Full HTML for

Basic foilset Introduction to Network WANs

Given by Roman Markowski at Lectures at Xi'an Jaotong University on Sept 1998. Foils prepared Dec. 6 98
Outside Index Summary of Material

Modems
HSSI
Cellular
T1 / T3
ISDN
Switched 56 K
xDSL
SDLC / HDLC
X.25
Frame Relay
SMDS
ATM

Table of Contents for full HTML of Introduction to Network WANs

 Denote Foils where Image Critical
Denote Foils where HTML is sufficient
1 Internetworking: WAN Technologies
2 Wide Area Network Technologies
3 Definitions - LAN / WAN
4 WAN Basics (1)
5 WAN Basics (2)
6 WAN Basics (3)
7 WAN - speeds (1)
8 WAN - speeds (2)
9 Modems
10 56 Kbps modem technology (1)
11 56 Kbps modem technology (2)
12 56 Kbps modem technology (3)
13 56K modem technology (3)
14 Cable modems
15 High-Speed Serial Interface
16 Cellular - CSC
17 Cellular - CDPD (1)
18 Cellular - CDPD (2)
19 Cellular - CDPD (3)
20 Cellular - CDPD (4)
21 Cellular - CDPD (5)
22 Cellular - CDPD (6)
23 Cellular - CDPD (7)
24 Cellular - CDPD (8)
25 T1 / T3 Services (1)
26 T1 / T3 Services (2)
27 T1 / T3 Services (3)
28 T1 / T3 service (4)
29 ISDN - Integrated Services Digital Network
30 ISDN - Integrated Services Digital Network
31 ISDN - Integrated Services Digital Network
32 ISDN - BRI
33 ISDN - PRI
34 ISDN - LAN-to-LAN
35 Switched 56 K
36 xDSL - Digital Subscriber Line Technology (1)
37 xDSL - Digital Subscriber Line Technology (2)
38 xDSL Digital Subscriber Line Technology (3)
39 xDSL Digital Subscriber Line Technology (4)
40 SDLC and derivatives (1)
41 SDLC and derivatives (2)
42 SDLC and derivatives (3)
43 SDLC and derivatives (4)
44 X.25 (1)
45 X.25 (2)
46 X.25 (3)
47 X.25 (4)
48 Frame Relay (1)
49 Frame Relay (2)
50 Frame Relay (3)
51 SMDS - Switched Multi-megabit Data Services (1)
52 SMDS - Switched Multi-megabit Data Services (2)
53 SMDS - Switched Multi-megabit Data Services (3)
54 ATM technology (1)
55 ATM technology (2)
56 ATM technology (3)
57 ATM technology (4)
58 ATM technology (5)
59 ATM technology (6)
60 ATM technology (7)
61 ATM technology (8)
62 ATM technology (9)
63 ATM technology (10)
64 ATM technology (11)
65 ATM technology (12)
66 ATM technology (13)
67 ATM technology (14)
68 ATM technology (15)
69 PPT Slide
70 ATM technology (17)
71 ATM technology (18)
72 ATM technology (19)
73 ATM technology (23)
74 ATM technology (24)

Outside Index Summary of Material

HTML version of Basic Foils prepared Dec. 6 98

Foil 1 Internetworking: WAN Technologies

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Roman Markowski
IS Manager
Northeast Parallel Architectures Center
September 1998
http://www.npac.syr.edu/users/roman/
HTML version of Basic Foils prepared Dec. 6 98

Foil 2 Wide Area Network Technologies

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Modems
HSSI
Cellular
T1 / T3
ISDN
Switched 56 K
xDSL
SDLC / HDLC
X.25
Frame Relay
SMDS
ATM
HTML version of Basic Foils prepared Dec. 6 98

Foil 3 Definitions - LAN / WAN

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
LAN - Local Area Network. A network that interconnects PCs, terminals, workstations, servers, printers, and other peripherals at high speed over short distances (Ethernet, token ring, FDDI, ATM, wireless)
WAN - Wide Area Network. A network that covers long-haul areas and usually utilizes public phone companies (T1/T3, ISDN, xDSL, Frame Relay, SMDS, ATM)
HTML version of Basic Foils prepared Dec. 6 98

Foil 4 WAN Basics (1)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
WAN is a data communication network that covers broad geographic area and uses facilities provided by telephone companies
WAN technologies function at the lower 3 layers of the OSI RM: physical, datalink and network
Point-to-point link provides pre-established WAN path (leased lines)
  • datagram transmission (individually addressed frames)
  • data-stream transmission (address checking occurs only once)
HTML version of Basic Foils prepared Dec. 6 98

Foil 5 WAN Basics (2)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Circuit switching - dedicated physical circuit is established, maintained and terminated (example ISDN)
Packet switching - network devices share a single point-to-point link. Multiplexing is used (ATM, SMDS, X.25,FR)
WAN Virtual Circuits - logical circuit to enable reliable communication between network device (PVC, SVC)
HTML version of Basic Foils prepared Dec. 6 98

Foil 6 WAN Basics (3)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Dial-up services
Devices:
  • switches - operate at the Data Link Layer of the OSI RM
  • access servers - work as concentration point
  • modems - modulation/demodulation analog-digital
  • CSU/DSU - channel/data service unit - adapts physical interface on DTE to a switched circuit network
  • ISDN terminal adapters - ISDN modem
HTML version of Basic Foils prepared Dec. 6 98

