Figure 5.3-1: Various multiple access channels
Figure 5.3-2: A broadcast channel interconnecting four nodes.
- When only one node has data to send, that node has a throughput of R bps.
- When M nodes have data to send, each of these nodes has a throughput of R/M bps. This need not necessarily imply that each of the M nodes always have an instantaneous rate of R/M , but rather that each node should have an average transmission rate of R/M over some suitably-defined interval of time.
- The protocol is decentralized, i.e., there are no master nodes that can fail and bring down the entire system.
- The protocol is simple, so that it is inexpensive to implement.
5.2.1 Channel Partitioning Protocols
Figure 5.3-3: A four-node TDM and FDM example
Figure 5.3-4: A simple CDMA example: sender encoding, receiver decoding
(Equation 5.3-1)
(Equation 5.3-2)
(Equation 5.3-3)
Figure 5.3-5: A two-sender CDMA example
5.2.2. Random Access Protocols
Slotted ALOHA
- All frames consist of exactly L bits.
- Time is divided into slots of size L/R seconds (i.e., a slot equals the time to transmit one frame).
- Nodes start to transmit frames only at the beginnings of slots.
- The nodes are synchronized so that each node knows when the slots begin.
- If two or more frames collide in a slot, then all the nodes detect the collision event before the slot ends.
- When the node has a fresh frame to send, it waits until the beginning of the next slot and transmits the entire frame in the slot.
- If there isn't a collision, the node won't consider retransmitting the frame. (The node can prepare a new frame for transmission, if it has one.)
- If there is a collision, the node detects the collision before the end of the slot. The node retransmits its frame in each subsequent slot with probability p until the frame is transmitted without a collision.
Figure 5.3-6: Nodes 1, 2 and 3 collide in the first slot. Node 2 finally succeeds in the fourth slot, node 1 in the eighth slot, and node 3 in the ninth slot.
The notation C, E and S represent 'collision slot', 'empty slot' and 'successful slot', respectively
ALOHA
Figure 5.3-7: Interfering transmissions in pure Aloha
CSMA – Carrier Sense Multiple Access
Slot Time Aviation
- Listen before speaking. If someone else is speaking, wait until they are done. In the networking world, this is termed carrier sensing - a node listens to the channel before transmitting. If a frame from another node is currently being transmitted into the channel, a node then waits ('backs off') a random amount of time and then again senses the channel. If the channel is sensed to be idle, the node then begins frame transmission. Otherwise, the node waits another random amount of time and repeats this process.
- If someone else begins talking at the same time, stop talking. In the networking world, this is termed collision detection - a transmitting node listens to the channel while it is transmitting. If it detects that another node is transmitting an interfering frame, it stops transmitting and uses some protocol to determine when it should next attempt to transmit.
Figure 5.3-7: Space-time diagram of two CSMA nodes with colliding transmissions
Figure 5.3-8: CSMA with collision detection.
5.2.2 Taking-Turns Protocols
5.2.3 Local Area Networks
Figure 5.3-9: User hosts access an Internet Web server through a LAN. The broadcast channel between a user host and the router consists of one 'link'.
Ethernet Slot Time Example Entry
References
- [Abramson 1970] N. Abramson, 'The Aloha system,' AFIPS Conf. Proc., Vol. 37, 1970 Fall Joint Computer Confernce, AFIPS Press, Montvale, N.J., 1970, pp. 281-285.
- [Abramson 1985] N. Abramson, 'Development of the Alohanet,' IEEE Transactions on Information Theory,' Vol. IT-31, No. 3 (March 1985), pp. 119-123.
- [Bertsekas 1992] D. Bertsekas and R. Gallager, Data Networks, Second Edition, Prentice Hall, Englewood Cliffs, New Jersey, 1992.
- [Boggs 1988] D. Boggs, J. Mogul, and C. Kent, 'Measured capacity of an Ethernet: myths and reality;' Proc ACM Sigcomm 1988, pp. 222 - 234
- [IEEE 1998] IEEE, Token Ring Access Method (ISO/IEC 8802-5: 1998 and 8802-5 : 1998/Amd 1), 1998. See the 802.5 standards page at http://www.8025.org/802.5/documents/
- [IEEE 1998b] IEEE, 'Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications.' See the IEEE 802.3 publication catalog at http://standards.ieee.org/catalog/IEEE802.3.html
- [Jain 1994] R. Jain, 'FDDI Handbook : High-Speed Networking Using Fiber and Other Media,' Addison-Wesley (Reading MA, 1994).
- [Kleinrock 1975] L. Kleinrock and F. A. Tobagi, 'Packet Switching in Radio Channels: Part I -- Carrier Sense Multiple-Access Modes and Their Throughput-Delay Characteristics,' IEEE Transactions on Communications, Vol. COM-23, No. 12, pp. 1400-1416, Dec. 1975.
- [Lam 1980] S. Lam, A Carrier Sense Multiple Access Protocol for Local Networks,' Computer Networks, Volume 4, pp. 21-32, 1980.
- [Metcalfe 1976] R. Metcalfe, D. Boggs, 'Ethernet: Distributed packet switching for local computer networks,' Communications of the ACM, 19(7) (1976), pp. 395-404.
- [Molle 87] M. Molle, 'Space Time Analysis of CSMA Protocol,' IEEE Journal on Selected Areas in Communications, 1987.
- [Pickholtz 1982] R. Pickholtz, D. Schilling, L. Milstein, 'Theory of Spread Spectrum Communication - a Tutorial,' IEEE Transactions on Communications, Col. COM-30, No. 5 (May 1982), pp. 855-884.
- [Rom 1990] R. Rom and M. Sidi, 'Multiple Access Protocols: Performance and Analysis,' Springer-Verlag, New York, 1990.
- [Spurgeon 1999] C. Spurgeon, 'Charles Spurgeon's Ethernet Web Site,' http://wwwhost.ots.utexas.edu/ethernet/ethernet-home.html
- [Viterbi 1995] A. Viterbi, CDMA: Principles of Spread Spectrum Communication, Addison-Wesley, (Reading MA 1995).
Use display ethernet statistics to display the Ethernet statistics.
Syntax
display ethernet statisticsslot slot-number
Views
User view
Predefined user roles
network-admin
network-operator
Parameters
slot slot-number: Displays the Ethernet statistics on the specified IRF member device. The slot-number argument represents the ID of the IRF member device.
Examples
# Display the Ethernet statistics on IRF member 1.
Field | Description |
---|---|
ETH receive packet statistics | Statistics about the Ethernet packets received on the Ethernet interface module. |
Totalnum | Total number of received packets:
|
ETH receive error statistics | Statistics about the error Ethernet packets in the outbound direction on the Ethernet interface module. Errors might be included in packets or occur during the receiving process. The items include:
|
ETH send packet statistics | Statistics about the Ethernet packets sent by the Ethernet interface module:
|
ETH send error statistics | Statistics about the error Ethernet packets in the outbound direction on the Ethernet interface module:
|