Wide Area Connectivity Options in Pakistan

Transcription

Evaluation of Wireless Local Loop and
Page 1 of 17
Wide Area Connectivity Options in Pakistan
A Survey By:
Abid Raza Khan
Ahmad Zaka-ur-Rehman
Ateeq Zaman Khan
Table of Contents
1 – Introduction
2
2 – Connectivity Requirements
3
3 – Security Issues
3
4 – Connectivity Options
4
4.1 – Dial-up Modem / Dial-up Internet
4
4.2 – ISDN
4
4.3 – xDSL
5
4.4 – Fiber Optic
7
4.5 – Cable Modem
7
4.6 – Wireless Technologies
8
4.6.1 – Radio Modem
8
4.6.2 – WLL
9
4.6.3 – Wireless LAN 802.11b
4.7 – Free Space Optics
4.8 – VSAT
10
Infrared Laser
11
12
5 – Technology & Cost Comparison
13
6 – Recommendations
14
7 – Exhibits
15
8 – References
17
file://C:\Documents and Settings\saqibr\Desktop\2003 Projects\group01_f.html
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1 – INTRODUCTION
With the Deregulation of the Telecommunication Industry in Pakistan on 31st December 2002, the connectivity
options have increased dramatically because of private investment in various emerging technologies. This study
intends to provide an unbiased technological and cost benefit analysis of various connectivity solutions. Because
of the continuous evolution of the communication sector, an exhaustive analysis of all possible technologies is
near to impossible, therefore we will focus on the most feasible and practical solutions for Pakistan.
This report is useful for organizations with geographically dispersed units throughout Pakistan wanting to
establish a secure network between their multiple sites. Businesses wanting to invest in the fast growing
communication sector in Pakistan can also use this report as a starting point. Our objective is to provide the reader
with an insight into the following:
-
Provide an understanding of each technology and its hardware requirements.
Analyze their pros and cons.
Present a cost / benefit analysis of these technologies.
Derive a comprehensive plan about which solution should be used for which scenario.
The basic choice that one has to make is to either establish one’s own indigenous network or to subscribe to an
already established network of an Internet Service Provider (ISP) or Pakistan Telecommunication Company
Limited (PTCL). Of course, most organizations would eventually have a mix of the two. We have categorized
technologies into the independent and established options based on the required investment. For technologies
which can be implemented with little investment, organizations may establish their own indigenous network.
[1]
can only be provided by the backbone internet
However, those technologies that require massive investment
providers and are considered to be the established options. In this case, the options elaborated are those which
allow the client nodes to connect to the backbone established network. The backbone communication
infrastructure of Pakistan (Exhibit 1) is fiber optic based and it is controlled by Pakistan Internet Exchange (a
subsidiary of PTCL). However, other ISP’s have established regional networks spanning various cities.
1.1 - Independent Network Options
1.
2.
3.
4.
Dial-up Modem
Radio Modem
Wireless 802.11b (Point to multi-point with long range antennas)
Free Space Optics (FSO) Infrared Laser
1.2 - Established Network Options
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Dial-up Internet
ISDN (Integrated Services Digital Network)
xDSL (Digital Subscriber Line)
Fiber Optic
Cable Modem
Radio Modem
WLL (Wireless Local Loop)
Wireless 802.11b (multiple hot spots throughout the city)
Free Space Optics (FSO) Infrared Laser
VSAT
2 – CONNECTIVITY REQUIREMENTS
[2]
The connectivity requirements of organizations will dictate the required communication bandwidth
and
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reliability of the required connection. Transmission requirements can generally be classified as:
z
z
z
Data Transfer
Audio Conferencing
Video Conferencing.
Data transfer requirements depend upon the application destined to use the network, such as Distributed
Databases and E-Commerce. Each application has its own bandwidth and reliability requirements. Audio and
[3]
Video communications which have real-time traffic require a specific Quality of Service (QoS) to ensure that
the communication is understandable. Video Conferencing, even in compressed form, has very high bandwidth
requirements. Some backbone providers might restrict delivery of Audio / Video packets because of their high
[4]
bandwidth requirements. Generally Voice-over-IP
and Video-over-IP can be implemented with most of the
technologies unless the backbone provider specifically disallows them.
3 – SECURITY ISSUES
Security is an issue both in the independent network (especially the wireless options) and the established network.
Security can be implemented on an end-to-end basis by establishing a Virtual Private Network (VPN), which is a
private network that is implemented over a public network. Data is transferred across the network using tunneling
techniques that create virtual paths between various nodes. There are multiple techniques for developing a VPN
which can be classified as:
3.3.1 -   Tunneling: VPN uses a tunneling protocol that establishes a "tunnel" or path through the Internet or
other public network to allow the transfer of data between network nodes. Among the primary protocols used for
VPN tunneling is Point-to-Point Tunneling Protocol (PPTP) and Layer 2 Tunneling Protocol (L2TP).
