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Any Questions?. Ch 13- Frame Relay Concepts. Frame Relay Overview Frame Relay Addressing Network Layer Concerns with Frame Relay Controlling Speed and Discards in the Frame Relay Cloud. Do I know this?. Go through the Quiz- 5 minutes.

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Ch 13 frame relay concepts
Ch 13-Frame Relay Concepts

  • Frame Relay Overview

  • Frame Relay Addressing

  • Network Layer Concerns with Frame Relay

  • Controlling Speed and Discards in the Frame Relay Cloud


Do i know this
Do I know this?

Go through the Quiz-

5 minutes


1. Which of the following is a protocol used between the Frame Relay DTE and the

Frame Relay switch?

a. VC

b. CIR

c. LMI

d. Q.921

e. DLCI

f. FRF.5

g. Encapsulation


1. Which of the following is a protocol used between the Frame Relay DTE and the

Frame Relay switch?

a. VC

b. CIR

c. LMI

d. Q.921

e. DLCI

f. FRF.5

g. Encapsulation

Answer: C


2. Which of the following statements about Frame Relay are true?

a. The DTE typically sits at the customer site.

b. Routers send LMI messages to each other to signal the status of a VC.

c. A frame’s source DLCI must remain unchanged, but the frame’s destination DLCI is allowed to change, as the frame traverses the Frame Relay cloud.

d. The Frame Relay encapsulation type on the sending router should match the encapsulation type on the receiving router for the receiving router to be able to understand the frame’s contents.


2. Which of the following statements about Frame Relay are true?

a. The DTE typically sits at the customer site.

b. Routers send LMI messages to each other to signal the status of a VC.

c. A frame’s source DLCI must remain unchanged, but the frame’s destination DLCI is allowed to change, as the frame traverses the Frame Relay cloud.

d. The Frame Relay encapsulation type on the sending router should match the encapsulation type on the receiving router for the receiving router to be able to understand the frame’s contents.

Answer: A &D


3. What does DLCI stand for?

a. Data-link connection identifier

b. Data-link connection indicator

c. Data-link circuit identifier

d. Data-link circuit indicator

Answer: A


4. Router R1 receives a frame from router R2 with DLCI value 222 in it. Which of the following statements about this network is the most accurate?

a. 222 represents Router R1.

b. 222 represents Router R2.

c. 222 is the local DLCI on R1 that represents the VC between R1 and R2.

d. 222 is the local DLCI on R2 that represents the VC between R1 and R2.


4. Router R1 receives a frame from router R2 with DLCI value 222 in it. Which of the following statements about this network is the most accurate?

a. 222 represents Router R1.

b. 222 represents Router R2.

c. 222 is the local DLCI on R1 that represents the VC between R1 and R2.

d. 222 is the local DLCI on R2 that represents the VC between R1 and R2.

Answer: C


5. A Frame Relay planning diagram shows the number 101 beside R1, 102 by R2, 103 by R3, and 104 by R4. No other DLCIs are listed. The lead network engineer tells you that the planning diagram uses global DLCI addressing and that a full mesh of VCs exists. Which of the following are true?

a. Frames sent by R1 to R2, as they cross R2’s access link, have DLCI 102.

b. Frames sent by R1 to R2, as they cross R2’s access link, have DLCI 101.

c. Frames sent by R3 to R2, as they cross R3’s access link, have DLCI 102.

d. Frames sent by R3 to R1, as they cross R3’s access link, have DLCI 102.


5. A Frame Relay planning diagram shows the number 101 beside R1, 102 by R2, 103 by R3, and 104 by R4. No other DLCIs are listed. The lead network engineer tells you that the planning diagram uses global DLCI addressing and that a full mesh of VCs exists. Which of the following are true?

a. Frames sent by R1 to R2, as they cross R2’s access link, have DLCI 102.

b. Frames sent by R1 to R2, as they cross R2’s access link, have DLCI 101.

c. Frames sent by R3 to R2, as they cross R3’s access link, have DLCI 102.

d. Frames sent by R3 to R1, as they cross R3’s access link, have DLCI 102.

