Another interesting article in Communication news talking about
PoS technology and ATM .
INTERNET/IP
TECHNOLOGIES
Packet Over SONET
Networking's packet-packed future
Packet over SONET grabs the spotlight as a solo performer.
by Mike Foley, Executive Editor
With IP over SONET's emergence as a competent dance partner
for--and competitor with--ATM in the backbone, information gets to
experience a sort of "Dance of the Protocols" in the Netcracker
Suite. It's interesting to watch the pair mix, while each also tries to show off individual moves and talents.
ATM flaunts a certain amount of maturity onstage, an ability to
perform well with multiple partners (voice, data, and video), and
quality-of-service (QoS) delivery. But the ATM dance (although we
are talking backbone speeds that outpace spins and leaps by
light-years) is not without its latency-plagued missteps. The central
problem is in transferring Internet protocol (IP) traffic (or any other frame-based protocol) to ATM cells and then back. Those two steps of conversion result in wasted bandwidth when compared to pure IP throughout the entire transfer.
PICK YOUR DATA'S PARTNER WISELY
"When you try to marry ATM and IP, you've got some troubles," says
Yuval Boger, VP business development at RADCOM Ltd. This
inefficiency is often referred to as the "cell tax," which is the overhead of various ATM layers that have to be converted. Inefficiency equals wasted bandwidth. And wasted bandwidth equals lost profits.
Boger gives this example: "Let's say a typical IP packet for Internet
browsing is around 576 bytes. If you transfer this over ATM on an
OC-3 link, you are going to be able to use less than 80% (actually
79.6%) of your bandwidth for the actual IP transfer. The other 20% is
overhead--ATM overhead or SONET overhead. Now, if you take the
same packet and put it over Packet over SONET (PoS) technology,
you find that you get 95.4% efficiency. So, over 95% of your
bandwidth can be used for IP, and that's a big savings."
RISING STAR
As large enterprises, and ISPs especially, begin to deploy PoS in
their backbones, the technology is not shy about showing off its best
moves.
"What I'm seeing is that many major ISPs either are using PoS today
or they are moving their backbones to PoS," says Boger. "And this is
Sprint, IBM, UUNET, and others. A lot of ISPs are saying PoS is the
way to go."
"Due to greater payload efficiencies, acceptance of Packet over
SONET technology is booming," says Bruce Bowers, software
development test engineer, optical internetworking business unit,
Cisco Systems.
It makes sense, for example, if you're an ISP delivering
predominantly IP traffic (Internet browsing) that you would stick with IP from end to end. And ISPs especially may not need all of the
advantages that ATM currently has for carrying voice.
There is another difference between PoS and ATM, and it is one of
complexity. When you're working with PoS, you're potentially using all
of the same protocols that you used when you were just using IP
routing. All the routing protocols in the IP suite carry over to PoS. In contrast, bringing ATM into the show requires a whole set of new
controls for ATM that need to be dealt with and managed.
"It is a very attractive proposition for an ISP to see end-to-end
frames--not having to translate into any cells in the middle--and
getting more efficient transfer," says Boger. "And since it is also a
simpler technology, it will probably turn out to be cheaper.
There are critics in the audience (there always are), but PoS can
provide a markedly more efficient way of carrying certain types of
traffic. One way to actually "see" the effectiveness of PoS and to
maximize bandwidth use over large networks is through testing. |
