1. Protocols and Protocol Suit Review
Lecture 13

2. Overview Network Access Layer Transport Layer Protocols
Protocol Data Unit
Protocol Architecture
TCP/IP Stack
Layered Approach and its Advantages
Router

3. Network Access Layer
Q:- What is the major function of the network access layer?

4. OSI Model Application Layer 7 Presentation Layer 6 Session Layer 5
Transport
Layer 4
Network
Layer 3
Data link
Layer 2
Physical
Layer 1
7 layers OSI model

5. Physical Layer Functions
Establishment and termination of a connection to a communication medium
Process for effective use of communication resources (e.g., contention resolution and flow control)
Conversion between representation of digital data in the end user’s equipment
The physical layer is responsible for movements of individual bits from one hop (node) to the next.

6. Data Link Layer Functions
Responds to service requests from the network layer and issues requests to the physical layer.
Provides functional and procedural means to transfer data between network entities and to detect and correct errors that may occur in the physical layer.
Concerned with:
Framing
Physical addressing (MAC address)
Flow Control
Error Control
Access Control
The data link layer is responsible for moving frames from one hop (node) to the next.

7. Hop-to-hop Delivery

8. Network Layer Functions
Provides for transfer of variable length sequences from source to destination via one or more networks
Responds to service requests from the transport layer and issues requests to the data link layer
Concerned with:
Data Packet
Logical addressing (IP address)
Routing
The network layer is responsible for the delivery of individual packets from the source host to the destination host.

9. Source to Destination Delivery

10. Transport Layer Functions
Provides transparent data transfer between end users
Responds to service requests from the session layer and issues requests to the network layer.
Concerned with:
Service-point addressing
Segmentation and reassembly
Connection control and Flow Control (end-to-end)
Error Control
的資料傳輸及控制，是OSI模型中的關鍵角色，它可以將一個較大的資料切割成多個適合傳輸的資料，替模型頂端的第五、六、七等三個通訊層提供流量管制及錯誤控制。
The transport layer is responsible for the delivery of a message from one process to another.

11. Reliable Process to Process Delivery

12. Session Layer Functions
Provides mechanism for managing a dialogue between end-user application processes
Responds to service requests from the presentation layer and issues requests to the transport layer
Supports duplex or half- duplex operations.
Concerned with:
Dialogue control
Synchronization (Check point)
The session layer is responsible for dialog control and synchronization.

13. Presentation Layer Functions
Relieves application layer from concern regarding syntactical differences in data representation with end-user systems
Responds to service requests from the application layer and issues requests to the session layer
Concerned with:
Translation
Encryption
Compression
第六層︰展示層（Presentation Layer） 應用層收到的資料後，透過展示層可轉換表達方式，例如將ASCII編碼轉成應用層可以使用的資料，或是處理圖片及其他多媒體檔案，如JPGE圖片檔或MIDI音效檔。 除了轉檔，有時候當資料透過網路傳輸時，需要將內容予以加密或解密，而這個工作就是在展示層中處理。
The presentation layer is responsible for translation, compression, and encryption.

14. Application Layer Functions
Interfaces directly to and performs common application services for application processes
Issues service requests to the Presentation layer
Specific services provided:
Network virtual terminal
File transfer, access and management
Mail services
Directory services
HTTP, FTP, DHCP…
第七層︰應用層（Application Layer） 應用層主要功能是處理應用程式，進而提供使用者網路應用服務。這一層的協定也很多。使用者常見的通訊協定，有DHCP（Dynamic Host Configuration Protocol）、FTP（File Transfer Protocol）、HTTP（HyperText Transfer Protocol）及POP3（Post Office Protocol-Version 3）等，依據不同的網路服務方式，這些協定能定義各自的功能及使用規範等細部規則。
The application layer is responsible for providing services to the user.

15. OSI Layered Model

16. TCP/IP Protocol
The lower four layers correspond to the layer of the OSI model
The application layer of the TCP/IP model represents the three topmost layers of the OSI model.
The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application.

