bab vi.c. wan technology 3

7/31/2019 Bab VI.c. WAN Technology 3

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Bab VI.c

WAN Technologies 3

Komputer

Komputer Komputer

Komputer

WANOption

Komputer

Komputer Komputer

Komputer

WANOption

FRAMERELAYISDN

Wan Tech. Option

1. X.25

2. Frame Relay

Intro to X.25

X.25 is a packet-switching WAN

Developed in 1976 by ITU-T

X.25 is an interface between data terminalequipment (DTE) and Data Circuit-terminating equipment (DCE) for terminaloperation in the packet mode on public

data networks

Intro to X.25

X.25 define how a packet-mode terminalcan be connected to a packet network for the exchange of data

X.25 describes the procedures necessaryfor establishing, maintaining andterminating connections.

X.25 is what is known as a Subscriber Network Interface (SNI) protocol.

Intro to X.25

SNI defines how the user’s DTEcommunicates with the network and howpackets are sent over that network using

DCE.It uses a virtual circuit approach to packetswitching (SVC and PVC) and uses

asynchronous connection.

SVC Basics(Switched Virtual Circuits)

An easy way to imagine this distinctionis to think of your telephone. Every timeyou want to exchange data (i.e., the sound

of your voice), you need to make a call bydialing a number. When someone answersthe phone on the other end of the line, theconnection is established, and you can

talk to each other. When you are finishedtalking, you hang up and break theconnection. This is an SVC connection.

SVC Basics(Switched Virtual Circuits)

PVC Basics(Permanent Virtual Circuits)

Limitations on PVCs and SVCs

PVC connections are less flexible, inthat only one endpoint at a time can beconnected with another on a given LCN.

SVC connections are very flexible in that itis possible for multiple callers to call thesame number.

X.25 layers

X.25 protocol specifies three layersn Physicaln Framen Packet

These layers define functions at thephysical, data link and network layers of

the OSI model

X.25 layers

Physical Layer

At the physical layer, X.25 specifies aprotocol called X.21

X.21 has been specifically defined for X.25

by the ITU-TX.21 is similar enough to other physicallayer such as EIA-232 (Serial)

Frame Layer

X.25 provides data link control using Link Access Procedure, Balanced (LAPB),which is a subset of HDLC

The flag, address, control and FCS fieldsare exactly the same in HDLC

Frame Layer

3 categories of Framesn I-Frames

Are used to encapsulate packet from the network

layer n S-Frames

Are for flow and error control in the frame layer

n U-Frame

Are used to set up and disconnect the links betweenDTE and DCE

Frame layer phases

In the frame layer, communicationbetween a DTE and a DCE involves 3phasesn Link Setupn Transferring datan Link Disconnect

Frame layer phases

Link Setupn The link between DTE and DCE must be

setup before packets from the packet layer

can be transferred. Either the DCE or the DTEcan set up the link by sending an SABM (Set

Asynchronous Balance Mode) frame, theresponding party sends an ACK frame

( Acknowledgement ) to show the link is ready

Frame layer phases

Transferring datan After the link has been established, the 2

parties can send and receive network layer

packets using I-frames and S-framesLink Disconnectn When the network layer no longer needs the

link, one of the parties can issue a disconnect

(DISC) frame to request a disconnection

Packet Layer

The network layer in X.25 is called thePacket Layer Protocol (PLP).

This layer is responsible for establishing

the connection, transferring the data, andterminating the connection

In addition, it is responsible for creating

the virtual circuits and negotiating networkservices between 2 DTEs

Packet Layer

While the frame layer is responsible for making a connections between a DTE anda DCE, the packet layer is responsible for

making a connection between 2 DTEsNote (important)n X.25 uses flow and error control at two levels

Flow and error control between DCE and DTE are

under jurisdiction of the frame layer Flow and error control between 2 DTEs are under jurisdiction of the packet layer

Packet Layer

Virtual Circuits

X.25 protocol is a packet-switched VirtualCircuit network

The Virtual circuit in X.25 are created at

the network layer (not the data link layer)This means that a physical connectionbetween a DTE and DCE can carryseveral virtual circuits at the network layer

with each circuit responsible for carryingeither data or control information.

