Campus Networks: GE or ATM?
Ahmet Tevfik İnan
Yıldız Technical University 80750 - İstanbul / TURKEY
tevfik@ce.yildiz.edu.tr
Abstract. With the evolution of computer technology, computer networks
became more popular. Especially the wide use of Internet and related
technologies changed the LAN traffic model from the conventional 80/20 rule
(80% of the traffic stays in the workgroup, 20% moves over the backbone) to
20/80 rule [1]. By the development of bandwidth hungry and delay sensitive
applications, design and operability of the networks became a serious problem.
This paper overviews physical media types, topologies, network technologies,
and analyzes benefits and drawbacks of challenging technology like Gigabit
Ethernet (GE) and Asynchronous Transfer Mode (ATM) in terms of technology
and cost of ownership in the design stage of a new Campus Network.
1 Computer Networks
Interconnected collections of autonomous computers are named computer networks
[2]. The benefits and drawbacks of computer networks are shown in Table 1.
Table 1. Benefits and Drawbacks of Computer Networks
Benefits





Resource sharing
Incremental growth (ease to expand)
Placing power where it is needed
Autonomy
Redundancy
Drawbacks




Backup issues
Security issues
Interoperability issues
System failure issues
To design a "campus network" based on open standards, the layered structure of OSI
reference model must be followed. So we will first focus on different physical media
characteristics and then go on with topology and LAN standards (media access
technologies) concluding with a comparison of challenging networking technologies.
1.1 Physical Media
There is a wide range of media available to the network designer and the one chosen
must suite, Environmental Requirements (speed and physical distance), Cost
Requirements and Operational Requirements (modularity, extendibility, ease of
installation and maintenance).
Coaxial cable is a type of communication cable in which a solid center conductor is
surrounded by an insulated spacer, which in turn surrounded by a braided wire. An
insulating layer then covers the entire assembly. The comparison of two types of
coaxial cabling is shown in Table 2.
Table 2. Coaxial Cabling Specifications
Thicknet
Thinnet
Impedance
(ohm)
50
50
Thickness
(mm)
10
5
Transmission
speed (Mbps)
10
10
Segment
length (m)
500
185
Max transceivers
per segment
100
30
Twisted pair cables are so named because pair of wires are twisted around one
another. Each pair consist of two insulated copper wire twisted together to reduce
cross talks and noise effect. In data network applications, higher quality cables known
as DGM (Data Grade Medium) must be utilized. 3 types of twisted pair cables are
widely used in data networks. UTP (Unshielded Twisted Pair) has an impedance of
100 ohm. The categories used are shown in Table 3. ScTP (Screened Twisted Pair) is
100 ohm UTP with a single foil screen surrounding all 4-pair in order to minimize
Electro Magnetic Interference (EMI) and outside noise. STP (Shielded Twisted Pair)
is 150 ohm twisted pair cables individually wrapped in a foil shield and enclosed in an
overall outer braided wire shield to eliminate EMI and outside noise.
Table 3. UTP Cabling Specifications [14]
Category
Type
Frequency(MHz)
Cat-1
Voice
-
Cat-2
Data
4
Cat-3
Data
16
Cat-4
Data
20
Cat-5
Data
100
Cat-5e
Proposal
100
Cat-6
Proposal
250
Cat-7
Proposal
600
Table 4. Twisted Pair Cabling Benefits and Drawbacks




Benefits
Simple, easy to install
Flexible
Low weight
Easy spliced and connected
Drawbacks
 Possible to tap
 EMI (if not shielded)
 Attenuation
Fiber optic cabling is the technology where electrical signals are converted into
optical signals, transmitted through a thin glass fiber and reconverted back into
electrical signals. Light source can be LED (Light Emitting Diode) or LD (Laser
Diode). The specifications of are shown in Table 5.
