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Communications Services

1. Private (or leased)

2. Measured

3. Special Services

4. SONET

5. ISDN

6. SMDS,

7. Frame Relay

8. MLPS

9. ATM

10. ADSL

11. VPNs.

1. Private (or leased)

2. Measured

3. Special Services

4. SONET

5. ISDN

6. SMDS,

7. Frame Relay

8. MLPS

9. ATM

10. ADSL

11. VPNs.

What are the services that companies buy from communications carriers?

What are the services companies offer?

What are the services that companies buy from communications carriers?

What are the services companies offer?

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Overview

Source: Held, Wiley

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T-1 Frame Layout

GOLDMAN: DATACOMM FIG. 08-17

1 0 0 0 0 0 0 1 1 1 1 1 1 0 0 1 1 0 1 1 1 0 0 0 1 0 0 1 1 0 1 0

Channel 1 (8 bits)

Channel 2 (8 bits)

Channel 3 (8 bits)

Channel 24 (8 bits)

Frame (193 bits)

T-1 Transmission Service (1.544 Mbps)

bits Framing bit marks the end of this 24-channel frame

24 channels/frame · 8 bits/channel

192 data bits + 1 framing bit

= 192 data bits/frame

= 193 total bits/frame

193 bits/frame · 8,000 frames/second sampling rate= 1,544,000 bits/second

= 1.544 Mbps

= DS-1

= T-1

Digital Leased Lines

T1 channels 6 to 30 times more cost effective than voice grade lines.

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Digital Service Hierarchy and CCITT Standards

GOLDMAN: DATACOMM FIG. 08-19

Digital Service Level

Number of Voice Channels

Transmission Rate Corresponding Transmission Service

DS-0

DS-1

DS-1C

DS-2

DS-3

DS-4

1

24

48

96

672

4032

64

1.544

3.152

6.312

44.736

274.176

Kbps

Mbps

Mbps

Mbps

Mbps

Mbps

DS-0 or switched 64K

T-1 or switched T-1

T-1C

T-2

T-3

T-4

Digital service (DS) hierarchy.

Digital Service Level

Number of Voice Channels

Transmission Rate Corresponding Transmission Service

1

2

3

4

5

30

120

480

1920

7680

2.048

8.448

34.368

139.264

565.148

Mbps

Mbps

Mbps

Mbps

Mbps

E-1

E-2

E-3

E-4

E-5

CCITT digital hierarchy – CCITT is now known as International Telecommunications Union (ITU)

Kai Larsen:

Short for International Telecommunication Union, an intergovernmental organization through which public and private organizations develop telecommunications. The ITU was founded in 1865 and became a United Nations agency in 1947. It is responsible for adopting international treaties, regulations and standards governing telecommunications. The standardization functions were formerly performed by a group within the ITU called CCITT, but after a 1992 reorganization the CCITT no longer exists as a separate body (Source: Webopia.internet.com)

Kai Larsen:

Short for International Telecommunication Union, an intergovernmental organization through which public and private organizations develop telecommunications. The ITU was founded in 1865 and became a United Nations agency in 1947. It is responsible for adopting international treaties, regulations and standards governing telecommunications. The standardization functions were formerly performed by a group within the ITU called CCITT, but after a 1992 reorganization the CCITT no longer exists as a separate body (Source: Webopia.internet.com)

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Other types of Leased Lines OptionsFractional T-1: At speeds of 128K, 256K,512K, etc.

AT &T Accunet T1.5 Service: Full-duplex private line service that transmits digital signals at 1.544 Mbps.

(Primarily for large volume users for data, voice and fax transmissions)

AT&T Accunet T45 services: 45Mbps digital transmission over dedicated lines.

(Provides broadcast quality television and data transmission. Can also be used for videoconferencing, image and electronic document transmission, etc.)

International Accunet Digital Services: transmit overseas at various speeds such as 64K, 1.544M, 2.048 Mbps.

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Measured Rate Services

1. Direct Distance Dial2. WATS (Wide Area Telephone Service)

• Inward WATS (800,888, 877, 866 service)

• Outward WATS

• 6 Geographical Zones

• Flat Fee based on usage hours

3. A multitude of other 800 services• (see hidden page)

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Measured Rate Services (contd.)

4. 900 Numbers

•Can handle up to 7000 simultaneous calls.

• Caller is usually charged for these calls

• Used for providing Services and dis(services)!

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Special Services

1. Foreign Exchange

• Leased Line from one exchange to another

Customers BusinessOffice

DenverLeased Line

• Customers dial a local number in Longmont and incur the cost of a local call.

• Both incoming and outgoing calls are handled

2. Hotline

Greeley

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SONET(Sychronous Optical NETwork)

• Provides a reliable physical transport mechanism for ATM and Frame Relay.