Virtual Circuits

n X.25 also checks for errors from source todestination at the network layer

n Two layer operations for error checking and

flow controln Much of the traffic on an X.25 network is

devoted to error checking to ensure reliabilityof the service

Only one-fourth of this traffic is message data

Such extensive traffic wan necessary at the timeX.25 was introduced because transmissionmedia were more error prone then, than they aretoday

Virtual Circuit Identifiers

Each virtual circuit in X.25 should beidentified for use by the packets

The Virtual Circuit Identifiers is used

The VCI in X.25 is called Logical ChannelNumber (LCN)

X.25 SVC networking allows for multiplesimultaneous connections

Summary

X.25 is an old and used to be popular packet-switching WAN

The X.25 protocol defines the procedures

for data transmission between a DTE anda DCE

The X.25 protocol specifies three layersn Physical layer n Frame layer n Packet layer

Summary

LAPB is the protocol used by X.25 at theframe layer for data link control functions

The packet layer handles connection

establishment, data transfer, connectiontermination, virtual circuit creation andnegotiation of network services between

two DTEs

Summary

There are 3 types of X.25 packetsn I framesn S framesn

U framesThe first is a data packet,The latter two arecontrol packets

There are flow and error control at both the

frame layer and the packet layer The virtual circuit identifier in X.25 is called LCN

Wan Tech. Option

1. X.252.

Frame Relay

2. Frame Relay Network

Frame Relay Intro

Frame Relay is a Virtual-Circuit technologythat provides low-level (physical and datalink layers) service.

Frame relay provides the following servicen Higher data rates at lower costn Bursty data

Frame relay can provide Bandwidth on Demand

n Less overhead

Differences between X.25 andFrame Relay

The bad things about X.25n X.25 provides extensive error checking and

flow control

n Frames are checked for accuracy at eachstation

n Each station keeps a copy of the originalframe until it receives confirmation from the

next station that the frames has arrivedcorrectly

n X.25 also checks for errors from source todestination at the network layer

n Two layer operations for error checking and

flow controln Much of the traffic on an X.25 network is

devoted to error checking to ensure reliabilityof the service

Only one-fourth of this traffic is message data

Such extensive traffic wan necessary at the timeX.25 was introduced because transmissionmedia were more error prone then, than they aretoday

n Improvements in traditional transmissionmedia and greater use of fiber-optic cable,which is far less susceptible to noise thanmetallic cable, have decreased the probabilityof transmission error to a point where thislevel of caution is not only unnecessary butcounterproductive as well.

n Frame relay does not provide error checkingor require acknowledgment in the data linklayer.

n All error checking is left to the protocols at thenetwork and transport layer.

n Many data link layer operations are eliminated

while others are combined

Advantages of Frame Relay

Frame Relay operates at a higher speed(up to 1.544 Mbps and recently 44.376Mbps)

Frame Relay operates in just the physicaland data link layersn Means it easily can be used as a backbone

network to provide services to protocols thatalready have a network layer protocol

n If TCP/IP wants to use the services of X.25,there is a duplication in the network layer andFrame Relay fucntions, X.25 has its ownnetwork layer and TCP/IP has its own

n There is no duplication in the case of FrameRelay, TCP/IP uses it s own network layer andFrame Relay provides services at the Physicaland the data link layers

Frame Relay allows bursty data. Users donot have to adhere to a fixed data rate

Frame Relay is less expensive than other

traditional WANs

Disadvantage of Frame Relay

Not fast enough

Frame Relay uses variable-length framesn This may create a varying delays for different users,

example : Delay of a small frame following a largeframe may be different than the delay of a small framefollowing another small frame

