Multiple Standards Develop Frame relay is a protocol defined by both ANSI and ITU-T Frame relay derives from the Link Access Protocol-D

(LAP-D) signaling portion of the new ISDN signaling standard

Frame relay is also a transport technique offered by many network providers

Frame relay is a connection-oriented frame mode bearer service

Both ANSI and ITU-T ISDN standards use the LAP-D data link layer and the ANSI standard has provisions to supplement frame relay using the LMI extensions

Frame relay is sometimes confused with the term “fast packet”

Fast packet is a generic term used for many high-speed packet technologies, such as frame relay and cell relay, and has been used to represent multiplexer upgrades to faster X.25 packet switching

Frame relay and frame switching are synonymous only with the ITU-T switching implementation of frame relay called type II

The LMI specifications span both standards organizations

ITU-T/CCITT Standards ITU-T standards are given numbers with letter prefixes The “I” recommendations tend to provide the framework

for services, protocols, and operations The “Q” recommendations tend to define the detailed

operations of subjects such as signaling, transport, and implementations

Frame relay shares much o fits architecture and protocol structures with the ITU-T ISDN standards

Frame relay is referred to as an end-user service under the ISDN bearer services standards. This defines frame relay as an “interface” between the user and the network service

ITU-T/CCITT Standards (Continue…) The addressing of frame relay is defined through Data

Link Connection Identifiers (DLCIs), enabling multiple logical channels (PVCs) per a single physical interface

ITU-T also calls for three functions to be implemented in the upper half of the layer two: link utilization, flow control, and error recovery

These functions are often performed by the user DTE equipment or other higher-level protocol implementations such as TCP/IP

ITU-T/CCITT Standards (Continue…) ISDN standards are at the root of frame relay protocol

operation There are two main types of frame relay defined:\

– Type I : private or virtual private frame relay

– Type II : public frame relay

ANSI Standards Many of the ANSI standards are designed to complement

the ITU-T ISDN Recommendations While many frame relay implementations comply with

ANSI standards, it is the LMI specifications with extensions that made early implementations of frame relay possible

These interface specifications are enhanced by the LMI extensions as defined by the “Gang of Four” (StrataCom, Digital Equipment Corporation, Cisco Systems, and Northern Telecom)

ANSI Standards (Continue…) ANSI T1.617, T1.618, and T1.606 provide customer

interface standards for access speeds of DS0, Nx56 kbps, Nx64 kbps, and DS1, primarily defining the user-to-network interface (UNI) and the network-to-network interface (NNI)

Annex D and NNI, along with LMI, are the most common implementations

Both permanent virtual circuits (PVCs) and Switched Virtual Circuits (SVCs) provide call connection service via the ANSI standards

LMI Extension and Proprietary Solutions These extensions have features which, even though they are

of a proprietary implementation, complement and supplement both the ANSI and ITU-T standards, as well as represent the views of private and public network suppliers

This common platform of the Gang of Four for interoperability has become the de facto standard in the industry for the interconnection of CPE equipment, via a frame relay access interface, to frame relay switches

These proprietary LMI features handle the information exchange between the network and user-attached devices, providing standards for such things as support of automatic reconfiguring of devices and fault detection

LMI Extension and Proprietary Solutions (Continue…)

LMI features also enhance service by providing the user with status and configuration information on the PVCs active at that time.

OSRM level 1 connectivity is also addressed, along with customer network-management functions

Refer to Figure 11.1 (p. 420) There are two types of LMI extensions:

– standard: is used by almost every major CPE vendor offering a frame relay interface for its equipment

– optional: is not used and some options remain under development

Standard LMI Extensions The standard LMI extensions perform the following

functions:– Notify user of PVC status (active and present DLCI)

– Notify user of add/delete/change PVC

– Notify user of physical link “keep-alive” signal and logical link status

Optional LMI Extensions Multicast capabilities: allow multiple LAN interconnected

user devices to function with simpler address resolution Flow control: enhancements to congestion indication and

user notification Global addressing convention: allows the network to

provision DLCIs on a port-by-port basis Asynchronous status updates: allows he network to notify

the user device of a change in logical channel DLCI status

FR Parameters and SizingCalculating the Committed Information rate (CIR) and

Excess Information Rate (EIR) The CIR is a quality-of-service measurement that provides

a “statistically guaranteed” rate of throughput on the transmit or receive path of a PVC during any one period of time

