Frame Relay: A Packet-Switching Technology for WANs, Summaries of Technology

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13. Frame Relay

Contents

a. Operation

b. Congestion levels and control

c. Traffic control

d. Applications and use in the REDDIG

a. Operation

Evolution of packet-switching technologies

A

B

C

1970 1900 1990 2000 A : Conmutación de paquetes X.25 B : Frame Relay C : ATM

FRAME RELAY is a packet-switching technology

It is based on ITU-T standards:

Q.922 and

Q.

Application of the various technologies

based on speed and size

1000

100

10

FAST Ethernet FDDI ATM

Rate (Mbit/s)Ethernet Frame Relay

25 Mbps ATM

LAN MAN WAN

1

T1/E

Token Ring

MUX

F

E

Typical Frame Relay Network

E1 RED

FRAME RELAY

P

R

O

U TR

FRAD

T

E

R

Nodo X.

Based on a packet-switching network made up by switches and concentrators linked through bidirectional medium- or high-speed lines.

Frame Relay Network Service

ENC S C N LAN RDSI1 RDSI2 DTE1 DTE2 DTE3 DTE4 DTE5 DTE 6 NUCLEOX PLUS

ENC (^) S C N LAN RDSI1 RDSI2 DTE1 DTE2 DTE3 DTE4 DTE5 DTE 6 ENC (^) S C N LAN RDSI1 RDSI2 DTE1 DTE2 DTE3 DTE4 DTE5 DTE 6 NUCLEOX PLUS NUCLEOX PLUS

ENC S C N LAN RDSI1 RDSI2 DTE1 DTE2 DTE3 DTE4 DTE5 DTE 6 NUCLEOX PLUS

ENC S C N LAN RDSI1 RDSI2 DTE1 DTE2 DTE3 DTE4 DTE5 DTE 6 NUCLEOX PLUS UNI

UNI

UNI

UNI

NNI NNI

V.35, V.24, G.702, etc.

Router, FRAD, multiplexor

Frame Relay

UNI ENCS C N LAN RDSI1 RDSI2 DTE1 DTE2 DTE3 DTE4 DTE5 DTE 6NUCLEOX PLUS FRAD (Frame Relay Assembler disassembler)

Frame Relay Interfaces

User (^) User

Frame Relay network

Frame Relay network

UNI (^) NNI UNI

Frame Relay

Frame Relay emerged as a de facto standard issued by a group of equipment manufacturersissued by a group of equipment manufacturers.

Frame Relay Forum

Frame Relay, proposed in 1990 by ANSI (T1.606), evolved from the X.25 service, as a result of quality improvements in transmission and switching media.improvements in transmission and switching media.

Frame Relay

Describes an optimised standard for the transport of data-oriented protocols in discrete information units (generic packets)units (generic packets).

It statistically multiplexes data, thus sharing bandwidth and creating efficiency.

It eliminates much of the protocol processing by the network, thus reducing transmission latency.the network, thus reducing transmission latency.

II. ARCHITECTURE

Frame Relay Architecture

Capas 3 a 7 (propias del

Modelo OSI Capas 3 a 7 (propias del

Modelo OSI

usuario)

Capa 2

Capa 2 Núcleo

Nivel enlace

LAP-D

Interface

usuario)

Capa 2

Capa 2 Núcleo

Capa 1

Interface

física Nodo A Nodo B Las capas 1 y 2 soportan al Frame Relay

Capa 1

Frame Relay Architecture

Q.933 Funciones

Plano C Plano U Plano U Plano C

Q Q.

Q.

Seleccionables por el terminal del usuario

Funciones de núcleo de

Q

Q. Funciones de núcleo de

I.430 o I.

Q.

USUARIO S/T RED

I.430 o I.

Q.

Th fi l d i t di t t h t

Frame Relay Architecture

The final and intermediate systems have two

different and separate architectures :

The user layer

The control layer

User layer :

Frame Relay Architecture

Level 2: (in the ITU-T recommendation, the protocol used is LAP-F)

Control layer : Level 2: LAP-D Level 3: Q.933 (recommendation similar to Q.931,( used in ISDN)

Frame Relay Format

Flag (^) de direcciónCabecera Información FCS

1 2 - 4 Variable 2 1

Flag

Octetos

DLCI ( d )

de dirección

EA 0

C/R 0/

(a) Formato de la trama

8 7 6 5 4 3 2 1 bits

(mayor orden) 0/1 0

DLCI (menor orden) FECN BECN^ DE^

EA 1

DLCI 10 bits

(b) Cabecera de dirección de 2 octetos (usada por defecto)

Flag: It has the same format as in LAP-B (01111110), and is also used for separating frames. When there are no frames to send, flags are generated continuously.

EA (Extended Address)

More than two octets are allowed in the control field ⇒ EA indicates (when marked with a '0') that more octets follow behind or (when marked with a '1') that it is the last one in the control field.