Frame Relay operation

Frame relay provides Permanent VirtualCircuit and Switched Virtual Circuit

Frame Relay Virtual Circuit

Frame Relay is a virtual circuit networkLike any other virtual circuit network, ituses a virtual circuit identifier

Virtual Circuit in Frame Relay operates at

the data link layer, in contrast with X.25,they operate at the network layer

Virtual circuit in Frame Relay is identifiedby a number called Data Link ConnectionIdentified (DLCI)----- in X.25 LCN

When a virtual circuit is established by thenetwork, a DTE is given a DLCI number that it can use to access the remote DTE

The local DTE uses this DLCI to sendframes to the remote DTE

Frame Relay Layers

Frame Relay has only physical and datalink layers

C i l i F R l

Comparing layers in Frame Relayand X.25

Wan Tech. Option

1. X.252. Frame Relay

(Asynchronous Transfer Mode)

ATM adalah interface untuk transfer cell (cell relay) dengan kecepatantinggi.

Memungkinkan koneksi lojik ganda di-multiplex-kan pada sebuahinterface fisik tunggal.

ATM bagian dari broadband ATM

Arsitektur Protokol

1. User plane• Provides for user information transfer

2. Control plane•

Call and connection control3. Management plane

• Plane management• whole system functions

• Layer management• Resources and parameters in protocol entities

ATM Logical Connections

Virtual channel connections (VCC)Analogous to virtual circuit in X.25Basic unit of switchingBetween two end usersFull duplexFixed size cellsData, user-network exchange (control) and

network-network exchange (networkmanagement and routing)

Virtual path connection (VPC)Bundle of VCC with same end points

ATM Connection Relationships

ATM Cells

ATM Service Categories

Real time1. Constant bit rate (CBR) ; kecepatan konstan terus-menerus.2. Real time variable bit rate (rt-VBR); kecepatan tidak konstan.

Non-real time1. Non-real time variable bit rate (nrt-VBR)2. Available bit rate (ABR)3. Unspecified bit rate (UBR)4. Guaranteed frame rate (GFR)

CBR(Constant bit rate)

Fixed data rate continuously available

Tight upper bound on delay

Uncompressed audio and videon Video conferencingn Interactive audion A/V distribution and retrieval

rt VBR

rt-VBR (Real time variable bit rate)

Time sensitive applicationn Tightly constrained delay and delay variation

rt-VBR applications transmit at a rate that

varies with timee.g. compressed videon Produces varying sized image framesn

Original (uncompressed) frame rate constantn So compressed data rate varies

Can statistically multiplex connections

nrt VBR

nrt-VBR(Non-real time variable bit rate )

May be able to characterize expectedtraffic flow

Improve QoS in loss and delay

End system specifies:n Peak cell raten Sustainable or average raten

Measure of how bursty traffic ise.g. Airline reservations, bankingtransactions

UBR(Unspecified bit rate )

May be additional capacity over andabove that used by CBR and VBR trafficn Not all resources dedicated

n Bursty nature of VBRFor application that can tolerate some cellloss or variable delaysn

e.g. TCP based trafficCells forwarded on FIFO basis

Best efforts service

ABR(Available bit rate)

Application specifies peak cell rate (PCR)and minimum cell rate (MCR)

Resources allocated to give at least MCR

Spare capacity shared among all ARBsources

e.g. LAN interconnection

GFR(Guaranteed Frame Rate)

Designed to support IP backbone subnetworksBetter service than UBR for frame based trafficn Including IP and Ethernet

Optimize handling of frame based traffic passingfrom LAN through router to ATM backbonen Used by enterprise, carrier and ISP networksn Consolidation and extension of IP over WAN

ABR difficult to implement between routers over

ATM networkGFR better alternative for traffic originating onEthernetn Network aware of frame/packet boundaries

n When congested, all cells from frame discarded

ATM Bit Rate Services

AAL P t l

AAL Protocols

Convergence sublayer (CS)n Support for specific applicationsn AAL user attaches at SAP