Table 5. Fiber Optic Specifications [3]
Core
Cladding
Attenuation
Frequency
5-10/125 SMF
5-10
125
0.8 dB/Km
> 1000 MHz
50/125 MMF
50
125
3-4 dB/Km
> 400 MHz
62.5/125 MMF
62.5
125
3,75-6 dB/Km
160 MHz
85/125 MMF
85
125
5 dB/Km
200 MHz
100/140 MMF
100
140
5-6 dB/Km
10-100 MHz
MMF (Multi Mode Fiber) allows many paths of light to propagate down the fiber
optic path. It has good coupling from inexpensive LEDs light sources and use of
inexpensive couplers and connectors. SMF (Single Mode Fiber) has a core diameter
that is so small that only a single mode of light is propagated. Small core of singlemode fiber makes coupling light into the fiber more difficult. So more expensive
lasers must be used as a light source. Single-mode fiber is capable of supporting much
longer segment lengths than multi-mode fiber.
Table 6. Benefits and Drawbacks of Fiber Optic Cable




Benefits
Larger bandwidth
Longer distance
No EMI, no cross-talk, no attenuation
Impossible to tap
Drawbacks
 Difficult to install
 Special connection techniques
Using radio waves as a communication media brings to mind the idea of mobility. But
atmosphere poses some limitations due the changing weather conditions and national
and international radio communication regulations. Frequencies between 300 GHz
and 100 THz are called infrared [26].
Table 7. Radio Waves Frequencies [26]
Frequency
3 KHz
30 KHz
30 KHz
300 KHz
300 KHz
3 MHz
3 MHz
30 MHz
30 MHz
300 MHz
300 MHz
3 GHZ
3 GHz
30 GHz
30 GHz
300 GHz
VLF (Very Low Frequency.)
LF (Long Frequency)
MF (Middle Frequency)
HF (High Frequency)
VHF (Very High Frequency)
UHF (Ultra High Frequency)
SHF (Super High Frequency)
EHF (Extremely High Frequency)
Long Range
Communication.
Multi Dimensional
Radio Communication
Microwave Communication
Space Communication
Table 8. Benefits and Drawbacks of Radio Waves
Benefits
 No physical link
 Node can be mobile
Drawbacks
 Depends on atmospheric conditions
Table 9. Benefits and Drawbacks of Infrared
Benefits
 No physical link
Drawbacks
 In door use
 Shadowing
1.2 Topology
The pattern of interconnection of nodes in a network is called topology. The key
issues in the topology are cost, flexibility and reliability. The benefits and drawbacks
of Star, Bus, Ring, Tree and Mesh topologies are shown in Table 10.
Table 10. Benefits and Drawbacks of Various Topologies
STAR
BUS
RING
TREE
MESH





Benefits
Drawbacks
Ease of service
 Central node dependency
One device per connection
 Wiring closet space required
Centralized diagnosis,problem determination
Simple access
Long cable length
 Short cable length
 Simple wiring layout
 Easy to extend










 Short cable length
 No wiring closet required
 Suitable for optical fiber
Adding a station stops network
Fault diagnosis is difficult
Fault isolation is difficult
Broken cable causes failure
Limited number of users (shared media)
Must listen the media (CSMA/CD)
If node fails, network fails
Difficult to diagnose faults
Difficult to reconfigure
Topology affects the access
 Easy to extend
 Fault isolation is simple
 Depends on the root
 Redundant
 Routing problem
 Complex cabling/interfacing
2 LAN Standards (Media Access)
2.1 Ethernet
Announced as a product in 1980. But the development work dates backs to the early
70's. (Created by XEROX in 1972. In 1980, Digital, Intel and Xerox - DIX [3]
developed Ethernet Version 2.0). Many of the original ideas come from the ALOHA
wide area network used in the University of HAWAII. [4] Ethernet is a base-band
network with a bus topology and data transmission rate of 10 Mbps. The access
method is CSMA/CD (IEEE 802.3) In a CSMA/CD environment a station can access
the network any time. Before sending data, stations listen to the network until no
traffic detected. A collision occurs when two stations transmit simultaneously. In this
situation both transmission are damaged and stations must retransmit at some later
time. A back-off algorithm determines when the colliding stations should retransmit.
