Скачать презентацию Computer Networks Set 10 X 25 ATM and Скачать презентацию Computer Networks Set 10 X 25 ATM and

46722603740fd20b1e779f1c38d146f3.ppt

  • Количество слайдов: 101

Computer Networks Set 10 X. 25, ATM and Frame Relay Computer Networks Set 10 X. 25, ATM and Frame Relay

X. 25 Ñ 1976 Ñ Interface between host and packet switched network Ñ Almost X. 25 Ñ 1976 Ñ Interface between host and packet switched network Ñ Almost universal on packet switched networks and packet switching in ISDN Ñ Defines three layers Ñ Physical Ñ Link Ñ Packet

X. 25 - Physical Ñ Interface between attached station and link to node Ñ X. 25 - Physical Ñ Interface between attached station and link to node Ñ Data terminal equipment DTE (user equipment) Ñ Data circuit terminating equipment DCE (node) Ñ Uses physical layer specification X. 21 Ñ Reliable transfer across physical link Ñ Sequence of frames

X. 25 - Link, Packet Ñ Link Access Protocol Balanced (LAPB) Ñ Subset of X. 25 - Link, Packet Ñ Link Access Protocol Balanced (LAPB) Ñ Subset of HDLC Ñ Packet: External virtual circuits Ñ Logical connections (virtual circuits) between subscribers

X. 25 Use of Virtual Circuits X. 25 Use of Virtual Circuits

Virtual Circuit Service Ñ Virtual Call Ñ Dynamically established Ñ Permanent virtual circuit Ñ Virtual Circuit Service Ñ Virtual Call Ñ Dynamically established Ñ Permanent virtual circuit Ñ Fixed network assigned virtual circuit

Virtual Call Virtual Call

Packet Format Packet Format

Multiplexing Ñ DTE can establish 4095 simultaneous virtual circuits with other DTEs over a Multiplexing Ñ DTE can establish 4095 simultaneous virtual circuits with other DTEs over a single DTC-DCE link Ñ Packets contain 12 bit virtual circuit number

Virtual Circuit Numbering Virtual Circuit Numbering

Flow and Error Control Ñ HDLC (Chapter 7) Flow and Error Control Ñ HDLC (Chapter 7)

Packet Sequences Ñ Complete packet sequences Ñ Allows longer blocks of data across network Packet Sequences Ñ Complete packet sequences Ñ Allows longer blocks of data across network with smaller packet size without loss of block integrity Ñ A packets Ñ M bit 1, D bit 0 Ñ B packets Ñ The rest Ñ Zero or more A followed by B

Reset and Restart Ñ Reset Ñ Reinitialize virtual circuit Ñ Sequence numbers set to Reset and Restart Ñ Reset Ñ Reinitialize virtual circuit Ñ Sequence numbers set to zero Ñ Packets in transit lost Ñ Up to higher level protocol to recover lost packets Ñ Triggered by loss of packet, sequence number error, congestion, loss of network internal virtual circuit Ñ Restart Ñ Equivalent to a clear request on all virtual circuits Ñ E. g. temporary loss of network access

ATM: Protocol Architecture Ñ Similarities between ATM and packet switching Ñ Transfer of data ATM: Protocol Architecture Ñ Similarities between ATM and packet switching Ñ Transfer of data in discrete chunks Ñ Multiple logical connections over single physical interface Ñ In ATM flow on each logical connection is in fixed sized packets called cells Ñ Minimal error and flow control Ñ Reduced overhead Ñ Data rates (physical layer) 25. 6 Mbps to 622. 08 Mbps

Protocol Architecture (diag) Protocol Architecture (diag)

Reference Model Planes Ñ User plane Ñ Provides for user information transfer Ñ Control Reference Model Planes Ñ User plane Ñ Provides for user information transfer Ñ Control plane Ñ Call and connection control Ñ Management plane Ñ Plane management Ñ whole system functions Ñ Layer management Ñ Resources and parameters in protocol entities

ATM Logical Connections Ñ Virtual channel connections (VCC) Ñ Analogous to virtual circuit in ATM Logical Connections Ñ Virtual channel connections (VCC) Ñ Analogous to virtual circuit in X. 25 Ñ Basic unit of switching Ñ Between two end users Ñ Full duplex Ñ Fixed size cells Ñ Data, user-network exchange (control) and network-network exchange (network management and routing) Ñ Virtual path connection (VPC) Ñ Bundle of VCC with same end points

