Presentation on theme: "Chi-Cheng Lin, Winona State University CS 313 Introduction to Computer Networking & Telecommunication Chapter 5 Network Layer."— Presentation transcript:
Chi-Cheng Lin, Winona State University CS 313 Introduction to Computer Networking & Telecommunication Chapter 5 Network Layer
2 Topics l Design Issues l Routing Algorithms l Congestion Control l Internetworking
3 Congestion Control l Congestion Too many packets present in the subnet l Effects Performance degraded Packet lost
Congestion Control Algorithms (2) When too much traffic is offered, congestion sets in and performance degrades sharply. (Could be achieved by congestion control) (Without congestion control)
5 Causes of Congestion l Causes Too many packets need an output line queuing Problem: not enough memory packets dropped Solution(?): adding more memory New problem: timeout and retransmit worse Slow processors Low bandwidth lines l Congestion tends to feed upon itself and become worse
6 Congestion Control l Congestion = (Load > Resources) l Solutions Increase resources Decrease load
Approaches to Congestion Control Timescales of approaches to congestion control
Traffic-Aware Routing A network in which the East and West parts are connected by two links.
Admission Control (a) A congested network. (b) The portion of the network that is not congested. A virtual circuit from A to B is also shown.
11 Choke Packets l Approach Each router monitors output line utilization Threshold for "warning state" A receiving router Checks packet to see if output line in warning state If yes then send a "choke packet" back to source host original packet tagged and forwarded
12 Choke Packet l Source, upon receiving a choke packet Reduces traffic by a percentage after receiving choke packet Choke packet referred to same destination is ignored for a fixed time interval After time interval expired, listens If choke packet received then goto the step of reducing traffic else increase traffic
13 Choke Packet l Typically First choke packet causes data rate reduced to 50%, then 25%, … Traffic is increased in smaller increments l Why?
14 Hop-by-Hop Choke Packets l Problem in high speed and long distance slow reaction l Solution Hop-by-hop choke packets l Buffers needed in routers l Effects: Quick relief at the price of more buffers
15 Load Shedding l Discard whatever cannot be handled l Which packets to drop? Application-dependent Priorities
16 Load Shedding l Strategies Wine or milk Priority Priority classes Coupled with traffic shaping token bucket Packet without token sent with lowest priority Allowing VC set up with exceeding specification Contingent on low priority Header field needed Example: ATM CLP field (1-bit, 0 means high priority) l Rule of thumb Discard as early as possible!
Choke Packets A choke packet that affects only the source.
Choke Packets A choke packet that affects each hop it passes through.
19 Internetworking l A collection of interconnected networks.
How Networks Differ Some of the many ways networks can differ
How Networks Can Be Connected (a) A packet crossing different networks. (b) Network and link layer protocol processing.
22 Tunneling l Encapsulating packets of a protocol in the payload of packets of another protocol l Useful in Internetworking VPN IPv4 to IPv6 transition …
Tunneling Tunneling a packet from Paris to London.
Tunneling Tunneling a car from France to England