The 10Base Ethernet Specifications is shown in Table 11.
Table 11. 10Base Ethernet Specifications [5]
Transmission speed
Media
Topology
Devices attached to
Segment length (m)
10Base5
10 Mbps
Coax (50)
Bus
Transceiver
500
10Base2
10 Mbps
Coax (50)
Bus
NIC by BNC
185
10BaseT
10 Mbps
UTP
Star
Hub/Switch
100
10BaseFL
10 Mbps
Fiber(62,5)
Star
Hub/Switch
2000
2.2 Fast Ethernet
The IEEE Higher Speed Ethernet Study Group was formed to assess the feasibility of
running Ethernet at speeds of 100Mbps. The Study Group established several
objectives for this new higher speed Ethernet but disagreed on the access method. An
issue was whether this new faster Ethernet would support CSMA/CD to access the
network medium or some other access method. The Study Group divided into two
camps over this access method disagreement: The Fast Ethernet Alliance and the
100VG-AnyLAN Forum. Each group produced a specification for running Ethernet at
higher speeds: 100BaseT and 100VG-AnyLAN respectively [5].
100BaseT. 100BaseT use the existing IEEE 802.3 CSMA/CD specifications. It
supports all applications and networking software currently running on existing
Ethernet infrastructure. In addition, 100BaseT supports dual speeds of 10 and
100Mbps, and using Fast EtherChannel technology it is possible to achieve
4x100Mbps bandwidth (800Mbps full duplex). The 100Base Ethernet Specifications
is shown in Table 12
Table 12. 100Base Ethernet Specifications [5]
Transmission speed
Topology
Devices attached to
Number of repeaters
Segment length (m)
Cable type
100BaseT4
10/100 Mbps
Star
Hub/Switch
2
100
4 Pair UTP/ScTP
Cat 3-4-5
100BaseTX
10/100 Mbps
Star
Hub/Switch
2
100
2Pair UTP/ScTP
Cat 5
100BaseFX
10/100 Mbps
Star
Hub/Switch/PP
1
400
Fiber
(MMF 62.5/125)
Benefits and drawbacks of using Fast Ethernet over is shown in Table 13.
Table 13. Benefits and Drawbacks of Fast Ethernet Technology
Feature
True Ethernet Technology
Auto Negotiation
10/100 Scalability
Uses same physical layer
interface asby
FDDI
Supported
all major
network component providers
Benefits
Compatible with 10 Mbps
Transparent interoperability in
mixed Ethernet
environments
Transparent
migration
from
10Mbps
to 100Mbps and
Proven functionality
compatibility
Large
selection of compatible
equipment
Drawbacks
Reduces number of allowable
repeater
in anot
segment
Full feature
implemented by all
vendors
100
Mbps operation require cable
or
hub upgrade
None
None
100VG-AnyLAN. HP developed 100VG-AnyLAN as an alternative to CSMD/CD
for newer time sensitive application such as multimedia. The access method is based
on station demand. A node waiting to transmit signals its request to the hub/switch. If
the network is idle, the hub immediately acknowledges the request and the node
begins transmitting a packet to the hub. If more than one request received at the same
time, the hub uses a round robin technique to acknowledge each request in turn. High
priority requests, such video conferencing applications, are serviced ahead of normal
priority requests [5].
Table 14. 100VG-AnyLAN Specifications
4-pair (Cat-3 UTP)
2-pair (Cat-4/-5 UTP)
Node-Hub distance (m)
100
150
Hubs tree deep
3
3
End to end distance (m)
600
900
2.3 Token Ring (TR)
IBM originally developed the Token Ring in the 1970s. Although dissimilar in some
respects, IBM's Token Ring Network and IEEE 802.5 are generally compatible (Table
15). Stations are directly connected to MAU (Media Access Unit), which can be
wired together to form one large ring. Token passing networks move a small frame,
called token, around the network. Possession of the token grants the right to transmit.