Foil 7 WAN - speeds (1)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Modem 9.6, 14.4, 19.2, 28.8, 33.6, 56 Kbps
Switched 56 KBPS 56 Kbps
ISDN B, BRI(2B+D) 64 Kbps, 144 Kbps
ISDN PRI(23B+D) 1.544 Mbps
T1 (DS-1) 1.544 Mbps
X.25 up to (64 Kbps) 2 Mbps
Frame Relay 56 Kbps-(1.544 Mbps)-36 Mbps
HDSL 1.544 Mbps
SDSL 160 Kbps- 2 Mbps
ADSL 1.5 - 8 Mbps
VDSL 2.3 - 51.84 Mbps
HTML version of Basic Foils prepared Dec. 6 98

Foil 8 WAN - speeds (2)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
SMDS 56Kbps - 34 Mbps
T3 (DS-3) 45.736 Mbps
SONET OC-1/STS-1 51.84 Mbps
ATM-25 25 Mbps
ATM DS-3 44.736 Mbps
ATM TAXI 100 Mbps
ATM OC-3 155.52 Mbps
ATM OC-12 622.08 Mbps
ATM OC-48 2.488 Gbps
ATM OC-128 6.4 Gbps
HTML version of Basic Foils prepared Dec. 6 98

Foil 9 Modems

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Modems (modulators / demodulators) are data communication equipment (DCE) devices that provide connections for computers into the Public Switched Telephone Network (PSTN). They convert (modulate) the digital signal generated by a computer into analog signal that can be transmitted over telephone line.
The most important CCITT (ITU) standards are listed below:
  • V.22 1,200 bits/sec full duplex
  • V.22bis 2,400 bits/sec full duplex
  • V.28 defines circuits in RS-232
  • V.32 async / syn 4,800 and 9,600 bits/sec
  • V.32bis async / syn 14,400 bits/sec
  • V.32turbo 19,200 bits/sec
  • V.34 28.8 Kb/sec
  • V.34+ 33.6 Kb/sec
  • V.42 defines error check-in standard
HTML version of Basic Foils prepared Dec. 6 98

Foil 10 56 Kbps modem technology (1)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
asymmetrical : 56 Kbps (downstream); 33.6 Kbps (upstream)
ITU V.90 - standard covering 56 Kbps modems (will be probably ratified in September 1998). At the moment there are 2 proprietary and incompatible specifications: X2, developed by US Robotics, and K56flex by Lucent and Rockwell Semiconductors Systems.
about 70% of the 56K modems use K56flex technology. Recently 28 data communications and computer vendors created Open 56K Forum which intends to push K56flex technology as new standard.
Cost: $129-$500
HTML version of Basic Foils prepared Dec. 6 98

Foil 11 56 Kbps modem technology (2)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Before switching to 56K modem we should take into account that:
  • only the best phone lines (with the lowest noise level) can handle 56-Kbps transmission. According to analysts, only 50% of US connections are clean enough
  • Some ISPs need to upgrade their connections to carrier phone networks
  • If lines are not pure digital and additional conversions take place, 56 K cannot be obtained.
  • There is also legal limit on speed: an FCC regulation dating back 20 years does not allow for higher modem transmission than 53.3 Kbps
HTML version of Basic Foils prepared Dec. 6 98

Foil 12 56 Kbps modem technology (3)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Before switching to 56K modem ...
  • If we buy now the vendor should offer upgrade to eventual standard.
  • And of course the full K56bps is available for download only. Upload of data is available at standard rates (max 33.6 Kbps).
  • There are also other issues which should be taken into account (vendor, technology, type, upgradability to new standard, remote configuration and management)
  • PC must be fast enough to keep up with the modem : it is important when data are compressed more than 2:1. The serial interface in PC (which usually is 115.2 Kbps can be too slow and must be accelerated.)
HTML version of Basic Foils prepared Dec. 6 98

Foil 13 56K modem technology (3)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
PSTN
Server modem
modem
modem
modem
PSTN
33.6 Kbps
56 Kbps
33.6 Kbps
33.6 Kbps
digital
D/A converter
HTML version of Basic Foils prepared Dec. 6 98

Foil 14 Cable modems

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Cable-modem allows high-speed access to the Internet via cable TV coaxial wiring, ADSL, twisted-pair copper, and direct broadcast satellite dishes. Works in bi-directional way
Characteristics:
  • Shared bandwidth technology
  • 10 Mbps to 30 Mbps downstream
  • 128Kbps-3 Mbps upstream
  • Distance from provider to customer site 30 miles;
  • 2000 miles with additional amplifiers
HTML version of Basic Foils prepared Dec. 6 98

Foil 15 High-Speed Serial Interface

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
HSSI is a DTE/DCE interface developed by Cisco Systems and T3plus Networking
Defines both the electrical and the physical DTE/DCE interfaces - corresponds to the Physical layer of the OSI Characteristics:
  • max. cable length : 50 feet
  • max. signaling rate : 52 Mbps
  • number of connector pins : 50
  • topology: point to point
  • cable type: shielded twisted-pair wire
  • electrical technology: ECL (emitter-coupled logic)
HTML version of Basic Foils prepared Dec. 6 98

