CPEG 514

CPEG 514

Lecture 11

Asynchronous Transfer

Mode (ATM)

CPEG 514

Outline

ATM Introduction

Virtual Circuit Setup – PVC vs. SVC

Quality of Service and Congestion Control

IP over ATM

ATM and Frame Relay interworking

CPEG 514

ATM Network (integrated voice, video, and data services)

Private Carrier to carrier Is not really common Integrated via IP

CPEG 514

ATM Standards

ITU-T, ATM Forum, IETF User-to-Network Interface (UNI) 2.0 UNI 3.0, UNI 3.1, UNI 4.0 Network-to-Network Interface (NNI) PNNI

• Private NNI • Public-Network Node Interface

RFC 2684 (Multiprotocol encapsulation over ATM)

LAN Emulation (LANE) Multiprotocol over ATM (MPoA)

CPEG 514

Synchronous vs. Asynchronous ATM- cell switching technology

(asynchronous) • NO clock synch between xmt/rcv

TDM – circuit switching technology (synchronous) • clock synch between xmt/rcv

ATM is more efficient than TDM. (why?)

• TDM: dedicated time slots.

• ATM: time slots are available on demand with

information identifying the destination address of the transmission contained in the header of each ATM cell.

CPEG 514

ATM Network Components

ATM Network

ATM?

If i/f is not ATM, the switch would have to do the interworking function

CPEG 514

ATM PCI NIC

(ATM to the desktop)

http://www.techstore.com/Item.aspx?sku=227610TD&sgd=330d316d317d314d315

Price: $605 (cf. how much is Gigabit-E NIC?)

ATM Network

ATM OC-3c OC-3 155Mbps

Q: is there still a market for ATM to the desktop? why?

Ethernet is cheaper even at the Gbps, 1Gb Ethernet = $30, 100 BaseT = $7-10

CPEG 514

ATM UNI, PNNI, and NNI

NNI? PNNI

Is there a public ATM? Is there a public Frame Relay?

Private NNI (PNNI): connecting two private networks through a public one.

or Inside the same carrier’s network

CPEG 514

ATM Cell Format

CPEG 514

ATM Cell Format Generic Flow Control (GFC) – typically not used.

Virtual Path Identifier (VPI) – 8 (UNI) or 12 (NNI) bits Virtual Channel Identifier (VCI) – 16 bits

Payload Type (PT)— 3 bits

• first bit: user data (0) or control data (1)

• second bit: Congestion Indicator 0 = no congestion, 1 = congestion), Set to 1 if pkt encountered congestion

• third bit: whether the cell is the last cell (1) in a series of AAL5 frame

Cell Loss Priority (CLP)—Indicates whether the cell should be discarded (1) if it encounters extreme congestion as it moves through the network.

• Similar to - DE (Discard Eligibility in Frame Relay)

Header Error Control (HEC)—checksum on the first 4 bytes of the header.

CPEG 514

ATM PVC and SVC PVC (permanent virtual circuit ) allows direct connectivity between

sites, and is similar to a leased line.

• +++ guarantees availability of a connection

• +++ does not require call setup procedures between switches.

• --- requires manual setup between the source and the destination.

• --- no network resiliency/Flexibility is available with PVC.

SVC (Switched virtual circuits) is created and released

dynamically and remains in use only as long as data is being transferred. In this sense, it is similar to a telephone call. Dynamic call control requires a signaling protocol between the ATM endpoint and the ATM switch.

• +++ connection flexibility

• +++ call setup that can be handled automatically by a networking device.

• --- the extra time and overhead required to set up the connection.

• --- network management and trouble shooting due to dynamic nature of SVC

CPEG 514

ATM Virtual Connections

ATM switching is based on VPI/VCI

However, VPI+VPI is not called ATM address.

VPI/VCI has local significance only at the port level of the ATM switch.

CPEG 514

ATM Physical Layer ATM over T1

ATM over multiple T1 - Inverse Multiplexing over ATM (IMA)

•Up 8 T1s as one link using IMA

ATM over DS3, OC-3, OC-12, OC-48, and OC-192

http://www.nwfusion.com/edge/news/2002/1002marconi.html

Note: Marconi bought Fore Switch in 2000.