If a node receiving the token has no information to send, it passes the token to the
next end station. Each station can hold the token for a maximum period of time. If the
station possessing the token does have information to transmit, it seizes the token,
alters one bit of the token, which turns the token into a start of frame sequence,
appends the information it wants to transmit, and sends this information to the next
station on the ring. While the information is circling the ring other stations wanting to
transmit must wait. Therefore a collision cannot occur in Token Ring networks. The
information frame circulates the ring until it reaches the intended destination station,
which copies the information. The token continues to circulate and is removed when
it reaches the sending station, then in turn checks if the frame is copied by the
destination. In addition, a priority mechanism also exists in Token Ring networks [6].
Table 15. Token Ring Specifications [6]
Transmission speed (Mbps) / Media Type
Ring diameter (m) / Maximum closet per ring
Maximum Node-Closet distance (m)
Maximum Closet-Closet distance (m)
4-16 / Data Grade Medium
800 / 12
100 (in multiple closet ring)
200
2.4 FDDI (Fiber Distributed Data Interface)
FDDI is a standard defined by ANSI for 100 Mbps LAN communication using fiber
optical medium designed as a backbone network and desktop delivery system for
high-end workgroups. FDDI uses dual ring or dual ring to tree topology and a token
passing media access method. Up to 1000 stations can be connected to an FDDI
network, with up to 3km between stations. Compared to Fast Ethernet, FDDI is
complex and costly to implement. Its advantage is its large domain diameter (which is
50 km) and inherent redundancy [7] (Table 16).
Table 16. Benefits and Drawbacks of FDDI
Feature
Benefit
Stable
Industry Multiple vendors available
Standard
Difficult to tap.
Security
Improved immunity
Cable/device
failures do not disturb
Redundancy
critical applications
Drawback
Requires new hub, protocols and drivers.
Expensive
for desktop
Requires fiber
optic cable
Requires expensive dual attach devices
2.5 ATM (Asynchronous Transfer Mode)
Organizing different streams of traffic in separate calls allows the user to specify the
resources required and allows the network to allocate resources based on these needs
[8]. The session's establishment, which is the most time consuming and complex
process, is done once and fixed size cells are routed directly from source to the
destination without any trouble. During the session establishment, traffic type
specification brings the required prioritization to sustain the necessary Quality of
Service (QoS). ATM operates from 25Mbps to 622 Mbps and serves as an excellent
backbone merging Fast Ethernet and FDDI networks. It is also suitable for WAN
connection, LAN backbone, and desktop networking technology. And it may become
a protocol of choice for meeting the extremely high bandwidth requirements of realtime, bi-directional multimedia applications merging voice, video and data. ATM
does not directly support the way LAN currently work, but instead must be
configured to emulate conventional LAN operation [9]. ATM is a switched,
connection-oriented LAN and WAN technology that allows a virtually unlimited
number of users to have dedicated, high speed connections with each other and with
high-performance network servers. There are three primary differences between ATM
and conventional shared-media networks such as those based on Ethernet, Token
Ring and FDDI. These three differences are ATM's use of dedicated media, its fixed
length and its connection-oriented nature [10]. ATM tries to emulate Ethernet
networks via LANE (LAN Emulation) and IPOA (IP over ATM).
2.6 Gigabit Ethernet (GE)
Gigabit Ethernet (GE) is an extension of IEEE 802.3 Ethernet standard. GE increases
speeds tenfold over Fast Ethernet to 1000Mbps or 1Gbps. To accelerate from
100Mbps to 1Gbps, several changes need to be made to the physical interface. GE is
identical to Ethernet from data link layer upward. To sustain necessary speed, IEEE
802.3 and ANSI X3T11 Fiber Channel technologies are merged (Fig. 1.). The MAC
layer of GE is similar to those of standard Ethernet and Fast Ethernet. The MAC layer
of GE supports both full and half-duplex transmission. The characteristics of Ethernet,
such as collision detection, maximum network diameter, repeater rules, and so forth,
are the same of GE. As it is in Fast EtherChannel technology, 4x1 GE can form a
Gigabit EtherChannel to obtain 4 Gbps (8 Gbps full duplex) bandwidth. "GE is an
evolution not revolution"[7].
