TDC 461: Wide Area Network Services

DePaul University

22 May, 2001

Agenda

• Frame Relay

– PVCs, CIR and Pricing

• Packetized Voice

– Voice over IP

• Over the Internet

• Over Frame Relay

• SS7

• Integrated Services Digital

Networks (ISDN)

– Basic Rate Interface (2B +

D)

– Primary Rate Interface

(23B + D)

• DSL

• Cable Modems

Frame Relay

• Telecommunications carriers maintain networks of Frame Relay switches

• Customer get access line to nearest switch to get Frame Relay service

• Higher data rates than X.25

• Lower delays, higher throughputs and better security than the Internet

Frame Relay Basics• Frame Relay = “Son of X.25”

–

– Frame Assembler/Disassemblers (FRADs) • Similar to X.25 PADs

Frame Relay Basics• Frame Relay = “Son of X.25” - except:

– Data only sent over Permanent Virtual Circuits (PVCs), which are set up by the carrier, not customer - always available!

– Customer can access network at data rates from 56 Kbps to 45 Mbps !

– No error control done by network switches (error control is responsibility of customer)

Frame Relay Basics• Frame Relay = “Son of X.25” - except:

– Fixed monthly price based on • “Port charge”

• “PVC charge”

– Frame Relay is a layer 2 protocol, so •

•

IP RouterCustom er S iteIP Router withFram e Relay

software

LANPCs with LAN cardand TCP/IP Software

LeasedAccess Line

IP RouterCustom er S iteIP Router withFram e Relay

software

LANPCs with LAN cardand TCP/IP Software

LeasedAccess Line

Fram eSwitch

Fram eSwitch

Fram eSwitch

National F rame RelayNetwork

Fram eSwitch

CSUCSU

Chicago Boston

Frame Relay Setup• Typically used to replace leased lines:

– Customer gets one Frame Relay PVC to replace each leased line

– Customer still gets guaranteed delay and throughput (CIR) similar to leased line

– Customer uses one access line at each business location for all frame relay data

– Customer saves money - PVCs cost less than leased lines

Leased Line Problem:

Number of leased circuits (and cost!) grows very large as number of sites increases!!

EthernetHub

Router

ClientClientFile Server

TokenRingHub

Router

ClientFile Server

TokenRingHub

Router

ClientFile Server

EthernetHub

Router

Client ClientFile Server

AmeritechSwitch

AmeritechSwitch

AmeritechSwitch

AmeritechSwitch

The Frame Relay Solution:

1 Access Line for each site!!

EthernetHub

Router

ClientClientFile Server

TokenRingHub

Router

ClientFile Server

TokenRingHub

Router

ClientFile Server

EthernetHub

Router

Client ClientFile Server

AmeritechSwitch

AmeritechSwitch

AmeritechSwitch

AmeritechSwitch

Frame Relay Addressing• The carrier assigns each PVC a 10-bit Data

Link Connection Identifier (DLCI).

• Customer sets up a table in each access router that maps each possible destination to its DLCI.

• Router puts correct DLCI into each frame header before sending frame into network.

IP RouterCustom er S iteIP Router withFram e Relay

software

LANPCs with LAN cardand TCP/IP Software

LeasedAccess Line

IP RouterCustom er S iteIP Router withFram e Relay

software

LANPCs with LAN cardand TCP/IP Software

LeasedAccess Line

Fram eSwitch

Fram eSwitch

Fram eSwitch

National F rame RelayNetwork

Fram eSwitch

CSUCSU

Chicago Boston

CIR• For each PVC, customer specifies a Committed

Information Rate (CIR):– CIR represents a guaranteed throughput for this PVC

– Carrier also guarantees limited data delivery time if customer does not exceed CIR

– Price of PVC is directly related to CIR• High CIR =

• Low CIR =

CIR• Example:

– I have a T1 (1.536 Mbps) access line into the frame relay network in Chicago

– I ask my carrier to create a PVC from Chicago to Dallas with CIR = 512 Kbps.

– If I stay within my CIR (i.e., send less than 512,000 bps Chicago-Dallas, on average):

• Carrier guarantees 99.99% traffic gets through

• Carrier guarantees <= 20 ms. Network delay

Frame Relay PVCs with CIRs

EthernetHub

Router

ClientClientFile Server

TokenRingHub

Router

ClientFile Server

TokenRingHub

Router

ClientFile Server

EthernetHub

Router

Client ClientFile Server

AmeritechSwitch

AmeritechSwitch

AmeritechSwitch

AmeritechSwitch

56 Kbps 56 Kbps

56 Kbps 56 Kbps

PVC with16 Kbps CIR

Frame Relay Pricing• Example:

– 4 sites, each with T1 access line

– 6 PVCs providing connectivity between sites,

with 512 Kbps CIR on each PVC

• Monthly Costs:

– 4 x (T1 access port cost) plus

– 6 x (512 Kbps PVC cost)

What if I exceed my CIR?• Example:

– I have a T1 (1.536 Mbps) access line into the frame relay network in Chicago

– I ask my carrier to create a PVC from Chicago to Dallas with CIR = 512 Kbps.

