ITEC4610 Network Switching and Routing ดร. ประวิทย์ ชุมชู หัวหน้าสาขาวิชาวิศวกรรมสารสนเทศและการสื่อสาร(ICE) MUT Email: prawit@mut.ac.th ห้องทำงาน: F402 เบอร์โทรศัพท์ที่ทำงาน: (02)9883655 ต่อ 220 เบอร์โทรศัพท์เคลื่อนที่: 065343850

Class II IP over ATM ดร. ประวิทย์ ชุมชู หัวหน้าสาขาวิชาวิศวกรรมสารสนเทศและการสื่อสาร(ICE) MUT Email: prawit@mut.ac.th ห้องทำงาน: F402 เบอร์โทรศัพท์ที่ทำงาน: (02)9883655 ต่อ 220 เบอร์โทรศัพท์เคลื่อนที่: 065343850

Outlines ATM Architectures ATM Addressing ATM Adaptation layers The ATM Layer The ATM Physical Layer LAN Emulation (ELAN) IP over ATM

ATM Data Voice Video

IP over ATM

ATM Based on cell relay protocol designed by the “ATM Forum” Asynchronous Transfer Mode (ATM) is a Broadband Integrated Services Digital Networks B-ISDN designed by the ITU‑T. Based on cell relay protocol designed by the “ATM Forum”

ATM Cell ATM is packet switching technology It uses short/fixed size packet, hence it is called cell technology Long cells are better suited for data Short cells are better suited for voice As a compromise: ATM cell is 48 bytes + 5 bytes header = 53 bytes

Protocol Architecture Similarities between ATM and packet switching Transfer of data in discrete chunks Multiple logical connections over single physical interface In ATM flow on each logical connection is in fixed sized packets called cells Minimal error and flow control Reduced overhead Data rates (physical layer) 25.6Mbps to 622.08Mbps

Protocol Architecture (diagram)

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

Architecture of an ATM Network

Architecture of an ATM Network User end points are connected through user-to-network interface (UNI) Switches are connected through network-to-network interface (NNI)

Multiplexing Using Different Packet Sizes Variable delays: small packet served after long packet will experience longer delay as compared to a short packet

Multiplexing Using Cells Multiplexing fixed, small size cells results in constant short delay

ATM Multiplexing ATM is based on statistical (asynchronous) multiplexing Asynchronous TDM (no empty slots) is more efficient than synchronous TDM (possible empty slots if user has no data to send)

TDM Data rate of the transmission medium is greater than sending and receiving devices. Link is divided in time 1 4 4

Synchronous TDM Synchronous: multiplexer allocates exactly the same time slot to each deviceb Frame: consists of one complete cycle of time slots

Asynchronous (Statistical) TDM Each time slot can be assigned to any input device. The number of time slots (m) in the frame is based on statistical analysis

Frames and Addresses a. Only three lines sending data Address bits are needed for each time slots More overhead. No empty slots in the frames. Higher efficiency a. Only three lines sending data

Frames and Addresses b. Only four lines sending data

Frames and Addresses c. All five lines sending data

Outlines ATM Architectures ATM Addressing ATM Adaptation layers ATM Layer The ATM Physical Layer LAN Emulation (ELAN) IP over ATM

ATM Addressing The ITU-T standard is based on the use of E.164 addresses (similar to telephone numbers) for public ATM (B-ISDN) networks. The ATM Forum extended ATM addressing to include private networks. It decided on the subnetwork or overlay model of addressing, in which the ATM layer is responsible for mapping network layer addresses to ATM addresses.

ATM Addressing

ATM Address Fields AFI—Identifies the type and format of the address (E.164, ICD, or DCC). DCC—Identifies particular countries. High-Order Domain-Specific Part (HO-DSP)—Combines the routing domain (RD) and the area identifier (AREA) of the NSAP addresses. The ATM Forum combined these fields to support a flexible, multilevel addressing hierarchy for prefix-based routing protocols. End System Identifier (ESI)—Specifies the 48-bit MAC address, as administered by the Institute of Electrical and Electronic Engineers (IEEE). Selector (SEL)—Is used for local multiplexing within end stations and has no network significance. ICD—Identifies particular international organizations. E.164—Indicates the BISDN E.164 address.

