4- what is the maximum distance between any two points in a autonm. system? 40,000 Km / 2 = 20,000 Km. -:)

And I know at least 1 example, surely there is dozen of such networks.

Date: Thu, 14 Oct 1999 11:02:04 -0400 (EDT) From: Bulent Yener <yener@research.bell-labs.com> Subject: IP-Internets [...] 2- how commonly is IP over ATM used?

From the ATM Forum Board of Directors Report - Rome, Italy, April 23,1999: ... Fred [Baker, chair of the IETF] stated that 75% of all Internet traffic today touches an ATM device and acknowledged the importance of the role of ATM in providing traffic engineering in today's networks. ... I don't really know where this number comes from nor whether it is really true. A number of facilities-based carriers are either migrating or talking about migrating from ATM to some sort of IP-over-fiber solution. I believe that the economics of ATM versus IP-over-fiber solutions are tremendously different for those who own fiber compared to those who don't own the fiber.

Do network operators really care about the cell-tax? [...]

Define "care". Certainly, one sees a lot of whining about the ATM "cell tax". On the other hand, if Fred Baker is correct, ATM is heavily used in the Internet. Having said that, I believe that any ISP that selects a service on the basis of some sort of overhead measurement, rather than an evaluation of cost versus performance, is confused. -tjs

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