3 ICS132-MAC-layer

3 ICS132-MAC-layer - Medium Access Sublayer Medium Access...

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edium Access Sublayer Medium Access Sublayer
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edium Access Sublayer Medium Access Sublayer Network Layer ata Link Layer Medium Access Sublayer Logical Link Control Sublayer Data Link Layer Physical Layer
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EE 802 Standards IEEE 802 Standards
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edium Access Sublayer t d ) Medium Access Sublayer (cont’d) Medium access (MAC) sublayer is not important on point-to-point links The MAC sublayer is only used in roadcast or shared channel networks broadcast or shared channel networks Examples: Satellite, Ethernet, Cellular
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ogical Link Control Sublayer Logical Link Control Sublayer Logical Link Control (LLC) sublayer provides mechanisms for reliable communications cknowledgement, etc acknowledgement, etc
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AC Sublayer: Contents MAC Sublayer: Contents Fixed Assignment Protocols emand Assignment Protocols Demand Assignment Protocols Contention Access Protocols IEEE 802 LANs DQDB and FDDI
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ixed Assignment Protocols 1. Fixed Assignment Protocols Static and predetermined allocation of channel access: independent of user activity le users may be assigned to the Idle users may be assigned to the channel, in which case channel capacity wasted is wasted Examples: TDMA, FDMA, WDMA
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emand Assignment Protocols 2. Demand Assignment Protocols Allocate channel capacity to hosts on a demand basis (i.e., only to active users) Requires methods for measuring the emand for the channel demand for the channel Polling eservation schemes Reservation schemes Token Passing Scheme
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1 olling 2.1 Polling A central controller interrogates each host and allocates channel capacity to those who need it Good for systems with: Short propagation delay Small polling messages Non-bursty traffic
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2 eservation Schemes 2.2 Reservation Schemes Hosts independently reserve the channel for period of time Reservations are usually piggybacked on data messages passing along the channel ood for systems with : Good for systems with : short propagation delay no central controller node non-bursty traffic
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eservation Protocols t d ) Reservation Protocols (cont’d) Reservation protocol examples: it- ap Protocol Bit Map Protocol Binary Countdown Protocol
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21 it ap Protocol 2.2.1 Bit-Map Protocol Contention and data transmission periods alternate The contention period is divided into slots, with 1 bit- wide slot for each host in the network. If a host wants to transmit a packet, it sets its ontention slot equal to 1. Otherwise, it sets it to 0. contention slot equal to 1. Otherwise, it sets it to 0. The slots pass all hosts in sequence, so every host is aware of who will transmit 1 1 1 1 1 1 2 4 5 6 01234567 01234567 0 4 data frame
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it ap Protocol t d ) Bit-Map Protocol (cont’d) But what if there are a large number of hosts in the network?
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3 ICS132-MAC-layer - Medium Access Sublayer Medium Access...

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