Transcript Communications Services

Communications Services
What are the services that
companies buy from
communications carriers?
1. Private (or leased)
What are the services
companies offer?
4. SONET
2. Measured
3. Special Services
5. ISDN
6. SMDS,
7. Frame Relay
8. MLPS
9. ATM
10. ADSL
11. VPNs.
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Overview
Source: Held, Wiley
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Digital Leased Lines
T-1 Frame Layout
T-1 Transmission Service
(1.544 Mbps)
Channel 1
(8 bits)
Channel 2
(8 bits)
Channel 3
(8 bits)
1 0 0 0 0 0 0 1 1 1 1 1 1 0 0 1 1 0 1 1 1 0 0 0
bits
Frame
(193 bits)
Channel 24
(8 bits)
1 0 0 1 1 0 1 0
Framing bit marks the end
of this 24-channel frame
24 channels/frame · 8 bits/channel
= 192 data bits/frame
192 data bits + 1 framing bit
= 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
GOLDMAN: DATACOMM
FIG. 08-17
T1 channels 6 to 30 times more cost effective than voice grade lines.
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Kai Larsen:
for International
Telecommunication
Union, Standards
an intergovernmental
Digital Short
Service
Hierarchy
and CCITT
organization through which public and private organizations develop
telecommunications.
The ITU was founded in 1865 and became a United
Digital service
(DS) hierarchy.
Nations agency in 1947. It is responsible for adopting international treaties,
Digital
Service andNumber
of Voice
Transmission
Rate
Corresponding
regulations
standards
governing
telecommunications.
The standardization
Level
Channels
Transmission Service
functions were formerly performed by a group within the ITU called CCITT, but
after
the CCITT
longer exists
a separate
body
DS-0a 1992 reorganization
1
64 no
Kbps
DS-0 or as
switched
64K
(Source:
Webopia.internet.com)
DS-1
24
1.544 Mbps
T-1 or switched T-1
DS-1C
48
3.152 Mbps
T-1C
DS-2
96
6.312 Mbps
T-2
DS-3
672
44.736 Mbps
T-3
DS-4
4032
274.176 Mbps
T-4
CCITT digital hierarchy – CCITT is now known as International Telecommunications Union (ITU)
Digital Service
Level
Number of Voice
Channels
Transmission Rate
1
30
2.048 Mbps
E-1
2
120
8.448 Mbps
E-2
3
480
34.368 Mbps
E-3
4
1920
139.264 Mbps
E-4
5
7680
565.148 Mbps
E-5
GOLDMAN: DATACOMM
FIG. 08-19
Corresponding
Transmission Service
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Other types of Leased Lines Options
Fractional 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 Dial
2. 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
Greeley
Customers
Leased Line
Denver
Business
Office
• Customers dial a local number in Longmont
and incur the cost of a local call.
• Both incoming and outgoing calls are handled
2. Hotline
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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 Mbps
OC-3
155.52 Mbps
OC-12
620.08 Mbps
OC-24
1244.16 Mbps.
…
OC-255
…
13.21 Gbps
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ISDN - It Still Does Nothing!
(Integrated
Objective:
Services Digital Network)
1) Integrate data, voice, video Transmission on single
high-speed network (single plug in the wall!)
2) Develop International standards for such
communication
2B+D
64K bps "data"
Channel
16K bps "control" channel
1. "Intelligence"
2. Ability to detect nature
of terminals and provide
desired service
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Switched Network Services Hierarchy
Switching
Circuit switching
Leased lines
Dial-up circuits
Packet switching
Original packet switching
X.25
Fast packet switching
Frame relay
Cell relay
GOLDMAN: DATACOMM
FIG. 08-27
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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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Comparing Leased line versus Frame Relay Networks
Leased line network
Frame Relay network
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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)
Local Carrier Central Office
HOME
Central Office
voice switch
10baseT
ethernet NIC
up to 640 Kbps
POTS
ADSL
modem
Central Office
data switch
PSTN
up to 6 Mbps
Rack mounted
ADSL modems
analog
phone
Internet
GOLDMAN: DATACOMM
FIG. 08-15
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
• All data packets are encrypted by the security gateways.
• The VPN creates a tunnel between the two end-points.
Source: Kosier, Wiley.
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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.
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