3 Design Criteria for a Campus Network
As mentioned in the previous sections the major point to care about campus networks
are, environmental requirements, cost and operational. In addition, Network
Complexity must be taken into account to. Use of different protocols, vendors,
products and type of applications brings the Network Complexity. But, it is always
not possible to implement a single technology due to different needs. So it is usual to
see heterogeneous networks, which takes advantage of all challenging technologies.
IEEE 802.3z
LLC
IEEE 802.3z LLC
FC-4
Upper layer
IEEE 802.3
CSMA/CD
CSMA/CD
Fullduplex MAC
FC-3
Common services
IEEE 802.3
Physical Layer
8B/10B
Encode /Decode
FC-2
Signalling
Serializer
Deserializer
FC-1
Encode / Decode
Connector
FC-0
Interface & Meida
IEEE 802.3z
Gigabit Ethernet
ANSI X3T11
Fibre Channel
IEEE 802.3
Ethernet
Fig. 1. Layered Structure of Gigabit Ethernet [5]
Table 17. 1000Base Ethernet Specifications
Laser type
Transmission media
Distance
(m)
Media diameter
(micron)
1300 nm
850 nm
2pair STP
Cat-5
1000BaseLX
LW
SMF
MMF
1000BaseSX
SW
MMF
5/9
50
62,5
50
62,5
1000BaseCX
N/A
Copper
(150 Ohm)
N/A
3000
N/A
N/A
N/A
550
N/A
N/A
N/A
550
N/A
N/A
N/A
N/A
550
N/A
N/A
N/A
250
N/A
N/A
N/A
N/A
25
N/A
1000BaseT
N/A
Copper
(100 Ohm)
N/A
N/A
N/A
N/A
100
3.1 Environmental Requirements
Intranet experiences have shown that networks are evolving. The Client/Server type
distributed computing applications flipped the classical 80/20 rules [1]. In addition,
support for more complex data streams such as graphics, animations and sound
requires more bandwidth (Table 18).
Today the challenging technologies for campus networks bring 100Mbps FDDI,
100/200Mbps Fast Ethernet, 155/622Mbps ATM, 400/800Mbps Fast EtherChannel,
1000Mbps GE and 4/8Gbps Gigabit EtherChannel as common speeds on copper or
fiber links within the range of 100m up to few kilometers.
3.2 Cost Requirements
The cost of network ownership is the sum of capital equipment, support staff and
facility costs with a percentage of 48%, 36% and 18% respectively. The cost of
ownership goes beyond the price/performance of initial capital equipment purchased
and takes into account the long-term effects of technology change on support staff and
facilities. As a consequence, the complexity drivers for two competing technology
represents 31.2 person/month for the ATM implementation conversely 16.2
person/month for GE. This impact, called complexity inflation, is multiplied with
fixed staff cost [11].
3.3 Operational Requirements
While designing the network infrastructure besides the speed, one had to take into
account the non-blocking architecture and solve the over-subscription problem at
distribution points in order to obtain the required performance. Can a device handle
the traffic load that all its interfaces can accept or generate? Non-blocking means that
a device's internal capacity matches or exceeds the full capacity bandwidth
requirements of its ports and will not drop packet due to architecture [13]. To provide
relative balance, non-blocking switches must support trunk link that are several times
faster then the incoming links and their back plain capacity must be greater or equal to
the switching load generated by all its ports.
Table 18. Application and Their Impact on the Network [11]
Application
Scientific Modeling,
Engineering
Publication,
Medical Data
Data Warehouse
Network Backup
Data Size/Types
100's MB to GB
Data
100's MB to GB
Data
1MB-100MB
Data/Audio/Video
GB to TB
Data
Desktop Video
Conferencing
1.5-3.5 Mbps
Data Stream
Internet / Intranet
Traffic Implication
Bandwidth (BW) required
BW required
BW required, Low latency,
High volume of data stream.