ATM Connection Relationships ATM Connection Relationships

Advantages of Virtual Paths Ñ Simplified network architecture Ñ Increased network performance and reliability Advantages of Virtual Paths Ñ Simplified network architecture Ñ Increased network performance and reliability Ñ Reduced processing Ñ Short connection setup time Ñ Enhanced network services

Call Establishment Using VPs Call Establishment Using VPs

Virtual Channel Connection Uses Ñ Between end users Ñ End to end user data Virtual Channel Connection Uses Ñ Between end users Ñ End to end user data Ñ Control signals Ñ VPC provides overall capacity Ñ VCC organization done by users Ñ Between end user and network Ñ Control signaling Ñ Between network entities Ñ Network traffic management Ñ Routing

VP/VC Characteristics Ñ Quality of service Ñ Switched and semi-permanent channel connections Ñ Call VP/VC Characteristics Ñ Quality of service Ñ Switched and semi-permanent channel connections Ñ Call sequence integrity Ñ Traffic parameter negotiation and usage monitoring Ñ VPC only Ñ Virtual channel identifier restriction within VPC

Control Signaling - VCC Ñ Done on separate connection Ñ Semi-permanent VCC Ñ Meta-signaling Control Signaling - VCC Ñ Done on separate connection Ñ Semi-permanent VCC Ñ Meta-signaling channel Ñ Used as permanent control signal channel Ñ User to network signaling virtual channel Ñ For control signaling Ñ Used to set up VCCs to carry user data Ñ User to user signaling virtual channel Ñ Within pre-established VPC Ñ Used by two end users without network intervention to establish and release user to user VCC

Control Signaling - VPC Ñ Semi-permanent Ñ Customer controlled Ñ Network controlled Control Signaling - VPC Ñ Semi-permanent Ñ Customer controlled Ñ Network controlled

ATM Cells Ñ Fixed size Ñ 5 octet header Ñ 48 octet information field ATM Cells Ñ Fixed size Ñ 5 octet header Ñ 48 octet information field Ñ Small cells reduce queuing delay for high priority cells Ñ Small cells can be switched more efficiently Ñ Easier to implement switching of small cells in hardware

ATM Cell Format ATM Cell Format

Header Format Ñ Generic flow control Ñ Only at user to network interface Ñ Header Format Ñ Generic flow control Ñ Only at user to network interface Ñ Controls flow only at this point Ñ Virtual path identifier Ñ Virtual channel identifier Ñ Payload type Ñ e. g. user info or network management Ñ Cell loss priority Ñ Header error control

Generic Flow Control (GFC) Ñ Control traffic flow at user to network interface (UNI) Generic Flow Control (GFC) Ñ Control traffic flow at user to network interface (UNI) to alleviate short term overload Ñ Two sets of procedures Ñ Uncontrolled transmission Ñ Controlled transmission Ñ Every connection either subject to flow control or not Ñ Subject to flow control Ñ May be one group (A) default Ñ May be two groups (A and B) Ñ Flow control is from subscriber to network Ñ Controlled by network side

Single Group of Connections (1) Ñ Terminal equipment (TE) initializes two variables Ñ TRANSMIT Single Group of Connections (1) Ñ Terminal equipment (TE) initializes two variables Ñ TRANSMIT flag to 1 Ñ GO_CNTR (credit counter) to 0 Ñ If TRANSMIT=1 cells on uncontrolled connection may be sent any time Ñ If TRANSMIT=0 no cells may be sent (on controlled or uncontrolled connections) Ñ If HALT received, TRANSMIT set to 0 and remains until NO_HALT

Single Group of Connections (2) Ñ If TRANSMIT=1 and no cell to transmit on Single Group of Connections (2) Ñ If TRANSMIT=1 and no cell to transmit on any uncontrolled connection: Ñ If GO_CNTR>0, TE may send cell on controlled connection Ñ Cell marked as being on controlled connection Ñ GO_CNTR decremented Ñ If GO_CNTR=0, TE may not send on controlled connection Ñ TE sets GO_CNTR to GO_VALUE upon receiving SET signal Ñ Null signal has no effect

Use of HALT Ñ To limit effective data rate on ATM Ñ Should be Use of HALT Ñ To limit effective data rate on ATM Ñ Should be cyclic Ñ To reduce data rate by half, HALT issued to be in effect 50% of time Ñ Done on regular pattern over lifetime of connection

