased Lines…  Multiple logical links = Multiple connections  Four nodes = 12 ports (full mesh)  12 local exchange carrier (LEC) access lines,  6 interexchange 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 36X.25/Frame Relay Niche  6 IXC circuits (star vs full mesh: FR network is like a “hub” or “switch” in a startopology)  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 “closeduser groups” (CUGs))  Tradeoffs:  Packetized L2 (FR) or L3 (X.25) service instead of digital L1 service (Tcarrier)  Service guarantees weaker (delay, jitter, loss; PIR/CIR vs peak rate) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 37X.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 38X.25 vs Frame Relay  X.25: interface between host and packetswitching network  3 layers: phy, link, packet  Heavyweight: error control at every link as well as layer 3: twelve messages for one packet transfer  X.25 offers no QoS capability  Frame relay breaks up linklayer into two parts:  LAPFcore and LAPFcontrol  Network nodes only implement LAPFcore  Frame Switching is a service that implements both  Frame relay uses a separate VC for control channel in vs inband control approach used in X.25 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 39Frame Relay Overview  Frame Relay: “digital packet network” providing benefits dedicated T1 link, but without the expense of multiple dedicated circuits.  Frame Relay leverages the underlying telephone network  Frame Relay distanceinsensitive and averagerate pricing is an ideal, costeffective 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 higherspeed, low errorrate underlying PHY.  Switches do not perform hopbyhop error correction (other than discarding corrupted frames) or flow control (other than setting FECN/BECN bits) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 40Frame Relay: Key Features  X.25 simplified  No flow and error control  Outofband 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 41Frame Relay Reference Model Lingo  PVC: Permanent Virtual Circuit  DLCI: Data Link Connection Identifier  CIR: Committed Information Rate  CSU: Channel Service Unit  UNI: UsertoNetwork Interface  NNI: NetworktoNetwork Interface  DTE: Data Terminal Equipment  DE: Discard Eligible  FRAD: Frame Relay Access Device Shivkumar Kalyanaraman  DSU: Data Service Unit Rensselaer Polytechnic Institute 42Frame 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 Relaycompatible 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 userset 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 43Frame 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 networkowned equipment used in conjunction with customerowned 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 44Datalink Control Identifiers (DLCI) Similar to X.25 DLCI: Only local significance Multiple logical connections over one physical circuit Some ranges preassigned Eg: DLCI = 0 is used for signaling Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 45Frame Relay UNI (aka FUNI)  UNI = Usernetwork 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 reused for signaling messages  Service Access Point Identifier (SAPI) in LAPD = 0 = Q.933 + Q.931 Frame relay message Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 46Frame Relay: Data (User) Plane  Link Access Procedure for FrameMode bearer services (LAPF)  Q.922 = Enhanced LAPD (Q.921) = LAPD + Congestion Control  Functions:  Frame delimiting, alignment, and flag transparency  Virtual circuit multiplexing and demultiplexing  Octet alignment = Integer number of octets before zerobit insertion  Checking min and max frame sizes  Error detection, Sequence and nonduplication  Congestion control  LAPF control may be used for endtoend signaling  A FRvariant called “frameswitching” uses this at every hop Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 47Frame Relay: LAPFCore Protocol  LAPF is similar to LAPD: Flag, bit stuffing, FCS  No control frames in LAPFCore = No control field  No inband 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 48LAPF Address Field Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 49Frame 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 PIR  Network usually overprovisioned for CIR, but under provisioned for PIR  Can drop packets with DE set during congestion (I.e. when absolutely necessary)  Congestion control hooks:  Backward Explicit Congestion Notification (BECN)  Forward Explicit Congestion Notification (FECN)  Very nice ideas later proposed as ECN in TCP/IP  But generally ignored in practice by CPE equipment Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 50CIR/PIR Service Example Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 51Leaky Bucket Policing Network Edge Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 52Leaky Bucket Parameters  Committed Information Rate (CIR)  Committed Burst Size (Bc):  Excess Burst Size (Be)  Measurement interval T T = Bc/CIR  Policing actions: Between Bc and Bc + Be = Mark DE bit Over Be = Discard Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 53FECN  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 minW+1, Wmax)  If idle for a long time, reset R = CIR (or W=1) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 54BECN  Backward Explicit Congestion Notification (BECN)  Set BECN bit in reverse traffic or send Consolidated Link Layer Management (CLLM) message to source  On first BECN bit: Set R = CIR  On further "S" BECNs: 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 55BECN (Contd)  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 56ATM: Asynchronous Transfer Mode Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 57Why ATM networks  Driven by the integration of services and performance requirements of both telephony and data networking  “broadband integrated service vision” (BISDN)  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 58ATM Concepts 1. Virtual circuits 2. Fixedsize 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 endtoend quality of service Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 59ATM Applications  ATM Deployments:  Frame Relay backbones  Internet backbones  Aggregating Residential broadband networks (Cable, DSL, ISDN)  Carrier infrastructures for the telephone and private line networks  Failed market tests of ATM:  ATM workgroup and campus networks  ATM enterprise network consolidation  Endtoend ATM… Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 60ATM vs Synchronous (Phone) Networks  Phone networks are synchronous (periodic).  ATM = Asynchronous Transfer Mode  Phone networks use circuitswitching.  