3.3.2 -   Encryption: Since VPN traffic travels over a public network, encryption technology is required to
provide security for confidential and proprietary data. Encryption is done using a secret-key which is required at
the far end to decrypt the data. The most common secret-key cryptography scheme used today is the Data
Encryption Standard (DES) [[1]], designed by IBM in the 1970s, which uses a 56-bit key that operates on 64-bit
blocks. However, there are various available cryptography algorithms using keys of 64 to 1024 bits.
3.3.3 -   Authentication and Access Control: Because thousands of users may be sharing the network utilized by a
VPN, it is imperative to utilize a robust authentication and access control system to keep unwanted users from
entering the VPN. Some VPN solutions utilize simple password authentication, while more sophisticated methods
use key exchange systems like Diffie-Hellman key exchange.
VPN solutions may be hardware based (incorporated in routers) or Software-based (Client-to-LAN VPN
[5]
are required to
applications usually part of Operating Systems). More often than not, Static IP addresses
establish a VPN. Although all technologies can be used to establish a VPN, some backbone service providers do
not give static IP addresses or they may charge extra for static IP’s.
4 - CONNECTIVITY OPTIONS
4.1 – Dial-Up Modem / Dial-Up Internet
Dial-up modems utilize traditional copper wired Public Switched Telephone Network (PSTN) to transmit analog
signals in the 0 – 3,400 Hz frequency range. Out of all types of modems (dial-up, ISDN, DSL, cable) dial-up
connections offer the slowest transmission speeds. Connectivity is achieved by dialing to a network via a modem
using the PSTN. Dial-up access is just like a phone connection, except that the parties at the two ends are
computing devices. Because dial-up access uses normal telephone lines, the quality of the connection is not
always good and data rates are limited. The maximum data rate with dial-up access is 56 Kbps using V90
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Modems.
An organization can develop an independent
network by attaching their corporate server to a
modem pool. All the client nodes can then dial
up to this modem pool and a corporate network
is established. However, there will be repeat call
charges every 5 minutes since PTCL does not
allow non-repeat call numbers such as 131 to
non-ISP businesses. In the case of Dial-up
Internet, all the sites link to the Internet using
any ISP, however they must subscribe to static
IP addresses if they want to establish a VPN.
Internet
ISP server/Corporate Server
Modem Pool
PSTN
Pros and Cons
Dial-up Modem
Advantages include low initial cost asNode
thewithexisting
PSTN is utilized. Since the PSTN is spread throughout
Pakistan, any place which has a sizable population can be reached. Initial hardware cost is very low since only a
modem costing Rs 1,500 is required at each line. Recurring cost for Dial-up Internet has dramatically reduced
recently and a 24 Hour Internet connection now costs only Rs 1,000 per Month. The recurring cost of a Dial-up
Corporate Network is however very high since telephone calls are charged repeatedly every 5 minutes (approx. Rs
[6]
for a 2 Hour a day connection). The major drawback is however the low achievable
2,880 per month
bandwidth i.e. less than 56 Kbps. The connections are intermittent and have to be established repeatedly, thus
continuous reliable communication is not possible.
4.2 - ISDN
ISDN (Integrated Services Digital Network) uses PSTN to transmit data using end-to-end digital connectivity.
Voice and data are carried by bearer channels (B channels) occupying a bandwidth of 64 Kbps. Some switches
limit B channels to a capacity of 56 Kbps. A data channel (D channel) handles signaling at 16 kbps or 64 kbps,
depending on the service type. There are two basic types of ISDN service: Basic Rate Interface (BRI) and
Primary Rate Interface (PRI). To access BRI service, it is necessary to subscribe to an ISDN phone line. BRI
consists of two 64 kbps B channels and one 16 kbps D channel for a total of 144 kbps. This basic service is
intended to meet the needs of most individual users. PRI is intended for users with greater capacity requirements
having 23 B channels plus one 64 kbps D channel for a total of 1536 kbps (also known as T1). In Europe, PRI
consists of 30 B channels plus one 64 kbps D channel for a total of 1984 kbps (also known as E1).
Internet
Computer
PSTN
(ISDN equipped)
ISP Server
Public switch
ISDN Telephone
Customer must be within 5.5 km of an IDSN equipped Telephone Exchange for BRI service; beyond that,
expensive repeater devices are required. Customers require an ISDN modem which costs approximately Rs 3,500
while Telephone Exchange requires an ISDN Terminal Adapter to communicate with the client. Within the
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PSTN, ISDN equipped Telephone Exchanges communicate via ISDN Routers or other backbone infrastructure.