Two Queue Model Ñ Two counters Ñ GO_CNTR_A, GO_VALUE_A, GO_CNTR_B, GO_VALUE_B Two Queue Model Ñ Two counters Ñ GO_CNTR_A, GO_VALUE_A, GO_CNTR_B, GO_VALUE_B

Header Error Control Ñ 8 bit error control field Ñ Calculated on remaining 32 Header Error Control Ñ 8 bit error control field Ñ Calculated on remaining 32 bits of header Ñ Allows some error correction

HEC Operation at Receiver HEC Operation at Receiver

Effect of Error in Cell Header Effect of Error in Cell Header

Impact of Random Bit Errors Impact of Random Bit Errors

Transmission of ATM Cells Ñ 622. 08 Mbps Ñ 155. 52 Mbps Ñ 51. Transmission of ATM Cells Ñ 622. 08 Mbps Ñ 155. 52 Mbps Ñ 51. 84 Mbps Ñ 25. 6 Mbps Ñ Cell Based physical layer Ñ SDH based physical layer

Cell Based Physical Layer Ñ No framing imposed Ñ Continuous stream of 53 octet Cell Based Physical Layer Ñ No framing imposed Ñ Continuous stream of 53 octet cells Ñ Cell delineation based on header error control field

Cell Delineation State Diagram Cell Delineation State Diagram

Impact of Random Bit Errors on Cell Delineation Performance Impact of Random Bit Errors on Cell Delineation Performance

Acquisition Time v Bit Error Rate Acquisition Time v Bit Error Rate

SDH Based Physical Layer Ñ Imposes structure on ATM stream Ñ e. g. for SDH Based Physical Layer Ñ Imposes structure on ATM stream Ñ e. g. for 155. 52 Mbps Ñ Use STM-1 (STS-3) frame Ñ Can carry ATM and STM payloads Ñ Specific connections can be circuit switched using SDH channel Ñ SDH multiplexing techniques can combine several ATM streams

STM-1 Payload for SDH-Based ATM Cell Transmission STM-1 Payload for SDH-Based ATM Cell Transmission

ATM Service Categories Ñ Real time Ñ Constant bit rate (CBR) Ñ Real time ATM Service Categories Ñ Real time Ñ Constant bit rate (CBR) Ñ Real time variable bit rate (rt-VBR) Ñ Non-real time variable bit rate (nrt-VBR) Ñ Available bit rate (ABR) Ñ Unspecified bit rate (UBR)

Real Time Services Ñ Amount of delay Ñ Variation of delay (jitter) Real Time Services Ñ Amount of delay Ñ Variation of delay (jitter)

CBR Ñ Fixed data rate continuously available Ñ Tight upper bound on delay Ñ CBR Ñ Fixed data rate continuously available Ñ Tight upper bound on delay Ñ Uncompressed audio and video Ñ Video conferencing Ñ Interactive audio Ñ A/V distribution and retrieval

rt-VBR Ñ Time sensitive application Ñ Tightly constrained delay and delay variation Ñ rt-VBR rt-VBR Ñ Time sensitive application Ñ Tightly constrained delay and delay variation Ñ rt-VBR applications transmit at a rate that varies with time Ñ e. g. compressed video Ñ Produces varying sized image frames Ñ Original (uncompressed) frame rate constant Ñ So compressed data rate varies Ñ Can statistically multiplex connections

nrt-VBR Ñ May be able to characterize expected traffic flow Ñ Improve Qo. S nrt-VBR Ñ May be able to characterize expected traffic flow Ñ Improve Qo. S in loss and delay Ñ End system specifies: Ñ Peak cell rate Ñ Sustainable or average rate Ñ Measure of how bursty traffic is Ñ e. g. Airline reservations, banking transactions

UBR Ñ May be additional capacity over and above that used by CBR and UBR Ñ May be additional capacity over and above that used by CBR and VBR traffic Ñ Not all resources dedicated Ñ Bursty nature of VBR Ñ For application that can tolerate some cell loss or variable delays Ñ e. g. TCP based traffic Ñ Cells forwarded on FIFO basis Ñ Best efforts service

ABR Ñ Application specifies peak cell rate (PCR) and minimum cell rate (MCR) Ñ ABR Ñ Application specifies peak cell rate (PCR) and minimum cell rate (MCR) Ñ Resources allocated to give at least MCR Ñ Spare capacity shared among all ARB sources Ñ e. g. LAN interconnection