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 61ATM 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 endtoend resource reservations not possible  RSVP is a new signaling protocol in the Internet  ATM Cells: Fixed/small size: tradeoff between voice/data  IP packets: variable size  ATM provides QoS routing coupled to signaling (PNNI)  Internet provides “besteffort” routing (combination of RIP/OSPF/ISIS/BGP4), aiming only for connectivity  Addressing:  ATM uses 20byte global NSAP addresses for signaling and 32 bit locallyassigned labels in cells  IP uses 32bit global addresses in all packets  ATM offers sophisticated traffic management  TCP/IP: congestion control is packetlossbased Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 62Brief History of ATM  1996+: death of ATM in the enterprise, rollouts in carrier networks Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 63ATM Interfaces  UNI = UserNetwork Interface (Private Public)  NNI = Network Node Interface (Private and Public)  BICI = Broadband InterCarrier Interface  DXI = Data Exchange Interface Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 64ATM Forum Standards Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 65ATM Switch Hierarchy Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 66ATM 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 67AAL 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 higherlevel user data into 48byte cells at the sending node and reassembles cells at receiving node Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 68AAL Lingo…. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 69AAL Types  AAL1: CBR voice  AAL5: data… Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 70ATM Physical Layer Functions  Transports ATM cells on a communications channel and defines mechanical specs (connectors, etc.)  2 Sublayers  Transmission Convergence Sublayer  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 Sublayer  Medium dependent functions like bit transfer, bit alignment, OEO Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 71Physical Layers  Multimode Fiber: 100 Mbps using 4b/5b,  155 Mbps SONET STS3c, 155 Mbps 8b/10b  Singlemode Fiber: 155 Mbps STS3c, 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)  UTP3 (phone wire) at 25.6, 51.84, 155 Mbps  UTP5 (Data grade UTP) at 155 Mbps  DS1, DS3, STS3c, STM1, E1, E3, J2, n × T1  Takehome message: Serious attempt to interoperate with several L1, L2 and L3 technologies Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 72ATMSONET Mapping Cells are mapped rowwise into the frame Cells could contain data or be empty Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 73ATM Concepts: Virtual Paths Virtual Channels  VCs: way to „dial‟ up and get bandwidth Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 74Virtual circuits: Label Concept Rationale for Signaling  Two ways to use “packets”  carry entire destination address in header  carry only an identifier, a.k.a “label”  Labels have “local” significance, addresses have “global” significance  Signaling protocol: fundamentally maps “global addresses” or paths (sequence of addresses) to local labels Data Sample VCI Data ATM cell Datagram Addr. Data Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 75VPI/VCI Assignment and Use  All packets must follow the same path (why)  Switches store perVCI 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 (longestprefix match)  Setup must precede data transfer  delays short messages  Switched vs. Permanent virtual circuits Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 76ATM Switches Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 77ATM Cell Structure Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 78ATM Cell Structure: Different View Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 79ATM Concepts: Fixedsize 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 80ATM 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 81Error Characteristics Header Protection Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 82ATM Concepts: Statistical multiplexing with QoS  Trade off worstcase 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 zerosum games of delay and bandwidth  Key to building packetswitched networks with QoS Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 83QoS Big Picture: Control/Data Planes Control Plane: Signaling + Admission Control or SLA (Contracting) + Provisioning/Traffic Engineering Router Workstation Router Router Workstation Internetwork or WAN Data Plane: Traffic conditioning (shaping, policing, marking etc) + Traffic Classification + Scheduling, Buffer management Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 84ATM 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.  rtVBR (Realtime): Conferencing. Max delay guaranteed.  nrtVBR (nonreal time): Stored video. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 85CBR and VBR Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 86Classes 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. packetmode 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 87ABR vs UBR  ABR  Queue in the source  Pushes congestion to edges  Good if endtoend ATM  Fair  Good for the provider  UBR  Queue in the network  No backpressure  Same endtoend or backbone  Generally unfair  Simple for user Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 88Guaranteed 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 framebased.  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 89ATM Signaling and QoS Routing (PNNI) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 90ATM: Connection Setup Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 91ATM: Control/Data/Management Planes Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 92ATM: Control Plane Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 93Protocol Stacks for ATM Signaling Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 94Q.931 Message Format Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 95Sample Q.931 Message Types Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 96Information Element Formats Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 97Sample Information Elements Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 98ATM Bandwidth Contract Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 99ATM Addresses: Basis for Signaling  Three NSAPlike (Network Service Access Point) address formats:  DCC ATM Format,  ICD ATM Format,  E.164 ATM Format Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 100Address Hierarchy in ATM  Multiple formats.  All 20 Bytes long addresses.  Lefttoright hierarchical  Level boundaries can be put in any bit position  13byte prefix = 104 levels of hierarchy possible Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 101Recall: 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 102ATM 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 F 16 is padded to make 8 bytes.  