All the client nodes can connect to the ISP Server by dialing its 131 number, thus a network of the nodes is
created through the ISP. Alternately, if the nodes are directly connected to an ISDN modem at the corporate
server, then expensive call repeat charges will have to be paid (every 5 minutes).
Pros and Cons
Although the initial cost is low, current ISPs in Pakistan do not offer ISDN connectivity without Internet access.
This means that Internet access charges have to be paid at each site whether one needs it or not. Thus the running
cost is very high i.e. Rs 10,000 per month for 128 Kbps and Rs 20,000 per month for 256 Kbps. Also, ISDN is
only available in the major telephone exchanges of the country. For other areas, the customer has to bear the cost
[7]
of ISDN card in the Telephone Exchange which is usually more than Rs 200,000 depending on the exchange .
4.3 - xDSL
xDSL technology achieves up to 7 Mbps asymmetric access over ordinary phone wires. Traditional PSTN based
networks were designed with guidelines that limited transmissions to a 3,400 Hz analog voice channel.
Telephones and dial-up modems therefore limit their transmissions to the frequency spectrum that exists between
0 Hz and 3,400 Hz, thus the highest achievable bandwidth is 56 Kbps. DSL eliminates the 3,400 Hz boundary
utilizing a much broader range of frequencies and uses a multi-carrier modulation technology. Thus
communication is between two complementary devices over a wide range of frequencies over the standard copper
wire loop of PSTN. However, the quality of the digital transmission is reduced by the following factors:
z
Attenuation - The dissipation of power of a transmitted signal as it travels over copper. DSL’s use of higher
frequencies to increase bandwidth also results in shorter loop reach. This is because high-frequency signals
transmitted over metallic loops attenuate energy faster than the lower-frequency signals. Attenuation can
be minimized by using low-resistance, thicker-gauge wires.
z
Bridged Taps - These are un-terminated extensions of the loop that cause additional loop loss with loss
peaks around the frequency corresponding to the quarter wavelength of the extension length.
z
Crosstalk - The interference between two wires in the same bundle, caused by the electrical energy carried
by each.
PSTN
(DSL equipped)
Internet
DSL Service Provider
Desktop with
DSL equipment
Telephone Tower
with DSL equipment
Because of the above mentioned problems, there is a tradeoff between achievable bandwidth and distance. There
are different variants of DSL which provide different bandwidth and distance coverage with symmetric or
asymmetric access. ADSL (Asymmetric DSL) provides different downlink and uplink stream sizes.
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•
•
•
ADSL (asymmetric)
CAP SDSL (symmetric)
G.shdsl (symmetric)
Page 6 of 17
5.5 Km @ 1.5 Mbps or 1.8 Km @ 7 Mbps
8.9 Km @ 128 Kbps or 6.4 Km @ 768 Kbps
4.4 Km @ 1.5 Mbps
Voice channels may also be provided on the DSL connection utilizing Voice over DSL (VoDSL). Typically 4-12
phone lines capability can be provided on one DSL line. Voice traffic is routed to a VoDSL gateway and then
onto the PSTN (Public Switched Telephone Network). This approach offers DSL customers the cost and
convenience advantages of using a single service provider for both data and voice needs, without the need to have
additional phone lines provisioned. A DSL modem is required at the customer site for the service user's
connection to the DSL loop. In addition to providing basic DSL modem functionality, many endpoints contain
additional functionality such as bridging, routing, TDM is multiplexing or ATM multiplexing. The current PSTN
network in Pakistan has been tested to provide up to 6mbps data rate using DSL technology.
Pros and Cons
There are currently only three DSL service providers providing service only in some parts of Lahore, Karachi and
Islamabad. Therefore, other areas don’t have this option available. Just like ISDN, the DSL providers are mostly
selling their service with Internet. Monthly charges are Rs. 12,000 for 128 Kbps, Rs. 22,000 for 256 Kbps and Rs.
8,000 for 256 Kbps without internet. DSL modem cost in Rs. 12,000. This current price makes it expensive vis-àvis other broadband options.
4.4 – Fiber Optic (FO)
FO technology consists of a glass core, roughly fifty micrometers in diameter, surrounded by a glass "optical
cladding" giving an outside diameter of about 120 micrometers. It is used to carry signals in the form of light
pulses over distances up to 50 km, without the need for repeaters, providing bandwidth in the order of Gbps. They
make use of TIR to confine light within the core of the fiber. These signals may be coded voice communications
or computer data. It requires specialized equipment such as Connectors, Adaptors, Cable Assemblies, Attenuators,
Links, Splices, Tools and Test Equipment. Because of this massive investment, Fiber Optic networks are only
established by back bone service providers. FO is usually implemented in rings within the city as shown in
Exhibit 2. Multiple networks of different topologies can connect to this Gbps fiber ring through gateways.