BW required, Transmitted
during fixed time period
Class of Service reservation,
High volume of data streams
Network Need
Higher BW for desktop,
server & backbone
Higher BW for desktop,
server & backbone
Higher BW for server &
backbone, Low latency
Higher BW for server &
backbone, Low latency
Higher BW for server &
backbone,
Low
and
predictable latency
Table 19. Complexity Drivers and Their Impacts [11]
Complexity Driver
Initial Cost
Protocol
Equipment
Management Agents
Management Applications
4.2
2.3.
2.2.
2.2.
Complexity Impact
ATM
GE
4.0
1
1.
2.
3.0
2.0
2.5
2.5
ATM
16.8
2.3
6.6
5.5.
31.2.
Staff Impact
GE
4.2
2.3
4.2
5.5.
16.2
Speed and non-blocking architecture do not always meet demands of new
applications. Quality of Service (QoS), which provides theoretical service level
guarantees for users who need guaranteed timely delivery data, has also an effect over
the performance issue. Today there is two paradigms. GE paradigm says, "buy
bandwidth instead of bandwidth management because bandwidth is cheap enough to
oversupply your network". The ATM paradigm says "bandwidth management is
important; capacity can't be taken for granted, so you will need a network
architecture that can manage capacity for you" [24].
In order to obtain ATM like QoS, there is a need for prioritization, which requires a
classification of traffic. In a LAN switch, classification of traffic can take place based
upon physical port or on information already included within each packet such as
MAC address, IP address, TCP/UDP port number, or actual contents of the packet
[25]. Since classic Ethernet does not provide the ability to distinguish between
applications and provide QoS guarantees, it has not been considered suitable for
networks supporting multiple traffic types including applications using audio or
video. However, recent works on new protocols such as RSVP (Resource reSerVation
Protocol) suggests that appropriate bandwidth reservation can be provided the
emergence of new standards such as IEEE 802.1Q (VLAN) and IEEE 802.1p
(CoS/Prioritization) will provide VLAN capability and explicit priority information
for packets in all networks, including Ethernet. IEEE 802.1p, when combined with
RSVP enhances the ability of end systems and switches to deliver high quality, low
latency bandwidth on a campus scale [19]. In order to have RSVP function and
deliver defined and consistent quality to an application, each network component in
the chain between the client and the server must support RSVP and communicate
appropriately. IEEE 802.1p and IEEE 802.1Q facilitates quality of service over
Ethernet providing a means for "tagging" packets with indications of priority or CoS
desired for the packet. These tags allow applications to communicate the priority of
packets to internetworking devices. RSVP support can be achieved by mapping RSVP
sessions into 802.1p service class. Together, these standards provides a base for endto-end policy based QoS in Ethernet networks [22]. To deliver true policy based QoS,
an amount of bandwidth, a mechanism between applications and networking
equipment, prioritized traffic and an administration and management of the available
bandwidth in the network is needed.
To be effective, policy based QoS needs to manage entire data path from the
beginning of the frame to its final destination. This end to end connectivity is unusual
in the LAN environment because most LANs care only about the frame as far as it
remains in the same segment. Once the frame crosses over a bridge or router
boundary, not enough is known to determine if the frame arrived at its destination.
This problem is solved with end-to-end policy based QoS guaranties. To achieve end
to end QoS, successful LAN switches must implement multiple queues to support
QoS levels assigned. The use of multiple queues will reduce the potential problem of
head-of-line blocking, where a lower priority frame could block a higher priority
frame [22].
IP ToS (Type of Service) is similar to 802.1p, but implemented at Layer-3. IP ToS
also sets aside three bits, in precedence sub-field located in the IP header. It requires
Layer-3 intelligence to be recognized by net devices. Many switches now can map
802.1p to IP ToS in order to preserve CoS priorities beyond the LAN. With either
CoS type, priorities may be set at the user desktop, through applications or other
intelligent software, or priorities may be set at switches in the LAN. Higher priority
applications will then get favored treatment in switches output queues. 802.1p and IP
ToS technology can set only relative priorities because the connectionless nature of
LAN packet rules out the kind of absolute guarantees that true end-to-end circuit
would provide. At the ATM edge, however, absolute guarantees are possible due to
the connection-oriented nature of ATM [20]. Thus, the supposed unique QoS
advantage of ATM is now or will soon be available to all networks [7]. Further more,
GE and ATM will both deliver the same effective level of QoS in most real world
application, because ATM QoS doesn't extend beyond the ATM cloud [18].