Foil 16 Cellular - CSC

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
CSC - Circuit Switched Cellular
  • uses AMPS (Advanced Mobile Phone System) for sending data with rate: 1.2-14.4 Kbps (analog transmission)
  • after dialing you receive a dedicated link for data transmission with SLIP or PPP
  • uses 800 MHz frequency
  • matching modems required on both ends (with support for MNP7, NMP10, ETC)
  • during activation carrier assigns PHONE NUMBER
  • Components: MBS - Mobile Base Station, MTSO - Mobile Telephone Switching Office, pool of modems, PSTN - Public Switched Telephone Network
HTML version of Basic Foils prepared Dec. 6 98

Foil 17 Cellular - CDPD (1)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
CDPD - Cellular Digital Packet Data
  • rate: 19.2 Kbps
  • digital transmission
  • runs over existing mobile infrastructure
  • uses its own suite of protocols to encapsulate TCP/IP data over the airlink
  • higher reliability, better security
  • based on TCP/IP - easy integration with Internet
  • during activation carrier assigns IP ADDRESS
  • not recommended for Web browsing (rather for short messages, e-mail, web pages without graphics)
  • security based on public key negotiation and RC-4 encryption
HTML version of Basic Foils prepared Dec. 6 98

Foil 18 Cellular - CDPD (2)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
What is CDPD?
The Cellular Digital Packet Data (CDPD) System overlays the cellular voice network to provide a wireless extension of existing packet data networks. It provides secure wireless packet data connectivity and is based on standard Internet Protocol (IP).
CDPD is a transmission technology that allows messages to be broken down into a series of packets that are sent along idle or dedicated channels of existing cellular voice networks (commonly referred to as AMPS - Advanced Mobile Phone System) at rates of speed of up to 19,200 bits per second (BPS).
CDPD is a mobile data networking architecture. This layered architecture allows addition of different media access methods.
HTML version of Basic Foils prepared Dec. 6 98

Foil 19 Cellular - CDPD (3)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
CDPD provides customers with a flexible, fast and convenient method for sending and receiving data to and from mobile devices
CDMA and TDMA (Code/Time Division Multiple Access) are digital cellular voice standards. Both are being extended to allow incorporation into the CDPD mobility management architecture. CDMA and TDMA will extend the acceptance of CDPD.
CDPD network consists of five components.
  • Mobile End System (MES)
  • Mobile Data Base Station (MDBS)
  • Mobile Data Intermediate System (MD-IS)
  • Intermediate System (IS)
  • Fixed End System (FES)
HTML version of Basic Foils prepared Dec. 6 98

Foil 20 Cellular - CDPD (4)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
CDPD
network
MBS
MDBS
MD-IS
Internet
MTSO
PTSN
Voice
*Data
Digital Data
Laptop
Cell Phone
Laptop
Cell Phone
Cell
MES
HTML version of Basic Foils prepared Dec. 6 98

Foil 21 Cellular - CDPD (5)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
The MES consists of a personal communications device, such as a laptop computer connected to a cellular data modem. The MES may operate as a normal computer, used for downloading files or checking email, etc, or it may serve a specialized purpose, such as credit card verification. The MES both sends data to the network via the MDBS and receives data from the network via the MDBS at a rate of 19.2 Kbps. (Because of overhead, the actual data rate is approximately 9.6 Kbps.) Before transmitting the data, the MES packetizes it and also encrypts it for security.
HTML version of Basic Foils prepared Dec. 6 98

Foil 22 Cellular - CDPD (6)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
The MDBS lies within a cell site. It uses the same antenna as the voice network to receive and send data between the MES and the MD-IS. The MDBS is mainly responsible for channel matters. While CDPD calls are taking place, the MDBS monitors the channels to detect the existence of competing voice calls, and also monitors all unused channels to find suitable "hopping" channels. A hop occurs when a CDPD call must give up its channel for a voice call. Hops also occur when a user moves from one service area to another, such as from one base station's coverage area to another's.
HTML version of Basic Foils prepared Dec. 6 98

Foil 23 Cellular - CDPD (7)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
The MD-IS acts as the liason between the cellular portion and the fixed, or land-line, portion of the network. It accepts packets sent from the MDBS and converts them to IP format for transmission over the fixed network. Similarly, it accepts packets from the fixed network and encrypts and further processes them for transmission over the airlink via SNDCP (Sub-network Dependent Connection Protocol). The MDIS also handles registration (connection establishment) for the MES's in its service area. MDIS's can be divided into 2 categories: home and serving. A home MDIS is an MES's primary MDIS, the one it normally registers to. A serving MDIS is an MDIS in another coverage area which an MES registers to if I is within that area. Home MDIS's are responsible for forwarding packets to the appropriate serving MDIS's of all of its MES's.
HTML version of Basic Foils prepared Dec. 6 98

Foil 24 Cellular - CDPD (8)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
The Intermediate Systems (IS) and Fixed-End Systems (FES) comprise the fixed network. These are off-the-shelf products which are "invisible" to the mobile network. IS's are routers which direct the packets to the correct location. FES is a general lump term used to describe the different possible destinations of the packets. FES's include external computer networks (such as campus networks), administrative servers, and network accounting servers, as well as many other examples.
http://www.cdpd.org/ CDPD Forum
http://www.bam.com/ Bell Atlantic Mobile
HTML version of Basic Foils prepared Dec. 6 98

