host Switch/router data link Broadcast Switched Point to point Page 164
TDC-460 Data Link Protocol Key Services A Data Link layer protocol may support some or all of the following services across a link 1. Framing 2. Client layer encapsulation 3. Physical addressing 4. Flow control 5. Error detection 6. Error control 7. Link management (aka OAMPT) user authentication, exchange of settings, troubleshooting Link establishment/termination 8. Congestion notification 9. Switching (virtual circuit or datagram) 10.Media access control for broadcast (aka multipoint links) 11.Traffic management (CoS, QoS, Policing, Shaping) Page 165 Discussed in following pages Discussed in later lectures
TDC-460 Data Link Layer Framing Data Link Layer framing is responsible for providing a way of determining the start and end of a frame and then finding the component parts inside a frame a Data Link frame is composed of one, some, or all of the following fields: start of frame end of frame Source address Destination address Control field(s) Error detection (aka Frame Check Sequence) Data field (PDU from client layer) Page 166
TDC-460 Data Link Layer Framing Methods General framing methods: Fixed frame size – frame size does not vary Start of frame indication is all that is required Example: Variable frame size– frame sizes varies Both start and end of frame indication required (or) Start of frame and frame size field is required Example: Page 167
TDC-460 Data Link Layer Framing method examples Page 168 PPP Ethernet Frame Relay
TDC-460 Data Link Layer Client Layer Encapsulation A data link layer must encapsulate the client layer (aka network layer) Encapsulation requires: Definition of how the client layer is to be embedded into the data link layer’s PDU Indication of what type of client protocol is being embedded into the PDU Often supported through the use of a type field or protocol field in the data link protocol Examples: Page 169 PPP Ethernet
TDC-460 Data Link Layer Addressing Data link protocols may support one of the following physical address field options source address field and destination address field Question : Network topology that requires address support? Answer : 1. Peer to Peer Broadcast, 2. Peer to Peer switched Specific DL protocol examples? one destination address field Question : Network topology that requires address support? Answer : Primary-Secondary Broadcast Specific DL protocol examples? no address fields Question : Network topology that requires address support? Answer : point to point, non-switched Specific protocol examples? Page 170
TDC-460 Data Link Layer Flow Control Flow control is a set of procedures that manages the flow of data from the sender to ensure that the receiver is not overwhelmed (prevents receiver buffer overflow) Flow control is controlled by the receiver NOTE: Data Link flow control is generally not utilized in modern networks today – Why?
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