Oda020004 Fr Principle Issue1_0

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ODA020004 FR Principle

ISSUE 1.0

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The Frame Relay (FR) protocol is a simplified X.25 WAN protocol. On the control plane, it manages virtual circuits (VCs) and bandwidth and prevents congestion. FR can multiplex multiple logical connections over one physical connection to achieve bandwidth multiplexing and dynamic bandwidth allocation. Thus, it facilitates multi-user and multi-rate data transmission and makes full use of network resources.




References

l FR protocol principle

l RFC1490

l Operation manual




Upon completion of this course, you will be able to:

[Master FR concept

[Be familiar with FR application




Chapter 1 network switch technologyChapter 1 network switch technology

Chapter 2 FR principle conceptChapter 2 FR principle concept

Chapter 3 FR applicationChapter 3 FR application




Network switch technology

l Circuit Switched (CS) mode: The CS mode is based on the circuit

switching principle of the Public Switched Telephone Network (PSTN). In

the CS mode, the switch establishes a physical data transmission path

between the calling and called parties to address the user demand for data

transmission. The CS mode features the following:

[ Small delay

[ “Transparent” transmission

[ Large throughput of the information transmission.

[ The CS mode also exposes such disadvantages as fixed bandwidth

and low network resource utilization.

Circuit modeCircuit mode





l Packet Switched mode : As a storing/forwarding switching mode,

the PS mode disassembles the information to be transmitted into

the packets of certain length and then stores/forwards them in the

unit of packet. The PS mode features the following:

[High transmission quality.

[High reliability.

[Packet multi-path communication.

[Disadvantage: Large delay.

Packet Switched mode Packet Switched mode





l Cell Model: The cell model is a cell-based transmission technology

which disassembles a message into cells of fixed length. The cell

consists of the cell header and payload. In the cell model, the

network does not check the user data of the cell. The cell model

features the following:

[ Integrate the advantages of both the PS and CS modes.

[ Adopt the asynchronous time division multiplexing.

Cell Mode Cell Mode





l Switched Multimegabit Data Service (SMDS): The SDMS is a type

of high-speed connectionless cell switching service. The SMDS

transmits messages on the network after disassembling them into

cells of fixed length (53 bytes). It adopts the similar mechanism as

the frame relay mode and implements error check and

retransmission through the end system.

SSMDS modeMDS mode





l Frame relay: The frame relay adopts simplified mode to transmit and switch data units at the layer 2 of the OSI reference model,that is, the data link layer.

l FR supports the functions only on the physical layer and the core part of the link layer of OSI. It leaves traffic control and error check to intelligent terminals to simplify protocols greatly between node machines.

l By adopting the VC technology, FR can make full use of network resources. Therefore, FR features high throughput, low time delay and adaptability to outburst services.

Frame relay Frame relay










physicaldata link

application

network

网络层

transport

session

representation

应用层

physical

Frame relay

l The core part of FR functions corresponds to the two lower layers of OSI:

FR protocol stackFR protocol stack

FR principle concept




IETF encapsulation

FR formatFR format


Flag(7E hexadecimal)

Frame Check Sequence (two octets)

Data

NLPID

Optional Pad (0x00)

Control (UI=0x03)

Q.922 Address*

Flag (7E hexadecimal)




l DTE：Data Terminal Equipment

l DCE：Data Communication Equipment

l UNI：interface between DTE and DCE，user-network interface

l NNI：interface between network and network

LAN LANFR

DCEDCE

DTE

DTE

FR model FR model


DLCI

DLCI

PVC use (DLCI)

Local Management Interface (LMI)




l The frame relay adopts the connection-oriented switching technology, and establishes virtual circuit before communication. two types of the virtual circuits :

[ PVC，Permanent Virtual Circuit：Refers to the fixed virtual circuit provided for users. This type of virtual circuit is manually generated and exists all along unless it is cancelled.