Foil 25 T1 / T3 Services (1)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
The highest frequency transmitted for voice communication is 4 kHz. In order to recreate the analog wave from digital stream of data, we need to sample the analog wave at twice the rate of the highest frequency, it means 8 KHz = 8000 times per second. To represent 4KHz in digital, we generate 8-bit samples 8000 times per second. (Voice channel = 64,000 bps)
Service Class:
  • DS0 the basic 64 Kbps channel in digital voice networking
  • DS1 collection of 24 DS0 = 1.544 Mbps
  • DS2 28 DS1 channels (this service is not commonly available)
  • DS3 7 DS2 channels or 672 DS0 channels = 44.736 Mbps
T-carrier services are traditionally dedicated, but switched services are also available. T-carrier services are typically leased on a month-to-month basis and include initial setup charge.
HTML version of Basic Foils prepared Dec. 6 98

Foil 26 T1 / T3 Services (2)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
T1 it is DS1 delivered over copper wire (throughput 1.536 Mbps; bandwidth 1.544 Mbps (8Kbps lost for channel synchronization))
  • ISDN PRI = 23 B + D Primary Rate Interface; T1 = 24 DS0
T3 it is DS3 delivered over copper wire ( throu 43.008 Mbps; bw 44.736 Mbps )
Synchronization within one 64 Kbps channel
  • AMI - Alternate Mark Inversion - encoding for 56 Kbps channel
  • B8ZS- Bipolar 8 Zero Substitution - encoding for 64 Kbps channel
In T1 we need to put 24 channels on one four-wire circuit
  • TDM - Time Division Multiplexing
How to identify the first channel in 24-channel rotation ?
  • D4 - Super Frame : = 12 frame format
  • ESF - Extending Super Frame (framing); enhancement of D4 based on 24 frames
HTML version of Basic Foils prepared Dec. 6 98

Foil 27 T1 / T3 Services (3)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Frame: a group of all 24 T1 sub-channels with 8 bits per channel and one framing bit. One frame equals 193 bits; 12 frames = D4; 24 frames = ESF
Channelized T1 - used to supply 24 individual channels to different locations
E1 - 32 DS0 channels = 2,048 Kbps (in Europe) AMI is not used; B8ZS is replaced by HDB3 encoding (High Density Bipolar)
Devices required:
  • CSU / DSU = Channel Service Unit / Digital Service Unit
  • V.35, EIA RS449 or RS 530 interface to DTE; RJ48C or RJ48X jack
LAN---bridge --(V.35)---CSU/DSU---(T1)---CSU/DSU--(V.35)---bridge--LAN
Bell Atlantic: installation $622; usage $642/month (in 1997)
HTML version of Basic Foils prepared Dec. 6 98

Foil 28 T1 / T3 service (4)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
router
CSU/DSU
LAN
1.5 Mbps
router
CSU/DSU
LAN
1.5 Mbps
Syracuse
Boston
T1 line
24x64 Kbps
HTML version of Basic Foils prepared Dec. 6 98

Foil 29 ISDN - Integrated Services Digital Network

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
ISDN integrates data, voice, and video signals into a digital telephone line
Specification:
  • CCITT in 1984 (spec I.100-400), 1988 (I.500-600) ; 96 basic specifications
    • Physical I.430/431 basic/primary interface
    • Logical Link I.441/Q.921 Link Access Protocol D channel (LAPD)
    • Network I.451/Q.931 control signaling, call control
Narrow-band ISDN (N-ISDN)- original standard operates over copper cable (operates on physical,logical and network layers)
BRI = Basic Rate Interface (2B+D=144 Kbps)
  • B = 64 Kbps, B (bearer) - data transmission channel
  • D = 16 Kbps, D (delta) - Signaling (2 modes: 64 Kbps and 56Kbps)
PRI = Primary Rate Interface (23B+D=1.544 Mbps) in Europe 30B+D (D = 64 Kbps, signaling channel)
HTML version of Basic Foils prepared Dec. 6 98

Foil 30 ISDN - Integrated Services Digital Network

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
B channels can be bundled as described below:
  • ISDN-B - 64 Kbps ( 1xB channel)
  • ISDN-D - B+D
  • ISDN-H (H0) - 384 Kbps ( 6xB channels)
  • ISDN-H11 - 1.536 Mbps (24xB channels)
  • ISDN-H12 - 1.92 Mbps (30xB channels)
Broadband ISDN (B-ISDN) - emerging standard
  • operates over fiber with rates 150 - 600 Mbps
  • standard created for videoconferencing, video on demand and based on SONET Synchronous Optical Network (physical transport backbone)
  • ATM Asynchronous Transfer Mode (switching service)
HTML version of Basic Foils prepared Dec. 6 98

Foil 31 ISDN - Integrated Services Digital Network

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Hardware:
  • Popular switches : 5ESS AT&T, DMS100
  • NT1 (Network Termination) converts the 2-wire (U) ISDN line into 4-wire (2 pairs) connection for the terminal adapter (S/T)
  • Terminal Adapter: minimalist approach (only ISDN): ISDN*tek Internet+Plus; Analog and ISDN in one device (ISDN and fax, analog phone or modem): Digi DataFire Go!; High End TAs : Motorola BitSURFER Pro
Services: ISDN (digital) phone, ISDN fax, PC with ISDN, videoconferencing
Security: PAP - Password Authentication Protocol, CHAP - Challenge Handshake Authentication Protocol
SPID: Service Provider ID (example:31547792030000/31547788030000)
Service cost - installation: $160; usage: $36/per line per month; TA ~$500
HTML version of Basic Foils prepared Dec. 6 98