17. Lower level vendor implementations
TCP/IP Protocol stack
OSI layers
TCP/IP layers
Application
Presentation
Session
FTP,
Telnet,
SMTP
DNS
Transport
TCP
UDP
Network
Data link
Physical
Lower level vendor implementations IP
OSPF
IGMP
DHCP
ICMP

19. Topics discussed in this section:
Addressing
Four levels of addresses are used in an internet employing the TCP/IP protocols: physical, logical, port, and specific.
Topics discussed in this section:
Physical Addresses Logical Addresses Port Addresses Specific Addresses

20. Addressing

21. Addressing

22. Example
In Figure below a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link (bus topology LAN). As the figure shows, the computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver.

23. A 6-byte (12 hexadecimal digits) physical address.
Example
Most local-area networks use a 48-bit (6-byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below:
07:01:02:01:2C:4B
A 6-byte (12 hexadecimal digits) physical address.

24. Example
Figure shows a part of an internet with two routers connecting three LANs. Each device (computer or router) has a pair of addresses (logical and physical) for each connection. In this case, each computer is connected to only one link and therefore has only one pair of addresses. Each router, however, is connected to three networks (only two are shown in the figure). So each router has three pairs of addresses, one for each connection.

25. Example
Figure below shows two computers communicating via the Internet. The sending computer is running three processes at this time with port addresses a, b, and c. The receiving computer is running two processes at this time with port addresses j and k. Process a in the sending computer needs to communicate with process j in the receiving computer. Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination.
The physical addresses will change from hop to hop, but the logical addresses usually remain the same.

27. Lower level vendor implementations
TCP/IP Protocol stack
OSI layers
TCP/IP layers
Application
Presentation
Session
FTP,
Telnet,
SMTP
DNS
Transport
TCP
UDP
Network
Data link
Physical
Lower level vendor implementations IP
OSPF
IGMP
DHCP
ICMP

28. Internet Protocol (IP)
Provides connection-less, best-effort service for delivery of packets through the inter-network
Best-effort: No error checking or tracking done for the sequence of packets (datagrams) being transmitted
Upper layer should take care of sequencing
Datagrams transmitted independently and may take different routes to reach same destination
Fragmentation and reassembly supported to handle data links with different maximum – transmission unit (MTU) sizes

29. Internet Control Message Protocol (ICMP)
Companion protocol to IP
Provides mechanisms for error reporting and query to a host or a router
Query message used to probe the status of a host or a router
Error reporting messages used by the host and the routers to report errors

30. Internet Group Management Protocol (IGMP)
Used to maintain multicast group membership within a domain
Similar to ICMP, IGMP query and reply messages are used by routers to maintain multicast group membership
Periodic IGMP query messages are used to find new multicast members within the domain
A member sends a IGMP join message to the router, which takes care of joining the multicast tree

31. Dynamic Host Configuration Protocol (DHCP)
Used to assign IP addresses dynamically in a domain
Extension to Bootstrap Protocol (BOOTP)
Node Requests an IP address from DHCP server
Helps in saving IP address space by using same IP address to occasionally connecting hosts

32. Internet Routing Protocols
Routing Information Protocol (RIP)
An intra-domain distance vector routing protocol
Uses the Bellman-Ford algorithm to calculate routing table
Distance information about all the nodes is conveyed to the neighbors.
Open Shortest Path First (OSPF)
Based on shortest path algorithm, sometimes also known as Dijkstra algorithm
Hosts are partitioned into autonomous systems (AS)
AS is further partitioned into OSPF areas that helps boarder routers to identify every single node in the area
Link-state advertisements sent to all routers within the same hierarchical area

33. Internet Routing Protocols
Border Gateway Protocol (BGP)
Intra-autonomous systems communicate with each other using path vector routing protocol
Each entry in the routing table contains the destination network, the next router, and the path to reach the destination

