Transport Layer

1. Transport Layer
Shashikant V. Athawale
Assistant Professor
Department of Computer Engineering, AISSMS COE ,Pune

2. TCP
(Transmission Control Protocol)

3. ● TCP is a connection-oriented protocol; it
creates a virtual connection between two
TCPs to send data.
● In addition, TCP uses flow and error
control mechanisms at the transport level

4. TCP/IP Protocol Suite

6. Stream Delivery

7. UDP
(User Datagram Protocol)

8. ● The User Datagram Protocol (UDP) is
called a connectionless, unreliable
transport protocol.
● It does not add anything to the services of
IP except to provide process-to-process
communication instead of host-to-host
communication.

9. Well known ports used with
UDP

10. User Datagram Format

11. Socket Programming

12. Socket
● An interface between application and
network
● The application creates a socket
● Build distributed, client server
applications

14. TCP Flow Control

15. Flow Control
● Sender won’t overrun receiver’s buffers
by transmitting too much, too fast
● RcvBuffer = size or TCP Receive Buffer
● RcvWindow = amount of spare room in
Buffer

16. Congestion Control

17. ● Informally: “too many sources sending
too much data too fast for network to
handle”
● Manifestations:
◦ lost packets (buffer overflow at routers)
◦ long delays (queuing in router buffers)
● A highly important problem

18. End-end congestion control
● No explicit feedback from network
● Congestion inferred from end-system
observed loss, delay
● Approach taken by TCP

19. Network-assisted congestion
control
● Routers provide feedback to end systems
◦ Single bit indicating congestion (SNA,
DECbit, TCP/IP ECN, ATM)
◦ Explicit rate sender should send at

20. Goals of Congestion Control
● Throughput
◦ Maximize good put
◦ the total number of bits end-end
● Fairness
◦ Give different sessions “equal” share.
◦ Max-min fairness
⚫Maximize the minimum rate session.
◦ Single link
⚫Capacity R
⚫sessions m
⚫Each sessions: R/m

21. Real Time Transport Protocol

22. ● A session consists of an RTP/RTCP pair
of channels
● Usually works over UDP/IP
● End-to-end protocol

23. RTP Features
◦ Multicasting
◦ Payload type identification
◦ Time shaping
◦ Sequencing
◦ Delivery monitoring

24. ● RTP Issues
◦ No QoS guarantees
◦ No guarantee of packet delivery
● RTP Timestamp (TS) and Sequence Number
(SN)
◦ TS used to order packets in correct timing
order
◦ SN to detect packet loss
◦ For a video frame that spans multiple
packets – TS is same but SN is different

25. ● RTCP
◦ Synchronize across different media
streams
◦ Provide feedback on the quality of data
using lost packet counts
◦ Identify and keep track of participants
◦ Retransmission requests

26. SCTP
(Stream Control Transmission
Protocol)

27. ● Stream Control Transmission Protocol
(SCTP) is a new reliable, message
oriented transport-layer protocol
◦ Message-oriented, Reliable
◦ Other innovative features
⚫Association, Data transfer/Delivery
⚫Fragmentation, Error/Congestion
Control

28. Multiple stream concept

29. SCTP vs. TCP
● Control information
◦ TCP: part of the header
◦ SCTP: several types of control chunks
● Data
◦ TCP: one entity in a TCP segment
◦ SCTP: several data chunks in a packet
● Option
◦ TCP: part of the header
◦ SCTP: handled by defining new chunk
types

30. ● Mandatory part of the header
◦ TCP: 20 bytes, SCTP: 12 bytes
◦ Reason:
⚫TSN in data chunk’s header
⚫Ack. # and window size are part of
control chunk
⚫No need for header length field (∵no
option)
⚫No need for an urgent pointer
● Checksum
◦ TCP: 16 bits, SCTP: 32 bit

31. ● Association identifier
◦ TCP: none, SCTP: verification tag
◦ Multihoming in SCTP
● Sequence number
◦ TCP: one # in the header
◦ SCTP: TSN, SI and SSN define each data
chunk
◦ SYN and FIN need to consume one seq. #
◦ Control chunks never use a TSN, SI, or
SSN number

32. SCTP Packet Format

33. QoS
(Quality Of Service)

34. QoS
● Definition: Methods for differentiating traffic and
services
● To some, introducing an element of predictability
and consistency into a highly variable best-effort
network
● To others, obtaining higher network throughput
while maintaining consistent behavior
● Or, offering resources to high-priority service
classes at the expense of lower-priority classes
(conservation law)
● Or, matching network resources to application
demands

35. Applications
● Real-time: voice, video, emergency control,
stock quotes
● Non-real-time (or best-effort): telnet, ftp etc
● Real-time:
- hard with deterministic or guaranteed QoS:
no loss, packet delay less than deadline,
difference in delays of 2 packets less than
jitter bound
- soft with statistical or probabilistic QoS: no
more than x% of packets lost or experience
delay greater than deadline

36. SLA(Service Level Agreement)
● Service Level Agreement between client
(subscriber) and network (provider): the
network keeps its promise as long as the
flow conforms to the traffic specification
● The network must monitor/police/shape
incoming traffic
● The shape is important: E.g. a gigabit
network contracting with a 100Mbps
flow. A big difference between sending
one 100Mb packet every second and
sending 1Kb packet every 10 microsec.

37. Differentiated Services

38. ● In DiffServ, flows are aggregated into
classes that receive “treatment” by class.
● More complex operations are pushed out
to edge routers and simpler operations
done by core routers.
● motivated by:
◦ scalability, flexibility, and better-than-
best-effort service without RSVP
signaling.

39. ● edge functions:
◦ packet classification
◦ packet marking
◦ traffic conditioning
● core functions:
◦ forwarding based on per-hop behavior
(PHB) associated with packet’s class

40. Integrated Services

41. ● IntServ framework was developed within
IETF to provide individualized QoS
guarantees to individual sessions.
● provides services on a per flow basis
where a flow is a packet stream with
common source address, destination
address and port number.
● IntServ routers must maintain per flow
state information.

42. Features
◦ Reserved Resources
⚫the router must know the amount of its
resources currently reserved for on-going
sessions.
⚫standard resources: link capacity, router
buffers
◦ Call Setup
⚫A flow requiring QoS guarantees must be
able to reserve sufficient resources at each
router on path to ensure QoS requirements are
met.

43. Conclusion
● TCP and UDP are explained with packet
formats
● Socket is explained in detail
● TCP flow control and congestion control
is explained
● RTCP, SCTP, QoS , Integrated and
Differentiated services are explained

44. References
● http://www.routeralley.com.
● D.E. Comer, Internetworking with
TCP/IP: Principles, Protocols, and
Architectures, 4th edition, Prentice Hall,
NJ, 2000.
● Data communication and networking by
Behrouz A Forouzan

45. Thank You!!!!!!!