X.25 Overview

• IP• AppleTalk• Novell IPX• Banyan VINES• XNS

• DECnet• ISO-CLNS• Apollo• Compressed TCP• Bridging

SS SS

X.25 Cloud

X.25

VirtualCircuit

X.25

LAN Protocol

LAN Protocol

SSSS

An Introduction to X.25

OSI Reference Model

Application

Presentation

Session

Transport

Network

Data Link

Physical1

2

3

4

5

6

7

X.25 Protocol

•

•

•

•

X.25

LAPB

Physical 1

2

3

X.25 Protocol Stack

Data Network ID Code Network Terminal Number

4 decimal digits Up to 10 or 11 decimal digits

X.25 (X.121) Addressing Format

• Addressing set by service provider

X.25

IP Network IP Network

IP DatagramX.25Header

Data-LinkFrame(LAPB)

X.25 Encapsulation

• Protocol datagrams are reliably carried inside X.25 frames

Switched Virtual Circuits(SVCs)

Permanent Virtual Circuits(PVCs)

X.25 Virtual Circuits

• Numbering for up to 4095 VCs per X.25 interface

X.25 Configuration Example

interface serial 1

encapsulation x25

x25 address 311082194567

ip address 10.60.8.1 255.255.248.0

x25 map ip 10.60.8.2 311082191234 broadcast

Cisco A

interface serial 0

encapsulation x25

x25 address 311082191234

ip address 10.60.8.2 255.255.248.0

x25 map ip 10.60.8.1 311082194567 broadcast

Cisco B

IP Address: 10.60.8.2X.121 Address: 311082191234

S1

X.25

IP Address: 10.60.8.1X.121 Address: 311082194567

Cisco A Cisco B

S0TokenRing

X.25 Local and XOT Switching

x25 route [ # position ] x.121-address [ cud pattern ] interface type-number

Router(config)#

X.25 PAD

Local Switching

Remote Switching

IP Internetwork

X.25 PAD

X.25 PADX.25 PAD

Frame Relay Overview

Frame Relay Overview

• Virtual circuits make connections

• Connection-oriented service

DTE or CPE router

Frame Relay works here.TokenRing

CSU/DSU

DCE or FrameRelay Switch

Frame Relay Terminology

Local AccessLoop=T1

DLCI=400

DLCI=500

LMI500=Active400=Active

Local AccessLoop=64 kbps

Local AccessLoop=64 kbps

Frame Relay Terminology (cont.)

BECN

FECN

I am congested.

CIR=64 kbps

T1

Bc=32 kbps

Selecting a Frame Relay Topology

Star (Hub and Spoke)

Full Mesh

Partial Mesh

Multipoint Subinterfaces Configuration Example

RTR1

RTR3

RTR2

RTR4

s2.1=10.17.0.2/24

s2.2=10.17.0.1/24

s2.1=10.17.0.4/24

s2.1=10.17.0.3/24

Multipoint Subinterfaces Configuration Example

<Output Omitted>!interface Serial2 no ip address encapsulation frame-relay!interface Serial2.2 multipoint ip address 10.17.0.1 255.255.255.0 bandwidth 64 frame-relay map ip 10.17.0.2 120 broadcast frame-relay map ip 10.17.0.3 130 broadcast frame-relay map ip 10.17.0.4 140 broadcast!router rip network 10.0.0.0<Output Omitted>

Point-to-Point Subinterfaces Configuration Example

RTR1

RTR3

s2.1 RTR2

RTR4

s2.2s2.3s2.4

s2.1

s2.1

10.17.0.0/24

10.18.0.0/24

10.20.0.0/24

Point-to-Point Subinterfaces Configuration Example

<Output Omitted>interface Serial2 no ip address encapsulation frame-relay!interface Serial2.2 point-to-point ip address 10.17.0.1 255.255.255.0 bandwidth 64frame-relay interface-dlci 110!interface Serial2.3 point-to-point ip address 10.18.0.1 255.255.255.0 bandwidth 64frame-relay interface-dlci 120!interface Serial2.4 point-to-point ip address 10.20.0.1 255.255.255.0 bandwidth 64 frame-relay interface-dlci 130<output omitted>