34. Example
Interior Router
BGP Router

35. Abstract model of a wireless network in the form of a graph
A routing table maintained at each node, indicating the best known distance and next hop to get there
Calculate w(u,v), is the cost associated with edge uv
Calculate d(u), the distance of node u from a root node
For each uv, find minimum d(u,v)
Repeat n-1 times for n-nodes
TCP 6
Root 2 4 3 1 -1
Abstract model of a wireless network in the form of a graph
Application Layer
Top three layers (session, presentation, and application) merged into application layer
Routing using Bellman-Ford Algorithm

36. TCP (ctd) Abstract model of a wireless 6 41 2 3 -1 4 6
Root
Abstract model of a wireless
network in the form of a graph
To Node 1 2 3 4
Pass 0 *
Pass 1
Pass 2
Pass 3
Pass 4
To Node 1 2 3 4
Pass 0
Pass 1
Pass 2 7
Pass 3
Pass 4 8 8
Successive calculation of distance D(u) from node 0
Predecessor from node 0 to other network nodes

37. TCP over Wireless
The wireless domain is not only plagued by the mobility problem, but also by high error rates and low BW
Traditional TCP: provides a connected-oriented, reliable, and byte stream service
TCP functions: flow-control (controlled by sliding window), congestion-control (congestion window), data segmentation, retransmission, and recovery
Slow Start: resets the congestion window (CW) size to one and let threshold to half of the current CW size
Double the CW on every successful transmission until the CW reach threshold and after that increases the CW by one for each successful transmission

38. Solutions for Wireless Environment
Networking layering provides good abstraction in the network design
Wireless networks are interference limited, and the information delivery capability is closely dependent on current channel quality
Adoption in physical and link layer broadcast could lead to efficient resource usage
Protocol changes need to be made in MSs and mobile access points to ensure compatibility with existing TCP applications

39. End-to-End Solutions TCP-SACK WTCP Protocol Freeze-TCP Protocol
Selective Acknowledgement and Selective Retransmission.
Sender can retransmit missing data due to random errors/mobility
WTCP Protocol
Separate flows for wired (Sender to AP) and wireless (AP to MS) segments of TCP connections
Local retransmission for mobile link breakage
AP sends ACK to sender after timestamp modification to avoid change in round trip estimates
Freeze-TCP Protocol
Mobile detects impending handoff
Advertises Zero Window size, to force the sender into Zero Window Probe mode

40. End-to-End Solutions (Cont’d)
Explicit Band State Notification (EBSN)
Local Retransmission from BS (AP) to shield wireless link errors
EBSN message from BS to Source during local recovery
Source Resets its timeout value after EBSN
Fast Retransmission Approach
Tries to reduce the effect of MS handoff
MS after handoff sends certain number of duplicate ACKs
Avoids coarse time-outs at the sender, accelerates retransmission

41. Link Layer Protocols Snoop Protocol
Transport layer aware Snoop Agent at BS
Agent monitors all TCP segments destined to MS, caches it in buffer
Also monitors ACKs from MS
Loss detected by duplicate ACKs from MS or local time-out
Local Retransmission of missing segment if cached
Suppresses the duplicate ACKs

42. Split TCP Approach
Indirect TCP: splits the TCP connection into two distinct connections, one is MS and BS and another is BS and corresponding node (CN)
The AP acts as a proxy for MS
The AP acknowledges CN for the data sent to MS and buffers this data until it is successfully transmitted to MS
Handoff may take a longer time as all the data acknowledged by AP and not transmitted to MS must be buffered at the new AP

43. Indirect TCP
Wireless link
Wired Domain MS AP CN
(Acts as proxy)

44. Split TCP Approach (Cont’d)
M-TCP Protocol
Split the connection into wired component and wireless component
BS relays ACKs for sender only after receiving ACKs from MS
In case of frequent disconnections, receiver can signal sender to enter in persist mode by advertising Zero Window size

45. Impact of Mobility
Handoffs occur in wireless domains when an MN moves into a new BS’s domain
The result of the packet loss during handoff is slow start
The solution involves artificially forcing the sender to go into fast retransmission mode immediately, by sending DUP ACK after the handoff, instead of go into slow start
Using multicast: the MN is required to define a group of BSs that it is likely to visit in the near future
Reduce the handoff latency: Only one BS is in contact with the MN and the others buffer the packets addressed to the multicast address

