Review of Designing Large Scale LANS, by Kevin Dooley
Good book! This is what the title implies: a book about designing large networks. It's not primarily an implementation book. It treats its subject rigorously, but without tons of detail at the end points. For example, you won't find cat5e pinouts discussed. You will see a redundant, heirarchical network design. I like a book with real math as , and the author actually provides some for aggregate Meant Time Between Failure (MTBF) calculations. Stats and probability! Cool! He gives less rigorous but useful rules of thumb for capacity planning.
Lot's of advice reflecting his extensive real-world experience. Like the importance of physically redundant trunk links (rather than just two circuits in the same fiber bundle|conduit). My impression was that stuff never failed unless a backhoe severed it, but I was...incorrect. Thanks! I will be working on a plan to get redundant links in place.
I had an intuitive sense that there is a trade-off between redundancy and complexity. Reliability is the goal, and you can add features (primarily redundant circuits and components) to a point where the complexity reduces reliability. Dooley gives a fairly clear impression of where the trade off is profitable.
The VLAN treatment is extensive. Again, I knew that trunking all VLANS on the campus net across all trunks was wasteful; he quantifies it.
Overall, the book stands up well after 4 years. He doesn't spend much more than a sentence or two on wildly obsolete media like 10Base2 (coax). There's the occasional PanAm moment (the shuttle taken to the space station in the movie "2001" is operated by PanAm) like when he refers to Compaq as a manufacturer of network interface cards. I still see issues with 10BaseT and probably you do too, so I don't begrudge him any space on the topic. He was forward thinking enough to mention gigabit ethernet. He refers to Cat6 cable as a future standard. He cautions against using intermediate patch panels, which I was given to understand are o.k. One major building on our campus uses them, at the behest of the wiring designer. Oops. I haven't noticed any problems, but now I know to look.
Wireless is the area where change has been fastest, I think. Probably something to do with inexpensive, commodity hardware (with broken initial specs) leading to faster refresh rates. He mentions (back in 2002, I remind you) the utter brokenness of the WEP encryption standard. But if wireless in detail is your thing, this is not your book.
There isn't much on different types of fiber optic cable. (not in book - this is my own accretion of data) What I know of is: single-mode has 9nm cores, and goes from 10km to 80km depending on the fiber transceivers. Multi-mode is in 50nm (newer(?) better distance|speeds) and 62.5nm (more common) cores. If you reach this page trying to see what the difference is etc., you can actually sub the multimode cable pretty freely. You will lose signal going from 62.5 to 50nm, but the optical power budget may support a connection even with the loss. Every splice and connection costs signal power. Every meter of distance costs signal power. Takeaway
is that SX transceivers (for multimode) don't care which you use, so you might as well install 50nm fiber. Single-mode transceiver vendors HP, Cisco, and Transition Networks use different names to designate stuff for the 10 km vs. 80 km stuff. For Transition, you have to look at the specs for particular units. They make a variety and call them all LX.
The IP routing/subnetting stuff is good.
QoS treatment is good: he shows why you can't just throw bandwidth at a problem to give good video|voice. Variable latency (called "jitter") makes it hard for voice|video apps to buffer, leading to pops and crackle that drive users up a tree. Of the three approaches, he recommends only Guaranteed Delivery will suffice.
Multicast treatment is good. I have never had a handle on that stuff. Now I do.
Some good operational details - in the network monitoring section, he urges us to monitor even quiet backup links. If the backup failed and nobody noticed, they will when the primary dies.
In sum, this book is worth the time to read it. It's a little old, but the stuff that is essential to its topic has not changed. Heck, the age just means you can get it dirt cheap. Check ebay or amazon used.
Good book! This is what the title implies: a book about designing large networks. It's not primarily an implementation book. It treats its subject rigorously, but without tons of detail at the end points. For example, you won't find cat5e pinouts discussed. You will see a redundant, heirarchical network design. I like a book with real math as , and the author actually provides some for aggregate Meant Time Between Failure (MTBF) calculations. Stats and probability! Cool! He gives less rigorous but useful rules of thumb for capacity planning.
Lot's of advice reflecting his extensive real-world experience. Like the importance of physically redundant trunk links (rather than just two circuits in the same fiber bundle|conduit). My impression was that stuff never failed unless a backhoe severed it, but I was...incorrect. Thanks! I will be working on a plan to get redundant links in place.
I had an intuitive sense that there is a trade-off between redundancy and complexity. Reliability is the goal, and you can add features (primarily redundant circuits and components) to a point where the complexity reduces reliability. Dooley gives a fairly clear impression of where the trade off is profitable.
The VLAN treatment is extensive. Again, I knew that trunking all VLANS on the campus net across all trunks was wasteful; he quantifies it.
Overall, the book stands up well after 4 years. He doesn't spend much more than a sentence or two on wildly obsolete media like 10Base2 (coax). There's the occasional PanAm moment (the shuttle taken to the space station in the movie "2001" is operated by PanAm) like when he refers to Compaq as a manufacturer of network interface cards. I still see issues with 10BaseT and probably you do too, so I don't begrudge him any space on the topic. He was forward thinking enough to mention gigabit ethernet. He refers to Cat6 cable as a future standard. He cautions against using intermediate patch panels, which I was given to understand are o.k. One major building on our campus uses them, at the behest of the wiring designer. Oops. I haven't noticed any problems, but now I know to look.
Wireless is the area where change has been fastest, I think. Probably something to do with inexpensive, commodity hardware (with broken initial specs) leading to faster refresh rates. He mentions (back in 2002, I remind you) the utter brokenness of the WEP encryption standard. But if wireless in detail is your thing, this is not your book.
There isn't much on different types of fiber optic cable. (not in book - this is my own accretion of data) What I know of is: single-mode has 9nm cores, and goes from 10km to 80km depending on the fiber transceivers. Multi-mode is in 50nm (newer(?) better distance|speeds) and 62.5nm (more common) cores. If you reach this page trying to see what the difference is etc., you can actually sub the multimode cable pretty freely. You will lose signal going from 62.5 to 50nm, but the optical power budget may support a connection even with the loss. Every splice and connection costs signal power. Every meter of distance costs signal power. Takeaway
is that SX transceivers (for multimode) don't care which you use, so you might as well install 50nm fiber. Single-mode transceiver vendors HP, Cisco, and Transition Networks use different names to designate stuff for the 10 km vs. 80 km stuff. For Transition, you have to look at the specs for particular units. They make a variety and call them all LX.
| Vendor | 10km | 80km |
| HP | LX | LH |
| Cisco | LX/LH | ZX |
| TransitionNetworks-doesn't follow pattern | LX | LX |
The IP routing/subnetting stuff is good.
QoS treatment is good: he shows why you can't just throw bandwidth at a problem to give good video|voice. Variable latency (called "jitter") makes it hard for voice|video apps to buffer, leading to pops and crackle that drive users up a tree. Of the three approaches, he recommends only Guaranteed Delivery will suffice.
Multicast treatment is good. I have never had a handle on that stuff. Now I do.
Some good operational details - in the network monitoring section, he urges us to monitor even quiet backup links. If the backup failed and nobody noticed, they will when the primary dies.
In sum, this book is worth the time to read it. It's a little old, but the stuff that is essential to its topic has not changed. Heck, the age just means you can get it dirt cheap. Check ebay or amazon used.
posted by JimmytheGeek at 11:50 AM
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