ATM Adaptation Layer Ñ Support for information transfer protocol not based on ATM Ñ ATM Adaptation Layer Ñ Support for information transfer protocol not based on ATM Ñ PCM (voice) Ñ Assemble bits into cells Ñ Re-assemble into constant flow Ñ IP Ñ Map IP packets onto ATM cells Ñ Fragment IP packets Ñ Use LAPF over ATM to retain all IP infrastructure

ATM Bit Rate Services ATM Bit Rate Services

Adaptation Layer Services Ñ Handle transmission errors Ñ Segmentation and re-assembly Ñ Handle lost Adaptation Layer Services Ñ Handle transmission errors Ñ Segmentation and re-assembly Ñ Handle lost and misinserted cells Ñ Flow control and timing

Supported Application types Ñ Circuit emulation Ñ VBR voice and video Ñ General data Supported Application types Ñ Circuit emulation Ñ VBR voice and video Ñ General data service Ñ IP over ATM Ñ Multiprotocol encapsulation over ATM (MPOA) Ñ IPX, Apple. Talk, DECNET) Ñ LAN emulation

AAL Protocols Ñ Convergence sublayer (CS) Ñ Support for specific applications Ñ AAL user AAL Protocols Ñ Convergence sublayer (CS) Ñ Support for specific applications Ñ AAL user attaches at SAP Ñ Segmentation and re-assembly sublayer (SAR) Ñ Packages and unpacks info received from CS into cells Ñ Four types Ñ Type 1 2 3/4 5

AAL Protocols AAL Protocols

Segmentation and Reassembly PDU Segmentation and Reassembly PDU

AAL Type 1 Ñ CBR source Ñ SAR packs and unpacks bits Ñ Block AAL Type 1 Ñ CBR source Ñ SAR packs and unpacks bits Ñ Block accompanied by sequence number

AAL Type 2 Ñ VBR Ñ Analog applications AAL Type 2 Ñ VBR Ñ Analog applications

AAL Type 3/4 Ñ Connectionless or connected Ñ Message mode or stream mode AAL Type 3/4 Ñ Connectionless or connected Ñ Message mode or stream mode

AAL Type 5 Ñ Streamlined transport for connection oriented higher layer protocols AAL Type 5 Ñ Streamlined transport for connection oriented higher layer protocols

CPCS PDUs CPCS PDUs

Example AAL 5 Transmission Example AAL 5 Transmission

Frame Relay Ñ Designed to be more efficient than X. 25 Ñ Developed before Frame Relay Ñ Designed to be more efficient than X. 25 Ñ Developed before ATM Ñ Larger installed base than ATM Ñ ATM now of more interest on high speed networks

ATM speed, small cell size, limited overhead bits Ñ High Traffic Management Ñ Still ATM speed, small cell size, limited overhead bits Ñ High Traffic Management Ñ Still evolving Ñ Requirements Ñ Majority of traffic not amenable to flow control Ñ Feedback slow due to reduced transmission time compared with propagation delay Ñ Wide range of application demands Ñ Different traffic patterns Ñ Different network services Ñ High speed switching and transmission increases volatility

Latency/Speed Effects Ñ ATM 150 Mbps Ñ ~2. 8 x 10 -6 seconds to Latency/Speed Effects Ñ ATM 150 Mbps Ñ ~2. 8 x 10 -6 seconds to insert single cell Ñ Time to traverse network depends on propagation delay, switching delay Ñ Assume propagation at two-thirds speed of light Ñ If source and destination on opposite sides of USA, propagation time ~ 48 x 10 -3 seconds Ñ Given implicit congestion control, by the time dropped cell notification has reached source, 7. 2 x 106 bits have been transmitted Ñ So, this is not a good strategy for ATM

Cell Delay Variation Ñ For ATM voice/video, data is a stream of cells Ñ Cell Delay Variation Ñ For ATM voice/video, data is a stream of cells Ñ Delay across network must be short Ñ Rate of delivery must be constant Ñ There will always be some variation in transit Ñ Delay cell delivery to application so that constant bit rate can be maintained to application

Time Re-assembly of CBR Cells Time Re-assembly of CBR Cells

Network Contribution to Cell Delay Variation Ñ Packet switched networks Ñ Queuing delays Ñ Network Contribution to Cell Delay Variation Ñ Packet switched networks Ñ Queuing delays Ñ Routing decision time Ñ Frame relay Ñ As above but to lesser extent Ñ ATM Ñ Less than frame relay Ñ ATM protocol designed to minimize processing overheads at switches Ñ ATM switches have very high throughput Ñ Only noticeable delay is from congestion Ñ Must not accept load that causes congestion

