I'm trying to mark a paper that deals with networks and I'm trying to establish whether a question is correct.
The question offers a diagram of a network topology bringing together ethernet (star and bus) and token rings (includes a printer). A number of devices are attached to each of the networks. These networks are joined by a gateway.
The question is whether any of the following statements is correct.
Not all data packets pass through the gateway (My guess, since the token ring only passes packets to those with the correct token)
Data packets are sent only to the intended receiver (the ethernet broadcasts to all nodes, so this can't be true)
All data packets are transmitted to all devices (again the token ring networks fails this)
Printing cannot be initiated from the devices in the star network (this must be wrong since a gateway joins the ring and star)
Would the answer be different if there were a hub rather than a gateway (I assume this would divide the token ring from the rest of the network)?
Are you talking only about level two, that is ethernet & token ring? Or IP? Makes a big difference. Also, define gateway. While it's is technically possible to bridge ethernet & token ring, it's not common. Gateways usually refer to IP (or other routable protocol) routers.
It's possible, though not likely.
If a switch is used, only broadcast frames are sent to all nodes (assuming the switch tables are current).
Not necessarily. Can't say for sure, without further details. For example, if IP it is possible. However, this one conflicts with the previous question.
More info about protocols used please.
In ethernet, a hub forwards all frames to all devices and in the conventional sense is a different device from a gateway. Also a hub cannot connect ethernet to token ring. Ethernet and token ring can be connected either through a special type of bridge that can convert between token ring and ethernet or with a router which can connect different technologies.
You'll have to expand on the details. You also need to learn more about level two (ethernet, token ring etc.) and level three (IP, IPX etc.) networking. Also read up on hubs, switches (including bridges) and routers.
When you say you're "trying to mark a paper" do you mean "grade a test"? If so, then the "right answer" would be the one that matches what the students were told in class and in their texts--anything else would be unfair and if what they were told in class and in the texts is wrong then you need to address that rather than punishing the students for the faculty's error. If you are a grader or a TA then you really should ask the professor this question.
If you mean that you are trying to answer a homework question then you really should learn to research this sort of thing yourself, however since the question seems to be ill-posed in this case I can forgive a certain confusion.
Right here there's a problem. "Gateway" is a very fuzzy term. It could be a bridge, a router, or something at a higher level than that. The students are going to have to make some assumptions about the definition of "gateway"--the sharp ones will see this and state their assumptions, the less sharp ones will go on whatever notion they may have of its definition assuming that what they know is correct.
Leaving aside the nature of ring networks, since the gateway is between the Token Ring and something else, the nature of Token Ring has little to do with what gets passed through the gateway. That will be determined by the specific nature of the gateway--all, some, or none may be passed.
It can be if all the Ethernet and Token Ring ports are on a common bridge (such bridges do exist).
Well, actually, you seem to have a misconception about Token Ring. In a Token Ring each device sends data to one and only one device, the one on the other end of the cable connected to the transmitter in its NIC. The MAU is an essentially passive device.
If the ring is not switched, then the data goes from one machine to the next around the ring until it gets to its destination, and the destination then retransmits the data around the ring until it returns to the originator, which compares what was sent with what was received. So each frame actually passes through _all_ devices on a non-switched Token Ring. If it is switched then the switch sends the frame to its destination directly.
Depends on the design of the gateway. If it is one that either supports printing directly or passes the necessary packets then printing can take place, otherwise it can't.
A "hub" is, compared to a "gateway", a well defined device--these days with many devices sold as "hubs" actually being bridges it isn't as well defined as it once was, but it's still much clearer than "gateway". Since there is no such thing as a "hub" that will join Ethernet and Token Ring, they would indeed be isolated.
One other thing. There's no such thing a the "correct token". There is one token that gets passed around the ring and grabbed by a host wishing to transmit. When the transmission is completed, the token is put back on the ring, for the next host etc. A token has absolutely nothing to do with what gets passed through a "gateway.
Correct again, but this paper contains the ambiguity described and if there is no correct and sensible answer, or if there is more than one sensible answer I am ethically bound to deem all such answers correct.
Originally, I examined the paer and found the term "hub" where I said there was a gateway. I assumed this was an error and replaced it so that the ethernet linked-devices could exchange data with the token ring devices, but with hindsight, the "error" might have been intentional -- an attempt to psoe this very question and test knowledge of the difference between a gateway and a hub.
I've found this a little confusing myself as gateways and "bridges" are often used interchangeably in terminological terms at least. A "gateway" seems to be a more sophisticated bridge, and a "router" may well contain hardware components that allow it to move data between different protocols.
I'm a teacher working in a setting where this coterie here is likely to be the best qualified to answer.
Indeed
So does that mean that the question as posed is impossible to answer with certainty?
I assumed that it was a feature of token rings that any data packet passing within the ring (eg between a node and the attached printer) would not pass through the gateway.
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The diagram showed:
Area 1
Standard Star Network
Devices:
Hub; MinPC; Disk Array; IBM AS/400
a LAN cable of some sort joins it to the gateway/(hub in original)
Two LAN cables leave the gateway one to the:
Token Ring in Area 2
Devices: Laser Printer; IBM PC; Server;
and the other to:
Area 3 Standard Bus Network
Devices: iMAC; server; Printer; raid drive
||||||||||||||
OK
I see, so technically, the data packet does go to each device but is rejected until it reaches the one for which it was intended?
