DCN_4_Unicasts%2C+Multicasts+and+Broadcasts - Unicasts...

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Unicasts, Multicasts and Broadcasts Unicasts, Multicasts and Broadcasts (updated ) (updated )
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LANs as a Shared Medium LANs as a Shared Medium A "Private" Conversation A "Private" Conversation Multicast Addressing Multicast Addressing Contents Contents
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In this section we 'll describe the way that shared LAN technologies operate with respect to frame addressing and recognition . LANs as a Shared Medium LANs as a Shared Medium A "Private" Conversation A "Private" Conversation Multicast Addressing Multicast Addressing Contents Contents
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Here is a typical shared LAN. Multiple attached hosts, usually PCs, share a common communication channel. Host 1 Host 1 Host 2 Host 2 Host 3 Host 3 Shared LAN Cable Shared LAN Cable
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If Host 1 transmits information into the shared channel, then it "passes by" all of the other devices connected to the channel. Host 1 Host 1 Host 2 Host 2 Host 3 Host 3
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Host 2 Host 2 Host 3 Host 3 If Host 1 transmits information into the shared channel, then it "passes by" all of the other devices connected to the channel . Host 1 Host 1
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Note that the exact physical representation of "passing by" is installation-specific. This older Ethernet installation is a bus-based system. Ring-based LANs and hub-based LANs may look different but they operate under the same assumption that all devices in the shared channel will be able to see each others' messages. Host 2 Host 2 Host 3 Host 3 Host 1 Host 1
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Host 2 Host 2 Host 3 Host 3 Host 1 Host 1 Two reasons that this ‘broadcast nature’ in a LAN is not universally desirable. First, we often wish to send messages between two specific devices, such as Host 1 and Host 3 without other devices, such as Host 2, being able to see the information. Second, in a busy LAN, other devices' conversations should not be allowed to influence the performance of stations that are not involved in the conversation . "Private" Conversation?
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let's see how we can achieve the impression of privacy in our shared LAN systems . LANs as a Shared Medium LANs as a Shared Medium A "Private" Conversation A "Private" Conversation Multicast Addressing Multicast Addressing Contents Contents
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Host 1 Host 1 Host 2 Host 2 Host 3 Host 3 To achieve privacy in our conversations, we can give each device on the shared channel a unique address, and transmit our information in units which contain the address of the destination device. We can also include our own, sending address, so that the other device can reply directly to us. Note that these addresses operate at the MAC Layer of the OSI model, Address: H1 H2 H3
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Host 1 Host 1 Host 2 Host 2 Host 3 Host 3 The information units that contain these addresses are called ‘frames’. Frame Frame
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The information units that contain these addresses are called frames.
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