Common LAN Technologies

TokenRing

Ethernet

Token Ring

FDDI

LAN Technology Overview

FDDIDual Ring

Ethernet and IEEE 802.3

• Several framing variations exist for this common LAN technology

Ethernet Frame Variations

Ethernet Frame

802.3 Frame

PreamblePreamble DADA SASA TypeType DataData FCSFCS

8 6 6 2 4

PreamblePreamble DADA SASA LengthLength802.2

Headerand Data

802.2Header

and DataFCSFCS

8 6 6 2 4

DSAPDSAP SSAPSSAP CTRLCTRL

AAAA AAAA CTRLCTRL OUIOUI EtherTypeEtherType

Upper Layer DataIP, AppleTalk

Upper Layer DataIP, AppleTalk

DATADATA

Ethernet Frame Variations

802.3 Frame

PreamblePreamble DADA SASA LengthLength 802.2 Headerand Data

802.2 Headerand Data FCSFCS

802.2 Frame

SNAP Frame

High-Speed Ethernet Options

• 100BaseTX

• 1000BaseT/SX/LX/LH/ZX

Token Ring and IEEE 802.5

• IBM’s Token Ring is equivalent to IEEE 802.5

TokenRing

TokenRing

Physical Layer: Token Ring/802.5

• Logically a ring, but physically a star configuration to MAU relays

Shielded or Unshielded Twisted-Pair

MSAU

Logical Topology

The Token Ring/802.5 Interface

• Cisco router’s data link to Token Ring/802.5 uses interface named To plus a number (for example, To0)

To0TokenRing

TokenRing

Token Ring/802.5 Operation

• Token Ring LANs continuously pass a token

AA T = 0

TTTT

Token Ring/802.5 Operation

• Token Ring LANs continuously pass a token or a Token Ring frame

AA T = 1

AA T = 0

TTTT

TTTT DataDataDataData

Token Ring/802.5 Operation

• Token Ring LANs continuously pass a token or a Token Ring frame

AA T = 1

AA T = 0

TTTT

AA T = 0

TTTT

TTTT DataDataDataData

Token Ring/802.5 Media Control

• Fields in a frame determine priority and reservation for sharing media

T

P

M

R

Priority bits

Reservation bits

Monitor bit

Token bit

Access Control Field

PP PP PP TT MM RR RR RR

FDDI

• Devices on FDDI maintain connectivity on dual counterrotating rings

100 Mbps

FDDIDual Ring

When a failuredomain occurs...

FDDI Dual-Ring Reliability

FDDI Dual-Ring Reliability

When a failuredomain occurs...

FDDI Dual-Ring Reliability

When a failuredomain occurs...

...wrap primary and secondaryrings...

...wrap primary and secondaryrings...

...maintainingnetwork integrity

ATM

ATM Basics Review• A compromise for voice,

data, and video • Hardware-based cell relay• Larger frames are

segmented and reassembled at ATM endpoints

• Can span both LAN and WAN

• Scales from a few Mbps to multi-Gbps

• QoS defined/negotiated when initial connection is made

Voice Video Data

ATM cells

48-octet Payload

ATM 53-octet cells areswitched in hardware

ATM Cell Processing

TCP

IP

LLC/SNAPLLC/SNAP

AAL 5

ATM

PHY

Convergence Sublayer

SAR Sublayer

App DataTCP Header

App DataTCP Header

App DataTCP Header

IP HeaderIP Header

IP HeaderIP Header

App DataTCP HeaderIP HeaderIP HeaderLLC

LLC

TCP Packet

IP Datagram

AAL5-PDU

AAL5 SAR-PDU - 48 Bytes

AAL5 SAR-PDU - 48 BytesATM Hdr

5 Bytes

Transmission Convergence (STS3c, STM-1, DS3, 4B/5B, ...)

Physical Media (MMF, SMF, STP, UTP, Coax, …)

48 Bytes

53 Bytes ATM Cell

Virtual Path and Virtual Channel

ATM Physical LinkVirtual Channel Connection (VCC)

Virtual Path(VP)

Contains Multiple VCs

Virtual Channel Connection(VCC)

Contains Multiple VPs

VCLogical Path

between ATM End points

Virtual Channels (VCs)

Virtual Channels (VCs)

e.g., OC-3, E3,OC-12 Virtual Path (VP)

Virtual Path (VP)

Connection Identifier = VPI/VCIVPI/VCI

Well-Known VPI/VCIs

VPI/VCI(Logical)

x/5

x/16

x/18

Default(Physical)

0/5

0/16

0/18

Type

Signaling

ILMI

PNNI

Terminating Connections

ATM Cell Header—UNI Format

VPIVPI

VPIVPI VCI

VCI

VCI PT CLP

HEC

8 7 6 5 4 3 2 1

1

2

3

4

5

BitsBytes

GFCGFC

VPIVPI VCI PT CLP HEC

32 Bits 8 Bits CRC

8 16 3 1 8GFCGFC

4

PTUser data or maintenance flowCongestion experiencedEnd of message (AAL5)

ATM Cell Header—NNI Format

VPIVPI

VPIVPI VCI

VCI

VCI PT CLP

HEC

8 7 6 5 4 3 2 1

1

2

3

4

5

BitsBytes

VPIVPI VCI PT CLP HEC

32 Bits 8 Bits CRC

12 16 3 1 8

•Larger VP field for trunking

•Distinction not very useful for private network

VP Switching/VP Cross-Connect

VCI 1VCI 2

VCI 3VCI 4

VCI 5VCI 6

VCI 3VCI 4

VCI 5VCI 6

VCI 1VCI 2

VPI 1VPI 1

VPI 2VPI 2

VPI 3VPI 3

VPI 4VPI 4

VPI 5VPI 5

VPI 6VPI 6

VP Switch

•Switching based on VPI only

(central office trunk switching)