Foil 32 ISDN - BRI

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
HTML version of Basic Foils prepared Dec. 6 98

Foil 33 ISDN - PRI

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
HTML version of Basic Foils prepared Dec. 6 98

Foil 34 ISDN - LAN-to-LAN

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
HTML version of Basic Foils prepared Dec. 6 98

Foil 35 Switched 56 K

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Digital communication technology for transporting data over
  • switched synchronous lines at 56 Kbps, or
  • switched asynchronous lines at 57.6 Kbps
Compression can provide four times the bandwidth
ISDN offers 2x 64 Kbps channels, switched 56 provides only one 56 Kbps channel.
Switched 56 is digital and do not require modem. Instead, CSU/DSU is required to attach bridge/router to the line installed by a phone company. At each end CSU/DSU is required. A typical connection between CSU/DSU and router/bridge is V.35 serial cable.
The connection operates like dial-out link
HTML version of Basic Foils prepared Dec. 6 98

Foil 36 xDSL - Digital Subscriber Line Technology (1)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
xDSL - modem technology; allows mixing data, voice and video over conventional, copper phone lines.
The service under development (since 1987).
Competes with ISDN and cable modems
xDSL family : ADSL, RADSL, IDSL, HDSL, SDSL, VDSL
All xDSL technologies run on existing copper phone lines and use modulation to boost transmission rates.
  • CAP - amplitude phase modulation
  • DMT - discrete multi-tone modulation
  • DWMT- discrete wavelet multi-tone modulation.
HTML version of Basic Foils prepared Dec. 6 98

Foil 37 xDSL - Digital Subscriber Line Technology (2)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
The key in xDSL technology is modulation, a process in which one signal modifies a properties of another.
Hardware: DSL requires modems and splitters for end-users; carriers use DSLAMs (digital subscriber line access multiplexers)
Differences between xDSL technologies: speed, operating distance, applications, ratio between up and downstream
Different approaches: ATM-based ADSL, ISDN DSL. The important thing is what is running over xDSL...
HTML version of Basic Foils prepared Dec. 6 98

Foil 38 xDSL Digital Subscriber Line Technology (3)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
ADSL - Asymmetric Digital Subscriber Line
  • expected in general use in 1999
  • twisted pair copper
  • asymmetric: most commonly: 6Mbps (down), 640 Kbps (up)
    • downlink: 1.5 Mbps-8 Mbps
    • uplink : 176 Kbps - 1 Mbps
  • limited distance (18000 feet over 26-gauge copper)
RADSL - Rate-Adaptive Digital Subscriber Line
  • varying speeds depending upon line quality; asymmetric
    • downlink: 1.5 Mbps-8 Mbps
    • uplink : 176 Kbps - 1 Mbps
  • limited distance (18000 feet over 26-gauge copper)
HTML version of Basic Foils prepared Dec. 6 98

Foil 39 xDSL Digital Subscriber Line Technology (4)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
HDSL - High-speed Digital Subscriber Line
  • full-duplex, symmetric
    • 1.544 Mbps or 2.048 Mbps in each direction
  • two twisted pairs (for T1) and 3 pairs (for E1)
  • max distance 12,000 feet
VDSL - Very-high-bit-rate Digital Subscriber Line (known as BDSL)
  • asymmetric
    • downlink: 12.96-51.84 Mbps
    • uplink : 1.6 - 2.3 Mbps
  • max 4,500 - 1,000 feet
  • applications: High definition TV, multimedia
HTML version of Basic Foils prepared Dec. 6 98

Foil 40 SDLC and derivatives (1)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
SDLC - Synchronous Data Link Control
  • IBM mid-1970s; link layer protocol
  • synchronous, bit-oriented developed for SNA architecture
  • 2 types of nodes:
    • primary : control operation of secondaries
    • secondary : can transmit data when primary grants permission
  • supports variety of link types and topologies
    • point-to-point (one primary, one secondary)
    • multipoint (one primary, many secondaries)
    • loop (one primary, many secondaries)
    • hub go-ahead
  • can be used with full-duplex and half-duplex; circuit switched and packet switched
HTML version of Basic Foils prepared Dec. 6 98

Foil 41 SDLC and derivatives (2)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
SDLC - Synchronous Data Link Control
IBM
mainframe
Front-end
processor
Established
controller
Terminals
SDLC Link
(56 Kb leased line)
HTML version of Basic Foils prepared Dec. 6 98

Foil 42 SDLC and derivatives (3)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
HDLC - High-level Data Link Control
  • SDLC modified by ISO
  • considered to be compatible with SDLC; the same frame format; does not support loop or hub go-around
  • supports full-duplex, synchronous operation
  • 3 transfer modes:
    • Normal Transfer Mode (used also by SDLC) - secondary cannot communicate with primary without permission
    • Asynchronous Response Mode (ARM) - can communicate
    • Asynchronous Balanced Mode (ABM) - combine node: primary or secondary
HTML version of Basic Foils prepared Dec. 6 98

Foil 43 SDLC and derivatives (4)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
LAP - Link-Access Procedure; LAPB - LAP Balanced
  • HDLC modified by ITU-T (formerly CCITT)
  • subset of HDLC; present in X.25 protocol stack
  • restricted to ABM transfer mode, appropriate for combined stations
IEEE802.2
  • HDLC modified by IEEE; very popular
  • often referred as Logical Link Control (LLC) incorporated in IEEE 802.3, 802.4, 802.5
QLLC - Qualified Logical Link Control
  • defined by IBM: enables SNA data to be transported across X.25 networks
HTML version of Basic Foils prepared Dec. 6 98