Variants of FO cables include multimode fiber, single mode fiber, and graded index fiber. Typical bandwidth
distance product (B.D.P) of the three types of fibers are 6 – 25 MHz.km for multimode, 500 – 1500 MHz.km for
single mode, and 100 – 1000 MHz.km respectively. The end-points of the cable connect to a Fiber Optic Node or
a Digital Cross Connect (DXX) device that switches channel between two or more transmission facilities.
Pros and Cons
FO network offers huge bandwidth, low attenuation, and minimum running cost. The signal cannot be infiltrated
so the network is very secure. Its initial cost is high and requires special skills of personnel for network
establishment. The cable alone costs approximately Rs. 500 per meter. Adding all the other costs, the investment
for a single site would easily exceed Rs. 1,000,000 making it feasible only for the backbone service providers.
4.5 - CABLE MODEM
Cable modem gives users high-speed Internet access through a cable TV network at 1 Mbps. A single cable
network can be used to deliver multiple services like TV, Internet, etc. and a splitter is used to split the signal.
Cable modems connect to computers through a standard 10Base-T Ethernet interface using UTP Cat 5 cable [[2]].
All traffic from the cable modem termination system (CMTS) to the cable modem can be encrypted to ensure
privacy and security for users.
Internet
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The typical backbone network is formed by a combination of optical fiber and coaxial cable referred to as Hybrid
[8]
[3]
Fiber Coax (HFC) [ ]. The biggest challenge is to get the data from the home to the Head-end (H/E) , referred
to as the upstream or reverse channel. There are fewer hurdles associated with transmitting the data in the
opposite direction from the H/E to the home. Clusters of homes are served by a fiber link that runs from the H/E
to an optical fiber node. At the node the optical signal is transformed to an electrical signal and makes the
connection to the home via a relatively short section of coaxial cable, perhaps as short as 1 km in total length. The
number of houses served may vary from 50 - 2000.
HFC is an inherently shared medium. As the signal passes between the optical node and the station it passes
through a small number of amplifiers that boost the electrical signal, using separate amplifiers for the upstream
and downstream channels. Additionally, directional taps are used to distribute the signal to groups of stations. As
a result, while the signal may flow easily from the H/E to the station and from the station to the H/E the signal is
very highly attenuated between stations making it all but impossible to communicate directly between stations. It
is this characteristic that distinguishes the HFC channel from many others and rules out the efficient use of a
number of common protocols, such as Ethernet, used on other shared access media. A diagrammatic
representation of a typical network is shown in Exhibit 2.
Pros and Cons
Advantages include high access speeds from 500 Kbps to 1.5 Mbps. Running costs are lowest in the broadband
category (Rs. 1200 for 64 Kbps and Rs. 1800 for 128 Kbps). A modem costs Rs. 8,000. The disadvantages
include coaxial congestion as it is effectively a single shared medium. Also, the service is currently available only
in some parts of Lahore and Karachi. The current service providers do not provide static IPs so VPN cannot be
easily established.
4.6 – WIRELESS TECHNOLOGIES
Wireless technology is a rapidly expanding solution providing various options classified according to bandwidth,
range, and speed. Multiple unlicensed frequency ranges (2.4 GHz, 5.3 GHz and 5.8 GHz) are available worldwide for data transfer. For other frequency ranges, licenses have to be acquired from the government. Licensed
frequency has the benefit of no interruption as authorities disallow un-authorized interference. But there is a cost
associated with them according to country’s law. Unlicensed frequency can be used free of cost but intruders may
block certain channels affecting the data rates. Spread spectrum techniques are the solution, which use more
bandwidth than the system needs to avoid local interference. The two most widely used techniques are [[4]]:
- Direct Sequence Spread Spectrum (DSSS): It spreads the signal on a larger band by multiplying it with a
signature (the code) to minimize localized interference and background noise. To spread the signal, each bit of the
packet is modulated by a code (a fast repetitive pattern) while the receiver receives the whole spread channel
(averaging effect) and demodulates by the same code. For a 2 Mb/s signaling rate modulated by a 11 chips code,
the result is a signal spread over approximately 22 MHz of bandwidth.