The CIR is computed as the number of bits in a committed

Burst size, Bc, that can arrive during an averaging interval T such that CIR = Bc/T

Calculating the Committed Information rate (CIR) and Excess Information Rate (EIR) (Continue…)

If the number of bits that arrive during the interval T exceeds Bc, but is less than an excess threshold, Bc + Be, then the subsequent frames are marked as Discard Eligible (DE)

Setting T to a value on the order of the ground trip delay is a good guideline to achieve good TCP/IP throughput over frame delay

In public FR service it is the responsibility of the provider to set the value of T, and the value of 1 is often used to match the private line measure of bps

CIR Sizing CIR rates in public frame relay networks are chosen for

each PVC based on perceived traffic minimums and peak maximum

This measurement is made for both traffic transmitted and received by the FR access port

Two types of architecture– open-loop: frames that exceed the CIR are typically marked DE

– closed-loop: the switch will not allow the CIR to be exceeded unless there is end-to-end bandwidth available across the network to transmit the frame

CIR Sizing (Continue…) Some providers (e.x. MCI) offer the subscriber the capability

to use additional bandwidth over and above the CIR, marking all traffic above the CIR as DE ( statistical approach)

CIR rates are typically chosen based on the type of traffic and protocol being transmitted and the time required to get information from origin to destination

Refer to Figure 11.2 (p. 424) Some public frame relay network providers offer the option

of utilization reports (tell the user by PVC, for each direction, what the peak, average, and maximum average traffic load is at any time

FR Access Port Sizing FR access ports come in many speeds, from 56 kbps,

through 56/64 kbps increments, up to and including DS1 (1.544 Mbps) and DS3 (45 Mbps)

All PVC CIR rates both into and out of the FR access port should be added separately

The combined CIR speed in either direction should not exceed the port speed in either direction, unless you plan to oversubscribe the port

Refer to Figure 11.3 (p. 426)

Unidirectional, Asymmetrical, or Simplex PVCs Even though a PVC offers a full-duplex connection, CIR

rates are assigned unidirectionally Each PVC is assigned two CIRs - one for each direction-

transmit and receive There is the capability in some frame relay networks to

assign different CIRs to each direction of the PVC. These are called unidirectional, asymmetrical, or simplex CIRs

These CIRs dictate a small size request in one direction that triggers a large file transfer in the opposite direction as in an inquiry/response application

Refer to Figure 11.4 (p. 427)

Bursting over CIR In most cases, the transmitted traffic throughput will

exceed the assigned CIR. This is referred to as “bursting” Refer to Figure 11.5 (p. 428) Bursting over CIR may not have a good effect on

applications during congestion conditions, but most of the time multiple PVCs sharing the same UNI access circuit will not transmit data at the exact same moment

This leads to good statistical multiplexing on access ports, and in these instances FR can provide significant response time savings

Discard Eligible (DE) There are many ways to limit the amount of bandwidth

provided to a user at any time One method of delimiting the bandwidth to select users on

a priority basis is through the intellifent and selective use of the Discard Eligibility (DE) bit

User frames with DE set to 1 are discarded first. Higher-priority users would have DE set to 0

The Discard Eligible (DE) bit may be set by either the customer or by the network

Other methods employ proprietary implementations

Oversubscription There are two different ways in the setting of the CIR

– regular booking: the sum of the CIRs is no more than the access rate

– overbooking or oversubscription: the sum of CIRs exceeds the access line rate (statistical approach)

Oversubscription is the capability to oversubscribe or overbook the CIRs coming into a single physical access port

High oversubscription rates can yield greater throughput and savings in equipment and local loop costs

Oversubscription is typically chosen when users intimately understand their PVC traffic patterns and utilization

PVC Reroute Capability IF a physical path on which a PVC rides is broken, the FR

switches at both ends of the physical path can route the PVC via an alternate switch to the end switch destination

This capability does not exist for the UNI, only within the FR-switched fabric

Congestion in Frame Relay Networks Defined Network congestion occurs when the traffic attempting to

be passed across a specific portion of the network fabric is greater than the available bandwidth

When the network reaches a congestion point it will begin to discard frames using DE bit priorities