Q; What is the max speed for Frame Relay? Up to 30Mbps

CPEG 514

ATM Switching 10

20

video

data

10

30

audio

data

11

21

12

30

P1

P2

P3

P5

P4

IN/port VPI/VCI OUT/port VPI/VCI

P1 0/10 P3 0/11

P1 0/20 P4 0/21

P2 0/10 P4 0/12

P2 0/30 P5 0/30

For PVC, table done Manually SVC, table is done dynamically/on-demand

CPEG 514

ATM Reference Model

AAL

CPEG 514

ATM Protocol Layers

ATM

Applications

ATM Adaptive

Layer (AAL)

ATM

Layer

Physical

Layer

ATM

Layer

Physical

Layer

ATM

Applications

ATM Adaptive

Layer (AAL)

ATM

Layer

Physical

Layer

ATM End Station ATM Switch ATM End Station

CPEG 514

ATM Adaptation Layer Function: Add control information and break Protocol

Data Unit (PDU) into cells

Segmentation and Reassembly (SAR)

AAL1: • Designed for voice application

• Constant Bit Rate (CBR)

• Circuit Emulation Service (CES) (emulates TDM circuit)

AAL2 (Not covered in this class) • Variable Bit Rate (VBR)

• VBR-rt (voice)

• VBR-nrt (data)

AAL5:

• Designed for data application

• Unspecified Bit Rate (UBR)

Physical

ATM

AAL

CPEG 514

AAL1

SN: Sequence Number • 1 bit Convergence Sublayer Indicator (Clock recovery) + • 3 bit Sequence Count (for entire PDU from convergence sublayer)

SNP: Sequence Number Protection:

• 3 bit CRC for the SN + • Last bit, parity check for the previous 7 bits (SN and CRC)

Q: How much overhead in an AAL1 cell?

Payload = 47

SAR Hdr

Convergence Sublayer Sends 47 bytes to SAR Which adds 1 byte of SAR hdr

CPEG 514

AAL5

CPCS-PDU Payload

Padding (0-47)

CPCS-UU (1)

CPI (1)

Length (2)

CRC (4)

up to 216 -1

why do we need padding?

CPCS: Common Part Convergence Sublayer PDU: Protocol Data Unit UU: User-to-user interface information CPI: Common Part Indicator

48 bytes (0..47) Cell payload To make the Full PDU Divisible by 48 Bytes And divide it Evenly into 48 byte segments

Carries upper other Protocols inside CPCS payload (i.e. tcp/ip, ethernet

8 byte trailer

CPCS Payload Not including PAD

Trailer alignment to 32 bit

CPEG 514

ATM Segmentation and Reassembly (SAR)

AAL5 Frame

Cell1 Cell2 H H Celln H H:5-bytes

CPEG 514

ATM NSAP Address

This is required for NNI, but it is rarely used.

Note NSAP has global significance while VPI/VCI is an

addressing scheme that has local significance only. ATM NNI: same issue with Frame Relay.

NSAP: Network Service Access Point based on E.164 (phone #) 20 bytes

CPEG 514

ATM Connection Establishment

Goal: setup VPI/VCI between any two ATM devices

A

B

CPEG 514

ATM UNI Signaling (Q.2931) - SVC

SETUP

ALERT

CONNECT

ATM End Device

ATM Switch

ATM Switch

ATM End Device

Why do we need this signaling protocol?

Connection Established, control, mgmt, Does it look familiar (Q.931)?

PROCEEDING PROCEEDING

SETUP

SETUP

ALERT

ALERT CONNECT

CONNECT

VPI/VCI Will be Setup For each Direction

CPEG 514

Signaling VCI (VPI=0)

(UNI)

Q; What is the VPI/VCI in the ATM Q.2931 SETUP message? VPI= 0 VCI = 5

e.g. VPI =0, VCI for connection establishment signaling

CPEG 514

ATM ILMI (mgmt plain) Integrated Local Management Interface (ILMI) enables

devices to determine status of components at the other end of a physical link

and to negotiate a common set of operational

parameters to ensure interoperability.

ILMI operates over a reserved VCC of VPI = X, VCI = 16. Administrators may enable or disable ILMI at will, but it is highly recommended to enable

it. Doing so allows the devices to determine the highest UNI interface level to operate (3.0, 3.1, 4.0), UNI vs. NNI, as well as numerous other items.