– Isn’t it possible for me to exceed my CIR (send more than 512 Kbps Chicago-Dallas)?

• YES!!!!!

What if I exceed my CIR?• Burst Rate (Br)

• Discard Eligible (DE) bit–

The Tradeoff• Low CIR ==>

• High CIR ==>

• Note: Many customer still choose to pay lowest cost by selecting a Zero CIR option that provides no delivery guarantees

Frame Relay vs. The Internet• Frame Relay advantages:

–

–

• Frame Relay disadvantages–

–

Voice over IP• Voice can be send over packet-switched

networks in the following manner:

Voice Over the Internet

A/D Coder RouterPacketizer / Buffer

D/A CoderRouterDepacketizer &Playout Buffer

The Internet

Analog

Analog

ConstantRate BitStream

ConstantRate BitStream

DataPackets

DataPackets

Voice over Frame Relay• Voice samples can also be carried in IP

packets over Frame Relay networks

• Advantages of Voice over Frame Relay–

–

Voice over Frame Relay• Many businesses today are using spare

capacity on their Frame Relay networks to send voice between business sites.

IP/UDPHeader

VoiceHeader

Voice Information

28 bytes 6 bytes 40 bytes

Typical IP Voice Packet

IP Telephony Using a Computer as the Terminal

PSTN Internet

CMTS

Gateway

Router Cable Modem

Microphone

Cable ModemTermination System

PSTN Internet

CMTS

Gateway

Router

IP Telephony Using Phone Adapter

Cable Modem

TelephoneAdapter

PBX Extender

PSTN

Internet

CMTS

RouterCable Modem

TelephoneAdapter

CorporateIntranet

PBX

Gateway

Switch Unit

SS7

• Defined:

• Pre SS7

SS7- Out of Band Signaling

• What is it?

• Why do it?

SS7 Interconnection

• Defined:

• Links and Linksets

• Routes and Routesets

SS7 Call Setup

• ISUP

• SS7 Applications

ISDN• The Idea:

– Provides a fully-digital interface over current telephone lines

– Allows customer to do both 64 Kbps dial-up and X.25 data over same ISDN line

– Provides intelligent signaling channel (D-channel) between customer equipment and Central Office

ISDN - Types of Interfaces

• ISDN Basic Rate Interface

•

• ISDN Primary Rate Interface

•

Basic Rate Interface (2B+D)• 3 logical channels on one access loop:

– 2 B-channels (64-Kbps) used for•

• – 1 D-channel (16-Kbps) used for

• •

• Low Cost:

ISDN BRI• The Customer Requires:

– Network Termination Type 1 (NT1)•

– ISDN-Compliant devices •

• The Central Office Requires:– ISDN Line Card

• Terminates ISDN line at the Central Office and separates B channels and D channel

– –

ISDN Equipment

PCISDN

Telephone

ISDNCent r alOffi ce

NT1

SubscriberLoop

Basic Rate Interface• Up to 8 devices can connect to single BRI

through an NT1–

–

– Central Office determines which device has control over which B-channel at any time.

BRI Applications• Work-at-Home: Simultaneously use

– – –

• Internet Access –

• Low-cost Business Videoconferencing

• Low-speed dial-up LAN Interconnection

Primary Rate Interface (23B+D)• Primary Rate Interface is an enhanced T-1

circuit.–

–

–

PRI Advantage over T-1• Any PRI B-channel can be set up “call-by-call” to

provide any service–

–

• In contrast, each DS0 channel on a T-1 must be statically allocated to carry only a single voice or data service.

PRI Applications

• Integrated business services.

• Delivery of Caller ID / ANI (D-channel).

• High-speed videoconferencing.

• Medium-speed LAN interconnection.

• Dial-up data channels with flexible bandwidth (N x 64 Kbps).

Digital Subscriber Lines

• xDSL=>

• Asymmetric DSL=>

• Hype

DSL Modems

• Standards

• Security

Broadband Cable

• Cable Modems

• Standards

• Security

DSL vs. Cable

• Contention for network

• Network control

• Scalability