- Frequency Hopping Spread Spectrum (FHSS): It uses a set of narrow channels and walk through all of them
in sequence. For example, the 2.4 GHz ISM band is divided in 79 channels of 1 MHz. Periodically (every 20 to
400 ms usually), the system hops to a new channel, following a predetermined cyclic hopping pattern. Frequency
Hopping introduces more complications at the MAC level: scanning to find the network at the initialization (a
moving target), keeping the synchronization of the nodes, managing the hops. Also, the Frequency Hopping
system have to include a process called whitening, to conform to radio transmission constraints, inserting some
regular stuff bits in each packets (to avoid long strings of 0 or 1), adding more overhead.
4.6.1 - RADIO MODEM
Radio modems, also known as Digital Radio Signal (DRS), provide point to point communications over a range
of 0 - 80 km. As they operate over unlicensed 2.4 GHz or 5.8 GHz channels, no operating license is required.
Data is broadcasted from a transmitter which can be picked up by a receiver in the proximity. Radio Frequency
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(RF) communication works by creating electromagnetic waves at a source and being able to pick up those
electromagnetic waves at a particular destination. These electromagnetic waves travel through the air at near the
speed of light. A radio modem transmitter consists of a radio modulator, an amplifier, and an antenna. The radio
modulator takes the data from the receiver and converts it to a radio signal that can be transmitted. The amplifier
raises the power of the signal to a level that can reach other users, hence, is variable. The transmitter antenna then
transmits the amplified signal. The power of the amplifier directly affects the distance that the signal can travel
(the range) and the reliability of the communication. The range also depends on the terrain and the radio antenna
setup. Security can be implemented by encoding the transmissions in which case the receiver needs to know the
decoding key. Based on the form to which the data is converted for transmission, common variants are UHF,
VHF, and Spread Spectrum.
Pros and Cons
Currently available Radio Modems can provide a 2 Mbps point-to-point connection for a distance up to 80 Km
using high-gain antennas requiring line-of-sight [[5]]. Wireless 802.11x has replaced this technology as it can
provide higher bandwidth and point-to-multipoint transmission. 802.11x provides much better bandwidth and
costs less. Thus, Radio Modem is only suitable when a range of more than 60 km is required.
4.6.2 - Wireless Local Loop (WLL)
Wireless local loop (WLL) services may be defined as fixed wireless services intended to provide primary access
to the telephone network [[6]]. A base station, connected to PSTN (Public Switched Telephone Network) engages
in last mile communication with subscribers using radio signal. Wireless packet switching technology or circuit
switching can be used and the former is more suitable for IP based services. High capacity combined with
frequency reuse factor of 1 can be achieved using 6 sector antennas, each antenna providing 3mbps. Ideal access
radius is 5-15 km. Point to point links can, however, achieve significantly increased depths. WLL techniques can
operate in unlicensed as well as licensed frequencies.
PSTN
CAT 5
Site Node
Radio tower
Base Station
Base Station
Server
Internet
Following technologies are currently being used to establish WLL networks.
1- Code Division Multiple Access (CDMA)
CDMA is a spread spectrum technology using direct sequencing (discussed above). Each client is given a
different code and data is transmitted using this code. The coding of the data spreads the signal to greater
bandwidths. CDMA inherently provides increased privacy, due to the wideband spectrum signal used for
transmission. Problem is that noise is proportional to number of channels and the configuration needs to be a star
topology.
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2- Local Multipoint Distribution Service (LMDS)
LMDS is a broadband wireless point-to-multipoint communication system operating above 20 GHz (depending
on country of licensing) that can be used to provide digital two-way voice, data, Internet, and video services.
Various network architectures are possible within LMDS system design. The most common is a point-tomultipoint wireless access design although point-to-point systems and TV distribution systems can be provided
within the LMDS system. Both ATM and IP transport methodologies can be used. The LMDS network
architecture consists of primarily four parts: network operations center (NOC), fiber-based infrastructure, base
station, and customer premises equipment.
3- Multi channel Multipoint Distribution Service (MMDS)
This wireless technology has been traditionally used for TV signal transmissions. The service is delivered using
terrestrial based, radio transmitters located at the tallest feasible location in an area. Each customer obtains the
MMDS signal with a small, digital receiver with line of sight to the transmitters. The MMDS wireless spectrum
originally consisted of 33 analog video channels, which were 6 MHz wide. The evolution of video technology
into digital has converted these 33 analog MMDS channels into 99 digital data streams, each transmitting at 10
Mbps, providing a total of up to 1Gbps.
Pros and Cons
A backbone network can be created using WLL as opposed to a fiber optic network. The advantages would be
faster deployment, lower network maintenance & operating costs, greater flexibility to meet uncertain levels of
penetration and rates of growth. WLL is modular, scalable & flexible to meet uncertain levels of penetration and
growth rates. It can be used for cellular services as well. Disadvantages include heavy initial investment and
difficulty to provide stable QoS & high dependence on the base station for reliability. According to Pakistan
Government regulations, WLL cannot be used for data services before Jan 2004.