End System Identifier (ESI): 48bit 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 103NSAP vs SNPA Addressing: A Clarification  NSAP = Network Service Access Point. Identifies network layer service entry  SNPA = Subnetwork point of attachment. Identifies the interface to subnetwork  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 NSAPlike encoding but ATM addresses identify SNPA and not NSAP. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 104ATM Connection Types  Permanent and Switched  Point to point  Symmetric or asymmetric bandwidth (Uni or bi directional)  Pointtomultipoint: Data flow in one direction only.  Data replicated by network.  Leaf Initiated Join (LIJ) or nonLIJ Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 105ATM Switch: Model Call Processing Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 106ATM Connection Setup Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 107ATM Connection Release Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 108ATM Connection Release (contd) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 109ATM Routing: PNNI  Private Networktonetwork Interface  Private Network Node Interface Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 110Private Network to Node Interface (PNNI)  Link State Routing Protocol for ATM Networks  “A hierarchy mechanism ensures that this protocol scales well for large worldwide 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 111PNNI 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 112PNNI 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 113PNNI Terminology Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 114Hierarchical Routing: PNNI Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 115Hierarchical Routing (contd) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 116Topology State (QoS) Parameters Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 117Call Admission Control Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 118Source 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 119DTL Example Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 120Crank 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 121Traffic Management: ATM Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 122Traffic Management Functions  Connection Admission Control (CAC): Can requested bandwidth and quality of service be supported  Traffic Shaping: Limit burst length. Spaceout 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 noncompliant connections may be dropped  Frame Discarding  Feedback Control: ABR schemes Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 123CAC and UPC Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 124Traffic 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/SCR1/PCR)   BT (MBS1)(1/SCR1/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  Peaktopeak 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 125PeaktoPeak CDV Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 126Service Categories Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 127Leaky 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 (intercell arrival time) and limit (on earliness)  Two implementations: Virtual scheduling and leaky bucket Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 128Generic Cell Rate Algorithm Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 129GCRA: Virtual Scheduling Algorithm Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 130GCRA: Leaky Bucket Algorithm Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 131GCRA: Examples Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 132Maximum Burst Size Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 133ATM 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 134ABR: Explicit Rate Scheme Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 135ABR: SegmentbySegment Control Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 136Guaranteed 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 137IP OVER ATM Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 138ATM: Lan Emulation Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 139ATM 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 140LAN 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 141LAN Emulation (Contd) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 142Protocol Layering w/ LAN Emulation Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 143Terminology  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 144LAN Emulation Process  Initialization: Client gets address of LAN Emulation Configuration Server (LECS) from its switch, uses wellknown 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 145LANE 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 146ATM Virtual LANs Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 147IP 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 148IP over ATM: RFCs 1483, 1577 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 149RFC 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. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 150Encapsulation (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 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 151Address Resolution: ATMARP  IP address: 123.145.134.65  ATM address: 47.0000 1 614 999 2345.00.00.AA....  Issue: IP Address Û ATM Address translation  Address Resolution Protocol (ARP)  Inverse ATM ARP: VC Þ IP Address  Solution: ATMARP servers Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 152RFC 1577: Classical IP over ATM  ATM stations are divided in to Logical IP Subnets (LIS)  ATMARP server translates IP addresses to ATM addresses.  Each LIS has an ATMARP server for resolution  IP stations set up a direct VC with the destination or the router and exchange packets. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 153IP 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 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 154NextHop 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. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 155MultiProtocol 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 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 156MPOA (contd)  LANE operates at layer 2  RFC 1577 operates at layer 3  MPOA operates at both layer 2 and layer 3 Þ MPOA can handle nonroutable 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 157ATM interfaces w/ Internetworking Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 158
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