March 21, 1998
By Andrew Cray
Product Leaders: Remote Access Servers
Ratcheting Up RAS Performance
A bigger backplane and faster processors help Ascend's Max 6000 keep up with the calls
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Want to build a better RAS? Make it bigger and faster—which is just
what Ascend Communications Inc. has done. The vendor says that its Max
6000 remote access server o
utperforms its predecessor—the Max
4000—which wilted under the heat of end-users dialing into all 120
ports simultaneously.
How does the 6000 stand up to the strain? It has a larger
backplane, faster processors, and improved compression—plus more
memory, according to Ascend, which says the new and improved RAS
delivers full line speed on all 120 ports at once. Throw in a
100-Mbit/s fast Ethernet connection to the corporate LAN (instead of
the 4000's 10-Mbit/s link) and the ability to terminate more calls
from remote users, and net managers stand to see serious gains over
the Max 4000.
So much for the in-house comparison. What network managers really
need to know is how the new RAS rates against the rest of the
world—and many competing vendors say the performance of their products
at least equals that of the Max 6000's (there have been no independent
tests to verify claims). What's more, the 6000's compression may not
be all it's cracked up to be: With ISDN compression turne
d on, for
example, the 6000 squeezes about 112 kbit/s of throughput into a
56-kbit/s link. But that's only if up to 60 ports are running at once;
crank that up to 92 ports and the figure drops to about 78 kbit/s.
A Better Box?
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Cranking Up the Calls
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The Max 6000 chassis comes with six slots for modem cards, which
can carry 8, 12, or 16 56-kbit/s analog modems each (for a total of up
to 96 in a fully loaded unit). The RAS can terminate up to 120 ISDN B
channels via HDLC (high-level data link control) controllers built
into the chassis. The actual number of dial-in ports (either analog or
ISDN) is limited by the WAN interfaces: The Max 6000 has four, which
can be either T1 (1.544 Mbit/s), E1 (2.048 Mbit/s), or ISDN PRI
(primary-rate interface) (
see
the figure
).
Ascend's new RAS specifically addresses performance—an issue that
dogged its predecessor. According to Max product management director
Dana Harrison, the 4000 dropped below line speed after just 50
calls—and that's with compression turned off. Activate compression and
the figure fell to 40 calls, which basically meant users were better
off simply not applying the squeeze at all.
But the 6000 has a larger backplane—1.1 Gbit/s as opposed to
the 4000's 800-Mbit/s backplane. And with a bigger power supply, it
can handle more modems in a single chassis. It also boasts a processor
that runs at 64 MHz instead of just 25 MHz. Finally, two compression
coprocessors (instead of one) help it hit 2:1 compression on up to 60
simultaneous ISDN calls, dropping off gradually after that and never
falling below line speed.
Whether or not users really need that big a performance boost
depends on how they load their RASs. "I don't run my boxes above 30
percent capacity," sa
ys Larry Jones, manager of remote access services
at Computer Sciences Corp. (El Segundo, Calif.), a computer services
firm, explaining that he has strict SLAs (service-level agreements) to
stick to. But he adds the 6000 might be the way to go for net managers
with higher loads.
Dram-atic Increase
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MORE INFO
Product Summary
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There's more to the 6000, however, than improved performance. It
also comes with 16 Mbytes of DRAM (dynamic RAM), upgradable to 24 or
32 Mbytes. That means bigger buffers, fewer dropped packets, and the
ability to load more features (like support for more routing and
management protocols) into the vendor's True Access Operating System.
The Max 4000 had just 8 Mbytes of memory, so it couldn't route IPX and
Appletalk protocols whil
e handling OSPF (open shortest path first),
notes Ascend (Alameda, Calif.).
The Max 6000 also is more expandable. It can be loaded with the
vendor's voice-over-IP cards, and it also will work with Ascend's VPN
(virtual private network) encryption cards when they're launched later
this year. In addition, the box has 2 Mbytes of flash memory, which
means there's no need to take it out of service when making
upgrades.
So how does the new RAS size up against the competition? That's
hard to tell, since there haven't been any independent tests yet.
Ascend says the 6000 beats the AS5300 from Cisco Systems Inc. (San
Jose, Calif.) and the Portmaster 3 from Lucent Technologies Inc.
(Murray Hill, N.J.) on the performance front. Cisco begs to differ,
claiming its RAS also hits line speed out to 120 ports. What's more,
Cisco claims 2:1 compression (thanks to a 150-MHz processor) and
points out that the AS5300 boasts 32 Mbytes of memory.
And as might be expected, new and improved means a new (and hi
gher)
price: The Max 6000 costs $51,840 for a fully loaded chassis with 96
analog modems. Cisco's AS5300 with 96 modems costs $44,960. For a
48-modem unit, Ascend charges $31,440, while Cisco sets a price tag of
$26,100.
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