• Runs over optical fiber medium.• Configured as self-healing ring for high reliability.• Synchronous system.• Based on multiplexing low-speed streams into higher speed.• Basic frame: 810 bytes every 125 sec., i.e. 51.84 Mbps.• Data Rate options:

OC-1 51.84 MbpsOC-3 155.52 MbpsOC-12 620.08 MbpsOC-24 1244.16 Mbps.

… …

OC-255 13.21 Gbps

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ISDN - It Still Does Nothing!

(Integrated Services Digital Network)

Objective:

1) Integrate data, voice, video Transmission on single high-speed network (single plug in the wall!)

2) Develop International standards for such communication

2 B + D

64K bps "data"Channel

16K bps "control" channel1. "Intelligence"2. Ability to detect nature of terminals and provide desired service

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Switched Network Services Hierarchy

GOLDMAN: DATACOMM FIG. 08-27

X.25 Frame relay Cell relay

Fast packet switchingOriginal packet switching

Packet switchingCircuit switching

Leased lines Dial-up circuits

Switching

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Switched Megabit Data Service (SMDS)• First high-speed switched service offered to public.

• Developed at Bellcore in 80's and deployed in early 90's. Simple, connectionless packet delivery service.

• Designed to connect together multiple LANs and for bursty traffic. Also, has broadcasting feature.

• Excellent low-cost high-speed networking for distributed offices that need occasional remote connections (as an alternative to leased lines).

• Allows high speed links up to 45 Mbps and more at much lower costs compared to T-carrier services.

• Suitable for low volume high-speed traffic such as transmission of images, CAD/CAM, etc.

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Frame Relay

• High-speed successor to X.25. • Private, fast-packet based data service -- low delay.• Bare-bones, minimal, connection-oriented way to move bits.• Supports speeds from 56Kbps to 1.544Mbps• Operates in packet mode using PVCs (Permanent

Virtual Circuits)• Provides dedicated port access from your location to

network• Guarantees Committed Information Rate but allows higher

burst rate if bandwidth is available. • User benefits: flexible bandwidth allocation, high

throughput, cost effective.Available widely and has become very popular.

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Multiprotocol Label Switching(MPLS)• Versatile solution to provide:

•Speed•Scalability•Quality of Service

• Can exist on top of existing ATM and Frame Relay network• Integrates Layer 2 information about network links (bandwidth

, latency, utilization) into Layer 3 (IP) within a particular autonomous system--or ISP--in order to simplify and improve IP-packet exchange (from Webopedia with links to Webopedia).

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Leased line network Frame Relay network

Comparing Leased line versus Frame Relay Networks

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ATM(Asynchronous Transfer mode or cell

relay)• Based on 53-byte cells (48 bytes data + 5 bytes overhead)

• Designed for integrating voice, data, video.• Gives quality of service (QOS) guarantees.• All cells follow the same route.• No error checking at data link layer.• No delay in routing and no sequencing problem.• ATM switches are very high speed (Gigabit speeds).• Traffic classes or service categories:

- Constant bit rate traffic (CBR)- Variable bit rate traffic (VBR)- Available bit rate traffic (ABR)- Unspecified bit rate traffic (UBR)

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ADSL Technology Implementation(Asymmetric Digital Subscriber Line)

GOLDMAN: DATACOMM FIG. 08-15

Central Office voice switch

Central Office data switch

Rack mounted ADSL modems

PSTN

analog phone

ADSL modem

10baseT ethernet NIC

up to 6 Mbps

up to 640 Kbps

POTS

HOME

Local Carrier Central Office

Internet

Source: Goldman, Wiley Publishers

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Virtual Private Networks (VPN)

Inexpensive way for remote offices, telecommuters, business partners to connect to one another over the open, distributed infrastructure of the Internet by means of virtual circuits. There are no permanent links.

Companies using an Internet VPN connect to the POP’s of their ISP’s who provide the rest of the connectivity.

Special software provides an encrypted tunnel for secure communications.

Considerable time, cost and space savings.

Integrated VPN hardware box for tunneling, encryption, authentication, filtering and key management.

Several software products: e.g., Altavista Tunnel 98, BorderManager, RRAS/NT Server, SmartGate, etc.

This technology is becoming popular very rapidly.

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VPN and Tunneling

Source: Kosier, Wiley.

• All data packets are encrypted by the security gateways.• The VPN creates a tunnel between the two end-points.

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Summary• Understanding of available services is critical for

network managers. • New services are appearing every day.• Existing services are becoming faster and cheaper.• Often need to mix and match various services.• Need to evaluate services carefully according to

goals and requirements and select the right one.• This is the objective of network design, our next

topic.