Answer: B&C


6. FredsCo has five sites, with routers connected to the same Frame Relay network.

Virtual circuits (VC) have been defined between each pair of routers. What is the

fewest subnets that FredsCo could use on the Frame Relay network?

a. 1

b. 2

c. 3

d. 4

e. 5

f. 10


6. FredsCo has five sites, with routers connected to the same Frame Relay network.

Virtual circuits (VC) have been defined between each pair of routers. What is the

fewest subnets that FredsCo could use on the Frame Relay network?

a. 1

b. 2

c. 3

d. 4

e. 5

f. 10

Answer: A


7. BarneyCo has five sites, with routers connected to the same Frame Relay network. VCs have been defined between each pair of routers. Barney, the company president, will fire anyone who configures Frame Relay without using point-to-point subinterfaces. What is the fewest subnets that BarneyCo could use on the Frame Relay network?

a. 1

b. 4

c. 8

d. 10

e. 12

f. 15


7. BarneyCo has five sites, with routers connected to the same Frame Relay network. VCs have been defined between each pair of routers. Barney, the company president, will fire anyone who configures Frame Relay without using point-to-point subinterfaces. What is the fewest subnets that BarneyCo could use on the Frame Relay network?

a. 1

b. 4

c. 8

d. 10

e. 12

f. 15

Answer: D


8. R1 sends a Frame Relay frame over a VC to router R2. About the same time, a Frame Relay switch notices that too many packets are trying to exit the Frame Relay network over the access link connected to R2. Which of the following is the most likely result that could be caused by this scenario?

a. R1 eventually receives a frame with BECN set.

b. R1 eventually receives a frame with FECN set.

c. R1 eventually receives a frame with DE set.

d. None of the other answers is correct.


8. R1 sends a Frame Relay frame over a VC to router R2. About the same time, a Frame Relay switch notices that too many packets are trying to exit the Frame Relay network over the access link connected to R2. Which of the following is the most likely result that could be caused by this scenario?

a. R1 eventually receives a frame with BECN set.

b. R1 eventually receives a frame with FECN set.

c. R1 eventually receives a frame with DE set.

d. None of the other answers is correct.

Answer: A



Overview
Overview

  • PPP-usually enterprise will get a leased line from telco

    • Dedicated circuit

    • Each connection requires a physical interface

  • Frame-Relay lets you leverage the telco “cloud”

    • Can support multiple connections on same physical interface

Pg 461


Frame overview
Frame Overview

  • Multiaccess network

    • Multiple machines can connect

  • Nonbroadcast

    • Will not send data link brodcasts

Pg 461



Components
Components

  • Leased line from Router to Frame Switch

    • Router is DTE

    • Switch is DCE

  • Router and Switch communicate with Local Management Interface

    • LMI

  • Connection from R1 to R2 is by Virtual Circuit

    • You share connection, but it seems like a leased circuit to your router

Pg 462


Key terms
Key Terms

Pg 463



Standards
Standards

  • Cisco

  • IETF

  • ITU

  • ANSI

Pg 464


Virtual circuits
Virtual Circuits

  • Defines a logical path between tow Frame Relay DTEs

    • VC acts like a point-to-point connection

  • No true dedicated circuit

    • Share bandwidth with other frames

  • Bandwidth is assured with Committed Information Rate

    • CIR is assigned per VC

Pg 465


Frame vcs
Frame VCs

  • Costs less since a single access link can support multiple VCs

    • 100 sites would need 4950 physical links

    • 100 sites need 4950 VCs but only 100 physical links

  • Permanent virtual Circuits (PVC)