Foil 44 X.25 (1)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
ITU-T standard for WAN
typically used in packet switched networks (PSNs) to provide connectivity across public data networks (PDNs)
Devices
  • DTE - data terminal equipment (terminal, hosts)
  • DCE - data circuit terminating equipment (modems, switches)
  • PSE - packet switching exchange (switches)
  • PAD - packet assembler / disassembler (used between DTE and DCE when DTE is too simple to implement X.25 functionality)
HTML version of Basic Foils prepared Dec. 6 98

Foil 45 X.25 (2)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Devices must establish sessions to communicate
A virtual circuit (PVC, SVC) is a logical connection created to ensure reliable communication between two network devices (multiple virtual circuits can be multiplexed)
DTE
DTE
PAD
PAD
X
X
X
X
DCE
DCE
HTML version of Basic Foils prepared Dec. 6 98

Foil 46 X.25 (3)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
X.25 protocol suite
  • maps to the lowest three layers of the OSI RM
  • PLP : Packet Layer Protocol (network layer); PLP modes: call setup, data transfer, idle, call cleaning, restoring
  • LAPB : Link-Access Procedure, Balanced (data-link layer); LAPB use I-frame (information), S-frame (supervision), U-frame (unnumbered)
  • X.21bis, EIA/TIA-232, EIA/TIA-229, EIA-530, G.703 (physical layer)
X.121 addresses are used by X.25 PLP in call-setup mode to establish SVCs
HTML version of Basic Foils prepared Dec. 6 98

Foil 47 X.25 (4)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
X.121 addresses
  • IDN International Data Number (address)
  • DNIC - Data Network Identification Code (optional)
  • NTN - National Terminal Number (variable size)
  • PSN - Packet Switched Network
  • IDN = DNIC (4 digits) + NTN (up to 10 digits)
  • DNIC = Country (3 digits) + PSN (1 digit)
DNIC
NTN
Country
PSN
HTML version of Basic Foils prepared Dec. 6 98

Foil 48 Frame Relay (1)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Developed to address the slowness of X.25 network. FR specification removes flow control and error checking from the intermediate nodes.
FR evolved from X.25 and ISDN. It operates on the first and second layer of OSI Reference Model. The standard proposed in 1984.
Characteristics:
  • line speed: 56Kbps - 1.544 Mbps ---> 36 Mbps ---ᡥ Mbps
  • packet (variable size) oriented, switched communication method,
  • connection-oriented technology based on the leased point-to-point circuits (PVC - Permanent Virtual Channel)
  • not intended for time-sensitive applications due to its variable-length frames
HTML version of Basic Foils prepared Dec. 6 98

Foil 49 Frame Relay (2)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Hardware:
  • FRED - Frame Relay Assembler / Disassembler
  • FRND - Frame Relay Network Device (Node)
Frame Relay Forum supported by Cisco, DEC, Northern Telecom, StrataCom
Public network offering available from most public Carriers: AT&T, MCI, Sprint, RBOCs (RBOC=Regional Bell Operating Company)
HTML version of Basic Foils prepared Dec. 6 98

Foil 50 Frame Relay (3)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Frame Relay vs. ATM
both offer QoS
both connection-oriented technologies
FR top bandwidth - 45 Mbps
ATM lowest bandwidth -25 Mbps
FR: variable size packets; ATM : fixed length cells;
FR addresses E.164 and X.121 specifications
ATM addresses E.164, ICD, DCC
FRF.5 spec (network internetworking)
  • (FR)--X--(ATM)--X--(FR)
FRF.8 spec (service internetworking)
  • (FR)--X--(ATM)
HTML version of Basic Foils prepared Dec. 6 98

Foil 51 SMDS - Switched Multi-megabit Data Services (1)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
SMDS service allows to interconnect LANs in a citywide area. It is full service, not just technology. SMDS exists for several years
Characteristics
  • Fixed-size cell relay technology: cell size 53 Bytes
  • A cell is called "SMDS SIP Layer 2 PDU"
  • Packet size: up to 9,188 Bytes (split into 53 B cells)
  • Switching technology
  • Connection-less service (no wait for end-to-end connection)
  • Error checking and flow control done by end-nodes.
  • Transmission rates: 4, 10, 16, 25 and 34 Mbps
  • Multicast addressing is supported
  • LAN-to-LAN connection at high speeds and low delay
HTML version of Basic Foils prepared Dec. 6 98

Foil 52 SMDS - Switched Multi-megabit Data Services (2)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Media: SONET, DS-3, DS-1
Topology: physically star configured network with dual bus design
Limitations: up to 512 nodes on the bus;bus length: up to 160 km
Connection to SMDS network:
  • LAN---Bridge/Router---CSU---(T1/T3)---SMDS network
Main competitors: Frame Relay and ATM
OSI Reference Model
  • SMDS service defines 3 layers (SIPs = SMDS Interface Protocols)
  • physical, data link and network layers
SMDS is compatible with:
  • IEEE 802.6 Metropolitan Area Network, and Broadband ISDN
  • DQDB - Distributed Queue Dual Bus ; used as the interface and access method for the network
HTML version of Basic Foils prepared Dec. 6 98