The user or network access devices must have the intelligence of higher-level protocols to provide end-to-end error detection and correction and retransmission of missing data

Congestion in Frame Relay Networks Defined (Continue…)

There are two types of congestion-control methods– Implicit: congestion notification implies the use of a layer 4

transport protocol, such as TCP or SNA, in either the network device or the user premises equipment

– Explicit: congestion notification comes in three flavors

1 FECN: bit is set by the FR network nodes when they become congested and this informs the receiver flow-control protocols of the congestion situation

2 BECN: bit is set in FR frames headed in the downstream direction to inform a transmitter flow-control protocols of the congestion situation

3 CLLM: can contain a list of DLCIs that correspond to the congested frame relay bearer connections- all users affected are then notified of congestion. Multiple CLLM messages can be transmitted in a network with many DLCIs that require congestion notification

Public Network FR Services

Service Aspects of Frame Relay Frame relay is offered as a frame-based public data service

that allows access line speeds up to 1.544 Mbps from a Customer Premises Equipment (CPE) router, bridge, or Frame Relay Access Device (FRAD) into the public frame relay network

Service Aspects of Frame Relay (Continue…) FR network trunks can be of speeds from DS0 (56 kbps)

up to and including DS3 (45 Mbps). Dial-up access to frame relay is also available

Public frame relay services offer different interpretations of the Committed Information Rate (CIR) and Discard Eligible (DE functions depending on the network switching architecture used).

Customer network management, performance reporting, configuration and information management, and various fixed and usage-based billing services are offered by service providers.

Public versus Private Public frame relay service provides a consolidation of

private line meshing, instead performing the meshing through PVCs within the FR network and requiring each user to have a single access circuit to the public network

Refer to Figure 11.9 (p. 438) Private frame relay network designs are based on three types

of technologies– DS1/DS3 multiplexers employing fast-packet frame relay technology

and interface cards

– Bridges or routers employing dedicated links for frame relay interfaces into a network

– Fast-packet switches employing dedicated DS1/DS3

Public Frame Relay Service Offerings There are three main groups providing public frame relay

services: what were traditionally the ICCs, the RBOCs, and LECs, and Internet access providers

The major frame relay service providers in the United States include Ameritech, AT&T, Bell Atlantic, BellSouth, Cable & Wireless, CompuServe, GTE, MCI Communications, MFS, NYNEX, Pacific Bell, and Sprint

Most of today’s IXC frame relay public service offerings include StrataCom Integrated Packet Exchange IPX-32 with BPX, the Bay Network’s BCN and BNX frame relay switches, the Alcatel TPX1100, the Cascade STX-9000s, or the AT&T BNS-2000

Switched Virtual Circuits (SVCs) Both ANSI and ITU-T have published standards for

Switched Virtual Circuit (SVC) frame relay operation SVC service offers an excellent opportunity to users

requiring – Short connect, low volume, and transfer times with infrequent

connectivity and traffic patterns

– Connectivity provisioned on-the-fly

– Backup for PVC failure over dial access (POTS line or ISDN) to FR switch

Switched Virtual Circuits (SVCs) (Continue…)

SVCs allow a sending DTE to transmit the address of the receiving DTE along with the data at call setup time

When the first switch receives this address and data, it establishes the connection-oriented, virtual path to the receiver

This method eliminates the need for preconfigured PVCs

Network-to-Network Interface (NNI) The FR Network-to-Network (NNI) is defined by the

standards as a method for two frame relay networks to interconnect, pass frame relay traffic, and manage the logical connections (PVCs) which originate on one frame relay network and terminate on another

Refer to Figure 11.10 (p. 441) NNI circuits are also used to connect dissimilar switch

types, as is usually the case between different FR services, providing multivendor interoperability

Frame Relay Service Provider Interconnectivity Issues

Frame relay interconnectivity between service providers is just now beginning to proliferate

There is a published Frame Relay Forum (FRF) Implementers Agreement for the Network-to-Network (NNI) interface that almost everyone follows

Public Frame Relay Network Architectures

Open-Loop Architecture Open-loop algorithm systems operate on the concept of

congestion control after congestion begins to occur In an open-loop architecture, each user (PVC) is allocated

a committed burst size or CIR Users can transmit all their traffic and not mark any frames

discard eligible (DE) if the committed burst (CIR) is not exceeded

It is up to the applications to use some method to back-off-and-retransmit while the network recovers from congestion

