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payloads must be extended, SONET s poor signal concatenation
schemes do not allow for full use of the payload, and the payload s
bandwidth slot is left mostly empty. SONET is strictly a transport
technology and unaware of payload traffic. It cannot address data
transport requirements efficiently. Figure 4-15 depicts a SAN over
MAN architecture.
This brings us to the WAN s major data transmission technology:
ATM. Originally, ATM was considered the end-all solution for build-
ing a single topology across all networks. However, its complexity
and high cost made it another victim of Ethernet in the LAN, and
these same disadvantages could be its downfall in the WAN now that
Ethernet has developed a competitive solution for that space.
The main arguments for ATM s continued success is its ability to
provide true QoS and easy provisioning. In contrast with ATM s abil-
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Configuring SANs: Dos and Don ts
Configuring SANs: Dos and Don'ts
71
ISCSI ISCSI ISCSI
Figure 4-15
Extending SANs
over MANs
IP
Switch
ISCSI provides a native IP link to
IP
Metropolitan and Wide Area
Switch
Networks (MANs/WANs)
ISCSI ISCSI ISCSI
ISCSI ISCSI ISCSI
ISCSI Servers
Secondary Data Center
ISCSI Storage Network
IP
ISCSI ISCSI ISCSI
MAN/WAN
Shared or Dedicated
IP Network
IP
ISCSI Storage
Switch
Devices
ISCSI ISCSI ISCSI
IP
Switch
Primary Data Center
ISCSI Storage Network
ISCSI ISCSI ISCSI
Storage Service Provider
ISCSI Storage Network
ity to guarantee that certain data will have certain levels of service,
Ethernet, at its best, offers CoSs, basically as a best-effort service.
ATM s flexible provisioning ensures that customers receive the
bandwidths they pay for when they pay for them.
The advantages of ATM may be major pluses from a WAN stand-
point; they are much less a factor in the LAN. With Ethernet s cheap
and easy bandwidth, throwing extra bandwidth at them can solve
QoS and provisioning problems. Throwing bandwidth at a problem is
just not a traditional WAN way of solving a problem. And when the
costs involved in adding extra bandwidth to a traditional WAN sys-
tem are considered, this makes perfect sense. However, when your
bandwidth prices for 1 Gbps of service are cut from one-fifth to one-
tenth of customary levels, the  more bandwidth approach looks
more reasonable in the WAN.
The ability of 10 Gb Ethernet to compete with ATM and SONET
opens up a market that has never been available to Ethernet. In
2000, combined ATM and SONET revenues were almost $21 billion.
In 2004, the combined market will be $40 billion. However, the intro-
duction of Ethernet could change these numbers drastically. From a
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Configuring SANs: Dos and Don ts
Chapter 4
72
revenue standpoint, the overall size of the WAN infrastructure mar-
ket could fall as less-expensive Ethernet equipment floods the mar-
ket. However, equipment shipment numbers could rise due to its low
cost and ability to provide the extra bandwidth needed for QoS and
easy provisioning. Refer to Figure 4-16 for a combined ATM and
SONET market comparison.
The next 5 years will be interesting ones for the Ethernet world.
10 Gb Ethernet has the LAN locked up. The MAN space is already
taking on overtones of the LAN battle part II. It seems that the LAN
mindset is working just fine in the MAN space despite MAN s WAN
roots. The WAN is where true magic may happen. 10 Gb Ethernet s
use of SONET framing in the WAN physical layer asynchronous
Ethernet interface sets the stage for 10 Gb Ethernet compatibility
with all the traditional carriers legacy equipment. This optional
WAN physical layer interface includes a simple, inexpensive SONET
framer; it operates at a data rate compatible with the payload rate of
OC-192c/SDH VC-4-64c. There are significant invested interests in
SONET and ATM, so don t expect these technologies to go down
without a fight.
It is true that 10 Gb Ethernet has speed (100 Gb Ethernet could
be a reality in as little as 4 years), price, simplicity, SONET compat-
COMBINED ATM AND SONET/SDH MARKET
2000 & 2004
Figure 4-16
SONET versus ATM
$40
$30
$20
$10
$0
2000 2001
ATM SONET/SDH
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Configuring SANs: Dos and Don ts
Configuring SANs: Dos and Don'ts
73
ibility, and widespread industry support from LAN and WAN ven-
dors. What it does not have is true QoS, provisioning, or the long-
haul ranges of SONET.
The current advantages of 10 Gb Ethernet are almost the same as
the strengths that enabled Ethernet to win over the LAN. These [ Pobierz całość w formacie PDF ]