Computer Networking — A Top-down Approach Chpt 5

CHAPTER 5

1. the transportation mode is a link-layer protocol, and the travel agent is a routing protocol

2. Framing; Link access; Reliable delivery; Error Detection and Correction

3. Implemented in a network adapter; Network Interface Card — much of link layer services are implemented in hardware

4. the link layer is a combination of hardware and software

5. error-detection and -correction — 2 dimensional parity scheme can be use to detect and correct

6. Checksum — TCP/UDP check all header and data; IP only check IP header; checksum is designed to be fast and easy for software implementation

7. Cyclic Redundancy Check (CRC) — polynomial codes; hardware; strange calculation

8. Multiple Access Protocol — channel partitioning protocols; random access protocols; and taking-turns protocols

9. Channel Partitioning protocols — use TDM, time-division multiplexing; each node has rate of R/N; must wait for its turn; use FDM; speed is limited

• code division multiple access: CDMA; also a channel partitioning protocol

10. Random Access Protocol — delay randomly before transmitting

• slotted ALOHA — transmit at the beginning of slots; p probability to transmit at current new slot
• ALOHA — no fixed slot; collision occurs during transmitting, finish and retransmit with probability p
• Carrier Sense Multiple Access (CSMA) — listen before speaking; if speak at same time, then stop; CSMA and CSMA/CD (with collision detection); channel propagation delay; CSMA/CD contains binary exponential backoff algorithm; new frames are allowed to start their own detect algo; efficiency equition

11. Taking-turns Protocols

• master node polls each of node in a round-robin fashion; polling protocol; eliminates the collisions and empty slots;
• token-passing protocol — who hold the token can send frames; after sending, send token to next node

12. DOCSIS: The Link-Layer Protocol for Cable Internet Access — MAP frames for downsteam; minislot request frames in upstream

13. Link-layer Addressing and ARP

14. MAC address — physical address; 6 byte long; broadcast address all 1

15. ARP — Address Resolution Protocol; Used to get MAC address; Each host and router has an ARP table; Flow: construct ARP packet, broadcast, receive from unicast;

A hub is a physical-layer device that acts on individual bits rather than frames. When a bit, representing a zero or a one, arrives from one interface, the hub simply re-creates the bit, boosts its energy strength, and transmits the bit onto all the other interfaces.

hub-based star topology

16. Ethernet Frame Structure

• Data field — network packets/datagram
• Destination / Source address
• Type field — ARP 0x0806;
• Cyclic redundancy check (CRC)
• Preamble — Each of the first 7 bytes of the preamble has a value of 10101010, Last 10101011 → 2 consecutive 1s alert adapter at source: data is about to come

17. Ethernet simple and cheap — connectionless; no negetive ack; no shake hands

18. Switches

• Forwarding and Filtering — switch table; depends on interface & mac address
• Self-learning — plug-and-play devices

19. Properties of link-layer switching — Elimination of collisions; Heterogeneous links, can hold different devices with different media / speed; Mangement

20. Switches vs Routers

21. virtual local area networks (VLANs)

22. Link Virtualization: A Network as a Link Layer //TODO

23. Data Center Networking

24. Retrospective