Open-Loop Architecture (Continue…) Refer to Figure 11.12 (p. 446) Pure noncell frame switches typically use open-loop congestion

algorithms Frame relay switches that do not use cell switching will typically read

the entire frame into buffers before transmitting it to the user or next switch

Applications that react by retransmitting lost frames will cause congestion to intensify even further

Window-sizing flow-control protocols such as TCP can be used to scale down the volume of retransmissions and spread the load over a greater time period

Closed-Loop Architecture A closed-loop architecture is typically found in switches that

convert frames to fixed-size cells on the backbone These switches immediately slice frames into cells and transmit

the data, thus incurring less serialization delay The closed-loop architecture creates a closed environment,

where every switch within the FR network fabric knows the congestion condition from origin to destination

The FR network prevents the user from experiencing lost data due to congestion by slowly throttling back the available transport bandwidth at the user entry point to the FR network (UNI) to the predefined CIE rate

Refer to Figure 11.13 (p. 448)

FR over a Cell-Relay Backbone When frames are segmented into cells and transmitted as

soon as there is enough data to fill up a cell, the end-to-end delay can be decreased.

The frame relay switches do not have to wait until entire frame is read into buffers before segmenting into cells and transmitting

Serialization delay is decreased and end-to-end jitter is also reduced

Access Design Issues

Network Access Devices A variety of hardware devices exist on the market that

make frame relay network access possible (bridges, routers, gateways, FRADs, multiplexers, voice switches, etc.)

Much of the protocol conversion, processing, and switching is done through software. This minizes the hardware investment required to upgrade FR

When purchasing frame relay access or switching hardware, ensure that the equipment is compatible with the standards mentioned

Network Access Devices (Continue…) Primary difference between fast-packet and frame relay

switching is that fast-packet multiplexers still have dedicated paths for the data, while frame relay routers are based upon the DLCI in the address field

A true frame relay device has the flexibility of “dynamically allocating” all available bandwidth to whatever application needs it at a given time

Frame Relay Access Device (FRAD) The FRAD performs the framing function, placing the user

protocol into a FR frame Refer to Figure 11.14 (p. 451) The FRAD provides the connectivity to a private or public

switched FR network Access speeds are via DS0, fractional T1 (FT1), or full T1. A FRAD can also provide an interface for LAN protocols such

as Token Ring or Ethernet FRADs contain the powerful capability to carry SNA and LAN

traffic over a single interface or network access circuit, and some even provide “spoofing” or some level of PU4/PU5 emulation

Frame Relay Access Device (FRAD) (Continue…)

FRADs can perform a level of congestion control outside the frame relay network through SDLC congestion-control techniques

Most FRADs support frame relay protocol with transparent of X.25 and SDLC protocols over frame relay PVCs and SVCs

Some FRADs also support the ISDN PRI and SMDS SNI interfaces

Refer to Figure 11.15 (p. 452)

A device that can be used to assist transmission of video over frame relay is the video coder/decoder (codec).

A codec can transmit pixel updates for only that portion of the video that changes

Some vendors offer the capability of placing low-quality voice over FR, such as Motorola, Hypercom, and Micom. This feature is especially attractive with international communications

Dial Access and Dial Backup Users that are typically located at remote sites that do not

need continuous connectivity and cannot justify the expense of a dedicated line, can use dial up access

Dial access provides the capability to dial into a dedicated network device, such as the FR switch and terminal server

Refer to Figure 11.16 (p. 454) Dial access can also provide dial backup should a primary,

dedicated link fail or something else goes wrong. Refer to Figure 11.17 (p. 454) Dial backup can be initiated outside the FR Refer to Figure 11.17 (p. 455)

Cisco

Configuring Novell IPX

Objectives Identify the network and host in an IPX

address Configure IPX on a Cisco router and

configure interfaces Configure multiple encapsulations on an

interface by using secondary interfaces and subinterfaces

Monitor and verify IPX operation on the router

Introduction to Novell IPX

Novell IPX Protocol Stack and the OSI Model– IPX– SPX– RIP– SAP– NLSP– NCP

IPX Protocol Stack and the OSI Model

Client-Server Communication

NetWare servers provide the following services to clients:– File– Print– Message– Application– Database

Remote IPX Clients on a Serverless Network

Server-Server Communication

Service Advertising Protocol (SAP)

Routing Information Protocol (RIP)

IPX Addressing

Encapsulation– Ethernet

– Token Ring

– FDDI

Multiple Frame Types on a Single Ethernet Segment

Enabling IPX on Cisco Routers

Enabling IPX RoutingRouterA#config t

RouterA(config)#ipx routing

Enabling IPX on Individual Interfaces2501A#config t

2501A(config)#ipx routing

2501A(config)#int e0

2501A(config-if)#ipx network 10

Novell IPX Frame Types

Configuring Out Internetwork with IPX

Configuring IPX 2621A Router

2621A(config)#ipx routing2621A(config)#int f0/02621A(config-if)#ipx network 10

2501A Router2501A(config)#ipx routing2501A(config)#int e02501A(config-if)#ipx network 102501A(config-if)#int s02501A(config-if)ipx network 20

Configuring IPX (cont.)

2501B Router2501B(config)#ipx routing

2501B(config)#int e0

2501B(config-if)#ipx network 30

2501B(config-if)#int s0

2501B(config-if)#ipx network 20

2501B(config-if)#int s1

2501B(config-if)#ipx network 40

Configuring IPX (cont.)

2501C Router2501C(config)#ipx routing

2501C(config)#int e0

2501C(config-if)#ipx network 50

2501C(config-if)#int s0

2501C(config-if)#ipx network 40

Verifying the IPX Routing Tables

_______#sh ipx route

Adding Secondary Addresses

Configuring Secondary Addresses2501A#config t

Enter configuration commands, one per line. End with

CNTL/Z

2501A(config)#int e0

2501A(config-if)#ipx network 10a encap sap sec

Configuring Subinterfaces2621A(config)#int e0.10

2621A(config-subif)#ipx network 10a encap sap

2621A(config-subif)#^Z

2621A#

Configuring Our Internetwork with Multiple Ethernet Frame Types

2621A Router2621A(config)#int f0/0

2621(config-if)#ipx network 10a encap ?

arpa Novell Ethernet_II

hdlc HDLC on serial links

novell-ether Novell Ethernet_802.3

novell-fddi Novell FDDI RAW

sap IEEE 802.2 on Ethernet, FDDI, Token Ring

snap IEEE 802.2 SNAP on Ethernet, Token Ring, and FDDI

RouterA(config-if)#ipx network 10a encap sap sec

Configuring Our Internetwork (cont.)

2621A Router (cont.)2621A(config)#int f0/0.?

<0-4294967295> Ethernet interface number

2621(config)#int f0/0.10

RouterA(config-subif)#ipx network 10a encap sap sec

2621A(config-subif)#ipx network 10b encap arpa

2621A(config-subif)#int f0/0.100

2621A(config-subif)#ipx network 10c encap snap

Configuring Our Internetwork (cont.)

2501A Router2501A(config)#int e0

2501A(config-if)#ipx network 10a encap sap sec

2501A(config-if)#int e0.10

2501A(config-subif)#ipx network 10b encap arpa

2501A(config-subif)#int e0.100

2501A(config-subif)#ipx network 10c encap snap

Configuring Our Internetwork (cont.)

2501B Router2501B(config)#int e0

2501B(config-if)#ipx network 30a encap sap sec

2501B(config-if)#int e0.30

2501B(config-subif)#ipx network 30b encap arpa

2501B(config-subif)#int e0.300

2501B(config-subif)#ipx network 30c encap snap

Configuring Our Internetwork (cont.)

2501C Router2501C(config)#int e0

2501C(config-if)#ipx network 50a encap sap sec

2501C(config-if)#int e0.50

2501C(config-subif)#ipx network 50b encap arpa

2501C(config-subif)#int e0.500

2501C(config-subif)#ipx network 50c encap snap

Monitoring IPX on Cisco Routers

show ipx servers show ipx route show ipx traffic show ipx interface show protocol debug ipx IPX ping

Summary Identified the network and host in an IPX

address Configured IPX on a Cisco router and

configured interfaces Configured multiple encapsulations on an

interface by using secondary interfaces and subinterfaces

Monitored and verified IPX operation on the router