Cell Delay Variation At The UNI Ñ Application produces data at fixed rate Ñ Cell Delay Variation At The UNI Ñ Application produces data at fixed rate Ñ Processing at three layers of ATM causes delay Ñ Interleaving cells from different connections Ñ Operation and maintenance cell interleaving Ñ If using synchronous digital hierarchy frames, these are inserted at physical layer Ñ Can not predict these delays

Origins of Cell Delay Variation Origins of Cell Delay Variation

Traffic and Congestion Control Framework Ñ ATM layer traffic and congestion control should support Traffic and Congestion Control Framework Ñ ATM layer traffic and congestion control should support Qo. S classes for all foreseeable network services Ñ Should not rely on AAL protocols that are network specific, nor higher level application specific protocols Ñ Should minimize network and end to end system complexity

Timings Considered Ñ Cell insertion time Ñ Round trip propagation time Ñ Connection duration Timings Considered Ñ Cell insertion time Ñ Round trip propagation time Ñ Connection duration Ñ Long term Ñ Determine whether a given new connection can be accommodated Ñ Agree performance parameters with subscriber

Traffic Management and Congestion Control Techniques Ñ Resource management using virtual paths Ñ Connection Traffic Management and Congestion Control Techniques Ñ Resource management using virtual paths Ñ Connection admission control Ñ Usage parameter control Ñ Selective cell discard Ñ Traffic shaping

Resource Management Using Virtual Paths Ñ Separate traffic flow according to service characteristics Ñ Resource Management Using Virtual Paths Ñ Separate traffic flow according to service characteristics Ñ User to user application Ñ User to network application Ñ Network to network application Ñ Concern with: Ñ Cell loss ratio Ñ Cell transfer delay Ñ Cell delay variation

Configuration of VCCs and VPCs Configuration of VCCs and VPCs

Allocating VCCs within VPC Ñ All VCCs within VPC should experience similar network performance Allocating VCCs within VPC Ñ All VCCs within VPC should experience similar network performance Ñ Options for allocation: Ñ Aggregate peak demand Ñ Statistical multiplexing

Connection Admission Control Ñ First line of defence Ñ User specifies traffic characteristics for Connection Admission Control Ñ First line of defence Ñ User specifies traffic characteristics for new connection (VCC or VPC) by selecting a Qo. S Ñ Network accepts connection only if it can meet the demand Ñ Traffic contract Ñ Peak cell rate Ñ Cell delay variation Ñ Sustainable cell rate Ñ Burst tolerance

Usage Parameter Control Ñ Monitor connection to ensure traffic cinforms to contract Ñ Protection Usage Parameter Control Ñ Monitor connection to ensure traffic cinforms to contract Ñ Protection of network resources from overload by one connection Ñ Done on VCC and VPC Ñ Peak cell rate and cell delay variation Ñ Sustainable cell rate and burst tolerance Ñ Discard cells that do not conform to traffic contract Ñ Called traffic policing

Traffic Shaping Ñ Smooth out traffic flow and reduce cell clumping Ñ Token bucket Traffic Shaping Ñ Smooth out traffic flow and reduce cell clumping Ñ Token bucket

ATM-ABR Traffic Management Ñ Some applications (Web, file transfer) do not have well defined ATM-ABR Traffic Management Ñ Some applications (Web, file transfer) do not have well defined traffic characteristics Ñ Best efforts Ñ Allow these applications to share unused capacity Ñ If congestion builds, cells are dropped Ñ Closed loop control Ñ ABR connections share available capacity Ñ Share varies between minimum cell rate (MCR) and peak cell rate (PCR) Ñ ARB flow limited to available capacity by feedback Ñ Buffers absorb excess traffic during feedback delay Ñ Low cell loss

Feedback Mechanisms Ñ Transmission rate characteristics: Ñ Allowed cell rate Ñ Minimum cell rate Feedback Mechanisms Ñ Transmission rate characteristics: Ñ Allowed cell rate Ñ Minimum cell rate Ñ Peak cell rate Ñ Initial cell rate Ñ Start with ACR=ICR Ñ Adjust ACR based on feedback from network Ñ Resource management cells Ñ Congestion indication bit Ñ No increase bit Ñ Explicit cell rate field

Variations in Allowed Cell Rate Variations in Allowed Cell Rate

Cell Flow Cell Flow

Rate Control Feedback Ñ EFCI (Explicit forward congestion indication) marking Ñ Relative rate marking Rate Control Feedback Ñ EFCI (Explicit forward congestion indication) marking Ñ Relative rate marking Ñ Explicit rate marking