46. Internet Protocol Version 6 (IPv6)
Designed to address the unforeseen growth of the internet and the limited address space provided by IPv4
Features of IPv6:
Enhanced Address Space: 128 bits long, can solve the problem created by limited IPv4 address space (32 bits)
Resource Allocation: By using “Flow Label”, a sender can request special packet handling
Modified Address Format: Options and Base Header are separated which speeds up the routing process
Support for Security: Encryption and Authentication options are supported in option header

47. IPv4 Header Format Version(4 bits) Header length (4 bits)
Type of service (8 bits)
Total length (16 bits)
Identification (16 bits)
Flags
(3 bits)
Fragment offset
(13 bits)
Time to live
(8 bits)
Protocol (8 bits)
Header checksum (16 bits)
Source address (32 bits)
Destination address (32 bits)
Options and padding (if any)

48. IPv6 Header Format Version Traffic Class Flow Label Payload Length
Address Space
Resource Allocation
Modified Header Format
Support for Security
Version
Traffic Class
Flow Label
Payload Length
Next Header
Hop Limit
Source Address
Destination Address
Data

49. Format of IPv6 Name Bits Function Version 4 IPv6 version number
Traffic Class 8
Internet traffic priority delivery value
Flow Label 20
Used for specifying special router handling from source to destination(s) for a sequence of packets
Payload Length
16, unsigned
Specifies the length of the data in the packet. When set to zero, the option is a hop-by-hop Jumbo payload
Next Header
Specifies the next encapsulated protocol. The values are compatible with those specified for the IPv4 protocol field
Hop Limit
8, unsigned
For each router that forwards the packet, the hop limit is decremented by 1. When the hop limit field reaches zero, the packet is discarded. This replaces the TTL field in the IPv4 header that was originally intended to be used as a time based hop limit
Source Address
128
The IPv6 address of the sending node
Destination Address
The IPv6 address of the destination node

50. Differences between IPv4 and IPv6
Expanded Addressing Capabilities
Simplified Header Format
Improved Support for Options and Extensions
Flow Labeling Capabilities
Support for Authentication and Encryption

51. Network Transition from IPv4 to IPv6
Dual IP-Stack:
IPv4-hosts and IPv4-routers have an IPv6-stack, this ensures full compatibility to not yet updated systems
IPv6-in-IPv4 Encapsulation (Tunneling):
Encapsulate IPv6 datagram in IPv4 datagram and tunnel it to next router/host

53. Network Access Layer
The Internet Protocol Suite (commonly known as TCP/IP) is the set of communications protocols used for the Internet and other similar networks.
Transmission Control Protocol (TCP) and the Internet Protocol (IP)
The Internet Protocol Suite may be viewed as a set of layers. Each layer solves a set of problems involving the transmission of data, and provides a well-defined service to the upper layer protocols based on using services from some lower layers.
The TCP/IP model consists of four layers. This layer architecture is often compared with the seven-layer OSI Reference Model. From lowest to highest, these are
the Network Access Layer,
the Internet Layer,
the Transport Layer,
and the Application Layer
The TCP/IP Network Access Layer can
encompass the functions of two lower layers
of theOSI reference Model:
Data Link, and Physical.

54. Network Access Layer
Q:- What is the major function of the network access layer?
Ans: The network access layer is concerned with the exchange of data between a computer and the network to which it is attached.

56. Transport Layer Recap
Q:- What tasks are performed by the transport layer?
Isolates messages from lower and upper layers
Breaks down message size
Monitors quality of communications channel
Selects most efficient communication service necessary for a given transmission

57. Transport Layer
Concerned with reliable transfer of information between applications
Independent of the nature of the application
Includes aspects like flow control and error checking

58. Transport Layer Recap
Q:- What tasks are performed by the transport layer?
Ans:- The transport layer is concerned with data reliability and correct sequencing.