GE, by definition is compatible with legacy Ethernet LANs applications. ATM, on the
other hand, requires LANE to handle the routing of packets to cells and back again
which brings the complexity. Similarly, GE is IP compatible while ATM requires
RFC 1557, IP over LANE today, I-PNNI and/or MPOA in the future (Table 20). GE
is excellent choice for high speed LAN. However, GE is limited to a range of 3 km.
To achieve MAN or WAN capabilities, one will have to use either FDDI or ATM [7]
(10 GE will be another alternative [23]).
Table 20. Capabilities of Fast Ethernet, FDDI, GE and ATM [11]
Capability
IP compatible
Ethernet
Packets
Fast Ethernet
Yes
Multimedia
Yes
Yes
Yes
QoS
Yes
RSVP/802.1p
Yes
RSVP/802.1p
Yes
RSVP/802.1p
VLANs
802.1Q/p
Yes
Yes
Yes
Yes
FDDI
Yes
Yes
802.1h
Yes
GE
ATM
RFC 1577, I-PNN, MPOA
Yes
LANE, cell to packet routing
Yes
Applications need changes
Yes
SVCs / RSVP
Yes,
LANE, SVCs to 802.1Q
GE provides one of the most important mechanisms needed for "campus scaled"
multimedia applications, and that is very high capacity and low latency (Table 21).
Many multimedia applications are running today over Ethernet at 10 or 100 Mbps.
Ethernet's capabilities to support CoS are being enhanced at Layer 2 by work
completed in IEEE 802.1p. IEEE 802.1p specifies the use of priority queuing
mechanism to support traffic which may need lower or higher priority than normal,
best effort traffic (Ethernet frame allows 8 priorities) [19], [20].
According to IDC, in 1997, 80% of the installed network connections was based on
Ethernet [7] and the remaining were a combination of Token Ring, FDDI, ATM and
others [11]. Due the scaleable speed of 10/100/1000Mbps, backward compatibility,
modularity, ease of use and all ready installed base, Ethernet based local area
technology is the major candidate for millenium local area networks. According to
IDC 4Q99 researches worldwide GE switches represented 479.572 ports and $534
million in revenue [15]. GE switches soared almost 27% to 608.853 ports during
1Q00 and analysts say that, "The world is turning to GE and away from LAN ATM"
[16]. The projected revenue from GE market will be approximately $1.500 Million by
year 2001 (IDC #12382 Nov.1996) [17].
Table 21. Efficiency, Speed and Latency Comparison [18]
Packet Size (Byte)
64
256
1500
Latency
0.5
2
12
GE
Mbps
95
116
124
Efficiency
%76
%93
%99
Latency
1.4
4
22
ATM (622Mbps)
Mbps
Efficiency
47
%59
62
%77
69
%85
4 Conclusion
ATM is a technology where WAN and LAN can meet. Due its high performance
switching capability, dynamic bandwidth for burst traffic and QoS for multimedia it is
a good choice for WAN connections where managing bandwidth is a must. But we
had to keep in mind that;
 QoS supplied by ATM is only true within the ATM cloud [18].
 %80 of the LAN infrastructure is Ethernet based [7], so putting ATM to the
desktop is not feasible in terms of price/performance. Cost of ATM NICs and fiber
are higher than using CAT-5 and Fast Ethernet within the star topology.
 Since ATM does not have a native support for Ethernet and IP packets, frame to
cell conversion brings %25 to %30 overhead [18], so the real bandwidth for
622Mbps ATM is around 450Mbps which is nearly half of GE.
 In terms of protocol complexity, ATM is far beyond GE [11].
