Long Distance Connection and WAN

Long Distance Connection and WAN

• Digital Telephone, PCM and Nyquist Sampling Theorem

• DSU/CSU, T Line Series and OC line Series• Local Loop• DSL Technologies - ADSL, HDSL, SDSL, VDSL• Cable Modem• WAN and Packet Switch• Switch Addressing and Routing• Typical WANs - ARPANET, X.25, Frame Rely, SMDS, ATM• Wireless WANs, Cellular Networks

• Digital Telephone, PCM and Nyquist Sampling Theorem

• DSU/CSU, T Line Series and OC line Series• Local Loop• DSL Technologies - ADSL, HDSL, SDSL, VDSL• Cable Modem• WAN and Packet Switch• Switch Addressing and Routing• Typical WANs - ARPANET, X.25, Frame Rely, SMDS, ATM• Wireless WANs, Cellular Networks

Lecture 6

Lecture 6

Long Distance Telephone Network and OthersLong Distance Telephone Network and Others

- A single LAN can’t handle an arbitrary number of computers - A LAN is usually owned by a company, organization, university, …, which can’t build their own long distance links to connect computers in arbitrary sites- Telephone and other companies offer long distance connections which can be leased to build large computer networks covered many distance sites

Circuit Switch Analogy Network

Circuit Switch Digital Network

Packet Switch Digital Network

CATV/Power Network

Satellite Network. . .

Telephone Company

Other Company

CompLAN

Convert

AD/DAModem

Modem

Modem

Convert

Modem

Modem

Modem

AD/DA

CompLAN

Lecture 6

Digital Telephone Network and PCMDigital Telephone Network and PCM

Analogy telephone network: transfers analogy voice signal in the frequency range [0, 3.5KHz]Digital telephone network: transfers digital voice signalPCM (Pulse Code Modulation): a standard of conversion from analogy voice to digital voice - Analogy signal is first sampled in sampling interval T or with sampling frequency F=1/T - Nyquist sampling theorem: Original analogy signal can be reconstructed from a sequence of sampled values if F>2B where B is the maximum signal frequency - Sampling frequency of digital voice = 8 KHz - Each sampled value is quantized to an integer in [-127, 127] - Encoding the integer to an 8-bit binary value, PCM hardware is a analogy-to-digital (AD) device - Bit rate of one digital voice channel: 8KHz x 8 bits = 64 Kbps

TF=1/T, sampling frequencyT, sampling interval

00000000

0000011000000111

00000100

00000101

00000001

00000011

00000010

F<2B

F=2B

F>2B

Nyquist Rate

Lecture 6

DSU/CSUDSU/CSU

- Computer industry and telephone industry use own standards in different encoding- DSU/CSU perform the conversion between two standards- DSU (Data Service Unit): Translations between two encoding- CSU (Channel Service Unit): management of line termination and diagnose

DSU/CSU Gateway

http://en.wikipedia.org/wiki/Gateway_(telecommunications)

Lecture 6

Digital Telephone Line StandardDigital Telephone Line Standard

Japan

- Specified by the telephone industry in each country, different from the world- Fractional T1= 64, 9.6 or 4.8Kbps, use multiple fractional T1 with multiplxier- Can be leased in two points- Three campus networks in Hosei University are connected by T1 (before 2001)

Ichigaya

JapanJapan

Koganei Tama

T1

T1

T1

T2

To outside

Lecture 6

High Capacity Digital LinesHigh Capacity Digital Lines

- Use both electrical signal and optical signal- Electrical standard called Synchronous Transport Signal (STS)- Optical standard called Optical Carrier (OC)- Engineers usually use OC- terminology for everything- OC-3 is popular- OC-3: three OC-1 lines, OC-3C: a single line operating at 155.520 Mbps

Synchronous Optical Networking

Lecture 6

Local Loop: Analogy Line, ISDN and DSLLocal Loop: Analogy Line, ISDN and DSL

Analogy line: - Analogy signal (300~3300Hz), modem needed, low speed (34/56Kbps)ISDN (Integrated Services Digital Network): - BRI (Basic Rate Interface) = 2B+D, B=64Kbps for data, D=16Kbps for control - PRI (Primary Rate Interface)=23B+64D=1.544Mbps=T1 - called Narrowband ISDN (N-ISDN), relatively slow - B-ISDN (Broadband ISDN), 155 or 622 Mbps to each subscriberxDSL (Digital Subscriber Line) - use existing telephone line to provide high speed transmission, current technology

LocalCentralOffice( CO )

Telephone network

Analogy line

ISDN line

DSL lineSubscribers

Local Loop

Lecture 6

xDSL TechnologyxDSL Technology

xDSL is a family of technologies to use existing analogy telephone line (copper pair) for delivery of high-speed data between a subscriber and telephone central office.