You seem to be saying that there isn't sufficient information to say.
I haven't thought about token ring for a while, but I thought the data packets went all the way around the ring. The sender then removes it and sends a token to the next host.
(snip)
Hub is, traditionally, the device at the center of a hub and spoke network topology.
For ethernet in the beginning it was a repeater and it is often considered as a synonym for repeater, but that is technically incorrect. (As are many other commonly believed ethernet rules.)
I believe that hub was used for TR even earlier than ethernet, though I have known eight port 10base2 repeaters that could be considered hubs, even before UTP ethernet existed.
Generally speaking, a "bridge" connects two networks at the datalink layer (the layer that defines "ethernet" or "token ring" or "arcnet" or whatever), a router operates at the network or transport layer (the layer that defines "TCP/IP", "IPX/SPX", etc), and a gateway operates above this level.
Any literature that refers to a bridge as a gateway or vice versa is _not_ to be trusted--it is either very sloppy or very old.
You are correct.
If the gateway is attached to the token ring then each packet will be seen by the gateway--what the gateway does with it is another story.
AS/400? Now _that_ complicates things, and the effect depends on the vintage--early AS/400s could not communicate directly with PC printers--something emulating the kind of printer or print server it expects had to be attached to the network--I don't know to what extent this has changed in more recent models.
That might be Twinax--the AS/400 has its own unique network standard, called "System Application Architecture" (different from SNA, lurkers) used primarily to connect terminals and printers. That would make sense as SAA can have hubs, although there may be IBM-ese for them that I don't recall.
In any case with the AS/400 a gateway makes more sense--it would likely be an SAA gateway--a couple of examples are Novell "Netware for SAA" and Microsoft "SNA Server", which also supports SAA. Among other things it would probably expose PC printers to the AS/400 and provide terminal emulation, and may provide other services.
At one time, before IBM repositioned their midrange and mainframe systems as servers, this was one of the the standard ways to connect an AS/400 to a PC network, the other being to put 5250 (the standard AS/400 terminal was the IBM 5250) emulation boards in the PCs that were to be used as terminals.
I'm no AS/400 expert by the way, you might want to try to find a more specific newsgroup for advice on that end--it's really outside of the Ethernet world and the PC world as well--it's an IBM Midrange system, which used to be considered "heavy iron", and it's better to think of it as a mainframe than as a PC.
"Standard bus network" doesn't mean anything. In fact there isn't any bus network to which an iMac can be attached directly--its ports are 100TX IIRC--you'd need a converter to attach to 10base2 and I don't know if it works with localtalk at all.
Not rejected, just passed along and otherwise ignored.
On Token Ring it's a "Multistation Access Unit", aka "MSAU" or "MAU", the latter pronounced like the name of the late Premiere of the People's Republic of China.
I think you were correct in assuming that the term "hub" was an error; otherwise, the network diagram becomes totally meaningless. See below.
No, we're talking about different concepts here.
A hub is a passive ethernet repeater. It sends everything it receives on one port out all the other ports, and that's it. Some consider a hub a layer 1 device, but it's mostly referred to as a layer 2 device.
A bridge is _always_ a layer 2 device, meaning it forwards frames to and from two different network segments. A bridge can only function between segments made up of the same network topology, with one exception: It is possible to bridge between Ethernet and Token Ring. A switch is a bridge with more than two ports.
The main difference between a bridge/switch and a hub, is that a bridge automatically "learns" which layer 2 addresses are at which end of the bridge, by simply watching the source MAC addresses of the frames. It then stops forwarding frames that are not relevant to the segment.
A "gateway" is a rather loose term that usually means "a router", but it could conceivably also mean an application level proxy, and all sorts of other things as well. A gateway relates to a hub and a bridge a bit like "public transport" relates to a train and a taxi.
Token Ring is a type of layer 2 topology. It is highly unlikely that this "gateway", whatever it is, operates at layer 2.
Token Ring works roughly like this: All nodes in a ring are connected to a passive repeater unit called a MAU. The MAU is basically just a bunch of relays.
A short data frame, called "a token", is passed from node to node around the ring. Whenever a node needs to send data, it first waits for the token. It then attaches its data to the token, and sends it to its neighbour.
The neighbour recognizes that the token has data attached to it, and passes it on. It does this whether it is the intended recipient of the data or not. When the originating node gets its own token+data back, it generates a new token, and sends it to its neighbour.
Some newer versions of Token Ring supports "Early Release Token", which means that the transmitting node generates a new token immediately after sending the token+data frame.
But I digress. :)
The first thing this diagram tells me, it that the person who made it, has very limited knowledge about networks. First of all, there's no such thing as a "standard star network", and much less a "standard bus network". Also, "RAID drives" and "disk arrays" are not network units, they are either part of a server or inside a NAS unit.
But the diagram is relatively clear about one thing: We're talking about three different network topologies. The "star network" is probably Ethernet (although star-based ArcNet also exists), and the "bus network" is probably supposed to mean Apple LocalTalk (but could also be ArcNet or coax-based ethernet). Token Ring is the only unambiguous term here.
This means that your "gateway" must be a router. It can certainly not be a hub, since no such device exists that would allow one to connect Ethernet, Token Ring and LocalTalk.
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