 Latency of ATM (for 1500 bytes packet) is nearly twice of GE and its efficiency is
%85 compared to %99 of GE.
 GE has a superior price/performance, backward compatibility and scalability.
 The new coming Ethernet technology 10GE [23] (10-Gigabit Ethernet) will be a
strong opponent against ATMs WAN dominance.
So GE is and, continues to be the only choice on LANs (Table 22).
Table 22. ATM vs. GE
ATM
LANE (LAN Emulation) , IPOA (IP Over ATM)
MPOA (Multiprotocol Over ATM)
Due the fixed cell size, no one can occupy the
bandwidth for long Periods. Traffic type
specification brings the required QoS
Complex, Requires expertise to administer.
Also scaleable (ATM trunks 155- 622 Mbps)
Consume %25-30 of the bandwidth overhead.
(frame to cell and LANE overhead) 18
Costs more than the equivalent Ethernet option.
Requires training/expertise/management platform.
GE
Supports today's infrastructure. Based on existing,
proven and widely used technology and protocols
Uses RSVP and RTSP (Real Time Streaming
Protocol) to provide ATM functionality (QoS) over
Ethernet/IP infrastructure.
More affordable, practical and simpler alternative.
Scaleable. Operates with 10-100Mbps Ethernet
More efficient bandwidth utilization, with less
fragmentation and overhead.
Low cost of ownership and simple to use and
administer.
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
BRIAN, M. Leod, Gigabit Ethernet Full duplex Repeaters, Packet Engines
TANENBAUM A.S., (1989), Computer Networks , ISBN 0-13-166836-6
HARDY, K. James, Inside Networks, ISBN 0-02-350091-3
TANGNEY, Bredan; O'MAHONY, Donal, Local Area Networks and Their
Applications, ISBN 0-13-539560-7
Internetworking Technology Overview, Cisco, June 1999, Ethernet Technologies
Internetworking Technology Overview, Cisco, June 1999, Token Ring / IEEE 802.5
Gigabit Ethernet At The Core Of Network, ATG's Communication & Networking
Technology Guide Series
ATM Fundamentals Tutorial, http://www.webproforum.com/atm_fund/topic03.html
National Semiconductor, Fast Ethernet The Migration to High Performance LANs
The Road to ATM Networking, Technology White Paper, SynOptics
Implementing Gigabit Ethernet Cost-Performance & Cost of Network Ownership,
Extreme Networks
Gigabit Ethernet: Accelerating The Standard For Speed, Gigabit Ethernet Alliance, 1997
Network Design Guidelines, Extreme Networks
Ethernet Technical Summary, http://www.techfest.com/networking/lan/ethernet5.htm
LAN Equipment Market Navigates the Obstacles in 4Q99, IDC, February 24, 2000,
http://www.idc.com/communications/press/pr/CM022400PR.stm
Gigabit Router, Switch Purchases Soar During 1Q00, IDC, June 12, 2000,
http://www.idc.com/communications/press/pr/CM061200PR.stm
Gigabit Ethernet, Intel Networking Series, Intel
Building Unlimited Intranetworks / VOL 1: High Performance LAN Alternatives, Foundry
Networks
http://www.gigabit-ethernet.org/technology/faq.html
HALE, Tim; CULLEN, Cam, Mapping Ethernet CoS to ATM QoS, Network World
06/21/1999, http://www.nwfusion.com/news/tech/0621tech.html
http://www.ietf.org/html.charters/rsvp-charter.html
The Future of LAN Switching, Special Advertising Supplement to Data Communications,
Extreme Networks
Gigabit Ethernet Alliance, http://www.10gea.org
ATM vs. Gigabit Ethernet: Is this a real battle or no sense?
http://www.nwfusion.com/netresources/Quest2.html?nf
PASSMORE, L. David, Quality of Service in the LAN, June 1999,
http://www.netreference.com/PublishedArchive/Articles/BCR/BCR.6.99.html
FOROUZAN, Behrouz, TCP/IP Protocol Suit, ISBN 0-07-116268-2