Segmentation and re-assembly sublayer

(SAR)n Packages and unpacks info received from CS

into cells

Four typesn Type 1n Type 2n Type 3/4n Type 5

AAL Protocols

Segmentation and Reassembly PDU

AAL Type 1

CBR source

SAR packs and unpacks bits

Block accompanied by sequence number

AAL Type 2

Analog applications

AAL Type 3/4

Connectionless or connected

Message mode or stream mode

AAL Type 5

Streamlined transport for connectionoriented higher layer protocols

ATM Adaptation Layer

CBR rt-VBR Nrt-vbr ABR UBR

AAL1 Voice

AAL2 Voice Video

AAL3/4 Data Service

AAL5 LANEmulation

Voice FR, ATM EmulationLANE

ATM Network

ATM Network(integrated voice, video, and data services)

ATM St d d

ATM Standards

ITU-T, ATM Forum, IETFUser-to-Network Interface (UNI) 2.0UNI 3.0, UNI 3.1, UNI 4.0Network-to-Network Interface (NNI)

PNNIn Private NNIn Public-Network Node Interface

RFC 2684 (Multiprotocol encapsulation over ATM)

LAN Emulation (LANE)Multiprotocol over ATM (MPoA)

ATM N t k C t

ATM Network Components

Network

ATM C ll F t

ATM Cell Format

Generic Flow Control (GFC) – typically not used.Virtual Path Identifier (VPI) – 8 or 12 bits

Virtual Channel Identifier (VCI) – 16 bits

Payload Type (PT)— 3 bitsn first bit: user data (0) or control data (1)n second bit: 0 = no congestion, 1 = congestion),n third bit: whether the cell is the last cell (1) in a series of AAL5 frame

Cell Loss Priority (CLP)—Indicates whether the cell should bediscarded (1) if it encounters extreme congestion as it movesthrough the network.

Header Error Control (HEC)—checksum on the first 4 bytes of theheader.

Discussion: compare ATM cell with Frame Relay frame

ATM Vi t l C ti

ATM Virtual Connections

ATM switching is based on VPI/VCIHowever, VPI+VPI is not called ATM address.

VPI/VCI has local significance only.

ATM R f M d l

ATM Reference Model

ATM Ad t ti L

ATM Adaptation Layer Function: Add control information and break ProtocolData Unit (PDU) into cells

Segmentation and Reassembly (SAR)

AAL1:n Designed for voice application

n Constant Bit Rate (CBR)n Circuit Emulation Service (CES)

AAL2n Variable Bit Rate (VBR)n VBR-rt (voice)n VBR-nrt (data)

AAL5:n Designed for data applicationn Unspecified Bit Rate (UBR)

Physical

CPCS-PDU Payload

Padding (0-47)

CPCS-UU (1)

CPI (1)Length (2)

CRC (4)

up to 216 -1

why do we need padding?

CPCS: Common Part Convergence SublayerPDU: Protocol Data UnitUU: User-to-user interface informationCPI: Common Part Indicator

ATM Quality of Service (QoS)

ATM Quality of Service (QoS)CBR: Constant Bit Raten Guaranteed transmission rate

VBR: Variable Bit Raten rtVBR and nrtVBRn Peak Cell Rate (PCR), Sustained Cell Rate (SCR),

and Max Burst Size (MBR)

UBR: Unspecified Bit Raten No guarantee, best effort

Service

BitRate

ATM Q S

ATM QoS

How does a carrier ensure that QOS can be met?n Connection Admission Control (CAC)

Procedure for determining whether each new SETUPrequest should be granted or denied based on currentnetwork conditions

n Usage Parameter Control (UPC)Procedure for verifying whether customer is conforming totheir contractual Traffic Parameters.

n Resource Management (RM)Procedure for notifying ABR users when they should slowdown

n ABR: Available Bit Raten Selective Cell Discard (SCD)

Procedure for discarding cells (CLP=1)during congestion.

See U Next Week

bab vi.c. wan technology 3

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