    • Predefined by telco

  • Switched Virtual Circuit

    • Dynamically created on the fly

Pg 465


Full vs partial mesh
Full Vs. Partial Mesh

  • Full Mesh

    • Each location has a VC to each other location

  • Partial Mesh

    • Combination of multiple links and sinlge, point to point links

    • Hub and spoke

Pg 465


Partial mesh
Partial Mesh

  • R1 has multiple connections

  • R2 only connects to R1

    • No fully meshed

Pg 466



Virtual circuits1
Virtual Circuits

  • Since a single access link can support multiple VCs, the system must be able to identify them

    • Data Link Connection Identifier (DLCI)

      • Identifies the link (VC) to the destination

Pg 466


Lmi and encapsulation
LMI and Encapsulation

  • LMI is management between Router and Frame-Switch

    • Not and end to end link

    • Like a keepalive

  • Three choices

    • Cisco

    • ITU

    • ANSI

Pg 467


LMI

  • They perform a keepalive function between the DTE and DCE. If the access link has a problem, the absence of keepalive messages implies that the link is down.

  • They signal whether a PVC is active or inactive. Even though each PVC is predefined, its status can change. An access link might be up, but one or more VCs could be down. The router needs to know which VCs are up and which are down. It learns that information from the switch using LMI status messages.

Pg 467


LMI

Pg 468


Encapsulation
Encapsulation

  • Describes the Header style

    • Like PPP or Ethernet Frame

  • Original Header didn’t have protocol Type field

  • Cisco and IETF both have solutions

Pg 469



Frame relay addressing
Frame Relay Addressing

  • DLCI

    • There is only one DLCI field

      • No source and destination

  • Local Addressing

    • DLCI’s are locally significant

    • A DLCI can exist in mulitple places in the telco network, only has to be unique on access link (physical interface)

  • Remember-DLCI defines link to destination

Pg 469


Dlci example
DLCI Example

  • B and C can both use 40

    • 40 refers to a VC to Router A

Pg 470


Frame relay global addressing
Frame Relay Global Addressing

  • Set up by telco/Provider

  • Gives a DLCI to each location

    • Thus the dlci identifies the destination

  • Program routers with the DLCI of the destination

    • Either mapping or inverse arp(see page 492-497)

Pg 470



Dlci and frame switches
DLCI and Frame Switches

  • When a router sends the frame, the DLCI is the destination

    • En route, the Telco Frame Switches change this to the source

  • When a router receives a frame, the DLCI is the source

    • Can be used as reply-to address

Pg 472



Dlci global addressing
DLCI Global Addressing

  • If two VCs terminate at the same DTE, and a single DLCI is shown, it probably represents the global DLCI convention

  • If one DLCI is shown per VC, local DLCI addressing is depicted.

Pg 473



Network layer issues
Network Layer issues

  • One subnet containing all Frame Relay DTEs

    • Usually Full Mesh

  • One subnet per VC

    • Hub and Spoke

  • A hybrid of the first two options

    • Partial Mesh

Pg 474





Multipoint subinterface
Multipoint Subinterface

  • Terminate more than one VC

    • single subnet for point to pont

    • Shared subnet for meshed sections

Pg 477


Broadcasts
Broadcasts

  • Broadcasts from Router updates, etc.

  • Can send broadcasts to all VCs

    • Will cause lots of traffic with multiple VCs

  • Create different output queue for broadcasts

    • Try to limit spike in data

Pg 478



Controlling speed
Controlling Speed

  • Frame Networks are oversubscribed

  • Commited Information Rate (CIR) defines your guaranteed rate

    • Often you can burst above this rate

  • FECN, BECN and DE help tell network about congestions

Pg 479


Fecn and becn
FECN and BECN

  • Forward Explicit Congestion Notification

    • Set as frame travels through network

  • Backward Explicit Congestion Notification

    • Message back to sender to say it was congested

Pg 480


Discard eligible de
Discard Eligible (DE)

  • If you are transmitting over your CIR

    • Network will mark frames as DE

  • If congestion is noticed

    • Those frames may be discarded

      • Other systems will work to retransmit-like TCP

Pg 480



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