4.6.3 - Wireless LAN (802.11b)
802.11b, also known as WiFi, is a half duplex wireless protocol (it can either send or receive at a time). It usually
[9]
uses 2.4-GHz or 5.8 GHz unlicensed frequency band. A WiFi community (WECA)
is in place to ensure
interoperability between 802.11b products. Maximum bandwidth is 11 Mbps, however, it falls back to 5.5 Mbps,
2 Mbps and 1 Mbps depending on the strength of the signal (actual realistic throughput is only 2 – 5.5 Mbps
[[7]]). Newer 802.11a protocol is also available which has a maximum bandwidth of 54 Mbps but its equipment is
currently expensive. Security can be implemented by enabling WEP (wired equivalent privacy) using 64 or 128
bit key encryptions but this reduces the data rates by 20-50%. However WEP can be easily hacked and a higher
layer VPN must be established to increase security.
Operating Modes of WiFi [[8]]:
-
Infrastructure mode: A communication method that requires a wireless access point. An access point
controls encryption and bridging/routing wireless traffic to a wired Ethernet network (or the Internet).
Access points that act as routers can also assign IP addresses to PC's using DHCP services.
-
Ad-Hoc mode: Two or more wireless Ethernet devices may communicate with each other without a
wireless access point.
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Source: www.proxim.com
The base station has a high-gain sector antenna and a base station unit. Each subscriber site requires a tower
(tower height depends on distance from base station), a directional antenna and a subscriber station. Multiple
sector antennas can be joined together at the base station to cover 360 degrees around the base station. Another
[10] [9] [10]
option is to install omni-directional antennas at close locations to create multiple WiFi hotspots
[ ][
].
[11]
.
Approximately Rs. 100,000 is required for a subscriber station requiring a long range tower to communicate
Pros and Cons
The problem with 802.11b is its range because microwaves are seriously affected by physical obstacles, limiting
the range to within 500 meters. By using Yagi directional antennas and line of sight, the range can be increased to
40 miles [[11]]; however, the spread will be reduced to 10 degrees. Rapid reduction in equipment prices has made
this option most feasible for independent corporate networks within a city.
4.7 - Free Space Optics (FSO) Infrared Laser
Free Space Optics (FSO), also known as Optical
Wireless, refers to the transmission of infrared
(IR) beams through the atmosphere to obtain
optical communications. FSO works on the same
basic principle as the IR TV remotes. Invisible
environmentally safe light beams are transmitted
between telescopes using low power infrared
lasers in the Terahertz spectrum. FSO systems might be fixed-pointed or actively-tracked with the latter being
more expensive. Actively-tracked systems require multiple coordinated beams whereby sway in the beam is
detected and accordingly adjusted. Data Rates up to 1.25 Gbps can be achieved for a distance of 4 Km line-ofsight [[12]].
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Pros and cons
It is the only Gigabit wireless option. Unlike other wireless systems, FSO is an optical technology, therefore no
licensing is required. There is minimal interference from other systems, since point-to-point laser signal is
extremely difficult to intercept, and therefore secure. Since FSO transceivers can transmit and receive through
windows, they can be mounted inside buildings, thereby simplifying wiring. FSO however, requires exact line of
sight between the two ends of the link. The equipment cannot be installed on towers due to tower sway. Possible
usage in Pakistan is limited between tall buildings, usually in the major cities. The FSO signal must also contend
with atmospheric disturbances, since fog / pollution can attenuate FSO signal strength. By employing an adaptive
laser power scheme [[13]] in response to weather conditions, the reliability of FSO can be increased. Since it is a
relatively new technology, the equipment is very expensive and only affordable if Gbps bandwidth is required.
4.8 - VSAT - Two-Way Satellite Connectivity
VSAT (Very Small Aperture Terminal)
refers to receive / transmit terminals
installed at dispersed sites connecting to a
central hub via satellite using small
diameter antenna dishes (0.6 to 3.8 meter).
Internet
VSAT technology represents a cost
Satellite
effective solution for users seeking an
independent communications network
connecting
a
large
number
of
geographically
dispersed
sites. VSAT
Satellite dish
Satellite dish
networks offer value-added satellite-based
services capable of supporting the internet,
Service Provider
Server
data, voice and video. Generally, these
systems operate in the Ku-band and C-band
Site Node
frequencies. Ku-band based networks are
used primarily in Europe and North America and utilize the smaller sizes of VSAT antennas. C-band devices,
used extensively in Asia, Africa and Latin America, require larger antenna.