Local Central Office (CO)

Phone Computer

Spectrum of copper pair

f (KHz)

f (KHz)

0

0

20 25 Fa Fb Fc Downstream Upstream

Analogy phone DSL

Telephone Network

xDSL ADSL HDSL SDSL VDSLBit rate 32K~3M Up 1.5M 1.5M 1.5~2.3M Up 32K~40M Down 1.5M 1.5M 13~52M Down Mode Asymmetric Symmetric Symm Asym wire 1 pair 2 pairs 1 pair 1 pairLength 3.7~5.5km 3.7km 3.0km 1.4km

xDSL family ADSL: Asymmetric Digital Subscriber Line HDSL: High-rate Digital Subscriber Line SDSL: Symmetric Digital Subscriber Line VDSL: Very high bite rate Digital Subscriber Line

FDM – Frequency Division Multiplexing Frequency range (<20KHz) for analogy phone Frequency range (>25Kz) for data transmissionLocal line quality Low frequency is better than high frequency Characteristic of each line is different from others

More and latest at Digital Subscriber Line (DSL):http://en.wikipedia.org/wiki/Digital_subscriber_line

Lecture 6

ADSLADSL

- Concurrent and independent uses of analogy phone and data transmission- Upstream ~few Mbps, Downstream ~tenths M, suited for accessing Internet

0 20 25 200 250 1M Downstream Upstream

Analogyphone

… … … f (KHz)

DMT (Discrete MultiTone) by ANSI - FDM and QAM modulation - 31 channels (carriers) for upstream - 255 channels (carriers) for downstream

Spectrum of copper pair

f (KHz) 0

ADSL2/2+, VDSL2, etc. http://en.wikipedia.org/wiki/Asymmetric_Digital_Subscriber_Line_2

Lecture 6

Cable Modem Technology Cable Modem Technology

Cable TV already brings high bandwidth coax into houses

Conventional Cable TV is one direction - Signal broadcast at central location - Amplifiers boost signal through network - Amplifiers are unidirectional

Solutions: - Alternate upstream path - e.g., dialup - Replaced by bi-directional amplifiers

Cable modems encode and decode data from cable TV coax - One in cable TV center connects to network - One in home connects to computer

Users share the cable - Each subscriber is assigned an address - TDM is used like multiple computers in LAN

f (MHz)… TV TV

Upstream Downstream (shared by multiple users)

…

CATV Center

AmplifierM

MM

- Cable Modem

Lecture 6

Cable Modem Connections Cable Modem Connections

Hybrid Fibre-Coaxial (HFC)

Cable Modem Connections

Cable Modem Connections

Lecture 6

Lecture 6

FTTX - Fiber To The XFTTX - Fiber To The X

Fiber to the x

Lecture 6

WAN and SwitchWAN and Switch

WAN – Wide Area Network: A network that can span a large geographic area, e.g., multiple cities, countries or continents.WAN building blocks: (1) Long-distance connection (e.g., T1/T3 lines, OC1/OC3 lines, etc.) (2) Packet switch - A hardware device connected to other switches and computers - Has CPU, memory, I/O interface, etc. - Handles packet

Frame Data or PayloadHeader

Trailer

Dest Addr

Sour Addr

Packet

WAN, Wiki

Lecture 6

Illustration of A WANIllustration of A WAN

- Place one or more switches at each site- Interconnect switches: LAN technology for local connections Leased digital lines for long distance connections- Interconnections depend on traffic amount and reliability requirement- Packet is sent from source, travels switch-to-switch, and delivered to destination- Switch stores packet in memory, examines address, and forwards it toward destination

Animation

Leased Line

Lecture 6

Addressing in WANAddressing in WAN

- Each computer has a unique address- It is a two-part hierarchical address including 2 integers: [Integer1, Integer2]