Foil 53 SMDS - Switched Multi-megabit Data Services (3)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
SMDS vs. ATM:
  • ATM is one of technologies
  • SMDS is a service which can be provided by ATM, Frame Relay or can be offered without ATM.
  • SMDS is the first ATM service. It offers most of the same advantages as ATM
  • SMDS is data-only solution; adding time-sensitive application (audio, video) support can be relatively easy
  • SMDS and ATM cells are similar, but not quite the the same. Headers (5 bytes for ATM, 7 bytes for SMDS) must be translated
  • SMDS: connection-less; ATM: connection oriented
HTML version of Basic Foils prepared Dec. 6 98

Foil 54 ATM technology (1)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Fundamentals: ATM stands for Asynchronous Transfer Mode.ATM technology is viable for both local (LANs) and wide (WANs) area networks. It supports many types of traffic including voice, data, facsimile, real-time video, CD-quality audio, and imaging. ATM offers bandwidth of up to 155Mbps (and now 622 Mbps or 2.4 Gbps between switches) on the backbone and delivery pipes of 25 Mbps or more to the desktop. ATM is a transport protocol that operates roughly at the MAC sub-layer of the Data Link Layer (OSI)
HTML version of Basic Foils prepared Dec. 6 98

Foil 55 ATM technology (2)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Characteristics:
fixed size packets (cells) - 53 bytes
switching technology
high, scalable bandwidth
ability to dedicate a certain bandwidth to an application (QoS - Quality of Service)
can handle real-time applications
broadband technology (for voice, video, and data)
viable for LANs and WANs
still the most expensive service
ATM network consists of ATM switches
wireless ATM (28 GHz range), SMDS over ATM, Frame Relay over ATM
HTML version of Basic Foils prepared Dec. 6 98

Foil 56 ATM technology (3)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
HTML version of Basic Foils prepared Dec. 6 98

Foil 57 ATM technology (4)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
ATM switch simply relays cells. It looks at the header and immediately begins forwarding the cell. Because all the cells are the same size, the delay is minimal. ATM switch performs its switching in hardware.No error checking is done. ATM assumes the use of high-quality, error free transmission facilities.
ATM Architecture: ATM was originally defined as part of B-ISDN, developed by CCITT in 1988. ATM Forum, created in 1991, has been working on development of ATM standards.
Physical Interface methods
  • UNI - User-to-Network Interface (interface between host and a switch); specifications UNI 3.0, UNI 3.1, UNI 4.0
  • NNI - Network-to-Network Interface (interface between switches)
HTML version of Basic Foils prepared Dec. 6 98

Foil 58 ATM technology (5)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Logical connection between end-stations
  • VC - Virtual Channel
  • VP - Virtual Path (a bundle of VCs)
  • VPI - Virtual Path Identifier - in ATM cell header
  • VCI - Virtual Channel Identifier - in ATM cell header
Permanent vs. Switched Virtual Channels
  • PVC - connections in a connection-oriented network which are established through prior configuration, not dynamically
  • SVC - connections in a connection-oriented network which is established dynamically. SVCs are established by signaling protocols
HTML version of Basic Foils prepared Dec. 6 98

Foil 59 ATM technology (6)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
ATM virtual path switching
HTML version of Basic Foils prepared Dec. 6 98

Foil 60 ATM technology (7)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
ATM architecture model
HTML version of Basic Foils prepared Dec. 6 98

Foil 61 ATM technology (8)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
ATM Physical Layer:
medium:
  • single / multimode fiber with ST, SC, FC connectors
  • Unshielded Twisted Pair (UTP) category 5 with RJ45 connector
physical interface defined by ATM Forum:
  • DS-1 (T1) - 1.5 Mbps
  • ATM25 (TP25) - 25 Mbps
  • DS-3 (T3) - 45 Mbps
  • TAXI (4B/5B) -100 Mbps
  • Fiber Channel -155 Mbps
  • STS-3c/SMT-1 -155 Mbps
  • OC3c (SONET) -155 Mbps
  • OC12c -622 Mbps
  • OC48c -2.48Gbps
HTML version of Basic Foils prepared Dec. 6 98

Foil 62 ATM technology (9)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
SONET / SDH - Synchronous Optical Network / Synchronous Digital Hierarchy
physical layer standard for fiber optic transmissions standardized by ANSI and recommended by CCITT
SONET is the carrier format used in the USA in which OC3c corresponds to a 155 Mbps
SDH is a European carrier system in which STM-1 corresponds to 155 Mbps
ATM and SMDS operates on top of SONET
interface rates: OC1, OC3, OC9, OC12, OC18, OC24, OC36, OC48
  • OC-3c/STM-1 SONET/SDH
  • OC-12c/STM-4c SONET/SDH
fiber based or microwave based (OC3, 6 GHz)
framing STS-3c/STM
HTML version of Basic Foils prepared Dec. 6 98

Foil 63 ATM technology (10)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
ATM Layer defines:
  • the structure of ATM cell: cell 53 bytes (5 + 48)
  • virtual channel and path switching
  • UNI and NNI formats; and error control
ATM Adaptation Layer:
  • converges packets from upper layers into ATM cells
  • AAL types and classes
    • AAL1 - connection-oriented, constant bit rate (CBR), good for audio and video; class A
    • AAL2 - connection-oriented, variable bit rate (VBR), good for compressed video; not implemented; class B
    • AAL3/4 - variable bit rate (VBR), timing not required; class C or D
    • AAL5 - connection-oriented, variable bit rate (VBR), timing not required; subset of AAL3/4; popular implementation; class C
HTML version of Basic Foils prepared Dec. 6 98