VSAT networks come in various shapes and sizes ranging from point-to-point, point-to-multipoint, and on
demand for thousands of sites based on a dedicated facility located at their own site. Networks may have as many
as several hundred or even thousands of sites. VSAT connections can be only for downlink or both ways (uplink
& downlink). The VSAT transfer rates may be asymmetric or symmetric. Usually, asymmetric data transfers are
utilized allowing for bandwidth up to 500 Kbps for the downlink with the uplink being slightly slower at about
150 Kbps. A PCI card needs to be installed at the site node.
Pros & Cons
VSAT connectivity charges are not distance-dependent and VSAT connections cost the same whether sites are 1
or 1,000 miles apart. A VSAT network can be installed quickly since there are no countless miles of wire to be
installed. VSAT networks provide an efficient, cost-effective method for reliable distribution of data through a
multiple site organization, regardless of location. Each site node requires Rs. 30,000 initial investment (for dish
and PCI card) and Rs.20,000 per month. This makes VSAT very expensive and feasible only for remote sites.
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5 - TECHNOLOGY & COST COMPARISON
We have not done cost analysis for some of the technologies since they were either not available or not feasible.
Fiber optic is extremely expensive and therefore, only feasible for establishing a backbone network. Radio
modem has been replaced by 802.11x so we have not analyzed it further. WLL is currently not available in
Pakistan for data transfer. Free Space Optics equipment is currently very expensive and has limited use for
corporate networks. All the other technologies have been analyzed on a 5 year basis.
Tech
Option
Provider
Initial
Cost
Monthly
Cost
Bandwidth
Inter
Net
5 Year
Cost
Price
Red
Areas
Available
Range
Dial Up
Internet
WOL,
Paknet,
Nexlinx,
Brain
1,500
1,000
56 Kbps
Yes
41,839
20%
Urban
Areas
N/A
Dial Up
Server
Self
3,000
2,880
[12]
56 Kbps
No
175,800
0%
Urban
Areas
N/A
10,000
128 Kbps
20%
All Major
Cities
N/A
30%
Lahore,
Karachi,
Islamabad
6 km
from
DSL
ISDN
DSL
Cable
Modem
Wireless
802.11b
VSAT
WOL,
Paknet,
Nexlinx,
Brain
Habib
Rafiq,
Dancom,
Multinet
World Call,
Multinet
12,000
8,000
406,892
Yes
3,500
20,000
256 Kbps
12,000
128 Kbps
22,000
256 Kbps
8,000
1,200
1,800
256 Kbps
64 Kbps
128 Kbps
806,784
Yes
No
Yes
411,326
732,098
266,218
66,969
88,454
10%
Self
100,000
200
11 Mbps
No
112,000
N/A
Pak
Datacom,
Super,
Zaknet
30,000
20,000
256 Kbps
Yes
836,784
20%
Lahore,
Karachi
Every
Where
Every
Where
N/A
25 km
N/A
Initial cost includes all hardware required for a technology at a node. Monthly cost reflects the maintenance and
service charges. Some of the service providers package internet with the connection and this is mentioned in the
above table. This analysis has been done on a 5 year basis as some of the technologies may become obsolete after
that time. It is assumed that the service provider charges will reduce every year due to greater competition and
reduction in bulk internet bandwidth charges. The percentage reduction, however, is forecasted to be different for
each technology. Prices of newer technologies are expected to come down more rapidly (30% for DSL) compared
to established solutions (10% for cable modem). Five year cost is calculated by discounting the variable cost per
year according to the assumed price reduction.
3/10/2005
Page 13 of 17
6 - RECOMMENDATIONS
-
Dial up internet is the cheapest option but maximum bandwidth is 56 Kbps and connection is
intermittent.
-
Dial up Server is extremely expensive for 24 Hour connectivity and it is therefore not feasible until
PTCL allows use of non-repeat numbers such as 131 for the corporate sector.
-
DSL and ISDN provide higher data rates than conventional modems but they require special equipment
at the nearest Exchange and thus availability has to be checked.
-
Cable modem is the cheapest broadband option but it is congestion prone since it uses a shared medium.
Current providers do not offer Static IP’s so VPN is out.
-
Fiber optic network provides Gigabit bandwidth and guaranteed QoS, but expensive cables have to be
laid down. Therefore only the backbone providers can afford a fiber network for long distances.
-
VSAT is only recommended for remote regions which don’t have any PSTN facility, since it is very
expensive.
-
Within a range of 25 km, an independent network can be created using 802.11b with high-gain antennas.