Frame Relay Congestion Control Ñ Minimize discards Ñ Miantain agreed Qo. S Ñ Minimize Frame Relay Congestion Control Ñ Minimize discards Ñ Miantain agreed Qo. S Ñ Minimize probability of one end user monoply Ñ Simple to implement Ñ Little overhead on network or user Ñ Create minimal additional traffic Ñ Distribute resources fairly Ñ Limit spread of congestion Ñ Operate effectively regardless of traffic flow Ñ Minimum impact on other systems Ñ Minimize variance in Qo. S

Techniques Ñ Discard strategy Ñ Congestion avoidance Ñ Explicit signaling Ñ Congestion recovery Ñ Techniques Ñ Discard strategy Ñ Congestion avoidance Ñ Explicit signaling Ñ Congestion recovery Ñ Implicit signaling mechanism

Traffic Rate Management Ñ Must discard frames to cope with congestion Ñ Arbitrarily, no Traffic Rate Management Ñ Must discard frames to cope with congestion Ñ Arbitrarily, no regard for source Ñ No reward for restraint so end systems transmit as fast as possible Ñ Committed information rate (CIR) Ñ Data in excess of this liable to discard Ñ Not guaranteed Ñ Aggregate CIR should not exceed physical data rate Ñ Committed burst size Ñ Excess burst size

Operation of CIR Operation of CIR

Relationship Among Congestion Parameters Relationship Among Congestion Parameters

Explicit Signaling Ñ Network alerts end systems of growing congestion Ñ Backward explicit congestion Explicit Signaling Ñ Network alerts end systems of growing congestion Ñ Backward explicit congestion notification Ñ Forward explicit congestion notification Ñ Frame handler monitors its queues Ñ May notify some or all logical connections Ñ User response Ñ Reduce rate

Frame Relay Background - X. 25 Ñ Call control packets, in band signaling Ñ Frame Relay Background - X. 25 Ñ Call control packets, in band signaling Ñ Multiplexing of virtual circuits at layer 3 Ñ Layer 2 and 3 include flow and error control Ñ Considerable overhead Ñ Not appropriate for modern digital systems with high reliability

Frame Relay - Differences Ñ Call control carried in separate logical connection Ñ Multiplexing Frame Relay - Differences Ñ Call control carried in separate logical connection Ñ Multiplexing and switching at layer 2 Ñ Eliminates one layer of processing Ñ No hop by hop error or flow control Ñ End to end flow and error control (if used) are done by higher layer Ñ Single user data frame sent from source to destination and ACK (from higher layer) sent back

Advantages and Disadvantages Ñ Lost link by link error and flow control Ñ Increased Advantages and Disadvantages Ñ Lost link by link error and flow control Ñ Increased reliability makes this less of a problem Ñ Streamlined communications process Ñ Lower delay Ñ Higher throughput Ñ ITU-T recommend frame relay above 2 Mbps

Protocol Architecture Protocol Architecture

Control Plane Ñ Between subscriber and network Ñ Separate logical channel used Ñ Similar Control Plane Ñ Between subscriber and network Ñ Separate logical channel used Ñ Similar to common channel signaling for circuit switching services Ñ Data link layer Ñ LAPD (Q. 921) Ñ Reliable data link control Ñ Error and flow control Ñ Between user (TE) and network (NT) Ñ Used for exchange of Q. 933 control signal messages

User Plane Ñ End to end functionality Ñ Transfer of info between ends Ñ User Plane Ñ End to end functionality Ñ Transfer of info between ends Ñ LAPF (Link Access Procedure for Frame Mode Bearer Services) Q. 922 Ñ Frame delimiting, alignment and transparency Ñ Frame mux and demux using addressing field Ñ Ensure frame is integral number of octets (zero bit insertion/extraction) Ñ Ensure frame is neither too long nor short Ñ Detection of transmission errors Ñ Congestion control functions

LAPF Core Formats LAPF Core Formats

User Data Transfer Ñ One frame type Ñ User data Ñ No control frame User Data Transfer Ñ One frame type Ñ User data Ñ No control frame Ñ No inband signaling Ñ No sequence numbers Ñ No flow nor error control

Required Reading Ñ Stallings Chapter 11 Ñ ATM Forum Web site Ñ Frame Relay Required Reading Ñ Stallings Chapter 11 Ñ ATM Forum Web site Ñ Frame Relay forum