Topic Today TCP/IP

Content:

What are the issues that TCP/IP or any kind of networking thing is going to solve?

Look at several concrete examples

TCP/IP

Multiprocessing, or multiprocessor protocol. (Caltech “MRC” + Alewife CMMU)

Networking issues

• Metrics for this box
• Circuit switch / packet switch
• Flow control
• Reliability
• Deadlock

Metrics

1,2,3 bandwidth

4, latency

5, bisection bandwidth

6, Paccept(load) (in phone network etc.)

7. Packet size

8. Pdrop(load, other reasons)

Example1: Simple circuit switch network

Bandwidth = wire

Latency = 1

Need N^2 switches

Example2: Phone network

Example3: Packet switch

Circuit switch vs Packet switch

	Circuit switched		Packet switched
	Example	Why	Example	Why
Hardware	xbar	QoS -- Owns a connections	MRC	- Cheap->scale - Utilization->fine grained mux lets you steal idle time - Fault tolerance
Software model	Stream (TCP socket)	- Order of delivery - Look like file I/O or serial port I/O - “Session oriented” such as ssh/telnet	UDP socket STREAMS (system call) Echo GRIM	- Sometime ok to drop packet - Message Passing block of data - Request/receive like RPC

Flow control

Why?

• Avoid buffer overflow at receiver
• Avoid congestion if Bandwidth(load) curve is bad

How?

Using feedback

1) TCP: Sliding window (receiver->sender)

Source quench

Slow start

Exponential back off

2) MRC: