chapter 3. data networks. by sanghyun ahn, dept. of computer science and statistics, university of...

Chapter 3. Data Networks

By Sanghyun Ahn, Dept. of Computer Science and Statistics, University of Seoul

Frame Relay Networks

Key Features of X.25 inband signaling multiplexing of virtual circuits at layer 3 flow and error control at layer 2 & 3 considerable overhead not appropriate for modern digital

communication facilities which are high-quality and reliable


Frame Relay Networks (cont’d)

Key Features of FR (f 3.8) common-channel signaling multiplexing of logical connections at layer 2 no hop-by-hop flow & error control streamlined lower delay and higher throughput up to 2 Mbps


Frame Relay Architecture

LAPF Core Protocol (f 3.9) implemented in all end systems and network a minimal set of data link control functions

• frame delimiting, alignment, and transparency

• frame muxing/demuxing using the addr field

• inspection of frame to ensure length & format

• detection of transmission errors

• congestion control functions


FR Architecture (cont’d)

LAPF Control Protocol implemented only in end systems (optional) provide end-to-end flow & error control

Other Characteristics use a permanent control-oriented virtual

connection virtually no processing by intermediate network

nodes => a frame in error is discarded



User Data Transfer no control field in the frame format (f 3.11)

• impossible to do flow & error control

• connection set-up/tear-down carried out on separate channel at a higher layer

DLCI (Data Link Connection Identifier)• same as the virtual circuit number in X.25



Frame Relay Call Control establishment & release of a logical connection

is accomplished by the exchange of messages over a connection dedicated to call control, with DLCI = 0

message types• SETUP => CONNECT or RELEASE COMPLETE

• RELEASE => RELEASE COMPLETE


Chapter 4. Asynchronous Transfer Mode


ATM Protocol Architecture

Characteristics cell relay: short fixed-size packets a streamlined protocol with minimal error &

flow control high data rates: 155.52 Mbps, 622.08 Mbps


ATM Protocol Arch. (cont’d)

ATM-related Layers (f 4.1) ATM layer

• common to all services

• define the transmission of data in cells

• define the use of logical connections AAL

• service-dependent

• support info transfer protocols not based on ATM

• map between higher-layer info and ATM cells


ATM Protocol Arch. (cont’d)Protocol Planes

User plane• user info transfer with flow & error control

Control plane• call control and connection control functions

Management plane• plane management

– manage a whole system and coordinate between all planes

• layer management– manage resources and parameters residing in its protocol entities


ATM Logical ConnectionsTypes of Logical Connections (f 4.2, t 4.1)

VCC (Virtual Channel Connection)• the basic unit of switching

• cell sequence integrity is preserved within a VCC

• end points may be end users, network entities, or an end user and a network entity

• establish a VCC based on existing VPCs with sufficient available capacity & the appropriate QoS (f 4.3)

• switched and semipermanent VCC– switched: on-demand, by signaling

– semipermanent: long-lasting, by configuration or net mngt

• traffic parameter negotiation & usage monitoring


ATM Logical Conn. (cont’d)

Types of Logical Connections (cont’d) VPC (Virtual Path Connection)

• a bundle of VCCs having the same end points

• advantages of using VPCs– simplified network architecture

– increased network performance and reliability

– reduced processing and short connection setup time

– enhanced network services


ATM Logical Conn. (cont’d)

Control Signaling exchange of info involved in the setup &

release of VPCs and VCCs metasignaling channel

• permanent channel used to set up signaling VCCs


ATM Cells

ATM Cell Format (f 4.4) 53-byte cell with 5-byte header

• less queueing delay, easy switching Header format

• GFC: for flow control at UNI

• VPI/VCI: for routing

• PT: type of info in payload, user or net mngt data (t 4.2)

• CLP: indicate cell discard in case of congestion

• HEC: fig 4.5-6


ATM Service Categories

Real-time Services CBR (Constant Bit Rate)

• simplest service

• fixed data rate, tight delay upper bound

• uncompressed audio/video info

• video conf., interactive audio, A/V distribution/retrieval rt-VBR (Variable Bit Rate)

• tightly constrained delay and delay variation

• variable data rate, bursty


ATM Service Categories (cont’d)

Non-real-time Services nrt-VBR

• bursty, no tight constraints on delay and delay variation

• improved QoS in delay and loss

• data transfer application with critical response-time requirements (e.g., airline reservation)


ATM Service Categories (cont’d)Non-real-time Services (cont’d) (f 4.8)

UBR (Unspecified Bit Rate)• can tolerate variable delays and some cell losses• TCP-based traffic, best-effort service

ABR (Available Bit Rate)• better than UBR• PCR (Peak Cell Rate) & MCR (Min. Cell Rate): at least MCR• unused capacity is shared in a fair and controlled fashion among

all ABR sources• use explicit feedback to sources• LAN interconnection


ATM Adaptation Layer

AAL Services General services provided by AAL

• handling of transmission errors

• segmentation and reassembly

• handling of lost and misinserted cell conditions

• flow control and timing control


AAL (cont’d)AAL Protocol Layer

CS (Convergence Sublayer)• functions for specific applications using AAL• service dependent• SSCS(Service Specific CS), CPCS (Common Part CS) in

AAL 3/4, AAL 5 SAR (Segmentation And Reassembly) sublayer

• pack info received from CS into cells (48 bytes) and do the other way

Service Classes (t 4.3)


AAL (cont’d) (t 4.4)AAL Type 1

CBR CS

• clocking and synchronization SAR

• SN (Sequence Number): to check cell loss or misinsertion• SNP (SN Protection): SN error correction

AAL Type 2 VBR, for analog appl. Requiring timing info


AAL (cont’d)

AAL Type 3/4 connectionless or connection oriented

• connectionless– each data block is treated independently

• connection oriented– may define multiple SAR logical connections over a

single ATM connection


AAL (cont’d)

AAL Type 3/4 (cont’d) message mode or streaming mode

• message mode– transfer of frame-based data (ex. frame relay)

• streaming mode– transfer of low-speed continuous data with low delay

requirements


AAL (cont’d)

AAL Type 3/4 (cont’d) CPCS

• alert the receiver that a block of data is coming in segments and that buffer space must be allocated for that reassembly

• B/E tag: a number associated with a particular CPCS-PDU• BASize: max. buffer size at the receiving peer entitty for

reassembly• AL: a filler octet to make the length of the CPCS-PDU

equal to 32 bitsl


AAL (cont’d)

AAL Type 3/4 (cont’d) SAR

• ST: type of SAR-PDU; SSM, COM, BOM, EOM

• SN: for reassembly purpose

• MID– an identifier associated with the set of SAR-PDUs

carrying a single SAR-SDU

– used when multiplexing logical connections in a VCC


AAL (cont’d)AAL Type 5

provide a streamlined transport facility for higher-layer protocols that are connection oriented• reduce protocol processing overhead• reduce transmission overhead• ensure adaptability to existing transport protocols

similar to AAL 3/4 but appropriate for high-speed data communications

no multiplexing provided


Chapter 5. High-Speed LANs


Ethernet developed by Xerox the basis for a family of LAN standards by IEEE 802.3

committee operate at 10Mbps over a bus topology LAN

• 10BASE5, 10BASE-T use CSMA/CD MAC protocol

• if medium is idle, transmit• if medium is busy, continue to listen until channel is idle and

transmit• if collision is detected, wait random time and attempt

transmission again


Fast Ethernet a low-cost, Ethernet-compatible LAN operating

at 100Mbps use IEEE 802.3 MAC protocol and frame format 100BASE-T (f 5.5)

• star-wire topology, with all stations connected directly to a central point referred to as a multipoint repeater

• repeater detects collisions, repeats a valid signal on all output links, and transmits a jam signal in case of a collision


Fast Ethernet (cont’d)

can operate in full-duplex mode• upto 200Mbps

• use a switched hub, no collisions can support both 10Mbps and 100Mbps links


Gigabit Ethernet

compatible with 10BASE-T and 100BASE-T


ATM LANs LAN Generations

1st generation• CSMA/CD and token ring LANs• terminal-to-host connectivity, client-server architecture at moderate

data rates 2nd generation

• 100Mbps FDDI (Fiber Distributed Data Interface)• backbone LANs, high-performance workstations

3rd generation• ATM LANs• aggregate throughputs and real-time transport guarantee, multimedia

applications


ATM LANs (cont’d)Requirements for 3rd G. LAN

support multiple, guaranteed classes of service provide scalable throughput facilitate the interworking between LAN & WAN

technology

ATM LAN use ATM as a data transfer protocol somewhere within

the local premises use as gateway to ATM WAN, backbone ATM switch,

workgroup ATM

chapter 3. data networks. by sanghyun ahn, dept. of computer science and statistics, university of...

Documents

transmission of data

mbpsatm protocol

frame format f

higherlayer info

atm cellsatm protocol

appropriate qos f

network entityestablish

network entities