CR (command/response bit).

The network does not use this bit.

DE (Discard Eligibility Bit)

Fixed by the DTE (access device FRAD, router, etc.) or the network nodes (FR switches)

May be modified by the network nodes in case the user has exceeded the CIR and there is congestion in the network

The frames that have this bit set at "1" are subject to b ibeing discarded in case of congestion. di d d i f ti

FECN (FECN ( FF orward Explicit Congestion Notificationd E li it C ti N tifi ti ))

Bit fixed by the network node (FR switch) that is experiencing congestion

Congestion notification in the direction of the ttransmission. i i

BECN ( Backward Explicit Congestion Notification )

Bit fixed by the network node that is experiencing congestion

Congestion notification in the opposite direction of the transmission.

DLCI ( Data Link Connection Identifier )

Data link connection identifierData link connection identifier. Permits the definition of up to 1,024 virtual circuits (2^8 ). The multiplexing function is performed at level 2, and the DLCI identifies the logic channel to which each frame belongs. The logic channel numbers are assigned by contract.g g y

DLCI (4)

DLCI

values Function (Consortium assignment)

0

1 - 15

Reserved for call control signalling (in-band) Reserved

16 -1007 Used for assignment to^ frame relay PVCs

1008 - 1022 Reserved

1023 Local management interface (LMI)

User data. This information is placed in the frame and, when received, is sent directly to the higher level.

It has been defined with a maximum length of 8, octets. Manufacturers use up to 4,096 octets.

This field is aligned to the octet, that is, the service user is required to deliver an integer number of octets.

FCS. Two-octet cyclic redundancy field (Cyclic Redundancy Check – CRC-16)

™™ Given a message or frame ofGiven a message or frame of kk bits in length thebits in length, the sender generates a sequence of n bits, known as frame check sequence (FCS), in such a way that the resulting frame, consisting of k + n bits, is exactly divisible by some predetermined number. ™ Then the receiver divides the incoming frame by the same predetermined number and if there is nothe same predetermined number and, if there is no remainder, it is assumed that the frame arrived without errors.

III: LOCAL MANAGEMENT INTERFACE (LMI)

Local Management Interface (LMI) (1)

The LMI was defined by a consortium of companies (Cisco Systems Digital Equipment Northern(Cisco Systems, Digital Equipment, Northern Telecom, StrataCom) and then incorporated, with some modifications, into Rec. Q.933 Annex A and standard T1.617 Annex D

Local Management Interface (LMI) (1)

The LMI defines aThe LMI defines a pollingpolling protocol between the FRADprotocol between the FRAD and the network for the exchange of information on the status of the interface and the PVCs, such as:

• Notification of a new PVC
• Detection of a PVC cancellation
• Notification of PVC availabilityy
• Link integrity check (UNI)

Local Management Interface (LMI) (2)

The LMI protocol is asymmetric: The FRAD issues a periodicperiodic pollingpolling (STATUS ENQUIRY) to the network(STATUS ENQUIRY) to the network, and the network answers (with a STATUS )

• The polling period is 10 seconds, negotiable (between 5 and 30 seconds)

Originally, the DLCI was the DLCI 1023.

Annex D made it compatible with RDSI signallingp g g functions, and adopted DLCI 0; this is the most widely- used version.

Local Management Interface (LMI) (2)

TheThe popollinglling basbasically seeks to check if the accessically seeks to check if the access interface is active and operating properly.

This periodic polling permits the detection of errors, such as signalling channel errors or internal problems of the network.

Local Management Interface (LMI) (3)

Every given number of activity-detection pollings, thee y g e u be o act ty detect o po gs, t e FRAD requests the status of all the PVCs defined in the access interface. This full status is generally requested every 6 pollings.

Full-status messages contain information about all the PVCs configured in the carrier channel, including recent history and availability of PVCshistory and availability of PVCs.

IV. PHYSICAL LEVEL

Access to theAccess to the Frame RelayFrame Relay networknetwork

FRAD

R d F R l

UNI: User-network interface

Red Frame Relay

UNI FRAD: ( Frame Relay Assembler / Disassembler) , by analogy with the PAD X.25.

⌧ FRAD services: ’ Transfer of files ’ Multiplexing of low-speed applications in a high- speed channel ’ Asynchronous traffic

Access to theAccess to the Frame RelayFrame Relay networknetwork

FRAD

UNI: User-network interface

Network services: plain connection-oriented transport of frames

Red Frame Relay UNI

⌧⌧ UNI services:UNI services:  Bidirectional frame transfer  Preservation of the order of frames  Detection of transmission, formatting and operational errors  There is no confirmation of frame reception

Access to the Frame Relay Metwork

Q.931 Termination functionsthat may be selected by the user

C layer U layer Q.

