06-23-2004 08:24 AM - edited 03-02-2019 04:34 PM
Hi,
Is anyboby can tell me if an ATM switch can also be a IP router?
Have you a reference?
Regards,
Michelot
06-23-2004 09:10 AM
No, it can't! An ATM switch is a layer 2 device and its capabilities ranges all over layer 2 functions, mainly ATM cell switching (from an incoming VP/VC to an outgoing one), label switching and CoS procedures.
Some devices integrates ATM whit IP capabilities (or, we should better say, IP with ATM) but, in this case, we are dealing with a Router that supports ATM interfaces.
Usually Routers with ATM interfaces are capable of ATM cell termination (Segmentation and reassembly + ATM Adaption Layer) because these two functions are stictly necessary for the local 'reconstruction' of the IP packet.
These routers gives you some basic ATM functions like the switching (limited to the same physical ATM interface) and basic CoS management.
06-23-2004 10:57 AM
Hi Nekko,
Thanks for your very good explanations.
I mistook switch with ATM router (with ATM interfaces).
Most of the time, to draw an ATM network, we link the switches by a direct line (Switch A ---- Line for the link ---- Switch B).
But between switches, we can have a router with multiple ATM interfaces. Suppose a router with 3 ATM interfaces. In this case, I can represent an ATM-level diagram like that : switch A --- Y junction (output B to switch B, output C to switch C).
Is this network layout really exists? The router doesn't change (Vp, Vc) but cells are convey either to port B or C, according to IP address. Is it a none sens?
Thanks,
Michelot
06-24-2004 05:38 AM
Hi Michelot, I've just read your reply!
You can put a router in the 'core' of your network (the router, if I'm not wrong, realizes the Y junction, isn't it?) and everything will work! But this could not be the best solution:
here we face with your particular project; the number and type of network interfaces available on each devices, the 'type' and bandwidth of WAN links, the performance required among each node pair and other variables.
All these variables could lead to different (and sometime opposite) solutions: for example, if WAN links are leased lines you can manage them unconditionally; in this case you could put the ATM switch in the core, connect all the leased lines to the ATM to one side and to a router on the other and create the number and type of PVC (VP/VC)required (you can do this because YOU manage the ATM network). On the other side if WAN links are provided by an ISP they probably 'come' with a fixed and unchangeable PVC configuration: in this case a Router in the core of your network is mandatory and will be the only way to provide the flexibility and scalability you need!
You can use ATM in differnet ways: 'only' as a framing protocol OR as a framing + switching 'suite'; in your project you use ATM as a framing protocol over physical links: switching capabilities are fully damanded to layer 3 (that is, IP in the core router, that will decide how to route packets on a layer 3 and/or layer 4 information basis). Pros: extreme flexibility typical of IP. Cons: to be evaluated.
I usually prefer to design my project using ATM for its switching capabilities (like Ethernet) putting it everywhere is possible, beginning (mandatory) in the core's lower layer, and bringing IP to the edge, 'near the users'. This approach leads to a very performing and reliable network but, often, more expansive and complex to manage.
Hope this helps.
Bye
06-25-2004 01:09 PM
Hi, Nekko
I'm studying your very informative help
Regards,
Michelot
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