[ SVC，Switched Virtual Circuit：Refers to the virtual circuit automatically allocated through certain protocol. It will be cancelled after the communication.

l the PVC is the most commonly used mode in the frame relay network.


Virtual circuitVirtual circuit




lDLCI（Data Link Connection Identifier）：Used to differentiate virtual circuits ，features ：

[DLCI limitation：The DLCI is only applicable to local interface and the peer interface that connects with it.

[ Local meaning ： the same DLCI on different physical interfaces does not indicate the same virtual connection.

l The user interface of frame relay network supports a maximum of 1024 virtual circuits. The available DLCI range for users is 16–1007, and the rest values are reserved for special purposes.

l The local DLCI is the “Frame relay address” of the peer equipment.


DLCIDLCI




lLMI（Local Management Interface ）：The LMI is used to monitor the status of PVC.

l The system supports three types of local management interface protocols: Q.933 Appendix A of ITU-T, T1.617 Appendix D of ANSI and non-standard compatible protocol of CISCO.

l For the DTE, the status of the PVC is subject to the DCE.

l For the DCE, the status of the PVC is subject to the network.


LMILMI




DLCI 48

Frame Relay switch

l FR address mapping (MAP) correlates the protocol address (IP or IPX address) with the FR address (local DLCI) of peer equipment.

l The Address Mapping table can either be manually configured or dynamically maintained by the Inverse ARP.

172.16.11.2

172.16.11.3

DLCI 48Network Address

172.16.11.3

Token

Ring

MAPMAP





l Inverse ARP discovers network address of destination router automatically，simplify the FR configuration

Switch notify DLCI 48

Switch notify DLCI 66

B notify IP 172.16.11.2 to dlci 66

A notify IP 172.16.11.3 to dlci 48

FR

DCE DCE172.16.11.2

DLCI 48 DLCI 66

172.16.11.3Router B

Router A

Inverse ARPInverse ARP











Full-meshed starPartial-meshed

topologytopology

FR application

l The frame relay network enables connection of networks distributed in different places, and includes such network topologies as the Full-meshed, Partial-meshed and star structures.




l If three DLCIs at serial port S0 of router A are mapped to three routers, the routing update information coming from serial port S0 of router A will not be forwarded through this serial port. 。

S0

Router B

Router C

Router D

Router A

DLCI 16 to C

DLCI 16 to D

DLCI 16 to B

Router B forward update message to router C though S0

horizontal splitting

FR application




l Sub interfaces can solve the problem introduced by horizontal splitting.

l One physical interface can contain multiple logical sub interfaces.

l Routers need to connect with each other through the FR network.

S0.1

Router B

Router C

Router D

Router A

Subnet 2

Subnet 3

Subnet 1S0.2S0.3

SubSub--interfaceinterface

FR application




FR bandwidth managementFR bandwidth management


FR application




lCIR：Committed Information Rate

lBc：committed burst

lBe： committed explicit

lFECN：Forward Explicit Congestion Notification

lBECN：Backward Explicit Congestion Notification

lDE

FR application





lFRTS（Frame-Relay Traffic Shaping) is applied on the outgoing interface of the router in the frame relay network to implement traffic control during data transmission.

lFRTS implements the traffic control through parameter configurations. The major parameters include MINCIR, CIR, BC and BE.

lFRTS inherits the conventional Traffic Shaping (TS) algorithm and implements the traffic shaping through the token bucket algorithm.

FR application

FrameFrame--Relay Traffic Shaping Relay Traffic Shaping




FrameFrame--Relay Traffic ShapingRelay Traffic Shaping

FR application




The FrameThe Frame--Relay Traffic Policing Relay Traffic Policing

FR application




FR congestion managementFR congestion management

FR application




l This slide introduce common switch technology ;FR basic principle; common topology and the application.

SummarySummary

Slide Modify Archiving Notice



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Oda020004 Fr Principle Issue1_0