Furthermore, ILMI allows devices to share information such as NSAP addresses, peer interface names, and IP addresses.

Without ILMI, many of these parameters must be manually configured for the ATM attached devices to operate correctly.

CPEG 514

PVC or SVC Q1: What is the purpose of PVC and SVC?

Q2: What are differences between PVC and SVC?

Q3: For data services, is it better to use PVC or SVC?

• Core (SVC) vs. Access (PVC) • Using the dynamic setup in the core would be

easier

Q4: For voice services, is it better to use PVC or SVC? • Core (PVC – trunks are already there) vs. Access (SVC)

CPEG 514

ATM Quality of Service (QoS)

CBR: Constant Bit Rate • Guaranteed transmission rate EMULATING TDM circuit

VBR: Variable Bit Rate (Requires QoS attention) • rtVBR and nrtVBR (rt = real time)

• Peak Cell Rate (PCR) – MAX allowed data rate

The maximum cell rate at which the user will transmit • Sustained Cell Rate (SCR) – allowable cell rate over time

• Max Burst Size (MBR)

• Minimum Cell Rate (MCR)

UBR: Unspecified Bit Rate • No guarantee, best effort

CBR

VBR

UBR

PCR

SCR

Service

Bit Rate

CPEG 514

ATM QoS How does a carrier ensure that QOS can be met?

• Connection Admission Control (CAC)

Procedure for determining whether each new SETUP request should be granted or denied based on current network conditions

• Usage Parameter Control (UPC)

Procedure for verifying whether customer is conforming to their contractual Traffic Parameters. PER the SLA

• Resource Management (RM)

Procedure for notifying ABR users when they should slow down

• ABR: Available Bit Rate

• Selective Cell Discard (SCD)

Procedure for discarding cells (CLP=1)during congestion.

CPEG 514

IP over ATM Protocol (RFC 2684)

ATM

802.3: IEEE Media Access Control layer (also know as Ethernet)

802.3

PHY PHY

802.3 802.3

RFC 2684

ATM

PHY

IP

AAL5

802.3

PHY

IP

PHY

802.3 802.3

RFC 2684

ATM

PHY

AAL5

192.168.1.10/24 192.168.1.11/24

Both ATM and Ethernet Switching

Same Subnet Then we are Using switches

CPEG 514

Frame Relay and ATM Interworking

Frame Relay is an access technology, and it is rarely used on the carrier backbone (core).

The backbone is usually the ATM network, slowly migrating to IP/MPLS backbone.

How is Frame Relay carried over the ATM network?

CPEG 514

ATM/FR IWF

Frame Relay Service Specific Convergence Sublayer (FR-SSCS) uses the same PDU format

as Frame Relay (Q.922) minus the FCS and FLAG.

FR traffic parameters (FECN, BECN, and DI) are maintained in FR-SSCS PDU.

FRF.5 supports both one-to-one (one DLCI to one VPI/VCI) and many-to-one (many DLCIs to one VPI/VCI) mappings.

Q: is DLCI in FR-SSCS used for addressing?

CPEG 514

ATM/FR Network Interworking (FRF.5)

p1r1 p1r3

ATM Core Network

FR (T1)

FR (T1)

OC-3

FRF.5 Convert FR

frames to ATM cells

FRF.5 Convert ATM cells to FR

frames

CPEG 514

ATM/FR Network Interworking (FRF.5)

p1r1 p1r3

PHY

FR

ULP

PHY

FR FR-SSCS

AAL5

ATM

PHY

FR-SSCS

AAL5

ATM

PHY

PHY

FR

PHY

FR

ULP

FR-SSCS: Frame Relay Service Specific Convergence Sublayer IWF: Interworking Function

ATM/FR IWF ATM/FR IWF

ATM Core

CPEG 514

ATM/FR Network Interworking (FRF.8)

p1r1 p1r3

PHY

FR

RFC2427

PHY

FR FR-SSCS

AAL5

ATM

PHY

ATM

PHY PHY

ATM

IP

FR-SSCS: Frame Relay Service Specific Convergence Sublayer IWF: Interworking Function

ATM ATM/FR IWF

IP

RFC2684

AAL5

(FRF .8)

FR ATM

ATM Core