1. The document summarizes key topics from Lecture 04 including networking concepts like LAN, WAN, MAN, protocols, OSI layers, routing, and distributed systems. 2. It discusses routing protocols like RIP and how RIP addresses link failures, as well as transport layer protocols TCP and UDP. 3. MobileIP is described as a protocol that allows mobile devices to maintain connectivity even when moving between networks by using a home and foreign agent to reroute packets.

1. Recap
Lecture 04:
Networking (continue) Various types of Networks:LAN, WAN, MAN,
WLAN, WMAN
Switching Schemes: Broadcast, Circuit Switching,
packet Switching, ATM
Protocol, what? why?
OSI layers and protocol
Distributed Systems
Routing and RIP algorithm
Behzad Bordbar
School of Computer Science, University of Birmingham, UK
Lecture 04 1 Lecture 04 2
RIP (continue)
Overview When a link fails cost in the table is set to ∞
Routing and RIP (continue) Then, the cost in all table is set to ∞ (1+∞ = ∞)
other protocols: Transport layer protocols (UDP 3 timers: periodic, expiration, Garbage collection
, TCP) RIP is
Mobile routing slow in convergence
WLAN and its architectural issues But, most of the time system stables fast
Communication Service types: RIP 2 addresses some of the above issues and
connectionless communication (UDP) also Authentication and Multicasting (send
packets to all other router.
connection-oriented communication (TCP)
Lecture 04 3 Lecture 04 4
Review of some Protocols
Congestion control
IP: transfer datagram from one host to another
- Unreliable best effort
When load on network high (80% capacity)
- only header checksum
packet queues long, links blocked
TCP and UDP
Strategies to address the problem main transport level protocols used by IP
packet dropping
MobileIP
• reliable of delivery at higher levels
connectivity for mobile devices, even in transit
• Dropping some packets is better than others (MPEG) device retains single IP address
reduce rate of transmission re-routing by Home (HA) and Foreign Agents (FA)
• nodes send choke packets (Ethernet) transparent
• transmission control (TCP)
Wireless LAN (IEEE 802.11)
transmit congestion information to each node
radio or infra-red communications
• QoS guarantees (ATM)
Lecture 04 5 CSMA/CA based Lecture 04 6
1

2. IP Transport layer protocols
Internet Protocol is unreliable and connectionless
UDP (basic, used for some IP functions)
Best effort (no error checking or Ack) uses IP address+port number
Packets called Datagram have Header no guarantee of delivery, optional checksum
IP address of source and destination messages up to 64KB
Containing version, Header Length (HLEN), length (Header
+data) …
TCP (more sophisticated, most IP functions)
higher level protocol ?? (info encapsulated UDP, TCP, RIP2, data stream abstraction, reliable delivery of all data
…) messages divided into segments, sequence numbers
header checksum sliding window, acknowledgement+retransmission
Fragmentation buffering (with timeout for interactive applications)
Timestamp (IP address of the router + Universal time) checksum (if no match segment dropped)
… Both are process-to-process communication
Not all exploited by all higher level protocols
Lecture 04 7 Lecture 04 8
Communication service types Connectionless service
Connectionless: UDP
‘send and pray’ unreliable delivery UDP (User Datagram Protocol)
efficient and easy to implement messages possibly lost, duplicated, delivered out of order,
Connection-oriented: TCP without telling the user
with basic reliability guarantees maintains no state information, so cannot detect lost,
less efficient, memory and time overhead for error duplicate or out-of-order messages
correction each message contains source and destination address
may discard corrupted messages due to no error correction
(simple checksum) or congestion
Used e.g. for DNS (Domain Name System) or RIP.
Lecture 04 9 Lecture 04 10
MobileIP
Connection-oriented service
At home normal, when elsewhere mobile host:
TCP (Transmission Control Protocol) notifies HA before leaving
establishes data stream connection to ensure reliable, informs FA, who allocates temporary care-of IP address
in-sequence delivery & tells HA
error checking and reporting to both ends
Packets for mobile host:
attempts to match speeds (timeouts, buffering)
first packet routed to HA, encapsulated in MobileIP
sliding window: state information includes
• unacknowledged messages
packet and sent to FA (tunnelling)
• message sequence numbers FA unpacks MobileIP packet and sends to mobile host
• flow control information (matching the speeds) sender notified of the care-of address for future
communications which can be direct via FA
Used e.g. for HTTP, FTP, SMTP on Internet.
Problems
efficiency low, need to notify HA
Lecture 04 11 Lecture 04 12
2

3. MobileIP routing Wireless LAN (802.11)
Sender
Radio broadcast (fading strength, obstruction)
Subsequent IP packets
tunnelled to FA Mobile host MH
Collision avoidance by
Address of FA
returned to sender
slot reservation mechanism by Request to Send (RTS)
First IP packet
and Clear to Send (CTS)
addressed to MH stations in range pick up RTS/CTS and avoid
Internet
Foreign agent FA transmission at the reserved times
Home
agent
First IP packet collisions less likely than Ethernet since RTS/CTS short
tunnelled to FA
random back off period
Problems
security (eavesdropping), use shared-key authentication
Lecture 04 13 Lecture 04 14
Summary
Wireless LAN configuration
A B C
Laptops Routing and RIP, various timers
radio obstruction
IP
Wireless Transport layer protocols (UDP , TCP)
D LAN
Palmtop/
Mobile phone
E
Mobile routing
Base station/
access point
WLAN and its architectural issues
Communication Service types:
Server
Connectionless vs. Connection-oriented
LAN
Further reading: end of chapter 3 p. 130
Lecture 04 15 Lecture 04 16
Exercises (Lectures 3,4): Exercises:
client sends a 200 byte request message to a service, which 3.2: The Internet is far too large for any router to hold
produces a response ontaining 5000 bytes. Estimate the total routing information for all destinations. How does
time to complete the request in each of the following cases,
with the performance assumptions listed below:
the Internet routing scheme deal with this issue?
i) Using connection less (datagram) communication (for 3.6: Can we be sure that no two computers in the Internet
example, UDP); have the same IP addresses?
ii) Using connection-oriented communication (for example, 3.7: Compare connection less (UDP) and connection-
TCP); oriented (TCP) communication for the
iii) The server process is in the same machine as the client. implementation of each of the following application-
[Latency per packet (local or remote. incurred on both send and level or presentation-level protocols:
receive): 5 ms, Connection setup time (TCP only): 5 ms,
Data transfer rate: 10 Mbps MTU: 1000 bytes Server request i) “irtual terminal access (for example, Telnet); ii)file
processing time: 2 ms Assume that the network is lightly transfer (for example, FTP); iii)ser location (for
loaded.] example, rwho, finger); iv)information browsing (for
Lecture 04 17 example, HTTP); v)remote procedure call.
Lecture 04 18
3