1. Recap
Lecture 03:
Networking Architecture, what? and why?
Tiered Architecture
Various software layer: middleware
client/server Architecture
Multiple servers, Proxy servers, Peer
Distributed Systems
processes
Behzad Bordbar
Design requirements of DS: Performance,
School of Computer Science, University of Birmingham, UK
QoS, Dependability
Lecture 03 1 Lecture 03 2
Overview of the lecture Requirements of Networks
design and implementation
Requirements for networks
performance
Various types of networks
Scalability
How does it work? network principles
Reliability
Mode of transformation
Security
Protocols, what is a protocol?
Mobility
OSI
Multicast
Routing and RIP
Lecture 03 3 Lecture 03 4
Types of Networks LAN
messages are carried in high speed between connected
PAN (Personal Area Network) nodes by a single communication medium
LANs (Local Area Networks) Suitable for home office ,… radius of 1-2 km
WANs (Wide Area Networks) • High bandwidth 10-1000Mbps (total amount of data
MANs (Metropolitan Area Networks) per unit of time)
• Low latency 1-10 ms (time taken for a bit to reach
WPAN (Wireless PAN)
destination)
WLAN (Wireless LAN) Technology: predominantly Ethernet
WMAN (Wireless MAN)
WWAN (Wireless WAN)
Lecture 03 5 Lecture 03 6
1

2. LAN example: the old SoCS WAN
Campus
router
subn
et
router/
firewall Covers Worldwide,
Staff subnet Student subnet
compute
servers perky pinky
file server/
Low bandwidth 0.01-600 Mbps,
Eswitch Eswitch Data
gateway
wallace printers high latency (100-500 ms)
tinky-winky
gromit
other
Satellite/wire/cable, use of routers which also
file
server
Data servers
laa-laa
introduce delays
casper
web
server
felix
po
MAN
hub hub
Wire/cable, uses Digital Subscriber Line (DSL) and cable
desktop computers The Simpsons The Muppets modem
10 Mbps Ethernet
100 Mbps Ethernet
Range of technologies (ATM, Ethernet)
Eswitch: Ethernet switch
Lecture 03 7 Lecture 03 8
Wireless networks
Network comparison
WLANs (Wireless Local Area Networks)
to replace wired LANs Range Bandwidth (Mbps) Latency (ms)
LAN 1-2 kms 10-1000 1-10
WaveLAN technology (IEEE 802.11) WAN worldwide 0.010-600 100-500
WPANs (Wireless Personal Area Networks) MAN 2-50 kms 1-150 10
Wireless LAN 0.15-1.5 km 2-11 5-20
variety of technologies Wireless WAN worldwide 0.010-2 100-500
Internet worldwide 0.5-600 100-500
GSM, infra-red, BlueTooth low-power radio
WAP (Wireless Applications Protocol)
Lecture 03 9 Lecture 03 10
Network principles Mode of transmission
Mode of transmission Packet Transmission
Switching schemes messages divided into packets. Example: 01101110
Protocol suites packets queued in buffers before sent onto link
Routing QoS not guaranteed
Congestion control Data streaming
links guarantee QoS (rate of delivery)
for multimedia traffic
higher bandwidth
Lecture 03 11 Lecture 03 12
2