11 Mbps is achievable, however Rs 100,000 per site is required.
-
802.11b Wireless equipment can be setup in a very short time and with negligible maintenance cost. On a
5 year basis, it is cheaper than DSL, ISDN and Dial Up Server.
-
FSO provides Gigabit wireless connectivity, however it requires exact line of sight and is very expensive.
Furthermore, its signal is attenuated with atmospheric disturbances like fog and smoke. It is however
feasible for connecting two big office complexes within 4 Km range.
-
For organizations wanting to connect their regional networks spanning different cities, they can either get
[13]
a leased E1 line from PTCL
or subscribe to broadband internet connections at their regional gateways
and connect via Internet.
-
We feel that there is an opportunity for investors wanting to enter the broadband ISP sector by creating
[14]
for a base station covering a radius of 6
802.11x based networks. Approximate cost will be $5,000 x 6
km [[14]]. The subscriber units will cost $1,300 per site. Advantages include quick setup and high
bandwidth (11 Mbps). Target areas should be those which don’t have DSL or cable modem networks.
Hotpots using omni-directional antennas are also feasible for public places like airports etc.
3/10/2005
Page 14 of 17
7 - EXHIBITS
Exhibit 1
China
2002
Afghanistan
Iran
India
SDH/PDH
(525/622 Mbps)
backbone being
upgraded to
DWDM
10 Gbps
Status Report: Pakistan Education and Research Network by Dr. M. H. Zaidi
3/10/2005
Page 15 of 17
Exhibit 2
Reference: www.opto.eee.strath.ac.uk/BBN/acnet_index.html (May 11, 2003)
3/10/2005
Page 16 of 17
8 - REFERENCES
[1]
We have considered a technology which requires an investment greater than Rs 1 Million per site (for sites which are
more than 1 KM from each other) to be too expensive for the independent network option for a non-communication sector
organization.
[2]
Bandwidth is defined as the rate of data transfer per time unit. It is usually measured in Mega Bits per Second (Mbps) or
Kilo Bits per Second (Kbps). A rate of 1 Kbps means that 1,000 Bits of information can be transferred over the
communication channel in one second.
[3]
Internet services with guaranteed QoS are currently provided by very few ISP’s in Pakistan.
[4]
IP stands for Internet Protocol, and it is the most common communication protocol on the Internet.
[5]
Static IP addresses remain constant, as opposed to dynamically assigned IP addresses at boot up time.
[6]
2 Hours a day phone connection costs Rs 2,880 / month i.e. 2 Hours X 30 Days X 12 Calls/Hour X Rs 4/Call
[7]
Almost all the PTCL digital exchanges have an add-on facility of ISDN after installing the ISDN Equipment in the
exchange.
[8]
Head End is a central control device which provides functions such as remodulation, retiming, message accountability,
contention control, diagnostic control, and access to a gateway.
[9]
WECA – Wireless Ethernet Compatibility Alliance
[10]
WiFi hotspots are considered to be too expensive for an independent network; however, a backbone service provider can
create multiple hotspots to provide broadband internet access without laying down cables.
[11]
Rs. 60,000 for a 100 feet tower, Rs. 20,000 for an antenna and Rs. 20,000 for the subscriber station.
[12]
Two hour connectivity per day is assumed
[13]
E1 running costs are approximately Rs 800 per Km per 3 Months (Source: PTCL)
[14]
Six 60 degree base stations combine together to form a cell.
[1] www.itl.nist.gov/fipspubs/fip46-2.htm (May 11, 2003)
[2] www.cabledatacomnews.com/cmic/cmic1.html (May 11, 2003)
[3] Cable Modem Technology by John O. Limb
[4] www.hpl.hp.com/personal/Jean_Tourrilhes/Linux/Linux.Wireless.modem.html (May 11, 2003)
[5] www.airlinx.com (May 11, 2003)
[6] rf.rfglobalnet.com/library/ApplicationNotes/files/7/motivations.htm (May 11, 2003)
[7] www.oreillynet.com/pub/a/wireless/2001/03/02/802.11b_facts.html (May 11, 2003)
[8] www.homenethelp.com/802.11b/index.asp (May 11, 2003)
[9] www.80211-planet.com/news/article.php/2174501 (May 11, 2003)
3/10/2005
Page 17 of 17
[10] WiFi: What’s next? By Paul S. Henry et al
[11] www.oreillynet.com/pub/a/wireless/2001/05/03/longshot.html (May 11, 2003)
[12] www.freespaceoptics.com (May 11, 2003)
[13] www.lightpointe.com (May 11, 2003)
[14] www.proxim.com (May 11, 2003)
3/10/2005

Wide Area Connectivity Options in Pakistan

Transcription

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