Integer1 for switch number Integer2 for computer number

Lecture 6

Next-Hop Forwarding and Routing TableNext-Hop Forwarding and Routing Table

- Packet switch must choose outgoing connection for forwarding If destination is local computer, packet switch delivers computer port If destination is attached another switch, this packet switch forwards to next hop through connection to another switch - Packet switch doesn't keep complete information about all possible destination - A routing table just keeps next hop - For each packet, packet switch looks up destination in its routing table and forwards through connection to next hop- Next hop to destination does not depend on source of packet - Called source independence

Routing table of switch 2

Lecture 6

Routing Table and Graph Routing Table and Graph

- Each switch or node has a routing table: Left entry right entry destination switch edge number pair- Default route can remove duplicate routes, reduce memory and improve performance

Graph: Node models switch Edge models connection

Routing tableswithout default routes

Routing tableswith default routes

Lecture 6

Routing Table ComputationRouting Table Computation

- Static routing table: fixed in switch booting and does not change- Dynamic routing table: initialized in booting and alters as conditions in the network change

Shortest path computation: - Label on edge represents “distance” - Possible distance metric: geographic distance, economic cost, capacity, etc - “Shortest” means the minimum sum of distances in all paths between two nodes - Darkened path is minimum from node 4 to node 5

Algorithms for computing shortest paths - Dijkstra’s algorithm - Distance Vector (DV) algorithm

Dijkstra's algorithm

Distance Vector Routing

Lecture 6

History of WAN TechnologiesHistory of WAN Technologies

ARPANET - The first WAN, began in 1960s, low speed: 56Kbps - Funded by Advanced Research Projects Agency, an organization of US Defense Department - Incubator for many of current ideas, algorithms and internet technologies X.25 - Early standard for connection-oriented networking from ITU, which was originally CCITT - Early commercial service, more popular in Europe - Predates computer connections, used for terminal/timesharing connection Frame Relay - Telco service for delivering blocks of data - Connection-based service; - Typically 56Kbps or 1.5Mbps; can run to 100Mbps -SMDS - Switched Multi-megabit Data Service - Connectionless service; any SMDS station can send a frame to any other station - Typically 1.5-100Mbps ATM - Asynchronous Transfer Mode - Designed as single technology for voice, video, data, ... - Low jitter (variance in delivery time) and high capacity - Uses fixed size, small cells - 48 bytes data, 5 bytes header - Can connect multiple ATM switches into a network - Potential in future B-ISDN - Can be worked as a LAN

• Wireless LANs• Wireless WANs• Satellite Networks• Cellular Networks

TAXI

Region

Campus

City

In-Building

laptops, PDAs

Lecture 6

Wireless NetworksWireless Networks

BS: Base Station

BS BSBS

BS

BS BS

BS BS

F: Carrier Frequency

Lecture 6

Cellular Wireless NetworksCellular Wireless Networks

• Geographic region divided into cells• Frequencies/timeslots/codes reused at spatially-separated

locations.• Co-channel interference between same color cells.

Cllular Network: http://en.wikipedia.org/wiki/Cellular_network

Lecture 6

Cellular Phone NetworksCellular Phone Networks

Lecture 6

Handoff in Cellular NetworksHandoff in Cellular Networks

• Base stations/main stations coordinate handoff and control functions• Shrinking cell size increases capacity, as well as networking burden

Lecture 6

4 Generations of Data Communications4 Generations of Data Communications

Lecture 6

Data Transmission SpeedsData Transmission Speeds

4G WWAN: http://en.wikipedia.org/wiki/4G

Exercise 6Exercise 6

1. For an analogy TV signal, its frequency range is in [0, 6MHz]. To transmit the TV signal across a digital network, it is necessary to convert the analogy signal to a digital TV signal. What is the minimum sampling frequency in such conversion? Suppose that every sample will be encoded into 16 bits binary value (this is called TV PCM coding). Calculate bit rate of the digital TV signal after PCM coding.

2. Summarize the features and performance of typical long-distance connection technologies including T and OC series services, conventional modem, ISDN, xDSL and Cable modem.

3. Explain why bit rates of the upstream and the downstream in ADSL are not fixed?

4. In a packet switch network, the address of each computer consists two parts: one identifies a switch and other identifies a computer attached to that switch. Why?

5. Suppose that a packet switch network with a five nodes is given below. Give a routing table for each of the five nodes.

2

1 4

3

5