Outlines ATM Architectures ATM Addressing ATM Adaptation layers ATM Layer The ATM Physical Layer LAN Emulation (ELAN) IP over ATM

ATM Layers

ATM Layers ATM standard defines three layers Application adaptation layer AAL ATM layer Physical layer End points use all three layers Switches use only the bottom two layers

ATM Layers in End-Point Devices and Switches

AAL Types

Application Adaptation Layer AAL Allows existing networks (such as packet networks) to connect to ATM AAL protocols accept transmissions from upper- layer services (e.g., packet data) and map them into fixed-sized ATM cells Such transmission can be of any type (voice, data, audio, video) and can be of variable or fixed rates At Rx, this process is reversed, e.g., segments are are reassembled into their original format

Data-Stream Types ATM deals with four types of data streams Constant-bit rate (CBR): real time application, such as real-time voice (telephone calls), real-time video (TV) transmission delay must be minimal Variable-bit-rate (VBR): bit rate may vary from section to section of transmission: compressed voice and video, data Connection-oriented packet data: X.25, TCP protocol Connectionless packet data: datagram applications: IP protocols

Application Adaptation Layer : AAL1 Supports applications at constant bit rate (CBR): voice, video, existing digital telephone networks (E-1, T-1) AAL layer is divide into two sublayers: Convergence sublayer (CS) Segmentation and reassembly (SAR) Convergence sublayer (CS): divides the bit stream into 47-byte segments and pass them to the SAR below

AAL1

Segmentation and reassembly (SAR) Adds one-byte header to each 47-byte segment (payload) received from CS This header consists of four fields: CS identifier (CSI): one-bit for signaling purposes Sequence count (SC): three-bit (modulo 8) sequence number for end-to-end error and flow control CRC: three-bit cyclic redundancy check field calculated over the first four bits. Beside single and multiple bit error detection they can correct a single-bit error Parity (P): one-bit parity calculated over the first seven bits (detects an odd number of errors)

AAL2

AAL2 Supports variable bit-rate (VBR) applications SAR accepts 45-bit payload from the CS and adds one-byte header and two-byte trailer, the result is 48-byte data unit passed to ATM layer The overhead consists of three fields in the header and two fields in the trailer Header: CS identifier (CSI): one-bit for signaling purposes Sequence count (SC): three-bit (modulo 8) sequence number for end-to-end error and flow control Information type (IT): 4 bits identifying the data segment as falling in the beginning, middle or end of message

ALL-2 (Trailer) The trailer Length indicator (LI): The first six bits of the trailer are used with the final segment of a message (when the IT in the header of the message indicates the end of the message) to indicate the amount of padding in the final cell (LI indicates where in the segment those bits start) CRC: last 10 bits are CRC of the entire data unit. Can correct single-bit error in the data unit

AAL3/4

AAL3/4 Initially, AAL3 was intended to support connection-oriented data services and AAL4 to support connectionless services Combined later to a single format called AAL3/4 Convergence sublayer: accepts data packet of no more than 65,535 (216-1) bytes from upper layer service adds a header and trailer, which indicate the beginning and end of the message and how much of the final frame is padding (Padding size is 0 - 43 bytes) Message (including header/trailer/padding) is passed 1n 44-byte segment to the SAR layer

AAL3/4 CS header and trailer: Type (T): one byte T field set to zero Begin tag (BT): one byte beginning flag (synchronization) Buffer-allocation (BA): two bytes indicating the buffer size Pad (PAD): indicates the three possible padding size: If # of data in the final segment is 40 bytes, no padding If # of data < 40 bytes, add padding to bring total to 40 If # of data is between 41 and 44, add padding ) 43 to 40 to bring the total to 84. The first 44 bytes make a complete segment, the next 40 bytes and the trailer make the last segment

