Networking Systems (1)

1. Networking Systems (1) Hai Tao

2. LANs, MANs, and WANs • LANs (Local area networks) • Extension over a local area typically within a few kilometers • Usually owned by a single organization • High data rate • The number of stations connect to a LAN is usually less than 100 • Usually is based on broadcasting channels • Some examples include Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), local ATM (asynchronous transfer mode) networks • MANs (Metropolitan Area Networks) • Covers an entire city with LAN technology • Shared medium and distributed access control

3. LANs, MANs, and WANs • WANs (Wide Area Networks) • Typically span entire countries • Point-to-Point communication • Example: Internet

4. LANs, WANs, Layers, Protocols, and Services • Services provides a set of applications for the requesting application • Logically related services are grouped into layers • Each layer is a service provider to the layer lying above • Protocol consists of rules followed by two peers during any communications • Define protocol data units (PDU) in terms of format (syntax) and meaning (semantics)

5. ISO-OSI Reference Model (SearchNetworking.com)

6. Layers in ISO-OSI Reference Model • Physical Layer • Transmission method of individual bits over the physical medium such as fiber optics, cables, phone lines, etc • Concern with modulation, delay, etc • Data Link Layer • Transmission of data frame (block) • Access protocols to the physical medium • Error and recognition correction • Flow control and block synchronization

7. Data Link Layer • Medium access protocol • Multi-access channels • Medium access control (MAC) to determine access from competing parties • Very important in LANs • Timed Token Rotation Protocol • Carrier Sense Multiple Access with Collision Detection (CSMA/CD) • Point-to-Point connection

8. Network Layers • Transports data packets from one station to another • Provide services such as addressing, internetworking, error handling, congestion control, packet sequencing • For continuous media data, resource reservation and guarantees for through put can be achieved using Quality of Service (QoS) parameters

9. Transport Layers • Provides process-to-process connection • Bridge the gap between the requested transport and the provided services from network layers • Some functionalities include • Divide and assemble packets • Error handling between process (e.g. TCP)

10. Session Layer, Presentation Layer, and Application Layer • Session layer - Guarantee the existence of connection during a session • Point-to-point session • Multi-cast session – a connection with many destinations • Multi-drop session – a connection with many sources • Presentation layer – Definition, abstraction, and conversion of various data exchange formats • Examples: HTTP, TELNET, FTP, POP • Application Layer – Various applications based on the presentation layer (See figure for an example)

11. LANs - Ethernet • Bandwidth increases dramatically: 10Mbps to 100Mbps to 1GMbps to 10 Gbps • Bus-based network Three kinds of Ethernet cabling. (a) 10Base5, (b) 10Base2, (c) 10Base-T.

12. LANs - Ethernet A simple example of switched Ethernet.

13. LANs - Ethernet Cable topologies. (a) Linear, (b) Spine, (c) Tree, (d) Segmented.

14. LANs - Ethernet (a) A two-station Ethernet. (b) A multistation Ethernet.

15. LANs - Ethernet • Using CSMA/CD protocol to solve the multiple access problem • Sender station checks the network state (Listen) • Only send data when no other stations are transmitting data (Send) • When multiple stations send data simultaneously, sending stations detect collisions by finding errors in their own data • If collision detected, wait for randomly computed time and transmit again

16. Ethernet and Continuous Media • Ethernet does not explicitly guarantee end-to-end delay • To transmit continuous media data on the Ethernet, several methods can be used • Using fast Ethernet – end-to-end delay can be long if the network is congested, using fast Ethernet will solve this problem under most situations • Dynamic adaptation – Change the data rate of the media data according to the network load • Dedicated Ethernet for media data – one network for discrete date, one network for continuous data

17. LANs – Token Ring • All stations are connected to a logical ring • A special bit pattern (3Bytes) called a token circulate in the ring • A sender station will capture the token and break the ring. The station sends the data in data frames. Each frame include sender address and destination address • Connect the ring once the transmission is finished • A multiple priority scheme is used to control the network access

18. LANs – Local ATM Networks • Asynchronous Transfer Mode use fixed length packet (cell) • ATM allows systems to operate at higher rate because • No error protection or flow control on a link-to-link basis (but can be done in higher layers) • Operate in connection oriented mode with a setup phase for resource reservation • Information field is small to reduce the internal buffers in the switching nodes

19. WANs • Internet – DARPA experiment in 1973, see table 1 for illustration • Interconnection devices • Source and destination are connected by a sequence of interconnection devices (packet switches) • Packet switches cooperatively compute the path in the network. They are called routers in network layer • Routing protocols • Distance vector – each router keeps tracking and informing its neighbors of its distance to each destination. Slow propagation. • Link State - Each router determines the identities of its neighbors and the associated distance and constructs link state packet (LPS). LPS is sent to all all the other routers