U layer C layer

„ C layer: Executes control functions

Q. Physical interface standards (ANSI)

Basic functions of Q.922 Q. Physical interface standards (ANSI)

Basic functions of Q.

user network

y „ Uses RDSI channel D (16 or 64 kbit/s, for control and signalling) „ Provides call control, parameter negotiation, and management and maintenance functions

Access to the Frame Relay network

Q. Termination functions that may be selected by the user

C layer ¡U layer Q.

U layer C layer

„ U layer: interacts with the user

„ Uses channels B (64 kbit/s), D (16 / 64 kbit/s) or H (384,

Q. Physical interface standards (ANSI)

Basic functions of Q.922 Q. Physical interface standards (ANSI)

Basic functions of Q.

user network

„ Uses channels B (64 kbit/s), D (16 / 64 kbit/s) or H (384, 1472, 1536 or 1920 kbit/s) „ Rec. Q.922 – Functions: frame delimitation, alignment and transparency; virtual circuit multiplexing using the address field; frame check, error detection and congestion control.

Options for the Physical Access Layer

„ The FRF ( Frame Relay Forum ) recommends other physical interfaces for the UNI:

„ ANSI T1.403: metallic interface at 1,5 Mbit/s „ UIT-T V.35: duplex interface at 56 or 64 kbit/s „ UIT-T G.703: metallic interface at 2 Mbit/s „ UIT-T X.21: Synchronous data interface between user equipment and public networksequipment and public networks

It generally refers to an access channel of the user- network interface (UNI) or of the network-network

Access Channel

network interface (UNI) or of the network network interface (NNI).

This access channel is the path for a single user data stream.

Channel E

Used in Europe, Asia, Central and South America. It has a bandwidth of 2.048 Mbps.

Types of E1 access lines

There are three types of channels in a E1 line:

™™ Non-channeled E1Non channeled E ™ Channeled E ™ Fractional E

Non-channeled E1

The whole line is considered as a single access

Channeled E1

An access channel is one of the 30 channels. Each access channel is made up by a single time

g channel.

Each access channel is made up by a single time interval E1.

Fractional E1

AnAn accessaccess channelchannel isis aa groupinggrouping ofof NN

E1 time intervals (Nx64 Kbps, where N=1 at 30 time intervals for each fractional E1 access channel) that may be assigned in a consecutive and non-consecutive manner

Physical interfaces

• ITU V.35

• ITU G.703, G.704 (2 Mbps)

V.35 Interface

This interface is a combination of circuits under standards V.10 and V.11.

All data and timing terminals meet specification V.11 (balanced circuits and low voltage).

Control signals have V.10 voltages (non-balanced circuits).

V.35 Connector

Funciones tipo V.10 Funciones tipo V-11

C H M S W AA EE KK

A E K P U Y CC HH MM

D J N T X BB FF LL

BB FF LL RR VV ZZ DDDD JJJJ NNNN

PINES DEL TIPO V.35 PIN NOMBRE FUNCIÓN DTEDCE NORMA PS TxD - ATxD - B Transmisión de datos pin ATransmisión de datos pin B ÆÆ V.35V.35 RT RD - ARD - B Recepción de datos pin ARecepción de datos pin B ÅÅ V.35V.35 Y TxC - A Reloj de Transmisión pin A Å V.35 AAV TxC - BRxD - A (^) Reloj de recepción pin AReloj de Transmisión pin B ÅÅ V.35V.35 XU RxD - BXTC - A (^) Reloj Externo de datos pin AReloj de recepción pin B ÅÆ V.35V.35 WZ XTC - B (^) No asignadoReloj Externo de datos pin B Æ V.35 BBCC (^) No asignadoNo asignado DD No asignado EEFF No asignadoNo asignado HHJJ No asignadoNo asignado KKLL No asignadoNo asignado MMNN No asignadoNo asignado PINES DEL TIPO RS -232 A FG Tierra de chasis (Frame Ground) (^) Æ RS-232 B SG Tierra de señal (Signal Ground) Æ C RTS Request To Send Æ RS-232 DE CTSDSR Clear To SendData Set Ready ÅÅ RS-232RS-232 F DCD Detector de portadora Å RS-232 HJ DTRRI Data Terminal ReadyIndicador de timbrado Æ RS-232 KL Test Test localNo asignado MN No asignadoNo asignado

V. LINE CODES

Spectral density of line codes

1 2

S(t)/Eb NRZ (^) Bipolar

0 4

0.6

0.8

1.2

1.0

p AMI

Bifásico a

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

0.2

0.4

Frecuencia normalizada f/R

HDB3 Code

1 0 0 0 0 0 1 1 0 0 0

- -

+ + +

0 0 0 0 0 0 0 0

+

0 0

- -

+

- -

B 0 0 V B 0 0 V B 0 0 V B 0 0 V

B = normal or reverse polarity

V = violation of the rule

VI. LINK LEVEL