AAL3/4 CS header and trailer cont’d Alignment (AL): one byte AL field to make the trailre 4 bytes long Ending Tag (ET): one byte ending flag (synchronization) Length (L): two-byte field indicates length of data Segmentation and reassembly: accepts 44-byte pay load from CS and adds 2-byte header and 2-byte trailer. The resulting 48-byte data unit is passed to ATM for inclusion in the cell SAR Header and trailer: Segment type (ST): 2-bit ST indicates whether the segment belongs to the beginning, middle, or the end of a message, or is a single-segment message Convergence sublayer identifier (CSI): one-bit for signaling purposes

AAL3/4 SAR Header and trailer cont’d Sequence count (CS): three-bit (modulo 8) sequence number for end-to-end error and flow control Multiplex identification (MID): 10-bit identifies cells coming from different data flows and multiplexed on the same virtual connection Length indicator (LI): first 6-bit of the trailer indicate the amount of padding/message in the last segment. CRC: last 10 bits of the trailer are the CRC of the entire data unit

AAL5 Called “simple and efficient application layer (SEAL) Assumes that all cells travel sequentially and rest of functions provided by CS and SAR are already included in upper layers, hence no provision for addressing, sequencing or other CS and SAR heading information Only padding and four-field trailer are added at CS Padding and trailer are added to the end of the entire message of 65,536 bytes or less Segments consist of 48 bytes of data, last segment has 40 bytes of data and 8 bytes overhead (trailer)

AAL5 Trailer: Pad (PAD): between 0 and 47 bytes, making the message divisible by 48 User-to-user ID (UU): one byte UU field (user defined) Type (T); one-byte T field (not defined) Length (L): two-byte L fields indicates amount of padding/data CRC: 4-byte error check for the entire data unit

AAL5

Outlines ATM Architectures ATM Addressing ATM Adaptation layers ATM Layer The ATM Physical Layer LAN Emulation (ELAN) IP over ATM

ATM Layer Provides: routing, traffic management, switching, and multiplexing services Accepts 48-byte segments from AAL sublayers and adds to them 5-bytes headers

ATM Header

ATM Header Format Two formats, one for user-to-user interface (UNI) and one for network-to-network interface (NNI) Generic flow control (GFC): 4-bit field flow control at UNI level (flow control is not necessary for NNI, hence bits are added to VPI in the NNI header) Virtual path identifier (VPI): 8-bit field for the UNI and 12-bit for the NNI Virtual channel identifier (VCI): 16-bit field in both frames Payload type (PT): 3-bit PT field, defines the payload as user data or managerial information

PT Fields The interpretation of the last two bits depends on the first bit

ATM Header cont’d Cell loss priority (CLP): one-bit CLP field for congestion control Cells with CLP bit = 0 are cell of higher priority, they should not be discarded as long as there are cells with a CLP set to 1 Users who violate the rate assigned to them by sending at higher rate, the network will set the CLP to 1 to indicate that these cells must be dropped if the link becomes overloaded Header error correction (HEC): one-byte field used for multiple bit error detection and a single-bit error correction over the first four bytes of the header

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

Effect of Error in Cell Header

Outlines ATM Architectures ATM Addressing ATM Adaptation layers ATM Layer The ATM Physical Layer LAN Emulation (ELAN) IP over ATM

The ATM Physical Layer The ATM physical layer has four functions: Cells are converted into a bitstream the transmission and receipt of bits on the physical medium are controlled, ATM cell boundaries are tracked cells are packaged into the appropriate types of frames for the physical medium. The ATM physical layer is divided into two parts: the physical medium-dependent (PMD) sublayer and the transmission convergence (TC) sublayer. The PMD sublayer provides two key functions. synchronizes transmission and reception by sending and receiving a continuous flow of bits with associated timing information. specifies the physical media for the physical medium used, including connector types and cable. Examples of physical medium standards for ATM include Synchronous Digital Hierarchy/Synchronous Optical Network (SDH/SONET), DS-3/E3, 155 Mbps over multimode fiber (MMF) using the 8B/10B encoding scheme, and 155 Mbps 8B/10B over shielded twisted-pair (STP) cabling. The TC sublayer has four functions: cell delineation, header error control (HEC) sequence generation and verification, cell-rate decoupling, and transmission frame adaptation.