3. Switching schemes Protocol
Broadcasts (Ethernet, wireless) well-known set of rules and formats to be used for
send messages to all nodes
communication between processes to perform a
nodes listen for own messages (carrier sensing)
given task
Circuit switching (phone networks)
Packet switching (TCP/IP) Two parts:
store-and-forward specification of sequence of messagegs that
unpredictable delays
must be exchanged
Frame/cell relay (ATM)
bandwith & latency guaranteed (virtual path) specification of the format of the data in each
small, fixed size packets (padded if necessary) message
avoids error checking at nodes (use reliable links)
Lecture 03 13 Lecture 03 14
Protocols (OSI view) Message encapsulation
HTTP, FTP, ...
Message sent Message received
External data representation., encryption
Application-layer message
Layer n
Failure detection and recovery Presentation header
TCP, UDP
Session header
Layer 2 IP, ATM Transport header
Layer 1
Sender Communication Recipient Network header
medium
Definition: set of rules and formats for exchanging data, arranged
into layers called protocol suite/stack. Headers appended/unpacked by each layer.
Lecture 03 15 Lecture 03 16
OSI protocol summary Routing
Layer Description Example Necessary in non-broadcast networks (cf Internet)
Application Protocols for specific applications. HTTP, FTP, Distance-vector algorithm: each node
SMTP
Presentation Protocols for independent data representation and Secure Sockets,
stores table of state & cost info of links, cost infinity for
encryption if required. CORBA CDR faulty links
Session Protocols for failure detection and recovery. determines route taken by packet (the next hop)
Transport Message-level communication between ports TCP, UDP
attached to processes. Connection-oriented or
periodically updates the table and sends to neighbours
connectionless. may converge slowly [Bellman-Ford]
Network Packet-level transmission on a given network. IP, ATM
Requires routing in WANs and Internet. RIP-1 for Internet similar except
Data link Packet-level transmission between nodes connected Ethernet MAC, use default routes, plus multicast and authentication
by a physical link. ATM cell transfer
better convergence
Physical transmit sequence of binary data using Signalling,
various mediums ISDN
Lecture 03 17 Lecture 03 18
3

4. Routing example Routing tables
Routings from A Routings from B
To Link Cost To Link Cost
A local 0 A 1 1
B local 0 Routings from A Routings from B Routings from C
B 1 1
C 1 2 C 2 1 To Link Cost To Link Cost To Link Cost
D 3 1 D 1 2 A local 0 A 1 1 A 2 2
E 1 2 E 4 1
B 1 1 B local 0 B 2 1
A 1 B C 1 2 C 2 1 C local 0
2 D 3 1 D 1 2 D 5 2
Hosts E 1 2 E 4 1 E 5 1
3 Links 4
or local C
networks
5
D 6 E Routings from D Routings from E
To Link Cost To Link Cost
Routers A 3 1 A 4 2
B 3 2 B 4 1
C 6 2 C 5 1
D local 0 D 6 1
E 6 1 E local 0
Lecture 03 19 Lecture 03 20
RIP routing algorithm
RIP routing algorithm Variables: Tl local table, Tr table received.
Send: Each t seconds or when Tl changes, send Tl on each non-faulty
Update: Each 30 seconds or when local table changes, send outgoing link.
update on each non-faulty outgoing link. Receive: Whenever a routing table Tr is received on link n:
for all rows Rr in Tr {
if (Rr.link != n) {
Propagation:When router X finds that router Y has a Rr.cost = Rr.cost + 1;
shorter and faster path to router Z, then it will update its Rr.link = n;
local table to indicate this fact. Any faster path is quickly if (Rr.destination is not in Tl) add Rr to Tl;
propagated to neighbouring rotes through the Update // add new destination to Tl
else for all rows Rl in Tl {
process. if (Rr.destination = Rl.destination and
(Rr.cost < Rl.cost or Rl.link = n)) Rl = Rr;
Shown to converge by mathematicians (Bertsekas). // Rr.cost < Rl.cost : remote node has better route
See next slide for details. // Rl.link = n : remote node is more authoritative
}
}
Lecture 03 21 } Lecture 03 22
Sample routes Summary
Send from C to A:
Various types of Networks (LAN, WAN, …)
to link 2, arrive at B
to link 1, arrive at A Switching Schemes
Send from C to A if B table OSI layers and protocol
modified to: Routing and RIP algorithm
to link 5, arrive at E Routings from C
to link 4, arrive at B To Link Cost
to link 1, arrive at A
B 2 1 Further reading: page 65-96
NB extra hop. C local 0
E 5 1
default 5 -
Lecture 03 23 Lecture 03 24
4

5. Exercises:
will be included in the next lecture
Lecture 03 25
5