VP and VC Switching

VCI1

VCI2

VCI3

VCI4

VC Switch

VCI 1

VCI 2

VCI 1

VCI 2

VP Switch

VPI1

VPI3

VPI2

VPI 1

VPI 4

VPI 3

VPI 5

VPI 2 VCI 4

VCI 3

VCI 1

VCI 2

ATM Switch Translation Table

• ATM switches translate VPI/VCI values• VPI/VCI value unique only per interface—

e.g., locally significant and may be reused elsewhere in network

4/55

2/392/39

33

22

11

6/646/642/392/39

4/55

6/646/64

2/892/89

1

2

11

33

4/55

2/39

2/892/89

6/646/64

2

1

33

11

VPI/VCIPort VPI/VCIPort

Input Output

ATM Adaptation Layer

ServiceCategories

Bit Rate ConnectionMode

TimingConcern

ApplicationExamples

• Bandwidth andthroughput guaranteed

• Good for voice and video

AAL1 CBR(Constant)

Connection-Oriented

Yes

• Best effort bandwidth and throughput

• Good for live video,multimedia, LAN-to-LAN

AAL2 VBR

(Variable)

Connection-Oriented

Yes

• Best effort withcongestion feedback

• Reliable delivery of bursty traffic iflatency okay

AAL5 ABRUBR

VBR

(CBR)

Connection-Oriented

No

• No guarantee• For SMDS

AAL3/4 UBR(Un-

specified)

Connection-less

No

ATM Adaptation Layer (AAL)

ATM Adaptation Layer (AAL)

ATM Layer

Physical Layer

AAL5

•CS trailer Length CRC-32

•Cell header Type: empty, not EOM, EOM

•Payload: 48 bytes•Primary AAL for data

ConvergenceSublayer (CS)

SARSublayer

Convergence Sublayer PDU

Payload FrameData Frame

AAL5

ATM Layer

SAR PDU

SAR PDU

SAR PDU

SAR PDUATM Cell0x0

ATM Cell

ATM Cell

ATM Cell

0x0

0x0

0x1

AAL5—Frame and Cell FormatsAAL5 CPCS - PDU Frame = n x 48 bytes

0-65535 bytes

Payload Length

CRC-32Control(CPI and UU)

4 bytes2byte 2 bytes

PAD

CPI Common part indicator, current function: aligning the trailer to 8 bytes, currently unused and set to 0

UU User-to-user indication, currently unused and set to 0PAD 0-47 bytes

AAL5 CPCS PDU Trailer

User Data

AAL5 SAR PDU = 1 Cell Payload

SAR-PDU Payload = 48 bytes

•53 = 5 (cell header) + 48 (payload)

0-47bytes

ATM Signaling,ATM Address Formats

Switched Virtual Channels (SVCs)

• SVC requires signalingATM connection oriented

• ATM Forum UNI 3.x/4.0 signaling specificationBased on ITU-T Q.2931

TokenRing

B-ICI

UNI

NNI

NNI

NNI

Public ATM Network

Private ATM Network

Signaling Concept

•Signaling request

•Connection routed—setup path

•Connection accepted/rejected

•Data flow—along same path

•Connection teardown

Connect to B

OK Connect to B

OK

Connect to B

Connect to B

OK

ATM Router A

ATM Router B

ATM SVC Call Setup

•Call set up in software

•Cell switching in hardware

•Dynamic call establishment (call setup) with appropriate parameters (e.g., QoS: CLR, CTD, CDV)

Calling Party Called Party

Setup Call Proceeding

Call Proceeding

Connect ACK

Connect

Connect ACK

Set Up

Connect

Connect ACK

ATM NetworkES ES

ATM SVC Call Release

Calling Party Called Party

Release Release Complete

Release

Release Complete

ES ES

ATM Network

•Dynamic call teardown (call release) of virtual connection

Q.2931 Call Control

PD Call Ref

Mes Type

Mes Len

Info Elements

•Q.2931 call control message format at UNI

Q.2931

SSCOP

ATM Addressing Formats

DSP

AFIICD

AFI = 47

SELICD ESI

AFIE.164

AFI = 45

SELE.164

DSP

ESI

AFIDCC

AFI = 39

SELDCC

DSP

ESI

AFIDCCDSPE.164ESI

HO-DSPICDIDISel

High-order Part of DSPInternational Code DesignatorInitial domain identifierNSAP Selector

Authority and Format IdentifierData Country CodeDomain Specific PartISDN (telephone) NumberEnd-system Identifier (IEEE)