ATM Logical Connections Virtual channel connections (VCC) Analogous to virtual circuit in X.25 Basic unit of switching Between two end users Full duplex

ATM Logical Connections Cont’d Fixed size cells Data, user-network exchange (control) and network-network exchange (network management and routing) Virtual path connection (VPC) Bundle of VCC with same end points

ATM Logical Connections Virtual channel connections (VCC) Analogous to virtual circuit in X.25 Virtual path connection (VPC) Bundle of VCC with same end points Advantages of Virtual Paths: Simplified network architecture Increased network performance and reliability Reduced processing Short connection setup time

Example of VPs and VCs 8 endpoints are communicating using 4 VCs 1st two VCs share the same virtual path from switch I to switch III, hence these two VCs are bundled to form one VP Other two VCs share same path from I to IV and hence combined by another VP

Call Establishment Using VPs

Connection Identifiers A virtual connection is identified by a pair of numbers: the VPI and VCI

Virtual Connection Identifiers in UNIs and NNIs 256 x 65536 = 16,777,216 VCs 4096 x 65536 = 268,435,456 VCs

An ATM Cell

SVC Setup PVC (permanent virtual circuited) SVC ( swithed virtual circuits) Connection less

Routing with a VP Switch VP switch routes cells using only VPI Switch routing decision is based on four piece of information stored in switching table: (1) arrival interface number, (2) VPI, (3) corresponding o/g interface number and (4) the new VPI

A Conceptual View of a VP Switch

Routing with a VPC Switch VPC switch routes cells using both VPI and VCI Switch routing decision is based on six piece of information stored in switching table: (1) arrival interface number, (2) i/c VPI, (3) i/c VCI (4) corresponding o/g interface number, (5) o/g VPI and (6) o/g VCI

A Conceptual View of a VPC Switch

Outlines ATM Architectures ATM Addressing ATM Adaptation layers ATM Layer The ATM Physical Layer LAN Emulation (ELAN) IP over ATM

LAN Emulation (ELAN) Stations attached via ATM the same capabilities that they normally obtain from legacy LANs, such as Ethernet and Token Ring

LAN Emulation (ELAN)

Outlines ATM Architectures ATM Addressing ATM Adaptation layers ATM Layer The ATM Physical Layer LAN Emulation (ELAN) IP over ATM

IP Over ATM Objectives Upon completion you will be able to: Review the features of an ATM WAN Understand how an a datagram can pass through an ATM WAN Understand how an IP packet is encapsulated in cells Understand how cells are routed in an ATM network Understand the function of ATMARP

IP over ATM and LAN Emulation

An ATM WAN in the Internet

ATM layers in routers and switches

Note: End devices such as routers use all three layers, while switches use only the bottom two layers.

AAL5

The AAL layer used by the IP protocol is AAL5. Note: The AAL layer used by the IP protocol is AAL5.

ATM layer

ATM headers

Fragmentation Tr=000, not last cell Tr=001,last cell

Note: Only the last cell carries the 8-byte trailer added to the IP datagram. Padding can be added only to the last cell or the last two cells.

Note: The value of the PT field is 000 in all cells carrying an IP datagram fragment except for the last cell; the value is 001 in the last cell.

ATM cells

Entering-point and exiting-point routers

ATMARP ATMARP finds (maps) the physical address of the exiting-point router given the IP address of the exiting-point router. No broadcasting is involved.

ATMARP packet

Table 23.1 OPER field

Note: The inverse request and inverse reply messages can bind the physical address to an IP address in a PVC situation.

Binding with PVC

Binding with ATMARP

Note: The request and reply message can be used to bind a physical address to an IP address in an SVC situation.

Note: The inverse request and inverse reply can also be used to build the server’s mapping table.

Building a table

LOGICAL IP SUBNET (LIS) An ATM network can be divided into logical (not physical) subnetworks. This facilitates the operation of ATMARP and other protocols (such as IGMP) that need to simulate broadcasting on an ATM network.

LIS

Note: LIS allows an ATM network to be divided into several logical subnets. To use ATMARP, we need a separate server for each subnet.

Summary ATM IP over ATM IP over Ethernet IP over Pla. Pla.