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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: IP-Internets
Bulent,
I thought Lucent and Bell Labs already knew everything! :-)
> 1- are there any all-IP backbones? what is the layer 2 in IP
> backbones (PPP, ATM, Frame relay...)?
All networks which run IP are "all-IP" backbones. Perhaps
this definition means "A Layer 2 forwarding infrastructure
with only IP traffic". In this case, there are many.
An RBOC FR network could be considered a backbone w/ partial
IP, partial SNA, partial IPX, etc.
Most all facilities-based ISPs run their IP networks on
infrastructures with dedicated L1 TDM or WDM bandwidth.
In Marketing-ese many companies, perhaps mine, say they have a
"pure IP network" -- where they mean that there is no ATM or
FR in the middle, no SONET APS below that, such that all of
the brains and intelligence is embedded in the IP stuffs.
Most of us that use to think that was a really sexy idea now
think MPLS is sexy, so we're calling MPLS the 'forwarding
protocol for IP' and putting some intelligence into MPLS
and some into IP; so as to get the proper blend of intelligence
for constructing robust, scalable, resilient IP transport
networks. Except those wacky people at Qwest who just want
to be different and are overtly influenced by brilliant
yet obstinate swedes.
All IP networks need a layer 2 framing protocol. Most use
ATM, Frame_Relay, HDLC or PPP.
------------------------ = ------------------------
wr1.sfo1#show int pos0/0
POS0/0 is up, line protocol is up
Hardware is Packet over SONET
Description: WR2.SFO1-POS0/0-OC48
Internet address is 206.132.110.73/30
Encapsulation HDLC, crc 32, loopback not set
------------------------ = ------------------------
Some stick MPLS in the middle ala IP/MPLS/HDLC or IP/MPLS/SONET.
Additionally, IP/SONET may actually be IP/DWDM wherein the
Layer 2 framing protocol uses SONET frames but w/out BLSR APS.
> 2- how commonly is IP over ATM used? Do network operators really care
> about the cell-tax?
Fairly commonly, especially among 'mature established large backbones'.
Approximately 5 years ago, ATM switches had OC-12 interfaces while
IP routers only had DS3 or partial-rate OC-3 interfaces.
I'd estimate that 40-60% of Internet traffic traverses IP networks built on
top of dedicated ATM networks. This is shrinking significantly, with at
least one large atm based network transitioning to IP/MPLS.
Therefore the backbone trunks were done w/ ATM to provide interface
capacity. Since then perhaps people/systems have invested so much
in them that it's hard to move away.
Another benefit to using an ATM or FR infrastructure is the Traffic
Engineering (TE) ability.
Network operators care about the 'cell tax' but often one can
increase the overall efficacy of the network with TE to result
in higher gains than are costed by the ATM 'cell tax'.
> 3- what is the approximate number of connections to a
> router (i.e., fan-in, fan-out of a router (i) at the edge, (ii) at the
> core, and (iii) at the backbone?
This is a function of design.
In an ATM network, there will likely be 2 physical connections
to the backbone ATM fabric, w/ N PVCs, in a full mesh, or truncated
start topology.
edge - usually 2 to the BB - 1 to 50,000 for customer aggregation
varies by design
core - usually 2-64 backbone links. most routers have 8-16
line interface slots. Each slot will support 1 - 4
interfaces, kinda usually...
varies by design
BB - see core, generally kinda the same.
> 4- what is the maximum distance between any two points in a autonm.
> system?
I suppose this is infinite. In practice, IP packets provide
8 bits for the TTL, so a maximum 'diameter' is 2^8== 256 IP
hops.
Note that IP hops are just that, Layer 3 opportunities for
Layer 3 forwarding decisions along w/ requisite TTL decrementation.
These are often hidden, in networks with IP/ATM or IP/FR, and also
sometimes with IP/MPLS. This is psuedo analagous to not counting
SONET switches, amplifiers, repeaters, monitors, etc...
>
> 5- what is the approximate ratio of copper/fiber
> at the edge, core, backbone links?
edge : 90% copper, 10 optical
core: usually inter-office cabling is mostly optical, be it
OC-n or gig-e.
backbone: if BB ge OC-3; optical, if under OC-3, copper.
> 6- how tight is the physical space in the router rooms
> (i.e., is it almost a must to take out an old box in order to add one)?
space is one of the limited resources that an ISP has. It is
generally a very significant issue.
In many cases, 'silicon economics' allows folks to take out 2 boxes
to put in one box that does 4 times as much.
'forklift upgrades' are not always required.
utopian designs provide 'buffer floor space' such that unused rack
capacity is always available for new product insertion to avoid the
need for 1:1 swap-outs during real time modifications.
> 7- in case of a node/link failure what is the average/approx period of
> time for (i) detection and (ii) recovery
depends. SONET/APS is alleged to be 50ms.
ATM and FR PVCs tend to re-route on the order of 1-5 seconds.
IP convergence tends to re-route on the order of 30 seconds.
MPLS tends to reroute today on the order of 30 seconds, but real
soon now on the order of 1 second.
-alan
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