Foil 64 ATM technology (11)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
HTML version of Basic Foils prepared Dec. 6 98

Foil 65 ATM technology (12)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
ATM multilayer architecture
HTML version of Basic Foils prepared Dec. 6 98

Foil 66 ATM technology (13)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Quality of Service (QoS) classes and Traffic Classification
  • service class A - CBR Constant Bit Rate
  • service class B - rt-VBR real time Variable Bit Rate
  • service class C - nrt-VBR non real time Variable Bit Rate
  • service class D - ABR Available Bit Rate
  • unspecified - UBR Unspecified Bit Rate
ATM addressing and signaling
  • signaling is necessary to set up SVCs
  • SPANS, Q.93B (UNI3.0), Q.2931 (UNI3.1), UNI4.0
  • addressing: 20 octets
    • E.164- public addressing
    • ICD ATM format
    • DCC ATM format
  • ILMI - Interim Local Management Interface (address registration protocol)
HTML version of Basic Foils prepared Dec. 6 98

Foil 67 ATM technology (14)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Classical IP-Over-ATM (IPOA RFC 1577)
ATM is a connection-oriented protocol, which means that connection must be established between two communicating entities before data transfer can begin. IP is inherently connectionless. There are 2 ways to run transparently IP traffic over ATM: Classical IP and LAN emulation
The term "classical" indicates that the ATM network has the same properties as existing legacy LANs.
SVC management is performed via UNI specification, which defines signaling: Q.93B (UNI3.0), Q.2931 (UNI3.1).
Once a Classical IP connection has been established, IP datagrams are encapsulated using IEEE 802.2 LLC/SNAP and are segmented into ATM cells using AAL5.
There is no support for broadcast and multicast in a Classical IP environment. The Classical network is divided into LISs (Logical IP Subnets).
Each LIS must have only on ATM ARP server configured on a switch or a host ARP server is responsible for resolving an IP addresses into ATM addresses.
HTML version of Basic Foils prepared Dec. 6 98

Foil 68 ATM technology (15)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
LAN Emulation: IP-Over-ATM (IPOA LANE 1.0)
LANE over ATM is the natural path for migrating ethernet and token ring LANs to fault tolerant ATM network. LANE ver1.0 emulates MAC layer ; standard 1996
Applications can run unmodified over an ATM network. LANE works by allowing the OS and all protocols at and above Layer 2 to seamlessly operate with ATM
components: LES, LEC, LECS, BUS
version 1.0 permits only one LES / BUS on an emulated network creating single point of failure
LECS - LAN Emulation Configuration Server contains the configuration of the emulated networks
LES - LAN Emulation Server mapping between MAC addresses and ATM addresses
BUS - Broadcast and Unknown Server handles broadcast and multicast as well as unknown addresses
LEC - LAN Emulation Client runs on every workstation
Emulated LAN operates in client/server environment applying Virtual LAN concept
HTML version of Basic Foils prepared Dec. 6 98

Foil 69 PPT Slide

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
HTML version of Basic Foils prepared Dec. 6 98

Foil 70 ATM technology (17)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
LAN Emulation protocol stack
HTML version of Basic Foils prepared Dec. 6 98

Foil 71 ATM technology (18)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
LANE vs. Classical
HTML version of Basic Foils prepared Dec. 6 98

Foil 72 ATM technology (19)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Voice over ATM (VTOA - Voice and Telephone over ATM)
QoS parameters: delay, jitter in delay, loss rate
CBR for voice current ATM Forum specification
silence detection (voice has 60% of silence)
unstructured circuit emulation: maps entire T1 circuit to a single ATM VC
structured circuit emulation: maps individual 64 Kbps circuits to ATM VCs
Compression: G.726 ADPCM, G.728 LD-CELP, G.729 CS-ACELP
average national network delay for voice traffic specified by G.114, G.131, G.126
current VTOA: lack of compression, lack of silence suppression, limitations of AAL1
HTML version of Basic Foils prepared Dec. 6 98

Foil 73 ATM technology (23)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Other ATM Protocols
MPOA - Multi Protocol Over ATM : layer 3 protocols like IP or IPX can be carried transparently over an ATM network
  • mapping on network layer on ATM network
  • performance, scalability
  • sends routed traffic over connection-oriented circuits
NHRP - Next Hop Reservation Protocol is used for forwarding and ATM address resolution based on classical IP
CIF - Cells in Frames; solution for delivering ATM to the desktop
IISP - Interim Inter-switch Signaling Protocol - uses UNI-based signaling for switch to switch communication
HTML version of Basic Foils prepared Dec. 6 98

Foil 74 ATM technology (24)

From Introduction to Network WANs Lectures at Xi'an Jaotong University -- Sept 1998. *
Full HTML Index
Other ATM Protocols
PNNI - Private Network to Network Interface: the NNI used in private networks for efficient, dynamic, and scalable routing of SVC requests in a multivendor private ATM environment
I-PNNI- Integrated PNNI: is a single routing protocol that is used between IP routers and ATM switches
Hardware: ATM switch, ATM analyzer, ATM adapter
ATM Carrier Services: MCI, WorldCom, Sprint, AT&T, GTE, Pacific Bell, US West, Ameritech, Southwestern Bell, Bell Atlantic. The services are provided by hundreds POPs (Point of Presence)
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